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

Recent studies have revealed a strong relation between sample-averaged black-hole (BH) accretion rate (BHAR) and star formation (SFR) among bulge-dominated galaxies, i.e., "lockstep" BH-bulge growth, in the distant universe. This might be closely related to mass correlation observed local To understand further coevolution, we present ALMA CO(2-1) or CO(3-2) observations of 7 star-forming galaxies at z=0.5-2.5. Using data, detect significant ($>3\sigma$) CO emission from 4 objects. For our sample measure (or constrain with upper limits) their line fluxes estimate molecular gas masses ($M_{gas}$). We also stellar ($M_{star}$) SFRs by modelling spectral energy distributions (SEDs). these physical properties, derive gas-depletion timescales ($t_{dep} = M_{gas}/SFR$) compare them bulge/BH growth ($t_{grow} M_{star}/SFR \sim M_{BH}/BHAR$). Our generally has $t_{dep}$ shorter than $t_{grow}$ median factor $\gtrsim 4$, indicating that cold will depleted before takes place. result suggests lockstep is mainly responsible for maintaining relation, not creating it. note small limited $z<2.5$; JWST able probe higher redshifts near future.