High-redshift ( z ≳ 6) quasars are signposts of the earliest supermassive black holes and intense star formation, offering key laboratories for black hole–galaxy evolution at cosmic dawn. While far-infrared studies have revealed large dust reservoirs and strong [C II ] emission, the physical condition and molecular gas content of their interstellar medium (ISM) remain uncertain. We present sensitive Atacama Large Millimeter/submillimeter Array Band 3 observations of the redshifted CO(7–6) and [C I ](2–1) emission lines and the underlying dust continuum in a sample of 18 quasars at z ∼ 6. We detected CO(7–6) in 15/18, [C I ](2–1) in 6/18, and continuum in 13/18 sources. Line luminosities and continuum fluxes were used to estimate molecular gas masses from CO, [C I ], and dust, and a hierarchical Bayesian cross-calibration of all four tracers yielded consistent per-source M H 2 estimates and global conversion factors. Comparison with photodissociation region (PDR) and X-ray dominated region model grids using the L [CII] / L [CI] and L CO(7–6) / L TIR ratios suggests gas densities of n > 10 4 cm −3 and radiation fields of G 0 ∼ 10 3 –10 4 for the subset of sources consistent with PDR solutions, while many quasars fall outside the model parameter space. Additional diagnostics based on the L ′ CO(7 − 6) / L ′ [CI](2 − 1) ratio indicate that a large fraction of the molecular gas resides in a warm and highly excited phase. Together these results suggest that classical PDR heating alone cannot explain the observed line ratios and that additional volumetric processes such as X-ray irradiation, turbulence and shocks, or enhanced cosmic-ray heating likely influence the excitation of the cold ISM. These results demonstrate the power of multi-line diagnostics in revealing the excitation and structure of the cold ISM in early quasar host galaxies and highlight the need for a joint analysis of CO, [C I ], [C II ], and dust emission to fully characterize star formation and heating driven by active galactic nuclei at cosmic dawn.

We present JWST observations of the radio galaxy TGSSJ1530+1049, spectroscopically confirmed at z=4.0. NIRCam images and NIRSpec/IFU spectroscopy (R=2700) show that TGSSJ1530+1049 is part of one of the densest-known structures of continuum and line-emitting objects found at these redshifts. NIRCam images show a number of distinct continuum objects and evidence of interactions traced by diffuse emission, and the NIRSpec IFU cube reveals further strong line emitting regions. We identify six continuum and four additional strong Halpha emitting sources with weaker or no underlying continuum within the 3”x3” IFU field. From spatial alignment with high-resolution radio data and emission line profiles, the radio AGN host galaxy is clearly identified. The bright Halpha emission (but not the optical components) is distributed remarkably linearly along the radio axis, suggestive of a biconical illumination zone by a central obscured AGN. The emission line kinematics indicate jet-gas interactions on scales of a few kpc. However, due to large relative velocities and presence of underlying continuum, the alignment with the radio structure appears to be, at least partly, caused by a particular configuration of interacting galaxies. At least four objects within a 10x10 (projected) kpc^2 area which includes the radio source have high stellar masses (log(M_⋆/M_⊙)>10.3) and star formation rates in the range 70-163 M_⊙ yr^-1. Using a stellar mass-based analysis, we predict a total dark matter halo mass of ≈10^13 M_⊙. Based on the physical separations and velocity differences between the galaxies, it is expected that these galaxies will merge to form a massive galaxy within a few Gyr. The system qualitatively resembles the forming brightest cluster galaxies in cosmological simulations that form early through a rapid succession of mergers.

We present optical and near-infrared (NIR) spectroscopic observations for a sample of 45 quasars at 6.50] is median < SNRJ >=9.7, median < SNRH >=10.3, and median < SNRK >=11.7; demonstrating the good data quality. This work presents the largest medium-/moderate-resolution sample of quasars at z>6.5 from ground-based instruments. Despite the diversity in instrumental set-ups and spectral quality, the data set is uniformly processed and well-characterized, making it ideally suited for several scientific goals, including the study of the quasar proximity zones and damping wings, the Ly alpha forest, the intergalactic medium's metal content, as well as other properties such as the distribution of SMBH masses and Eddington ratios. Our composite spectrum is compared to others at both high and low z from the literature, showing differences in the strengths of many emission lines, probably due to differences in luminosity among the samples, but a consistent continuum slope, which proves that the same spectral features are preserved in quasars at different redshift ranges.

