Abstract: CASS All-Hands Meet & Greet this Friday, October 6, 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: I will present results from two projects investigating two different puzzles in galaxy evolution.

First, I will address the question of why star-formation rates in z~1 galaxies are elevated compared with their z~0 counterparts: is this a result of an increased supply of molecular gas to galaxies or a more efficient conversion of existing molecular gas into stars? With new sensitive mm and sub-mm facilities such as PdBI and ALMA, we are able to directly probe signatures of the molecular gas reservoir in high-z galaxies; however, extracting a measurement of the molecular gas content of these objects relies on an uncertain conversion from the observed tracer (typically Carbon Monoxide) luminosity to the molecular gas gas mass. Motivated by the dependence of this conversion factor (alpha_CO) on ISM properties observed locally, I will present an investigation of the variation between alpha_CO and integrated galaxy properties, in particular mass surface density, in 38 massive star-forming galaxies at z~1. Overall, I find that the molecular gas conditions at z~1 are remarkably consistent with those at z=0, suggesting that the process of converting molecular gas to stars in z~1 galaxies is similar to that identified in local galaxies.

Additionally, I will discuss a model for the formation of Ultra-Diffuse Galaxies (UDGs). These dwarf galaxies, with half-light radii similar to that of the Milky Way, but only 1% of its stellar mass, present a significant challenge to our understanding of dwarf-galaxy evolution. Motivated by the environmental dependence of UDG abundance, I investigate the effects of tidal stripping on the dwarf galaxy population using a semi-analytic model for the influence of tidal-stripping on the stellar mass and half-light radius of dwarf galaxies applied to dark-matter halos in the Bolshoi simulation. In particular, simulations show that dwarf galaxies occupying cored dark-matter halos expand significantly as a result of tidal heating as they pass through a massive cluster. By applying this relatively simple model, I am able to reproduce the observed stellar mass and half-light radii distributions of UDGs, as well as the observed UDG abundance across a range of environments remarkably well.

 Abstract: Discussion will take place this Friday, October 27 from 12:00-1:00 pm in SERF 383. Pizza and soda will be provided.

Alessondra's Abstract: Abstract: Asteroids do concern me, Admiral: short of sending spacecraft to an asteroid, the best way to learn about asteroids is to zap them with radar. Arecibo Observatory in Puerto Rico is home to the world's largest single-dish radio telescope and the most powerful planetary radar system for asteroid studies. The 305-meter diameter facility dedicates hundreds of hours a year to improving our knowledge of near-Earth asteroids and comets with planetary radar. Radar observations reveal a wide variety of asteroids shapes, surface features, and sizes, as well as asteroid moons. Important not only for robotic solar system exploration of asteroids, radar-derived asteroid shape models help us plan for potential asteroid hazard mitigation and future human exploration of asteroids. I will show recent results from the Arecibo planetary radar system and discuss the upcoming asteroid sample return mission OSIRIS-REx that launched in September 2016 to bring pieces of an ancient asteroid to Earth.

 Abstract: Understanding the gaseous halo surrounding a galaxy is an integral part to understanding galaxy evolution. The z ~ 2 universe is interesting as this is when universal star formation and AGN activity peak. My work is part of the Quasars Probing Quasars survey, which is nearing conclusion, and have employed 17 optical and near-IR instruments on 8 m class telescopes. Quasars Probing Quasars is designed for studying massive galaxy formation and quasar feedback. I use background quasar sightlines that pass close to foreground quasars to study the circumgalactic medium of quasar-host galaxies in absorption. In present results on the statistical and physical properties of the absorbing gas clumps. Compared to coeval star-forming galaxies, the circumgalactic medium surrounding quasars is more massive, more enriched, and exhibits more extreme kinematics. These results pose challenges for cosmological hydrodynamic simulations. Then I present evidence that the ionizing radiation from the quasar is anisotropic or intermittent and that the gas is not in inflow. Finally I will discuss future studies of (1) joint constraints from absorption and emission on the gaseous environments of quasars using IFU (2) other science goals that can be facilitated using the databases and analysis tools already built.

 Abstract: Perhaps surprisingly, a strictly physical answer can be given to this seemingly metaphysical question. The explanation ties together the initial conditions of the universe, the origin of life on Earth, and the thermo-
dynamics of memory. This talk will parallel my recent paper: arXiv:1801.01783.

 Abstract: In this talk I will present an overview of the upgrade to the polarization-sensitive camera on the Atacama Cosmology Telescope known as Advanced ACTPol (AdvACT). This upgrade targets ambitious science goals using advanced technologies including dense arrays of cryogenic bolometers with superconducting sensors and continuously-rotating silicon-metamaterial half-wave plates for modulation of incoming polarization. I will discuss work on the detector arrays, advances in our understanding of our bolometers, and the data processing pipeline under development to handle polarization-modulated data.

 Abstract: In October 2017 the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) observed an unusual cigar-shaped asteroid that originated from outside the solar system. Since dubbed 'Oumuamua, this interstellar visitor is the first if its kind ever discovered, although many such objects are thought to pass through the solar system all the time. Traveling too fast to be caught into orbit around the Sun, 'Oumuamua passed inside the orbit of Mercury before being slingshot back out into the Milky Way.

Bili's Abstract: Abstract: Reading material

 Abstract: I will review the very recent two Nature papers:
<doi:10.1038/nature25792> and <doi:10.1038/nature25791>.

 Abstract: Galaxy chemical properties place some of the best constraints on models of galaxy evolution. Both gas and stellar metal abundances in galaxies depend upon the integrated star formation history of the galaxy, gas accretion, outflows, and the effectiveness of metal mixing within the interstellar medium (ISM). Capturing the physics that governs these processes in detail, however, is challenging, in part due to the difficulty in self-consistently modelling stellar feedback physics that impacts each of these processes. Using high resolution hydrodynamics simulations of isolated dwarf galaxies where we follow stars as individual star particles, we examine the role of feedback in driving dwarf galaxy chemical evolution. This star-by-star method allows us to directly follow feedback from stellar winds from massive and AGB stars, stellar ionizing radiation and photoelectric heating, and supernovae. Additionally, we track 15 individual metal species yields from these stars as they pollute the ISM and enrich new stellar populations. I will present initial results from these simulations in the context of observational constraints on the retention/ejection of metals from Local Group dwarf galaxies. In addition, I will discuss the variations with which individual elements evolve in the various phases of the ISM, as they progress from hot, ionized gas down to cold, star forming regions. I will conclude by outlining the implications of these results on interpretations of observed chemical abundances in dwarf galaxies and on standard assumptions made in semi-analytic chemical evolution models of these galaxies.