Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session B1: Astrophysics I |
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Chair: Kelsey Johnson, University of Virginia Room: West Ballroom |
Thursday, November 10, 2016 10:45AM - 10:57AM |
B1.00001: Distinct Metal-Poor Populations in the Milky Way Seen by APOGEE Christian Hayes The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has obtained high-resolution infrared spectra (from 1.5 to 1.7 $\mu$m) for $\sim 146,000$ stars using the Sloan Digital Sky Survey (SDSS) 2.5-m Telescope (Majewski et al. 2015). From their APOGEE observed spectra, radial (Doppler) velocities, stellar parameters (e.g., surface temperatures and gravities), and chemical abundances of 21 different elements have been determined for a large fraction of these stars. Using this large sample of stars, we examine those with a metal composition (i.e., all elements heavier than helium) less than about $1/10$ that of the Sun. These metal-poor stars trace the early history and evolution of our Milky Way galaxy, and we find that in this sample there appear to be two unique stellar populations based both on chemical abundances and observed radial velocities. This is consistent with the findings of previous studies that used samples smaller by about an order of magnitude. Finally, we use the chemical and kinematic differences between these two populations to explore their distinct origins, and their place in the history and evolution of our Galaxy. [Preview Abstract] |
Thursday, November 10, 2016 10:57AM - 11:09AM |
B1.00002: Exploring the Evolutionary Stages of Massive Star Formation Mengyao Liu, Jonathan Tan, Shuo Kong Massive stars play a key role in the regulation of galactic environments. However, there is little consensus on the basic formation mechanism of massive stars. Theories range from Core Accretion, which is approximately a scaled-up version of low-mass star formation, to Competitive Accretion in which massive stars form hand in hand with star clusters, to Protostellar Collisions. A detailed multi-wavelength comparison between theoretical models and observations of massive protostars will help advance our understanding of the massive star formation process. Here we present multi-wavelength observations of a series of high and intermediate-mass protostellar candidates that are expected to span a wide range of the evolutionary sequence. We characterize the early-stage sample with SiO outflows observed by ALMA. The different morphology and kinematics of the outflows indicate different core structures, accretion histories and ambient cloud environments. For more evolved stages, we focus on mid and far infrared data observed by SOFIA. The spectral energy distributions (SEDs) of the protostars are used to constrain detailed radiative transfer models that test massive star formation theories. [Preview Abstract] |
Thursday, November 10, 2016 11:09AM - 11:21AM |
B1.00003: The ALMA View of Dense Molecular Gas in 30 Doradus Lauren Bittle, Remy Indebetouw, Crystal Brogan, Todd Hunter, Adam Leroy The 30 Doradus region within the Large Magellanic Cloud hosts several sites of star formation including R136, a starburst region home to dozens of evolved O stars. The intense radiation from R136 creates an extreme environment for nearby star formation in such a low-metallicity, dwarf galaxy. We have targeted a star-forming region $\sim$15 pc away from R136 within 30 Doradus using the Atacama Large Millimeter/submillimeter Array (ALMA) to map the dense (HCO$^+$, HCN, CS, H$^{13}$CO$^+$, H$^{13}$CN) and diffuse (CO, $^{13}$CO, C$^{18}$O) molecular gas to trace star formation at sub-parsec resolution. We are conducting a clump-by-clump analysis of intensities and line ratios to determine the physical conditions of the $\sim$100 identified clumps (e.g. size, internal turbulence, molecular abundance). We compare observations to non-LTE Radex model grids of the excitation temperature, molecular column density, and volume density of the H$_2$ collider to determine the physical excitation conditions within the clumps. We compare these properties of each clump to both associated and embedded star formation properties to quantify the relative importance of internal feedback from the star formation itself versus external feedback processes from R136 and determine which process dominates. [Preview Abstract] |
Thursday, November 10, 2016 11:21AM - 11:33AM |
B1.00004: Galactic Winds Driven by Supernovae and Radiation Pressure Dong Zhang, Shane Davis, Todd Thompson, Eliot Quataert, Norman Murray Galactic winds are ubiquitous in most rapidly star-forming galaxies. They are crucial to the process of galaxy formation and evolution, shaping the stellar mass function and the mass-metallicity relation, and enriching the intergalactic medium with metals. Although important, the physics of galactic winds is still unclear. Winds may be driven by the heating of the interstellar medium by overlapping supernovae explosions, the radiation pressure by continuum absorption and scattering of starlight on dust grains and so on. The comparison between theory and observation is still incomplete. The growing observations of emission and absorption of cold molecular, cool atomic, and ionized gas in galactic outflows in a large number of galaxies have not been well explained by any models over a vast range of galaxy parameters. A full understanding of these issues requires both better theoretical explorations and comparisons with observations. I will be taking about the theoretical models of both supernova-driven and radiation-pressure-driven galactic winds, and compared these models with observations. I will also be talking about our radiative hydrodynamical numerical simulations on momentum coupling between gas and radiation field in rapidly star-forming galaxies. [Preview Abstract] |
