The WISSH quasar Project: Giant star nurseries in hyper-luminous quasars
F.Duras, A.Bongiorno,E.Piconcelli,S.Bianchi,C.Pappalardo,E.Piconcelli,F.La Franca, M.Bischetti, C.Feruglio,R.Schneider,R.Valiante,G.Vietri,C.Vignali,L.Zappacosta,and F.Fiore
Studying the coupling between the energy output produced by the central quasar and the host galaxy is fundamental to fully understand galaxy evolution. Quasar feedback is indeed supposed to dramatically affect the galaxy properties by depositing large amounts of energy and momentum into the ISM. In order to gain further insights on this process, we study the Spectral Energy Distributions (SEDs) of sources at the brightest end of the quasar luminosity function, for which the feedback mechanism is supposed to be at its maximum, given their high efficiency in driving powerful outflows. We model the rest-frame UV-to-FIR SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6 based on SDSS, 2MASS, WISE and Herschel/SPIRE data. Through an accurate SED-fitting procedure, we disentangle the different emission components deriving physical parameters of both the nuclear component (i.e. bolometric and monochromatic luminosities) and the host galaxy (i.e. Star Formation Rate SFR, mass and temperature of the cold dust). We also use a radiative transfer code to account for the contribution of the quasar-related emission to the FIR fluxes. Most SEDs are well described by a standard combination of accretion disk+torus and cold dust emission. However, about 30% of them require an additional emission component in the NIR, with temperatures peaking at ~ 750 K, which indicates the presence of a hotter dust component in these powerful quasars. We measure extreme values of both AGN bolometric luminosity (LBOL>10^47 erg/s) and SFR (up to 2000 solar masses per year) based on the host galaxy, quasar-corrected, IR luminosity. A new relation between quasar and star-formation luminosity is derived by combining several Herschel-detected quasar samples from z ~ 0 to ~ 4. WISSH quasars have masses (~ 10^8 solar masses) and temperatures (~ 50 K) of cold dust in agreement with those found for other high-z IR luminous quasars.
Thanks to their extreme nuclear and star-formation luminosities, the WISSH quasars are ideal targets to shed light on both the feedback mechanism and its effect on the evolution of their host galaxies, and the merger-induced scenario which is commonly assumed to explain these exceptional luminosities. Future observations will be crucial to measure the molecular gas content in these systems, probe the impact between quasar-driven outflows and on-going star-formation, and reveal the presence of merger signatures in their host galaxies.
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