The Suzaku view of highly ionized outflows in AGN – I. Statistical detection and global absorber properties

Abstract

We present the results of a new spectroscopic study of Fe K-band absorption in active galactic nuclei (AGN). Using data obtained from the Suzaku public archive we have performed a statistically driven blind search for Fe xxv Heα and/or Fe xxvi Lyα absorption lines in a large sample of 51 Type 1.0-1.9 AGN. Through extensive Monte Carlo simulations we find that statistically significant absorption is detected at E ≳ 6.7 keV in 20/51 sources at the P_MC ≥ 95 per cent level, which corresponds to ∼40 per cent of the total sample. In all cases, individual absorption lines are detected independently and simultaneously amongst the two (or three) available X-ray imaging spectrometer detectors, which confirms the robustness of the line detections. The most frequently observed outflow phenomenology consists of two discrete absorption troughs corresponding to Fe xxv Heα and Fe xxvi Lyα at a common velocity shift. From xstar fitting the mean column density and ionization parameter for the Fe K absorption components are log (N_H/cm⁻²) ≈ 23 and log (ξ/erg cm s⁻¹) ≈ 4.5, respectively. Measured outflow velocities span a continuous range from −1 up to ∼100 000 km s⁻¹, with mean and median values of ∼0.1 c and ∼0.056 c, respectively. The results of this work are consistent with those recently obtained using XMM–Newton and independently provides strong evidence for the existence of very highly ionized circumnuclear material in a significant fraction of both radio-quiet and radio-loud AGN in the local universe.