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Activity > Colloquium

Colloquium (2016)

ASIAA Colloquium is usually held on Wednesdays at 2:20-3:20 pm in Room 1203 of the Astronomy-Mathematics Building, NTU. All scientists are welcome to attend.

The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.

Contact: Colloquium Committee (talks_replace2@_asiaa.sinica.edu.tw)

No. Time/Place Speaker Topic / Abstract
download PDF: download talk PDF file
12016-12-21 Wed
14:20~15:20
R1203
Siyi Xu
[ESO]
Planetary Systems around White Dwarfs
Abstract

Recent studies have shown that extrasolar planetary systems are prevalent around main-sequence stars in the Milky Way. However, little is known about their fate towards the end of the stellar evolution. In this talk, I will show various evidence that some white dwarfs are dynamically active and planetary systems could be prevalent around white dwarfs. I will also talk about the recent discovery of an actively disintegrating asteroid around a white dwarf and how this system fits into our overall understanding of the fate of planetary systems.

22016-12-20 Tue
14:20~15:20
R1203
Hsin-Yu Chen
[University of Chicago]
*Special Seminar*
Cosmology and Astrophysics with Gravitational-Wave Observations
Abstract

The first detections of gravitational waves by LIGO-Virgo initiated the era of Gravitation-Wave Astronomy. Gravitational-waves serve as a new and independent probe of the Universe. In addition, the combination of gravitational-waves with information from other messengers, such as electromagnetic emission from the same source, will lead to a more complete and accurate understanding of cosmology and astrophysics. In this talk, I will discuss what we learned from the LIGO-Virgo first observing run, and what scientific goals we expect to reach in the next few years.

32016-12-15 Thu
14:20~15:20
R1203
Chia-Yu Hu
[Center for Computational Astrophysics]
*Special Seminar*
The interstellar medium in dwarf galaxies
Abstract

Dwarf galaxies are the most numerous type of galaxy in the local Universe. They tend to have low metallicity and low dust-to-gas ratio compared to spiral galaxies. Understanding the interstellar medium in dwarf galaxies may provide crucial insights on the high-redshift galaxies that have comparable metallicity. In this talk, I will show the recent results from high-resolution numerical simulations of isolated dwarf galaxies, which can start to resolve the cold gas and stellar feedback on galactic scales. In particular, I will focus on the formation of molecular hydrogen and its (non-)correlation with star formation, which has important implications to the sub-grid recipes widely adopted in many large-scale cosmological simulations. I will also discuss the interplay of different types of stellar feedback that shapes the interstellar medium in dwarf galaxies, where the gas is driven far out of thermal- and chemical-equilibrium. Finally, I will demonstrate how the galactic outflows are controlled by the number of supernovae that occur in low-density environments.

42016-12-14 Wed
14:20~15:20
R1203
Martin Bizzarro
[Natural History Museum of Denmark]
Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules
Abstract

The most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. Using uranium-corrected Pb-Pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after formation of the Sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. This is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. An abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion.

52016-12-07 Wed
14:20~15:20
R1203
Andreas Schulze
[NAOJ]
Black hole growth and black hole - galaxy co-evolution
Abstract

Supermassive black holes (SMBHs), found in the center of galaxies, are thought to play an essential role in the evolution of galaxies. Their growth seems to be closely connected to the star formation history of their host galaxies. However, observationally there are still several fundamental unanswered questions regarding the growth of black holes. How is SMBH growth triggered and fueled? What role does AGN feedback and AGN outflows play for galaxy evolution? How do SMBHs grow over cosmic time scales? What role do SMBH mass and accretion rate play in their evolution? I will present recent results and upcoming projects to address these questions observationally and shed new light on the growth history of SMBHs and the connection to their host galaxies. In particular, I will discuss results on the cosmic evolution of the active black hole mass function, accretion rate function and AGN host galaxy mass function and their implications.

62016-11-30 Wed
14:20~15:20
R1203
Tien-Hao Hsieh
[ASIAA]
Widening of Protostellar Outflows: an Infrared Outflow Survey in Low Luminosity Objects
Abstract

We present an outflow survey toward 20 Low Luminosity Objects (LLOs), namely protostars with an internal luminosity less than 0.2 Lsun. Although a number of studies have reported the properties of individual LLOs, the reasons for their low luminosity remain uncertain. To answer this question, we need to know the evolutionary status of LLOs. Protostellar outflows are found to widen as their parent cores evolve, and therefore, the outflow opening angle could be used as an evolutionary indicator. The infrared scattered light escapes out through the outflow cavity and highlights the cavity wall, giving us the opportunity to measure the outflow opening angle. Using the Canada-France-Hawaii Telescope, we detected outflows toward eight LLOs out of 20 at Ks band, and based on archival Spitzer IRAC1 images, we added four outflow-driving sources from the remaining 12 sources. By fitting these images with radiative transfer models, we derive the outflow opening angles and inclination angles. To study the widening of outflow cavities, we compare our sample with the young stellar objects from Arce & Sargent (2006) and Velusamy et al. (2014) in the plot of opening angle versus bolometric temperature taken as an evolutionary indicator. Our LLO targets match well the trend of increasing opening angle with bolometric temperature reported by Arce \& Sargent and are broadly consistent with that reported by Velusamy et al., suggesting that the opening angle could be a good evolutionary indicator for LLOs. Accordingly, we conclude that at least 40\% of the outflow-driving LLOs in our sample are young Class 0 objects.

72016-11-23 Wed
14:20~15:20
R1203
Elizabeth Tasker
[JAXA]
From Galaxies to Planets (A medley!)
Abstract

Star formation occurs in the dense molecular gas clouds within the galaxy's interstellar gas. But while these clouds are relatively small (of order 10s pc) their properties are morphed and shaped by the galactic-scale structure and interactions with neighbouring clouds. The first part of this talk explores how large-scale interactions affect these stellar cradles and the resultant star formation using hydrodynamical simulations. The second part of the talk turns to look at planet formation. Exoplanet observations have revealed a large population of planets on short orbits close to their host star. Their origin is a debated topic, however a popular theory suggests they migrated inwards after forming in the outer parts of the protoplanetary disc. Such motion would allow planets to undergo heavy accretion of smaller planetesimals. This second part of the talk discusses whether an observational signature of such an event might be detectable.

82016-11-16 Wed
14:20~15:20
R1203
Christian Fendt
[Max Planck Institute for Astronomy]
How to make astrophysical jets?
Abstract

I will present MHD simulations investigating the launching of astrophysical jets. First, a brief introduction into MHD wind and jets is given. Our simulations treat the time-dependent evolution of the accretion-ejection structure and the subsequent collimation of the disk wind into a high-velocity jet. The setup considers various models for a physical (turbulent) magnetic diffusivity that is essential for the mass loading of the outflow. We find relatively high mass fluxes in the outflow, about 20-40% of the accretion rate. Recent simulations include a mean-field accretion disk dynamo and the launching of outflows by a self-generated disk magnetic field. We have run a parameter survey of disk-wind launched by disk of different magnetization and find that the disk magnetization is the main parameter that governs the jet dynamics. Special relativistic jet formation simulations allow to construct synchrotron radiation maps from the dynamical outflow structure that can be compared to the observations. Finally I will present preliminary results from GR-MHD simulations treating the accretion-ejection structure of outflows from resistive accretion disks.

92016-11-09 Wed
14:20~15:20
R1203
Erik Rosolowsky
[University of Alberta]
The Care and Feeding of Star Forming Regions
Abstract

In the local Universe, all stars form in clouds of molecular gas. On the largest scales in galaxies, the ensemble of molecular clouds produces a simple star formation law: more molecular gas is linearly correlated with more star formation. This star formation law must emerge from behaviour of groups of individual molecular clouds. In this talk, I will present recent observations of molecular clouds and star forming regions in our Galaxy. Using a suite of novel analysis approaches, we are able to untangle maps of molecular gas and match them to the regions of star formation. This analysis finds good evidence that significant mass flows are essential for feeding star forming regions across the Galactic disk. Additionally, higher mass molecular clouds show evidence for increased rates of star formation, suggesting again these clouds are fed from their environment over their lifetime. The large apparent scatter in the efficiency of the star formation process can be attributed in part to viewing the effects of this mass accretion over time.

102016-11-02 Wed
14:20~15:20
R1203
Edwige Chapillon
[LAB/IRAM]
Study of protoplanetary disks at millimeter wavelength
Abstract

The study of protoplanetary disks is essential to constrain the planets formation mechanism. Because these disks are small and cold objects, (sub)millimeter interferometry is a key to unveil their physical conditions, providing us with information on both the dust and gas content. However, one needs physical and chemical models to interpret the observations. In this talk I will present recent results based on observations with the IRAM instruments and ALMA.

112016-11-01 Tue
14:20~15:20
R1203
Mikako Matsuura
[Cardiff University]
*Special Seminar*
Dust and molecules in Supernova 1987A
Abstract

Supernovae (SNe) play a crucial role in the chemical evolution of galaxies by enriching their interstellar media (ISM) with heavy elements and dust. The formation of dust in core-collapse supernovae (SNe) is one of the unresolved issues in the chemical and physical evolution of supernovae. I will present Herschel Space Observatory’s discovery of a large dust reservoir in SN 1987A. The estimated dust mass is 0.1-1 solar masses, which are typically 1000 times higher than previously thought. A significant fraction of the elements synthesized by the supernova can condense into dust grains. That suggests that SNe may be important source of dust in ISM of galaxies. With ALMA, we discovered CO, SiO, HCO+ and SO lines in SN 1987A. The observations can probe insight of molecular chemistry, leading dust formation in SN. In millimetre wavelength, isotopologue lines appear at separated wavelengths, enabling constraining isotope ratios of 28Si/29Si and 28Si/30Si. ALMA can provide crucial limit on nuclear synthesis in high mass stars and supernovae.

