Lunch Talk (2015)

Understanding how the cluster and group baryon components evolve with redshift is a key question today. While there have been many detailed studies of intermediate and high redshift galaxy clusters, most previous observational studies of large cluster samples have focused on nearby systems due to the difficulty of defining high redshift samples and of following them up in the X-ray and with adequately deep optical or near-infrared imaging. That is changing now with the recent analyses of Sunyaev-Zel’dovich effect selected clusters and groups at intermediate and high redshift. In this talk I will present the recent work of the multi-wavelength study of baryon content for massive galaxy clusters selected by South Pole Telescope.

A variety of methods have been proposed to define and to quantify galaxy environments. While these techniques work well in general with spectroscopic redshift samples, their application to photometric redshift surveys remains uncertain. To investigate whether galaxy environments can be robustly measured with photo-z samples, we quantify how the density measured with the nearest neighbor approach is affected by photo-z uncertainties by using the Durham mock catalogs in which the 3D real-space environments and the properties of galaxies are exactly known. Furthermore, we present an optimization scheme in the choice of parameters used in the 2D projected measurements which yields the tightest correlation with respect to the 3D real-space environments. By adopting the parameters in the density measurements, we show that the correlation between the 2D projected optimized density and real-space density can still be revealed, and the color-density relation is also visible even for a photo-z uncertainty (σ∆z/(1+z)) up to 0.06. We find that a deep (i ∼ 25) photometric redshift survey with σ∆z/(1+z) = 0.02 yields a comparable performance of density measurement to a shallower i ∼ 22.5 (24.1) spectroscopic sample with 40% (20%) sampling rate. Finally, we discuss the application of the local density measurements to the Pan-STARRS Medium Deep survey, one of the largest on-going deep imaging surveys. Using data from ∼ 5deg2 of survey area, our results show that it is possible to measure local density and to probe the color-density relation in the PS-MDS, confirming the simulation results. The color-density relation, however, quickly degrades for data covering smaller areas.

In the course of star formation, infalling envelopes around protostars are considered to transform into Keplerian rotating disks. The disk formation process is, however, still not understood well. Our ALMA Cycle 0 observations toward the late-phase protostar TMC-1A have revealed the existence of a 100 AU-size Keplerian disk surrounded by an infalling envelope around the protostar. Interestingly, the infall velocity of the envelope is found to be 0.3 times as large as the corresponding free fall velocity. Possible mechanism to reduce the infall velocity and a disk formation scenario are also discussed.

I will briefly introduce some interesting aspects of gas dynamics and star formation in barred spiral galaxies. The central bar not only drives the gas into the center of the galaxy, but also excites spiral density waves in the outer part. Questions such as what are differences between them and grand-design spirals will be discussed.

Observations and simulations have now reached the point where the giant molecular cloud (GMCs) populations can be studied over a whole galaxy. This is immensely helpful for understanding star formation, since the cloud properties set the conditions for new star birth. Yet, are these two groups really comparing the same objects? While simulators work in position-position-position (PPP) space, observers see projected properties along the line of sight, identifying clouds in position-position-velocity (PPV) space. If these methods do not identify the same objects, then the interpretation and comparisons between the data sets may be highly misleading. In this research we generated PPV and PPP data for a high-resolution simulated galaxy and compared the identified cloud properties in both data sets.

During last summer, we developed a new Graphics Processing Unit (GPU)-based code, Odyssey, for ray-tracing computation in curved space-time. In this talk, we will (1) introduce how Odyssey works, (2) Education: show real time photon trajectories when black hole spin or inclination angle changes, by using the educational software we designed, (3) Science: demonstrate the related physics behind time-dependent event (e.x., orbiting hot spot ), and general relativistic radiative transfer (GRRT).

The central image of a strongly lensed background source places constraints on the foreground lens galaxy's inner mass profile slope, core radius and mass of its nuclear supermassive black hole. Using high-resolution long-baseline ALMA observations and archival HST imaging, we model the gravitational lens SDP.81 and search for the demagnified central image. There is central continuum emission from the lens galaxy's AGN but no evidence of the central lensed image in any molecular line. We use the CO J=5-4 map to determine the flux limit of the central image excluding the AGN continuum. We predict the flux density of the central image and use the limits from the ALMA data to constrain the inner mass distribution of the lens. For the core radius of 0.15" measured from HST photometry of the lens galaxy assuming that the central flux is completely attributed to the AGN, we find that a black hole mass of log(M_BH/M_sun) > 8.4$ is preferred. Deeper observations with a detection of the central image will significantly improve the constraints of the inner mass distribution of the lens galaxy.

Direct images of scattered light from protoplanetary disks provide valuable information about their surface geometries, and thereby possible ongoing planet formation. A recent 5-year survey with Subaru-HiCIAO (SEEDS) has been successful in observing diverse disk morphologies in these disks. I present our results for the SU Aur disk, which is associated with intriguing tails not seen in other disks. These tails may be due to an encounter with an unseen brown dwarf (de Leon, Takami et al., ApJL, submitted).

