午餐會報 (2018)

I will talk about observational results that have puzzled me for the past 14 years, and show how the Hyper SuprimeCam Survey could help shed light on these.

The galaxy integrated star formation rate(SFR)-stellar mass(M∗) relation holds important information for understanding the star formation history and evolution of galaxies. Although the SFR-M∗ relation has been reported with a variety of different data sets, their appearance can vary significantly from one to another. In this work, we determine what controls the integrated and the spatially-resolved SFR-M* relation in both star-forming and quiescent galaxies by linking the spatially resolved SFR-M* relation with various galaxy properties such as stellar mass and bulge-to-total light ratio using MaNGA data (Mapping Nearby Galaxies at APO).

Mass discrepancy-acceleration relation (MDAR) is a relation in dark matter problem found in spiral galaxies. The mass ratio between observational mass divided by baryonic mass strongly related to baryonic acceleration (or observational acceleration) but unrelated to other physical quantities (ex, radius). Recently, McGaugh et al. 2016 (PRL117.201101) revealed a tight relation between observational acceleration and baryonic acceleration in 153 spiral galaxies from SPARC database which is consistent to the MDAR. It can well explain Tully-Fisher relation, deficient dark matter in ordinary elliptical galaxies, surface densities discrepancy etc. However, our work focus (Tian & Ko 2017) on elliptical galaxies in strong lensing such as Einstein rings. We found the MDAR in 57 elliptical lenses is consistent with spiral galaxies.

Whether magnetic fields are important in the star formation is a fundamental question in astrophysics. The studies in past decades show that the role of magnetic fields in star formation is complicated and diverse, and that neither of the two extreme case theories (dominating or negligible magnetic fields) can fully explain the star formation activity. Hence, the detailed investigations of the role of magnetic fields in particular physical scale, density, and environments are necessary to reveal the full picture, which thus requires multi-wavelength observations to trace. In this talk, I would present our polarization observations in optical, infrared, and submillimeter wavelengths toward the filamentary clouds IC5146. I would first discuss how deep we can trace using each data set, and further show how the role of magnetic fields possibly change in different scale.

I will present an analysis of the quenching of star formation (SF) in galaxy clusters since z~1, based on a sample of 220 galaxy clusters from the SpARCS survey in the XMM-LSS and ELAIS-N1 fields, using the public data release from HSC-SSP and Sptizer SWIRE survey data in these fields. In particular, we examine the star-forming galaxy fraction (f_SF) as a function of redshift, galaxy stellar mass, and cluster-centric radius. I will also present some preliminary results on the SFR-stellar mass relation (the "main sequence") in the field and in clusters, using a combination of HSC and Spitzer SWIRE MIPS data, over the same redshift range.

We explore the early growth of supermassive black holes (SMBHs) by using a near-infrared (NIR) spectrum of a recently discovered z = 6.621 QSO PSO J006+39 in three physical properties: (1) According to the standard thin disk model, the NIR (rest-frame FUV) spectrum of this QSO is dominated by the emission from the accretion disk. We found that the power-law slope of the continuum αλ of this QSO in NIR, −2.94 ± 0.03, is much bluer than the expected slope −1.5 from the standard thin disk model. We will discuss two possibilities to explain this unique slope: the black hole spin and the Comptonisation corona of the accretion disk. (2) The growth rate can be estimated by the Eddington ratio (Lbol/LEdd). We first estimated the SMBH mass by using the Mg ii line width and the rest frame luminosity L3000Å to be ∼ 108 M⊙ . Then we derived Eddington ratio Lbol/LEdd ∼ 1. (3) There are surprisingly many metal-rich QSOs found in the early universe, given the required time for metal formation. We present two probes to estimate the metallicity of this QSO. The Fe ii/Mg ii ratio is often used as an indicator for high-z QSOs because Fe metallicity requires a certain time to be enhanced by the Type-Ia supernovae. The detection of the faint He ii line in this QSO provides another path to measure the metallicity. We used N v/He ii ratio to estimate the metallicity by considering the blue FUV continuum in the photoionization calculation. We will discuss implications of these physical properties of this QSO about the growth of SMBHs in the early universe.

