The XMM deep survey in the CDF-S - IX. An X-ray outflow in a luminous obscured quasar at z ≈ 1.6

摘要

In active galactic nuclei (AGN)-galaxy co-evolution models, AGN winds and outflows are often invoked to explain why super-massive black holes and galaxies stop growing efficiently at a certain phase of their lives. They are commonly referred to as the leading actors of feedback processes. Evidence of ultra-fast (v ? 0.05c) outflows in the innermost regions of AGN has been collected in the past decade by sensitive X-ray observations for sizable samples of AGN, mostly at low redshift. Here we present ultra-deep XMM-Newton and Chandra spectral data of an obscured (NH≈ 2 × 1023 cm-2), intrinsically luminous (L2?10 keV≈ 4 × 1044 erg s-1) quasar (named PID352) at z ≈ 1.6 (derived from the X-ray spectral analysis) in the Chandra Deep Field-South. The source is characterized by an iron emission and absorption line complex at observed energies of E ≈ 2?3 keV. While the emission line is interpreted as being due to neutral iron (consistent with the presence of cold absorption), the absorption feature is due to highly ionized iron transitions (FeXXV, FeXXVI) with an outflowing velocity of 0.14+0.02-0.06c, as derived from photoionization models. The mass outflow rate – ~2 M⊙ yr-1 – is similar to the source accretion rate, and the derived mechanical energy rate is ~9.5 × 1044 erg s-1, corresponding to 9% of the source bolometric luminosity. PID352 represents one of the few cases where indications of X-ray outflowing gas have been observed at high redshift thus far. This wind is powerful enough to provide feedback on the host galaxy.