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.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science