Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session E3: Astrophysics III: Extragalactic/Cosmology |
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Chair: Carl Covatto, Arizona State University Room: MU242A |
Friday, October 16, 2015 3:17PM - 3:29PM |
E3.00001: ABSTRACT WTIHDRAWN |
Friday, October 16, 2015 3:29PM - 3:41PM |
E3.00002: Observing the first billion years of universe. V. Tilvi, C. Papovich, S. Finkelstein, J. Long, M. Song, A. Koekemoer, M. Dickinson, H. Ferguson, M. Giavalisco, B. Mobasher, S. Malhotra, J. Rhoads Epoch of reionization-- one of the major milestones in the history of the universe when the universe transitioned from a completely neutral medium to an ionized phase, occurred within the first billion years. However, our knowledge about this epoch--- how and when did this transition occur, remains limited. To probe this epoch, we have obtained very sensitive spectroscopic observations of galaxies within the first 800 Myrs after the Bigbang. Our results suggest that by redshift \textasciitilde 8 (about 650 Myrs after the Bigbang), the universe is significantly neutral, and the transition from a neutral to an ionized universe occurs over a very short timescale of \textasciitilde 300 Myrs. [Preview Abstract] |
Friday, October 16, 2015 3:41PM - 3:53PM |
E3.00003: Spectrophotometric Redshifts in the Faint Infrared Grism Survey John Pharo A galaxy's redshift is vital for understanding its place in the growth and evolution of the universe. Determination of a galaxy’s redshift generally requires measuring prominent features in the galaxy’s spectrum with known rest-frame wavelengths, such as known strong emission or absorption lines (eg, H$\alpha$) or characteristic breaks. Spectroscopic redshifts maintain high accuracy, but are unable to probe fainter sources. Redshifts for these sources can also be calculated with photometric catalogs, but with a generally less accurate result. Using a technique pioneered by Ryan et al. 2007, one can combine spectra and photometry to yield an accurate spectrophotometric redshift (SPZ) while still measuring faint sources. By taking mid-resolution spectra from the HST Faint Infrared Grism Survey, SPZs can be found for measurements potentially down to 27th magnitude (the typical brightness of a dwarf galaxy at redshift $\sim$1.5), more completely filling the faint-end and high-redshift portions of the luminosity function than before. The improved redshift and distance measurements allowed for the identification of a structure at z=0.83 in one of the FIGS fields. [Preview Abstract] |
Friday, October 16, 2015 3:53PM - 4:05PM |
E3.00004: H$\alpha$ Emitting Galaxies in the Deep And Wide Narrow-band Survey Alicia Gonzalez H$\alpha$ is an spectral line of hydrogen that occurs when an electron transitions from its third to its second lowest energy level. H$\alpha$ emission ($\lambda$=6563 \AA) comes mainly from early-type stars, so its presence is the best tracer of recent star formation. Studying the H$\alpha$ luminosity of galaxies permits then the calculation of their star formation rates. The Deep And Wide Narrow-band Survey (DAWN) is an ongoing and uniquely deep survey that stands out for its sensitivity and area coverage. It is being done using a custom-made narrow-band filter, centered at 10660 {\AA} and 35 {\AA} wide. DAWN is an NOAO survey project that uses the 4-meter Mayall telescope at Kitt Peak National Observatory (Arizona) equipped with the NEWFIRM instrument,an infrared camera with a 28x28 arcmin field of view. This filter is suitable for the detection of H$\alpha$ emission at z $\sim$ 0.6, a redshift that corresponds to a time when the Universe was roughly half of its current age. From this survey we have $\sim$120 H$\alpha$ candidates in the COSMOS field with available photometric or spectroscopic redshifts. A fraction of these candidates are fainter than those in other similar surveys, which leads us to extend the H$\alpha$ luminosity function to fainter luminosities. [Preview Abstract] |
Friday, October 16, 2015 4:05PM - 4:17PM |
E3.00005: GREEN PEA GALAXIES REVEAL SECRETS OF Ly? ESCAPE Huan Yang In star-forming galaxies, a lot of Ly$\alpha$ photons were generated in HII regions surrounding massive stars. The escape of Ly$\alpha$ photons from galaxies is a key issue in studying high redshift galaxies and probing cosmic reionization with Ly$\alpha$. To understand Ly$\alpha$ escape, it is valuable to study high quality Ly$\alpha$ profiles in Ly$\alpha$ emitters. However, such studies are rare due to the faintness of high-z Ly$\alpha$ emitters and the lack of local analogs with high Ly$\alpha$ equivalent width. Here we show that "Green Pea" galaxies are the best local analogs of high-z Ly$\alpha$ emitters and their high quality Ly$\alpha$ profiles demonstrate low HI column density is the key to Ly$\alpha$ escape. The Ly$\alpha$ escape fraction shows correlations with a few features of Ly$\alpha$ profiles. We compared the Ly$\alpha$ profiles with outflowing HI shell radiative transfer model and found that the best-fit HI column density is anti-correlated with the Ly$\alpha$ escape fraction. We also found an anti-correlation between Ly$\alpha$ escape fraction and galactic metallicity. Our results support that LAEs with high Ly$\alpha$ escape fraction have low metallicity, low HI column density, and mild HI gas outflow. [Preview Abstract] |
Friday, October 16, 2015 4:17PM - 4:29PM |
E3.00006: The Energy-Dependence of GRB Minimum Variability Timescales V. Zachary Golkhou, Nathaniel Butler, Owen Littlejohns We constrain the minimum variability timescales for 938 GRBs observed by the \textit{Fermi}/GBM instrument prior to July 11, 2012. The tightest constraints on progenitor radii derived from these timescales are obtained from light curves in the hardest energy channel. In the softer bands -- or from measurements of the same GRBs in the hard X-rays from \swift -- we show that variability timescales tend to be a factor 2--3 longer. Applying a survival analysis to account for detections and upper limits, we find median minimum timescale in the rest frame for long-duration and short-duration GRBs of 45 ms and 10 ms, respectively. Fewer than 10\% of GRBs show evidence for variability on timescales below 2 ms. These shortest timescales require Lorentz factors ${\raise-.5ex\hbox{$\buildrel>\over\sim$}}\ 400$ and imply typical emission radii $R \approx 1 {\times} 10^{14}$ cm for long-duration GRBs and $R \approx 3 {\times} 10^{13}$ cm for short-duration GRBs. We discuss implications for the GRB fireball model and investigate whether GRB minimum timescales evolve with cosmic time. \\ Source: \url{http://arxiv.org/abs/1501.05948} [Preview Abstract] |
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