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

Bertemes, C.; Trakhtenbrot, B.; Schawinski, K.; Done, C.; Elvis, M.

Abstract

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.

Citation

Bertemes, C., Trakhtenbrot, B., Schawinski, K., Done, C., & 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), 4041-4051. https://doi.org/10.1093/mnras/stw2207

• Journal Article Type: Article
• Acceptance Date: Aug 31, 2016
• Online Publication Date: Sep 2, 2016
• Publication Date: Sep 2, 2016
• Deposit Date: Jul 24, 2017
• Publicly Available Date: Jul 26, 2017
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 463
• Issue: 4
• Pages: 4041-4051
• DOI: https://doi.org/10.1093/mnras/stw2207
• Public URL: https://durham-repository.worktribe.com/output/1351569
• Publisher URL: https:/doi.org/10.1093/mnras/stw2207