We present JWST/NIRSpec Integral Field Spectroscopy in the rest-frame optical
bands of the system PJ308-21, a quasar at $z=6.2342$ caught as its host galaxy
interacts with companion galaxies. We ...detect spatially extended emission of
several emission lines (H$\alpha$, H$\beta$, OIII, NII, SII, HeII), which
we use to study the properties of the ionized phase of the interstellar medium:
the source and hardness of the photoionizing radiation field, metallicity, dust
reddening, electron density and temperature, and star formation. We also
marginally detect continuum starlight emission associated with the companion
sources. We find that at least two independent satellite galaxies are part of
the system. While the quasar host appears highly enriched and obscured, with
AGN-like photoionization conditions, the western companion shows minimal dust
extinction, low metallicity ($Z\sim0.4$ Z$_\odot$), and star-formation driven
photoionization. The eastern companion shows higher extinction and metallicity
($Z\sim0.8$ Z$_\odot$) compared to the western companion, and it is at least
partially photoionized by the nearby quasar. We do not find any indication of
AGN in the companion sources. Our study shows that while the quasar host galaxy
is already very massive ($M_{\rm dyn}>10^{11}$ M$_\odot$), it is still rapidly
building up by accreting two relatively massive ($M_{\rm star}\sim 10^{10}$
M$_\odot$) companion sources. This dataset showcases the power of JWST in
exposing the build-up of massive galaxies in the first Gyr of the Universe.
Our knowledge of galaxy formation and evolution has incredibly progressed through multi-wavelength observational constraints of the interstellar medium (ISM) of galaxies at all cosmic epochs. ...However, little is known about the physical properties of the more diffuse and lower surface brightness reservoir of gas and dust that extends beyond ISM scales and fills dark matter haloes of galaxies up to their virial radii, the circumgalactic medium (CGM). New theoretical studies increasingly stress the relevance of the latter for understanding the feedback and feeding mechanisms that shape galaxies across cosmic times, whose cumulative effects leave clear imprints into the CGM. Recent studies are showing that a -- so far unconstrained -- fraction of the CGM mass may reside in the cold (T < 1e4 K) molecular and atomic phase, especially in high-redshift dense environments. These gas phases, together with the warmer ionised phase, can be studied in galaxies from z ~ 0 to z ~ 10 through bright far-infrared and sub-millimeter emission lines such as C II 158\({\mu}\)m, O III 88 \({\mu}\)m, C I 609\({\mu}\)m, C I 370\({\mu}\)m, and the rotational transitions of CO. Imaging such hidden cold CGM can lead to a breakthrough in galaxy evolution studies but requires a new facility with the specifications of the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST). In this paper, we use theoretical and empirical arguments to motivate future ambitious CGM observations with AtLAST and describe the technical requirements needed for the telescope and its instrumentation to perform such science.
The identification of bright quasars at z>6 enables detailed studies of supermassive black holes, massive galaxies, structure formation, and the state of the intergalactic medium within the first ...billion years after the Big Bang. We present the spectroscopic confirmation of 55 quasars at redshifts 5.6<z<6.5 and UV magnitudes -24.5<M1450<-28.5 identified in the optical Pan-STARRS1 and near-IR VIKING surveys (48 and 7, respectively). Five of these quasars have been independently discovered in other studies. The quasar sample shows an extensive range of physical properties, including 17 objects with weak emission lines, ten broad absorption line quasars, and five with strong radio emission (radio-loud quasars). There are also a few notable sources in the sample, including a blazar candidate at z=6.23, a likely gravitationally lensed quasar at z=6.41, and a z=5.84 quasar in the outskirts of the nearby (D~3 Mpc) spiral galaxy M81. The blazar candidate remains undetected in NOEMA observations of the CII and underlying emission, implying a star-formation rate <30-70 Msun/yr. A significant fraction of the quasars presented here lies at the foundation of the first measurement of the z~6 quasar luminosity function from Pan-STARRS1 (introduced in a companion paper). The quasars presented here will enable further studies of the high-redshift quasar population with current and future facilities.
