Sep 5

"A Systematic Approach to Studying Galaxy Cluster Formation in the Early Universe" (held during the Wednesday 5 Sepember, 3 pm Cosmos Seminar time slot)
Yi-Kuan Chiang, University of Texas at Austin

Observations of massive galaxy clusters have shown that the overall cluster properties evolved very little since z < 1-2. Stellar populations of the cluster red sequence are old, with implied formation redshifts of z ~ 2-4. To understand how these galaxy clusters form and how their overdense environments influence galaxy evolution, it is crucial to probe the epoch of cluster formation at 2 < z < 5. With the ultimate goal of building a roadmap for interpreting future surveys like HETDEX, we are performing a statistical, simulations-assisted study of (proto-)cluster evolution. We use the LCDM predictions for dark matter and accurate semi-analytic models for galaxies to quantify the relations between galaxy clusters and overdensities in the distributions of the dark matter, halos, and galaxies as a function of, e.g., redshift and galaxy type. We model the selection and projection effects as found in observational surveys even more accurately by using lightcones and simulated data. We use our simulations predictions to interpret observations of a range of structures found at z > 2, and to make feasibility predictions for future experiments.

Oct 18

"Metallicities of Anomalous-Velocity Gas in the Vicinity of the Milky Way: A Status Update"
John Barentine, University of Texas at Austin

Five decades ago, the first observations were reported of neutral hydrogen seen in radio surveys at velocities incompatible with models of Galactic differential rotation. In the past decade, their distances have been determined, placing them a few kiloparsecs above the disk of the Milky Way. Proposed explanations for their existence includes infall from the halo, circulation of gas between disk and halo in a "Galactic Fountain", and tidal stripping of gas from orbiting dwarf galaxies. Key to distinguishing among these origin scenarios is the metal content of this gas, but to date there have been few reliable, published measurements. I will report on progress made in an effort to improve our understanding of this phenomenon by measuring the metallicity of anomalous-velocity gas along ~40 sightlines toward background quasars and AGN with UV spectroscopy from space observatories.

Oct 24

"Searching Galaxies at Cosmic Dawn"
Vithal Tilvi, Texas A & M University

The epoch of reionization (z~7) marks a major milestone in the history of the universe when most of the neutral hydrogen was reionized. Because star-forming galaxies are likely responsible for the reionization, significant efforts in searching and understanding galaxies during this epoch are underway. Recently, we have discovered a few z~7 candidate galaxies using medium-band imaging from the zFOURGE survey. The medium-bands cleanly distinguish between compact high-redshift galaxies and nearby brown dwarf stars, one of the main contaminants in high-redshift galaxy samples obtained from ground-based observations. In addition, multiwavelength medium-band photometry allow us to derive more accurate physical properties of galaxies, compared with broad-band derived properties. Thus, ground-based medium-band surveys provide both, a larger survey area needed to discover brighter, rarer galaxies and better constraints on the physical properties of high-redshift galaxies.

Nov 16

"Active Galactic Nuclei and their Hosts"
Jonathan Stern, Israel Institute of Technology (Technion)

We study the properties of low redshift broad line AGN, and their relation to their host galaxies, based on a new sample derived from the SDSS survey. The sample is supplemented by data from the GALEX, ROSAT, and 2MASS surveys. We find the following. The average AGN hosts are regular non emission line galaxies (NEG), which become bluer with increasing AGN luminosity, suggesting a correlation of the AGN luminosity and the host star formation rate. The observed AGN optical-UV emission is subject to some reddening, and the intrinsic emission is blue, consistent with accretion disk model predictions. The narrow emission lines reveal that the covering factor of circumnuclear gas (10s - 100s pc) decreases with increasing AGN luminosity, and the gas metallicity follows the host mass, similar to the mass - metallicity relation of normal galaxies. The metallicity of the broad line region (0.01s - 0.1s pc) also appears to be related to the host mass.

Dec 13

"The Morphological Nature of LAEs at z=2 and z=3"
Tania Penuela, Swiss Federal Institute of Technology (ETH), Zurich

The physical properties of Lyman Alpha Emitters (LAEs) continue to be a matter of debate. Recent studies have shown that LAEs at z < 3 can be dusty, redder, with narrower equivalent width (EW) distributions and in general more evolved than at higher redshifts i.e. z > 3. However, one of their most fundamental property i.e. their morphology, has been largely neglected and remains unknown. Their disorganized nature, clumpy and multicomponent structure together with their faintness in the optical bands corresponding to the UV rest-frame make their morphology a very complex problem to study. Furthermore, morphology may contain valuable information about the distribution of the star formation in the galaxies, or about recent merger activity. We believe that in the presence of a really strong evolution in the properties of LAEs from z ~3 to z~2, we may be able to track also a morphological change. In my talk, I would like to present results for a morphological analysis of LAEs at z~2 and z~3 using rest-frame HST/ACS UV imaging from the GOODS and COSMOS fields and HST/WFC3 rest-frame optical images from the CANDELS survey. I will also discuss whether the narrow band technique is the most adequate tool for the selection of LAEs at z < 3.