Abstract: Redshift of z ~ 2 is an important era in the history of the universe, as it contains the peak of star formation rate density and quasar activity. I will talk about the properties of galaxies during this era from two different, yet complementary, aspects: star formation and mass assembly, and galactic dust enrichment. In this study, I use a wealth of spectroscopic data obtained by the MOSDEF survey. I will introduce the MOSDEF survey, which is a multi-institutional project that uses the near-IR MOSFIRE spectrograph on the Keck I telescope to characterize the gaseous and stellar contents of ~ 1500 rest-frame optically selected galaxies at 1.37 < z < 3.80. Furthermore, I incorporate the mid- and far-IR data from the Spitzer and Herschel telescopes to obtain a complete census of obscured and unobscured star formation in galaxies. Specifically, I explore the star-formation rate and stellar mass relation at z ~ 2, using multi-wavelength star-formation rate tracers (UV, Hα, 24 micron, and far-IR). Moreover, I investigate, for the first time, the variation of the PAH emission at 7.7 micron, traced by Spitzer/MIPS 24 micron, in galaxies spanning a wide range in metallicity at z ~ 2. Our results have important implications for high-redshift studies that adopt 24 micron flux to derive total IR luminosity and star-formation rate.

 Abstract: CASS All-Hands Meet & Greet this Friday, October 14, from 12:00 to 1:00 pm in SERF 383. This meeting will be an opportunity for new members of CASS to introduce themselves and present a quick overview of their research. It will also give established members of CASS a chance to summarize their recent work. New graduate students are especially encouraged to attend. Pizza and soda will be provided. Journal Club is an informal environment in which graduate students can give short talks on any subject of interest to them, be it a recent paper, their own research, or any other topic. Talks will resume next week. All are welcome to attend.

 Abstract: The structure of interstellar hydrogen (HI) is crucial for star formation, feedback and accretion in galaxies. Absorption line spectroscopy is an important tool for understanding the multi-phase nature of HI, especially in the local Galaxy where high sensitivity and resolution can be achieved. In this talk, I will present results from 21-SPONGE: the largest and most sensitive survey for Galactic HI absorption ever at the Karl G. Jansky Very Large Array. Our excellent sensitivity enables us to detect unexpectedly warm neutral gas at T=7000 K, which suggests a newfound influence of the Lya radiation field density in the ISM. To understand the physics behind our observations, we analyze 1000s of synthetic HI spectra from 3D numerical simulations using machine learning and derivative spectroscopy. For the first time, we statistically quantify the ability of resolved spectral lines to recover simulated clouds and their important physical properties, such as temperature and density. With the biases of our analysis tools in hand, we measure the fractions of local HI in the cold, warm and thermally-unstable gas phases, which is directly relevant to the nature of star formation in the Milky Way.

 Abstract: The origin and extent of volatile depletion in airless bodies such as the Moon or Vesta remain largely unconstrained. These two planetary bodies are unique end-members, but provide complementary datasets for understanding the evolution of the rocky bodies; Vesta is an early-formed, low-mass asteroid while the Moon exhibits geochemical similarities to the Earth. The Moon exhibits evidence of evaporative fractionation of the moderately-volatile element, zinc, which may have occurred during lunar magma ocean differentiation. This concept can be extended to Vesta, for which the eucrite meteorites have been used to investigate asteroidal magmatic differentiation and volatile depletion. Criteria for 'pristine' lunar samples can be further applied to eucrite samples to assess primary signatures of volatile depletion on the Vesta parent body. Both the Moon and Vesta provide important insight to volatile depletion mechanisms on rocky planetary bodies, which can be applied to planetesimals in our Solar System and beyond.

 Abstract: I will be discussing problems with inflation and advantages of bouncing models.

 Abstract: In this talk I'll give my (fledgling) perspective on the black hole information paradox, which remains mystifying even after 40+ years of attempted resolutions. This area of study was galvanized a few years ago by the publication of an alarming paper arguing for the existence of firewalls in place of BH event horizons. Although the firewall frenzy is still ongoing, it appears likely that at least one fundamental tenet of physics will have to be revised in order to make sense of the puzzle. I'll overview BH information and firewalls as a lead-in to talking about a recent imaginative proposal that evades firewalls by invoking (implausible though it may sound) a principle from computer science.

 Abstract: It is well known that stars observed in the local Universe form with something very close to a universal initial mass function (IMF) where the vast majority are of low mass. However, theory and simulations of the formation of the first stars in the Universe predict a top-heavy IMF with significant dependence on environment. This is supported by the apparent total absence of completely metal-free, Population III stars in the Milky Way. Thus, it seems that a transition in star formation modes must have taken place at some point in the history of the Universe. I will review the theory of Pop III star formation and the transition to modern-day star formation, including what we can learn from observations of the stellar content of the Milky Way. I will also discuss some of the highly flexible, open-source tools for simulation and analysis that are used in this research that have a great deal of potential for impact in other areas.

 Abstract: Roughly 1/1000 of nearby active galactic nuclei (AGN), and a larger fraction of AGN with tidal features in stars or cool gas, are accompanied by extended emission-line regions on scales 10 kpc and larger (beyond the normal interstellar medium of the host galaxy). In about 40% of these, the AGN falls short of the energy budget needed to photoionize these clouds by 1-3 orders of magnitude, implying that the AGN have faded over the relevant light-travel times. All these are in interacting or postmerger systems, possibly needed for sufficient distant, cold neutral hydrogen to trace the AGN's ionization history. In many of the fading candidates, low abundances and quiescent kinematics indicate that we see photoionized gaseous debris from tidal interactions, rather than outflowing material; separate signatures of sub-kiloparsec outflows are seen in some cases, giving an intriguing hint that the mode of energy output incidental to accretion (and thus the dominant source of feedback to the surrounding material) may be changing, and not just the accretion rate itself. Luminosity histories derived from recombination balance show e-folding timescales from centuries to a few millenia, short compared to simple accretion-disk expectations. These rapid, large-amplitude changes may be associated with supermassive black holes in binary systems or with local feedback processes. These results suggest that the demographics of accreting supermassive black holes are broader than derived from surveys of ongoing AGN signatures alone, a conclusion supported by new samples of analogous objects in both very nearby and moderate-redshift systems. These discoveries have been an important byproduct of citizen engagement in the Galaxy Zoo project.

 Abstract: Recent observations have shown the star formation activity changing between galactic-scale environments. The star formation efficiencies (SFEs) have systematic variations larger than one order of magnitude between different galaxy types and between different regions within a galaxy. Why does the star formation activity differ depending on the galactic structure's different environments? This question is key to understanding the galactic-scale star formation and has been the focus of my doctoral research. To understand this, it is important to investigate how the formation and evolution of GMCs is affected by the galactic structures. This is because the GMCs are the star formation spots in a galaxy; they are formed from the cold phase of the ISM, and their densest pockets are the birth place of stars. We performed three-dimensional hydrodynamical simulations of an M83-type barred spiral galaxy. We clarified that galactic environments and stellar feedbacks affect GMC formation and evolution, and that could explain the different star formation activities in a barred spiral galaxy.