122016-10-31 Mon
14:20~15:20
R1203
Dominique Bockelee-Morvan
[LESIA, Observatory of Paris]
*Special Seminar*
Comet composition : clues to Solar System formation
Abstract

The composition of cometary ices provides clues to the chemistry and conditions prevailing in the early solar system. Since the detection of HCN at millimeter wavelengths in comet C/1973 E1 (Kohoutek), almost 30 molecules have been identified in cometary atmospheres from remote sensing observations from ground or from space platforms. Thanks to progresses in instrumentation and the availability of large telescopes, complex organic molecules have been identified. Measurements will be reviewed and the observed chemical diversity among comets will be presented. The relative abundances will be compared to values measured in star-forming regions to discuss the possible formation routes of cometary molecules. The talk will also present new findings about comet composition obtained from the Rosetta mission to comet 67P/Churyumov-Gerasimenko.

132016-10-26 Wed
14:20~15:20
R1203
Scott Chapman
[Dalhousie University]
Gas, Dust, and Quenching in Dusty Star-Forming Galaxies in the Early Universe
Abstract

The most intense star formation in the universe takes place in dusty, star-forming galaxies at high redshift. Recent observations and circumstantial evidence suggest that these galaxies are the likely progenitors of the earliest generation of massive, quiescent galaxies. I will discuss recent efforts to detect and resolve the gas and dust on sub-kiloparsec scales using observations of gravitationally lensed dusty galaxies discovered by the South Pole Telescope conducted by ALMA and other facilities. These observations demonstrate the richness of the molecular ISM, shed light on the relative distribution of star formation and the gas from which stars form, and offer a unique window into the evolution of dusty galaxies impossible to obtain without the aid of gravitational lensing. Finally, I will present new ALMA observations which show signs of feedback on the molecular ISM in dusty star-forming galaxies, providing tantalizing evidence of an evolutionary connection between high-redshift dusty galaxies and the first massive, quiescent systems.

142016-10-25 Tue
14:20~15:20
R1203
Min S. Yun
[University of Massachusetts]
*Special Seminar*
The Large Millimeter Telescope (LMT) and the Most Luminous Infrared Galaxies in the Universe
Abstract

The Large Millimeter Telescope (LMT) is now in the final phase of completing the full 50-m aperture with fully operating active surface system, but it has been conducting a productive Early Science campaign since 2013 by illuminating the inner 32-m diameter using first light instruments 1.1mm bolometer camera AzTEC and the Redshift Search Receiver (RSR). In this talk, I will present some of the highlights of the ES scientific results, including my own research on the most luminous IR galaxies in the Universe through the LMT follow-up of the candidate sources we identified from the Planck database. I will also briefly discuss the next generation LMT instruments currently in construction and their key science programs.

152016-10-24 Mon
14:20~15:20
R1203
Sergio Martin
[ALMA]
*Special Seminar*
Astrochemistry in opaqueness Compact Obscured Nuclei: Arp 220
Abstract

Probing the inners regions behind the optically thick dust layer of heavily obscured LIRGs and ULIRGs are a major observational challenge. The obscuration of Av>1000 mag prevent the direct observation at all wavelenghts. Understanding the nuclear engines of these galaxies may be key for a complete AGN and starburst census as well as understanding nuclear growth and feedback mechanisms. Molecular observations have been usually exploited as a way to circunvent obscuration, however molecular diagnostics are still debated in "unobscured" galaxies, let alone towards this objects. The prototypical ULIRG Arp 220, usual suspect and closest example of ULIRG CON, has been the target of multiple ALMA observations showing that obscuration and absorption (both self-absorption and continuum absorption) may actually be preventing direct observation of the nuclear few tenths of parsercs even with high density molecular probes. Molecular transitions in particular excitation conditions might be the answer to peer into these objects. That is the case of the vibrationally excited transitions of dense molecular tracers such as HCN and HC3N. Here i will summarize the latest observational results towards Arp 220 which illustrates the observational difficulties inherent to such obscured nuclei. I will also present the recent results on vibrationally excited emission in (U)LIRGs which have gain relevance during the last few years.

162016-10-19 Wed
14:20~15:20
R1203
Ue-Li Pen
[CITA]
The Cosmic Neutrino Background
Abstract

Neutrinos are now established to have mass, but their total mass and hierarchy remain unknown. These massive neutrinos constitute the fourth largest matter component in the universe, after dark energy, dark matter, and baryons. I will describe the current status of the field, and our group’s effort and quantifying non-linear gravitational interaction of neutrinos and dark matter. Based on the world’s largest N-body simulation, TianNu and analytic theory, we propose a new suite of effects to detect these elusive particles.

172016-10-18 Tue
14:20~15:20
R1203
Toshifumi Futamase
[Kyoto Sangyo University, Japan]
*Special Seminar*
Constraints on Neutrino Masses from the Lensing Dispersion of Type Ia Supernovae
Abstract

We investigate how accurately the total mass of neutrinos is constrained from the magnitude dispersion of Type Ia supernovae due to the effects of gravitational lensing. For this purpose, we use the propagation equation of light bundles in a realistic inhomogeneous universe and propose a sample selection for supernovae to avoid difficulties associated with small scale effects such as strong lensing or shear effects. With a fitting formula for the non-linear matter power spectrum taking account of the effects of massive neutrino, we find Σmν < 1.1 eV (95% CL) for future optical imaging surveys: WFIRST and LSST. Furthermore, we show that it is possible to realize the current tightest limit Σmν < 0.2 eV from deeper surveys, z > 2.5, if we are able to reduce the magnitude error except for lensing to about half of the present value.

182016-10-12 Wed
14:20~15:20
R1203
Nobuo Arimoto
[NAOJ]
Origin of Elliptical Galaxies -- A Transition from Star Forming Main Sequence Galaxies to Passively Evolving Early Type Galaxies
Abstract

We investigate the stellar population properties of a sample of 24 massive quenched galaxies at 1.25< zspec< 2.09 identified in the COSMOS field with our Subaru/Multi-object Infrared Camera and Spectrograph near-IR spectroscopic observations. Tracing the stellar population properties as close to their major formation epoch as possible, we try to put constraints on the star formation history, post-quenching evolution, and possible progenitor star-forming populations for such massive quenched galaxies. By using a set of Lick absorption line indices on a rest-frame optical composite spectrum, the average age, metallicity [Z/H], and α-to-iron element abundance ratio [α/Fe] are derived as log(age/Gyr)=0.04-0.08+0.10, [Z/H]=0.24-0.14+0.20, and [α /Fe]=0.31-0.12+0.12, respectively. If our sample of quenched galaxies at < z≥1.6 is evolved passively to z = 0, their stellar population properties will align in excellent agreement with local counterparts at similar stellar velocity dispersions, which qualifies them as progenitors of local massive early-type galaxies. Redshift evolution of stellar population ages in quenched galaxies combined with low redshift measurements from the literature suggests a formation redshift of zf∼ 2.3, around which the bulk of stars in these galaxies have been formed. The measured [α/Fe] value indicates a star formation timescale of ≲ 1 Gyr, which can be translated into a specific star formation rate of ≃ 1 Gyr-1 prior to quenching. Based on these findings, we discuss identifying possible progenitor star-forming galaxies at z≃ 2.3. We identify normal star-forming galaxies, i.e., those on the star-forming main sequence, followed by a rapid quenching event, as likely precursors of the quenched galaxies at

192016-10-05 Wed
14:20~15:20
R1203
Eva Villaver
[Autonomous University of Madrid]
Single rotating stars and their AGB winds
Abstract

Heavy modulated mass-loss takes place during the Asymptotic Giant Branch evolution of low-and intermediate-mass stars. In the process several processes play their role: metallicity, stellar mass, rotation, magnetic fields, the presence of companions and a possible interaction with the ISM. I will describe how our new stellar evolution models with rotation can rule out single main sequence stars to achieve the needed physical conditions to cause asymmetrical mass-loss. We have quantified under which circumstances the presence of companions can induce sufficient tidal spin-up to form bipolar Planetary Nebulae. Finally, by computing models of star-planet interactions we have explored the role that substellar companions have in the overall stellar evolution and thus how they might influence PNe properties.

202016-10-04 Tue
14:20~15:20
R1203
Jifeng Liu
[NAOC]
*Special Seminar*
Ultraluminous Supersoft X-ray sources as super-critical accretion onto stellar black holes
Abstract

While ultraluminous supersoft X-ray sources (ULSs) bear features for intermediate mass black holes or very massive white dwarfs possibly close to Chandrasekhar mass limit, our recent discovery of processing relativistic baryonic jets from a prototype ULS in M81 demonstrate that they are not IMBHs or WDs, but black holes accreting at super-Eddington rates. This discovery strengthens the recent ideas that ULXs are stellar black holes with supercritical accretion,as demonstrated in the case of M101 ULX-1, and provides a vivid manifestation of what happens when a black hole devours too much, that is, it will generate thick disk winds and fire out sub-relativistic baryonic jets along the funnel as predicted by recent numerical simulations.

212016-10-03 Mon
14:20~15:20
R1203
I-Ting Ho
[Univ. Hawai'i & Australian National Univ.]
*Special Seminar*
Gas flows in star-forming galaxies in 3D
Abstract

Gas flows are one of the fundamental yet poorly understood processes driving galaxy evolution. This talk focuses on exploring gas flows in local galaxies by studying metallicity gradients and galactic-scale outflows in normal star-forming galaxies. This is made possible by new integral field spectroscopy data that provide simultaneously spatial and spectral information of galaxies. With the new 3D data, I study metallicity gradients and galactic winds to understand inflows and outflows in star-forming galaxies. I show that metallicity gradients in isolated disk galaxies are remarkably simple and universal. Simple chemical evolution models reveal that these simple metallicity gradients are a direct result of the coevolution of gas and stellar disk while galactic disks build up their masses from inside-out. Tight constraints on their mass outflow rates and inflow rates can be placed. I also investigate galactic winds in normal star-forming galaxies using data from the SAMI Galaxy Survey. I show that galactic winds are found to be very common even in normal star-forming galaxies that were not expected to host winds. By comparing galaxies with and without hosting winds, I show that galaxies with high star formation rate surface densities and bursty star formation histories are more likely to develop large-scale galactic winds.