A SPectroscopic survey of bIased halos in the Reionization Era is a quasar legacy survey primarily using JWST to target a sample of 25 z > 6 quasars with NIRCam slitless spectroscopy and imaging. The first study in this series found evidence of a strong overdensity of galaxies around J0305−3150, a luminous quasar at z = 6.61, within a single NIRCam pointing obtained in JWST Cycle 1. Here we present the first results of a JWST Cycle 2 mosaic that covers 35 arcmin ^2 with NIRCam imaging/wide-field slitless spectroscopy of the same field to investigate the spatial extent of the putative protocluster. The F356W grism data target [O iii ]+H β at 5.3 < z < 7 and reveal a population of 124 line emitters down to a flux limit of 1.2 × 10 ^−18 erg s ^−1 cm ^−2 . Fifty-three of these galaxies lie at 6.5 < z < 6.8 spanning 10 cMpc on the sky, corresponding to an overdensity within a 2500 cMpc ^3 volume of 12.5 ± 2.6, anchored by the quasar. Comparing to the [O iii ] luminosity function from the Emission line galaxies and Intergalactic Gas in the Epoch of Reionization project, we find a dearth of faint [O iii ] emitters at log( L /erg s ^−1 ) < 42.3, which we suggest is consistent with either bursty star formation causing galaxies to scatter around the grism detection limit or modest suppression from quasar feedback. While we find a strong filamentary overdensity of [O iii ] emitters consistent with a protocluster, we suggest that we could be insensitive to a population of older, more massive Lyman break galaxies with weak nebular emission on scales >​​​​​​10 cMpc.

We present a stringent measurement of the dust-obscured star formation rate density (SFRD) at z = 4-6 from the ASPIRE JWST Cycle-1 medium and ALMA Cycle-9 large program. We obtained JWST/NIRCam grism spectroscopy and ALMA 1.2 mm continuum map along 25 independent quasar sightlines, covering a total survey area of similar to 35 arcmin2 where we search for dusty star-forming galaxies (DSFGs) at z = 0-7. We identify eight DSFGs in seven fields at z = 4-6 through the detection of H alpha or [O iii] lambda 5008 lines, including fainter lines such as H beta, [O iii] lambda 4960, [N ii] lambda 6585, and [S ii] lambda lambda 6718,6733 for six sources. With this spectroscopically complete DSFG sample at z = 4-6 and negligible impact from cosmic variance (shot noise), we measure the infrared luminosity function (IRLF) down to LIR similar to 2 x 1011 L circle dot. We find flattening of IRLF at z = 4-6 towards the faint end (power-law slope alpha=0.59-0.45+0.39 ). We determine the dust-obscured cosmic SFRD at this epoch to be log[rho SFR,IR/(M circle dot yr-1Mpc-3)]=-1.52-0.13+0.14 . This is significantly higher than previous determinations using ALMA data in the Hubble Ultra Deep Field, which is void of DSFGs at z = 4-6 because of strong cosmic variance (shot noise). We conclude that the majority (66% +/- 7%) of cosmic star formation at z similar to 5 is still obscured by dust. We also discuss the uncertainty of SFRD propagated from far-IR spectral energy distribution and IRLF at the bright end, which will need to be resolved with future ALMA and JWST observations.

We present [NII] 205 μm fine structure line observations of three submillimeter galaxies (SMGs) and three quasar host galaxies at 4≲z≲6 using the Institut de radioastronomie millimetrique (IRAM) interferometer. The [NII] emission is detected in three sources, and we report detections of the underlying dust continuum emission in all sources. The observed [NII]-to-infrared luminosity ratio spans at least 0.5 dex for our sources. Comparing our estimates with sources detected in the [NII] 205 μm at similar redshifts shows that the overall [NII]-to-IR luminosity ratio spans over a dex in magnitude from L_[NII]/L_IR 10^-4 - 10^-5 and follows the trend of the so-called [NII] fine structure line deficit observed in (ultra)-luminous infrared galaxies in the local Universe. The [CII]-to-[NII] luminosity ratio is >10 for most of our sources, indicating that the bulk of the [CII] 158 μm line emission (f([CII]^PDR)>75 neutral medium. From our analysis, we do not find significant differences in the [NII] 205 μm emission and the respective ratios between SMGs and QSOs, suggesting a negligible contribution to the boosting of [NII] 205 μm emission due to the active galactic nucleus (AGN) photoionization. Future investigations involving other fine structure lines and optical diagnostics will provide further insight into a suite of ionized medium properties and reveal the diversity between AGN and non-AGN environments.

