The WISSH quasars project: IX. Cold gas content and environment of luminous QSOs at z ~2.4-4.7

Astronomy &Astrophysics manuscript no. main ©ESO 2020 October 14, 2020 The WISSH QSOs project IX. Cold gas content and environment of luminous QSOs at z∼2.4−4.7 M. Bischetti1,2?, C. Feruglio1, E. Piconcelli2, F. Duras3,2, M. Pérez-Torres4,5, R. Herrero6,7, G. Venturi8, S. Carniani9, G. Bruni10, I. Gavignaud11, V. Testa2, A. Bongiorno2, M. Brusa12,13, C. Circosta14, G. Cresci15, V. D’Odorico1,9, R. Maiolino16,17, A. Marconi18,15, M. Mingozzi19, C. Pappalardo20, M. Perna21,15, E. Traianou22, A. Travascio2, G. Vietri23, L. Zappacosta2, and F. Fiore1 (Affiliations can be found after the references) ABSTRACT Context. Sources at the brightest end of the quasi-stellar object (QSO) luminosity function, during the peak epoch in the history of star formation and black hole accretion (z∼2−4, often referred to as "Cosmic noon") are privileged sites to study the cycle of feeding & feedback processes in massive galaxies. Aims. We aim to perform the first systematic study of cold gas properties in the most luminous QSOs, by characterising their host-galaxies and environment. These targets exhibit indeed widespread evidence of outflows at nuclear and galactic scales. Methods. We analyse ALMA, NOEMA and JVLA observations of the far-infrared continuum, CO and [CII] emission lines in eight QSOs (bolometric luminosity LBol &3×1047 erg s−1) from the WISE-SDSS selected hyper-luminous (WISSH) QSOs sample at z∼2.4−4.7. Results. We report a 100% emission line detection rate and a 80% detection rate in continuum emission, and we find CO emission to be consistent with the steepest CO ladders observed so far. Sub-millimetre data reveal presence of (one or more) bright companion galaxies around ∼80% of WISSH QSOs, at projected distances of ∼6−130 kpc. We observe a variety of sizes for the molecular gas reservoirs (∼1.7−10 kpc), mostly associated with rotating disks with disturbed kinematics. WISSH QSOs typically show lower CO luminosity and higher star formation efficiency than infrared matched, z∼0−3 main-sequence galaxies, implying that, given the observed SFR ∼170−1100 Myr−1, molecular gas is converted into stars in .50 Myr. Most targets show extreme dynamical to black-hole mass ratios Mdyn/MBH ∼3−10, two orders of magnitude smaller than local relations. The molecular gas fraction in the host-galaxies of WISSH is lower by a factor of ∼10 −100 than in star forming galaxies with similar M∗. Conclusions. Our analysis reveals that hyper-luminous QSOs at Cosmic noon undergo an intense growth phase of both the central super-massive black hole and of the host-galaxy. These systems pinpoint the high-density sites where giant galaxies assemble, where we show that mergers play a major role in the build-up of the final host-galaxy mass. We suggest that the observed low molecular gas fraction and short depletion timescale are due to AGN feedback, whose presence is indicated by fast AGN-driven ionised outflows in all our targets. Key words. galaxies: high-redshift – galaxies: ISM – quasars: emission lines – quasars: supermassive black holes – submillimeter: galaxies – techniques: interferometric 1. Introduction Our understanding of the complex interplay between supermassive black hole (SMBH) activity, properties of the hostgalaxy interstellar medium (ISM) and of the circum-galactic environment is still incomplete. According to models of active galactic nucleus (AGN) and galaxy co-evolution, two main processes are expected to drive the evolution of massive galaxies (stellar mass M∗>1011 M): (i) galaxy interactions and mergers, and (ii) radiative and mechanical feedback related to AGN activity (e.g. Croton et al. 2006; Sijacki et al. 2007; MartínNavarro et al. 2018; Choi et al. 2018), during the growth of heavy SMBHs (MBH/M∗∼10−3, where MBH is the black hole mass, e.g. Häring & Rix 2004). These two processes are tightly correlated, as galaxy interactions destabilise the gas and make it available fuel for both star formation (SF) and nuclear accretion (e.g. Volonteri et al. 2015; Anglés-Alcázar et al. 2017). In turn, powerful AGN-driven, galaxy-scale outflows can hamper further SF and nuclear gas accretion by injecting energy and entropy into the host-galaxy ISM (e.g. King & Pounds 2015; Richings & ?e-mail: [email protected] Faucher-Giguère 2018; Menci et al. 2019) and circum-galactic environment (van de Voort 2017; Travascio et al. 2020). It is crucial to probe the cycle of feeding & feedback processes in massive galaxies and the AGN-galaxy co-evolution during Cosmic noon (z∼2−4.5), that is the peak epoch of galaxy assembly and SMBH accretion. Indeed, hyper-luminous quasi-stellar object (QSOs, bolometric luminosity LBol >1047 erg s−1) are preferred targets, being powered by massive (MBH & 109M), highly accreting SMBHs (Banerji et al. 2015; Shen 2016; Vietri et al. 2018). These heavy SMBHs have been found to reside in most local giant elliptical galaxies (Kormendy & Ho 2013; Shankar et al. 2019), although most of their mass has been assembled at early times during bright AGN phases (e.g. Marconi et al. 2004; Delvecchio et al. 2014). Giant ellipticals have also built most of their stellar mass at z&2 (∼80 % for sources with M∗>1011 M) and then rapidly evolved offthe galaxy Main Sequence (MS) becoming “red & dead” (e.g. Santini et al. 2009; McDermid et al. 2015). Overall, this strongly suggests that high-z, hyper-luminous QSOs are the assembly sites of giant galaxies. Indeed, the huge luminosities of these QSOs are likely triggered by galaxy interactions (e.g. Urrutia et al. 2008; Menci et al. 2014), and drive powerful outflows which may afArticle number, page 1 of 22 arXiv:2009.01112v3 [astro-ph.GA] 13 Oct 2020 A&A proofs: manuscript no. main fect the host-galaxy (Carniani et al. 2015; Zakamska et al. 2016; Bischetti et al. 2017, 2019b; Perrotta et al. 2019; Villar Martín et al. 2020; Herrera-Camus et al. 2020). Investigating the properties of the cold ISM (that is the raw material of SF) in objects at the brightest end of the QSO luminosity function is mandatory to constrain the impact of AGN activity on the host-galaxy evolution. Our knowledge of the hostgalaxies of z>1 QSOs has been revolutionised by interferometric observations at sub-millimetre wavelengths. Specifically, CO rotational emission is the most targeted transition in z.4 QSOs and probes the molecular gas reservoir. At higher redshift, it is possible to more easily exploit the bright [CII] fine structure emission line at λ158 µm, which is mostly associated with cold neutral gas (Solomon & Vanden Bout 2005; Carilli & Walter 2013; Zanella et al. 2018; Veilleux et al. 2020). Previous studies of luminous QSOs at z∼2−6 revealed a variety of host-galaxy properties. These sources typically reside in compact hosts, in some of which rotating disks are in place, while others show irregular morphology and disturbed kinematics (Díaz-Santos et al. 2016; Banerji et al. 2017; Brusa et al. 2018; Feruglio et al. 2018; Talia et al. 2018; Pensabene et al. 2020). Intense SF activity of hundreds to thousands solar masses per year is usually observed (Maiolino et al. 2012; Duras et al. 2017; Fan et al. 2019; Nguyen et al. 2020), although it is unclear whether this is linked to galaxy interactions (Trakhtenbrot et al. 2017; Bischetti et al. 2018; Fan et al. 2018, 2019). While great emphasis has been put in uncovering the formation and early growth of QSOs and their host-galaxies at 5.z.7 ( e.g. Wang et al. 2013, 2016; Decarli et al. 2018; Venemans et al. 2017a, 2019; Bañados et al. 2019), currently there is a lack of systematic investigation into the ISM and environment properties of QSOs shining at Cosmic noon. There is a series of works based on individual, often gravitationally-lensed sources (e.g. Carilli & Walter 2013, and references therein) or peculiar AGN types, such as heavily-reddened and hot, dust-obscured QSOs (e.g. Banerji et al. 2017; Fan et al. 2018). Few studies, based on heterogeneous samples including QSOs with different selection criteria (Feruglio et al. 2014; Perna et al. 2018) suggested a typically higher star formation efficiency (SFE) in QSOs, defined as the rate of SF per unit of molecular gas mass, with respect to non-active sources on the galaxy MS, although e.g. Kirkpatrick et al. (2019) found no significant correlation between the SFE and the AGN fraction at mid-infrared wavelengths. An increased SFE in QSOs is expected in the standard paradigm of a QSO expelling/heating gas from the host-galaxy in the transitory phase from starburst to blue QSO (Di Matteo et al. 2007; Hopkins 2012). Indeed, few works probing the molecular gas content in z∼1.5−2.5 QSOs with known presence of AGN-driven outflows reported a lower molecular gas content with respect to MS galaxies (Brusa et al. 2015, 2018; Carniani et al. 2017; Kakkad et al. 2017), while others found no difference (e.g. Herrera-Camus et al. 2019). In this framework, we have undertaken the WISE-SDSS selected hyper-luminous (WISSH) QSOs project to study the most powerful AGN in the Universe, which happen to shine at Cosmic noon and show widespread evidence of strong, AGN-driven outflows on nuclear to circum-galactic scales (Bischetti et al. 2017; Vietri et al. 2018; Bruni et al. 2019; Travascio et al. 2020). These QSOs are therefore ideal targets to shed light on the AGNgalaxy feeding and feedback cycle. In this work, we present submillimetre and millimetre observations of eight WISSH QSOs at z∼2.4−4.7 to probe SMBH and galaxy assembly at the massive end of the mass function and investigate the interplay between nuclear activity and the physical properties of the hostgalaxy ISM. The paper is organised as follows. In Sect. 2 we describe the targets and the (sub-)millimetre observations, detailing data reduction and analysis in Sect. 2.2. The main results are presented in Sect. 3, focusing on continuum (3.1), CO and [CII] emission (3.2). The CO spectral line energy distribution (SLED) and the UV-to-FIR spectral energy distribution (SED) are described in Sect. 3.3 and Sect. 4. Sect. 5 is dedicated to the cold gas kinematics. We discuss environment, star-formation efficiency, gas excitation, dynamical mass and molecular gas fraction of WISSH QSOs in Sect. 6. Finally, our conclusions are summarised in Sect. 7. Throughout this paper, we assume a ΛCDM cosmology with H0=67.3 km s−1Mpc−1,ΩΛ=0.69 and ΩM=0.31 (Planck Collaboration et al. 2016). 