The ALMA view of the high-redshift relation between supermassive black holes and their host galaxies

Abstract

Context. The existence of tight correlations between supermassive black holes (BHs) and their host galaxies properties in the local Universe suggests a closely linked evolution. Investigating these relations up to the high redshifts (z 6) is crucial to understand the interplay between star-formation and BH growth across the cosmic time and to set constraints on galaxy formation and evolution models. In this work we focus on the relation between BH mass (M BH ) and the dynamical mass (M dyn ) of the host galaxy. Aims. Previous works suggest an evolution of the M BH − M dyn relation with redshift indicating that BH growth precedes the galaxy mass assembly during their co-evolution at z > 3. However, dynamical galaxy masses at high redshift are often estimated through the virial theorem thus introducing significant uncertainties. This work aims at studying the M BH − M dyn relation of a sample of 2 < z < 7 quasars by constraining their galaxy masses through a full kinematical modelling of the cold gas kinematics thus avoiding all possible biases and effects introduced by the rough estimates usually adopted so far. Methods. For this purpose we retrieved public observations of 72 quasar host galaxies observed in [CII] 158µm or CO transitions with the Atacama Large Millimeter Array (ALMA). We then selected those quasars whose line emission is spatially resolved and performed a kinematic analysis on ALMA observations. We estimated the dynamical mass of the systems by modelling the gas kinematics with a rotating disc taking into account geometrical and instrumental effects. Our dynamical mass estimates, combined with M BH obtained from literature and our own new CIVλ1550 observations have allowed us to investigate the M BH /M dyn in the early Universe. Results. Overall we obtained a sample of 10 quasars at z ∼ 2 − 7 in which line emission is detected with high SNR ( 5 − 10) and the gas kinematics is spatially resolved and dominated by ordered rotation. The estimated dynamical masses place 6 out of 10 quasars above the local relation yielding to a M BH /M dyn ratios ∼ 10× higher than those estimated in low-z galaxies. On the other hand we found that 4 quasars at z ∼ 4 − 6 have dynamical-to-BH mass ratios consistent with what is observed in early type galaxies in the local Universe.

The ALPINE-ALMA [C ii] Survey: kinematic diversity and rotation in massive star-forming galaxies at z ~ 4.4–5.9

“…A vast sample of rotating galaxies has been well studied at < 4 (e.g., Epinat et al 2008;Förster Schreiber et al 2009;Gnerucci et al 2011), revealing dynamical masses and empirical scaling relations. While a number of clumpy or merging galaxies have been detected at > 4 (e.g., Carniani et al 2018;Pavesi et al 2018;Díaz-Santos et al 2018), and a handful of rotating starburst or quasar host galaxies at ∼ 4 − 6 have been well-modelled (e.g., Jones et al 2017;Pensabene et al 2020;Tadaki et al 2020;Fraternali et al 2021;Lelli et al 2021), only two unlensed rotating main sequence galaxies have been observed at ∼ 4 − 6: HZ9 (Capak et al 2015) and J0817 (Neeleman et al 2017(Neeleman et al , 2020 5 . In this section, we add six new ∼ 4 − 6 rotators from the ALPINE sample to this class: CG32, DC396844, DC494057, DC552206, DC881725, and VC.7875.…”

Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). XIII. Large-scale Feedback and Star Formation in a Low-luminosity Quasar at z = 7.07 on the Local Black Hole to Host Mass Relation

“…While the MS is not well constrained at z  5, we compare the SFR of J1243+0100 and other HSC quasars (Izumi et al 2018(Izumi et al , 2019 and optically luminous quasars at z  6 (Decarli et al 2018) with the MS at z ∼ 6 (Salmon et al 2015). Here we assume M dyn = M å , as is frequently done in z > 6 quasar studies (e.g., Wang et al 2013;Willott et al 2015;Venemans et al 2016;Pensabene et al 2020). The dynamical masses of course have large uncertainties and represent an upper limit to the stellar mass.…”

“…High-resolution interferometric observations predominantly performed by the Atacama Large Millimeter/submillimeter Array (ALMA) have allowed studies of cold gas dynamics in quasar host galaxies (Wang et al 2013;Venemans et al 2016;Decarli et al 2018;Pensabene et al 2020). These studies revealed that z  6 optically luminous (M 1450  −26 mag) quasars have, on average, ∼10× more massive SMBHs than the local coevolution relations for a given velocity dispersion and/or dynamical mass of the host, suggesting that SMBHs were formed significantly earlier than their host galaxies.…”

A massive stellar bulge in a regularly rotating galaxy 1.2 billion years after the Big Bang

“…The 158-mm emission line of singly ionized carbon, [C II], is a major coolant of the interstellar medium of galaxies and traces a combination of atomic and molecular hydrogen phases. The [C II] line has been observed up to z ≃ 7:5 (5), and several rotating disks have been identified at z > 3 (6)(7)(8). Most existing observations only marginally resolve the [C II] distribution and kinematics, and thus cannot distinguish between rotating disks, galaxy mergers, or gas inflows and outflows.…”

“…The two additional components (bulge and DM halo) are modeled with analytic functions (9). The bulge component implicitly includes the contribution of the central supermassive black hole, which contributes <10% of the central mass in high-z galaxies (8).…”