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2001AJ....122.2156A - Astron. J., 122, 2156-2176 (2001/November-0)
The Chandra Deep Field North survey. VI. The nature of the optically faint X-ray source population.
ALEXANDER D.M., BRANDT W.N., HORNSCHEMEIER A.E., GARMIRE G.P., SCHNEIDER D.P., BAUER F.E. and GRIFFITHS R.E.
Abstract (from CDS):
We investigate the multiwavelength properties of optically faint X-ray sources. Nine optically faint X-ray sources have µJy radio counterparts; ~53+24–17% of the optically faint µJy radio sources in this region. The most likely origin of the X-ray emission in these X-ray detected, optically faint µJy radio sources is obscured AGN activity. However, two of these sources have been previously detected at submillimeter wavelengths, and the X-ray emission from these sources could be due to luminous star formation activity. Assuming the spectral energy distribution of NGC 6240, we estimate the 175 µm flux of a typical optically faint X-ray source to be less than 10 mJy; however, those sources with detectable submillimeter counterparts (i.e., f_850 µm_>3 mJy) could be substantially brighter. Hence, most optically faint X-ray sources are unlikely to contribute significantly to the far-IR (140-240 µm) background radiation. However, as expected for sources with AGN activity, the two optically faint X-ray sources within the most sensitive area of the ISOCAM HDF-N region have faint (≲50 µJy) 15 µm counterparts.
We also provide constraints on the average X-ray properties of classes of optically faint sources not individually detected at X-ray energies. Stacking analyses of optically faint µJy radio sources not individually detected with X-ray emission yields a possible detection (at 98.3% confidence) in the 0.5-2.0 keV band; this X-ray emission could be produced by star formation activity at z=1-3. None of the optically faint AGN-candidate sources in the HDF-N itself are detected at X-ray energies either individually or with stacking analyses, showing that these sources have low X-ray luminosities if they are indeed AGNs.
Abstract Copyright: ∼
Journal keyword(s): Cosmology: Observations - Galaxies: Active - Galaxies: Nuclei - Surveys - X-Rays
Nomenclature: Table 1: CXOHDFN JHHMMSS.s+DDMMSS N=41 added.
Simbad objects: 57
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