Starburst or AGN Dominance in Submillimetre-Luminous Candidate AGN?

摘要

It is widely believed that ultraluminous infrared (IR) galaxies and activegalactic nuclei (AGN) activity are triggered by galaxy interactions andmerging, with the peak of activity occurring at z~2, where submillimetregalaxies are thousands of times more numerous than local ULIRGs. In thisevolutionary picture, submillimetre galaxies (SMGs) would host an AGN, whichwould eventually grow a black hole (BH) strong enough to blow off all of thegas and dust leaving an optically luminous QSO. To probe this evolutionarysequence we have focussed on the 'missing link' sources, which demonstrate bothstrong starburst (SB) and AGN signatures, in order to determine if the SB isthe main power source even in SMGs when we have evidence that an AGN is presentfrom their IRAC colours. The best way to determine if a dominant AGN is presentis to look for their signatures in the mid-infrared with the Spitzer IRS, sinceoften even deep X-ray observations miss identifying the presence of AGN inheavily dust-obscured SMGs. We present the results of our audit of the energybalance between star-formation and AGN within this special sub-population ofSMGs -- where the BH has grown appreciably to begin heating the dust emission.