Volume 617, September 2018
|Number of page(s)||12|
|Published online||24 September 2018|
The WISSH quasars project
V. ALMA reveals the assembly of a giant galaxy around a z = 4.4 hyper-luminous QSO⋆
INAF - Osservatorio Astronomico di Roma, Via Frascati 33, 00078, Monte Porzio Catone (Roma), Italy
2 Università degli Studi di Roma “Tor Vergata”, Via Orazio Raimondo 18, Roma, 00173, Italy
3 INAF - Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34143, Trieste, Italy
4 Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, Roma, 00146, Italy
5 Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK
6 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK
7 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
8 Centro de Astronomia e Astrofísica da Universidade de Lisboa, OAL, Tapada da Ajuda, 1349-018 Lisboa, Portugal
9 Instituto de Astrofísica e Ciencias do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, 1349-018 Lisboa, Portugal
10 Università degli Studi di Roma “La Sapienza”, Piazzale Aldo Moro 5, 00185 Roma, Italy
11 Excellence Cluster Universe, Technische Universität München, Boltzmannstr., 85748 Garching, Germany
12 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
Accepted: 19 May 2018
We present an ALMA high-resolution (0.18″ × 0.21″) observation of the 840 μm continuum and [CII] λ157.74 μm line emission in the WISE-SDSS selected hyper-luminous (WISSH) quasi-stellar object (QSO) J1015+0020, at z ∼ 4.4. Our analysis reveals an exceptional overdensity of [CII]-emitting companions with a very small (<150 km s−1) velocity shift with respect to the QSO redshift. We report the discovery of the closest companion observed so far in submillimetre observations of high-z QSOs. It is only 2.2 kpc distant and merging with J1015+0020, while two other [CII] emitters are found at 8 and 17 kpc. Two strong continuum emitters are also detected at <3.5 arcsec from the QSO. They are likely associated with the same overdense structure of J1015+0020, as they exceed by a factor of 100 the number of expected sources, considering the log(N)–log(S) at 850 μm. The host galaxy of J1015+0020 shows a star formation rate (SFR) of about 100 M⊙ yr−1, while the total SFR of the QSO and its companion galaxies is a factor of ∼10 higher, indicating that substantial stellar mass assembly at early epochs may have taken place in the QSO satellites. For J1015+0020 we computed a black hole mass MBH ∼ 6 × 109 M⊙. As we resolve the [CII] emission of the QSO, we can compute a dynamical mass of Mdyn ∼ 4 × 1010 M⊙. This translates into an extreme ratio Mdyn/MBH ∼ 7, i.e. two orders of magnitude smaller than what is typically observed in local galaxies. The total stellar mass of the QSO host galaxy plus the [CII] emitters in the ALMA field of view already exceeds 1011 M⊙ at z ∼ 4.4. These sources will likely merge and develop into a giant galaxy of ∼1.3 × 1012 M⊙. Under the assumption of constant Ṁacc or λEdd equal to the observed values, we find that the growth timescale of the host galaxy of J1015+0020 is comparable or even shorter than that inferred for the SMBH.
Key words: quasars: individual: SDSSJ101549.00+002020.03 / galaxies: high-redshift / galaxies: star formation / quasars: supermassive black holes / quasars: emission lines
© ESO 2018
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