2. Sample and Observations Fig. 1. Panel (a): bolometric luminosity as a function of redshift for the total WISSH sample, compared to SDSS QSOs from Shen et al. (2011) and COSMOS QSOs from Lusso et al. (2012). Cyan stars indicate WISSH QSOs with (sub-)millimetre observations. Panel (b): bolometric luminosity vs black hole mass. We include WISSH QSOs with Hβ-based MBH from Vietri et al. (2018) and luminous SDSS QSOs from Shen (2016). Lines correspond to LBol/LEdd =1 (dashed), LBol/LEdd = 0.5 (solid), and LBol/LEdd =0.1 (dotted). 2.1. Sample description The targets presented in this work are drawn from the WISSH QSOs sample (Bischetti et al. 2017), including 86 hyperluminous, Type I QSOs at z∼1.8−4.8, selected to have a flux density S22µm>3 mJy by cross correlating the WISE all sky source catalogue with the SDSS DR7 catalogue. As shown in Fig. 1a, the WISSH sample collects the most luminous AGN known, characterised by bolometric luminosities LBol Article number, page 2 of 22 M. Bischetti et al.: The WISSH QSOs project Table 1. Journal of observations. Columns give the following information: (1) SDSS ID, (2-3) celestial coordinates, (4) redshift based on SDSS DR12 (Alam et al. 2015), (5) observation telescope, (6) observed transition, (7) angular resolution, (8) observed continuum frequency, (9) rms sensitivity for a channel width of 40 km s−1, and (10) continuum rms sensitivity. ID RA Dec zSDSS Telescope Transition Beamsize νcont σ40 km s−1σcont arcsec2GHz mJy beam−1mJy beam−1 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) J0209−0005 02:09:50.71 −00:05:06.22 2.849 NOEMA CO(5−4) 4.9×2.7 148.7 0.90 0.040 JVLA CO(1−0) 3.1×2.3 31.6 0.08 0.005 J0801+5210 08:01:17.82 +52:10:34.94 3.217 NOEMA CO(5−4) 3.8×1.9 136.6 1.05 0.100 JVLA CO(1−0) 3.4×2.3 30.2 0.16 0.010 J1433+0227 14:33:52.21 +02:27:14.01 4.622 ALMA [CII] 0.44 ×0.34 338.1 0.43 0.051 J1538+0855 15:38:30.49 +08:55:17.42 3.542 ALMA CO(4−3) 1.1×0.7 94.3 0.49 0.028 J1549+1245 15:49:38.71 +12:45:09.25 2.386 ALMA CO(4−3) 1.0×0.9 141.8 0.10 0.007 J1555+1003 15:55:14.86 +10:03:51.23 3.512 ALMA CO(4−3) 1.0×0.7 94.30 0.57 0.028 J1639+2824 16:39:09.11 +28:24:47.16 3.786 ALMA CO(4−3) 0.20 ×0.13 100.4 0.43 0.026 J1701+6412 17:01:00.60 +64:12:09.32 2.724 NOEMA CO(5−4) 4.0×2.1 154.7 1.03 0.100 J1015+0020∗10:15:49.00 +00:20:20.03 4.400 ALMA [CII] 0.22 ×0.18 357.3 0.19 0.040 ∗presented in Bischetti et al. (2018) >1047 erg s−1(Duras et al. 2017). The selection of Type 1 SDSS QSOs includes sources affected by low-moderate extinction (Duras et al. 2017), for a large fraction of which we collected reliable estimates of the SMBH mass via broad emission line-widths. Near-IR spectroscopy revealed that WISSH QSOs are powered by highly accreting SMBHs (accretion rate λEdd =LBol/LEdd ≃0.4−3 (Fig. 1b), where LEdd is the Eddington luminosity) with typical masses MBH>2×109M(Bischetti et al. 2017, 2018; Vietri et al. 2018). Here we present observations of WISSH QSOs performed with the Atacama Large Millimetre/submillimetre Array (ALMA), the Northern Emisphere Millimetre Array (NOEMA), and the Karl G. Jansky Very Large Array (JVLA). We include ALMA band 3 data from projects 2013.1.00417.S (P.I. I. Gavignaud) and 2019.1.01070.S (P.I. G. Venturi), and band 7 data from project 2016.1.00718.S (P.I. F. Fiore); NOEMA band 2 data from projects S17BW and W17DT (P.I. G. Bruni) and JVLA Ka band data from project VLA/18A−028 (P.I. M. Bischetti). We also collected all publicly available archival data from the ALMA archive as of December 2019, including ALMA projects 2015.1.01602.S (band 3, P.I. M. Schramm), 2016.1.01515.S (band 7, P.I. P. Lira), and ACA project 2018.1.01806.S (band 6, P.I. K. Hall). The combination of these projects has provided us with observations of sub-millimetre to centimetre continuum (observed frequency range ∼350 −30 GHz) and cold gas emission for a sample of nine WISSH QSOs (Fig. 1). Specifically, CO rotational emission is available for seven targets at z∼2.7−3.8, including CO(4−3)(νrest =461.04 GHz) and CO(5−4)(νrest = 576.27 GHz) transitions, as listed in Table 1. For two QSOs, namely J0209−0005 and J0801+5210, we have combined information about the ground transition CO(1−0)(νrest =115.27 GHz) and CO(5 −4). Moreover, we have collected observations of the [CII](νrest =1900.54 GHz) fine structure emission line for two WISSH QSOs at z>4. The results about J1015+0020 at z∼4.4 were presented in Bischetti et al. (2018), while in this work we analyse J1433+0227 at z∼4.7 (see also Nguyen et al. 2020). The sub-sample of WISSH QSOs analysed here derives from different projects, originally designed with different purposes. The three targets J1538+0855, J1549+1245 and J1555+1003 were selected to have AGN-driven outflows in the ionised gas phase (Bischetti et al. 2017; Vietri et al. 2018). Our analysis revealed that all WISSH QSOs in which we investigated the presence of [OIII] or CIV outflows satisfy this criterion (Vietri et al. 2018). These three QSOs (out of nine targets) also show broad absorption line (BAL) features in their UV spectra, consistently with the BAL fraction of ∼25% measured for the parent WISSH sample by Bruni et al. (2019). Targets J0209−0005, J0801+5210, J1433+0227, J1701+6412 (and J1015+0020 in Bischetti et al. 2018) were chosen to be detected by Herschel/SPIRE photometry in the far-infrared. Nevertheless, ∼90% of WISSH QSOs with Herschel/SPIRE coverage are detected (Duras et al. 2017). The QSO J1639+2824 was selected to have a nearby bright star, suitable for adaptive optics (AO)- assisted observations, in order to perform a joint Subaru and ALMA study of the host galaxy properties and of the SMBHgalaxy mass ratio (Schramm et al. 2019). Fig. 1a shows that our targets well represent the zand LBol range covered by the total WISSH sample. Similarly, their MBH span over a similar interval than that covered by WISSH QSOs with Hβ-based MBH (Vietri et al. 2018), except for the more massive SMBH in J1639+2824 (Fig. 1b). We note that the MBH of J0801+5210, J1538+0855 and J1549+1245 is derived from the Hβemission line (Vietri et al. 2018), that of J1433+0227 is MgII-based (Trakhtenbrot et al. 2011), while the MBH of the remaining targets is CIVbased (Weedman et al. 2012) and corrected for the presence of CIV outflows (Coatman et al. 2017). Globally, the selection of our targets does not introduce strong biases and the results of the following analysis can be considered as representative of the total WISSH sample. 2.2. Data reduction and analysis ALMA data were calibrated using the CASA software (McMullin et al. 2007) in the pipeline mode. For each source, we used the CASA version indicated by the ALMA observatory and the default phase, bandpass and flux calibrators. The absolute flux accuracy is better than 10%. To estimate the far-IR continuum emission, we averaged visibilities over all spectral windows excluding the spectral range covered by CO or [CII] emission lines, for a total of ∼7 GHz. Moreover, to model the continuum emission next to the line, we combined the adjacent spectral windows in the ALMA baseband containing CO or [CII]. Article number, page 3 of 22 A&A proofs: manuscript no. main We performed a fit in the uv plane to all channels with velocity |v|>500 km s−1by adopting a first order polynomial continuum model. We subtracted this fit to produce continuum-subtracted visibilities. Continuum-subtracted data cubes were created with the CASA 5.4.0 task tclean, using the hogbom cleaning algorithm (Högbom 1974) in non-interactive mode, and a threshold equal to three times the rms sensitivity. For all sources except J1639+2824, a natural weighting of the visibilities and a common spectral channel width of 40 km s−1were chosen. The same deconvolution procedure was adopted to produce continuum maps. In the case of J1639+2824, we applied a tapering of the visibilities beyond 900 kλ, corresponding to a baseline length &2800 km, to decrease the very high native resolution (0.11 ×0.06 arcsec2) to a tapered beam of 0.20 ×0.13 arcsec2. This resulted into a higher significance of CO(4−3) detection by a factor of ∼1.5, similarly to what found by Schramm et al. (2019) for this QSO. Regarding NOEMA data, project S17BW was acquired with the WideX correlator and span a total spectral range of ∼4 GHz, while project W17DT was obtained with the PolyFiX correlator and span a wider spectral interval of ∼14 GHz. We calibrated the visibilities using the CLIC pipeline of the GILDAS software (www.iram.fr/IRAMFR/GILDAS). The absolute flux accuracy is better than 10%. Imaging was performed with MAPPING, following the same procedure described above for ALMA observations. Given the redshift of J0209−0005 and J0801+5210, we used JVLA Ka-band observations. We observed each QSO using two separate windows of eight 128 MHz wide sub-bands for a total bandwidth of 1 GHz per window. Each sub-band had a native spectral resolution of 1 MHz. We calibrated the visibilities, both continuum and spectral line CO(1−0), following standard procedures within the CASA software package. The absolute flux accuracy is better than 15%. We imaged our sources using the CASA task tclean, following the same procedures applied to our ALMA data. Table 1 presents the journal of observations. For each target, we list the resulting beamsize, the rms sensitivity of the datacube for a channel width of 40 km s−1(σ40 kms−1) and the rms sensitivity of the continuum map (σcont). To derive flux density and size of the continuum emission in our targets, we (i) fitted the data in the image plane with a two-dimensional Gaussian profile by using CASA task imfit, and (ii) performed a fit of the visibilities in the uv plane with MAPPING task uvfit. In (ii), channels associated with the continuum emission, were spectrally and temporally averaged (to 30 s). We then fitted point source or Gaussian source models to the visibilities. In the case of multiple sources, we first fitted and subtracted emission from the QSO host-galaxy, then fitted emission from nearby emitters. A Gaussian model was preferred when resulting into an increased significance of the detection and a size different from null size at >3σ(where σis the error associated with the Gaussian axis derived from the fit in the uv plane). We checked that subtracting the models resulted into uniform residual noise maps. Similarly, we measured the integrated CO or [CII] flux density by averaging channels related to line emission (filled histogram in Fig. 4) and fitting the data in both image and uv plane. We verified that (i) and (ii) give consistent sizes and flux density values. One-dimensional spectra were extracted from the continuum-subtracted datacubes from a region centred on the peak of CO or [CII] integrated flux density, including emission detected at SNR >2. Given the modest signal-to-noise ratio of most spectra (see Fig. 4), we fitted them with a Gaussian profile by using the python package scipy.optimize.curve_fit leaving all parameters free to vary. We verified that by fitting the spectra with a two-Gaussian model, the line significance and parameters were consistent within the uncertainties with the single Gaussian fit. This provided us with FWHM and centroid of the emission line profiles, which was used to infer the CO or [CII] based redshift (zcold) of our targets listed in Table 2. 