We investigate the molecular gas content of z~6 quasar host galaxies using the IRAM / Northern Extended Millimeter Array. We target the 3mm dust continuum, and the line emission from CO(6-5), ...CO(7-6), CI2-1 in 10 infra-red-luminous quasars that have been previously studied in their 1mm dust continuum and CII line emission. We detect CO(7-6) at various degrees of significance in all the targeted sources, thus doubling the number of such detections in z~6 quasars. The 3mm to 1mm flux density ratios are consistent with a modified black body spectrum with a dust temperature \(T_{dust}\)~47 K and an optical depth \(\tau_{\nu}\)=0.2 at the CII frequency. Our study provides us with four independent ways to estimate the molecular gas mass, \(M_{H2}\), in the targeted quasars. This allows us to set constraints on various parameters used in the derivation of molecular gas mass estimates, such as the mass per luminosity ratios \(\alpha_{CO}\) and \(\alpha_{CII}\), the gas-to-dust ratio \(\delta_{g/d}\), and the carbon abundance C/H2. Leveraging either on the dust, CO, CI, or CII emission yields mass estimates of the entire sample in the range \(M_{H2}\)~\(10^{10}\) to \(10^{11}\) M\(_{\odot}\). We compare the observed luminosities of dust, CII, CI, and CO(7-6) with predictions from photo-dissociation and X-ray dominated regions. We find that the former provide better model fits to our data, assuming that the bulk of the emission arises from dense (\(n_H>10^4\) cm\(^{-3}\)) clouds with a column density \(N_{H}\)~\(10^{23}\) cm\(^{-2}\), exposed to a radiation field with intensity \(G_0\)~\(10^3\) (in Habing units). Our analysis reiterates the presence of massive reservoirs of molecular gas fueling star formation and nuclear accretion in \(z\)~6 quasar host galaxies. It also highlights the power of combined 3mm and 1mm observations for quantitative studies of the dense gas content in massive galaxies at cosmic dawn.
State-of-the-art models of massive black hole formation postulate that quasars at \(z>6\) reside in extreme peaks of the cosmic density structure in the early universe. Even so, direct observational ...evidence of these overdensities is elusive, especially on large scales (\(\gg\)1 Mpc) as the spectroscopic follow-up of \(z>6\) galaxies is observationally expensive. Here we present Keck / DEIMOS optical and IRAM / NOEMA millimeter spectroscopy of a \(z\sim6\) Lyman-break galaxy candidate originally discovered via broadband selection, at a projected separation of 4.65 physical Mpc (13.94 arcmin) from the luminous \(z\)=6.308 quasar J1030+0524. This well-studied field presents the strongest indication to date of a large-scale overdensity around a \(z>6\) quasar. The Keck observations suggest a \(z\sim6.3\) dropout identification of the galaxy. The NOEMA 1.2mm spectrum shows a 3.5\(\sigma\) line that, if interpreted as CII, would place the galaxy at \(z\)=6.318 (i.e., at a line-of-sight separation of 3.9 comoving Mpc assuming that relative proper motion is negligible). The measured CII luminosity is \(3\times10^8\) L\(_\odot\), in line with expectations for a galaxy with a star formation rate \(\sim15\) M\(_\odot\) yr\(^{-1}\), as inferred from the rest-frame UV photometry. Our combined observations place the galaxy at the same redshift as the quasar, thus strengthening the overdensity scenario for this \(z>6\) quasar. This pilot experiment demonstrates the power of millimeter-wavelength observations in the characterization of the environment of early quasars.
