ChandraDetection of a Type II Quasar atz= 3.288
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Abstract
We report on observations of a type II quasar at redshift z = 3.288, identified as a hard X-ray source in a 185 ks observation with the Chandra X-Ray Observatory and as a high-redshift photometric candidate from deep, multiband optical imaging. CXO J084837.9+ 445352 ( hereafter CXO 52) shows an unusually hard X-ray spectrum from which we infer an absorbing column density N-H = (4.8 +/- 2.1) x 10(23) cm(-2) (90% confidence) and an implied unabsorbed 2-10 keV rest-frame luminosity of L2-10 = 3.3 x 10(44) ergs s(-1), well within the quasar regime. Hubble Space Telescope imaging shows CXO 52 to be elongated with slight morphological differences between the WFPC2 F814W and NICMOS F160W bands. Optical and near-infrared spectroscopy of CXO 52 shows high-ionization emission lines with velocity widths similar to1000 km s(-1) and flux ratios similar to a Seyfert 2 galaxy or radio galaxy. The latter are the only class of high-redshift type II luminous active galactic nuclei that have been extensively studied to date. Unlike radio galaxies, however, CXO 52 is radio quiet, remaining undetected at radio wavelengths to fairly deep limits, f(4.8GHz) < 40 μJy. High-redshift type II quasars, expected from unification models of active galaxies and long thought necessary to explain the X-ray background, are poorly constrained observationally, with few such systems known. We discuss recent observations of similar type II quasars and detail search techniques for such systems, namely, (1) X-ray selection, (2) radio selection, (3) multicolor imaging selection, and (4) narrowband imaging selection. Such studies are likely to begin identifying luminous, high-redshift type II systems in large numbers. We discuss the prospects for these studies and their implications for our understanding of the X-ray background.