The discovery of over 4,000 exoplanet candidates has unmasked the strangeness of planetary systems in the solar neighborhood. For instance, most of the confirmed planets reside in orbital periods of less than 100 days around their respective host stars, which places them well within the orbit of Mercury. In this talk, I present a prescription to expand the capabilities of the stellar evolution code Modules for Experimental Stellar Astrophysics (MESA) to model gaseous planets in highly irradiated environments. I will illustrate how we modified MESA to include planet core luminosity, heavy element enrichment, and mass loss due to hydrodynamic winds. Using these dynamical models, we then constructed mass-radius relationships of planets from 1 to 20 Earth Mass and investigated how mass-loss impacts their composition and evolution history. We anticipate that this versatile, user-friendly code will see widespread applications in complementing future exoplanetary surveys such as K2, TESS and PLATO.

The detection and characterization of filamentary structures in the cosmic web allows cosmologists to constrain parameters that dictates the evolution of the Universe. To detect cosmic filaments, we propose a density ridge model and introduce the subspace constrained mean shift algorithm. The density ridges are collection of curves that represent high density regions. By comparing density ridges to both smoothed particle hydrodynamics simulation and the Sloan Digital Sky Survey, we have found that several properties of galaxies, including principal axes, color, stellar mass and size, are influenced by filaments.

The Cosmicflows Project compiles distances and peculiar velocities for over 8000 galaxies. The purpose is to develop a three-dimensional map of the distribution of matter and motions of galaxies in the local universe, in order to study the large-scale structure and the formation process. One of the important methods of acquiring distance in the Cosmicflows Project is the Tip of the Red Giant Branch (TRGB) method. The TRGB method is highly accurate and efficient in distance determination, allowing detailed studies in our neighboring Universe. I will introduce the current status and the public product of the Cosmicflow Project, and some new findings derived from the product, especially from the TRGB method.

I have been visiting CFHT as a resident astronomer from Taiwan in the past nine months. In this period, interesting and not-so-interesting things had happened inside and outside CFHT. I will brief you several of them, my contribution to CFHT operation, and how my life there is like.

Analytical calculations and hydrodynamical simulations have shown that in massive dark matter halos (> 10^12 solar mass), gas is shock heated to virial temperature that little cool gas can survive. However, deep 21 cm observations reveal that some early-type galaxies are in fact rich in HI gas. The presence of cold gas challenges the theoretical understanding of how massive galaxies grow and evolve. Beyond the local Universe, observations of QSO absorption-line systems offer a powerful tool for studying the otherwise invisible gas. I will summarize absorption-line studies that probe the presence of cool (~10^4 K) gas around massive galaxies. In particular, I will talk about our recent study of cool gas content around massive, luminous red galaxies (LRGs) at z~0.5 from SDSS DR12, the largest galaxy and QSO samples available to date. The unparalleled constraints on the presence of cool gas gives us insights into the origin of the gas. I will discuss possible physical mechanisms which could attribute to the observed cool gas and how we could test different scenarios in the future.

Projects such as Galaxy Zoo and Planet Hunters have established that the involvement of volunteers in astronomical data processing can produce remarkable results, sorting through large datasets and enabling serendipitous discoveries. Yet the next generation of large surveys threaten to overwhelm such projects, especially when decisions are needly rapidly in response to transient events. Taking seriously the promise of citizen science in the era of LSST and SKA requires efficient allocation of tasks, collaboration between human and machine classifiers and a focus on the areas where humans can really make a difference. This talk will use examples drawn from the Zooniverse platform to illustrate the latest thinking on these problems, and explain how rapid project iteration enabled by new software puts citizen science in reach of all astronomers.

I will talk about the connection among activity of nuclear accretion, star formation, and galaxy morphology. In our work, we focus on mid-infrared power-law emission selected AGNs, which are complementary samples of X-ray selected AGNs. We fit optical to far-infrared photometry by the latest SED techniques to derive stellar masses, star formation rates, dust properties, and AGN contribution in the COSMOS field. We also explore galaxy morphologies through ACS and WFC3 images, which provide structural properties of galaxy stellar component at high redshift. We compare AGN host galaxies with other star-forming galaxies and discuss the effect of nuclear activity on galaxy structures and their evolution.

