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Does the Lockstep Growth between Black Holes and Bulges Create Their Mass Relation?

Yang, Guang; Brandt, W. N.; Alexander, David M.; Boquien, Médéric; Ni, Qingling; Papovich, Casey; Spilker, Justin S.; Vito, Fabio; Walsh, Jonelle L.; Zhang, Chengpeng

Does the Lockstep Growth between Black Holes and Bulges Create Their Mass Relation? Thumbnail


Guang Yang

W. N. Brandt

Médéric Boquien

Qingling Ni

Casey Papovich

Justin S. Spilker

Fabio Vito

Jonelle L. Walsh

Chengpeng Zhang


Recent studies have revealed a strong relation between the sample-averaged black hole (BH) accretion rate (BHAR) and star formation rate (SFR) among bulge-dominated galaxies—i.e., "lockstep" BH–bulge growth—in the distant universe. This relation might be closely connected to the BH–bulge mass correlation observed in the local universe. To further understand BH–bulge coevolution, we present Atacama Large Millimeter/submillimeter Array (ALMA) CO(2–1) or CO(3–2) observations of seven star-forming bulge-dominated galaxies at z = 0.5–2.5. Using the ALMA data, we detect significant (>3σ) CO emission from four objects. For our sample of seven galaxies, we measure (or constrain with upper limits) their CO line fluxes and estimate their molecular gas masses (Mgas). We also estimate their stellar masses (Mstar) and SFRs, by modeling their spectral energy distributions. Using these physical properties, we derive the gas depletion timescales (τdep ≡ Mgas/SFR) and compare them with the bulge/BH growth timescales (τgrow ≡ Mstar/SFR ∼ MBH/BHAR). Our sample generally has τdep shorter than τgrow by a median factor of ≳4, indicating that the cold gas will be depleted before significant bulge/BH growth takes place. This result suggests that BH–bulge lockstep growth is mainly responsible for maintaining the mass relation, not creating it. We note that our sample is small and limited to z < 2.5; JWST and ALMA will be able to probe to higher redshifts in the near future.


Yang, G., Brandt, W. N., Alexander, D. M., Boquien, M., Ni, Q., Papovich, C., …Zhang, C. (2022). Does the Lockstep Growth between Black Holes and Bulges Create Their Mass Relation?. Astrophysical Journal, 940(2), Article 146.

Journal Article Type Article
Acceptance Date Oct 17, 2022
Online Publication Date Nov 30, 2022
Publication Date Dec 1, 2022
Deposit Date Oct 31, 2023
Publicly Available Date Oct 31, 2023
Journal The Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 940
Issue 2
Article Number 146
Keywords Space and Planetary Science; Astronomy and Astrophysics
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Copyright Statement
© 2022. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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