Abstracts
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"A Systematic Approach to Studying Galaxy Cluster Formation in the Early Universe" (held during the Wednesday 5 Sepember, 3 pm Cosmos Seminar time slot)
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. |
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"Metallicities of Anomalous-Velocity Gas in the Vicinity of the Milky Way: A Status Update"
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. |
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"Searching Galaxies at Cosmic Dawn"
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. |
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"Active Galactic Nuclei and their Hosts"
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. |
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"The Morphological Nature of LAEs at z=2 and z=3"
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. |
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