Computer Science
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006phdt.........1g&link_type=abstract
PhD dissertation. Proquest Dissertations And Theses 2006. Section 0054, Part 0606 224 pages; [Ph.D. dissertation].United State
Computer Science
Dust, Quasars
Scientific paper
I have constructed a sample of bright near-infrared sources which are detected at radio wavelengths but undetected on the POSS I plates in order to search for a population of dust-obscured quasars. Optical and infrared spectroscopic follow-up of the sample has led to the discovery of seventeen heavily reddened quasars ( B - K > 6.5), fourteen of which are reported here for the first time. Based on this, I define a region in the R - K, J - K color plane in which 50% of the radio-selected objects are highly reddened quasars. I compare the surface density of this previously overlooked population to that of UVX-radio- selected quasars, finding that they make up ~ 20% of the total quasar population for K [Special characters omitted.] 15.5.
I present a near-infrared quasar composite spectrum spanning the wavelength range 0.58-3.5 mm. The spectrum has been constructed from observations of 27 quasars obtained at the NASA IRTF telescope and satisfying the criteria K s < 14.5 and M i < -23; the redshift range is 0.118 < z < 0.418. The signal-to- noise is moderate, reaching a maximum of 150 between 1.6 and 1.9 mm. While a power-law fit to the continuum of the composite spectrum requires two breaks, a single power-law slope of a = -0.92 plus a 1260 K blackbody provides an excellent description of the spectrum from Ha to 3.5 mm, strongly suggesting the presence of significant quantities of hot dust in this blue-selected quasar sample. I measure intensities and line widths for ten lines, finding that the Paschen line ratios rule out Case B recombination. I compute K -corrections for the J, H, K , and Spitzer 3.6 mm bands which will be useful in analyzing observations of quasars up to z = 10.
I present the complete F2M candidate list in which I have identified over 100 heavily reddened quasars (0.1 < E(B - V) < 1.2) using the FIRST and 2MASS surveys. I present a detailed study of the reddening to determine whether these colors arise from dust extinction and/or a red synchrotron component associated with a flat radio spectrum. I also analyze a spectroscopically complete subsample of this survey commenting on the spatial distribution of obscured quasars, and predict the fraction of quasars missing from flux-limited optically-selected quasar surveys to be as high as ~ 50%.
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