A Compton-Thick Wind in the High-Luminosity Quasar, PDS 456

Abstract

PDS 456 is a nearby (z=0.184), luminous (L bol ∼ 10 47 erg s −1 ) type I quasar. A deep 190 ks Suzaku observation in February 2007 revealed the complex, broad band X-ray spectrum of PDS 456. The Suzaku spectrum exhibits highly statistically significant absorption features near 9 keV in the quasar rest-frame. We show that the most plausible origin of the absorption is from blue-shifted resonance (1s − 2p) transitions of hydrogen-like iron (at 6.97 keV in the rest frame). This indicates that a highly ionized outflow may be present moving at near relativistic velocities (∼ 0.25c). A possible hard X-ray excess is detected above 15 keV with HXD (at 99.8% confidence), which may arise from high column density gas (N H > 10 24 cm −2 ) partially covering the X-ray emission, or through strong Compton reflection. Here we propose that the iron K-shell absorption in PDS 456 is associated with a thick, possibly clumpy outflow, covering about 20% of 4π steradian solid angle. The outflow is likely launched from the inner accretion disk, within 15-100 gravitational radii of the black hole. The kinetic power of the outflow may be similar to the bolometric luminosity of PDS 456. Such a powerful wind could have a significant effect on the co-evolution of the host galaxy and its supermassive black hole, through feedback.

Evidence for ultra-fast outflows in radio-quiet AGNs

“…These features are commonly identified with Fe XXV and/or Fe XXVI K-shell resonant absorption from a highly ionized, log ξ 3−6 erg s −1 cm, zone of circumnuclear gas, with column densities as large as N H 10 22 −10 24 cm −2 . The blue-shifted velocities of the lines are also often quite large, reaching mildly relativistic values, up to ∼0.2−0.4c (e.g., Pounds et al 2003a;Dadina et al 2005;Markowitz et al 2006;Braito et al 2007;Cappi et al 2009;Reeves et al 2009). In some cases also short term variability has been reported (e.g., Dadina et al 2005;Braito et al 2007;Cappi et al 2009, and references therein).…”

“…However, even if in recent years there have been several papers in the literature reporting the detection of blueshifted Fe K absorption lines in radio-quiet AGNs (e.g., Chartas et al 2002Chartas et al , 2003Pounds et al 2003a;Dadina et al 2005;Markowitz et al 2006;Braito et al 2007;Cappi et al 2009;Reeves et al 2009), there is still some debate on their real statistical significance and therefore there are doubts on the effective existence of UFOs. In fact, the detections of these blue-shifted absorption features in the spectra of different sources have been published by several authors using distinct instruments, analysis and statistical techniques.…”

Quasar feedback revealed by giant molecular outflows

“…Crenshaw et al 2003;Turnshek 1984;Pounds et al 2003), which accounts only for a minor fraction of the gas mass in the host galaxy, and are generally confined in the nuclear region on pc scales or in the photoionization cones. High-velocity energetic winds, whose kinetic energy is comparable to the bolometric energy of the quasar, are observed in the galactic nuclei (Reeves et al 2009;Moe et al 2009;Dunn et al 2010;Bautista et al 2010). A&A 518, L155 (2010) Morganti et al (2010) reported evidence for AGN-induced massive and fast outflows of neutral H in powerful radio galaxies, possibly driven by the AGN jets.…”

Evidence for a radiatively driven disc-wind in PDS 456?

“…The importance of these winds is supported by their frequent detection, as they are observed in the X-ray spectra of approximately 40% of AGN (Tombesi et al 2010;Gofford et al 2013), suggesting that their geometry is characterized by a wide opening angle as recently confirmed in the luminous quasar PDS 456 by Nardini et al (2015, hereafter N15). These outflows are characterized by considerably high column densities (NH ∼ 10 23 cm −2 ) and a mean velocity vw ∼ 0.1c (Tombesi et al 2010) up to mildly relativistic values of ∼ 0.2-0.4c in the most extreme cases (e.g., Chartas et al 2002;Reeves et al 2009;Tombesi et al 2015). The high velocities and high columns can result in a large amount of mechanical power, possibly exceeding the 0.5-5% of the bolometric luminosity (L hereafter), as required for significant AGN feedback (King 2003;Di Matteo, Springel & Hernquist 2005;Hopkins & Elvis 2010).…”

“…Since the first XMM-Newton (40 ks) observation carried out in 2001 (Reeves, O'Brien & Ward 2003), PDS 456 has showed the presence of a persistent deep absorption trough in the Fe K band above 7 keV. This can be associated to highly ionized Fe K-shell absorption with a corresponding outflow velocity of vw ∼ 0.25-0.3c (Reeves et al 2009(Reeves et al , 2014Gofford et al 2014;N15;Matzeu et al 2016, hereafter M16), which originates from an accretion disk wind. In this letter we present a new correlation between the discwind velocity derived from the Fe K profile and the intrinsic X-ray luminosity, which we interpret in the framework of a radiatively driven wind.…”