X-shooter reveals powerful outflows in z ∼ 1.5 X-ray selected obscured quasi-stellar objects

Abstract

We present X-shooter at the Vewry Large Telescope observations of a sample of\n10 luminous, X-ray obscured QSOs at z$\\sim1.5$ from the XMM-COSMOS survey,\nexpected to be caught in the transitioning phase from starburst to active\ngalactic nucleus (AGN)-dominated systems. The main selection criterion is X-ray\ndetection at bright fluxes (L$>=10^{44}$ erg s$^{-1}$) coupled to red\noptical-to-NIR-to-MIR colors. Thanks to its large wavelength coverage,\nX-shooter allowed us to determine accurate redshifts from the presence of\nmultiple emission lines for five out of six targets for which we had only a\nphotometric redshift estimate, with an 80 percent success rate, significantly\nlarger than what is observed in similar programs of spectroscopic follow-up of\nred QSOs. We report the detection of broad and shifted components in the\n[OIII]$\\lambda\\lambda$5007,4959 complexes for six out of eight sources with\nthese lines observable in regions free from strong atmospheric absorptions. The\nfull width half-maximum (FWHM) associated with the broad components are in the\nrange FWHM$\\sim900-1600$ km s$^{-1}$, larger than the average value observed in\nSDSS Type 2 AGN samples at similar observed [OIII] luminosity, but comparable\nto those observed for QSO/ultraluminous infrared galaxies systems for which the\npresence of kpc scale outflows have been revealed through integral field unit\nspectroscopy. Although the total outflow energetics (inferred under reasonable\nassumptions) may be consistent with winds accelerated by stellar processes, we\nfavour an AGN origin for the outflows given the high outflow velocities oberved\n(v$>1000$ km s$^{-1}$) and the presence of strong winds also in objects\nundetected in the far infrared.\n