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Physical Sciences and Mathematics Commons™
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Articles 1 - 4 of 4
Full-Text Articles in Physical Sciences and Mathematics
A Uv To Mid-Ir Study Of Agn Selection, Sun Mi Chung, Christopher S. Kochanek, Roberto Assef, Michael J. I. Brown, Daniel Stern, Buell T. Jannuzi, Anthony H. Gonzalez, Ryan C. Hickox, John Moustakas
A Uv To Mid-Ir Study Of Agn Selection, Sun Mi Chung, Christopher S. Kochanek, Roberto Assef, Michael J. I. Brown, Daniel Stern, Buell T. Jannuzi, Anthony H. Gonzalez, Ryan C. Hickox, John Moustakas
Dartmouth Scholarship
We classify the spectral energy distributions (SEDs) of 431,038 sources in the 9 deg2 Boötes field of the NOAO Deep Wide-Field Survey (NDWFS). There are up to 17 bands of data available per source, including ultraviolet (GALEX), optical (NDWFS), near-IR (NEWFIRM), and mid-infrared (IRAC and MIPS) data, as well as spectroscopic redshifts for ~20,000 objects, primarily from the AGN and Galaxy Evolution Survey. We fit galaxy, active galactic nucleus (AGN), stellar, and brown dwarf templates to the observed SEDs, which yield spectral classes for the Galactic sources and photometric redshifts and galaxy/AGN luminosities for the extragalactic sources. …
Obscuration By Gas And Dust In Luminous Quasars, S. M. Usman, S. S. Murray, R. C. Hickox, M. Brodwin
Obscuration By Gas And Dust In Luminous Quasars, S. M. Usman, S. S. Murray, R. C. Hickox, M. Brodwin
Dartmouth Scholarship
We explore the connection between absorption by neutral gas and extinction by dust in mid-infrared (IR) selected luminous quasars. We use a sample of 33 quasars at redshifts 0.7 < z < 3 in the 9 deg^2 Bo\"otes multiwavelength survey field that are selected using Spitzer Space Telescope Infrared Array Camera colors and are well-detected as luminous X-ray sources (with >150 counts) in Chandra observations. We divide the quasars into dust-obscured and unobscured samples based on their optical to mid-IR color, and measure the neutral hydrogen column density N_H through fitting of the X-ray spectra. We find that all subsets of quasars have consistent power law photon indices equal to 1.9 that are uncorrelated with N_H. We classify the quasars as gas-absorbed or gas-unabsorbed if N_H > 10^22 cm^-2 or N_H < 10^22 cm^-2, respectively. Of 24 dust-unobscured quasars in the sample, only one shows clear evidence for significant intrinsic N_H, while 22 have column densities consistent with N_H < 10^22 cm^-2. In contrast, of the nine dust-obscured quasars, six show evidence for intrinsic gas absorption, and three are consistent with N_H < 10^22 cm^-2. We conclude that dust extinction in IR-selected quasars is strongly correlated with significant gas absorption as determined through X-ray spectral fitting. These results suggest that obscuring gas and dust in quasars are generally co-spatial, and confirm the reliability of simple mid-IR and optical photometric techniques for separating quasars based on obscuration.
A Comparison Of X-Ray And Optical Emission In Cassiopeia A, Daniel J. Patnaude, Robert A. Fesen
A Comparison Of X-Ray And Optical Emission In Cassiopeia A, Daniel J. Patnaude, Robert A. Fesen
Dartmouth Scholarship
Broadband optical and narrowband Si XIII X-ray images of the young Galactic supernova remnant Cassiopeia A (Cas A) obtained over several decades are used to investigate spatial and temporal emission correlations on both large and small angular scales. The data examined consist of optical and near infrared ground-based and Hubble Space Telescope images taken between 1951 and 2011, and X-ray images from Einstein, ROSAT, and Chandra taken between 1979 and 2013. We find weak spatial correlations between the remnant’s X-ray and optical emission features on large scales, but several cases of good optical/X-ray correlations on small scales for features which …
Star Formation And Substructure In Galaxy Clusters, Seth A. Cohen, Ryan C. Hickox, Gary A. Wegner, Maret Einasto, Jaan Vennik
Star Formation And Substructure In Galaxy Clusters, Seth A. Cohen, Ryan C. Hickox, Gary A. Wegner, Maret Einasto, Jaan Vennik
Dartmouth Scholarship
We investigate the relationship between star formation (SF) and substructure in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey (SDSS). Several past studies of individual galaxy clusters have suggested that cluster mergers enhance cluster SF, while others find no such relationship. The SF fraction in multi-component clusters (0.228 +/- 0.007) is higher than that in single-component clusters (0.175 +/- 0.016) for galaxies with M^0.1_r < -20.5. In both single- and multi-component clusters, the fraction of star-forming galaxies increases with clustercentric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all clustercentric distances and local densities. Comparing the SF fraction in individual clusters to several statistical measures of substructure, we find weak, but in most cases significant at greater than 2 sigma, correlations between substructure and SF fraction. These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.