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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Yang(杨光), G, Brandt, W N, Alexander, D M, Chen(陳建廷), C-T J, Ni(倪清泠), Q, Vito, F & Zhu(朱飞凡), F-F (2019). Evident black hole-bulge coevolution in the distant universe. Monthly Notices of the Royal Astronomical Society 485(3): 3721-3737.

Author(s) from Durham

Abstract

Observations in the local universe show a tight correlation between the masses of supermassive black holes (SMBHs; MBH) and host-galaxy bulges (Mbulge), suggesting a strong connection between SMBH and bulge growth. However, direct evidence for such a connection in the distant universe remains elusive. We have studied sample-averaged SMBH accretion rate (⁠BHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯
BHAR¯
⁠) for bulge-dominated galaxies at z = 0.5–3. While previous observations found BHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯
BHAR¯
is strongly related to host-galaxy stellar mass (M⋆) for the overall galaxy population, our analyses show that, for the bulge-dominated population, BHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯
BHAR¯
is mainly related to SFR rather than M⋆. This BHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯
BHAR¯
–SFR relation is highly significant, e.g. 9.0σ (Pearson statistic) at z = 0.5–1.5. Such a BHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯
BHAR¯
–SFR connection does not exist among our comparison sample of galaxies that are not bulge dominated, for which M⋆ appears to be the main determinant of SMBH accretion. This difference between the bulge-dominated and comparison samples indicates that SMBHs only coevolve with bulges rather than the entire galaxies, explaining the tightness of the local MBH−Mbulge correlation. Our best-fitting BHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯
BHAR¯
–SFR relation for the bulge-dominated sample is logBHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ =logSFR−(2.48±0.05)
log⁡BHAR¯=log⁡SFR−(2.48±0.05)
(solar units). The best-fitting BHAR ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯ /SFR
BHAR¯/SFR
ratio (10−2.48) for bulge-dominated galaxies is similar to the observed MBH/Mbulge values in the local universe. Our results reveal that SMBH and bulge growth are in lockstep, and thus non-causal scenarios of merger averaging are unlikely the origin of the MBH−Mbulge correlation. This lockstep growth also predicts that the MBH−Mbulge relation should not have strong redshift dependence.