UNLV Department of Physics and Astronomy

Forum Schedule:   Fall 2008

DateSpeakerTitle & Abstract
Sep 5
Sep 12
Sep 19Dr. Nick Schurch
(IHEP, Chinese Academy of Sciences)
(host: Proga)
"Where are the accretion disk winds in AGN?"
Hydrodynamic simulations of accretion disks in active galaxies ubiquitously predict the presence of mass-outflows originating from the accretion flow. Strong evidence for the existence of these outflows comes from the blue-shifted, highly ionized, absorption lines detected in the optical/ultra-violet/X-ray spectra of broad absorption line quasi-stellar objects, however other properties of these outflows are conspicuous by their absence (notable exceptions are the few instances of high ionization iron absorption lines observed in some nearby quasars). I will describe the recent development of the numerical code XSCORT, which simulates UV/X-ray spectra of AGN observed through ionized outflowing material. This code allows us to predict and investigate the detailed characteristic spectral features imprinted on the UV/X-ray spectra by an accretion disk wind. We couple this code with the best available hydrodynamic simulations of accretion disk winds in a quasar to enable us to explore the X-ray spectral features produced by a realistic, self-consistent, line driven accretion disk wind. The resulting spectra represent the most realistic picture to date of the direct AGN X-ray continuum seen through an accelerating accretion disk wind, are strongly dependent on viewing angle, and are strongly time variable. The simulated spectra do not reproduce the smooth soft X-ray excess, instead showing considerable, sharp, atomic features imprinted across the spectrum. While the higher inclination angles are dominated by Compton scattering and nearly neutral absorption, spectra from smaller inclination angles show highly-ionized, blue-shifted, Fe absorption features in the 6.7-9 keV range that are qualitatively similar to features observed in the X-ray spectra of a growing number of AGN. Finally I will give an overview of my recent work developing a code that will allow the model spectra to be compared quantitatively to the X-ray observations. When compared to a large sample of AGN that all show features thought to be associated with accretion disk winds, this work will (hopefully) illuminate the importance of including accretion disk outflows in the unified AGN schemes.
Sep 26Prof. S. M. Clark
(host: Pravica)
"Is the Earth's core leaking? Solubility of wustite in liquid iron at the Earth's core mantle boundary"
Oct 3
Oct 10Dr. George Chartas
(Penn State Univ.)
(host: Proga)
"Inflows and Outflows from Supermassive Black Holes"
The current paradigm for the AGN phenomenon is a central engine that consists of an inflow of hot material accreting in the form of a disk onto a supermassive black hole. Recent observations also find powerful and high velocity ionized material outflowing from the black hole. I will present recent X-ray observations of AGN that suggest the presence of near-relativistic outflows of ionized absorbing material with velocities of up to 0.7c. These studies indicate that these winds may be important in regulating the growth of the supermassive black hole, controlling the formation of the host galaxy, and enriching the intergalactic medium. Based on our recent X-ray and optical observations of AGN with highly blueshifted narrow and broad absorption lines I will present a unified picture to describe the outflow properties of most quasars. Regarding studies of quasar inflows, direct imaging of the accretion disks of black holes requires angular resolutions of the order of tens of nano-arcseconds at redshifts of about 1. I will show that by employing natures own telescopes we can indirectly image quasar accretion disks by multi-wavelength monitoring of microlensing events in AGN.
Oct 16Mr. Kohta Murase (Special Seminar)
(Kyoto Univ.)
(host: Zhang)
"Astrophysical Accelerators and High-Energy Neutrino Astronomy"
The origin of high-energy cosmic rays is one of the big mysteries in the Universe. Detection of high-energy neutrinos and gamma rays will be useful as a probe of cosmic-ray acceleration in astrophysical sources. Large neutrino telescopes such IceCube and KM3Net are being constructed. Not only high-energy gamma-ray astronomy but also neutrino astronomy may be possible in the near future. In my talk, I will consider various possibilities of high-energy cosmic-ray acceleration in extragalactic objects such as gamma-ray bursts. The high-energy neutrino emission from such objects and future prospects of detection will be discussed.
Oct 17Mr. Yu Niino
(Kyoto Univ.)
(host: Nagamine)
"Lyman-alpha emission of long GRB host galaxies and the metallicity dependent GRB production"
Theoretical and observational studies suggest that long gamma-ray bursts (GRBs) preferentially occur in low-metallicity environment. Lyman-alpha equivalent width is a property of galaxies that is closely connected to the metal abundance of the galaxies, and hence Lyman-alpha emission luminosity of GRB host galaxies can provide us with an important clue to the metallicity dependence of long GRB production. Accroding to the optical follow up observations of high redshift (> 2) long GRBs, most of the detected host galaxies of GRBs have strong Lyman-alpha emission lines, while the fraction of such galaxies in Lyman-break galaxies selected by galaxy surveys at similar redshifts is less than 30 %. Using a model of hierarchical galaxy formation, we predict the distribution of various properties of GRB host galaxies including Lyman alpha luminosity at a given redshift, assuming several models of metallicity dependence of GRB production rate. The predictions are then compared with available observational results. We find that the larger mean Lyman alpha luminosity of GRB host galaxies than that for LBGs can indeed be reproduced by a model in which GRBs occur only in low metallicity environments. However, the currently available sample of host galaxies is not large enough to exclude the case of metallicity-independent GRB production rate. Future observations of GRB host galaxies will put more strict constraint on the metallicity dependence of long GRB production, and hence on the progenitor of long GRBs.