Ly\(\alpha\) nebulae ubiquitously found around z>2 quasars can supply unique constraints on the properties of the Circumgalactic Medium, such as its density distribution, provided the quasar halo ...mass is known. We present a new method to constrain quasar halo masses based on the line-of-sight velocity dispersion maps of Ly\(\alpha\) nebulae. By using MUSE-like mock observations obtained from cosmological hydrodynamic simulations under the assumption of maximal quasar fluorescence, we show that the velocity dispersion radial profiles of Ly\(\alpha\)-emitting gas are strongly determined by gravity and that they are thus self-similar with respect to halo mass when rescaled by the virial radius. Through simple analytical arguments and by exploiting the kinematics of HeII1640Ȧ emission for a set of observed nebulae, we show that Ly\(\alpha\) radiative transfer effects plausibly do not change the shape of the velocity dispersion profiles but only their normalisation without breaking their self-similarity. Taking advantage of these results, we define the variable \(\eta^{140-200}_{40-100}\) as the ratio of the median velocity dispersion in two specifically selected annuli and derive an analytical relation between \(\eta^{140-200}_{40-100}\) and the halo mass which can be directly applied to observations. We apply our method to 37 observed quasar Ly\(\alpha\) nebulae at 3<z<4.7 and find that their associated quasars are typically hosted by ~\(10^{12.16 \pm 0.14}\) M\(_{\odot}\) haloes independent of redshift within the explored range. This measurement, which is completely independent of clustering methods, is consistent with the lowest mass estimates based on quasar auto-correlation clustering at z~3 and with quasar-galaxies cross-correlation results.
Radio sources at the highest redshifts can provide unique information on the first massive galaxies and black holes, the densest primordial environments, and the epoch of reionization. The number of ...astronomical objects identified at z>6 has increased dramatically over the last few years, but previously only three radio-loud (R2500>10) sources had been reported at z>6, with the most distant being a quasar at z=6.18. Here we present the discovery and characterization of P172+18, a radio-loud quasar at z=6.823. This source has an MgII-based black hole mass of ~3x10^8 Msun and is one of the fastest accreting quasars, consistent with super-Eddington accretion. The ionized region around the quasar is among the largest measured at these redshifts, implying an active phase longer than the average lifetime of the z>6 quasar population. From archival data, there is evidence that its 1.4 GHz emission has decreased by a factor of two over the last two decades. The quasar's radio spectrum between 1.4 and 3.0 GHz is steep (alpha=-1.31) and has a radio-loudness parameter R2500~90. A second steep radio source (alpha=-0.83) of comparable brightness to the quasar is only 23.1" away (~120 kpc at z=6.82; projection probability <2%), but shows no optical or near-infrared counterpart. Further follow-up is required to establish whether these two sources are physically associated.
We present the discovery of PSO J083.8371+11.8482, a weak emission line quasar with extreme star formation rate at \(z=6.3401\). This quasar was selected from Pan-STARRS1, UHS, and unWISE photometric ...data. Gemini/GNIRS spectroscopy follow-up indicates a MgII-based black hole mass of \(M_\mathrm{BH}=\left(2.0^{+0.7}_{-0.4}\right)\times10^9~M_\odot\) and an Eddington ratio of \(L_\mathrm{bol}/L_\mathrm{Edd}=0.5^{+0.1}_{-0.2}\), in line with actively accreting supermassive black hole (SMBH) at \(z\gtrsim6\). HST imaging sets strong constraint on lens-boosting, showing no relevant effect on the apparent emission. The quasar is also observed as a pure point-source with no additional emission component. The broad line region (BLR) emission is intrinsically weak and not likely caused by an intervening absorber. We found rest-frame equivalent widths of EW(Ly\(\alpha\)+NV) \(=5.7\pm0.7\) Angstrom, EW(CIV) \(\leq5.8\) Angstrom (3-sigma upper limit), and EW(MgII) \(=8.7\pm0.7\) Angstrom. A small proximity zone size (\(R_\mathrm{p}=1.2\pm0.4\) pMpc) indicates a lifetime of only \(t_\mathrm{Q}=10^{3.4\pm0.7}\) years from the last quasar phase ignition. ALMA shows extended CII emission with a mild velocity gradient. The inferred far-infrared luminosity (\(L_\mathrm{FIR}=(1.2\pm0.1)\times10^{13}\,L_\odot\)) is one of the highest among all known quasar hosts at \(z\gtrsim6\). Dust and CII emissions put a constraint on the star formation rate of SFR \(=900-4900~M_\odot\,\mathrm{yr^{-1}}\), similar to that of hyper-luminous infrared galaxy. Considering the observed quasar lifetime and BLR formation timescale, the weak-line profile in the quasar spectrum is most likely caused by a BLR which is not yet fully formed rather than continuum boosting by gravitational lensing or a soft continuum due to super-Eddington accretion.