3. Results from sub-mm and mm observations 3.1. Continuum emission Figure 2 shows the (sub-)millimetre continuum maps for the eight WISSH QSOs analysed in this work. Observed ∼90 −340 GHz (rest-frame ∼430 −1935 GHz) continuum emission is detected at >4σcont significance in five out of eight sources (namely J0209−0005, J1433+0227, J1549+1245, J1555+1003, and J1701+6412) while emission is observed at ∼3σcont significance at the location of the QSO in J0801+5210 and J1639+2824. We also detect rest-frame ∼125 GHz continuum in the JVLA maps of J0209−0005 and J0801+5210 at ∼8σcont and ∼9σcont significance, respectively. Measured continuum flux densities range from ∼0.04 mJy at rest-frame 125 GHz to ∼0.1 mJy at 460 GHz and ∼0.6 mJy at 580 GHz (Table 2). For the WISSH QSO J1433+0227 we measure a strong restframe 1935 GHz continuum flux density of 7.7±0.3 mJy. The latter is a factor of ∼10 higher than the 1935 GHz continuum flux density found for the WISSH QSO J1015+0020 at z∼4.4 in Bischetti et al. (2018), suggesting a large variety of far-infrared continuum properties in our sample, similarly to what observed in z∼5−6 QSOs (e.g. Trakhtenbrot et al. 2017; Nguyen et al. 2020). The limited angular resolution of most observations presented in this work hampers a detailed study of the continuum emission morphology in these QSOs. Continuum morphology is consistent with a point source in all targets except J1433+0227 and J1549+1245 for which we measure a deconvolved angular size of (0.31±0.02)×(0.27±0.02) arcsec2and (0.69±0.19)×(0.50±0.20) arcsec2, corresponding to ∼2.0×1.8 kpc and ∼5.7×4.2 kpc2, respectively. In the field of view of J1549+1245, a strong continuum emitter is detected at ∼2.4 arcsec from the nucleus (Fig. 2e), associated with a companion source (see Sect. 3.2) whose continuum emission is comparable to that of the QSO host-galaxy, with a size of (0.74±0.22)×(0.43±0.23) arcsec2, corresponding to ∼6.1×3.6 kpc2. Weak, elongated continuum emission can be also observed along the QSO-companion direction, possibly linked to a tidal feature. Also in J0209−0005, the elongated continuum structure which can be observed at ∼5σcont in the northeast direction, up to ∼5 arcsec from the nucleus, reveals the presence of a continuum-emitting nearby source (see Sect. 3.2) whose continuum flux is about 45% of that of the QSO. 3.2. CO and [CII] emission Figure 3 shows the continuum-subtracted, velocity-integrated maps of CO and [CII] emission for the eight WISSH QSOs analysed in this work. The detection rate in mid−JCO and [CII] emission is 100% with significance of ∼4.5−30 σcold, where σcold is the rms sensitivity (also given in Fig. 3) of the velocity-integrated emission line maps. CO(1−0) is also detected at ∼5σcold in one of the two WISSH QSOs targeted by JVLA, namely J0209−0005, while no significant CO(1−0) emission is observed in J0801+5210. In Fig. 3, the location of the maxiArticle number, page 4 of 22 M. Bischetti et al.: The WISSH QSOs project Fig. 2. Maps of the continuum emission for the WISSH QSOs analysed in this work. For each panel, the observed continuum frequency is indicated by the top label. Grayscale defines the region where emission from the QSO host-galaxy and nearby continuum emitters is detected with SNR &4.5. Black contours correspond to [-3, -2, 2, 3, 4, 5, 6, 8, 12, 16, 32,...]σcont, where σcont values are listed in Table 1. Dashed contours are for negative values. The beam of each observation is also shown by the grey ellipse. In panels (d) and (g), the red star indicates the QSO optical position from SDSS. mum FIR continuum emission (or the optical position of the QSO, in the case of continuum-undetected sources J1538+0855 and J1639+2824) is also shown by yellow (red) stars. For most sources, a small offset between continuum and CO or [CII] emission can be observed, typically smaller than 0.5 arcsec. The largest offset, that is ∼1 arcsec, is observed between the SDSS optical position and the peak of CO(4−3) emission in J1538+0855, although consistent within the uncertainty on the optical coordinates. In addition to cold gas emission from the host-galaxies of the WISSH QSOs, CO and [CII] maps revealed the presence of several line emitters detected within an angular separation of ∼0.8 arcsec up to ∼16 arcsec from the nuclei, as shown by coloured contours in Fig. 3. Specifically, six out of eight WISSH QSOs analysed here show line emitters within the ALMA or NOEMA field of view, detected at &5σcold significance. Two of them, namely CompJ0209 and CompJ1549, are also detected in continuum emission (Sect. 3.1). For each of these sources, the proximity to the QSO in terms of sky frequency of the line emission (corresponding to a velocity shift in the range ∼40 −1800 km s−1) and angular separation suggests that they are companion CO and [CII] emitters, located at approximately the same redshift of the QSO. Fig. 4 shows the continuum-subtracted CO and [CII] spectra of the eight WISSH QSOs and of their companion galaxies, extracted from regions where line emission is detected at >2σcold in the QSO host-galaxy. For each source, the best-fit Gaussian model of the line is also displayed by the red curve. The redshift inferred from the Gaussian centroid (zcold), the FWHM and integrated flux density for each line are listed in Table 2. Details about individual QSOs are given below. J0209−0005: this QSO has been detected in both CO(5−4) and CO(1−0) emission in the NOEMA and JVLA maps (Fig. 3a). At the resolution and sensitivity of our observations, both transitions show a morphology which is consistent with a point source, although a low-significance tail can be observed in CO(1−0) south of the QSO location. Redshift and line width estimates based on CO(5−4) and CO(1−0) are consistent within the uncertainties. A strong CO(5−4) emitting companion is located north-east of the QSO at an angular separation of ∼4 arcsec, corresponding to a projected distance of ∼32 kpc at the redshift of the QSO. It shows a broad CO(5−4) profile, redshifted by ∼800 km s−1with respect to the QSO. Continuum emission associated with the companion can be also seen at ∼150 GHz in the observed frame, as the elongated structure in Fig. 2a. Article number, page 5 of 22 A&A proofs: manuscript no. main Fig. 3. Maps of the cold gas emission for the WISSH QSOs analysed in this work, obtained by integrating over the spectral range covered by CO or [CII] emission. For each source, the targeted transition is indicated by the top label. Grayscale defines the region where line emission from the QSO host-galaxy is detected with SNR &4.5. Black contours correspond to [-3, -2, 2, 3, 4, 5, 6, 8, 12, 16, 32, ...]σcold in the QSO map, where σcold =0.16,0.012 Jy beam−1km s−1for CO(5-4) and CO(1-0) observations in panel (a) and 0.22,0.032 Jy beam−1km s−1in panel (b). In panels (c-h) σcold =0.091,0.098,0.021,0.11,0.082,0.18 Jy beam−1km s−1, respectively. Similarly, magenta and blue contours identify emission from companion line emitters. In panel (e) blue contours have been created by masking QSO emission in a circular aperture of 1 arcsec radius centred on the QSO location. Dashed contours are for negative values. Yellow(red) stars indicate the QSO position as traced by the millimetre(optical) continuum. The beam of each observation is also shown by the grey ellipse. J0801+5210: although characterised by a bright CO(5−4) emission with a peak flux density of 5 mJy, this source shows no detected CO(1−0) in the JVLA map (Fig. 3b). To infer an upper limit on the CO(1−0) integrated flux density S∆v1−0, we have integrated the JVLA datacubes around zcold over 685 km s−1, assuming the same FWHM of CO(5−4). We have then computed S∆v1−0=3×σCO,1−0, where σCO,1−0is the rms sensitivity of the velocity-integrated CO(1−0) map (Table 2). In the NOEMA map, a nearby source emitting in CO(5−4) can be also seen at a projected distance of ∼40 kpc from J0801+5210. J1433+0227: this QSO at zcold =4.728 shows a strong [CII] line with an integrated flux density of 5.40 ±0.24 Jy km s−1, which is consistent within the errors to the value of 4.79±0.38 Jy km s−1found for this source by Nguyen et al. (2020) for the same observation. [CII] emission in J1433+0227 is a factor of ∼10 brighter than what found in the WISSH QSO J1015+0020 at zcold ∼4.4, also targeted in [CII] by Bischetti et al. (2018). This result is consistent with the variety of [CII] properties typically observed in high-zQSOs (e.g. Trakhtenbrot et al. 2017; Nguyen et al. 2020). [CII] emission in J1433+0227 is spatially resolved, with a deconvolved size of (0.44±0.03)×(0.38±0.03) arcsec2, corresponding to ∼2.9×2.5 kpc2. A second weak (peak flux density ∼1 mJy) [CII] emitter has been detected at a distance of 12 kpc (Figure 3c), showing an almost null velocity shift of 60 ±40 km s−1with respect to the QSO redshift. J1538+0855: we have detected CO(4−3) emission with a modest significance of ∼4.5σCO from the host-galaxy of this QSO, located at zcold ∼3.572. The peak of CO emission is separated by ∼1 arcsec from the SDSS optical position of the QSO, the offset being comparable to the uncertainty on the SDSS position. The line profile has a peak flux density of ∼1 mJy and a FWHM of 400±40 km s−1. No additional sources have been detected in the ALMA maps. J1549+1245: CO(4−3) emission in this QSO is characterised by a narrow line profile, with a FWHM=245±50 km s−1, and a peak flux density of ∼1 mJy. Despite the modest resolution of ALMA observations (1 arcsec), CO emission is resolved and has a deconvolved size of (1.10±0.16)×(0.86±0.16) arcsec2. Indeed, J1549+1245 is a peculiar case, showing two line emitting sources within a small separation of ∼2.4 arcsec (Figure 3e). Article number, page 6 