arXiv subjects

Knud Jahnke

Publications and source records attributed to Knud Jahnke.

At least 19 recordsLinked to original sources

arXiv2026

SHELLQs. Black Hole Mass and Eddington Ratio Distributions of Intermediate-Luminosity Quasars at 6<z<7

We present near-infrared spectroscopy of 21 quasars at 6.07 < z < 6.90 obtained with JWST/NIRSpec and Subaru/MOIRCS. These targets have absolute ultraviolet magnitudes of -25 < M_1450 < -22 and are drawn from a sample of z>6 quasars identified in the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project. These quasars occupy the intermediate-luminosity regime between luminous quasars and the faint high-redshift AGNs uncovered by JWST. We detect broad Balmer emission lines and MgII 2798 with underlying continua from the NIRSpec and MOIRCS targets, respectively. The virial black hole masses of this sample span a wide range of 7.2 < log M_BH/M_sun < 9.4, with Eddington ratios of -1.3 < log L_bol/L_Edd < 0.4. Combining these measurements with our previous mass estimates for other SHELLQs quasars, we construct a sample of 27 quasars with M_BH estimates at 6 < z < 7 and derive the distributions of M_BH and L_bol/L_Edd. When compared with luminosity-matched quasars at z ~ 1.3, we find median offsets of delta log M_BH/M_sun = -0.4 and Delta log L_bol/L_Edd = 0.2 in the high-redshift sample. In addition, 11% of the high-redshift quasars are accreting near or above the Eddington limit. As a systematic check, adopting the Eddington-ratio-dependent calibration of single-epoch M_BH estimates increases the inferred super-Eddington fraction to 22%. These results indicate that a representative population of distant supermassive black holes undergo a rapid accretion phase, although not as extreme as that seen in the most luminous quasar population, consistent with the anti-hierarchical growth scenario of supermassive black holes.

astro-ph.GA↗

arXiv2026

Spectroscopic confirmation of dual and offset quasars from the Subaru HSC-SSP program

We present a spectroscopic follow-up program targeting closely-separated dual quasar candidates selected from imaging of SDSS quasars with the Subaru Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using two-dimensional image decomposition, our selection identifies PSF-like companions within 0.6-4 arcsec separation (< 30 kpc) around the SDSS quasar. We newly confirm six broad-line dual quasars and eleven offset quasars (quasar-galaxy pairs), spanning 1.5 < z < 3.3 for the duals and predominantly z < 0.6 for the offset systems. No obvious lensed quasars were discovered from this program. We obtained 99 spectra of these candidates from NTT/EFOSC2, Gemini/GMOS-N, Keck/NIRES, and Subaru/FOCAS. From the spectra, we measure the emission-line properties of these dual black holes (BH). At z > 1.5, the confirmed duals exhibit high black hole mass ($M_{\rm BH}$ $=10^{8.5}$-$10^{10} M_{\odot}$) with high bolometric luminosities ($L_{bol}$ $=10^{45.5}$-$10^{47.5}$ erg s$^{-1}$), yet accrete at moderate Eddington ratios ($\lambda_{\rm Edd}=$0.01-0.4). From the spectroscopically-confirmed samples, we estimate the dual fraction of SDSS quasars with separations of 0.6-4 arcsec to be 0.2%-1.2% at z<0.8, 0.08%-0.24% at 0.8<z<1.5, and 0.06% at 1.5<z<3.3. These values are broadly consistent with other recent optical studies, but lower than theoretical expectations of a rising dual fraction at cosmic noon. However, we note that these fractions, especially at high $z$, still need a more accurate assessment of selection and observation effects.

astro-ph.GA↗

arXiv2026

Merger-driven buildup of the $M_{\rm BH}$ - $M_*$ relation bridging high-$z$ overmassive black holes with the local relation