We present high-angular resolution (0.068", ~400pc) ALMA imaging of the [CII] line and dust continuum emission of PSO J352.4034-15.3373, a radio-loud quasar at z=5.83. The observations reveal a remarkably close match between the orientation of the [CII] and thermal dust emission mapped by ALMA, and radio synchrotron emission of a radio jet previously mapped by the VLBA. This narrow alignment extends over ~4kpc, reminiscent of the well-studied 'alignment effect' in lower-redshift radio galaxies. The [CII] kinematics show a linear increase in velocity with galactocentric radii up to ~200 km/s at r=2kpc, consistent with bulk motions within the galaxy potential, and not relativistic jet motions. The kinematics and respective morphologies are consistent with a picture in which the relativistic jet injects energy into the interstellar medium (potentially leading to subsequent star formation), giving rise to the observed alignment and significant (> 100 km/s) [CII] velocity dispersion within the host galaxy on kiloparsec scales. Indeed, the astonishingly close alignment and narrow linearity of the radio jet with the [CII] and dust emission are hard to conceive without some fundamental relationship between the two.

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

The temperature of the cold dust in z > 6 galaxies is a potential tracer of the presence of an active galactic nucleus (AGN) and stellar feedback. This is also the dominant source of uncertainty in inferring properties from the far-infrared (FIR) emission of these galaxies. We present the first resolved dust temperature map in a z > 6 quasar host galaxy. We combined new 360 parsec (pc) resolution ALMA Band 9 continuum observations with 190 pc Band 6 observations from the literature to derive the dust temperature and opacity at 0.1 < r < 0.5 kpc scales in a z = 6.9 luminous quasar host galaxy (J2348-3054). We find that the dust temperature (and opacity) increases at the center (r < 216 pc) of the galaxy up to T-d = 73 - 88 K, potentially rising up to T-d < 149 K at r < 110 pc. The combination of the resolved and integrated FIR spectral energy distribution (SED) further reveal a dust temperature gradient and a significant contribution of the AGN hot dust torus at nu(obs) greater than or similar to 700 GHz. By taking into account the torus contribution and resolved optically thick emission, we derived the total IR luminosity (L-TIR = 8.78 +/- 0.10) x 10(12) L-circle dot) and corresponding star formation rate (SFR = 1307 +/- 15 M(circle dot)yr(-1)), which are at least a factor of similar to 3.6 (similar to 0.56 dex) lower than previous measurements based on the assumption of optically thin emission. We compared the resolved dust temperature, mass, and IR luminosity profiles to simulations where they are only reproduced by models that include the AGN radiation heating the dust in the center of the galaxy. Our observations provide evidence that dust in J2348-3054 cannot be assumed to be uniformly cold and optically thin. Whether J2348-3054 is representative of the larger population of high-redshift quasars and galaxies remains to be determined with future dedicated high-resolution and high-frequency ALMA observations.

We present high-angular-resolution (0 . ″ 068, ∼400 pc) Atacama Large Millimeter/submillimeter Array (ALMA) imaging of the [C ii ] line and dust continuum emission of PSO J352.4034–15.3373, a radio-loud quasar at z = 5.83. The observations reveal a remarkably close match between the orientation of the [C ii ] and thermal dust emission mapped by ALMA and radio synchrotron emission of a radio jet previously mapped by the Very Long Baseline Array. This narrow alignment extends over ∼4 kpc, reminiscent of the well-studied “alignment effect” in lower-redshift radio galaxies. The [C ii ] kinematics show a linear increase in velocity with galactocentric radii up to ∼200 km s −1 at r = 2 kpc, consistent with bulk motions within the galaxy potential, and not relativistic jet motions. The kinematics and respective morphologies are consistent with a picture in which the relativistic jet injects energy into the interstellar medium (potentially leading to subsequent star formation), giving rise to the observed alignment and significant (≳100 km s −1 ) [C ii ] velocity dispersion within the host galaxy on kiloparsec scales. Indeed, the astonishingly close alignment and narrow linearity of the radio jet with the [C ii ] and dust emission are hard to conceive without some fundamental relationship between the two.