of 22 M. Bischetti et al.: The WISSH QSOs project 2 0 2 4QSO CO(5-4) (a) J0209-0005 0.0 0.1 0.2 QSO CO(1-0) 1.5 0.0 1.5 3.0 Comp CO(5-4) 2 0 2 4 6QSO CO(5-4) (b) J0801+5210 0.0 0.2 0.4 QSO CO(1-0) 1.5 0.0 1.5 3.0 Comp CO(5-4) 0 4 8 12 QSO [CII] (c) J1433+0227 0.5 0.0 0.5 1.0 Comp [CII] 0.6 0.0 0.6 1.2 QSO CO(4-3) (d) J1538+0855 0.4 0.0 0.4 0.8 1.2 QSO CO(4-3) (e) J1549+1245 0.0 0.4 Comp1 CO(4-3) 0.05 0.00 0.05 0.10 Comp2 CO(4-3) 0.6 0.0 0.6 1.2 1.8 QSO CO(4-3) (f) J1555+1003 0.3 0.0 0.3 0.6 Comp CO(4-3) 2000 1500 1000 500 0 500 1000 1500 2000 0 2QSO CO(4-3) (g) J1639+2824 1.5 0.0 1.5 3.0 QSO CO(5-4) (h) J1701+6412 2000 1500 1000 500 0 500 1000 1500 2000 1.5 0.0 1.5 Comp CO(5-4) Velocity (km s 1) Flux density (mJy) Fig. 4. Spectra of the CO or [CII] emission lines for the WISSH QSOs analysed in this work. For each source, the targeted transition is indicated by the top label. Spectra were extracted from the region where emission from the QSO host-galaxy is detected with SNR>2 (see Fig. 3) and show the velocity range v∈[−2000,+2000] km s−1in channels of 40 km s−1. In case of (e), we preferred a circular extraction region with size of the ALMA beam, centred on the QSO position, to limit contamination from a nearby line emitting source at 0.6 arcsec separation (see Fig. 3e). The best-fit, Gaussian profiles are shown by the red curve. The filled histogram indicates velocity channels in which emission in the QSO and companion spectra is >5% than the peak flux of the best-fit model. In panels (a) and (b), grey spectral regions were excluded from the fit because associated with line emission from nearby sources (see Sect. 3.2) partially unresolved by the NOEMA beam. The strongest one, located at ∼19 kpc south-east of the nucleus, shows CO(4−3) emission as bright as that of the QSO, with a deconvolved size of (1.24±0.15)×(0.55±0.13) arcsec2. Such emission is blue-shifted by ∼950 km s−1with respect to the redshift of J1549+1245 and shows a FWHM∼540 km s−1. A second, fainter CO(4−3) emitting companion is also observed ∼12 kpc north of the QSO, with a modest velocity shift of 200±40 km s−1. J1555+1003: this QSO shows a broad (FWHM=615±90 km s−1) CO(4−3) emission line profile peaking at ∼1.4 mJy, located at zcold ∼3.529. The resolution of our ALMA observations has allowed us to marginally resolve CO(4−3) emission produced by a nearby companion galaxy, distant only 6 kpc from the QSO in the west direction (Fig. 3f). J1639+2824: for this QSO, we measure a CO(4−3) based redshift zcold =3.846 ±0.001, significantly larger than the redshift z=3.840 derived from the same data by Schramm et al. (2019). However, we note that the latter would correspond to an observed νobs ∼95.37 GHz, inconsistent with the CO(4−3) spectrum shown in their Fig. 3. The CO(4−3) emission line profile has a FWHM=615 ±90 km s−1, and an integrated flux density of ∼0.9 Jy km s−1. By fitting a 2D elliptical Gaussian to the data (in the image and uv plane), we measure an emission size of (0.15±0.02)×(0.11±0.02) arcsec2(Fig. 3g). We note Article number, page 7 of 22 A&A proofs: manuscript no. main Table 2. Properties of continuum and line (CO or [CII]) emission for the WISSH QSOs analysed here. Columns give the following information: (1) SDSS ID, (2) observed transition, (3) redshift estimated from (sub-)mm emission lines with typical uncertainty ∆zcold ∼0.001, (4-5) FWHM and integrated flux of CO or [CII], (6) CO luminosity, (7) [CII] luminosity and (8) continuum flux. Uncertainties do not include errors on abso ID Transition zcold FWHM S∆vL0 CO L[CII] Scont km s−1Jy km s−11010 K km s−1pc2109LmJy (1) (2) (3) (4) (5) (6) (7) (8) J0209−0005 CO(5−4) CO(1−0) 2.870 2.870 435±95 440±85 1.4±0.3 0.062±0.012 2.15±0.46 2.39±0.46 −0.38±0.04 0.039±0.005 J0801+5210 CO(5−4) CO(1−0) 3.256 − 685±70 − 3.68±0.40 <0.095a 6.99±0.76 <4.48 −<0.30b 0.091±0.010 J1433+0227 [CII] 4.728 400±40 5.40±0.24 −3.72±0.16 7.7±0.3 J1538+0855 CO(4−3) 3.572 320±90 0.36±0.11 1.23±0.38 −<0.087b J1549+1245 CO(4−3) 2.374 245±40 0.27±0.03 0.47±0.05 −0.12±0.01 J1555+1003 CO(4−3) 3.529 605±90 0.87±0.14 2.94±0.68 −0.10±0.02 J1639+2824 CO(4−3) 3.846 615±90 0.92±0.15 3.55±0.66 −<0.090b J1701+6412 CO(5−4) 2.753 595±120 1.50±0.34 2.15±0.49 −0.60±0.06 J1015+0020∗[CII] 4.407 340±40 0.47±0.05 −0.29±0.03 0.60±0.06 CompJ0209 CO(5−4) CO(1−0) 2.881 − 600±95 − 1.1±0.3 <0.044a 1.74±0.46 <1.71 −0.14±0.03 <0.014b CompJ0801 CO(5−4) CO(1−0) 3.271 − 385±65 − 0.71±0.26 <0.058a 1.36±0.49 <2.78 −<0.30b <0.30b CompJ1433 [CII] 4.728 100±43 0.11±0.02 −0.08±0.02 <0.015b Comp1J1549 CO(4−3) 2.363 540±95 0.29±0.05 0.49±0.08 −0.12±0.01 Comp2J1549 CO(4−3) 2.374 540±110 0.046±0.013 0.08±0.02 −<0.021b CompJ1555 CO(4−3) 3.531 370±70 0.29±0.06 0.98±0.20 −<0.084b CompJ1701 CO(5−4) 2.753 130±60 0.50±0.19 0.84±0.27 −<0.30b ∗presented in Bischetti et al. (2018) aupper limit computed for a point source as 3 ×σcold, where σcold is the rms of the velocity integrated JVLA map produced by assuming the same FWHM of CO(5−4) bupper limit computed for a point source as 3 ×σcont (Table 1). that our measured minor axis is a factor of about two larger than the value reported by Schramm et al. (2019), likely due to the larger velocity range that we used to produce the velocityintegrated CO(4−3) map (solid histogram in Fig. 4g), compared to Schramm et al. (2019), who reported a FWHM=495 ±30 km s−1. No additional sources have been detected in the ALMA maps. J1701+6412: we have detected CO(5−4) emission from this QSO, associated with a zcold =2.753. Similarly to the other CO(5−4) targets in our sample, the line peaks at >2mJy, with an associated integrated flux density of 1.5±0.35 Jy km s−1. In the NOEMA maps we have detected a companion galaxy distant ∼130 kpc from J1701+6412, showing CO(5−4) blue-shifted (by ∼1800 km s−1) emission, whose flux is about one third of that of the QSO. For each target and for the companion galaxies, we compute CO or [CII] luminosity according to Eq. (3) and Eq. (1) in Solomon & Vanden Bout (2005), respectively. The resulting CO luminosities, listed in Table 2, are in the range L0 CO ∼(0.5−7) × 1010 K km s−1pc2for the QSO host galaxies. For the companion galaxies, we measure L0 CO in the range (0.1−1.7)×1010 K km s−1 pc2. The CO luminosity of the companion is typically a factor of ∼3−5 lower or, in the case of J0209−0005 and J1549+1245, comparable to that of the QSO host. In the case of J1433+0227, we measure a [CII] luminosity L[CII] =(3.72 ±0.16) ×109L. 3.3. Investigating the CO spectral line energy distribution As mentioned in Sect. 3.2, J0209−0005 and J0801+5210 have been observed in both CO(5−4) and CO(1−0) rotational transitions. It is therefore possible to derive some information on the excitation conditions of the gas in WISSH QSOs from the relative strength of these two lines. In the case of J0209−0005, we measure a ratio of the integrated flux densities S∆v5−4/S∆v1−0= 22.5±6.0, while for J0801+5210 we infer the lower limit S∆v5−4/S∆v1−0>36.0. Figure 5 shows the CO SLED of J0209−0005 and J0801+5210, compared to few QSOs from literature with accurate measure of CO transitions up to J&5 (Carilli & Walter 2013). We also include the z∼2.5 reddened QSO ULAS J1234+0907 from Banerji et al. (2018). We note that the S∆v5−4/S∆v1−0ratio measured for J0209−0005 is similar to the values reported in other QSOs, while that of J0801+5210 suggests that CO can be highly excited in our hyper-luminous QSOs (see Sect. 6.3 for further discussion). By translating CO flux ratios in CO luminosity ratios, we obtain L0 CO(5−4)/L0 CO(1−0) =0.90±0.24 and L0 CO(5−4)/L0 CO(1−0) >1.39 for J0209−0005 and J0801+5210, respectively. The ratio measured for J0209−0005, based on the detection of both CO(1−0) and CO(5−4), is consistent within the uncertainty with the typical luminosity ratio reported for QSO host galaxies by Carilli & Walter (2013). We thus adopt L0 CO(5−4)/L0 CO(1−0) ≃0.69 and L0 CO(4−3)/L0 CO(1−0) ≃0.87 (Carilli & Walter 2013) to infer CO(1−0) luminosity in the remaining WISSH QSOs from the observed mid−JCO rotational transitions. We note that by assuming the CO SLED of J0209−0005, the inferred L0 CO(1−0) Article number, page 8 of 22 M. Bischetti et al.: The WISSH QSOs project would be lower by a factor of &2. On the other hand, by considering the CO ladder of the Cloverleaf QSO (Riechers et al. 2011a), which shows the minimum measured CO(5−4)/CO(1− 0) ratio in Fig. 5, the inferred L0 CO(1−0) would be higher by a factor of ∼1.3. Finally, the CO(5−4) and CO(1−0) observations also probe molecular gas excitation in the companion galaxies around J0209−0005 and J0801+5210 (see Sect. 3.2). The lower limits inferred for the integrated CO(5−4)/CO(1−0) flux ratios in CompJ0209 and CompJ0801 are shown in the bottom panel of Fig. 5, compared with CO SLEDs of sub-millimetre galaxies (SMGs) from literature (Carilli & Walter 2013). The S∆v5−4/S∆v1−0> 25 measured in CompJ0209 indicates a high CO excitation, similar to the excitation in the QSO host-galaxy, while in CompJ0801 we found S∆v5−4/S∆v1−0>12, consistent with the typical CO SLED of SMGs (e.g. Casey et al. 2014). Upper J 0 10 20 30 40 50 60 70 80 S v J J 1/S v1 0 J0209-0005 J0801+5210 QSOs (Carilli+13, Banerji+18) 0 2 4 6 8 10 Upper J 0 10 20 30 S v J J 1/S v1 0 CompJ0209 CompJ0801 SMGs (Carilli+13) Fig. 5. Top panel shows the CO SLED of J0209−0005 and J0801+5210 with CO(1−0) and CO(5−4) observations, compared to QSOs from literature with available measure of the ground transition (Carilli & Walter 2013). Bottom panel displays the CO ladder of companion galaxies CompJ0209 and CompJ0801, together with CO SLEDs of SMGs. 4. Broad band SEDs and millimetre emission The observations presented in Sect. 3.1 have provided us with a measure of the rest-frame 430−1935 GHz continuum, which can be used to extend to (sub-)millimetre wavelengths the coverage of the spectral energy distribution (SED) presented in Duras et al. (2017) for the half of our sample with available Herschel photometry. For QSOs with no Herschel coverage, we combine ALMA and NOEMA continuum measurements with the average infrared properties of WISSH-Herschel QSOs to provide an estimate of LIR. We complement sub-mm data with archival SDSS DR12 (Alam et al. 2015), 2MASS (Skrutskie et al. 2006), WISE (Wright et al. 2010), and Herschel/SPIRE (Pilbratt et al. 2010; Griffin et al. 2010) broad-band photometry. For target Fig. 6. Rest-frame SED of J0209−0005 (top) and J0801+5210 (bottom). In each panel, black circles indicate the photometric points considered (arrows represent 