ChandraDetection of a Type II Quasar atz= 3.288

Abstract

1 Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the CaliforniaWe 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 (hereinafter CXO52) shows an unusually hard X-ray spectrum from which we infer an absorbing column density N H = (4.8 ± 2.1) × 10 23 cm −2 (90% confidence) and an implied unabsorbed 2−10 keV rest-frame luminosity of L 2−10 = 3.3 × 10 44 ergs s −1 , well within the quasar regime. Hubble Space Telescope imaging shows CXO52 to be elongated with slight morphological differences between the WFPC2 F814W and NICMOS F160W bands. Optical and near-infrared spectroscopy of CXO52 show high-ionization emission lines with velocity widths ∼ 1000 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 AGN which have been extensively studied to date. Unlike radio galaxies, however, CXO52 is radio quiet, remaining undetected at radio wavelengths to fairly deep limits, f 4.8GHz < 40µJy. 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) multi-color imaging selection, and (4) narrow-band 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 to our understanding of the X-ray background.

A Luminosity Function of Lyα‐emitting Galaxies atz≈ 4.5

“…Moreover, deep ($170 ks) Chandra X-Ray Observatory ACIS imaging of LALA z % 4:5 candidates in both Boötes ( Malhotra et al 2003) and in Cetus ( Wang et al 2004) resulted in X-ray nondetections to an average 3 limiting luminosity of L 2Y8keV < 2:8 ; 10 42 ergs s À1 . This limit is roughly an order of magnitude fainter than what is typically observed for even the heavily obscured, type II AGNs (e.g., Stern et al 2002;Norman et al 2002;Dawson et al 2003). By comparing the upper limit on the typical X-rayYtoYLy luminosity ratio for the Ly galaxy sample to the observed values of this ratio for quasar and Seyfert galaxy samples, Malhotra et al (2003) and Wang et al (2004) concluded that AGNs account for P5% of the Ly galaxy sample.…”

The correlation of narrow line emission and X-ray luminosity in active galactic nuclei

“…Work of this type is discussed in Evans (1998), Vernet et al (2001), Stern et al (1999), Rottgering et al (1997), Stern et al (2002) and Norman et al (2002). Out of these references we found 11 objects that were considered appropriate to investigate the…”

“…There are a handful of notable exceptions (see Stern et al 2002;Norman et al 2002) but, so far, the numbers were far from enough to make a detailed study of the population. Almost the only way to cure this deficiency is to combine X-ray fluxes and follow-up spectroscopy in X-ray selected samples.…”

The XMM‐Newton Wide‐Field Survey in the COSMOS Field. IV. X‐Ray Spectral Properties of Active Galactic Nuclei

“…Four objects are characterized by a high X-ray luminosity (L X ½0:5Y 10 keV > 10 44 ergs s À1 ) and substantial absorption (N H > 10 22 cm À2 ) and we can therefore classify them as type 2 QSOs. Radio-loud type 2 QSOs are known since long times thanks to radio surveys (see McCarthy 1993 for a comprehensive review), while radio-quiet type 2 QSOs have been observed only recently in Chandra and XMM-Newton X-ray surveys (Dawson et al 2001;Norman et al 2002;Mainieri et al 2002;Stern et al 2002;Della Ceca et al 2003;Fiore et al 2003;Tozzi et al 2006) and optical surveys (SDSS; Zakamska et al 2005). Two of our type 2 QSOs candidates, xid ¼ 70 and 2289, are clearly detected in the radio at 20 cm using the Very Large Array ( VLA) with an integrated flux of 540 AE 24 and 52 AE 11 Jy, respectively (Schinnerer et al 2007).…”