RAPID COEVAL BLACK HOLE AND HOST GALAXY GROWTH IN MRC 1138-262: THE HUNGRY SPIDER

Abstract

We present a detailed study of the infrared spectral energy distribution of\nthe high-redshift radio galaxy MRC 1138-26 at z = 2.156, also known as the\nSpiderweb Galaxy. By combining photometry from Spitzer, Herschel and LABOCA we\nfit the rest-frame 5-300 um emission using a two component, starburst and\nactive galactic nucleus (AGN), model. The total infrared (8 - 1000 um)\nluminosity of this galaxy is (1.97+/-0.28)x10^13 Lsun with (1.17+/-0.27) and\n(0.79+/-0.09)x10^13 Lsun due to the AGN and starburst components respectively.\nThe high derived AGN accretion rate of \\sim20% Eddington, and the measured star\nformation rate (SFR) of 1390pm150 Msun/yr, suggest that this massive system is\nin a special phase of rapid central black hole and host galaxy growth, likely\ncaused by a gas rich merger in a dense environment. The accretion rate is\nsufficient to power both the jets and the previously observed large outflow.\nThe high SFR and strong outflow suggest this galaxy could potentially exhaust\nits fuel for stellar growth in a few tens of Myr, although the likely merger of\nthe radio galaxy with nearby satellites suggest bursts of star formation may\nrecur again on time scales of several hundreds of Myr. The age of the radio\nlobes implies the jet started after the current burst of star formation, and\ntherefore we are possibly witnessing the transition from a merger-induced\nstarburst phase to a radio-loud AGN phase. We also note tentative evidence for\n[CII]158um emission. This paper marks the first results from the Herschel\nGalaxy Evolution Project (Project HeRGE), a systematic study of the\nevolutionary state of 71 high redshift, 1 < z < 5.2, radio galaxies.\n