UNLV Department of Physics and Astronomy

Forum Schedule:  Fridays 3:45pm - 4:45pm

DateSpeakerTitle & Abstract
Jan 25
Feb 1
Feb 8Dr. Ian Parrish
(UC Berkeley)
(host: Proga)
"Galaxy Clusters from Inside to Out: Thermal Instability and Non-thermal Pressure Support"
Clusters of galaxies are the largest gravitationally-bound objects in the universe, and as such are useful as probes of both cosmology and astrophysics. To understand these objects as well as related problems in galaxy formation and black hole growth, we must understand the hot, dilute intracluster medium (ICM) that dominates the baryonic mass. In the cores of cool-core galaxy clusters, I will explore the balance between heating and cooling processes and explain when and how thermal instability occurs. The resulting cool gas can form filaments or feed a central black hole. Our results are in generally good agreement with observations. I will describe a degree of thermal self-regulation of clusters and hot halos that can be achieved from this process and its consequences. Finally, I will move to the cluster outskirts and highlight the role of conduction-driven convection in the outskirts of galaxy clusters. The non-thermal pressure support from this vigorous convection has implications for our interpretation of ongoing SZ surveys.
Feb 15Dr. Francisco Muller-Sanchez
(host: Proga)
"Mapping Sub-kpc Gas Flows in Nearby AGN"
Over the last few years we have been pursuing a program to investigate the physical mechanisms of feeding and feedback in nearby AGN using Adaptive Optics assisted integral-field spectroscopy. This work has shown that we can model the narrow-line and coronal-line region (NLR/CLR) kinematics as a combination of rotating and outflowing components. High-ionization emission is seen in both components, suggesting it is leaking out of a clumpy torus. The mass outflow rates are 2-3 orders of magnitude greater than the accretion rates, implying that the outflow is mass loaded by the surrounding interstellar medium. In half of the AGN measured so far, the kinetic energy of the outflows appears sufficient to provide the eagerly-sought ''AGN feedback'' invoked to explain fundamental galaxy properties such as the M-sigma relation. Inflows of molecular gas are found in approximately half of the sources, where they occur mostly in nuclear spiral structures or nuclear bars with mass inflow rates of ~0.1-10 M_sun yr-1. This is of the order of the outflow rates, suggesting that most mass which flows towards the nucleus to feed the supermassive black hole is expelled by the AGN.
Feb 22
(Joint Chemistry-Physics talk, CHE-101, 2:30pm)
Prof. Steven Manson
(Georgia State Univ.)
(host: Prof. Lindle, Chemistry)
"Studies of Photoabsorption by Free and Confined Atomic Systems: Recent Developments"
Photoabsorption by atomic and molecular systems, one of the fundamental processes of nature, has been the subject of both experimental and theoretical investigations for more than a century, and still there is much to learn. In this talk, a variety of examples will be presented to give the flavor of the diversity of recent studies of free and confined (inside a fullerene cage) atoms and ions, along with what these studies teach us about the underlying mechanism(s) of the process in the various cases, i.e, what are the essential elements of each particular phenomenology observed. The connection between experiment and theory, and how they stimulate each other, shall be emphasized.
Mar 1Dr. Gabriel Altay
(Georgia Institute of Technology)
(host: Nagamine)
"Radiative Transfer, the UV Background, and Galaxy Formation"
I will discuss recent radiative transfer code developments that allow for the treatment of self-shielding from the UV background in cosmological simulations using only a few free parameters. In addition I will advertise a tool called AMUSE that is being developed to couple codes with different goals together (i.e. hydrodynamics and radiative transfer). Finally, I will present scientific results on the HI column density distribution function and what they imply for theories of galaxy formation.
Mar 8Prof. Zheng Zheng
(Univ. of Utah)
(host: Nagamine)
"A Theoretical Exploration of Lyman-alpha Emitting Galaxies"
Lyman-alpha emitting galaxies or Lyman-alpha emitters (LAEs), galaxies selected by their Lyman-alpha emission, are becoming an important probe of galaxy formation, cosmic reionization, and cosmology. Correct interpretations of the growing observations of LAEs require a full consideration of the radiative transfer (resonant scattering) of Lyman-alpha photons. I will present a theoretical investigation of LAEs based on radiative transfer modeling performed in cosmological simulations. The study reveals a coupling between the observed Lyman-alpha emission and the circumgalactic and intergalactic environments, induced by the resonant scattering of Lyman-alpha photons. I will show that such an environment-dependent radiative transfer effect helps to explain many observational properties of LAEs. Furthermore, it gives rise to interesting features in the clustering of LAEs, which leads to a new type of potentially strong distortions of non-gravitational origin in galaxy clustering. Finally, I will discuss the challenges and opportunities in using LAEs to study structure formation and cosmology.
