Cosmic Microwave Background (CMB) is a vestige radiation generated during the Recombination era, some 390,000 years after the Big Bang, when the Universe had become transparent for the first time. Initial observations of CMB made by the Wilkinson Microwave Anisotropy Probe (WMAP) led to determining the age of the Universe. The mechanisms that drove the recombination have been discovered by using modeling of the primordial plasma and seeking agreement with the observations. The new Plank Surveyor Instrument launched in 2009 has been expected to produce data about the recombination era of an unprecedented accuracy, that require including better information regarding the basic atomic physics processes into the present models. In this talk, I will review the results for various Rydberg atom - charge particle collisions and establish their relative importance during the stages of recombination era, with respect to each other and to radiative processes. Energy changing and angular momentum changing collisions with electrons and ions are considered.

The remarkable progress of large-scale astronomical surveys in the last two decades have allowed us to constrain the current cosmological model to an unprecedented precision. At the same time, the field of computational cosmology has emerged, and evolved hand-in-hand with the observational cosmology. In this talk, I will review the history and current status of observational cosmology, and describe how supercomputers have helped to shape our current views of cosmological structure formation. In the field of computational cosmology, I argue that we are now entering the third revolution in the cosmological study of galaxy formation. In the latter part of my talk, I will also discuss a separate work on the accretion onto supermassive black holes, and its cosmological importance.

The circumgalactic medium contains signatures of key processes in galaxy formation, such as gas accretion and outflow, and may account for the majority of baryons in the Universe. To probe gas in this environment, I developed new methods to model quasar spectra and measure absorption induced by gas in galaxy halos. Applying the new tools to all quasar spectra in the SDSS, I have compiled a metal absorber catalog of ~50,000 systems and, for the first time, measured the large-scale distribution of gas from galaxies out to ~20 Mpc, linking the gas properties of individual galaxies to their large-scale environment. I will further discuss the new constraints of these results bring to the physics of circumgalactic medium and its role in galaxy formation and evolution in general.

The variety of observations of Active Galactic Nuclei (AGN) show that the nuclear activity is powered by a central massive black hole that drives radio emitting jets and ionizes surrounding line-emitting clouds. This central engine is surrounded by an obscuring torus, comprised of optically thick dusty clouds in a rotating configuration. As a result, sources viewed pole-on have a direct sight-line to the central engine and their spectra show broad lines (~ 10,000 km/sec) that are missing from AGN observed edge-on.  Viewing angle was generally considered the only property controlling the AGN line spectrum. Instead, I will present evidence that line emission is actually evolving as the accretion rate to the central black-hole is decreasing and show that this evolution is explained naturally by the dynamical properties of the toroidal obscuration.

If the baryonic content of galaxies consists primarily of stars, ISM, and hot (10^7 K) x-ray halo gas, then galaxies are missing between 70 - 95 % of their baryons relative to the cosmological fraction. When accounting for the baryon budget of galaxies, however, we must not overlook the cooler (10^4 K) photo-ionized gas phase that makes up the circumgalactic medium (CGM). Our collaboration, COS-Halos, has been working to characterize the elusive multiphase CGM that extends out to at least 300 kpc from stellar components of galaxies. Specifically, we have observed the halo gas of 50 galaxies drawn from the imaging dataset of the Sloan Digital Sky Survey (SDSS) whose angular offsets from quasar sightlines and redshifts imply impact parameters (rho < 150 kpc) well inside their virial radii. As we have shown in previous empirical studies, these data comprise a carefully-selected statistically-sampled map of the physical state and metallicity of the CGM for L ~ L* galaxies. Of particular relevance to the halo missing baryon problem is the total baryonic mass contained in the multiphase CGM, as traced by absorption from hydrogen and metal lines in various ionization states (e.g. MgII, SiII, CII, SiIII, CIII, SiIV, OVI). In this talk, I will describe how I have modeled the photoionized gas of the CGM with a range of physical conditions, and rigorously determined the CGM gas ionization parameters and metallicities along 33 of the COS-Halos sightlines that provide the best-determined measurements of HI and metal-line column densities. With the constraints imposed by the data and models, I am able to provide the most reliable mass estimate of the CGM to date, and show definitively that the CGM is an important reservoir of baryons on galactic scales.

Our understanding of galaxy evolution centers around questions of how gas gets into galaxies, how it participates in star formation and black hole growth, and how it is returned to its galactic surroundings via feedback. I will present observational results on the relationship between gas that forms stars and gas that accretes onto supermassive black holes, and the nature of feedback that is capable of removing gas from galaxies. These results have important implications for how radiation, momentum, and kinetic energy from stars and black holes regulate the cold gas supply in galaxies. I will also discuss prospects for characterizing the physical properties of gas in and around galaxies using multi-wavelength spectroscopy with existing and future facilities.

Title: Detecting the rapidly expanding outer shell of the Crab Nebula: where to look Abstract: We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emission from high ionization lines that will not be emitted by the Crab’s filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The NIR [Ne VI] l7.652 mm line is a particularly good case; it should be dramatically brighter than the optical lines commonly used in searches. The C IV l1549Å doublet is predicted to be the strongest absorption line from the shell, which is in agreement with HST observations. We show that the cooling timescale for the outer shell is much longer than the age of the Crab, due to the low density. This means that the temperature of the shell will actually “remember” its initial conditions. However, the recombination time is much shorter than the age of the Crab, so the predicted level of ionization should approximate the real ionization. In any case, it is clear that IR observations present the best opportunity to detect the outer shell and so guide future models that will constrain early events in the original explosion.

Astronomers now know that supermassive black holes are a natural part of nearly every galaxy, but how these black holes form, grow, and interact within the galactic center is still a mystery. In theory, gas-rich major galaxy mergers can easily generate the central stockpile of fuel needed for a low mass central black hole 'seed' to grow quickly and efficiently into a supermassive one. Because of the clear theoretical link between gas-rich major mergers and supermassive black hole growth, this major merger paradigm has become a well-accepted way to form the billion solar mass black holes that power bright quasars in the early universe. It's much less clear, though, how well this paradigm works for growing the 'lightest' supermassive black holes; these million solar mass black holes tend to lie in galaxies like our own Milky Way, where the supermassive black hole is currently quiescent and major mergers were few and far between. This talk will touch on some current and ongoing work on refining our theories of black hole growth for this lightest supermassive class.

Abstract: Reverberation mapping, or "echo" mapping, of nearby (z<0.1) active galaxies has provided direct constraints on the mass of the central supermassive black hole in about 50 galaxies. Furthermore, the size of the region of photoionized gas from which the broad emission lines emanate has been found to scale with the luminosity of the central source. This radius-luminosity relationship is heavily used to estimate black hole masses in quasars at cosmological distances, and is foundational for our understanding of the interplay between black hole and galaxy growth and evolution. I will present an overview of the state of the field and discuss current and future work aimed at minimizing the uncertainties in black hole mass determinations. Speaker Bio: I grew up in Spokane, WA and earned a dual degree (BS+BS) in physics and astronomy at University of Washington in Seattle. I then attended The Ohio State University and worked on my dissertation with Brad Peterson. After earning my PhD in 2007, I worked with Aaron Barth at UC Irvine for two years before being awarded a Hubble Fellowship in 2009 and then accepting a tenure-track faculty position at Georgia State University in 2010. Earlier this year, I was awarded an NSF CAREER grant, and I'm a current member of the NASA Astrophysics Roadmap Committee.