Oct 24
Oct 31No Forum - Nevada Day
Nov 7Prof. Mikhail Medvedev
(Kansas State Univ.)
(host: Zhang)
Do Extragalactic Cosmic Rays Induce Cycles in Fossil Diversity?
Recent work has revealed a 62 +/- 3 Myr cycle in fossil diversity in the past 542 Myr; however, no plausible mechanism has been found. We propose that the cycle may be caused by modulation of cosmic-ray (CR) flux by the solar system vertical oscillation (64 Myr period ) in the Galaxy, the Galactic north-south anisotropy of CR production in the Galactic halo/wind /termination shock (due to the Galactic motion toward the Virgo Cluster), and the shielding by Galactic magnetic fields. We revisit the mechanism of CR propagation and show that CR flux can vary by a factor of about 5 and reach a maximum at northernmost displacement of the Sun. The very high statistical significance of (1) the phase agreement between solar northward excursions and the diversity minima and (2) the correlation of the magnitude of diversity drops with CR amplitudes through all cycles provide solid support for our model. Various observational predictions which can be used to confirm or falsify our hypothesis are presented.
Nov 14Prof. Tzihong Chiueh
(National Taiwan University)
(host: Nagamine)
"Secondary CMBR Anisotropy"
Occasional photon scattering against hot electrons provides a mechanism for creating the secondary anisotropy in CMBR after the last scattering surface. This mechanism, called Sunyaev-Zeldovich effects, involves inverse Compton processes to distort the CMB photon spectrum from a perfect black-body. In this talk, I will review the current popular topics in CMB research, and then focus on experiments that aim to detect galaxy clusters through the Sunyaev-Zeldovich effect.
Nov 21Prof. Eiichiro Komatsu
(Univ. of Texas, Austin)
(host: Nagamine)
"5-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation"
We have announced the results from 5 years of observations of the Wilkinson Microwave Anisotropy Probe (WMAP) on March 5. In this talk I will give the cosmological interpretation of the WMAP 5-year data, and discuss implications for dark matter, dark energy, neutrinos, cosmic reionization, and inflation.
Nov 28No Forum - Thanksgiving
Dec 5Prof. David Axon
(Rochester Institute Tech)
(host: Proga)
"Falling in and Blowing Out - new insights into the inner structure of Active Galactic Nuclei"
Spectropolarimetry of the broad emission lines provides a direct means of probing the kinematics of the circum-nuclear material within the unresolved central parsec of AGN. We describe two key results that have been obtained using this method which are direct evidence for a disk-like component to the broad line region of type 1 Seyfert galaxies and the observational confirmation of the existance of accretion disk winds in Broad Absorption Lines QSO.
Dec 11Mr. Gabriel Altay (Special Forum)
(2-3pm; Carnegie Mellon Univ.)
(host: Nagamine)
"SPHRAY Tracing a Quasar Proximity Zone"
In the local Universe, it is observed that the properties of super massive black holes (SMBHs) are correlated with their host galaxies. This suggests significant interaction between these systems of vastly different scale. During periods of high accretion the central regions of these galaxies are observed as quasars. The large ionizing fluxes produced by these quasars is expected to decrease the amount of lyman alpha absorption in the spectrum of the host quasar (the line of sight proximity effect) and in the spectra of coincident background quasars (the transverse proximity effect). Observations of these these spectra have the potential to constrain quasar luminosities, the overdensity of a region that hosts a quasar, and the amount of time that a galaxy is in the active stage. I will present detailed numerical models of the ionization state around a single quasar cut from a cosmological box.
Dec 12Prof. Makoto Fujiwara
(TRIUMF, Univ. of Calgary)
(host: Zygelman)
"Casting Light on Antimatter: Fundamental Physics with ALPHA Antihydrogen Project at CERN"
Testing fundamental symmetries plays an important role in our understanding of Nature. Experiments at CERN's Antiproton Decelerator facility aim to make precision tests of matter-antimatter symmetry, in particular CPT (charge, parity, time reversal), by comparing the properties of hydrogen with those of its antimatter counterpart, antihydrogen. In 2002, the ATHENA and the ATRAP experiments have achieved the first goal: production of antihydrogen at low velocity, and in large quantities. These first cold anti-atoms, however, were not confined and annihilated on the trap walls shortly after their creation. In order to perform precision measurements, stable trapping of antihydrogen is essential. This is the main goal of a new experiment ALPHA (Antihydrogen Laser Physics Apparatus). In this talk, I will review ATHENA's achievements, and discuss the status and the prospects of ALPHA for fundamental physics with cold antihydrogen.