Mar 12
(Special: Tue 1-2pm)
Dr. Yohai Meiron
(KIAA Beijing)
(host: Kashi/Nagamine)
"Stellar kinematic signature of massive black hole binaries"
We present a novel way to detect the current and past presence of massive black hole binaries in galactic centers. The inspiral of the two black holes from galactic scale up to the formation of a bound pair induces a unique kinematic fingerprint: an inner stellar core counter-rotating with respect to the binary's orbital motion, followed by a co-rotating population at larger scales. The inner core is between five and ten times the scale of the binary separation, and has velocity dispersion dropping towards the center. We present high-resolution maps of the projected velocity distribution moments; our results are based on a simulation technique that uses conservation laws to study the dynamics, and allows for a very large number of stars.
Mar 15Prof. Nahum Arav
(Virginia Tech)
(host: Proga)
"Kinetic Luminosity of Quasar Outflows and its Implications to AGN Feedback: VLT/Xshooter and HST/COS Observations"
Sub-relativistic outflows are seen as blueshifted absorption troughs in the spectra of roughly one third of all quasars. I will describe recent results from VLT HST/COS observations, that yield the mass flux and kinetic luminosity for the majority of these outflows. The derived values suggest that quasar absorption outflows have a profound effect on their host galaxy and maybe the major agent of AGN feedback.
Mar 22
(Special Public Lecture)
Prof. Karl Gebhardt
(UT Austin)
(host: Rhee)
Russell Frank Astronomy Public Lecture: "Exploring the Dark Side of the Universe: Black Holes, Dark Matter and Dark Energy"
We will discuss three key findings in astronomy. A new force of nature, dark energy, is causing the expansion of the universe to speed up. The nature of dark matter that dominates mass around galaxies is unknown. Black holes are thought to be exist in all galaxies, yet we do not understand how they form and interact with galaxies. Each of these three areas is ripe for significant advances. We will review the current discoveries and understanding of these dark components of the Universe. We will discuss new data that show that we are living through a unique time for Astronomy.
Mar 29NO FORUMSpring Break
Apr 5Dr. Jon Swift
(host: Rhee)
"The Formation and Frequency of Compact Planetary Systems"
The populations of planets being revealed by the Kepler space telescope appear significantly different than our own Solar System. The vast majority of exoplanetary systems are more compact, and preferentially contain planets with radii 1-4 times the Earth; a size absent from our family of familiar planets. Our group based at Caltech has undertaken a comprehensive program to understand the planet populations around the smallest and most numerous stars in the Galaxy using the unprecedented data from the Kepler telescope. I will share some of our latest results including observational constraints on planet formation mechanisms, and a statistical analysis of planet frequency. I will then turn to address the implications of these findings, and present a new robotic, cost effective observatory under development within our group called Minerva that will discover some of our nearest neighboring exoplanetary systems.
Apr 12
Apr 19Dr. Pascal Oesch
(UC Santa Cruz, Hubble Fellow)
(host: Nagamine)
"Probing the Dawn of Galaxies at z~9-12"
Over the last few years, the advent of the WFC3/IR camera on HST has completely revolutionized galaxy science in the reionization epoch, as it pushed the observational frontier out to z~9-12, only ~450 Myr from the Big Bang. From several large HST programs such as the HUDF09, CANDELS, or CLASH, it became possible to identify large samples of more than 200 galaxies at z~7-8, and we are now starting to build up the sample sizes of even z~9-11 galaxy candidates. Using new, ultra-deep data over the HUDF, combined with a search for z~10 galaxies in all the WFC3/IR data around the GOODS-South field, we infer that the cosmic star-formation rate density in galaxies with SFR>0.7Msol/yr increases by more than an order of magnitude in only 170 Myr from z~10 to z~8, indicating that the galaxy population was growing very rapidly at these early times. Together with ultra-deep Spitzer IRAC observations from our IUDF10 program, these WFC3/IR samples allowed for the first robust rest-frame optical detections and mass measurements of individual z~8 galaxies. The combination of deep HST and Spitzer data therefore enables us to directly track the star-formation and mass build-up of galaxies across the reionization epoch, and it provides detailed new insights into the stellar population properties of galaxies down to z~4. In this talk I will highlight some of our recent progress in exploring the build-up of the earliest galaxy population and what this implies for the contribution of galaxies to cosmic reionization.
