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Paper: Testing the Evolutionary Link between SMGs and QSOs: Are Submm-Detected QSOs at z ~ 2 ‘Transition Objects’ between these Two Phases?
Volume: 408, The Starburst−AGN Connection
Page: 399
Authors: Coppin, K.
Abstract: Local spheroids show a relation between their masses and those of the super-massive black holes (SMBH) at their centres, indicating a link between the major phases of spheroid growth and nuclear accretion. These phases may correspond to high-z submillimetre galaxies (SMGs) and QSOs, separate populations with surprisingly similar redshift distributions which may both be phases in the life cycle of individual galaxies, with SMGs evolving into QSOs. Here we briefly discuss our recent results in Coppin et al. (2008), where we have tested this connection by weighing the black holes and mapping CO in submmdetected QSOs, which may be transition objects between the two phases, and comparing their baryonic, dynamical and Hα-derived SMBH masses to those of SMGs at the same epoch. Our results split our sample of submm-detected QSOs into two categories (although a bigger sample would probably show a continuous trend): (1) CO is detected in 5/6 very optically luminous (MB ~ .28) submmdetected QSOs with BH masses MBH≅ 109−1010Mʘ, confirming the presence of large gas reservoirs of Mgas ≅ 3.4 × 1010Mʘ. Our BH masses and dynamical mass constraints on the host spheroids suggest, at face value, that these optically luminous QSOs at z = 2 lie about an order of magnitude above the local BH-spheroid relation, MBH/Msph. However, we find that their BH masses are ~ 30 times too large and their surface density is ~ 300 times too small to be related to typical SMGs in an evolutionary sequence. (2) We measure weaker CO emission in four fainter (MB ~ −25) submm-detected QSOs with properties, BH masses (MBH ≅ 5 × 108Mʘ), and surface densities similar to SMGs. These QSOs appear to lie near the local MBH/Msph relation, making them plausible ‘transition objects’ in the proposed evolutionary sequence linking QSOs to the formation of massive young galaxies and BHs at high-z.
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