http://arxiv.org/abs/1402.2279
We investigate the origin of the spectral energy distribution of SDSS J1148+5251, using it as a prototype for the more general class of high-luminosity high-redshift quasars. To this aim, we run the radiative transfer code TRADING using a simple model for the central source,including all the radiation that can travel beyond the dusty torus, and following the transfer of radiation from the central source and from stellar sources through the dusty environment of the host galaxy. Comparing the model predictions with the observational data, including the recently published Herschel detections, we find that the spectral energy distribution of SDSSJ1148+5251 points to an evolutionary scenario where ~ 60% of the observed FIR luminosity is due to dust heating by the central AGN; heating due to stellar radiation provides a necessary but not dominant component to the emission at 20 – 60 micron. We also find that the required stellar luminosity can only be achieved if the host galaxy is able to sustain a star formation rate of ~ 1000 Msun/yr at 6.4 < z < 8 through efficient merger-driven bursts; even if all the stars were formed in this last burst of ~200 Myr of star formation, this inevitably leads to a final stellar mass that exceeds the limits imposed by dynamical mass measurements for SDSSJ1148+5251, Mdyn ~ 5.5 x 10^{10} Msun; moreover, a larger stellar mass in the range [2.3 – 4.6] x 10^{11} Msun is also required to reproduce the observed dust mass if the stars form with a standard Salpeter-like initial mass function. We discuss the implications of these results for the more general population of high-z quasars, which also show large dust masses and relatively under-massive stellar bulges.
R. Schneider, S. Bianchi, R. Valiante, et. al.
Wed, 12 Feb 14
29/67
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