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The black hole and host galaxy growth in an isolated $z6$ QSO observed with ALMA

, , , , , , , , , , , , , and . (2022)cite arxiv:2207.03314Comment: 15 pages, 10 figures, 4 tables. Accepted in A&A.

Abstract

The outstanding mass growth of supermassive black holes (SMBHs) at the Reionisation Epoch and how it is related to the concurrent growth of their host galaxies, poses challenges to theoretical models aimed at explaining how these systems formed in short timescales (<1 Gyr). To trace the average evolutionary paths of quasi-stellar objects (QSOs) and their host galaxies in the BH mass-host mass ($M_dyn$) plane, we compare the star formation rate (SFR), derived from the accurate estimate of the dust temperature and the dust mass ($T_dust, M_dust$), with the BH accretion rate. To this aim, we analysed a deep, $900$ pc resolution ALMA observation of the sub-mm continuum, CII and H$_2$O of the $z6$ QSO J2310+1855, enabling a detailed study of dust properties and cold gas kinematics. We performed an accurate SED analysis obtaining a dust temperature of $T_dust = 71$ K and a dust mass of $M_dust= 4.4 10^8\ M_ødot$. The implied AGN-corrected SFR is $1240 \ M_ødotyr^-1$, a factor of 2 smaller than previously reported for this QSO. We derived the best estimate of the dynamical mass $M_dyn = 5.210^10\ M_ødot$ within $r = 1.7$ kpc, based on a dynamical model of the system. We found that $SFR/M_dyn>\dot M_BH/M_BH$, suggesting that AGN feedback might be efficiently acting to slow down the SMBH accretion, while the stellar mass assembly is still vigorously taking place in the host galaxy. In addition, we were also able to detect high-velocity emission on the red and blue sides of the CII emission line, that traces a gaseous outflow, and for the first time, we mapped a spatially-resolved water vapour disk through the H$_2$O v=0 $3_(2,2)-3_(1,3)$ emission line detected at $\nu_obs = 274.074$ GHz, whose kinematic properties and size are broadly consistent with those of the CII disk.

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The black hole and host galaxy growth in an isolated $z\sim 6$ QSO observed with ALMA

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