Galaxy interactions and mergers are often accompanied by an increase in star formation rate (SFR). Since the properties of the molecular gas are essential for star formation, it is vital to establish whether, and by how much, galaxy interaction affects the molecular gas properties, and that in turn lead to the change in SFR. We investigate the influence of galaxy interactions on global molecular gas properties by studying a sample of 61 interacting galaxies, and compare their gas properties with galaxy-properties-matched control sample (isolated galaxies). We find that SFR, gas mass, and gas fraction are gradually enhanced with respect to the control sample as two galaxies approaching each other, and also enhanced from minor to major mergers. On the other hand, dependence of gas star formation efficiency on merger properties is less obvious. According to our analysis, we conclude that galaxy interaction can modify the molecular gas properties of a galaxy, although the strength of the influence is merger properties dependent. Moreover, on the galaxy-wide scale, the total gas content, but not SFE, plays a more important role in the interaction-triggered SFR.

In this lunch talk, I will present the state-of-the-art result of the X-ray observable to mass scaling relations based on a sample of galaxy clusters selected by the South Pole Telescope out to redshift 1.5.

Utilizing James Clark Maxwell Telescope (JCMT) 850 micron SCUPOL dust polarization data, we investigate the configuration of the magnetic (B) field in the circumnuclear disk (CND) of the Galactic Center (GC). The SCUPOL data show a highly improved polarization coverage and resolution compared to earlier 100 micron observations. The 850 micron data have a resolution and coverage similar to previous 350 micron polarimetry data. However, with a proper sampling on a 10" grid, we find the 850 micron data trace the morphological structures of the CND substantially better. Furthermore, because the 850 micron trace the field deeper into the material near Sgr A*, they represent the highest resolution submillimeter probe to date of the CND magnetic field. The observed B-field morphology is well described by a self-similar axisymmetric disk model where the radial infall velocity is one quarter of the rotational velocity. A detailed comparison with higher-resolution interferometric maps from the Submillimeter Array further reveals that the $B$-field aligns with the neutral gas streamers connecting to the CND. Moreover, the innermost observed $B$-field structure also appears to trace and align with the mini-spiral located inside the CND. This suggests that there is one underlying B-field structure that is connecting the CND with its streamers and the inner mini-spiral. An estimate of beta_Plasma<=1 - based on the global B-field morphology that constrains the azimuthal-to-vertical field strength ratio of around 40 combined with a measurement of the azimuthal velocity--indicates that the B-field appears dynamically significant towards the CND and also onwards to the inner mini-spiral.

In this talk, I will introduce the CLAD ( Certified Labview Associate Developer) and share my experiment to get the CLAD complimentary last year.

We investigate the influence of the random velocity of molecular gas on the star forming activities in molecular clouds. It is known that physical states of a molecular cloud, such as temperature and density, will influence the star forming activities in the cloud. Besides, it is believed that local and turbulent motions of the molecules in the cloud might provide a significant amount of pressure against gravitational collapse and might thus prevent or reduce star formation in the cloud. However, the influence of the gas motions on the star formation activities is still poorly understood. We used the Atacama Large Millimeter/submillimeter Array (ALMA) data to obtain 12CO(J=1-0) flux and velocity dispersion, combining with the 3.6 and 8 micron mid-infrared data of the Spitzer Space Telescope to probe the effects of gas motion on star formation activities for several nearby galaxies. From our results we were able to derive a modified Kennicutt-Schmidt law with velocity dispersion as an additional parameter. We found that the higher the velocity dispersion in molecular clouds, the lower the star formation activities.

In this talk I will present the first high-resolution, submillimetre-wavelength, polarimetric observations of - and thus direct observations of the magnetic field morphology within - the dense gas of the Pillars of Creation in M16. These recent results from the JCMT BISTRO (B-fields in Star-forming Region Observations) survey show that the magnetic field runs along the length of these photo-ionized columns, perpendicular to, and decoupled from, the field in the surrounding photoionized cloud. I will discuss estimation of the magnetic field strength in the columns, and its implications for the formation of the Pillars. I will further discuss the energy balance in the Pillars, and hypothesize on the effect of the magnetic field on the future evolution and lifetime of the Pillars.