3σupper limits). Photometric points at λ < 1216Å are not included in the fits due to Lyαabsorption (grey circles). Restframe 125 GHz continuum data (not included in the fit) are shown by diamonds. Black curve represents the total best fit model, while blue(orange) curve refers to the QSO(cold dust) emission component. Synchrotron and free free emission are shown by the dashed and dotted lines, respectively. J1555+1003, undetected by 2MASS, we include photometric points obtained from dedicated observations at the ESO-INAF Rapid Eye Mount (REM) telescope (P.I. M. Bischetti) and INAF Telescopio Nazionale Galileo (TNG, P.I. V. Testa). These observations provided us with magnitudes J=17.4±0.11, H= 16.47 ±0.12 and K0=16.16 ±0.13 for J1555+1003. ALMA has revealed the presence of a strong continuum emitter close to J1549+1245 (Fig. 2). QSO and companion being separated by ∼2.4 arcsec, cannot be resolved as distinct objects in the WISE images, given the PSF, which is in the range 6.1−12 arcsec. However, we have verified that emission is centred at the QSO location in all WISE bands and estimated the companion contamination, as traced by irregular morphology of the WISE contours, to be <10%. Moreover, the J1549+1245 companion is undetected in one hour exposure VLT/SINFONI H and K band observations of the SUPER ESO large program 196.A-0377 (P.I. V. Mainieri, Circosta et al. 2018, Kakkad et al. 2020 A&A accepted). An upper limit of Scont <0.54 mJy on the QSO continuum emission at ∼785 GHz inferred from ACA observations has also been included in the SED (Fig. 12). In the case of J0209−0005, the continuum emission associated with the companion galaxy is ∼25 −35% of the QSO continuum in the NOEMA band (Fig. 2a). To compute the SED of J0209−0005, we assume Herschel photometry to be similarly dominated by emission from the QSO host-galaxy. SED Fitting was performed by using the procedure presented in Duras et al. (2017); Zappacosta et al. (2018) with a combination of QSO and host-galaxy emission components. In summary, the QSO component is described as the superposition of accretion disk emission (Feltre et al. 2012), and of radiation coming Article number, page 9 of 22 A&A proofs: manuscript no. main 10.00 10.25 10.50 10.75 11.00 11.25 11.50 11.75 12.00 Log( M dyn/ M ) 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 Log( M BH/ M ) (a) J1433+0227 J1549+1245 J1639+2824 J1015+0020 z 2 QSOs z 4.5 QSOs z 6 QSOs 9.0 9.5 10.0 10.5 11.0 11.5 12.0 Log( M */ M ) 2.5 2.0 1.5 1.0 0.5 0.0 0.5 1.0 Log f corr gas (b) WISSH CO WISSH Dust Comp1J1549 z>1 QSOs SUPER PG QSOs IBISCO AGN+CO outflow Fig. 11. Panel (a) shows the black hole mass as a function of the dynamical mass of WISSH QSOs (cyan symbols), compared with z∼2−6, luminous QSOs from literature, as indicated in the legend (see text for details). The total dynamical mass associated with the QSO +companion galaxies with measured Mdyn are also shown by the empty symbols. For WISSH QSOs and companions (as most literature sources), Mdyn values are based on the FWHM of the CO or [CII] emission lines. The MBH −Mdyn relation found for local galaxies by Jiang et al. (2011) is also indicated by the dashed line, with the associated 0.4 dex intrinsic scatter (shaded region). Panel (b) displays the molecular gas fraction (corrected for the dependence on redshift and offset from main-sequence) as a function of the host-galaxy stellar mass for WISSH QSOs and a compilation of high-z QSOs and local AGN (see text). WISSH QSOs with dust-based Mgas are indicated by orange stars. The average fgas −M∗relation found for z<4 star-forming galaxies from the PHIBSS survey (Tacconi et al. 2018) is shown by the solid line. Li et al. 2020) and the high−JCO rotational energy levels become more populated with respect to photo-dissociation regions (PDRs, Hollenbach & Tielens 1999), dominated by UV photons from young stars, which mostly contribute to the CO SLED of non active, star forming galaxies (e.g. Narayanan & Krumholz 2014; Greve et al. 2014). The steep CO SLED observed in CompJ0209 suggests that the AGN radiative output might be able to affect cold gas excitation also in nearby sources. The limited sampling of the CO ladder in J0209−0005 and J0801+5210 as well as in their companion galaxies does not allow us to quantify the different contributions to CO excitation. Further observations of high−JCO rotational transitions, that is J∼6−10, close to the peak of the CO SLED (Mashian et al. 2015; Li et al. 2020), will be important to probe the physical properties of the molecular gas and the main excitation source in these luminous targets. 6.4. Dynamical masses 6.4.1. Size of CO and [CII] emission In Sect. 3.2 and Sect. 5 we investigated the CO and [CII] spatial extent and kinematics of the WISSH QSOs J1433+0227, J1549+1245 and J1639+2824, in which line emission is spatially resolved by the ALMA observations. Specifically, we find the cold gas reservoir in J1433+0227 as traced by [CII] emission, to be distributed in a rotating disk with size D=4.4±0.3 kpc. The latter was computed by multiplying the major axis derived in Sect. 3.2 by a factor of 1.5 (e.g. Wang et al. 2013; Venemans et al. 2016). This value is in agreement with typical sizes (2 −5 kpc) of [CII] emission measured in luminous, high-z QSOs at z∼4.5−5 (Trakhtenbrot et al. 2017; Pensabene et al. 2020; Nguyen et al. 2020), and a factor of three larger than the [CII] disk size of the WISSH QSO J1015+0020 (Bischetti et al. 2018). In the case of J1549+1245, the CO(4−3) emission is peculiarly extended over D=12.5±2.0 kpc, as also observed in the companion galaxy Comp1J1549, which is characterised by an even larger CO(4−3) size D=15.4±1.9 kpc for the molecular gas reservoir. The large size measured in J1549+1245 differs from the majority of previous observations targeting mid−JCO rotational transitions in QSO host-galaxies, finding the bulk of molecular gas located in compact regions of few kpc size (e.g. Fan et al. 2018; Bischetti et al. 2019b; D’Amato et al. 2020). On the other hand, CO(3−2) emitting regions with D>10 kpc have been measured in hyper-luminous, reddened QSOs at z∼2.5 by Banerji et al. (2017), with comparable LBol. Given that several SMGs show evidence for similarly extended reservoirs but in lower excitation molecular gas (e.g. Ivison et al. 2011; Riechers et al. 2011b), this may suggest that the huge QSO radiative output in our targets is able to affect CO excitation out to tens of kpc scale and in nearby galaxies, in agreement with our findings for the CO SLED of J0209−0005 and its companion (Sect. 3.3). Concerning J1639+2824, we instead measure a compact size for the CO(4−3) emission D=1.7±0.2 kpc, which is a factor of two larger than the CO size measured for this QSO by Schramm et al. (2019) from the same observation. We note that the detection of gas on larger scales might be hampered by the very high native angular resolution of the ALMA observations (Sect. 2.2). 6.4.2. Dynamical vs SMBH mass To calculate the dynamical mass of J1433+0227, we (a) adopt the virial relation Mdyn =Dvv2 rot/2G=5.6+5.1 −1.9×1010 M, where vrot is provided by the BAROLO model of the high-resolution ALMA datacube (Sect. 5). As the BAROLO model is limited Article number, page 16 of 22 M. Bischetti et al.: The WISSH QSOs project to [CII] emission from the central region with (deconvolved) size of 0.31 ±0.03 arcsec, the virial estimate corresponds to the dynamical mass within the inner Dv=3.5±0.3 kpc; (b) use the FWHM of the [CII] emission line as a proxy of the circular velocity, according to the relation Mdyn =1.16 ×105× (0.75 ×FWHM/sini)2×D=1.4+1.3 −0.5×1011 M(e.g. Wang et al. 2013; Venemans et al. 2016). Similarly, by using (b) we find Mdyn =1.2+1.7 −0.5×1011 Mfor J1549+1245, and a larger mass by a factor of three Mdyn =3.6+1.1 −0.4×1011 Mfor its companion galaxy Comp1J1549, supporting an interpretation of the QSO-companion interaction as major merger. The measured dynamical mass of J1639+2824 is Mdyn =8.9+9.7 −3.2×1010 M, which is about one order of magnitude larger than the value in Schramm et al. (2019) which, however, reported their estimate of Mdyn for a rotating disk to be smaller than the black hole mass for this QSO. We point out that in the case of marginally resolved sources such as our targets, detected with moderate significance, inclination and, in turn, Mdyn estimates can be significantly altered by non-circular beam shapes. Also, non-rotating ISM components may be missed given the angular resolution of our observations. Moreover, our Mdyn are based on a single emission line whose kinematics may represent only the inner regions of the galaxy (e.g. de Blok & Walter 2014; Lupi et al. 2019). Further discussion about these issues can be found in Trakhtenbrot et al. (2017) and references therein. Finally, we note that assuming WISSH systems to be dispersion-dominated would result in smaller Mdyn by a factor of 3 −4 (e.g. Decarli et al. 2018). Both J1549+1245 and J1639+2824 benefit from singleepoch measurements of the SMBH mass (MBH) based on the Hβ λ4861 Å emission line which, being mostly dominated by virial motions, is the best estimator of MBH (Denney 2012; Marziani & Sulentic 2012; Vietri et al. 2018) for QSOs up to z∼3.8. Specifically, Bischetti et al. (2017) and Schramm et al. (2019) found very large log(MBH/M)≃10.1−10.4. For the higher redshift QSO J1433+0227, a log(MBH/M)≃9.11 measured from the MgII λ2800 Å emission line was reported by Trakhtenbrot et al. (2011). Figure 11a shows the location of the WISSH QSOs in the MBH −Mdyn plane (cyan stars), including J1015+0020 analysed in Bischetti et al. (2018). QSOs from literature with measure of Mdyn based on CO or [CII] emission lines and single epoch estimate of MBH are also displayed. We include dusty-obscured QSOs at z∼2 from Banerji et al. (2015, 2017); Bongiorno et al. (2014); Brusa et al. (2018) and luminous z∼4.5−6 QSOs from the works of Venemans et al. (2016, 2017a); Willott et al. (2013, 2015, 2017); Kimball et al. (2015); Trakhtenbrot et al. (2017); Feruglio et al. (2018); Mortlock et al. (2011); De Rosa et al. (2014); Kashikawa et al. (2015). The MBH −Mdyn relation, derived from local galaxies in a wide range of Mdyn ∼109−1012M by Jiang et al. (2011), is also shown for comparison. All WISSH QSOs but J1433+0227 are characterised by a ratio between dynamical mass and SMBH mass Mdyn/MBH ∼3−10, among the smallest observed so far. According to the local relation, the typical Mdyn/MBH ratio should be ∼600 which, given the very massive black holes hosted by our targets, should translate into host-galaxy dynamical masses &1012 M. Such large values of Mdyn suggest that that hyper-luminous QSOs are the likely placeholders of high-density regions were local giant galaxies have been assembled (see also Jones et al. 2017; Díaz-Santos et al. 2018). We also note that small Mdyn/MBH ratios are expected in the early growth phases (z&3) of very massive BHs, for a scenario in which black-hole accretion is triggered by galaxy interactions (e.g. Lamastra et al. 2010; Menci et al. 2014). In the case of J1549+1245, the empty star in Fig. 11a represents the total dynamical mass log(Mdyn/M)∼11.68 associated with the QSO plus Comp1J1549 system, under the likely hypothesis that these two sources will merge (see Sect. 3.2) and build up the mass of the QSO host-galaxy. A similar result was reported for J1015+0020 (whose mass plus that of its companion galaxy is also reported in Fig. 11a as the empty square) by Bischetti et al. (2018), who found this QSO to be associated with multiple nearby (<16 kpc) companion galaxies, for a total a log(Mdyn/M)>11 already in place at z∼4.4. Given the widespread presence of bright companion galaxies in the surroundings of WISSH QSOs, most of which are located at close projected distance (∼6−30 kpc), we expect them to significantly contribute to the final mass of the QSO host-galaxies and consequently move the WISSH points closer to the local relation. 