We present JWST/NIRSpec integral field data of the quasar PJ308-21 at \(z=6.2342\). As shown by previous ALMA and HST imaging, the quasar has two companion sources, interacting with the quasar host ...galaxy. The high-resolution G395H/290LP NIRSpec spectrum covers the \(2.87-5.27\ \rm \mu m\) wavelength range and shows the rest-frame optical emission of the quasar with exquisite quality (\(S/N\sim 100-400\) per spectral element). Based on the H\(\beta\) line from the broad line region, we obtain an estimate of the black hole mass \(M_{\rm BH,H\beta}\sim 2.7\times 10^{9}\ \rm M_{\odot}\). This value is within a factor \(\lesssim 1.5\) of the H\(\alpha\)-based black hole mass from the same spectrum (\(M_{\rm BH, H\alpha}\sim 1.93\times 10^{9}\ \rm M_{\odot}\)) and is consistent with a previous estimate relying on the MgII \(\lambda 2799\) (\(M_{\rm BH, MgII}\sim 2.65\times 10^{9}\ \rm M_{\odot}\)). All these \(M_{\rm BH}\) are within the \(\sim 0.5\) dex intrinsic scatter of the adopted mass calibrations. The high Eddington ratio of PJ308-21 \(\lambda_{\rm Edd,H\beta}\sim 0.67\) (\(\lambda_{\rm Edd,H\alpha}\sim 0.96\)) is in line with the overall quasar population at \(z \gtrsim 6\). The relative strengths of the OIII, FeII and H\(\beta\) lines are consistent with the empirical "Eigenvector 1" correlations as observed for low redshift quasars. We find evidence for blueshifted OIII \(\lambda 5007\) emission with a velocity offset \(\Delta v_{\rm OIII}=-1922\pm 39\) km s\(^{-1}\) from the systemic velocity and a \(\rm FWHM(OIII)=2776^{+75}_{-74}\) km s\(^{-1}\). This may be the signature of an outflow from the nuclear region, despite the true values of \(\Delta v_{\rm OIII}\) and \(\rm FWHM(OIII)\) are likely more uncertain due to the blending with H\(\beta\) and FeII lines. Our study demonstrates the unique capabilities of NIRSpec in capturing quasar spectra at cosmic dawn and studying their properties in unprecedented detail.
We present JWST/NIRSpec Integral Field Spectroscopy in the rest-frame optical bands of the system PJ308-21, a quasar at \(z=6.2342\) caught as its host galaxy interacts with companion galaxies. We ...detect spatially extended emission of several emission lines (H\(\alpha\), H\(\beta\), OIII, NII, SII, HeII), which we use to study the properties of the ionized phase of the interstellar medium: the source and hardness of the photoionizing radiation field, metallicity, dust reddening, electron density and temperature, and star formation. We also marginally detect continuum starlight emission associated with the companion sources. We find that at least two independent satellite galaxies are part of the system. While the quasar host appears highly enriched and obscured, with AGN-like photoionization conditions, the western companion shows minimal dust extinction, low metallicity (\(Z\sim0.4\) Z\(_\odot\)), and star-formation driven photoionization. The eastern companion shows higher extinction and metallicity (\(Z\sim0.8\) Z\(_\odot\)) compared to the western companion, and it is at least partially photoionized by the nearby quasar. We do not find any indication of AGN in the companion sources. Our study shows that while the quasar host galaxy is already very massive (\(M_{\rm dyn}>10^{11}\) M\(_\odot\)), it is still rapidly building up by accreting two relatively massive (\(M_{\rm star}\sim 10^{10}\) M\(_\odot\)) companion sources. This dataset showcases the power of JWST in exposing the build-up of massive galaxies in the first Gyr of the Universe.
