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.

Dust suffuses our diffuse universe, obscures our view, and is a direct product of the formation of stars and galaxies. In this era of large area digital surveys it is both necessary and possible to explore dust in our universe at a level once unheard of. I will discuss new results on dust, both extreme in precision and extreme in position. In my discussion of high precision dust observations, I show how crucial accurate dust maps are to our understanding of cosmology, and I will introduce a new cosmological parameter: the opacity of the universe, tau_z. I will show new results (and a new class of objects) using dust in low density environments, both at the surface of our own galaxy and filling the virial radii of galaxies throughout the universe. I will introduce the idea of exploring feedback from galaxies by studying their dust, and using these observations to constrain our models of galaxy formation.

We are constantly intrigued by how dramatically galaxies evolve when we probe closer to the cosmic dawn. Ten billion years ago, galaxies were forming stars ten times more fiercely than they do today. This phenomenon can be understood in the framework of cold dark matter simulations only if star formation is suppressed in massive dark matter halos. However, the physical mechanisms responsible for the suppression are unclear. Starburst galaxies in massive halos offer a unique laboratory to constrain the suppression processes, because, unlike most galaxies, such processes have apparently failed to operate in these starbursts. Thanks to the Herschel Space Telescope, for the first time we have identified a sample of gravitationally lensed massive starbursts at the peak epoch of cosmic star formation. I will show how high-resolution multi-phase observations in combination with gravitational lensing have helped us gain a comprehensive understanding of these unusual galaxies. I will also describe future projects aimed at constraining the star formation history and the halo-scale gas supply of such massive starbursts. By contrasting with normal galaxies, the results of these studies will be fundamental to a physical understanding of galaxy evolution. Finally, I will present my vision of this field with future ground- and space-based observatories.

Samir Salim (Indiana University)