222016-09-27 Tue
14:20~15:20
R1203
Houjun Mo
[UMass]
Reconstructing the initial conditions to simulate the formation of the local universe
Abstract

I will describe a method that can be used to reconstruct the initial conditions of the local universe accurately. The method is applied to the SDSS volume. High-resolution simulations of the reconstructed initial conditions have been carried to recover of the formation histories and structures observed in the local universe. I will also describe how the results can be used to study the formation and structure of the local cosmic web and of galaxies that are embedded in it.

232016-09-21 Wed
14:20~15:20
R1203
Wen-Ping Chen
[National Central University]
Formation and Dynamical Evolution of Star Clusters
Abstract

Stars are formed in clustered environments out of dense molecular cloud cores. The initial spatial distribution of massive versus low-mass member stars is dictated by the conditions in the molecular cloud. Yet, there seems to be a universal origin of stellar masses, the "initial mass function" among stellar systems including star clusters. With time, via mutual gravitational interaction among member stars, the cluster is virialized and tends to become spherical. The low-mass members, however, are vulnerable and prone to escaping from the system. Furthermore, external Galactic perturbation act to disrupt the originally bound system, manifest by tidal tails and moving stellar groups. Eventually all the members are dispersed and supply the disk population. I will review the theories and our recent observational diagnosis regarding the formation and dynamical processes of a star cluster, using photometric and kinematic data taken from sky survey projects supplied by our own imaging and spectroscopic observations.

242016-09-06 Tue
14:20~15:20
R1203
Alan Heays
[Leiden Observatory]
Laboratory astrochemistry: UV photodestruction of molecules and its observable isotope effects
Abstract

Finding ultraviolet photodestruction rates for the many atoms and molecules present in space is an interesting subject for fundamental study in laboratory and theoretical chemical physics. I will discuss the photodestruction process and its application to the molecules observed in interstellar clouds, protoplanetary disks, and planetary atmospheres. I will also discuss some detailed studies of N2 and CO photodissociation and their effect on the isotope-dependent fractionation of N, C and O atoms between different molecular forms, as observed in interstellar space and within the Solar system.

252016-08-19 Fri
14:20~15:20
R1203
Ting-Wen Lan
[JHU/Kavli IPMU]
*Special Seminar*
Exploring the diffuse interstellar bands with SDSS
Abstract

Diffuse interstellar bands (DIBs) are absorption features, observed ubiquitously in the interstellar medium (ISM). Understanding their nature is one of the longest unsolved problems in astronomy since their discovery in 1920s. I will present new results of their properties derived from an analysis of about half of a million of SDSS quasar, galaxy, and stellar spectra. Utilizing the SDSS spectroscopic dataset, we measure DIB absorption strengths at 0.1% level and create a map of the DIB distribution across the sky. With this new map, we are able to study how DIBs correlate with other ISM tracers such as dust, atomic hydrogen, and molecular hydrogen. Our results show that each DIB has a different correlation with atomic and molecular hydrogen which can be parametrized by a simple manner. Finally, I will show that our new DIB parametrization is sufficient to reproduce a large collection of observational results reported in the literature.

262016-08-17 Wed
14:20~15:20
1F auditorium
Scott Ransom
[NRAO]
download PDF Extraordinary Physics with Millisecond Pulsars
Abstract

Pulsars are some of physics and astrophysics' most exotic objects, and they have already earned two Nobel Prizes. We currently know of about 2500 of them in our Galaxy, but a small subset, the millisecond pulsars (MSPs), are truly remarkable. These systems are notoriously hard to detect, yet their numbers have more than doubled in the past 5 years via surveys using the world's most sensitive telescopes, new instrumentation, and huge amounts of computing. Specialized "timing" observations of these systems, accounting for each and every one of the billions of rotations of the stars, are providing fantastic results in basic physics. In this talk I'll focus on the efforts to directly detect gravitational waves from super-massive black hole binaries, make strong-field tests of general relativity, and determine the nature of the densest form of matter known in the universe.

272016-08-10 Wed
14:20~15:20
R1203
Yuichi Higuchi
[ASIAA]
Testing ΛCDM model with Subaru/Hyper Suprime-Cam survey
Abstract

Many observations have tested the standard cosmological model called LCDM which assumes dark matter and dark energy. Those observations revealed that phenomena predicted from LCDM model are almost consistent with observational results. However, the nature of dark energy is still unknown and this energy cannot be explained by known physics. Accordingly, another solution is also proposed which is called as f(R) gravity. In this theory, the cosmic acceleration is explained by modifying the gravitational theory. Since the effects from f(R) gravity are imprinted in matter distribution of the Universe, weak lensing which traces matter distribution on light path would be a powerful tool to give a constrain on the theory. In order to investigate the possibilities to constrain f(R) gravity with weak lensing analysis in Subaru/Hyper Suprime-Cam (HSC) survey, we carried out weak lensing simulations. Through the analysis of the weak lensing simulations, we found that weak lensing analysis with HSC could provide ten times stronger constraint on f(R) gravity model.

282016-08-03 Wed
14:20~15:20
R1203
Hsi-An Pan
[ASIAA]
Environmental Dependence of GMCs: simulation and observation
Abstract

A long-standing question about star formation is whether it is sensitive to large-scale galaxy structures. Observations show that strong bars (high ellipticity and long length) typically contain less or no star formation, while weak bars (low ellipticity and short) have more. This suggests that large-scale structure can indeed influence star formation. Yet galactic bar is a poorly-explored region, its actual effect on star formation is not yet clear. If star formation does care about galaxy structures, this should be reflected in the properties of giant molecular clouds (GMCs), because their conditions determine whether a star can form. In this research, we study the impact of bar on the properties of simulated GMCs formed in a set of galaxies for which their bar strength differs in a quantitatively controlled way. We also discuss the possibility to observe the environmental dependence of GMCs by considering the observational bias.

292016-07-27 Wed
14:20~15:20
R1203
Ting-Hui Lee/Steve Gibson
[Western Kentucky University]
(1) Chemical Abundances of Galactic Compact Planetary Nebulae (T.-H. Lee); (2) Mapping the Dark Neutral Medium (S. Gibson)
Abstract

(1) Chemical abundances of planetary nebulae (PNe) provide a powerful tool for constraining stellar and galactic evolutionary models. Both fields still have unanswered questions that can be addressed with higher-precision abundances. We are collecting a large sample of high-quality optical spectra of compact PNe to combine with already-acquired Spitzer mid-infrared spectra to determine the most accurate and uniform set of Galactic PN chemical abundances. In this talk, I will discuss the current status of the project and present the preliminary results. (2) Star formation requires cold, dense, gravitationally bound clouds, which must themselves form somehow from warmer ambient material. How does this process occur, and where? The cold, diffuse interstellar clouds making this transition are hard to detect in standard HI and CO emission line surveys, but they can be observed in HI self-absorption or narrow-line HI emission. I will describe how such "dark neutral medium" clouds can be mapped over large areas of the Galaxy, what we have learned so far, and the challenges involved in their analysis.

302016-07-26 Tue
14:20~15:20
R1107
Youngmin JeongAhn
[UNAM]
*Special Seminar*
Spatial distribution of steep lunar craters may be linked to size-dependent orbital distribution of impactors
Abstract

The depth/diameter (d/D) ratio of simple lunar craters (D<15km) is known to be ~0.2 at the time of formation; larger complex craters (D>15km) have smaller d/D ratios. We examine the spatial distribution of high d/D ratio (>0.18) craters using LU60645GT catalogue (Salamunićcar et al. 2012). We select craters larger than 8km for which the census is known to be almost complete over the whole lunar surface. We find that the number density of steep craters in maria is significantly lower than in highlands, which may be explained by the age differences of the background surfaces. We also find that the spatial density of steep craters in the equatorial region is lower than in the polar region. On the contrary, higher cratering flux on the lunar equator has been claimed: from the numerical calculations with the orbital distribution of observed Earth Crossing Objects (ECOs) larger than 1km (Le Feuvre & Wieczorek 2008; Ito & Malhotra 2010) and from the distribution of steepest slopes at a 25m baseline (Kreslavsky & Head, 2016). In order to reconcile our findings with previous observations, we hypothesize that the cratering rate at low latitudes has been higher for meter to decameter size ECOs than for kilometer size objects since the Late Imbrian epoch; smaller objects have triggered more frequent mass wasting on the pre-existing large steep craters (D>8km, d/D>0.18) at low latitudes, thereby reducing the surviving number of steep craters. Our hypothesis is supported by the finding that the power-law slope in the H magnitude distribution for the low inclination ECOs (i<15 deg) is steeper than for the high inclination objects.

312016-07-20 Wed
14:20~15:20
R1203
Ian Czekala
[Harvard/Smithsonian CfA]
The Fundamental Properties of Young Stars
Abstract

Accurate knowledge of the fundamental properties of stars--mass, temperature, and luminosity--are key to our understanding of stellar evolution. In particular, empirical measurements of stellar mass are difficult to make and are generally limited to stars that dynamically interact with a companion (e.g., eclipsing or astrometric binaries), a precious but ultimately small sample. First, I will discuss my development of a recent technique that uses the rotation of the protoplanetary disk--a consequence of the star formation process and still present around many pre-main sequence stars--to measure the stellar mass. To vet the absolute accuracy of this technique, I led the analysis of an ALMA Cycle 1/2 program to observe the few circumbinary disks around double-lined spectroscopic binary stars, enabling an independent confirmation of the total stellar mass. Our comparison with radial-velocity results demonstrates that the disk-based dynamical mass technique can reliably achieve precise measurements of stellar mass on the order of 2-5%, clearing the way for widespread application of this technique to measure the masses of *single* stars. Second, I will discuss our development of novel statistical techniques for spectroscopic inference. Young stars exhibit rich and variable spectra; although interesting phenomena in their own right, accretion veiling and star spots complicate the retrieval of accurate photospheric properties. Moreover, the uncertain spectral type--effective temperature scale for low mass pre-main sequence stars introduces a systematic error when placing a star on the Hertzsprung Russell diagram. The Gaussian process techniques we have developed to address these problems are also generally applicable to a wide range of spectroscopic problems. Lastly, I will discuss recent progress in measuring the masses of a large sample of single pre-main sequence stars observed with the Submillimeter Array, which will double the number of disk-based dynamical mass estimates of pre-main sequence stars. With ALMA, the disk-based technique holds enormous promise to become the primary means of stellar mass for statistically large samples of pre-main sequence stars, ushering in a new era of high precision in star and planet formation studies.