We performed a comprehensive analysis of the Herschel spectra of BHR71, an embedded Class 0 protostar. We recover 66 lines in the central spaxel, and more than 700 lines are detected in all spaxels in PACS, and SPIRE. The CO rotational diagram analysis shows four excitation temperature components, 51 K, 153 K, 408 K, and 1053 K. Low-J CO lines trace the outflow while the high-J CO lines are centered on the infrared source. The emissions of H2O traces the outflow on large scales, while H2O emissions populate along the equatorial plane on small scale scales. We model the structure of envelope using dust radiative transfer with Hyperion to fit the spectral energy distribution (SED) observed by Spitzer and Herschel. The model incorporates rotational collapse and an outer static envelope as well as outflow cavity and disk. Our exploration of parameter space shows that the evolution of collapsing envelope can be constrained by Herschel spectra and the structure of outflow cavity plays a critical role in the shorter wavelength. We found the density profile of cavity with a power law with a constant inner region can reproduce the observations. The high central luminosity in the best-fit model shows a hint of a higher accretion rate than the rate derived from collapse model. Our model constrains BHR71 to have an age of 29000 years and a total dust mass of 0.04 Solar mass.

We present a novel method to estimate the masses of galaxy clusters using the density enhancement of the background normal galaxies induced from the lensing magnification. Two background galaxy populations are selected for this study through their photometric colors; they have characteristic redshifts ⟨z⟩ ≃ 0.9 (low-z background) and ⟨z⟩ ≃ 1.8 (high-z background). Stacking these populations in a sample of 19 massive galaxy clusters selected by the South Pole Telescope (SPT) Sunyaev-Zel’dovich effect (SZE) survey at a median redshift z ≃ 0.42, we detect the magnification bias effect at 3.3σ and 1.2σ for the low- and high-z backgrounds, respectively. The resulting mass estimate is in a good agreement with the SZE-inferred masses and, moreover, the shear profiles predicted by magnification are consistent with the the observed ones. This approach only requires the accurate photometry and is well suited to the ongoing/future wide field survey (e.g., DES or HSC).

The population of nearby of gas-rich and highly dust-obscured Ultra Luminous Infrared Galaxies (ULIRGs) provides us with a unique opportunity to study the physical processes governing star formation in kinematically violent and radiation-harsh environments. As part of the Herschel Comprehensive (U)LIRG Emission Survey (HerCULES) we have obtained the full CO rotational ladder for a sample of 26 (U)LIRGs. In addition, we have compiled our ground-based spectral line observations of this sample, as well as all available data from the literature, of crucial dense gas tracers such as CS, HCN, and HCO+ (and in some cases their isotopologues). I will discuss some of the first results coming out of this unique data-set, from simple star formation relations to multi-phased Large Velocity Gradient (LVG) radiative transfer models that allow us to disentangle different molecular gas phases and possibly different molecular gas heating mechanisms in these galaxies.

Pluto is one of the largest dwarf planets residing in the Kuiper belt, a sea of icy planetesimals orbiting beyond Neptune. In mid-July, NASA's New Horizons spacecraft became the first mission to reach Pluto, making its closest approach to the dwarf planet and its largest moon Charon. The images and spectra obtained during the closest days and hours of the flyby will rewrite our understanding of the Pluto system. I'll present the New Horizons mission, talk briefly about what we knew previously about Pluto, and present some of the highlights from the preliminary fly-by data presented to the pubic.

Planet formation in protoplanetary disks is a fast-paced field. I will summarize a few interesting results I heard recently from the disk meeting held on the historic island of Cyprus.

The Kepler mission results indicate that systems of tightly packed inner planets (STIPs) are present around of order 5% of FGK field stars (whose median age is ~5 Gyr). We propose that STIPs initially surrounded nearly all such stars, and those observed are the final survivors of a process in which long-term metastability eventually ceases and the systems proceed to collisional consolidation or destruction, losing roughly equal fractions of systems every decade in time. In this context, we also propose that our solar system initially contained additional large planets interior to the current orbit of Venus, which survived in a metastable dynamical configuration for 1%-10% of the solar system’s age. Long-term gravitational perturbations caused the system orbits to cross, leading to a cataclysmic event that left Mercury as the sole surviving relic.

Strong gravitational lensing is a very powerful tool for measuring galaxy masses at cosmological distances and provides a unique opportunity for probing the distribution of dark matter and baryons in the most massive galaxies. We analysed a sample of 80 early-type galaxy strong lenses covering the redshift range 0.1 < z < 0.8. Using a Bayesian hierarchical inference approach we constrained the average properties of the distribution of dark matter masses and stellar Initial Mass Function across the population of massive galaxies. We find a positive correlation between galaxy mass and stellar IMF an anticorrelation between galaxy size and dark matter mass: at fixed stellar mass, the most compact systems appear to have a smaller amount of dark matter, in projection, within the inner 5 kpc. This result is consistent with a scenario in which central galaxies in more massive halos experience more mergers relative to their less massive halos counterparts.

Missing satellite problem is one of the mystery in modern cosmology. I will talk about how astronomers detect satellite galaxies and subhalos in distant galaxies with gravitational lensing. And why strongly lensed quasars provide an ideal approach to understand the missing satellite problem.