Evidence of intense hot(~340K) dust in 3CR radio galaxies The most dissipative source of cooling in AGNs

Abstract

The spectra of the powerful 3CR radio galaxies present a typical distribution in the far-infrared. From the observed radio to X-ray spectral energy distribution (SED) templates, we propose to subtract the typical energy distributions of, respectively, the elliptical galaxy host and the synchrotron radiation. The resulting SED reveals that the main dust emission is well fitted by the sum of two blackbody components at the respective temperatures 340K+-50K and 40K+-16K. When the AGN is active, the energy rate released by hot dust is much more dissipative than cold dust and stellar emission, even when the elliptical galaxy emission is maximum at age of ~ 90 Myr. Hot dust appears as a huge cooling source which implies an extremely short time-scale t(cool). In balance, with the short gravitational time-scale t(grav) of massive galaxies, the dissipative self-gravitational models (Rees & Ostriker, 1977) are favoured for radio sources. They justify the existence of massive radio galaxies at z=4 (Rocca-Volmerange et al., 2004). The synchrotron emission is emitting up to the X-ray wavelength range, so that strong "EXOs" sources could be assimilated to 3CR radio sources. This analysis applied to ISO and SPITZER data on a larger sample will statistically confirm these results.