On the presence of ultra-fast outflows in the WAX sample of Seyfert galaxies

The study of winds in active galactic nuclei (AGN) is of utmost importance as they may provide the long sought-after link between the central black hole and the host galaxy, establishing the AGN feedback. Recently, Laha et al. (2014) reported the X-ray analysis of a sample of 26 Seyferts observed with XMM-Newton, which are part of the so-called warm absorbers in X-rays (WAX) sample. They claim the non-detection of Fe K absorbers indicative of ultra-fast outflows (UFOs) in four observations previously analyzed by Tombesi et al. (2010). They mainly impute the Tombesi et al. detections to an improper modeling of the underlying continuum in the E=4-10 keV band. We therefore re-address here the robustness of these detections and we find that the main reason for the claimed non-detections is likely due to their use of single events only spectra, which reduces the total counts by 40%. Performing a re-analysis of the data in the whole E=0.3-10 keV energy band using their models and spectra including also double events, we find that the blue-shifted Fe K absorption lines are indeed detected at >99%. This work demonstrates the robustness of these detections in XMM-Newton even including complex model components such as reflection, relativistic lines and warm absorbers.Comment: 5 pages, 1 figure, accepted for publication in MNRA

Accretion and Outflow in Active Galaxies

I review accretion and outflow in active galactic nuclei. Accretion appears to occur in a series of very small--scale, chaotic events, whose gas flows have no correlation with the large--scale structure of the galaxy or with each other. The accreting gas has extremely low specific angular momentum and probably represents only a small fraction of the gas involved in a galaxy merger, which may be the underlying driver. Eddington accretion episodes in AGN must be common in order for the supermassive black holes to grow. I show that they produce winds with velocities $v \sim 0.1c$ and ionization parameters implying the presence of resonance lines of helium-- and hydrogenlike iron. The wind creates a strong cooling shock as it interacts with the interstellar medium of the host galaxy, and this cooling region may be observable in an inverse Compton continuum and lower--excitation emission lines associated with lower velocities. The shell of matter swept up by the shocked wind stalls unless the black hole mass has reached the value $M_{\sigma}$ implied by the $M - \sigma$ relation. Once this mass is reached, further black hole growth is prevented. If the shocked gas did not cool as asserted above, the resulting (`energy-driven') outflow would imply a far smaller SMBH mass than actually observed. Minor accretion events with small gas fractions can produce galaxy-wide outflows, including fossil outflows in galaxies where there is little current AGN activity.Comment: invited review, IAU Symposium 267, Co-Evolution of Central Black Holes and Galaxies, B.M. Peterson, R.S. Somerville, and T. Storchi-Bergmann, eds typos in eq (2.2) correcte