The origin of the mass scaling relation between supermassive black holes (SMBHs, $M_{\rm BH}$) and galaxies ($M_*$) remains a key open question. Rather than invoking AGN feedback, a non-causal mechanism has been proposed in which multiple mergers average out the $M_{\rm BH}/M_*$ ratio, thus decreasing its scatter ($\sigma$) and forming a tight local mass relation over cosmic history. A larger scatter in the relation at higher redshift suggested from a non-causal evolutionary scenario may be evident from recent JWST observations of overmassive SMBHs at high redshift. Here, we carry out a Monte Carlo simulation of solely merger-induced evolution of galaxies and their SMBHs which incorporates recent high-redshift observational constraints on $\sigma$ and the galaxy merger rate. We find that the dispersion in the local mass relation can be reproduced, even when starting from a highly scattered population at $z\sim6$ with $\sigma=0.8\,{\rm dex}$ or $1.0\,{\rm dex}$, which are in agreement with recent JWST studies. The redshift evolution of the scatter is highly sensitive to the mass ratio between merging pairs and the merger rate, and minor mergers with higher frequency than major mergers can also contribute to the scatter evolution, highlighting the importance of accurately constraining these parameters at high redshift through observations. Furthermore, statistical surveys aimed at determining the $M_*$-dependence of $\sigma$ and constraining $\sigma$ at $z\sim3-4$ will be effective in testing this scenario.

astro-ph.GA↗

arXiv2026

The Host Galaxies of Active Galactic Nuclei with Direct Black Hole Mass Measurements

Reverberation mapping (RM) determines the mass of black holes (BH) in active galactic nuclei (AGNs) by resolving the BH gravitational sphere of influence in the time domain. Recent RM campaigns yielded direct BH masses through dynamical modeling for a sample of 32 objects, spanning a wide range of AGN luminosities and BH masses. In addition, accurate BH masses have been determined by spatially resolving the broad-line region with GRAVITY for a handful of AGNs. Here, we present a detailed analysis of Hubble Space Telescope images using surface-brightness profile fitting with state-of-the-art programs. We derive AGN luminosity and host-galaxy properties, such as radii and luminosities for spheroid, disk, and bar (if present). The spheroid effective radii were used to measure stellar velocity dispersion from integral-field spectroscopy. Since the BH masses of our sample do not depend on any assumption of the virial factor needed in single-epoch spectroscopic mass estimates, we can show that the resulting scaling relations between the mass of the supermassive BHs and their host galaxies match those of quiescent galaxies, naturally extending to lower masses in these (predominantly) spiral galaxies. We find that the inner AGN orientation, as traced by the broad-line region inclination angle, is uncorrelated with the host-galaxy disk. Our sample has the most direct and accurate MBH measurements of any AGN sample and provides a fundamental local benchmark for studies of the evolution of massive black holes and their host galaxies across cosmic time.

astro-ph.GA↗

arXiv2025

SHELLQs-JWST perspective on the intrinsic mass relation between supermassive black holes and their host galaxies at z > 6

The relation between the masses of supermassive black holes (SMBHs) and their host galaxies encodes information on their mode of growth, especially at the earliest epochs. The James Webb Space Telescope (JWST) has opened such investigations by detecting the host galaxies of AGN and more luminous quasars within the first billion years of the universe (z > 6). Here, we evaluate the relation between the mass of SMBHs and the total stellar mass of their host galaxies using a sample of nine quasars at 6.18 < z < 6.4 from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey with NIRCam and NIRSpec observations. We find that the observed location of these quasars in the SMBH-galaxy mass plane (log M_BH/Msun ~ 8-9; log M_*/Msun ~ 9.5-11) is consistent with a non-evolving intrinsic mass relation with dispersion (0.80_{-0.28}^{+0.23} dex) higher than the local value (~0.3-0.4 dex) of their more massive descendants. Our analysis is based on a forward model of systematics and includes a consideration of the impact of selection effects and measurement uncertainties with an assumption on the slope of the mass relation. While degeneracies between parameters persist, the best-fit solution has a reasonable AGN fraction (2.3%) of galaxies at z ~ 6 with an actively growing UV-unobscured black hole. In particular, models with a substantially higher normalisation in M_BH would require an unrealistically low intrinsic dispersion (~0.22 dex). Consequently, our results predict a large population of AGNs at lower black hole masses, as are now just starting to be discovered in focused efforts with JWST.