Fermi bubbles, black hole feedback in our Galaxy, is a huge structure in our Galactic halo. One possible origin of the bubbles is repeated star captures by the supermassive black hole at the Galactic center. We model these processes as multiple energy outbursts (a.k.a. explosions) from a small volume into a layered exponential atmosphere. We study the formation of the bubbles by the MHD simulation code FLASH4. The evolution and morphology of the bubbles is compared under different initial poloidal and toroidal magnetic field configurations.

Asymptotic Giant Branch (AGB) stars in the Milky Way are often overlooked due to difficulties in obtaining distances. Understanding their dust emission properties and mass-loss histories leads to better comprehension of the ISM evolution in the Milky Way, in particular its dust reservoir. Most studies have determined the stellar dust mass using mid-IR emission, but a historic cold dust reservoir from a previous mass-loss phase may remain undetected in the mid-IR, requiring observations at longer wavelengths. We present results of a search for extended dust emission from a diverse sample of AGB stars within 1 kpc. This project is part of the Nearby Evolved Star Survey (NESS), which aims to determine gas and dust return from a volume limited sample of galactic evolved stars. Observations at 450​μm​ and 850​μm​ were carried out using the SCUBA-2 instrument on the JCMT and combined with Herschel PACS observations at 70​μm​ and 160​μm from the MESS survey (Groenewegen et al., 2011; Cox et al., 2012). Using azimuthally-averaged surface brightness profiles we determined extension and percentage flux of the extended component for each source at the four wavelengths. We derived extensions at the 3σ levels greater than ~40'' for majority of the sources at SCUBA-2 850​μm​. The fraction of the flux emitted from the extended region is ~40% at 850​μm​ and ~50% at PACS wavelengths. We report a clear detection of the detached shell of U Ant in both 450​μm​ and 850​μm​. This is the first time this detached shell has been detected in the sub-mm continuum. By fitting a modified black body to four-point SEDs at each radial point we derive the dust temperature, spectral index of emissivity, and column density to probe dust mass-loss history and detect changes in physical properties of dust as a function radius (hence, time). The resulting dust-to-gas ratios are consistent with canonicalvalues. The surface density profiles suggest deviation from constant mass loss in a majority of the sources.

Among the stellar spectral classifications, B-type stars are the fastest rotators with a equatorial speed of approximately 100 km/s. Some of them showing hydrogen emission line, known as Be stars, can rotate even faster, up to the break-up velocity. The formation of rapid rotation were thought to be part of the evolutionary effect, however, we found the least correlation between the age of the clusters and corresponding Be fraction through Palomar Transient Factory (PTF) project. In addition to the issue of evolution, Be stars are known variable stars, but mostly they show heterogeneous semi- or non-regular variation. Here comes Zwicky Transient Facility (ZTF) with a 47 square degree field of view, so the northern sky can be surveyed with high cadence e.g., over two times a night on galactic plan. Unlike the individual Be stars monitoring, ZTF provides an opportunity window over three years which makes systemic census possible for the photometric variability investigations of Be stars in the deeper sky. Here, we also present the preliminary light curves of Be stars from the ZTF commissioning data.

Dwarf planets in Kuiper belt are too far for us to study in detail by telescopic observations from Earth for past several decades. After the New Horizons spacecraft’s flyby observations of the Pluto-Charon system in July 2015, we now have a better understanding of these faraway objects. Sputnik Planitia of Pluto is one of the most important discoveries of the New Horizons spacecraft at its flyby observations of the Pluto-Charon system in July 2015. Sputnik Planitia is located at the northern mid-latitude hemisphere in the antipodal position to Charon on the opposite side. It contains a large quantity of the nitrogen ice on Pluto and the content of Pluto’s atmosphere is likely controlled by the variable sublimation rate of Sputnik Planitia’s ice. In this work, we use a coupled treatment to compute the surface temperature and pressure of Sputnik Planitia on Pluto when it revolves around the sun in its eccentric orbit with special attention to the sublimation process of the nitrogen ice stored in Sputnik Planitia. In addition, we will apply this model to other Pluto-like dwarf planets in Kuiper belt which surfaces could be mainly composed of nitrogen ice. This set of model calculations allows us to explore the range of the atmospheric contents and mass loss process of the icy dwarf planets.