Understanding the rapid formation of supermassive black holes (SMBHs) in the early universe requires insight into stellar mass growth in host galaxies. Here, we present NIRSpec rest-frame optical spectra and NIRCam imaging from JWST of two galaxies at z>6, both hosting moderate-luminosity quasars. These galaxies exhibit Balmer absorption lines, similar to low-redshift post-starburst galaxies. Our analyses of the medium-resolution spectra and multiband photometry show bulk of the stellar mass (log (M_* / M_sun) > 10.6) formed in starburst episodes at redshift 9 and 7. One of the galaxies shows a clear Balmer break and lacks spatially resolved H alpha emission. It falls well below the star formation main sequence at z = 6, indicating quiescence. The other is transitioning to quiescence; together, these massive galaxies are among the most distant post-starburst systems known. The blueshifted wings of the quasar [O III] emission lines suggest quasar-driven outflow possibly influencing star formation. Direct stellar velocity dispersion measurements reveal one galaxy follows the local black hole mass-sigma_* relation while the other is overmassive. The existence of massive post-starburst galaxies hosting billion-solar-mass BHs in short-lived quasar phases suggests SMBHs and host galaxies played a major role in each other's rapid early formation.

The interaction between radio-jets and quasar host galaxies plays a paramount role in quasar/galaxy co-evolution. However, very little has been known so far about this interaction at very high-z. Here, we present new Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 7 and Band 3 of six radio-loud quasars' host galaxies at $z > 5$. We recover [CII] 158 $\mu$m line and underlying dust continuum emission at $>2\sigma$ for five sources, while we obtain upper limits for the CO(6-5) emission line and continuum for the remaining source. At the spatial resolution of our observations ($\sim$1.0"-1.4"), we do not recover perturbed/extended morphologies or kinematics, signatures of potential mergers. These galaxies already host large quantities of gas, with [CII]-based star formation rates of $30-400 M_{\odot} $yr$^{-1}$. Building their radio/sub-mm spectral energy distributions (SEDs), we find that in at least four cases the 1mm continuum intensity arises from a combination of synchrotron and dust emission, with an initial estimation of synchrotron contribution at 300 GHz of $\gtrsim$10%. We compare the properties of the sources inspected here with a large collection of radio-quiet sources from the literature, as well as a sample of radio-loud quasars from previous studies, at comparable redshift. We recover a potential mild decrease in $L_{\rm [CII]}$ for the radio-loud sources, which might be due to a suppression of the cool gas emission due to the radio-jets. We do not find any [CII]-emitting companion galaxy candidate around the five radio-loud quasars observed in Band 7: given the depth of our dataset, this result is still consistent with that observed around radio-quiet quasars. Further higher-spatial resolution observations, over a larger frequency range, of high-z radio-loud quasars hosts will allow for a better understanding of the physics of such sources.

Relativistic jets are thought to play a crucial role in the formation and evolution of massive galaxies and supermassive black holes. Blazars, which are quasars with jets aligned along our line of sight, provide insights into the jetted population and have been observed up to redshifts of z = 6.1. Here, we report the discovery and multi-wavelength characterization of the blazar VLASS J041009.05-013919.88 at z = 7 (age of the Universe similar to 750 Myr), which is powered by a similar to 7 x 10(8) M-circle dot black hole. The presence of this high-redshift blazar implies a large population of similar but unaligned jetted sources in the early Universe. Our findings suggest two possible scenarios. In one, the jet in J0410-0139 is intrinsically low power but appears highly luminous due to relativistic beaming, suggesting that most ultraviolet-bright quasars at this redshift host jets. Alternatively, if J0410-0139 represents an intrinsically powerful radio source, there should be hundreds to thousands of radio-quiet quasars at z approximate to 7 with properties like those of J0410-0139, a prediction in tension with observed quasar densities based on their ultraviolet luminosity function. These results support the hypothesis that the rapid growth of black holes in the early Universe may be driven by jet-enhanced or obscured super-Eddington accretion, potentially playing a key role in forming massive black holes during the epoch of reionization.

