Secular evolution and A non-evolving black-hole-to-galaxy mass ratio in the last 7Gyr

Mauricio Cisternas, Knud Jahnke, Angela Bongiorno, Katherine J. Inskip, Chris D. Impey, Anton M. Koekemoer, Andrea Merloni, Mara Salvato, Jonathan R. Trump

Research output: Contribution to journalArticlepeer-review

87 Scopus citations


We present new constraints on the ratio of black hole (BH) mass to total galaxy stellar mass at 0.3 < z < 0.9 for a sample of 32 type-1 active galactic nuclei (AGNs) from the XMM-COSMOS survey covering the range M BH 107.2 - 8.7 M⊙. Virial M BH estimates based on Hβ are available from the COSMOS Magellan/IMACS survey. We use high-resolution Hubble Space Telescope (HST) imaging to decompose the light of each type-1 AGN and host galaxy, and employ a specially built mass-to-light ratio to estimate the stellar masses (M *). The M BH-M * ratio shows a zero offset with respect to the local relation for galactic bulge masses, and we also find no evolution in the mass ratio M BH/M *(1 + z)0.02 0.34 up to z 0.9. Interestingly, at the high-M BH end there is a positive offset from the z = 0 relation, which can be fully explained by a mass function bias with a cosmic scatter of σμ = 0.3, reaffirming that the intrinsic distribution is consistent with zero evolution. From our results we conclude that since z 0.9 no substantial addition of stellar mass is required: the decline in star formation rates and merger activity at z < 1 support this scenario. Nevertheless, given that a significant fraction of these galaxies show a disk component, their bulges are indeed undermassive. This is a direct indication that for the last 7Gyr the only essential mechanism required for these galaxies to obey the z = 0 relation is a redistribution of stellar mass to the bulge, likely driven by secular processes, i.e., internal instabilities and minor merging.

Original languageEnglish (US)
Article numberL11
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Nov 1 2011


  • galaxies: active
  • galaxies: evolution
  • galaxies: nuclei

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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