Using the N2H+(3-2) observed with the SMA and CSO, and N2H+(1-0) observed with the NRO 45m and ALMA + IRAM 30m, we study the structure and kinematics of the Orion Molecular Cloud 1 (OMC1). Unlike other molecular lines such as HCO+ or HCN, the observations in N2H+ are less affected by the expansion or explosion originated from the Orion KL, and can trace the dense gas distribution. Using the kinematics and structure, the OMC1 region is divided into three subregions. The northern region consists of multiple filaments parallel with each other, the western region consists of radial filaments, and the southern region is the OMC1-South. These three regions have different velocities, which exhibits a velocity structure similar to a global collapse scenario. We derived the physical parameters of these regions by conducting non-LTE analysis. The high-resolution N2H+ (3-2) and (1-0) images reveal multiple filamentary structure, having a typical width of 0.02-0.03 pc. Using the non-LTE analysis, we find that the filament regions have a higher density and a lower temperature than the non-filament regions. This may be explained by the blocking of external heating sources due to the dense gas in the filaments. We also study the gas motion inside the filaments, and compare them with the core formation model.

Genetic Algorithm is widely adopted on multi-variables optimization problem in the academia and the industry. I applied GA on our radiative simulator SPARX to find out a 1D model of density, temperature, and dust opacity profile of NGC 1333 I4A1 to fit the multi-wavelength continuum data. I will introduce the method and show the potential to apply the method on Astronomy.

In this 101 level lunch talk, I will introduce how to combine theories on large scale structure and the Sunyaev–Zel'dovich effect to constrain standard cosmology model. I will present the state-of-the-art cosmological constrains base on the SPT-selected clusters sample and discuss some future improvements through extra mass calibraters and enlarge SPT samples. Students with general interests in (observational) cosmology are especially welcome.

[HBS 2006] 40671 is a confirmed long period Mira found in M33.Using observed light curves from Hartmann et al (2006) data, Barsukova et al. (2011) found a period of 665 day for this Mira. In addition to Hartmann's data (2005~2006), we also collected PTF (Palomar Transient Factory) data taken from 2009 to 2016. Combining these two datasets that spanned ~10 years can be used to refine the period of this Mira. Based on the combined light curve, we found that this Mira could exhibit a long secondary variation. To aid in our investigation, we collected known Mira light curves data from the OGLE and LAMOST/ASAS database. According to the OGLE Mira, we found majority of Mira light curves are composed with a short pulsation period and a long secondary variation. We also use machine learning to classify these OGLE Mira target. Hence we also tried to look for additional features in Mira light curves using our method, and compared to the light curve of [HBS 2006]40671 to refine its pulsation period and to determine its long secondary period, hence we also tried to look for additional features using our method,and compared to the light curve of [HBS 2006]40671. Therefore, we can use those information to refine the short period and find out the long term variation. In this work, we present our latest investigation on the period refinement of this Mira.

X-ray population study of a galaxy has long been viewed as an important way of reflecting the environment of the galaxy as well as providing clues of its revolution. I will introduce the basics of the X-ray population study of a galaxy and what should be taken into account while analyzing it.