astro-ph.GA↗

arXiv2025

Gravitational Torques from a Lopsided Young Stellar Component Sustain High Black Hole Accretion Rates in NGC 4593

Supermassive black holes (SMBHs) grow primarily through gas accretion, observed as active galactic nuclei (AGNs). While mergers can drive luminous AGN episodes, secular processes may fuel a substantial portion of cosmic BH growth. Whether these mechanisms can sustain high BH accretion rates remains uncertain. This study aims to identify the secular mechanism driving high BH accretion rates, by targeting a galaxy with moderately massive SMBH, high central gas densities, accretion rates of a few percent of the Eddington limit, and gas kinematics resolved close to black hole-dominated scales. A blind search led to the identification of NGC 4593, which is representative of the AGN population driving BH mass density growth since $z=1$. A prominent single-arm ("$m=1$") molecular gas spiral with ${\rm log}\,M_{\rm mol}/{\rm M}_\odot=8.1\pm0.3$ extends from 1.3$\,$kpc down to the SMBH's sphere of influence ($1.7^{+0.5}_{-0.2}\,{\rm pc}$). Star formation in the spiral is inefficient (${\rm SFR} = 4.9 \times 10^{-2} \,{\rm M}_\odot {\rm /yr}$, $\langle t_{\rm dep}\rangle=3.9 \pm 0.6\,\rm{Gyr}$), whereas inflow rate exceeds the SFR by two orders of magnitude and is sufficient to sustain the current BH accretion rate for $\geq$35$\,$Myr, enabling $\sim$10% SMBH growth. A young, lopsided stellar component (${\rm log}\,M_\star/{\rm M}_\odot=7.5-9.3$) exerts torques on the molecular gas, likely driving the gas inflow. This young stellar component may serve as both a cause and a product of sustained gas funnelling towards the SMBH. These findings provide evidence for the sustained secular $m=1$ feeding mode at high BH accretion rates, linking kpc-scale gas dynamics to the black hole's sphere of influence. This mechanism, consistent with simulation predictions, may represent a key contributor to SMBH growth in luminous AGNs since cosmic noon.

astro-ph.GA↗

arXiv2025

SHELLQs-JWST Unveils the Host Galaxies of 12 Quasars at z>6

The advent of JWST has opened new horizons in the study of quasar host galaxies during the reionization epoch (z>6). Building upon our previous initial measurements of stellar light from two quasar host galaxies at these redshifts, we now report the detection of the stellar light from the full Cycle 1 sample of 12 distant moderate-luminosity quasar (M1450>-24 mag) host galaxies at z>6 from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using JWST/NIRCam observations at 1.5 and 3.6 um combined with 2D image decomposition analysis, we successfully detect the host galaxies in 11 of the 12 targets, underscoring the high detection rates achievable with moderate-luminosity quasars. Based on two-band photometry and SED fitting, we find that our host galaxies are massive, with logM*/M_sun = 9.5-11.0. The effective radii range from 0.6 to 3.2 kpc, comparable to the sizes of inactive galaxies with similar masses at z~6 as measured with imaging from COSMOS-Web.Intriguingly, the two quasar hosts with post-starburst features, which reside at the high-mass end of our sample and exhibit relatively compact morphologies, have similar size and stellar mass surface densities to quiescent galaxies at z~4-5. These findings suggest that the so-called galaxy compaction scenario is already in place at the reionization epoch, in which gas inflows during starburst phases drive centrally concentrated star formation followed by rapid quenching, bridging the structural transition of massive galaxies from relatively extended star-forming disks to compact quiescent systems.

astro-ph.GA↗

arXiv2024

The Soltan argument at $z=6$: UV-luminous quasars contribute less than 10% to early black hole mass growth