322016-07-19 Tue
14:20~15:20
R1107
Chia-Hsun Chuang
[AIP Potsdam]
*Special Seminar*
Baryon Acoustic Oscillation measurements from the BOSS final data release
Abstract

Recently, the BOSS collaboration submitted a set of papers (arxiv:1607.03143 ~​ 03155) analysing the final data release of the BOSS galaxy sample ​​ within redshift 0.2 < z < 0.75​ (~1.2 million galaxies)​. We obtained two independent 1% distance measurements at ​two ​ redshifts​ (z=0.38 and 0.61)​ which can be used to derive the evolution of our universe and understand better dark energy. I would like to explain the methodologies and the cosmological results. In the second part of this talk, I would like to present our studies of measuring BAO from void clustering (arxiv:1511.04405,1511.04391,1511.04299). It was not possible to measure BAO from voids because of the low statistical power. ​However, ​we have developed a methodology to extract the information from the large scale structure of void clustering observed from BOSS data. In addition, we investigate and model the redshift distortion effect of void clustering​ (arXiv:1605.05352)​ and found that it would be a challenge to measure growth history ​of our universe ​ from voids.

332016-07-13 Wed
14:20~15:20
R1203
Chi-Ting Chiang
[Stony Brook University]
Simulating the large-scale structure in different environments
Abstract

Understanding the structure formation is one of the most important issues in modern cosmology. In particular, in the era of big astronomical data, connecting observation and theory is crucial to improve precision cosmology, and possibly probe new physics. The observables of the large-scale structure such as galaxy number density generally depends on the density environment. The dependence can traditionally be studied by performing gigantic cosmological N-body simulations and measuring the observables in different density environments. Alternatively, we can perform the so-called ``separate universe simulations,'' in which the effect of the environment is absorbed into the change of the cosmological parameters. In other words, an overdense universe is equivalent to a positively curved universe, and so the structure formation would change accordingly. In this talk, I will introduce the separate universe mapping, and present how the power spectrum and halo mass function changes in different density environments, which are related to the squeezed-limit bispectrum and the halo bias, respectively. I will also discuss our recent progress on extending this approach to multiple fluids such as dynamic dark energy and massive neutrinos.

342016-07-06 Wed
14:20~15:20
R1203
Michael Aye
[LASP/University of Colorado]
Small scale structures and traveling features in Saturn’s rings and the importance of CO2 gas jets at the Martian southpole.
Abstract

Since the arrival of high resolution data from the Cassini mission we have learned that Saturn’s ring are far from understood, which many principle question open like the age of the rings and their origin. One of the crucial processes that is being studied by our group is the way the mainly water ice particles are clumping together and under what conditions those clumps can survive longer, potentially creating small moons, or would be destroyed again by the shearing forces of differential rotation. When these clumps grow in size they should become visible in imaging data and my work consists of image analysis techniques to quantify small scale structures visible in Cassini Imaging Science subsystem data. Our group also recently discovered via ultra-violet occultation measurements a traveling resonance feature caused by the Janus/Epimetheus moon swap that seems to travel approximately with constant speed radially outwards through Saturn’s rings. Using fitted velocity fits I am tasked to identify further ISS images that can identify the proposed solitary waves — caused by non-linear interactions with the linear standard density waves in the rings — in future ISS data. The Martian south-pole shows a high amount of visual surface activity caused by CO2 gas jets that break though the temporary CO2 ice layer that develops every winter at both poles of Mars. Interestingly, these activities are restricted to certain areas at the poles and it is currently not understood what precisely controls these restrictions in location. I will discuss the relevance of these CO2 gas jets for geomorphology and uncertainties of global and local atmosphere simulations and how the outcomes of the Planet Four project will improve our insights into both these fields.

352016-06-29 Wed
14:20~15:20
R1203
Yoshiki Toba
[ASIAA]
Dust Obscured Galaxies viewed with Subaru Hyper Suprime-Cam
Abstract

Dust Obscured Galaxies (DOGs) are optically-faint, but infrared (IR)-bright objects at z~2. Their mid-IR (MIR) flux densities are three orders of magnitude larger than those at optical wavelengths, which implies dust heating by significant star formation (SF), an active galactic nucleus (AGN), or both, and the bulk of the optical and ultraviolet (UV) emission from them is absorbed by dust.

Recently, some works have reported that the brighter MIR DOGs are more AGN-dominated, and indicated that black holes in the IR-bright DOGs are expected to show the highest accretion rate during a major merger event. In addition, IR-bright DOGs could tend to reside in richer environments than fainter ones, and the most luminous DOGs may evolve into brightest cluster galaxies. Therefore, particularly IR-bright DOGs are expected to be a crucial population in terms not only of the co-evolution of galaxies and supermassive black holes (SMBHs) but also of structure formation. However, efficient searches for luminous DOGs have been difficult in previous surveys due to their faintness in the optical and low surface densities. Therefore, high-sensitivity and wide-area surveys in both optical and MIR are required to search for the most IR-bright DOGs.

In this talk, I will present our recent studies on IR-bright DOGs based on the Subaru Hyper Suprime-Cam (HSC) and Wide-Field Infrared Survey Explore (WISE). In particular, I will focus on their statistical properties such as IR luminosity function, IR luminosity density, and clustering properties (Toba et al. 2015; 2016b in prep.).

362016-06-28 Tue
14:20~15:20
R1203
Anders Thygesen
[Caltech]
*Special Seminar*
Magnesium isotopes as a chemical evolution probe
Abstract

Over the recent years, the studies of the chemical evolution of the Milky Way have seen a major leap forward, in part due to large-scale spectroscopic surveys of stars, like APOGEE, Gaia-ESO, LAMOST and GALAH to name a few.

While these surveys have provided significant insight into the overall behavior of a large number of elements in different stellar populations, many details are still not understood. For instance, the mechanism behind the multiple population phenomenon in globular clusters, as well as the onset of AGB star contributions to the Milky Way halo chemistry is not yet well explained.

Nucleosynthesis models typically predict not only the bulk abundances of the elements, but also their isotopic composition. While elemental abundances in stars provide a wealth of information, in cases where the isotopic abundances can be measured even more can be learned, as this gives a detailed look into the preceding nucleosynthesis.

In this talk I will present how the measurement of Mg isotopes from high resolution stellar spectra can provide new insights into the Milky Way chemical evolution. Both in the context of globular clusters as well as other stellar populations. While earlier investigations have used standard 1D stellar atmospheric models, we have for the first time applied state-of-the-art 3D hydrodynamical models to this problem. This has resulted in significantly different isotopic distributions, and will help pave the way to answer some of the outstanding questions in our Galaxy's chemical evolution.

372016-06-22 Wed
14:20~15:20
R1203
Lee Mundy
[University of Maryland]
Filaments, Dense Gas and Stars: Connecting the Dots
Abstract

Molecular clouds form stars in regions of high density gas. That is not a mystery; it is a requirement. What drives the formation of the dense gas in specific places? What is the geometry of the regions of dense gas as they evolve toward star formation? What is the evolving relationship of the dense gas to forming stars as they grow? CARMA Large Area Star Formation Survey (CLASSy) imaged the dense gas structure and kinematics in five, roughly 1 pc scale, regions in the Serpens and Perseus clouds with 7" angular resolution. The spatial distribution and Class of the young stellar population (YSOs) is available for these regions from the Spitzer c2d and Gould Belt surveys. Together, these datasets allow us to compare, at similar spatial resolutions, the distributions of the dense gas and YSOs over regions containing up to 90 identified YSOs. This enable a detailed look at the relationship between the YSO and dense gas distributions, and some interesting answers for our picture of star formation.

382016-06-15 Wed
14:20~15:20
R1203
Woong Tae Kim
[SNU]
Star Formation in Nuclear Rings of Barred-Spiral Galaxies
Abstract

Barred-spiral galaxies contain star-forming nuclear rings at their centers. Star formation rates (SFRs) in the rings vary widely in the range of 0.1-10 M⊙ yr−1. Ring star formation appears long lived, lasting over a few Gyrs. Some rings show a well-defined azimuthal age gradient of star clusters along a ring, while others do not. To study what controls star formation in the rings, we use numerical simulations by including a prescription for star formation and feedback effects. In models without spiral arms, SFR in a ring exhibits a strong burst at early time and declines to small values at late time. On the other hand, models with spiral arms outside the bar region show multiple starburst activities at late time caused by arm-induced gas inflows. In all models, young star clusters in rings show an azimuthal age gradient only when the SFR is small. A linear stability analysis shows that rings with no age gradient appear gravitationally unstable, consistent with observations. I will also report our recent efforts on star formation in three-dimensional rings and their impact on hot halo gas.

392016-06-01 Wed
14:20~15:20
R1203
Lisa Kewley
[ANU]
Galaxy Formation and Evolution in 3D
Abstract

Throughout the history of the universe, shocks and large-scale gas flows have moulded the arms of spiral galaxies, formed the bulges of the most massive galaxies in the universe, fed supermassive black holes in the centers of galaxies, fueled generation upon generation of new stars, and enriched the intergalactic medium with metals. For local galaxies, we use multi-object integral field spectroscopy to build the largest sample of galaxies with wide 3-dimensional imaging spectroscopy. We combine these results with insights into the early universe probed through gravitational lensing and near-infrared integral field spectroscopy. I will present the latest results from our large local and high-z 3D surveys to understand the relationship between gas inflows, galactic-scale outflows, star-formation, and active galactic nuclei in galaxies as a function of environment and redshift. I will finish by discussing how this field will be transformed with JWST and in the GMT/TMT era.

