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

TL;DR

This paper reports the detection of a highly ionized, fast outflow in the quasar PDS 456, suggesting a powerful wind launched from near the black hole that could influence galaxy evolution.

Contribution

It presents the first evidence of a Compton-thick, high-velocity outflow in PDS 456, linking X-ray absorption features to a massive, clumpy wind impacting galaxy feedback.

Findings

Detection of blue-shifted iron absorption at 9 keV indicating relativistic outflow (~0.25c).

Presence of a possible hard X-ray excess suggesting high column density gas or reflection.

Outflow covering about 20% of the sky, launched within 15-100 gravitational radii of the black hole.

Abstract

PDS 456 is a nearby (z=0.184), luminous (L_bol ~10^47 erg/s) 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 (Nh>10^24cm^-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 $4\pi$ 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.