Fall 2008

Dec 11, 2008: Mr. Gabriel Altay (Carnegie Mellon Univ.)

"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 5, 2008: Prof. David Axon (RIT)

"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.

Nov 21, 2008: Prof. Eiichiro Komatsu  (UT Austin) 

"The 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 14, 2008: Prof. Tzihong Chiueh (National Taiwan Univ.)

“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 7, 2008: Prof. Mikhail Medvedev (Kansas State Univ.)

“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.

Oct 17, 2008: Mr. Yu Niinou (Kyoto Univ.)

“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 16, 2008: Mr. Kohta Murase (Kyoto Univ.)

"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 10, 2008: Dr. George Chartas (Penn State Univ.)

“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.

Sep 19, 2008: Dr. Nick Schurch (Chinese Academy of Sciences)

“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.

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Spring 2008

Apr 18, 2008: Dr. Aaron Dutton (UC Santa Cruz)

“The Structure of Disk Galaxies: A Challenge to CDM?”

The Cold Dark Matter  (CDM) framework successfully explains the origin of large  scale structure in the  Universe.  However, on  the scale of individual   galaxies  there   are  apparent   contradictions  between predictions of CDM and observations: these include the central density and angular momentum problems.  I will address the question: Are these fundamental  problems for  CDM, or  are  they simply  a reflection  of observational biases  and our incomplete  knowledge of the  physics of galaxy formation?

Apr 11, 2008: Ms. Ashley Ruiter (New Mexico State Univ.)

“Formation channels of Type Ia Supernovae and their associated delay times”

I will show expected SN Ia delay times for our population synthesis model calculations for various SN Ia formation channels, and discuss these results in context of recent observationally-derived delay times of SN Ia.  Further, I will comment on how the variation of model parameters (common envelope evolution, star formation history, metallicity) affect the resulting delay times, in order to constrain possible SN Ia evolutionary

history scenarios.

Apr 11, 2008: Mr. Glenn Kacprzak (New Mexico State Univ.)

“Extended Halo Gas and Galaxy Kinematics in The Lambda-CDM Paradigm”

We present new results on the kinematics connections between the galaxy rotational velocities and associated halo gas velocities as measured in absorption. We also analyze mock quasar absorption line observations of galaxies and their gaseous halos in L-CDM cosmological simulations in order constrain the dynamic interaction of the galaxy/halo/cosmic web environment and the distribution of gas within halos.  Previous observational results from six edge-on galaxies suggest that halo gas velocities are consistent with extended disk-like rotation. We demonstrate that the gas velocities are by and large not consistent with being kinematically coupled to the galaxy over galactocentric distances of 25-110 kpc.  Mock absorption line analysis of simulated galaxies are consistent with our new observations. Together, the suggested picture in which gaseous halos are chemically enriched by outflowing shock-heated supernovae winds while low metallicity gas inflowing along filaments produces an inhomogeneous temperature, velocity, and metallicity distributions with a non-unity gas covering fraction.

Apr 4, 2008: Prof. Evan Scannapieco (Arizona State Univ.)

“AGN Feedback in Galaxies and Galaxy Clusters ”

For the past 10 billion years, the typical mass of star-forming galaxies has been decreasing, seemingly in direct conflict with the prevailing model of cosmological structure formation.    On even larger scales, the gas in the centers of many galaxy clusters is observed to be rapidly cooling , yet this never leads to star formation on the central cD galaxy. Using smoothed particle and adaptive mesh hydrodynamic simulations, I will demonstrate that the solution to these mysteries is likely to lie in the formation of active galactic nucleii (AGN), which are capable of exerting strong feedback on their environments.  A wide range of observations are fast uncovering the details of the key role these objects  have played though cosmic time.

Mar 28, 2008: Prof. Mitch Begelman (Univ. of Colorado)

“The First Supermassive Black Holes?”

The existence of  a supermassive black hole in nearly every galactic nucleus is no longer in doubt, but the question of how these black holes formed is wide open.  I will argue that they could have formed directly via the infall and collapse of gas, without the intermediate stage of star formation, if the infall rate was high enough.  Black hole formation by very rapid infall could have occurred in pregalactic haloes as early as redshifts ~10-20, or at lower redshifts in the nuclei of protogalaxies. Global gravitational instabilities get rid of excess angular momentum, and the infalling gas forms a self-gravitating, optically thick structure - a "quasistar".  As matter piles on, the core of the quasistar heats up until it undergoes runaway neutrino cooling and collapses to form a 10 solar mass black hole.   The black hole then grows by accreting from the quasistar at an extremely super-Eddington rate, possibly reaching thousands of solar masses in less than a million years.  Concurrently, the quasistar expands to form a radiation pressure-dominated, convective envelope reminiscent of a red giant.  I will discuss the structure and evolution of quasistars and their detectability with the James Webb Space Telescope.

Mar 7, 2008: Prof. Jerry Ostriker (Princeton Univ.)

“Black Hole Accretion and Radiative Feedback”

Black holes resident in the centers of galaxies will be fed by accretion of ambient gas

whenever gas reaches those central regions. This can be due to mergers, but even without mergers the evolution of the stellar populations of normal galaxies provides very large amounts of gas, as stars pass through the planetary nebula stage, with the total mass release being greater than 1011 Msolar for normal massive ellipticals. Much of that gas will cool and fall to the centers of the systems, where it will induce starbursts and

accretion events onto the central black holes. We follow these events with a high

resolution hydrodynamic code, allowing for radiative transfer, supernovae and other

relevant physical processes. In addition, we know the spectral output of accreting black

holes and we find that the high energy output from these objects will strongly inhibit

inflow, causing episodic accretion and a low “duty cycle”. The simulations help us to

understand many phenomena including the black hole stellar mass relation, the paucity of gas in ellipticals, the incidence of the “K+A” phenomena and the observed fact that most of the black holes found in galactic centers are in the “off” state.

Feb 8, 2008: Prof. Isaac Schlosman (Univ. of Kentucky)

“Disk Evolution in Assembling Dark Matter Halos”

Disk galaxy formation is a complex problem.  In my talk, I will discuss

some aspects of disk formation and its subsequent evolution. Specifically,

I will include the disk-halo interaction and its dynamical feedback both on

the halo and on the disk, the dominant morphology of the early galactic

disks and the dark matter density profile in the galaxy.

Jan 14, 2008: Dr. Tom Jarrett (Caltech/IPAC/JPL/Spitzer)

“The Hidden Realm of Deeply Embedded Supernovae Remnants”

During its relatively short lifetime, a supernova dramatically alters the birth cloud in which it arises, compressing, heating, ionizing and metal enriching the interstellar medium.  In this regard, the most important class of supernovae (SNe) are those of the core collapse unique to the most massive stars.  And yet these SNe are the least understood because they are hidden by the formidable screen of stars, dust and gas that comprise the Plane of the Milky Way.  Infrared and radio observations have the ability to penetrate this obscuring mask to study and ultimately unlock the secrets within the dark molecular clouds. I will present new results of radio/infrared observations of deeply embedded SNe that we use to study how the interaction between SNe and their birth clouds evolve from the earliest stages to the relatively mature phase in which the remnant settles back into the ISM. The ground observations include near-infrared spectral imaging using the Hale 200" telescope and the 3.9-m Anglo-Australian Telescope.  The mid-infrared data are acquired with the Spitzer Space Telescope. The presentation will include some historical perspective on studies of SNe within the Milky Way and beyond to nearby galaxies.