402016-05-31 Tue
14:20~15:20
Room 104, CCMS-New Physics Building
David L. Meier
[California Institute of Technology]
*ASIAA/NTU Joint Colloquium*
Black Holes: The Ultimate Engines
Abstract

For nearly a century some of the most important astrophysical systems have been described in terms of every-day models or paradigms. For example, stellar interiors are likened to furnaces and the Big Bang is likened to an explosion. In the case of active galaxies and quasars, early observers, who studied the emission lines and ultraviolet continuum of these objects, often referred to the “central engine” that powered their energy output (often as great as 10^40 Watts or higher). We now are reasonably certain that, in each such active galaxy, the central object that is responsible for the “engine” is a supermassive black hole (as large as 20 billion solar masses), which is accreting gas and stars from the galaxy in which it resides. In fact, as more is learned about how an accreting black hole can produce the different types of behavior seen in active galaxies, the more accurate the Engine Paradigm appears to be. A black hole engine has most of the major subsystems that are in a standard automobile internal combustion engine and can be throttled from a quiet idle to an explosive roar. This includes an engine block (the black hole), a fuel supply (actually two types of fuel), a carburetion/fuel-injection system that converts gaseous fuel into a fine mist, a combustion chamber where the internal (gravitational) energy of the fuel is released, and five different exhaust systems to carry the spent fuel away from the combustion chamber. Black hole engines also produce enormous amounts of mechanical energy, which can be used to assist in the explosion of some stars, help trigger star formation in certain cases, and even shut off star formation in an entire galaxy. In this talk I will discuss the inner workings of black hole engines of different sizes and the important roles black holes play in the evolution of stars and galaxies.

412016-05-30 Mon
11:00~12:00
R1203
Ramesh Narayan
[Harvard]
*Special Seminar*
Numerical Simulations of Black Hole Accretion
Abstract

Accreting black holes are observed in a large variety of systems in astronomy: active galactic nuclei, X-ray binaries, tidal disruption events, gamma-ray bursts. While analytical one-dimensional models are very useful, some aspects of accretion physics such as the formation of jets and winds are beyond the scope of such models. Numerical general relativistic MHD simulations are able to include more physics than analytical models and are proving increasingly useful for studying the multidimensional gas dynamics and radiative properties of accretion flows. The talk will review some current progress.

422016-05-30 Mon
14:20~15:20
R1203
Hui Li
[Los Alamos National Laboratory]
*Special Seminar*
Asymmetries in Protoplanetary Disks and Implications for Planet Formation
Abstract

The majority of young low-mass stars are surrounded by disks, consisted of large reservoirs of gas and dust out of which planetary systems eventually form. In the recent years, high spatial resolution observations of such disks have revealed many details that are providing interesting constraints on the disk physics as well as dust dynamics, both of which are essential for understanding planet formation. In particular, large-scale features (e.g, gaps) and asymmetries (e.g., vortices?) are detected, including sources like HL Tau. In this talk we will give an introduction to the disk instabilities, in particular the Rossby wave/vortex instability and a new type of “heavy core” instability related to dust, that might be responsible for explaining asymmetries. We will discuss how gas+dust two-fluid modeling can be coupled with radiative transfer calculations to help interpret the observations and constrain the parameters in such systems. Implications for future observations will be explored as well.

432016-05-19 Thu
11:00~12:00
R1203
Andrew Cooper
[Univ. Durham]
*Special Seminar*
The Cosmological Context of Galactic Stellar Halos and Satellites
Abstract

The outskirts of massive galaxies are host to a rich variety of enigmatic phenomena, including diffuse stellar halos, tidal streams, dwarf satellites and globular clusters. The huge spatial extent and intrinsic faintness of such systems has so far limited our observational knowledge to the mere tip of this proverbial iceberg. Pioneering techniques with existing instruments are rapidly revising the status quo, and an even more dramatic revolution is due in the next decade as a deluge of data arrives from ultra-deep photometric surveys with HSC and LSST, Gaia’s survey of the Milky Way, and massively-multiplexed spectroscopy in the nearby Universe with DESI, 4MOST, WEAVE and PFS. These new surveys present exciting challenges in the synthesis of information from a wide range of methods, sources and scales, from the most massive galaxy clusters to the Milky Way and the earliest epoch of galaxy formation. In this talk, I will describe my work with cosmological simulations aimed at addressing those challenges and understanding what we can learn from such observations. In particular, I will discuss pressing issues in the ‘big picture’ of Lambda-CDM galaxy formation that could be tackled by testing predictions of a surprisingly intimate relationship between the properties of stellar halos, satellites and dark matter halos.

442016-05-19 Thu
14:20~15:20
R1203
Jun Yi Kevin Koay
[University of Copenhagen]
*Special Seminar*
The curious case of the changing-look Seyfert galaxy Mrk 590
Abstract

Sometime between the years 2006 and 2012, the broad Hbeta emission line of Mrk 590, once classified as a Seyfert 1 galaxy, completely disappeared! The optical-UV continuum emission has faded to the point where it can be fully accounted for by the host galaxy starlight. As such, Mrk 590 would now be classified as a Seyfert 1.9 or 2 galaxy, which goes against the prevailing scheme of AGN unification where the presence of broad emission lines depends only on source orientation. Similar decreases in the radio and X-ray continuum fluxes suggest that the central engine of Mrk 590 may be turning off or transitioning into a radiatively inefficient mode of accretion. I will talk about the origin of the compact, unresolved radio emission in Mrk 590 and the physical nature of its variability in relation to the variability observed at other wavelengths. I will also present recent CO line observations with ALMA, which provide the strongest limits to date on the molecular gas mass in the central regions, to determine if this AGN is indeed running out of gas to fuel it.

452016-05-18 Wed
14:20~15:20
Room 104, CCMS-New Physics Building
Chung-Pei Ma
[Department of Astronomy, University of California, Berkeley]
*ASIAA/NTU Joint Colloquium*
Supermassive Black Holes at the Centers of Galaxies
Abstract

Black holes are among the most fascinating astrophysical objects and have long entranced the public. I will describe recent progress in discovering black holes beyond one billion solar masses lurking at the centers of massive elliptical galaxies in the local universe. These massive black holes are plausible descendants of luminous quasars in the young universe and inform us of how cosmic structures evolved over the past 10 billion years. Merging black hole binaries in this mass range are also the primary sources of gravity waves in the nano-Hertz range targeted by ongoing pulsar timing array experiments.

462016-05-16 Mon
14:20~15:20
R1203
Teppei Okumura
[Kavli IPMU/University of Tokyo]
*Special Seminar*
Probing cosmic acceleration with large-scale structure of the Universe
Abstract

Revealing the acceleration of the cosmic expansion is one of the most important issues not only in cosmology but in fundamental physics. The mysterious dark energy could be driving the acceleration, or gravity law predicted from Einstein’s theory of general relativity could be breaking down at cosmological scales. To investigate the origin of the acceleration, one needs to probe both geometry (expansion history of the Universe) and gravity (structure growth history of the Universe). Thus, observations of large-scale structure of the Universe traced by galaxy surveys are considered as the best probe for this purpose, because the expansion history is probed by a measurement of baryon acoustic oscillations (BAO) and the growth history is probed using redshift-space distortions and weak lensing. In this talk, I will present the constraints on dark energy and gravity theory I obtained using current galaxy surveys. Then I will demonstrate that the accuracy of the current theoretical models for extracting the dark energy or gravity properties is not high enough for the future precision surveys such as the Subaru SuMIRe project (Hyper Suprime Cam / Prime Focus Spectrograph). Particularly, incorrect modeling of redshift-space distortions easily leads to a wrong constraint on gravity theories. In the latter part of my talk, I will present a new theoretical model of redshift-space distortions I have been developing, which achieves a percent level accuracy for galaxy power spectrum up to very small scales. Finally, I will mention how theoretical study of large-scale structure is related to other fields, such as galaxy formation, physics of galaxy clusters, etc.

472016-05-12 Thu
14:20~15:20
R1203
Harold A. Weaver, Jr.
[Johns Hopkins University Applied Physics Laboratory]
The Exploration of Pluto and the Kuiper Belt by New Horizons
Abstract

The New Horizons (NH) mission was selected by NASA in November 2001 to conduct the first in situ reconnaissance of Pluto and the Kuiper belt. The NH spacecraft was launched on 2006 January 19, received a gravity assist from Jupiter during closest approach on 2007 February 28, and flew 12,500 km above Pluto's surface on 2015 July 14. NH carried a sophisticated suite of seven scientific instruments, altogether weighing less than 30 kg and drawing less than 30 W of power, that includes panchromatic and color imagers, ultraviolet and infrared spectral imagers, a radio science package, plasma and charged particle sensors, and a dust counting experiment. The NH flyby of the Pluto system executed flawlessly, providing unprecedented detail on the Pluto-Charon binary and Pluto's four small moons (Styx, Nix, Kerberos, and Hydra, in order of their orbital distance from Pluto). Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, volatile transport, and glacial flow. NH discovered trace hydrocarbons in Pluto's atmosphere, multiple global haze layers, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long term activity raise fundamental questions about how small planets remain active many billions of years (Gyr) after formation. Charon displays tectonics, evidence for a heterogeneous crustal composition, and a puzzling giant hood of dark material covering its North Pole. Crater density statistics for Charon's surface give a crater retention age of 4-4.5 Ga, indicating that Charon's geological evolution largely ceased early in its history. Nix and Hydra have high albedos suggestive of H2O-ice covered surfaces. Crater densities on Nix and Hydra indicate surface ages > 4 Ga. All the small satellites have highly elongated shapes and are rotating much faster then synchronous with their orbital periods, with rotational poles clustered near the Pluto-Charon orbital plane. The NH spacecraft remains healthy and was targeted toward the flyby of a small (~30-40 km) KBO in late-2015, enabling the study of an object (2014 MU69) in a completely different dynamical class (cold classical) than Pluto, if NASA approves an Extended Mission phase. In addition to the flyby 2014 MU69, the proposed Extended Mission would also include observations of more than 20 other KBOs at resolutions and geometries not feasible from Earth, and studies of the heliospheric plasma, neutral H and He, and the dust environment out to 50 AU from the Sun.

