The WISSH quasars project. I. Powerful ionised outflows in hyper-luminous quasars

Abstract

Models and observations suggest that both the power and effects of AGN feedback should be maximised in hyper-luminous (L_Bol > 10^47 erg/s) quasars, I.e. objects at the brightest end of the AGN luminosity function. In this paper, we present the first results of a multiwavelength observing programme, focusing on a sample of WISE/SDSS selected hyper-luminous (WISSH) broad-line quasars at z ≈ 1.5-5. The WISSH quasars project has been designed to reveal the most energetic AGN-driven outflows, estimate their occurrence at the peak of quasar activity, and extend the study of correlations between outflows and nuclear properties up to poorly investigated, extreme AGN luminosities, I.e. L_Bol~10^47 - 10^48 erg/s. We present near-infrared, long-slit LBT/LUCI1 spectroscopy of five WISSH quasars at z ≈ 2.3 - 3.5, showing prominent [OIII] emission lines with broad (FWHM 1200-2200 km/s) and skewed profiles. The luminosities of these broad [OIII] wings are the highest measured so far, with L_[OIII]broad ≳ 5 × 10^44 erg/s, and reveal the presence of powerful ionised outflows with associated mass outflow rates Ṁ ≳ 1700 M☉/yr and kinetic powers Ė_kin≳ 10^45 erg/s. Although these estimates are affected by large uncertainties because of the use of [OIII] as a tracer of ionised outflows and the very basic outflow model adopted here, these results suggest that in our hyper-luminous targets the AGN is highly efficient at pushing large amounts of ionised gas outwards. Furthermore, the mechanical outflow luminosities measured for WISSH quasars correspond to higher percentages ( 1-3%) of L_Bol than those derived for AGN with lower L_Bol. Our targets host very massive (M_BH ≳ 2 × 10^9 M☉) black holes that are still accreting at a high rate (I.e. a factor of 0.4-3 of the Eddington limit). These findings clearly demonstrate that WISSH quasars offer the opportunity to probe the extreme end of both luminosity and supermassive black holes (SMBH) mass functions and revealing powerful ionised outflows that are able to affect the evolution of their host galaxies.