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Abstract
During the first half of the universe's age, a heyday of star-formation must have occurred because many massive galaxies are in place after that epoch in cosmic history. Our observations with the revolutionary Herschel Space Observatory reveal vigorous optically obscured star-formation in the ultra-massive hosts of many powerful high-redshift 3C quasars and radio galaxies. This symbiotic occurrence of star-formation and black hole driven activity is in marked contrast to recent results dealing with Herschel observations of X-ray selected active galaxies. Three archetypal radio galaxies, at redshifts 1.132,1.575, and 2.474 are presented here, with inferred star-formation rates of hundreds of solar masses per year. A series of spectacular coeval AGN/starburst events may have formed these ultra-massive galaxies and their massive central black holes during their relatively short lifetimes.
Highlights
The most massive galaxies known have stellar masses ∼5 × 1011 M, and the fact that they already exist at early epochs (Fontana et al 2006) implies that they must have formed rapidly (Daddi et al 2005), within just a few gigayears
Powerful high-redshift radio galaxies are ideal tracers of the extreme form of starburst–AGN symbiosis for several reasons. Their central black holes are being fed at a high rate, and are rapidly growing. Their large extended radio sources allow an unambiguous quantification of the accretion power, from the huge radio luminosities; their radio morphological properties permit an estimate of the duration of the AGN and possibly coeval star formation episodes
Quantification of the ongoing star formation is provided through far-infrared (FIR) observations, since dust absorbs the radiation of the young stars and reemits it at FIR wavelengths
Summary
The most massive galaxies known have stellar masses ∼5 × 1011 M , and the fact that they already exist at early epochs (Fontana et al 2006) implies that they must have formed rapidly (Daddi et al 2005), within just a few gigayears They are expected to host supermassive black holes (Haring & Rix 2004) which have periods of active accretion (De Breuck et al 2010). Powerful high-redshift radio galaxies are ideal tracers of the extreme form of starburst–AGN symbiosis for several reasons Their central black holes are being fed at a high rate, and are rapidly growing. The implications from the SED measurements, were uncertain: the amount of cool dust reradiating the emission of the newly formed stars was not well constrained, as data from the rest-frame far-infrared regions and the Rayleigh–Jeans tails were lacking
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