482016-05-11 Wed
14:20~15:20
R1203
Chian-Chou Chen
[Durham University]
Submillimeter “Pain-in-the-neck” Galaxy - challenging the models of galaxy formation and evolution for nearly two decades
Abstract

Almost 20 years ago, the discovery of submillimeter galaxies (SMGs) had opened up a whole new window for observational astronomy, which subsequently lead to a paradigm shift in our understanding of galaxy formation and evolution. Panchromatic follow-up studies and dedicated missions such as Herschel have improved our knowledge of SMGs immensely. However, many fundamental questions are still under debate; How many are they? How are they formed? How massive they are? Are they the long sought-after predecessors of present day massive ellipticals? In this talk, I will present our latest results from SCUBA-2, ALMA, and HST, and explain how some of these questions are starting to converge. In the meantime, I will also show new evidence that further challenges the current galaxy formation models. Finally, with new surveys such as S2COSMOS and STUDIES, I will explain how are we going to make a major step forward and push the observational constraints of SMGs to a new level.

492016-05-05 Thu
14:20~15:20
R1203
Keiichi Wada
[Kagoshima University]
*Special Seminar*
A new dynamical picture of AGNs
Abstract

Multi-wavelength observations of Active Galactic Nuclei (AGNs) have suggested that their internal structures are consisted of various components, such as an accretion disk, broad line regions, an obscuring dusty torus, and narrow line regions, over an extensive spatial scales. However, their origin and mutual relations have not been understood, andit is also unclear whether these structures are universal among AGNs.

In this seminar, I will review recent progress in theoretical modeling of circumnuclear gas structures in AGNs, mainly based on our radiation-hydrodynamic simulations. In a series of our studies, we found dynamic behavior of the gas around the SMBH due to the effect of the radiation feedback, in contrast to the classic picture. Spectroscopic properties in typical Seyfert galaxies are well reproduced in these models. Some characteristic features suggested by recent infrared and X-ray observations can be also explained.

I will also show preliminary results of modeling the multi-phase ISM affected by an AGN and nuclear starburst for a nearby AGN. These numerical approach with radiative transfer calculations could be a powerful tool for understanding observations of molecular/atomic gases by ALMA.

502016-05-04 Wed
14:20~15:20
R1203
Juntai Shen
[SHAO]
Gas inflow patterns and nuclear rings in barred galaxies
Abstract

Nuclear rings, dust lanes, and nuclear spirals are common structures in the inner region of barred galaxies, with their shapes and properties linked to the physical parameters of the galaxies. We use high-resolution hydrodynamical simulations to study gas inflow patterns in barred galaxies, with special attention on the nuclear rings. The location and thickness of nuclear rings are tightly correlated with galactic properties, such as the bar pattern speed and bulge central density, within certain ranges. We identify the backbone of nuclear rings with a major orbital family of bars. The rings form exactly at the radius where the residual angular momentum of inflowing gas balances the centrifugal force. We propose a new simple method to predict the bar pattern speed for barred galaxies possessing a nuclear ring, without actually doing simulations. We apply this method to some real galaxies and find that our predicted bar pattern speed compare reasonably well with other estimates. Our study may have important implications for using nuclear rings to measure the parameters of real barred galaxies with detailed gas kinematics. I will also discuss the latest results of extending current work to model the gas features in the Milky Way.

512016-05-03 Tue
14:20~15:20
R1203
Chao-Ling Hung
[University of Texas]
*Special Seminar*
Connecting dusty starburst galaxies and proto galaxy clusters: a case study at z=2
Abstract

The most prodigious starburst galaxies are absent in massive galaxy clusters today, but their connection with large scale environments is less clear at z>2. I present our search of dusty star-forming galaxies (DSFGs; SFR>100 Msun/yr) within and around a protocluster at z~2.1 in the COSMOS field. Both DSFGs and color-selected SFGs show significant overdensities around the protocluster, and this structure spans across several tens of cMpc, considerably larger than previously observed. The cluster core and the extended DSFG- and SFG-rich structure together demonstrate an active cluster formation phase, in which the cluster is accreting a significant amount of material from large scale structure while the more mature core may begin to virialize. The finding of this DSFG-rich structure, along with a number of other protoclusters with excess DSFGs and AGNs found to date, suggest that the overdensities of these rare galaxies indeed trace significant mass overdensities. However, it remains puzzling how these intense star formers are triggered concurrently. Although an increased probability of galaxy interactions and/or enhanced gas supply can trigger the excess of DSFGs, our stacking analysis based on 850 micron images and morphological analysis based on rest-frame optical imaging do not show such enhancements of merger fraction and gas content in this structure.

522016-04-29 Fri
14:20~15:20
R1203
Steve Charnley
[Goddard Space Flight Center, NASA]
*Special Seminar*
Models of Complex Molecule Formation in Space
Abstract

Pathways leading to the formation of complex organic molecules will be described. Gas phase processes that may build large carbon-chain species in cold molecular clouds will be summarised. Catalytic reactions on grain surfaces can lead to a large variety of organic species, and models of molecule formation by atom additions to multiply-bonded molecules will be presented. The subsequent desorption of these mixed molecular ices can initiate a distinctive organic chemistry in hot molecular cores.

The general ion-molecule pathways leading to even larger organics will be outlined. The predictions of this theory will be compared with observations to show how possible organic formation pathways in the interstellar medium may be constrained. In particular, the success of the theory in explaining trends in the known interstellar organics, in predicting recently-detected interstellar molecules, and, just as importantly, non-detections, will be discussed. The most urgently needed laboratory data required by these and future theoretical models, both for gas-phase and solid-phase reactions, will be emphasized.

Ehrenfreund, P. & Charnley, S.B. (2000), Annu. Rev. Astron. Astrophys., 38, 429

532016-04-27 Wed
14:20~15:20
R1203
Lei Hao
[SHAO]
The Co-evolution of AGNs and Galaxies, Viewed from 2D Spectroscopy
Abstract

It is well-established that galaxies and their central supermassive black holes co-evolve. The properties of AGN hosts and their interactions of, i.e. the feeding and feedback of AGNs, are key processes to understand these co-evolutions. In this talk, I will introduce some of our recent and ongoing work on the direct and indirect interactions of AGNs and their host galaxies, particularly using the data from 2D spectroscopy. I will also introduce our own 2D spectrograph, CHILI, and particularly its science implications. In the end, I will briefly mention our work that are not 2D-related, particularly the one that studies AGNs using infrared spectroscopy and explores high-z low-luminosity AGNs with the HETDEX survey.

542016-04-21 Thu
14:20~15:20
R1203
Fabien Defrance
[Observatoire de Paris]
Instrumentation of a 2.6 THz heterodyne receiver
Abstract

Knowledge of the interstellar medium (ISM) is essential to understand the stellar life cycle, beside others. The ISM can be traced by the emission or absorption lines of molecules, atoms and ions. Different molecules/atoms/ions trace different phases of the ISM, and some important molecules/ions/atoms can only be detected at frequencies above 1 THz. On sub-millimeter telescopes, heterodyne receivers are generally used for line observations. During my PhD, I built and characterized a 2.6 THz heterodyne receiver. This operating frequency of 2.6 THz is one of the highest reached by recent heterodyne receivers, and in order to characterize and improve this receiver, 3 important aspects were investigated: 1) The stability of the receiver, which determines the optimal integration time of the receiver before it has to be recalibrated. 2) The design and test of a Martin-Puplett interferometer which allows to superimpose the local oscillator signal and the observed signal with a very good efficiency. 3) The design, simulation and characterization of a new kind of phase grating (The Global phase grating) able to efficiently split the local oscillator beam into several beams, which allows the development of a multi-pixel heterodyne receiver. In conclusion, this work constitutes an important step toward the realization of a stable and highly sensitive 2.6 THz multi-pixel heterodyne receiver using a Martin-Puplett interferometer diplexer, for the next generation of sub-millimeter/farIR space missions.

552016-04-13 Wed
14:20~15:20
R1203
Benedikt Diemer
[CfA]
The Edge of Darkness, and Other Halo Surprises
Abstract

The density profiles of dark matter halos are an essential input for models of galaxy formation, as well as for the interpretation of numerous observations such as weak and strong lensing signals. These profiles are commonly thought to be universal and modeled using the NFW form, assuming that they depend on only two parameters: mass and concentration. In this talk, I will show that the outer density profiles depend on an additional parameter, the mass accretion rate, and present an accurate new fitting formula that takes this dependence into account. Similarly, I will present a universal model for halo concentrations that is based on a previously unknown dependence of concentration on the local slope of the matter power spectrum. Finally, I will introduce a novel feature in the density profiles, the splashback radius. Contrary to the common belief that halos have no well-defined edge, this radius provides a physically motivated definition of the halo boundary.

562016-04-07 Thu
14:20~15:20
R1203
Min-Kai Lin
[University of Arizona]
*Special Seminar*
Hydrodynamic activity in protoplanetary disks
Abstract

The realization that large portions of cold, dense protoplanetary disks do not support magnetically-driven turbulence have lead to renewed interest in purely hydrodynamical processes in accretion disks. Such processes may play significant roles in disk evolution, planet formation, as well as explaining observations of transition disks. I will discuss recent theoretical developments in three important examples of hydrodynamic instabilities in protoplanetary disks. I first describe the Rossby Vortex Instability, which has been invoked to form dust-trapping vortices to explain asymmetries observed in several transition disks. I will also present new simulations of vortices in massive 3D disks. I then describe the Vertical Shear Instability and its generic relevance to astrophysical disks. I show that, despite rather stringent thermodynamic requirements, that this instability is indeed viable in realistic, irradiated protoplanetary disks where cooling is regulated by dust opacity. Finally, I present a new analytical treatment of Gravitational Instabilities in rotating disks that includes cooling physics, irradiation and viscosity. I discuss how this generalized linear theory may aid the understanding of disk fragmentation, and show that application of our analyses predict where protoplanetary disks are expected to fragment, in agreement with the current consensus based on direct numerical simulations.

