Two channels of supermassive black hole growth as seen on the galaxies mass-size plane

Davor Krajnović*, Michele Cappellari, Richard M. McDermid

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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We investigate the variation of black hole masses (MBH) as a function of their host galaxy stellar mass (M*) and half-light radius (Re). We confirm that the scatter in MBH within this plane is essentially the same as that in the MBH-σ relation, as expected from the negligible scatter reported in the virial mass estimator σ v 2 = G × M*/(5 × Re). All variation in MBH happens along lines of constant σv on the (M*, Re) plane, or M* ∝ Re for M* ≲ 2 × 1011 M. This trend is qualitatively the same as those previously reported for galaxy properties related to stellar populations, like age, metallicity, alpha enhancement, mass-to-light ratio and gas content. We find evidence for a change in the MBH variation above the critical mass of Mcrit ≈ 2 × 1011 M. This behaviour can be explained assuming that MBH in galaxies less massive than Mcrit can be predicted by the MBH-σ relation, while MBH in more massive galaxies follows a modified relation, which is also dependent on M* once M* > Mcrit. This is consistent with the scenario where the majority of galaxies grow through star formation, while the most massive galaxies undergo a sequence of dissipation-less mergers. In both channels, black holes and galaxies grow synchronously, giving rise to the black hole-host galaxy scaling relations, but there is no underlying single relation that is universal across the full range of galaxy masses.

Original languageEnglish
Pages (from-to)5237-5247
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - Feb 2018

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 473, Issue 4, 1 February 2018, Pages 5237–5247, Copyright 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


  • galaxies: evolution
  • galaxies: fundamental parameters
  • quasars: supermassive black holes


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