We present 0.'' 026 (140 pc) resolution Atacama Large Millimeter/submillimeter Array observations of [C II] 158 mu m and dust continuum emission of the z = 6.6 quasar J0305-3150, resolved over similar to 300-400 independent resolution elements. The dust continuum emission is compact with similar to 80% recovered within r < 0.'' 3 (1.6 kpc), whereas the [C II] emission profile is composed of a central Gaussian (r < 0.'' 4, i.e., <2.2 kpc) and an extended component (detected up to similar to 10 kpc at >3 sigma). We infer a direct contribution of the quasar to the observed 260 GHz continuum S-nu,S-QSO/S-nu,S-QSO (+ Host) less than or similar to 1%. We report the detection of far-infrared (FIR)-detected star-forming clumps with r < 200 pc and properties similar to that of rest-frame UV-optical clumps reported in the literature. The 200 pc resolved [C II]/FIR ratio follows the global relation with the FIR surface brightness established in low- and high-redshift galaxies, even at the quasar location. We find that dust continuum is emitted in regions of similar to 0.'02- 0.'04 consistent with the size of photodissociation regions (PDRs), whereas 50% of the [C II] originates from larger physical scales (theta greater than or similar to 2 ''). The large-scale [C II] emission presents a velocity gradient aligned with a nearby companion with perturbed kinematics, and misaligned with the kinematics of the small-scale emission. The absence of significant [C II] emission by structures with physical scale less than or similar to 1 kpc implies that [C II] emission is not produced in dense PDRs located at the boundary of giant molecular clouds. We argue instead that [C II] is produced in low-density PDRs in the interstellar medium and diffuse H I gas tidally stripped during the ongoing merger.

We present millimeter observations of the host galaxy of the most distant blazar known, VLASS J041009.05-013919.88 (hereafter J0410-0139) at z = 7, using Atacama Large Millimeter/submillimeter Array (ALMA) and NOrthern Extended Millimeter Array (NOEMA) observations. The ALMA data reveal a (2.02 +/- 0.36) x 10(42) erg s(-1) [C II] 158 mu m emission line at z = 6.9964 with a [C II]-inferred star formation rate (SFR) of 58 +/- 9 M-circle dot yr(-1). We estimate a dynamical mass of M-dyn,[C II(]) = (4.6 +/- 2.0) x 10(9)M(circle dot), implying a black hole mass to host a dynamical mass ratio of 0.15(-0.05)(+0.08). The 238 GHz continuum (rest-frame IR) decreased by similar to 33% from the NOEMA to the ALMA observations taken similar to 10 months apart. The Very Large Array 3-10 GHz radio flux densities showed a similar to 37% decrease in a similar time frame, suggesting a causal connection. At face value, J0410-0139 would have the lowest [CII]-to-IR luminosity ratio of a z > 5.7 quasar reported to date (similar to 10(-4)). However, if only <20% of the measured IR luminosity was due to thermal emission from dust, the [C II]-to-IR luminosity ratio would be typical of (U)LIRGs, and the SFRs derived from [C II] and IR luminosities would be consistent. These results provide further evidence that synchrotron emission significantly contributes to the observed rest-frame IR emission of J0410-0139, similar to what has been reported in some radio-loud active galactic nuclei at z < 1.

We present millimeter observations of the host galaxy of the most distant blazar known, VLASSJ041009.05-013919.88 (hereafter J0410-0139) at z=7, using ALMA and NOEMA observations. The ALMA data reveal a 2e42 erg/s [CII] 158um emission line at z=6.9964 with a [CII]-inferred star-formation rate of 58 Msun/yr. We estimate a dynamical mass of 4.6e9 Msun, implying a black hole mass to host a dynamical mass ratio of 0.15. The 238 GHz continuum (rest-frame IR) decreased by 33 apart. The VLA 3-10 GHz radio flux densities showed a 37 similar time frame, suggesting a causal connection. At face value, J0410-0139 would have the lowest [CII]-to-IR luminosity ratio of a z>5.7 quasar reported to date ( 1e-4). However, if only <20 to thermal emission from dust, the [CII]-to-IR luminosity ratio would be typical of (U)LIRGS, and the star formation rates derived from [CII] and IR luminosities would be consistent. These results provide further evidence that synchrotron emission significantly contributes to the observed rest-frame IR emission of J0410-0139, similar to what has been reported in some radio-loud AGN at z<1.