572016-04-06 Wed
14:20~15:20
R1203
Hsiang-Yi Yang
[University of Maryland]
Solving the Cooling-Flow Problem in Galaxy Clusters
Abstract

Galaxy clusters with short central cooling times are predicted to host massive inflow of gas and large star formation rates, which are absent observationally – the so-called “cooling-flow problem”. Feedback from the central active galactic nuclei (AGN) is one of the most promising heating mechanisms to counteract radiative cooling. However, it is still uncertain how the feedback energy is transformed into heat and how to distribute heat isotropically. The role of conduction is also not well understood. In particular, it is unexplored whether the AGN-driven turbulence could halt the heat-flux driven buoyancy instability (HBI) that acts to insulate the cluster cores from conductive heating. I will present results from our recent simulations that aim to address the above two questions. Finally, few models to date consider cosmic-ray filled AGN bubbles, which are crucial for bubble evolution. I will discuss how we could use multi-wavelength observations of the Fermi bubbles as a nearby laboratory to understand the processes of AGN feedback.

582016-03-30 Wed
14:20~15:20
R1203
Nicolas Peretto
[Cardiff University]
The timescale of star formation: Clues from the gas dynamics of infrared dark clouds
Abstract

In order to form stars, matter has to transfer from large and diffuse interstellar clouds, to compact and dense protostellar cores. The physical conditions under which this transformation occurs are still highly debated. One particular sticking point is the timescale over which interstellar clouds contract to form cores: Is it rapid (a couple of free-fall times)? or is it slow (tens of free-fall times)? In this talk, I will present recent observational studies of Galactic plane infrared dark clouds (IRDCs). As a result of their infrared quietness IRDCs are ideal laboratories for the study of the earliest stages of star formation. I will focus on the analysis of the gas dynamics of IRDCs with the objective to evaluate their dynamical states (collapsing/expanding/pressure confined) and timescales. The latter will be then compared to the IRDC free-fall times providing some new elements to the debate on the star formation timescale.

592016-03-29 Tue
14:20~15:20
R1203
Ana Duarte-Cabral
[University of Exeter]
*Special Seminar*
Observing simulations: Molecular clouds and their journey in the Galaxy.
Abstract

In order to have a global picture of the cycle of matter in galaxies, we need to understand the interplay of large-scale galactic phenomena with the formation of giant molecular clouds and, ultimately, their subsequent star formation. In this context, we ran a set of SPH numerical simulations of spiral galaxies structurally resembling our own Milky Way, where we can track the formation and evolution of molecular clouds in detail. In this talk, I will present my recent study of such simulations, where I investigate the link between the molecular cloud properties and position with respect to spiral arms, both directly from the simulation (with the 3D densities of H2 and CO) and from an observer’s perspective (with CO emission in PPV space), providing predictions and tests for observations of molecular clouds and star formation in both the Milky Way, and external galaxies.

602016-03-28 Mon
14:20~15:20
R1203
Chihway Chang
[ETH Zurich]
*Special Seminar*
Mapping the Invisible Landscape — the Dark Energy Survey and Beyond
Abstract

The effect of gravitational lensing has left traces of cosmological information in the Universe for us to pick up. The full information is encoded in the 3D map of dark matter. As a first step to building up this map, I will describe our recent work using the Dark Energy Survey (DES) Science Verification data to make a weak lensing mass map on a large slice of our Universe. I then discuss a few topics where we combine this map and information from the CMB and galaxies. Looking forward to the completion of DES and several ongoing and future optical surveys, these explorations would allow us to take a new look at the invisible landscape of our Universe.

612016-03-24 Thu
14:20~15:20
R1203
Yao-Yuan Mao
[Stanford]
*Special Seminar*
Constraining the Flexibility in the Galaxy-Halo Connection
Abstract

The detailed relation between dark matter halos and galaxies is one of the most critical questions about galaxy formation. Among different models of the galaxy-halo connection, the abundance matching technique provides a simple, heuristic description to populate galaxies in dark matter halos, and has been shown to yield good fits to the clustering of galaxies and other observable spatial statistics. The choice of the halo property that is matched to galaxy luminosity (or stellar mass) further provides insights into the galaxy formation physics. In this talk I will discuss how the choice of the halo property used in the abundance matching technique acts as hidden parameters that control specific behaviors, such as assembly bias, in the resulting mock catalog. Our studies show the degeneracy among these parameters, and demonstrate that these parameters can be constrained by the observable clustering signals.

622016-03-23 Wed
14:20~15:20
R1203
Susanne Aalto
[Chalmers Univ. of Technology / Onsala Space Observatory]
The Cold Winds of Change - Hot Cores and Cool Outflows in Dusty Galaxies
Abstract

Molecular gas plays a fundamental role in feeding and regulating star formation and growth of supermassive black holes (SMBH) in galaxy nuclei and is therefore a primary evolutionary parameter in starburst and AGN activity. The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful instrument for studying galaxy evolution using molecules as observational tools - exploiting their ability to trace dynamical, chemical and physical conditions. These tools are particularly important in studying the "cold Universe" and to probe extremely dust-enshrouded galaxy nuclei which are not accessible by optical or even IR tracers.
I will present recent high resolution ALMA results on vibrationally excited molecules and how they can be used to peek inside the optically thick veil of extremely obscured galaxy nuclei. These lines are efficient probes even when N(H2) exceeds 1e24 cm-2 (A_V > 1000) and trace nuclear disks and bars, enclosed mass inside the dusty core - and are direct measures of the hidden mid-infrared luminosity densities. These nuclei may also drive massive, cold molecular winds that may empty the nuclear regions of gas and dust in a few tens of Myr. With ALMA and the IRAM PdBI telescope we have studied several spectacular outflows - including the peculiar molecular jet of the nearby lenticular NGC1377, the tantalizing twin-outflow of the merger NGC3256 and the powerful molecular wind of the quasar Mrk231. I will briefly discuss the link between the evolutionary phase of the nuclear activity and the onset of cold winds.
Finally, with ALMA the field of extragalactic astrochemistry is undergoing a revolution. If there is time towards the end of the presentation I will show you a few recent beautiful examples of this including the luminous infrarred galaxy NGC4418, the nearby Seyfert galaxy NGC1068 and the iconic ultraluminous infrared galaxy Arp220.

632016-03-22 Tue
11:00~12:00
R1203
Thiem Hoang
[Canadian Institute for Theoretical Astrophysics]
*Special Seminar*
Quantitative Polarimetry: from Star Formation to Cosmological Studies
Abstract

We are entering a golden age of dust polarimetry with numerous CMB experiments (e.g., SPIDER, BICEP/Keck, LiteBIRD) hunting for primordial gravitational waves through B-mode polarization, and a dozen of big instruments designed to elucidate the roles of magnetic fields in star formation through IR-mm dust polarimetry (e.g., SOFIA, SMA, ALMA, EVLA). The correct determination of B-mode signal, as well as solid understanding of magnetic fields in star formation, are only achieved when we have a quantitative treatment of dust polarization. In this talk, I will present first my results on quantifying the polarization spectrum of a newly discovered emission component, namely anomalous microwave emission. Second, I will review the quantitative, predictive theory of grain alignment based on radiative torques, and discuss ab-initio modeling of dust polarization that incorporates well-tested physics and comparisons with observational data. Third, I will present my plan to develop an accurate, physical model of CMB foreground polarization required for precision Cosmology with CMB-Stage IV experiments. Finally, I will discuss the unique potential of quantitative polarimetry in the next decade to elucidate the roles of magnetic fields in star and planet formation, and to reveal fundamental properties of magnetic turbulence and cosmic dust, through bridging solid theory, numerical simulations with observations.

642016-03-22 Tue
14:20~15:20
R1203
Ken Chen
[EACOA/NAOJ]
*Special Seminar*
Cosmic Dawn : Physics of the First Stars, Supernovae, and Galaxies
Abstract

One of the paramount problems in modern cosmology is to elucidate how the first generation of luminous objects, stars, supernovae, accreting black holes, and galaxies, shaped the early universe at the end of the cosmic dark ages. According to the modern theory of cosmological structure formation, the hierarchical assembly of dark matter halos provided the gravitational potential wells that allowed gas to form stars and galaxies inside them. Modern large telescopes have pushed the detection of galaxies up to a redshift of z ~ 10. However, models of the first luminous objects still require considerable effort to reach the level of sophistication necessary for meaningful predictions, Due to the complexity of involved physical phenomena, this physical understanding may only come by the proper use of numerical simulations. Therefore, I have used state-of-the-art simulations on some of largest supercomputers to study these objects. In my talk, I will discuss the possible physics behind the formation of these first luminous objects by presenting the results from our simulations. I will also give possible observational signatures of the cosmic dawn that will be the prime targets for the future telescopes such as the James Webb Space Telescope (JWST).

652016-03-16 Wed
14:20~15:20
R1203
Hyosun Kim
[ASIAA]
Circumstellar Spirals/Shells/Arcs: the Messages from Evolved Stars
Abstract

Evolved stars are the birth places of the chemical elements, and their extensive mass loss provides an important source of gas and dust to the interstellar medium. An understanding of the late stellar evolution and the nature of the mass loss process is important input for studies of the chemical evolution of a galaxy and the formation of next generations of stars. The shaping of the outflows is structured exhibiting arcs, shells, and spirals. Ever since the first discovery of a circumstellar spiral pattern of a heavily mass-losing evolved star, a paradigm whereby such patterns are induced by the orbital motions of the (postulated) central binary stars was emphasized. In addition, many ring-like patterns observed for longer than a few decades can be explained by the same spiral-shell pattern, but viewed at different angles. Recent high-resolution high-sensitivity molecular line maps from the ALMA and other sub-mm/mm interferometers facilitate new detections of circumstellar spiral-like patterns, and therefore the spirals/shells/arcs have led to a resurgence of interests. In this colloquium, I will describe the impact of binaries on the evolution of the late stages of stellar evolution. In particular, I suggest that the coexistence of bipolar (or multipolar) structures and shell-like patterns can both be understood within the framework of unified model.

