In:
Astronomy & Astrophysics, EDP Sciences, Vol. 619 ( 2018-11), p. A39-
Abstract:
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 H 2 conversion factor α CO = 0.8 M ⊙ K −1 (km s) −1 pc 2 , we infer a molecular gas mass of M (H 2 ) = (3.2±0.2)×10 10 M ⊙ . Assuming that the observed CO velocity gradient is due to an inclined rotating disk, we derive a dynamical mass of M dyn sin 2 ( i )=(2.4 ± 0.5)×10 10 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: M BH = (1.8 ± 0.5)×10 9 M ⊙ . We find a molecular gas fraction of μ = M (H 2 )/ M * ∼ 4.4, where M ∗ ≈ M dyn − M (H 2 ) − M (BH). We derive a ratio ν rot / 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.
Type of Medium:
Online Resource
ISSN:
0004-6361
,
1432-0746
DOI:
10.1051/0004-6361/201833174
Language:
English
Publisher:
EDP Sciences
Publication Date:
2018
detail.hit.zdb_id:
1458466-9
SSG:
16,12
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