Apr 26
Apr 30
(Special: Tue 1-2pm)
Prof. Steven Finkelstein
(UT Austin)
(host: Nagamine)
"Tracking Galaxy Evolution in the Early Universe with HST"
The field of high-redshift galaxy evolution has experience an explosion over the past three years, thanks to the installation of the infrared-sensitive Wide Field Camera 3 on the Hubble Space Telescope. In the first few months after the servicing mission, numerous papers were published detailing the discovery of the first robust galaxy samples at z = 7 and 8, with the most distant galaxies dating only 500 million years from the Big Bang. Since that time, new deep and wide area surveys, such as the HST Multi-cycle Treasury Program CANDELS, has allowed us to take a detailed look into the properties of these galaxies. These data allow us to probe into the epoch when we expect to see galaxies vigorously building up their stellar, chemical, and dust reservoirs. I will highlight my ongoing work examining these enigmatic galaxies, first on understanding the colors of these galaxies, from which we have learned about the build-up of dust in the universe, as well as the possible presence of primordial stars. I will also show how we use these galaxies to probe the reionization of the intergalactic medium, which was likely ending around this epoch. Finally, I will discuss recent results on the luminosity functions of these distant galaxies, using the largest volume yet probed at these redshifts with the CANDELS survey.
May 3Dr. Hidenobu Yajima
(Penn State)
(host: Nagamine)
"Multi-wavelength Properties of High-redshift Galaxies at the Epoch of Reionization"
Recent observations have detected a lot of high-redshift galaxies beyond redshift 7. Most of them were observed by detecting UV continuum or strong Lyman-alpha lines. In addition, recent sub-millimeter telescopes have started to detect dust and CO emission from high-redshift galaxies. These radiation properties are keys to understanding the formation/evolution mechanism of high-redshift galaxies and their physical state. Here, we investigate multi-wavelength properties of high-redshift galaxies by combining cosmological hydrodynamics simulations with three-dimensional radiative transfer calculations. We find that our model galaxies have a number of Lyman-alpha properties close to those of observed Lyman-alpha emitters (LAEs) at z ~ 2 - 6, and the Lyman-alpha power is produced by excitation cooling process via cold-gas accretion at high redshift. By combining our results of multi-wavelength radiative transfer with observed luminosity functions, I will present the redshift evolution of ionizing photon emissivity of LAEs, and discuss whether LAEs can contribute to cosmic reionization. In addition, our radiative transfer code calculates UV continuum from stars and thermal emission of dust simultaneously. Ongoing and future missions, e.g., James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array (ALMA), may observe the continuum radiation from high-redshift galaxies at z > 8. As a result, we predict that our modeled galaxies may be detected at z <~ 10 by JWST and ALMA with a reasonable integration time. Moreover, the escaped Lyman-alpha and UV continuum photons from galaxies could change spin temperature of neutral hydrogen in IGM, resulting in positive or negative signal at 21 cm. I will discuss the 21 cm structure around high-redshift galaxies in a simple 1D model.
May 10Prof. Aaron Barth
(UC Irvine)
(host: Proga)
"Black Hole Masses and Broad-Line Region Structure: New Results from Reverberation Mapping"
The method of reverberation mapping uses time delays between continuum and emission-line variations to determine the size and structure of the broad-line region in active galactic nuclei. Nearly all observational work on the cosmological growth history of black hole masses relies on reverberation mapping to calibrate the black hole masses of quasars. I will review the methods used to estimate black hole masses in active galaxies, and discuss the systematic uncertainties and biases that affect these mass estimates. I will present new reverberation-mapping results from the Lick AGN Monitoring Project, including velocity-resolved reverberation measurements that are providing our first look at the kinematics of the broad-line region in nearby Seyfert galaxies.

Past forums: Fall '08   Spring '09   Fall '09   Spring '10   Fall '10   Spring '11   Fall '11   Spring '12   Fall '12