We combine stellar mass functions and the recent first JWST-based galaxy--black hole scaling relations at $z=6$ to for the first time compute the supermassive black hole (SMBH) mass volume density at this epoch, and compare this to the integrated SMBH mass growth from the population of UV-luminous quasars at $z>6$. We show that even under very conservative assumptions almost all growth of supermassive black hole mass at $z>6$ does not take place in these UV-luminous quasars, but must occur in systems obscured through dust and/or with lower radiative efficiency than standard thin accretion disks. The `Soltan argument' is not fulfilled by the known population of bright quasars at $z>6$: the integrated SMBH mass growth inferred from these largely unobscured active galactic nuclei (AGN) in the early Universe is by a factor $\ge$10 smaller than the total black hole mass volume density at $z=6$. This is valid under a large range of assumption about luminosity and mass functions as well as accretion modes, and is likely still at least a factor $>$2 smaller when accounting for the known obscuration fractions at this epoch. The resulting consequences are: $>$90%, possibly substantially more, of SMBH-buildup in the early Universe does not take place in luminous unobscured quasar phases, but has to occur in obscured systems, with dust absorbing most of the emitted UV--visible AGN emission, potentially with accretion modes with super-Eddington specific accretion rates. This is consistent with short lifetime arguments for luminous quasar phases from quasar proximity zone studies and clustering. This would remove the empirical need for slow SMBH growth and hence exotic `high-mass seed' black holes at early cosmic time. It also predicts a large population of luminous but very obscured lower-mass quasars at $z>6$, possibly the JWST `Little Red Dots'.

astro-ph.GA↗

arXiv2024

Combining Direct Black Hole Mass Measurements and Spatially Resolved Stellar Kinematics to Calibrate the $M_{\rm BH}$-$\sigma_\star$ Relation of Active Galaxies

The origin of the tight scaling relation between the mass of supermassive black holes (SMBHs; $M_{\rm BH}$) and their host-galaxy properties remains unclear. Active galactic nuclei (AGNs) probe phases of ongoing SMBH growth and offer the only opportunity to measure $M_{\rm BH}$ beyond the local Universe. However, determining AGN host galaxy stellar velocity dispersion $\sigma_\star$, and their galaxy dynamical masses $M_{\rm dyn}$, is complicated by AGN contamination, aperture effects and different host galaxy morphologies. We select a sample of AGNs for which $M_{\rm BH}$ has been independently determined to high accuracy by state-of-the-art techniques: dynamical modeling of the reverberation signal and spatially resolving the broad-line region with VLTI/GRAVITY. Using IFU observations, we spatially map the host galaxy stellar kinematics across the galaxy and bulge effective radii. We find that that the dynamically hot component of galaxy disks correlates with $M_{\rm BH}$; however, the correlations are tightest for aperture-integrated $\sigma_\star$ measured across the bulge. Accounting for the different $M_{\rm BH}$ distributions, we demonstrate - for the first time - that AGNs follow the same $M_{\rm BH}$-$\sigma_\star$ and $M_{\rm BH}$-$M_{\rm bulge, dyn}$ relations as quiescent galaxies. We confirm that the classical approach of determining the virial factor as sample-average, yielding ${\rm log }f= 0.65 \pm 0.18$, is consistent with the average $f$ from individual measurements. The similarity between the underlying scaling relations of AGNs and quiescent galaxies implies that the current AGN phase is too short to have altered BH masses on a population level. These results strengthen the local calibration of $f$ for measuring single-epoch $M_{\rm BH}$ in the distant Universe.

astro-ph.GA↗

arXiv2024

A Post-Starburst Pathway for the Formation of Massive Galaxies and Black Holes at z>6

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.

astro-ph.GA↗

arXiv2024

Rich and diverse molecular gas environments of closely-separated dual quasars viewed by ALMA

