The chandra deep field-north survey. XVI. The x-ray properties of moderate-luminosity active galaxies at z > 4

C. Vignali, F. E. Bauer, D. M. Alexander, W. N. Brandt, A. E. Hornschemeier, D. P. Schneider, G. P. Garmire

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Abstract

We present X-ray spectral analyses of the three z > 4 active galactic nuclei (AGNs) thus far spectroscopically identified in the Chandra Deep Field-North Survey, at redshifts of 5.186, 4.424, and 4.137. These analyses are made possible by the extremely deep exposure (≈2 Ms) and the low Chandra background. The rest-frame ≈2.5-40 keV spectra are the first for optically faint (two of the three sources have I > 24) z > 4 AGNs. The z = 5.186 quasar is well fitted by a power-law model with photon index Γ = 1.8 ± 0.3, consistent with those of lower-redshift, unobscured AGNs. The other two AGNs have flatter effective X-ray photon indices (Γ ≈ 1.1-1.5), suggesting the presence of intrinsic absorption (provided their underlying X-ray continua are similar to those of lower redshift AGNs). It is possible that the flat X-ray continuum of the z = 4.424 AGN is partially related to its radio loudness. If the z = 4.137 AGN suffers from X-ray absorption, the implied column density is NH 2 × 10 23 cm-2.

Original languageEnglish (US)
Pages (from-to)L105-L109
JournalAstrophysical Journal
Volume580
Issue number2 II
DOIs
StatePublished - Dec 1 2002

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All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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