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Testing the completeness of the SDSS colour selection for ultramassive, slowly spinning black holes.

Bertemes, C. and Trakhtenbrot, B. and Schawinski, K. and Done, C. and Elvis, M. (2016) 'Testing the completeness of the SDSS colour selection for ultramassive, slowly spinning black holes.', Monthly notices of the Royal Astronomical Society., 463 (4). pp. 4041-4051.


We investigate the sensitivity of the colour-based quasar selection algorithm of the Sloan Digital Sky Survey (SDSS) to several key physical parameters of supermassive black holes (SMBHs), focusing on BH spin (a*) at the high BH-mass regime (MBH ≥ 109 M⊙). We use a large grid of model spectral energy distribution (SED), assuming geometrically thin, optically thick accretion discs, and spanning a wide range of five physical parameters: BH mass MBH, BH spin a*, Eddington ratio L/LEdd, redshift z, and inclination angle inc. Based on the expected fluxes in the SDSS imaging ugriz bands, we find that ∼99.8 per cent of our models with MBH ≤ 109.5 M⊙ are selected as quasar candidates and thus would have been targeted for spectroscopic follow-up. However, in the extremely high-mass regime, ≥1010 M⊙, we identify a bias against slowly/retrograde spinning SMBHs. The fraction of SEDs that would have been selected as quasar candidates drops below ∼50 per cent for a* < 0 across 0.5 < z < 2. For particularly massive BHs, with MBH ≃ 3 × 1010 M⊙, this rate drops below ∼20 per cent, and can be yet lower for specific redshifts. We further find that the chances of identifying any hypothetical sources with MBH = 1011 M⊙ by colour selection would be extremely low at the level of ∼3 per cent. Our findings, along with several recent theoretical arguments and empirical findings, demonstrate that the current understanding of the SMBH population at the high MBH, and particularly the low- or retrograde-spinning regime, is highly incomplete.

Item Type:Article
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2016. The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
Date accepted:31 August 2016
Date deposited:26 July 2017
Date of first online publication:02 September 2016
Date first made open access:26 July 2017

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