We present an ALMA high-resolution (0.18 '' x 0.21 '') observation of the 840 mu m continuum and [CII] lambda 157.74 mu m line emission in the WISE-SDSS selected hyper-luminous (WISSH) quasi-stellar object (QSO) J1015+0020, at z similar to 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 mu m. The host galaxy of J1015+0020 shows a star formation rate (SFR) of about 100 M-circle dot yr(-1), while the total SFR of the QSO and its companion galaxies is a factor of similar to 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 M-BH similar to 6 x 10(9) M-circle dot. As we resolve the [CII] emission of the QSO, we can compute a dynamical mass of M-dyn similar to 4 x 10(10) M-circle dot. This translates into an extreme ratio M-dyn/M-BH similar to 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 10(11) M-circle dot at z similar to 4.4. These sources will likely merge and develop into a giant galaxy of similar to 1.3 x 10(12) M-circle dot. Under the assumption of constant M-acc or lambda(Edd) 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.
The WISSH quasars project: V. ALMA reveals the assembly of a giant galaxy around a z = 4.4 hyper-luminous QSO / Bischetti, M.; Piconcelli, E.; Feruglio, C.; Duras, F.; Bongiorno, A.; Carniani, S.; Marconi, A.; Pappalardo, C.; Schneider, R.; Travascio, A.; Valiante, R.; Vietri, G.; Zappacosta, L.; Fiore, F.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - ELETTRONICO. - 617:(2018), pp. A82-0. [10.1051/0004-6361/201833249]
The WISSH quasars project: V. ALMA reveals the assembly of a giant galaxy around a z = 4.4 hyper-luminous QSO
Carniani, S.;Marconi, A.;
2018
Abstract
We present an ALMA high-resolution (0.18 '' x 0.21 '') observation of the 840 mu m continuum and [CII] lambda 157.74 mu m line emission in the WISE-SDSS selected hyper-luminous (WISSH) quasi-stellar object (QSO) J1015+0020, at z similar to 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 mu m. The host galaxy of J1015+0020 shows a star formation rate (SFR) of about 100 M-circle dot yr(-1), while the total SFR of the QSO and its companion galaxies is a factor of similar to 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 M-BH similar to 6 x 10(9) M-circle dot. As we resolve the [CII] emission of the QSO, we can compute a dynamical mass of M-dyn similar to 4 x 10(10) M-circle dot. This translates into an extreme ratio M-dyn/M-BH similar to 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 10(11) M-circle dot at z similar to 4.4. These sources will likely merge and develop into a giant galaxy of similar to 1.3 x 10(12) M-circle dot. Under the assumption of constant M-acc or lambda(Edd) 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.
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