Thursday, November 10, 2016 11:33AM - 11:45AM |
B1.00005: The Star Formation in Radio Survey (SFRS): Multi-Band VLA Imaging for 50 Nearby Star-Forming Galaxies in SINGS/KINGFISH Sean Linden Radio emission from galaxies is powered by a combination of distinct physical processes. And although it is energetically weak with respect to a galaxy’s bolometric luminosity, it provides critical dust un-biased information on the massive star formation activity, as well as access to the relativistic [magnetic field + cosmic rays (CRs)] component in the interstellar medium (ISM) of galaxies. Here I present the preliminary results from a Jansky Very Large Array (VLA) 33GHz (Ka-Band), 15GHz (Ku-Band) and 3 GHz (S-Band) imaging campaign of 112 extragalactic nuclei and star-forming regions in 50 nearby ($d \leq 30$Mpc) normal star-forming galaxies at scales of 30-300 pc, taken as part of the Star Formation in Radio Survey (SFRS). Our initial investigation includes comparisons of 33GHz source morphologies with H-alpha and 24um imaging, showing that in general the two trace each other very closely. By utilizing the lower frequency Ku- and S-band data we can do proper thermal/non-thermal spectral energy decompositions of each source and have begun making spectral index maps to compare how the contributions of each emission mechanism change as a function of distance from individual star-forming regions and global region in the galaxy. [Preview Abstract] |
Thursday, November 10, 2016 11:45AM - 11:57AM |
B1.00006: The Distribution of Star Formation in Interacting Dwarf Galaxies Sandra Liss, Kelsey Johnson, Sabrina Stierwalt, Nitya Kallivayalil, Gurtina Besla, David Patton, George Privon We present H$\alpha$ imaging of the interacting dwarf galaxies from the TiNy Titans (TNT) survey, providing an unparalleled view of the ongoing star formation in the first systematic study of these systems. Galaxy interactions are of fundamental importance to the evolution of massive galaxies - they impact morphology, star formation rates (SFRs), and interstellar medium composition. Although the majority of mergers at all redshifts are expected to occur between low mass galaxies, little is known about the extent of these effects in their shallow gravitational potentials. Early TNT results include the finding that fiber-based H$\alpha$ fluxes suggest an enhancement in the SFRs of paired versus unpaired dwarf galaxies, and that this enhancement may be more significant than in their more massive counterparts. To develop a more comprehensive view of the star formation in these interacting dwarf galaxies, we have obtained H$\alpha$ observations with the 8.1m Gemini North Telescope. These compelling images reveal the clumpy morphology and asymmetric distribution of the ongoing star formation in the TNT sample. We present a quantitative analysis of this morphology and discuss the impact of the clustered star formation on these low mass dwarf galaxies and their environments. [Preview Abstract] |
Thursday, November 10, 2016 11:57AM - 12:09PM |
B1.00007: The efficiency of star formation in the Antennae galaxies Allison Matthews, Kelsey Johnson Using Atacama Large Millimeter Array (ALMA) Cycle 0 data and Hubble Space Telescope (HST) images, we calculate the spatially resolved star formation efficiency (SFE) in the Antennae galaxies, a nearby major merger to the Milky Way. The SFE describes how effectively a galactic environment converts the gas in molecular clouds to stars, and is a fundamental parameter for simulations of galaxy evolution in the early universe. Specifically, we implemented new and objective methods (i.e. a weighted Voronoi tessellation) to divide the CO($J=3-2$) integrated intensity map, which traces star forming gas, into intensity-weighted bins which intelligently encapsulate star forming regions. This provides us with an empirical and standardized method to calculate spatially resolved SFE. By using the ALMA CO($J=3-2$) flux as a tracer of the total gas mass in conjunction with the mass of the stars derived from the optical and near-infrared images from HST, we calculated the star formation efficiency. We find a correlation of SFE with the age of the spatially coincident star clusters. With this correlation, we better constrain the timescales on which star formation occurs and determine the effect that young, massive stars have on the efficiency of star formation. [Preview Abstract] |
Thursday, November 10, 2016 12:09PM - 12:21PM |
B1.00008: Probing the distant Universe with ALMA and gravitational lensing Catherine Vlahakis The advent of the Atacama Large Millimeter/submillimeter Array (ALMA), located in the Atacama desert in northern Chile, has opened up unprecedented opportunities for studying galaxies in both the local and high redshift Universe at high resolution and with high sensitivity. In 2014-2015, ALMA achieved one of its major goals - the development and verification of the Long Baseline capability, providing imaging at resolutions of tens of milliarcseconds (requiring baselines of up to ~15 km). I will present results from the ALMA Long Baseline Campaign Science Verification observations of SDP. 81 (HATLAS J090311.6+003906) - a z~3 gravitationally lensed submillimeter galaxy - in which we detected the Einstein-ring structure in thermal dust emission and CO line emission at unprecedented tens-of-parsec resolution, as well as the highest resolution detection to date of thermal water emission in an extragalactic source. I will also discuss subsequent results presented by several groups that have used lensing models to reconstruct the source emission and investigate the properties of the dust and gas in this distant SDP.81 system, and the future possibilities for using ALMA and gravitational lensing as a powerful tool for probing the distant Universe. [Preview Abstract] |
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