6.5. Gas fraction and feedback from QSO winds To probe the amount of gas available for star-formation activity in the WISSH QSOs, we compute the molecular gas fraction, defined as fgas =Mgas/M∗. Our targets being unobscured QSOs, a derivation of the host-galaxy stellar mass from SED fitting is particularly challenging, given that the nuclear emission outshines the galaxy at wavelengths shorter than few tens of microns (Sect. 4). An alternative approach is to infer M∗via the dynamical mass, according to the relation M∗=Mdyn −Mgas −MBH (e.g. Venemans et al. 2017b; Nguyen et al. 2020), under the assumption that dark matter does not significantly contribute to the central mass of the host-galaxies (e.g. Wuyts et al. 2016). By using the latter method, we could therefore measure M∗for four of our targets and we find log(M∗/M)∼10.4−11.0 and a wide range of fgas ∼0.04 −1.6 for our targets, similarly to what has been found in other high−zQSOs (e.g. Venemans et al. 2017b; Banerji et al. 2018). However, we caution that large uncertainties affect these measurements, the main of which are related to the uncertainty on the galaxy inclination and to the assumption of an αCO (Sect. 6.2). This prevents us from putting tight constraints on M∗and, in turn, on fgas. Previous studies of molecular gas content in star-forming galaxies out to z∼4 (e.g. Genzel et al. 2015; Tacconi et al. 2018) highlighted a dependence of fgas on redshift and offset from the star-forming galaxies MS, ∆MS. To ensure a meaningful comparison of the molecular gas fraction of WISSH QSOs with other samples at different zand ∆MS, we thus correct fgas for these trends. Specifically, we use the functions f2(z) and g2(sS FR/sS FRMS) by Genzel et al. (2015); Tacconi et al. (2018), in which we parametrise sS FRMS according to Whitaker et al. (2012). Figure 11b shows fcorr gas (corrected for trends with zand ∆MS) of WISSH QSOs as a function of M∗, compared with QSO samples as in Sect. 6.2. We also include low-redshift AGN samples, such as (i) Palomar Green (PG) QSOs with CO(2−1) based molecular gas masses (Shangguan et al. 2020); (ii) X-ray selected INTEGRAL/IBIS AGN, characterised by log(LBol/erg s−1)∼43.5−45.6, with CO(1−0) and CO(2−1) measurements from the IBISCO survey (Feruglio et al. 2020 in prep.). We consider (iii) active galaxies with evidence of AGN-driven molecular outflows from Fiore et al. (2017); Brusa et al. (2018); Fluetsch et al. (2019); Herrera-Camus et al. (2019). For all these sources, molecular gas masses have been homogeneously computed as in Sect. 6.2. The average fcorr gas −M∗relation derived from ∼1400 star forming galaxies at z<4 from the IRAM Plateau de Bure HIgh-z Blue Sequence Survey (PHIBBS, Tacconi et al. 2018) is indicated by the solid line. Article number, page 17 of 22 A&A proofs: manuscript no. main We find that the molecular gas fraction of WISSH QSOs is systematically smaller by a factor of ∼10−100 than that of starforming galaxies with the same stellar mass. In general, AGN with log(M∗/M)<10.25 exhibit similar fcorr gas to star-forming galaxies, while at larger stellar masses the number of sources below the relation significantly increases, both in high-z QSOs and in z∼0 AGN. We note that part of the offset of WISSH QSOs (and other AGN in starbursting or merging systems, see Sect. 6.2) might be due to the adopted αCO =0.8, while the molecular gas fraction in PHIBBS galaxies is based on a complex conversion function, which takes into account metallicity and offset from MS (Genzel et al. 2015; Accurso et al. 2017). This may account for a factor of ∼4 in fcorr gas (error bar in Fig. 11b), given the M∗of our targets. However, even taking into account the uncertainty on αCO, WISSH QSOs and ∼50% of points at log(M∗/M)&10.5 fall short of the Tacconi et al. (2018) average fcorr gas . This result is in agreement with previous findings by Brusa et al. (2015); Perna et al. (2018), who reported a lower molecular gas fraction in obscured QSOs compared to MS galaxies and proposed AGN feedback as responsible for depleting the host-galaxy of the molecular gas content via outflows, during the transition, "blowout" phase from starburst galaxy to unobscured QSO (e.g. Menci et al. 2008; Hopkins et al. 2008). Moreover, Brusa et al. (2018) reported a low gas fraction in the z∼1.5 luminous, obscured QSO XID2028, in which an outflow has been detected in both the molecular and ionised gas phases (see also Cresci et al. 2015) Similarly, Fiore et al. (2017) reported a lower fcorr gas than MS galaxies in a collection of local AGN with evidence of molecular outflows, the gap increasing at large M∗. Carniani et al. (2017) targeted LBol ∼1047 erg s−1QSOs at z∼2.4 showing strong ionised winds, as traced by the [OIII] λ5007 Å emission line, and reported a significantly reduced gas reservoir compared to main-sequence galaxies at the same redshift. On the other hand, Herrera-Camus et al. (2019) found a fcorr gas consistent with the Tacconi et al. (2018) relation in a z∼2.4 QSO hosted by a massive (M∗∼1011 M), MS galaxy, with multi-phase outflows. It is worth noting that all WISSH QSOs analysed in this work show evidence of ionised outflows, from nuclear to circumgalactic scales, as traced by large blue-shifts of their emission lines in the rest-frame UV and optical spectrum with respect to the systemic QSO redshift, as traced by CO or [CII] (zcold in Table 2). Specifically, by analysing SDSS DR12 spectra (Alam et al. 2015) we measured the wavelength corresponding to the peak of the CIV λ1549 Å emission line (zSDSS in Table 1), and found large velocity blue-shifts in the range v∈[1200 −5600] km s−1with respect to the systemic redshift. Similar results were found by Vietri et al. (2018) who analysed the velocity shift between CIV and Hβfor 18 WISSH QSOs and revealed powerful, broad-line region winds with associated kinetic power ˙ Ekin ∼1043 −1044 erg s−1. The presence of strong nuclear winds in ∼25% of the total WISSH sample was also reported in Bruni et al. (2019), who found high velocity BAL features blue-wards of CIV and SiIV λ1400 Å emission lines. Three WISSH among the targets of this work are BAL QSOs, namely J1549+1245, J1555+1003, and J1538+0855, which shows an ultra-fast BAL outflow with velocity v∈38000 −47000 km s−1. Indeed, Bischetti et al. (2017) reported among the most powerful [OIII] outflows observed so far in five WISSH QSOs (including J1549+1245), with ˙ Ekin up to few percent of LBol and extending on kpc scale, while Travascio et al. (2020) discovered a Lyα λ1216 Å outflow propagating up to ∼30 kpc in the circumgalactic medium of J1538+0855. Feedback associated with QSO activity, responsible for heating and/or removing molecular gas from the host-galaxy via outflows, is a possible scenario for the low molecular gas fractions. We searched for the presence of cold gas outflows as traced by broad/asymmetric wings in the CO or [CII] spectra of the WISSH QSOs presented in this work. We found no detection of high-velocity cold gas. However, the limited sensitivity of our observations (Table 1) prevents us from putting meaningful upper limits on the luminosity of cold gas outflows in our targets. Indeed, molecular and neutral outflows observed in luminous QSOs typically correspond to ∼1/60 to ∼1/20 of the peak of CO and [CII] emission line profiles, respectively (e.g. Feruglio et al. 2017; Bischetti et al. 2019b; Cicone et al. 2015; Bischetti et al. 2019a). Therefore, deeper observations in the (sub-) millimetre band are required to detect the counterpart in the cold gas phase of the powerful ionised outflows in WISSH QSOs. 7. Conclusions We report on ALMA, NOEMA and JVLA observations of the far-infrared continuum, CO and [CII] line emission in a sample of eight hyper-luminous QSOs from the WISSH sample at z∼ 2.4−4.7. These data enable us to perform the first systematic study of cold gas properties in hyper-luminous QSOs at Cosmic noon. Our main findings can be summarised as follows: – We detect CO(4−3), CO(5−4) rotational or [CII] emission in the host-galaxies of our targets (100% detection rate). In the case of J0209−0005 we also detect CO(1−0). We find CO emission to be highly excited, as suggested by the CO SLEDs of J0209−0005 and J0801+5210, among the steepest observed in high-z QSOs so far. Far-infrared and/or mm continuum is detected in ∼75% of our targets. – For spatially resolved sources, we observe a variety of sizes for the molecular gas reservoirs, in the range ∼1.7−10 kpc. In J1433+0227, our dynamical modelling of the velocity gradient observed in the [CII] emission line indicates the presence of a fast rotating disk, in which gas motions not associated with rotation are also present. Similarly, disturbed kinematics is observed in J1549+1245 and J1639+2824. – Our hyper-luminous QSOs are preferentially located in highdensity regions, given the widespread presence of one or more line emitters around ∼80% of the QSOs. These submillimetre companions show bright CO or [CII] emission, in most cases comparable to