ABSTRACT We present the high-z quasar candidate archive (HzQCA), summarizing the spectroscopic observations of 207 z ≳ 5 quasar candidates using Keck/LRIS, Keck/MOSFIRE, and Keck/NIRES. We identify 14 candidates as z ∼ 6 quasars, with 10 of them newly reported here and 63 candidates as brown dwarfs. In the remaining sources, 79 candidates are unlikely to be quasars; 2 sources are inconclusive; the others could not be fully reduced or extracted. Based on the classifications, we investigate the distributions of quasars and contaminants in colour space with photometry measurements from DELS (z), VIKING/UKIDSS (YJHKs/YJHK), and unWISE (W1W2). We find that the identified brown dwarfs are consistent with the empirical brown dwarf model that is commonly used in quasar candidate selection methods. To refine spectroscopic confirmation strategies, we simulate synthetic spectroscopy of high-z quasars and contaminants for all three instruments. The simulations utilize the spectroscopic data in HzQCA. We predict the required exposure times for quasar confirmation and propose an optimal strategy for spectroscopic follow-up observations. For instance, we demonstrate that we can identify a mJ = 21.5 at z = 7.6 or a mJ = 23.0 at z = 7.0 within 15 min of exposure time with LRIS. With the publication of the HzQCA, we aim to provide guidance for future quasar surveys and candidate classification.

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 the spatially extended emission of several emission lines (H alpha, H beta, [O III], [N II], [S II], and He II), which we used 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 detected 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 photoionization conditions typical of an Active Galactic Nucleus, the western companion shows minimal dust extinction, low metallicity (Z similar to 0.4 Z(circle dot)), and star formation driven photoionization. The eastern companion shows higher extinction and metallicity (Z similar to 0.8 Z(circle dot)) 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-dyn > 10(11) M-circle dot), it is still rapidly building up by accreting two relatively massive (M-star similar to 10(10) M-circle dot) companion sources. This dataset showcases the power of JWST in exposing the buildup of massive galaxies in the first gigayear of the Universe.

We present rest-frame optical spectroscopy using JWST/NIRSpec IFU for the radio galaxy TN J1338-1942 at z=4.1, one of the most luminous galaxies in the early Universe with powerful extended radio jets. Previous observations showed evidence for strong, large-scale outflows on the basis of its large (~150 kpc) halo detected in Ly-alpha, and high velocity [O II] emission features detected in ground-based IFU data. Our NIRSpec/IFU observations spatially resolve the emission line properties across the host galaxy in great detail. We find at least five concentrations of line emission, coinciding with discrete continuum features previously detected in imaging from HST and JWST, over an extent of ~2'' (~15 kpc). The spectral diagnostics enabled by NIRSpec unambiguously trace the activity of the obscured AGN plus interaction between the interstellar medium and the radio jet as the dominant mechanisms for the ionization state and kinematics of the gas in the system. A secondary region of very high ionization lies at roughly 5 kpc distance from the nucleus, and within the context of an expanding cocoon enveloping the radio lobe, this may be explained by strong shock-ionization of the entrained gas. However, it could also signal the presence of a second obscured AGN, which may also offer an explanation for an intriguing outflow feature seen perpendicular to the radio axis. The presence of a dual SMBH system in this galaxy would support that large galaxies in the early Universe quickly accumulated their mass through the merging of smaller units (each with their own SMBH), at the centers of large overdensities. The inferred black hole mass to stellar mass ratio of 0.01-0.1 for TNJ1338 points to a more rapid assembly of black holes compared to the stellar mass of galaxies at high redshifts, consistent with other recent observations.

We present observations using the Northern Extended Millimetre Array (NOEMA) of CO and H2O emission lines and the underlying dust continuum in two quasars at z similar to 6, i.e., P215-16 at z = 5.78 and J1429+5447 at z = 6.18. Notably, among all published CO spectral line energy distributions (SLEDs) of quasars at z similar to 6, the two systems reveal the highest and the lowest CO levels of excitation, respectively. Our radiative transfer modeling of the CO SLED of P215-16 suggests that the molecular gas heated by active galactic nuclei could be a plausible origin for the high CO excitation. For J1429+5447, we obtain the first well-sampled CO SLED (from transitions from 2-1 to 10-9) of a radio-loud quasar at z greater than or similar to 6. Analysis of the CO SLED suggests that a component from a single photodissociation region could explain the CO excitation in the radio-loud quasar J1429+5447. This work highlights the utility of the CO SLED in uncovering the properties of the interstellar medium in these young quasar-starburst systems at the highest redshift. The diversity of the CO SLEDs reveals the complexities in gas conditions and excitation mechanisms at their early evolutionary stage.