We present a study of the molecular gas in five closely-spaced ($R_{\perp}<20$ kpc) dual quasars ($L_{\rm bol}\gtrsim10^{44}~\mathrm{erg~s}^{-1}$) at redshifts $0.4<z<0.8$ with the Atacama Large Millimeter/submillimeter Array. The dual quasar phase represents a distinctive stage during the interaction between two galaxies for investigating quasar fueling and feedback effects on the gas reservoir. The dual quasars were selected from the Sloan Digital Sky Survey and Subaru/Hyper Suprime-Cam Subaru Strategic Program, with confirmatory spectroscopic validation. Based on the detection of the CO J=2--1 emission line with Band 4, we derived key properties including CO luminosities, line widths, and molecular gas masses for these systems. Among the ten quasars of the five pairs, eight have line detections exceeding $5\sigma$. The detected sources prominently harbor substantial molecular gas reservoirs, with molecular gas masses ($M_{\text{molgas}}$) between $10^{9.6-10.5}~\mathrm{M_{\odot}}$, and molecular gas-to-stellar mass ratios ($\mu_{\text{molgas}}$) spanning $18-97\%$. The overall $\mu_{\text{molgas}}$ of these dual quasars agrees with that of inactive star-forming main-sequence galaxies at comparable redshifts, indicating no clear evidence of quenching. However, intriguing features in each individual system show possible evidence of AGN feedback, matter transfer, and compaction processes.

astro-ph.GA↗

arXiv2024

Astronomy's climate emissions: Global travel to scientific meetings in 2019

Travel to academic conferences -- where international flights are the norm -- is responsible for a sizeable fraction of the greenhouse gas (GHG) emissions associated with academic work. In order to provide a benchmark for comparison with other fields, as well as for future reduction strategies and assessments, we estimate the CO2-equivalent emissions for conference travel in the field of astronomy for the prepandemic year 2019. The GHG emission of the international astronomical community's 362 conferences and schools in 2019 amounted to 42,500 tCO2e, assuming a radiative-forcing index factor of 1.95 for air travel. This equates to an average of 1.0 $\pm$ 0.6 tCO2e per participant per meeting. The total travel distance adds up to roughly 1.5 Astronomical Units, that is, 1.5 times the distance between the Earth and the Sun. We present scenarios for the reduction of this value, for instance with virtual conferencing or hub models, while still prioritizing the benefits conferences bring to the scientific community.

physics.soc-ph↗

arXiv2024

Tip of the iceberg: overmassive black holes at 4<z<7 found by JWST are not inconsistent with the local $\mathcal{M}_{\rm BH}$-$\mathcal{M}_\star$ relation

JWST is revealing a new remarkable population of high-redshift ($z\gtrsim4$), low-luminosity Active Galactic Nuclei (AGNs) in deep surveys and detecting the host galaxy stellar light in the most luminous and massive quasars at $z\sim 6$ for the first time. Latest results claim supermassive black holes (SMBHs) in these systems to be significantly more massive than expected from the local BH mass - stellar mass ($\mathcal{M}_{\rm BH} - \mathcal{M}_\star$) relation and that this is not due to sample selection effects. Through detailed statistical modeling, we demonstrate that the coupled effects of selection biases (i.e., finite detection limit and requirements on detecting broad lines) and measurement uncertainties in $\mathcal{M}_{\rm BH}$ and $\mathcal{M}_\star$ can in fact largely account for the reported offset and flattening in the observed $\mathcal{M}_{\rm BH} - \mathcal{M}_\star$ relation toward the upper envelope of the local relation, even for those at $\mathcal{M}_{\rm BH} < 10^8\,M_{\odot}$. We further investigate the possible evolution of the $\mathcal{M}_{\rm BH} - \mathcal{M}_\star$ relation at $z\gtrsim 4$ with careful treatment of observational biases and consideration of the degeneracy between intrinsic evolution and dispersion in this relation. The bias-corrected intrinsic $\mathcal{M}_{\rm BH} - \mathcal{M}_\star$ relation in the low-mass regime suggests that there might be a large population of low-mass BHs (${\rm log}\,\mathcal{M}_{\rm BH} \lesssim 5$), possibly originating from lighter seeds, remaining undetected or unidentified even in the deepest JWST surveys. These results have important consequences for JWST studies of BH seeding and the coevolution between SMBHs and their host galaxies at the earliest cosmic times.

astro-ph.GA↗

arXiv2024

Tracing the rise of supermassive black holes: A panchromatic search for faint, unobscured quasars at z > 6 with COSMOS-Web and other surveys