662016-03-09 Wed
14:20~15:20
R1203
Michal Michalowski
[University of Edinburgh]
Massive stars formed in atomic hydrogen reservoirs
Abstract

I will discuss the process of gas inflow on galaxies and subsequent fueling of star-formation. Using recent ATCA HI observations I will show that galaxies with anomalous local metallicity decrements (gamma-ray burst host galaxies) have substantial atomic gas reservoirs, and are deficient in molecular gas. This suggests that star formation in these galaxies may be fuelled by recent inflow of metal-poor atomic gas. This is controversial, but can happen in low-metallicity gas near the onset of star formation because cooling of gas (necessary for star formation) is faster than the HI-to-H2 conversion.

672016-03-01 Tue
14:20~15:20
Physics 104
Howard K.C. Yee
[Department of Astronomy and Astrophysics, University of Toronto]
*ASIAA/NTU Joint Colloquium*
The Evolution of Galaxies in Clusters at z~1 and Beyond
Abstract

Galaxy clusters provide a large range of environments for the study of how the environment affects galaxy evolution. I will present some recent results on the evolution of galaxies in clusters at z~1 and beyond from two large cluster surveys. SpARCS is an imaging survey designed to search for galaxy clusters up to z~2 using the cluster red-sequence technique based on a combination of Spitzer Space Telescope’s IRAC 3.6um and ground-based z’-band images; GLASS is a multi-object spectroscopic survey of 10 of the richest SpARCS clusters at z~1 using the Gemini 8.2m telescopes. Analysis of GCLASS data show that galaxies in-falling into clusters at z~1 have their star formation suppressed in a relatively short time scale of less than 0.5 Gyr at an average location close to 0.5 r_200 (the cluster-centric radius within which the cluster is largely virialized). From imaging data obtain using the 24um MIPS camera on Spitzer, we also find that lower-mass in-falling galaxies show a possible last-gasp increase in their star formation before become quiescent. Using far-IR/submm data from the Herschel Space telescope, we will take a detailed look at the change in star formation via dust emission in 3 clusters at z~1.2 as galaxies in-fall into the clusters.

682016-02-24 Wed
14:20~15:20
R1203
Hauyu Baobab Liu
[ESO]
Gravitational unstable disks around FU Orionis objects?
Abstract

Young stellar objects (YSOs) may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp brightening events. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of these dense gaseous clumps onto the star. We report our high angular resolution, coronagraphic near-infrared polarization imaging observations using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) of the Subaru 8.2 m Telescope, towards four YSOs which are undergoing luminous accretion outbursts. The obtained infrared images have verified the presence of several hundred AUs scale arms and arcs surrounding these YSOs. In addition, our hydrodynamics simulations and radiative transfer models further demonstrate that these observed structures are indeed explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The apparently much smoother and older planet-forming disks may be merely the final products of these tempestuous and stochastic processes.

692016-02-17 Wed
14:20~15:20
R1203
Shigehisa Takakuwa
[ASIAA]
SMA and ALMA Study of Protostellar Binaries
Abstract

In this colloquium I will talk about our SMA / ALMA observations of protostellar binaries L1551 IRS 5, L1551 NE, and XZ Tau, including our latest ALMA cycle 2 results of L1551 NE. We found that the structures of the disks surrounding the binaries, circumbinary disks, are different among these protostellar binaries in the L1551 region. While in L1551 NE the circumbinary disk consists of two spiral arms stemming from the individual stars, in L1551 IRS 5 such arm features are not seen, and in XZ Tau no circumbinary disk is present. In L1551 IRS 5 and NE the gas motions in the circumbinary disks exhibit Keplerian rotation, but in the innermost part of the circumbinary disk in L1551 NE infalling motion toward the protostellar binary is also seen. I will discuss these results in the context of mass accretion onto the protostellar binaries and physical mechanism to set the final binary mass and mass ratio.

702016-02-03 Wed
14:20~15:20
R1203
Howard Yee
[University of Toronto]
The Evolution of Galaxy Cluster Shape and Brightest Cluster Galaxies since z~1.8
Abstract

I will examine two aspects of the growth of galaxy clusters from z~1.8 to the present time: the evolution of the shape of galaxy clusters and the growth of the brightest cluster galaxies (BGCs). Using two large samples of galaxy clusters from the Second Red-sequence Cluster Survey (RCS2) and the Spitzer Adaptation of RCS (SpARCS) survey, we measure the ellipticities of galaxy clusters from z~0.2 to 2.0. Using the 418 most massive clusters in the samples, we find the average ellipticity of the projected spatial distributions of galaxies in the clusters increases with redshift. This evolution in cluster shape is consistent with that measured from N-body simulations. I will also present recent results on the evolution of the star-formation rate and the growth of the stellar mass of BCGs using clusters from the SpARCS survey. I will briefly discuss possible connections between the BCG and the cluster shape.

712016-01-21 Thu
14:30~15:30
R1107
John Carpenter
[Joint ALMA Observatory]
*Special Seminar*
The Evolution of Circumstellar Disks: ALMA Observations of the Upper Sco OB Association
Abstract

The supply and lifetime of gas and dust in circumstellar disks are among the primary determinants of the properties of young planetary systems. Most of the information on disk evolution has so far come from infrared surveys, which have established that hot dust in primordial disks dissipates in approximately 5-10 Myr. ALMA is now playing a central role in these studies by probing colder gas and dust in disks. In this talk, I present recent results from an ALMA survey of 106 disks in the Upper Sco OB association. At an age of 5 Myr, Upper Sco is a benchmark region to establish the properties of disks at the end state of their evolution. By comparing Upper Sco with disk properties in young regions, we can assess how the gas and dust in disks evolve on timescales of 5 Myr. [This is a joint special seminar and planetary science group talk.]

722016-01-20 Wed
14:20~15:20
R1203
Jean Coupon
[University of Geneva]
Probing the relationship between Galaxies and Dark Matter with Lensing and Clustering in CFHTLenS/VIPERS
Abstract

I will present recent results on the connection between galaxies and dark matter haloes up to z=1, measured from a combined lensing and clustering analysis in the CFHTLS/VIPERS field. We obtained 30 deg2 of deep NIR data over the entire VIPERS area: whereas this program was initially designed to get robust stellar masses for the spectroscopic targets, we have shown that when properly calibrating photo-z's with spectro-z's and accounting for photo-z error in the modelling, one is able to get accurate constraints from projected clustering and galaxy-galaxy lensing from a photometric sample. This significant increase in survey area for such depths and good lensing data allowed us to consistently probe the Mstar-Mh relation from the peak of the stellar-to-halo mass ratio (SHMR) up to the most massive clusters, a key asset to bring new insights on galaxy evolution.

732016-01-18 Mon
14:20~15:20
R1203
Andrew Cooper
[Durham University]
*Special Seminar*
Modelling Galaxy Formation in a LambdaCDM Universe
Abstract

In this talk I will give an overview of the state of the art in two widely used techniques for modelling the cosmological galaxy population: hydrodynamical simulations and semi-analytic models. Over the last 25 years, these techniques have acted as focal points, drawing together theories for many different phenomena interacting over a wide range of scales. The result is something approaching a 'standard model' for galaxy formation, which provides a remarkably straightforward and consistent framework for interpreting a host of observations in the nearby Universe. Ambitious galaxy surveys planned for the next decade and new instruments such as ALMA will greatly improve this model by constraining the specific evolutionary paths that galaxies take from their first formation to the present day. This in turn will require a new era of interaction between `macroscopic' simulations and detailed modelling of astrophysics at 'sub-galactic' scales. I'll describe my work on two exciting but relatively under-exploited constraints on galaxy evolution: metal enrichment (including the case for an varying stellar initial mass function based on sub-mm number counts) and diffuse light in the outskirts of galaxies. Finally, I'll briefly advertise the Milky Way and Bright Galaxy surveys that will be carried out with the Dark Energy Spectroscopic Instrument.

742016-01-15 Fri
14:20~15:20
ASMAB 1F Auditorium
Rachel Mandelbaum
[CMU]
Galaxy halo masses and implications for galaxy evolution from weak lensing measurements
Abstract

In the past decade, weak gravitational lensing has become one of the best ways of measuring galaxy halo masses for galaxy samples at low to intermediate redshifts. Measurements of the average halo density profiles for galaxies with a given luminosity or stellar mass (observable mass proxies) have revealed a great deal about the connection between halo masses and these mass proxies. After a broad overview of what such measurements have shown us in several datasets, I will describe some recent measurements in the SDSS that illustrate a bimodality in halo mass at fixed stellar mass, with red galaxies that reside at the centers of dark matter halos having host halo masses that are a factor of 2-3 larger than those that host blue central galaxies. I will discuss the implications of these results for models of galaxy formation and evolution, and also propose future measurements with upcoming datasets such as HSC that will shed further light on the relevant galaxy formation and evolution processes.

752016-01-06 Wed
14:20~15:20
R1203
Dae-Won Kim
[ASIAA]
Gaia and Data Intensive Astronomy
Abstract

Gaia is an ESA satellite project launched at Dec. 2013. It will map our Galaxy in 3D by measuring six astrometric parameters (i.e. two positions, two proper motions, parallax, and radial velocity) of one billion stars over the whole sky. Astrometric accuracy of Gaia for G type star is 5-16 μas for bright stars, 24 μas at V = 15 mag and 540 μas at V = 20 mag, which is the highest accuracy that has ever been achieved. Gaia simultaneously obtains low-resolution spectrum of each star using Blue and Red Photometer (BP and RP: 330-680nm and 640-1000nm, respectively). By the nature of Gaia, it will produce enormous amount of complex data. Analyzing Gaia data is thus a challenging and huge task requiring Big Data experts and dedicated computing powers as well. In this talk, I will give an overview of the Gaia mission and efforts for Gaia data analysis in DPAC (Data Processing and Analysis Consortium).

TEL: 886-2-3365-2200 FAX: 886-2-2367-7849
General: asiaa_replace2@_asiaa.sinica.edu.tw Media Request: epo_replace2@_asiaa.sinica.edu.tw
11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C.