We calculated accretion-induced collapse (AIC) progenitor models starting from super- AGB stars to the ignition of oxygen burning and the start of gravitational instability, using MESA code with updated nuclear physics inputs. URCA cooling process and electron capture on 24Mg and 20Ne are modelled with the newly calculated beta rates table with fine grids provided by Suzuki et al., which gives a more accurate density threshold for the ignition of oxygen burning. Near the final moment, a convection zone is developed above the ignition point, which will alter the composition and thermal structure of AIC progenitor. This could have a significant influence on the fate of AIC, which is under intensive debate. We also point out two uncertain issues. For the case with the least massive star (8.2M_sun), an off-centre carbon-rich (2%) island of about 0.1M mass is left and will be reignited during electron capture on 24Mg. At the carbon-burning stage, the neutron capture on 24Mg nuclei with the JINA reaction rates would deplete 24Mg to become 25Mg. Further improvements in the stellar evolution calculation and nuclear physics inputs are still needed for a conclusive determination on the fate of AIC.

Among the ~4700 MaNGA galaxies, we identified ~1300 potential galaxy pairs and mergers based on their spectroscopic companions or morphologies. We have devised scheme for classifying the stage of an interaction based on the morphological appearance of the system. The effect of interactions on SFR is quantified by computing the global and spatially-resolved SFR relative to the control galaxies and spaxels. The preliminary results show that although the global SFR enhancement increases with merging sequence, there is considerable variation in the radial profile of local SFR enhancement across the stages.

On behalf of the CARTA team, I will introduce the CARTA (Cube Analysis and Rendering Tool for Astronomy) project. CARTA will serve as the next generation image viewer for the CASA package. In this informal talk, I will briefly report the development progress, then introduce the features we have implemented with a live demo.

The NOEMA (NOrthern Extended Millimeter Array), located at 2550m in the French Alps is the successor of the Plateau de Bure Interferometer. With twelve 15-meter antennas, 2SB receivers with 8 GHz IF per sideband and polarization, and baselines up to 1.6 kilometers, NOEMA is designed to offer ten times the sensitivity and four times the spatial resolution that was possible with the Plateau de Bure interferometer. As a unique combination of cutting-edge technology NOEMA will allow researchers address astronomical key questions as those related to the molecular complexity of star- and planet-formation processes in the Milky Way, and structure formation and galaxy evolution in the Universe. I will present the current status of the NOEMA project.

Investigation of variability is a powerful tool to understand the nature and process in the inner nuclear regions of AGNs. Variability can range time scales from intraday to years. However, variability on intraday timescales in AGNs is puzzled. Mechanisms for intraday variability include shock-in-jets models and instabilities of accretion disks. To extend the sample of AGN with intraday variability, we searched for intraday variability in ~3600 QSOs using high-cadence (20 mins) data of PTF/iPTF survey. I will present current preliminary results and status. Also, I will introduce future plans of using Zwicky Transient Facility (ZTF) data with a 47 square degree field of view (,and LSST) for this project.

The quenching "maintenance" and related "cooling flow" problems are important in galaxies from Milky Way mass through clusters. We investigate this in halos with masses ~1e12-1e14 solar mass, using non-cosmological high-resolution hydrodynamic simulations with the FIRE-2 (Feedback In Realistic Environments) stellar feedback model. We first focus on physics present without AGN, and show that various proposed "non-AGN" solution mechanisms in the literature, including Type Ia supernovae, shocked AGB winds, other forms of stellar feedback (e.g. cosmic rays from supernovae), magnetic fields, Spitzer-Braginskii conduction, or "morphological quenching" do not halt or substantially reduce cooling flows nor maintain "quenched" galaxies in this mass range. This all supports the idea that additional physics, e.g., AGN feedback, must be important in massive galaxies. We then test various AGN feedback toy models with different forms of energy input and ranges of coupling, exploring what scenario can possibly quench galaxy and suppress the cooling flows without resulting in halo properties that contradict observations. The test scenarios include momentum injection, turbulent stirring, thermal heating, and cosmic ray injection. We found that turbulent stirring confined within 100 kpc and cosmic ray injection can both maintain a stable, low-SFR halo for extended periods of time, because they provide non-thermal pressure form which can stably lower the core density and cooling rate. This can be much more efficient than heating up the gas thermally. We conclude that the enhancements of turbulence and cosmic ray energy are very important aspects of AGN feedback, and can be the dominant processes that quench the massive ellipticals.