We report the identification of 64 new candidates of compact galaxies, potentially hosting faint quasars with bolometric luminosities of $L_\mathrm{bol} = 10^{43}$--10$^{46}$ erg s$^{-1}$, residing in the reionization epoch within the redshift range of $6 \lesssim z \lesssim 8$. These candidates were selected by harnessing the rich multiband datasets provided by the emerging JWST-driven extragalactic surveys, focusing on COSMOS-Web, as well as JADES, UNCOVER, CEERS, and PRIMER. Our search strategy includes two stages: applying stringent photometric cuts to catalog-level data and detailed spectral energy distribution fitting. These techniques effectively isolate the quasar candidates while mitigating contamination from low-redshift interlopers, such as brown dwarfs and nearby galaxies. The selected candidates indicate physical traits compatible with low-luminosity active galactic nuclei, likely hosting $\approx10^5$--$10^7~M_\odot$ supermassive black holes (SMBHs) living in galaxies with stellar masses of $\approx10^8$--$10^{10}~M_\odot$. The SMBHs selected in this study, on average, exhibit an elevated mass compared to their hosts, with the mass ratio distribution slightly higher than those of galaxies in the local Universe. As with other high-$z$ studies, this is at least in part due to the selection method for these quasars. An extensive Monte Carlo analysis provides compelling evidence that heavy black hole seeds from the direct collapse scenario appear to be the preferred pathway to mature this specific subset of SMBHs by $z\approx7$. This work underscores the significance of further spectroscopic observations, as the quasar candidates presented here offer exceptional opportunities to delve into the nature of the earliest galaxies and SMBHs that formed during cosmic infancy.

astro-ph.GA↗

arXiv2024

The $M_{\rm BH}-M_*$ relation up to $z\sim2$ through decomposition of COSMOS-Web NIRCam images

Our knowledge of relations between supermassive black holes and their host galaxies at $z\gtrsim1$ is still limited, even though being actively sought out to $z\sim6$. Here, we use the high resolution and sensitivity of JWST to measure the host galaxy properties for 107 X-ray-selected type-I AGNs at $0.68<z<2.5$ with rest-frame optical/near-infrared imaging from COSMOS-Web and PRIMER. Black hole masses ($\log\left(M_{\rm BH}/M_\odot\right)\sim6.9-9.6$) are available from previous spectroscopic campaigns. We extract the host galaxy components from four NIRCam broadband images and the HST/ACS F814W image by applying a 2D image decomposition technique. We detect the host galaxy for $\sim90\%$ of the sample after subtracting the unresolved AGN emission. With host photometry free of AGN emission, we determine the stellar mass of the host galaxies to be $\log\left(M_*/M_\odot\right)\sim9.5-11.6$ through SED fitting and measure the evolution of the mass relation between SMBHs and their host galaxies. Considering selection biases and measurement uncertainties, we find that the $M_\mathrm{ BH}/M_*$ ratio evolves as $\left(1+z\right)^{0.48_{-0.62}^{+0.31}}$ thus remains essentially constant or exhibits mild evolution up to $z\sim2.5$. We also see an amount of scatter ($\sigma_{\mu}=0.30^{+0.14}_{-0.13}$), similar to the local relation and consistent with low-$z$ studies, and a non-causal cosmic assembly history where mergers contribute to the statistical averaging towards the local relation is still feasible. We highlight improvements to come with larger samples from JWST and, particularly, Euclid, which will exceed the statistical power of current wide and deep surveys.

astro-ph.GA↗

arXiv2023

Uncovering a Massive z~7.7 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web