emission from cold gas in the QSO host-galaxy, and are located at projected distances of ∼6−130 kpc. – We find that the majority of WISSH QSOs exhibit a lower L0 CO (by a factor of ∼4) than z∼0−3 MS galaxies with same LIR, after correcting for the AGN contribution to infrared wavelengths. This translates into SFE >100 L/(K km s−1pc2), implying that the observed SFRs ∈[165−1095] M yr−1are able to convert the molecular gas reservoir into stars on a timescale of .50 Myr, shorter by an average factor of ∼30 compared to the depletion timescale of MS galaxies of similar M∗and z. – All WISSH QSOs but J1433+0227 are characterised by extremely small Mdyn/MBH ratios of ∼3−10, which are about two orders of magnitude offset from local relations. We find hyper-luminous QSOs to pinpoint the high-density sites where giant galaxies assemble, with significant contribution of mergers to the host-galaxy mass. Article number, page 18 of 22 M. Bischetti et al.: The WISSH QSOs project – We also infer the molecular gas fraction in the host-galaxies of four WISSH QSOs, finding lower values by a factor of ∼10 −100 once compared to star forming galaxies with same M∗. This is likely linked to the widespread evidence of AGN-driven outflows in our targets having the effect of heating/depleting the gas reservoir in the galaxy. The ALMA, JVLA and NOEMA observations analysed in this work provide a wealth of information about the properties of cold ISM and environment for a homogeneous and statistically fair sample of LBol >1047 erg s−1Type 1 QSOs shining at the peak epoch of QSO activity and massive galaxy assembly. We find these hyper-luminous objects to be caught in an evolutionary phase of concurrent intense growth of both SMBH and host-galaxy. Such growth is likely being regulated by AGNfeedback and will use up the molecular gas reservoir in few tens of Myr, supporting a scenario in which hyper-luminous QSOs are the progenitors of "red & dead" giant ellipticals. Given the richness of companion galaxies, we expect these systems to further evolve towards the local MBH −Mdyn relation via mergers. The results presented here thus represent a critical step towards a better understanding of the SMBH-galaxy co-evolution for the objects at the extreme end of the mass function. Followup observations with higher angular resolution of these QSOs are needed to optimally map the cold gas kinematics in their hosts and in the companion galaxies, and better constrain the total mass and the merger state of these systems. Such observations may also be able to detect the cold gas counterparts of the ionised outflows revealed in all WISSH QSOs, assessing their multi-phase nature and global energetics. Acknowledgements. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00417.S, ADS/JAO.ALMA#2019.1.01070.S, ADS/JAO.ALMA#2015.1.01602.S, ADS/JAO.ALMA#2016.1.00718.S, ADS/JAO.ALMA#2016.1.01515.S, ADS/JAO.ALMA#2018.1.01806.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This work is based on observations carried out under project number S17BW and W17DT with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). We are grateful to the anonymous referee for useful feedback which helped us to improve the paper. We thank Dr. Y. Wang for providing us with SUBARU images of J0209−0005 and Dr. P. Santini for useful discussion about SFE in high−zgalaxies. MBi, MBr, CF, FF, AM, EP acknowledge support from PRIN MIUR project "Black Hole winds and the Baryon Life Cycle of Galaxies: the stone-guest at the galaxy evolution supper", contract #2017PH3WAT. MBi, CF and FF acknowledge support from INAF under PRIN SKA/CTA FORECaST and PRIN MAINSTREAM 2018 "Black hole winds and the baryon cycle". EP, LZ and MBi acknowledge financial support under ASI-INAF contract 2017-14-H.0. GB acknowledges financial support under the INTEGRAL ASI-INAF agreement 2019-35-HH.0 MPT acknowledges financial support from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and through grant PGC2018-098915-B-C21 (MCI/AEI/FEDER, UE). RM acknowledges ERC Advanced Grant 695671 “QUENCH” and support by the Science and Technology Facilities Council (STFC). GVe acknowledges support from CONICYT Basal-CATA AFB-170002 and FONDECYT Postdoctorado 3200802 grants. CC acknowledges support from the Royal Society. MP is supported by the Programa Atracción de Talento de la Comunidad de Madrid via grant 2018-T2/TIC-11715. GVi acknowledges financial support from Premiale 2015 MITiC (PI B. Garilli). References Accurso, G., Saintonge, A., Catinella, B., et al. 2017, MNRAS, 470, 4750 Alam, S., Albareti, F. D., Allende Prieto, C., et al. 2015, ApJS, 219, 12 Alloin, D., Kneib, J. P., Guilloteau, S., & Bremer, M. 2007, A&A, 470, 53 Anglés-Alcázar, D., Faucher-Giguère, C.-A., Kereš, D., et al. 2017, MNRAS, 470, 4698 Aravena, M., Spilker, J. S., Bethermin, M., et al. 2016, MNRAS, 457, 4406 Bañados, E., Novak, M., Neeleman, M., et al. 2019, ApJ, 881, L23 Banerji, M., Alaghband-Zadeh, S., Hewett, P. C., & McMahon, R. G. 2015, MNRAS, 447, 3368 Banerji, M., Carilli, C. L., Jones, G., et al. 2017, MNRAS, 465, 4390 Banerji, M., Jones, G. C., Wagg, J., et al. 2018, MNRAS, 479, 1154 Beelen, A., Cox, P., Benford, D. J., et al. 2006, ApJ, 642, 694 Bischetti, M., Maiolino, R., Carniani, S., et al. 2019a, A&A, 630, A59 Bischetti, M., Piconcelli, E., Feruglio, C., et al. 2018, A&A, 617, A82 Bischetti, M., Piconcelli, E., Feruglio, C., et al. 2019b, A&A, 628, A118 Bischetti, M., Piconcelli, E., Vietri, G., et al. 2017, A&A, 598, A122 Bolatto, A. D., Wolfire, M., & Leroy, A. K. 2013, ARA&A, 51, 207 Bongiorno, A., Maiolino, R., Brusa, M., et al. 2014, MNRAS, 443, 2077 Bothwell, M. S., Smail, I., Chapman, S. C., et al. 2013, MNRAS, 429, 3047 Briggs, D. S. 1995, in American Astronomical Society Meeting Abstracts, Vol. 187, American Astronomical Society Meeting Abstracts, 112.02 Bruni, G., Piconcelli, E., Misawa, T., et al. 2019, A&A, 630, A111 Brusa, M., Cresci, G., Daddi, E., et al. 2018, A&A, 612, A29 Brusa, M., Feruglio, C., Cresci, G., et al. 2015, A&A, 578, A11 Carilli, C. L., Kohno, K., Kawabe, R., et al. 2002, AJ, 123, 1838 Carilli, C. L., Lewis, G. F., Djorgovski, S. G., et al. 2003, Science, 300, 773 Carilli, C. L. & Walter, F. 2013, ARA&A, 51, 105 Carniani, S., Gallerani, S., Vallini, L., et al. 2019, MNRAS, 489, 3939 Carniani, S., Marconi, A., Biggs, A., et al. 2013, A&A, 559, A29 Carniani, S., Marconi, A., Maiolino, R., et al. 2015, A&A, 580, A102 Carniani, S., Marconi, A., Maiolino, R., et al. 2017, A&A, 605, A105 Casey, C. M., Narayanan, D., & Cooray, A. 2014, Phys. Rep., 541, 45 Choi, E., Somerville, R. S., Ostriker, J. P., Naab, T., & Hirschmann, M. 2018, ApJ, 866, 91 Cicone, C., Maiolino, R., Gallerani, S., et al. 2015, A&A, 574, A14 Circosta, C., Mainieri, V., Padovani, P., et al. 2018, A&A, 620, A82 Clements, D. L., Petitpas, G., Farrah, D., et al. 2009, ApJ, 698, L188 Coatman, L., Hewett, P. C., Banerji, M., et al. 2017, MNRAS, 465, 2120 Combes, F. 2018, A&A Rev., 26, 5 Conselice, C. J. 2014, ARA&A, 52, 291 Cresci, G., Mainieri, V., Brusa, M., et al. 2015, ApJ, 799, 82 Croton, D. J., Springel, V., White, S. D. M., et al. 2006, MNRAS, 365, 11 Croxall, K. V., Smith, J. D., Pellegrini, E., et al. 2017, ApJ, 845, 96 Daddi, E., Elbaz, D., Walter, F., et al. 2010, ApJ, 714, L118 D’Amato, Q., Gilli, R., Vignali, C., et al. 2020, A&A, 636, A37 Davies, R., Förster Schreiber, N. M., Cresci, G., et al. 2011, ApJ, 741, 69 de Blok, W. J. G. & Walter, F. 2014, AJ, 147, 96 De Rosa, G., Venemans, B. P., Decarli, R., et al. 2014, ApJ, 790, 145 Decarli, R., Dotti, M., Bañados, E., et al. 2019, ApJ, 880, 157 Decarli, R., Walter, F., Venemans, B. P., et al. 2017, Nature, 545, 457 Decarli, R., Walter, F., Venemans, B. P., et al. 2018, ApJ, 854, 97 Delvecchio, I., Gruppioni, C., Pozzi, F., et al. 2014, MNRAS, 439, 2736 Denney, K. D. 2012, ApJ, 759, 44 Di Matteo, P., Combes, F., Melchior, A. L., & Semelin, B. 2007, A&A, 468, 61 Di Teodoro, E. M. & Fraternali, F. 2015, MNRAS, 451, 3021 Díaz-Santos, T., Assef, R. J., Blain, A. W., et al. 2018, Science, 362, 1034 Díaz-Santos, T., Assef, R. J., Blain, A. W., et al. 2016, ApJ, 816, L6 D’Odorico, V., Feruglio, C., Ferrara, A., et al. 2018, ApJ, 863, L29 Downes, D., Solomon, P. M., & Radford, S. J. E. 1995, ApJ, 453, L65 Draine, B. T., Dale, D. A., Bendo, G., et al. 2007, ApJ, 663, 866 Dunne, L., Eales, S., Edmunds, M., et al. 2000, MNRAS, 315, 115 Duras, F., Bongiorno, A., Piconcelli, E., et al. 2017, A&A, 604, A67 Eales, S., Smith, M. W. L., Auld, R., et al. 2012, ApJ, 761, 168 Fan, L., Han, Y., Fang, G., et al. 2016, ApJ, 822, L32 Fan, L., Knudsen, K. K., Fogasy, J., & Drouart, G. 2018, ApJ, 856, L5 Fan, L., Knudsen, K. K., Han, Y., & Tan, Q.-h. 2019, ApJ, 887, 74 Feltre, A., Hatziminaoglou, E., Fritz, J., & Franceschini, A. 2012, MNRAS, 426, 120 Feruglio, C., Bongiorno, A., Fiore, F., et al. 2014, A&A, 565, A91 Feruglio, C., Ferrara, A., Bischetti, M., et al. 2017, A&A, 608, A30 Feruglio, C., Fiore, F., Carniani, S., et al. 2018, A&A, 619, A39 Fiore, F., Feruglio, C., Shankar, F., et al. 2017, A&A, 601, A143 Fluetsch, A., Maiolino, R., Carniani, S., et al. 2019, MNRAS, 483, 4586 Fogasy, J., Knudsen, K. K., Drouart, G., Lagos, C. D. P., & Fan, L. 2020, MNRAS, 493, 3744 Fogasy, J., Knudsen, K. K., Lagos, C. D. P., Drouart, G., & Gonzalez-Perez, V. 2017, A&A, 597, A123 Förster Schreiber, N. M., Genzel, R., Bouché, N., et al. 2009, ApJ, 706, 1364 Fudamoto, Y., Ivison, R. J., Oteo, I., et al. 2017, MNRAS, 472, 2028 Gallerani, S., Ferrara, A., Neri, R., & Maiolino, R. 2014, MNRAS, 445, 2848 Genzel, R., Tacconi, L. J., Combes, F., et al. 2012, ApJ, 746, 69 Genzel, R., Tacconi, L. J., Gracia-Carpio, J., et al. 2010, MNRAS, 407, 2091 Genzel, R., Tacconi, L. J., Lutz, D., et al. 2015, ApJ, 800, 20 Glikman, E., Simmons, B., Mailly, M., et al. 2015, ApJ, 806, 218 Greve, T. R., Leonidaki, I., Xilouris, E. M., et al. 2014, ApJ, 794, 142 Griffin, M. J., Abergel, A., Abreu, A., et al. 2010, A&A, 518, L3 Häring, N. & Rix, H.-W. 2004, ApJ, 604, L89 Article number, page 19 of 22 A&A proofs: manuscript no. main Helfand, D. J., White, R. L., & Becker, R. H. 2015, ApJ, 801, 26 Herrera-Camus, R., Janssen, A., Sturm, E., et al. 2020, A&A, 635, A47 Herrera-Camus, R., Tacconi, L., Genzel, R., et al. 2019, ApJ, 871, 37 Högbom, J. A. 1974, A&AS, 15, 417 Hollenbach, D. J. & Tielens, A. G. G. M. 1999, Reviews of Modern Physics, 71, 173 Hopkins, P. F. 2012, MNRAS, 420, L8 Hopkins, P. F., Hernquist, L., Cox, T. J., & Kereš, D. 2008, ApJS, 175, 356 Ivison, R. J., Morrison, G. E., Biggs, A. D., et al. 2008, MNRAS, 390, 1117 Ivison, R. J., Papadopoulos, P. P., Smail, I., et al. 2011, MNRAS, 412, 1913 Jiang, Y.