Volume 619, November 2018
|Number of page(s)||10|
|Published online||06 November 2018|
The dense molecular gas in the z ∼ 6 QSO SDSS J231038.88+185519.7 resolved by ALMA⋆
INAF – Osservatorio Astronomico di Trieste, Via G. Tiepolo 11, Trieste, Italy
2 Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge, CB3 0HE UK
3 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge, CB3 0HA UK
4 Dipartimento di Fisica, Universitá di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Roma, Italy
5 INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monte Porzio Catone, Italy
6 Instituto de Astronomia, Geofísica e Ciências Atmosféricas – Universidade de São Paulo (IAG-USP), Rua do Matão 1226, São Paulo, 05508-090 Brasil
7 Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
8 Dipartimento di Fisica e Astronomia, Universitá di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino (Firenze), Italy
9 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 2, 50125 Firenze, Italy
10 Centro Fermi, Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Piazza del Viminale 1, 00184 Roma, Italy
Accepted: 7 August 2018
We present ALMA observations of the CO(6-5) and [CII] emission lines and the sub-millimeter continuum of the z ∼ 6 quasi-stellar object (QSO) SDSS J231038.88+185519.7. Compared to previous studies, we have analyzed a synthetic beam that is ten times smaller in angular size, we have achieved ten times better sensitivity in the CO(6-5) line, and two and half times better sensitivity in the [CII] line, enabling us to resolve the molecular gas emission. We obtain a size of the dense molecular gas of 2.9 ± 0.5 kpc, and of 1.4 ± 0.2 kpc for the 91.5 GHz dust continuum. By assuming that CO(6-5) is thermalized, and by adopting a CO to H2 conversion factor αCO = 0.8 M⊙K−1 (km s)−1 pc2, we infer a molecular gas mass of M(H2) = (3.2±0.2)×1010 M⊙. Assuming that the observed CO velocity gradient is due to an inclined rotating disk, we derive a dynamical mass of Mdynsin2(i)=(2.4 ± 0.5)×1010 M⊙, which is a factor of approximately two smaller than the previously reported estimate based on [CII]. Regarding the central black hole, we provide a new estimate of the black hole mass based on the C IV emission line detected in the VLT/X-shooter spectrum: MBH = (1.8 ± 0.5)×109 M⊙. We find a molecular gas fraction of μ = M(H2)/M* ∼ 4.4, where M∗ ≈ Mdyn − M(H2) − M(BH). We derive a ratio νrot/σ ≈ 1 − 2 suggesting high gas turbulence, outflows/inflows and/or complex kinematics due to a merger event. We estimate a global Toomre parameter Q ∼ 0.2 − 0.5, indicating likely cloud fragmentation. We compare, at the same angular resolution, the CO(6-5) and [CII] distributions, finding that dense molecular gas is more centrally concentrated with respect to [CII]. We find that the current BH growth rate is similar to that of its host galaxy.
Key words: quasars: individual: SDSS J231038.88+185519.7 / quasars: general / quasars: emission lines / galaxies: high-redshift / quasars: supermassive black holes / galaxies: ISM
The reduced data cubes and images are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/619/A39
© ESO 2018
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.