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

By F. Tombesi, M. Cappi, J. Reeves, G. Palumbo, V. Braito, M. D. Nasagsfccresst, Umcp, Unibo, INAF-IASFbo, Keele University and 1 more. 2011

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X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet active galactic nuclei (AGNs). These have been detected essentially through blueshifted Fe xxv/xxvi K-shell transitions. In the previous paper of this series we defined UFOs as those highly ionized absorbers with an outflow velocity higher than 10,000 km s−1 and assessed the statistical significance of the associated blueshifted absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. The present paper is an extension of that work. First, we report a detailed curve of growth analysis of the main Fe xxv/xxvi transitions in photoionized plasmas. Then, we estimate an average spectral energy distribution for the sample sources and directly model the Fe K absorbers in the XMM-Newton spectra with the detailed Xstar photoionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35% and that the majority of the Fe K absorbers are indeed associated with UFOs. The outflow velocity distribution spans from ∼10,000 km s−1 (∼0.03c) up to ∼100,000 km s−1 (∼0.3c), with a peak and mean value of ∼42,000 km s−1 (∼0.14c). The ionization parameter is very high and in the range log ξ ∼ 3–6 erg s−1 cm, with a mean value of log ξ ∼ 4.2 erg s−1 cm. The associated column densities are also large, in the range NH ∼ 1022–1024 cm−2, with a mean value of NH ∼ 1023 cm−2. We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7 keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton-thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback from AGNs and their study can provide important clues on the connection between accretion disks, winds, and jets.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/9bead535e2484cc3a11af5a91fbba67db0d5e355

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Citations in the corpus

Powerful Outflows and Feedback from Active Galactic Nuclei (2015, methodology): “A later analysis based on broad-band modelling with XSTAR photoionized grids (Tombesi et al. 2011) led to several revised velocities and confirmed that the outflows were typically highly ionized, with log ξ ∼ 3 − 6 erg cm s−1, with column densities in the range NH ∼ 1022−1024 cm−2.”
The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow (2015, background): “Furthermore, there is growing evidence for the existence of ultra-fast outflows (UFOs) via the detection of highly ionized Fe K-shell absorption arising from a gas moving at velocities up to 0.2–0.4c (Pounds et al. 2003; Reeves et al. 2009; Tombesi et al. 2011, 2015 and references therein).”
NUMERICAL SIMULATION OF HOT ACCRETION FLOWS. II. NATURE, ORIGIN, AND PROPERTIES OF OUTFLOWS AND THEIR POSSIBLE OBSERVATIONAL APPLICATIONS (2012, methodology): “Outflow has been directly detected in AGNs such as broad absorption lines quasars (e.g., Crenshaw et al. 2003; Tombesi et al. 2010; 2011a; 2012).”
The Suzaku View of Highly Ionized Outflows in AGN. 1; Statistical Detection and Global Absorber Properties (2012, background): “As highly ionized outflows are thought to originate at relatively small distances from the central nucleus (e.g. Gofford et al. 2011; Tombesi et al. 2011a, 2012, hereafter T11 and T12, respectively), it is important that the primary continuum emission from the central nucleus, rather than that…”
Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers (2012, background): “It is important to note that Tombesi et al. (2010b, 2011b, 2012b) detected the presence of UFOs also in a small sample of (3 out of 5) radio-loud AGNs observed with Suzaku.”