-F., Greene, J. E., & Ho, L. C. 2011, ApJ, 737, L45 Jones, S. F., Blain, A. W., Assef, R. J., et al. 2017, MNRAS, 469, 4565 Kakkad, D., Mainieri, V., Brusa, M., et al. 2017, MNRAS, 468, 4205 Kashikawa, N., Ishizaki, Y., Willott, C. J., et al. 2015, ApJ, 798, 28 Kelly, B. C. 2007, ApJ, 665, 1489 Kennicutt, Robert C., J. 1998, ApJ, 498, 541 Kennicutt, R. C. & Evans, N. J. 2012, ARA&A, 50, 531 Kimball, A. E., Lacy, M., Lonsdale, C. J., & Macquart, J. P. 2015, MNRAS, 452, 88 King, A. & Pounds, K. 2015, ARA&A, 53, 115 Kirkpatrick, A., Sharon, C., Keller, E., & Pope, A. 2019, ApJ, 879, 41 Klamer, I. J., Ekers, R. D., Sadler, E. M., & Hunstead, R. W. 2004, ApJ, 612, L97 Kormendy, J. & Ho, L. C. 2013, ARA&A, 51, 511 Krips, M., Neri, R., & Cox, P. 2012, ApJ, 753, 135 Lamastra, A., Menci, N., Maiolino, R., Fiore, F., & Merloni, A. 2010, MNRAS, 405, 29 Leroy, A. K., Bolatto, A., Gordon, K., et al. 2011, ApJ, 737, 12 Lewis, G. F., Carilli, C., Papadopoulos, P., & Ivison, R. J. 2002, MNRAS, 330, L15 Li, J., Wang, R., Riechers, D., et al. 2020, ApJ, 889, 162 Lupi, A., Volonteri, M., Decarli, R., et al. 2019, MNRAS, 488, 4004 Lusso, E., Comastri, A., Simmons, B. D., et al. 2012, MNRAS, 425, 623 Magdis, G. E., Daddi, E., Béthermin, M., et al. 2012, ApJ, 760, 6 Maiolino, R., Gallerani, S., Neri, R., et al. 2012, MNRAS, 425, L66 Maloney, P. R., Hollenbach, D. J., & Tielens, A. G. G. M. 1996, ApJ, 466, 561 Marconi, A., Risaliti, G., Gilli, R., et al. 2004, MNRAS, 351, 169 Martín-Navarro, I., Brodie, J. P., Romanowsky, A. J., Ruiz-Lara, T., & van de Ven, G. 2018, Nature, 553, 307 Marziani, P. & Sulentic, J. W. 2012, New A Rev., 56, 49 Mashian, N., Sturm, E., Sternberg, A., et al. 2015, ApJ, 802, 81 McDermid, R. M., Alatalo, K., Blitz, L., et al. 2015, MNRAS, 448, 3484 McMullin, J. P., Waters, B., Schiebel, D., Young, W., & Golap, K. 2007, in Astronomical Society of the Pacific Conference Series, Vol. 376, Astronomical Data Analysis Software and Systems XVI, ed. R. A. Shaw, F. Hill, & D. J. Bell, 127 Mechtley, M., Jahnke, K., Windhorst, R. A., et al. 2016, ApJ, 830, 156 Meijerink, R., Kristensen, L. E., Weiß, A., et al. 2013, ApJ, 762, L16 Menci, N., Fiore, F., Feruglio, C., et al. 2019, ApJ, 877, 74 Menci, N., Fiore, F., Puccetti, S., & Cavaliere, A. 2008, ApJ, 686, 219 Menci, N., Gatti, M., Fiore, F., & Lamastra, A. 2014, A&A, 569, A37 Miettinen, O., Delvecchio, I., Smolˇ ci´ c, V., et al. 2017, A&A, 606, A17 Mingozzi, M., Vallini, L., Pozzi, F., et al. 2018, MNRAS, 474, 3640 Mortlock, D. J., Warren, S. J., Venemans, B. P., et al. 2011, Nature, 474, 616 Narayanan, D. & Krumholz, M. R. 2014, MNRAS, 442, 1411 Neeleman, M., Bañados, E., Walter, F., et al. 2019, ApJ, 882, 10 Nguyen, N. H., Lira, P., Trakhtenbrot, B., et al. 2020, arXiv e-prints, arXiv:2003.00525 Pensabene, A., Carniani, S., Perna, M., et al. 2020, A&A, 637, A84 Perna, M., Sargent, M. T., Brusa, M., et al. 2018, A&A, 619, A90 Perrotta, S., Hamann, F., Zakamska, N. L., et al. 2019, MNRAS, 488, 4126 Pilbratt, G. L., Riedinger, J. R., Passvogel, T., et al. 2010, A&A, 518, L1 Planck Collaboration, Ade, P. A. R., Aghanim, N., et al. 2016, A&A, 594, A13 Richings, A. J. & Faucher-Giguère, C.-A. 2018, MNRAS, 478, 3100 Riechers, D. A. 2011, ApJ, 730, 108 Riechers, D. A. 2013, ApJ, 765, L31 Riechers, D. A., Carilli, C. L., Maddalena, R. J., et al. 2011a, ApJ, 739, L32 Riechers, D. A., Hodge, J., Walter, F., Carilli, C. L., & Bertoldi, F. 2011b, ApJ, 739, L31 Saintonge, A., Lutz, D., Genzel, R., et al. 2013, ApJ, 778, 2 Salomé, P., Guélin, M., Downes, D., et al. 2012, A&A, 545, A57 Santini, P., Fontana, A., Grazian, A., et al. 2009, A&A, 504, 751 Sargent, M. T., Daddi, E., Béthermin, M., et al. 2014, ApJ, 793, 19 Sargsyan, L., Lebouteiller, V., Weedman, D., et al. 2012, ApJ, 755, 171 Schramm, M., Rujopakarn, W., Silverman, J. D., et al. 2019, ApJ, 881, 145 Scoville, N., Sheth, K., Aussel, H., et al. 2016, ApJ, 820, 83 Shangguan, J., Ho, L. C., Bauer, F. E., Wang, R., & Treister, E. 2020, ApJS, 247, 15 Shankar, F., Bernardi, M., Richardson, K., et al. 2019, MNRAS, 485, 1278 Shen, Y. 2016, ApJ, 817, 55 Shen, Y., Richards, G. T., Strauss, M. A., et al. 2011, ApJS, 194, 45 Sijacki, D., Springel, V., Di Matteo, T., & Hernquist, L. 2007, MNRAS, 380, 877 Silverman, J. D., Daddi, E., Rodighiero, G., et al. 2015, ApJ, 812, L23 Skrutskie, M. F., Cutri, R. M., Stiening, R., et al. 2006, AJ, 131, 1163 Solomon, P. M. & Vanden Bout, P. A. 2005, ARA&A, 43, 677 Speagle, J. S., Steinhardt, C. L., Capak, P. L., & Silverman, J. D. 2014, ApJS, 214, 15 Stalevski, M., Ricci, C., Ueda, Y., et al. 2016, MNRAS, 458, 2288 Symeonidis, M. 2017, MNRAS, 465, 1401 Tacconi, L. J., Genzel, R., Saintonge, A., et al. 2018, ApJ, 853, 179 Tacconi, L. J., Neri, R., Genzel, R., et al. 2013, ApJ, 768, 74 Talia, M., Pozzi, F., Vallini, L., et al. 2018, MNRAS, 476, 3956 Trakhtenbrot, B., Lira, P., Netzer, H., et al. 2017, ApJ, 836, 8 Trakhtenbrot, B., Netzer, H., Lira, P., & Shemmer, O. 2011, ApJ, 730, 7 Travascio, A., Zappacosta, L., Cantalupo, S., et al. 2020, A&A, 635, A157 Treister, E., Schawinski, K., Urry, C. M., & Simmons, B. D. 2012, ApJ, 758, L39 Urrutia, T., Lacy, M., & Becker, R. H. 2008, ApJ, 674, 80 Vallini, L., Tielens, A. G. G. M., Pallottini, A., et al. 2019, MNRAS, 490, 4502 van de Voort, F. 2017, Astrophysics and Space Science Library, Vol. 430, The Effect of Galactic Feedback on Gas Accretion and Wind Recycling, ed. A. Fox & R. Davé, 301 van der Werf, P. P., Isaak, K. G., Meijerink, R., et al. 2010, A&A, 518, L42 Veilleux, S., Maiolino, R., Bolatto, A. D., & Aalto, S. 2020, A&A Rev., 28, 2 Venemans, B. P., Neeleman, M., Walter, F., et al. 2019, ApJ, 874, L30 Venemans, B. P., Walter, F., Decarli, R., et al. 2017a, ApJ, 837, 146 Venemans, B. P., Walter, F., Decarli, R., et al. 2017b, ApJ, 845, 154 Venemans, B. P., Walter, F., Zschaechner, L., et al. 2016, ApJ, 816, 37 Venturini, S. & Solomon, P. M. 2003, ApJ, 590, 740 Vietri, G., Piconcelli, E., Bischetti, M., et al. 2018, A&A, 617, A81 Villar Martín, M., Perna, M., Humphrey, A., et al. 2020, A&A, 634, A116 Volonteri, M., Capelo, P. R., Netzer, H., et al. 2015, MNRAS, 449, 1470 Wang, R., Wagg, J., Carilli, C. L., et al. 2013, ApJ, 773, 44 Wang, R., Wu, X.-B., Neri, R., et al. 2016, ApJ, 830, 53 Wang, Y.-P., He, W., Yamada, T., et al. 2015, Research in Astronomy and Astrophysics, 15, 673 Weedman, D., Sargsyan, L., Lebouteiller, V., Houck, J., & Barry, D. 2012, ApJ, 761, 184 Weiß, A., Downes, D., Neri, R., et al. 2007, A&A, 467, 955 Whitaker, K. E., van Dokkum, P. G., Brammer, G., & Franx, M. 2012, ApJ, 754, L29 Willott, C. J., Bergeron, J., & Omont, A. 2015, ApJ, 801, 123 Willott, C. J., Bergeron, J., & Omont, A. 2017, ApJ, 850, 108 Willott, C. J., Omont, A., & Bergeron, J. 2013, ApJ, 770, 13 Wolfire, M. G., Hollenbach, D., & McKee, C. F. 2010, ApJ, 716, 1191 Wright, E. L., Eisenhardt, P. R. M., Mainzer, A. K., et al. 2010, AJ, 140, 1868 Wuyts, S., Förster Schreiber, N. M., Wisnioski, E., et al. 2016, ApJ, 831, 149 Wylezalek, D., Zakamska, N. L., Liu, G., & Obied, G. 2016, MNRAS, 457, 745 Yan, L., Tacconi, L. J., Fiolet, N., et al. 2010, ApJ, 714, 100 Yang, C., Omont, A., Beelen, A., et al. 2017, A&A, 608, A144 Yun, M. S. & Carilli, C. L. 2002, ApJ, 568, 88 Zakamska, N. L., Hamann, F., Pâris, I., et al. 2016, MNRAS, 459, 3144 Zanella, A., Daddi, E., Magdis, G., et al. 2018, MNRAS, 481, 1976 Zappacosta, L., Piconcelli, E., Duras, F., et al. 2018, A&A, 618, A28 Article number, page 20 of 22 M. Bischetti et al.: The WISSH QSOs project 1INAF - Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I–34143 Trieste, Italy 2INAF - Osservatorio Astronomico di Roma, Via Frascati 33, I– 00078 Monte Porzio Catone, Italy 3Dipartimento di Matematica e Fisica, Universitá Roma Tre, Via della Vasca Navale 84, 00146, Roma, Italy 4Instituto de Astrofísica de Andalucía (IAA, CSIC), Glorieta de las Astronomía, s/n, E-18008 Granada, Spain 5Departamento de Física Teorica, Facultad de Ciencias, Universidad de Zaragoza, Spain 6European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile 7Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Magrans, E-08193 Barcelona, Spain 8Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Avda Vicuna Mackenna 4860, 8970117 Macul, Santiago, Chile 9Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy 10 INAF - Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Roma, Italy 11 Dpto. de Ciencias Fisicas, Universidad Andres Bello, Campus La Casona, Fernandez Concha 700, 7500912 Santiago, Chile 12 Dipartimento di Fisica e Astronomia, Alma Mater Studiorum Universitá di Bologna, via Gobetti 93/2, 40129 Bologna, Italy 13 INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, 40129 Bologna, Italy 14 Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom 15 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 2, 50125, Firenze, Italy 16 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK 17 Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK 18 Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze, Via G. Sansone 1, 50019, Sesto Fiorentino, Firenze, Italy 19 INAF - Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy 20 Instituto de Astrofísica e Ciências do Espao¸, Universidade de Lisboa, OAL, Tapada da Ajuda, 1349-018, Lisboa, Portugal 21 Centro de Astrobiología (CAB, CSIC-INTA), Dpto. de Astrofísica, Ctra de Ajalvir km 4, 28850, Torrejón de Ardoz, Madrid, Spain 22 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D53121 Bonn, Germany 23 INAF - Istituto di Astrofisica Spaziale e Fisica cosmica Milano, via A. Corti 12, 20133, Milano, Italy Article number, page 21 of 22 A&A proofs: manuscript no. main Appendix: broad-band UV-to-FIR SEDs of WISSH QSOs Fig. 12. Rest-frame SED of the WISSH QSOs considered in this work. In each panel, black symbols indicate the photometric points considered in our modelling. Black circles identify detections while arrows represent 3σupper limits (see Table. 1). Photometric points at λ < 1216Å are not included in the fits due to Lyαabsorption (grey circles). Black curve represents the total best fit model, while blue and orange curves refer to the accretion disk plus torus and cold dust emission, respectively. In the case of J1555+1003, the green curve represents the best-fit template reproducing the near-IR excess (for details, see Duras et al. 2017). Article number, page 22 of 22