In this letter, we report the discovery of the highest redshift, heavily obscured, radio-loud AGN candidate selected using JWST NIRCam/MIRI, mid-IR, sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio observations and mid-IR photometry, we identify a powerful, radio-loud (RL), growing supermassive black hole (SMBH) with significant spectral steepening of the radio SED ($f_{1.28 \mathrm{GHz}} \sim 2$ mJy, $q_{24μm} = -1.1$, $α_{1.28-3\mathrm{GHz}}=-1.2$, $Δα= -0.4$). In conjunction with ALMA, deep ground-based observations, ancillary space-based data, and the unprecedented resolution and sensitivity of JWST, we find no evidence of AGN contribution to the UV/optical/NIR data and thus infer heavy amounts of obscuration (N$_{\mathrm{H}} > 10^{23}$ cm$^{-2}$). Using the wealth of deep UV to sub-mm photometric data, we report a singular solution photo-z of $z_\mathrm{phot}$ = 7.7$^{+0.4}_{-0.3}$ and estimate an extremely massive host-galaxy ($\log M_{\star} = 11.4 -12\,\mathrm{M}_{\odot}$) hosting a powerful, growing SMBH (L$_{\mathrm{Bol}} = 4-12 \times 10^{46}$ erg s$^{-1}$). This source represents the furthest known obscured RL AGN candidate, and its level of obscuration aligns with the most representative but observationally scarce population of AGN at these epochs.

astro-ph.GA↗

arXiv2023

Detection of stellar light from quasar host galaxies at redshifts above 6

The detection of starlight from the host galaxies of quasars during the reionization epoch ($z>6$) has been elusive, even with deep HST observations. The current highest redshift quasar host detected, at $z=4.5$, required the magnifying effect of a foreground lensing galaxy. Low-luminosity quasars from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) mitigate the challenge of detecting their underlying, previously-undetected host galaxies. Here we report rest-frame optical images and spectroscopy of two HSC-SSP quasars at $z>6$ with JWST. Using NIRCam imaging at 3.6$μ$m and 1.5$μ$m and subtracting the light from the unresolved quasars, we find that the host galaxies are massive (stellar masses of $13\times$ and $3.4\times$ $10^{10}$ M$_{\odot}$, respectively), compact, and disk-like. NIRSpec medium-resolution spectroscopy shows stellar absorption lines in the more massive quasar, confirming the detection of the host. Velocity-broadened gas in the vicinity of these quasars enables measurements of their black hole masses ($1.4\times 10^9$ and $2.0\times$ $10^{8}$ M$_{\odot}$, respectively). Their location in the black hole mass - stellar mass plane is consistent with the distribution at low redshift, suggesting that the relation between black holes and their host galaxies was already in place less than a billion years after the Big Bang.

astro-ph.GA↗

arXiv2023

Resolving galactic-scale obscuration of X-ray AGN at $z\gtrsim1$ with COSMOS-Web

A large fraction of the accreting supermassive black hole population is shrouded by copious amounts of gas and dust, particularly in the distant ($z\gtrsim1$) Universe. While much of the obscuration is attributed to a parsec-scale torus, there is a known contribution from the larger-scale host galaxy. Using JWST/NIRCam imaging from the COSMOS-Web survey, we probe the galaxy-wide dust distribution in X-ray selected AGN up to $z\sim2$. Here, we focus on a sample of three AGNs with their host galaxies exhibiting prominent dust lanes, potentially due to their edge-on alignment. These represent 27% (3 out of 11 with early NIRCam data) of the heavily obscured ($N_H>10^{23}$ cm$^{-2}$) AGN population. With limited signs of a central AGN in the optical and near-infrared, the NIRCam images are used to produce reddening maps $E(B-V)$ of the host galaxies. We compare the mean central value of $E(B-V)$ to the X-ray obscuring column density along the line-of-sight to the AGN ($N_H\sim10^{23-23.5}$ cm$^{-2}$). We find that the extinction due to the host galaxy is present ($0.6\lesssim E(B-V) \lesssim 0.9$; $1.9 \lesssim A_V \lesssim 2.8$) and significantly contributes to the X-ray obscuration at a level of $N_H\sim10^{22.5}$ cm$^{-2}$ assuming an SMC gas-to-dust ratio which amounts to $\lesssim$30% of the total obscuring column density. These early results, including three additional cases from CEERS, demonstrate the ability to resolve such dust structures with JWST and separate the different circumnuclear and galaxy-scale obscuring structures.

astro-ph.GA↗