EVIDENCE FOR ULTRA-FAST OUTFLOWS IN RADIO-QUIET ACTIVE GALACTIC NUCLEI. II. DETAILED PHOTOIONIZATION MODELING OF Fe K-SHELL ABSORPTION LINES

Abstract

X-ray absorption line spectroscopy has recently shown evidence for previously\nunknown Ultra-fast Outflows (UFOs) in radio-quiet AGNs. In the previous paper\nof this series we defined UFOs as those absorbers with an outflow velocity\nhigher than 10,000km/s and assessed the statistical significance of the\nassociated blueshifted FeK absorption lines in a large sample of 42 local\nradio-quiet AGNs observed with XMM-Newton. In the present paper we report a\ndetailed curve of growth analysis and directly model the FeK absorbers with the\nXstar photo-ionization code. We confirm that the frequency of sources in the\nradio-quiet sample showing UFOs is >35%. The outflow velocity distribution\nspans from \\sim10,000km/s (\\sim0.03c) up to \\sim100,000km/s (\\sim0.3c), with a\npeak and mean value of \\sim42,000km/s (\\sim0.14c). The ionization parameter is\nvery high and in the range log\\xi 3-6erg s^{-1} cm, with a mean value of log\\xi\n4.2 erg s^{-1} cm. The associated column densities are also large, in the range\nN_H\\sim10^{22}-10^{24} cm^{-2}, with a mean value of N_H\\sim10^{23} cm^{-2}. We\ndiscuss and estimate how selection effects, such as those related to the\nlimited instrumental sensitivity at energies above 7keV, may hamper the\ndetection of even higher velocities and higher ionization absorbers. We argue\nthat, overall, these results point to the presence of extremely ionized and\npossibly almost Compton thick outflowing material in the innermost regions of\nAGNs. This also suggests that UFOs may potentially play a significant role in\nthe expected cosmological feedback from AGNs and their study can provide\nimportant clues on the connection between accretion disks, winds and jets.\n