Does the lockstep growth between black holes and bulges create their mass relation?

分类： 天文学 >> 星系和宇宙学 提交时间： 2023-02-21

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

摘要： Recent studies have revealed a strong relation between 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 related to the BH-bulge mass correlation observed in the local universe. To understand further BH-bulge coevolution, we present ALMA CO(2-1) or CO(3-2) observations of 7 star-forming bulge-dominated galaxies at z=0.5-2.5. Using the ALMA data, we detect significant (>3) CO emission from 4 objects. For our sample of 7 galaxies, we measure (or constrain with upper limits) their CO line fluxes and estimate molecular gas masses (M_{gas}). We also estimate their stellar masses (M_{star}) and SFRs by modelling their spectral energy distributions (SEDs). Using these physical properties, we derive the gas-depletion timescales (t_{dep} = M_{gas}/SFR) and compare them with the bulge/BH growth timescales (t_{grow} = M_{star}/SFR \sim M_{BH}/BHAR). Our sample generally has t_{dep} shorter than t_{grow} 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 the BH-bulge lockstep growth is mainly responsible for maintaining their 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.

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