Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session E15: DAP Thesis Prize SessionInvited Prize/Award
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Sponsoring Units: DAP Room: Washington 2 |
Saturday, January 28, 2017 3:30PM - 4:03PM |
E15.00001: Distributions of Gas and Galaxies from Galaxy Clusters to Larger Scales Invited Speaker: Anna Patej We address the distributions of gas and galaxies on three scales: the outskirts of galaxy clusters, the clustering of galaxies on large scales, and the extremes of the galaxy distribution. In the outskirts of galaxy clusters, long-standing analytical models of structure formation and recent simulations predict the existence of density jumps in the gas and dark matter profiles. We use these features to derive models for the gas density profile, obtaining a simple fiducial model that is in agreement with both observations of cluster interiors and simulations of the outskirts. We next consider the galaxy density profiles of clusters; under the assumption that the galaxies in cluster outskirts follow similar collisionless dynamics as the dark matter, their distribution should show a steep jump as well. We examine the profiles of a low-redshift sample of clusters and groups, finding evidence for the jump in some of these clusters. Moving to larger scales where massive galaxies of different types are expected to trace the same large-scale structure, we present a test of this prediction by measuring the clustering of red and blue galaxies at z $\sim$ 0.6, finding low stochasticity between the two populations. These results address a key source of systematic uncertainty $-$ understanding how target populations of galaxies trace large-scale structure $-$ in galaxy redshift surveys. Such surveys use baryon acoustic oscillations (BAO) as a cosmological probe, but are limited by the expense of obtaining sufficiently dense spectroscopy. With the intention of leveraging upcoming deep imaging data, we develop a new method of detecting the BAO in sparse spectroscopic samples via cross-correlation with a dense photometric catalog. This method will permit the extension of BAO measurements to higher redshifts than possible with the existing spectroscopy alone. Lastly, we connect galaxies near and far: the Local Group dwarfs and the high redshift galaxies observed by Hubble and Spitzer. We examine how the local dwarfs may have appeared in the past and compare their properties to the detection limits of the upcoming James Webb Space Telescope (JWST), finding that JWST should be able to detect galaxies similar to the progenitors of a few of the brightest of the local galaxies, revealing a hitherto unobserved population of galaxies at high redshifts. [Preview Abstract] |
Saturday, January 28, 2017 4:03PM - 4:36PM |
E15.00002: Exploring non-standard stellar physics with lithium depletion Invited Speaker: Garrett Somers Standard models of stellar evolution generally rely on the assumption that the structure and evolution of stars are uniquely determined by their mass, composition, and age. This assumption is now known to be too simplistic, as there remain numerous features of the observed cluster and field stellar pattern which cannot be explained by standard stellar theory. One such discrepancy pertains to the evolving abundances of the light element lithium, which shows significant dispersions between stars of equal mass and age on the pre-main sequence, in defiance of standard predictions. Lithium is rapidly destroyed by proton capture in the deep interiors of stars, and consequently the Li abundance observed in a star's convective envelope encodes information about the evolution of the temperature of its interior, and about the history of material exchanged between the surface and hot central regions. This makes Li an extremely sensitive diagnostic of stellar physics. Identifying the ways in which standard lithium predictions differ from the observed pattern gives us a crucial laboratory for understanding how non-standard physical effects are influencing stellar structure and evolution. In this talk, I will argue that starspots, correlated with rotation, are the underlying driver of dispersion in lithium abundance on the pre-main sequence. Starspots are ubiquitously found on young, active stars, and may cover up to ~50\% of their surfaces. By modifying an existing stellar evolution code to account for spot effects on both the surface boundary conditions and the transport of energy in the interior, I will show that heavy spot coverage systematically increases the radii of the fastest spinning young stars. This effect cools their interiors, leading to a reduce rate of lithium destruction on the pre-main sequence. This insight demonstrates that stars of equal mass and age can have different stellar parameters, and holds important consequences for measuring the masses and ages of stars in young clusters. These are questions of deep importance to astrophysics, as young cluster ages anchor our knowledge of the formation timescale of planets, the lifetimes of circumstellar disks, and the accretion processes experienced by proto-stars. [Preview Abstract] |
Saturday, January 28, 2017 4:36PM - 5:09PM |
E15.00003: Social Stars: Modeling the Interactive Lives of Stars in Dense Clusters Invited Speaker: Morgan MacLeod This talk discusses computational modeling of phases of dramatic interaction that intersperse stellar lifetimes. In galactic centers stars trace dangerously wandering orbits dictated by the combined gravitational force of a central, supermassive black hole and all of the surrounding stars. During this talk, I will describe how stellar dynamics intertwines with stellar evolution and hydrodynamics to determine the properties of interactions between stars and black holes in galactic centers. These interactions can partially or completely disrupt stars through tidal forces, and they can fuel accretion-driven flares of the black hole. Disruptions of stars across the evolutionary spectrum give rise to transients with different characteristic timescales, luminosities, and wavelengths. I will focus on how the properties of these transients can reveal the demographics of black holes and the stellar populations that surround them. [Preview Abstract] |
Saturday, January 28, 2017 5:09PM - 5:42PM |
E15.00004: New Physics with Atmospheric and Astrophysical Neutrinos Invited Speaker: Carlos Arguellas Delgado In this talk I will use data from the IceCube Neutrino Observatory to search for effects of new physics in two contexts. First, using atmospheric neutrinos, I looked for evidence of a sterile neutrino by looking for deviations in atmospheric muon neutrino spectrum as a function of zenith angle and energy. Such a sterile neutrino, motivated by the anomalies in short-baseline experiments, is expected to have a significant effect on the $\bar{\nu_\mu}$ survival probability due to matter induced resonant effects for energies of order 1 TeV. This effect makes the search uniquely sensitive to small sterile mixings. No significant evidence for an eV-sterile neutrino is found and strong limits are put on the mixing angle which improve previous bounds by more than an order of magnitude. Second, using astrophysical neutrinos, I studied the effects of new physics on the astrophysical flavor ratio. In order to do so, a model independent parametrization of new physics was constructed. Using this parametrization, we explore the allowed new physics parameter space. We find that large deviations from the standard (1:1:1) flavor ratio expectation can be found but the impact of new physics is reduced in pion production scenarios. [Preview Abstract] |
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