arXiv subjects

Xuheng Ding

Publications and source records attributed to Xuheng Ding.

At least 37 records · Page 2Linked to original sources

arXiv2025

HST Confirms Sub-5 kpc Dual Quasar Pairs at Cosmic Noon

During cosmic noon ($z\sim1-3$), when both star formation and black hole growth peaked, galaxy mergers are predicted to trigger dual active galactic nuclei (AGN) that eventually coalesce as supermassive black hole (SMBH) binaries. However, observations of dual quasars with sub-5 kpc separations-the critical phase preceding final coalescence-have remained challenging due to angular resolution limitations. We present the discovery and confirmation of two sub-arcsecond dual quasars at $z>1$, selected from 59,025 SDSS quasars, which fall within the footprint of the Hyper Suprime-Cam Survey. Using high-resolution Hubble Space Telescope (HST) imaging and slitless spectroscopy, we confirmed SDSS J1625+4309 ($z=1.647$, separation 0.55"/4.7 kpc) and SDSS J0229$-$0514 ($z=3.174$, separation 0.42"/3.2 kpc), probing the sub-5 kpc separation regime. Through novel combination of WFC3/IR direct imaging (F140W) and grism spectroscopy (G141), we resolve both components morphologically and spectroscopically confirm their dual nature via detection of H$β$+[OIII] and MgII emission lines in each nucleus. Two-dimensional image decomposition reveals distinct host galaxy morphologies: J1625+4309 shows an extended, disturbed structure ($R_e$=4.7 kpc) indicative of an ongoing major merger, while J0229$-$0514 exhibits a compact host ($R_e$=1.4 kpc) suggesting an advanced coalescence stage. Black hole mass estimates based on virial relations yield M$_{\mathrm{BH}} \sim 10^{8.1}-10^{8.7} M_\odot$ with line-of-sight velocity offsets of $(0.7\pm0.1)\times10^{3}$ km s$^{-1}$ and $(1.0\pm0.2)\times10^{3}$ km s$^{-1}$, respectively. These confirmations directly constrain the frequency and properties of close dual quasars, opening new avenues for studying SMBH mergers at cosmic noon.

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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.

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arXiv2025

SHELLQs-JWST: Revealing the Spectra of Extended Emission in 12 z > 6 Quasar Host Galaxies using the JWST NIRSpec Fixed Slit

We present an analysis of the rest frame optical JWST NIRSpec Fixed Slit spectra of extended host galaxy emission in 12 quasars from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) sample at redshifts 6.0 < z < 6.4. The spatial point spread function is modeled primarily by a sum of two Gaussians as a function of wavelength and is used to fit and subtract the quasar from the 2D spectra, leaving only extended galaxy emission which we analyze. Ten of 12 systems show spatially extended line emission and five of 12 systems show an extended stellar continuum. From the extended [OIII]5008 emission line, we measure a 132 ${\pm}$ 19 km/s ionized outflow in one system and 52 ${\pm}$ 12 km/s rotation, suggesting a coherent disk, in another. From the extended narrow H$α$ emission, which we hypothesize is ionized by star-forming regions rather than the quasar, we measure star formation rates ranging from ${\sim}$ 7 to 111 M${_\odot}$/yr, the majority of which are consistent with the star-forming main sequence at z ${\approx}$ 6. The positions of our host galaxies on the log10[OIII]5008/H$β$ vs. log10[NII]6584/H$α$ (R3N2) Baldwin-Phillips-Terlevich (BPT) diagram indicate ionization rates typical of AGN activity in the low-redshift universe, but are consistent with the placement of similar z ${\approx}$ 6 quasar host galaxies, suggesting that the R3N2 line ratios cannot distinguish AGN and star-formation powered line emission at high redshifts. We conclude from the consistency between our quasar host sample with z ${\sim}$ 6 galaxies that the presence of a low-luminosity AGN causes little significant change in the properties of galaxies at z ${\approx}$ 6 on 10 Myr timescales.

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arXiv2025

Discovery of a Little Red Dot candidate at $z\gtrsim10$ in COSMOS-Web based on MIRI-NIRCam selection

JWST has revealed a new high-redshift population called little red dots (LRDs). Since LRDs may be in the early phase of black hole growth, identifying them in the early universe is crucial for understanding the formation of the first supermassive black holes. However, no robust LRD candidates have been identified at $z>10$, because commonly-used NIRCam photometry covers wavelengths up to $\sim5\,{\rm μm}$ and is insufficient to capture the characteristic V-shaped spectral energy distributions (SEDs) of LRDs. In this study, we present the first search for $z\gtrsim10$ LRD candidates using both NIRCam and MIRI imaging from COSMOS-Web, which provides the largest joint NIRCam-MIRI coverage to date ($0.20\,{\rm deg^2}$). Taking advantage of MIRI/F770W to remove contaminants, we identify one robust candidate, CW-LRD-z10 at $z_{\rm phot}=10.5^{+0.7}_{-0.6}$ with $M_{\rm UV}=-19.9^{+0.1}_{-0.2}\,{\rm mag}$. CW-LRD-z10 exhibits a compact morphology, a distinct V-shaped SED, and a non-detection in F115W, all consistent with being an LRD at $z\sim10$. Based on this discovery, we place the first constraint on the number density of LRDs at $z\sim10$ with $M_{\rm UV}\sim-20$ of $1.2^{+2.7}_{-1.0}\times10^{-6}\,{\rm Mpc^{-3}\,mag^{-1}}$, suggesting that the fraction of LRDs among the overall galaxy population increases with redshift, reaching $\sim3\%$ at $z\sim10$. Although deep spectroscopy is necessary to confirm the redshift and the nature of CW-LRD-z10, our results imply that LRDs may be a common population at $z>10$, playing a key role in the first supermassive black hole formation.

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arXiv2025

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XXIV. 54 New Quasars and Candidate Obscured Quasars at $5.71 \le z \le 7.02$

We present spectroscopic identification of 43 quasars and 11 candidate obscured quasars in the epoch of reionization (EoR) at $5.71 \le z \le 7.02$, along with 29 galaxies at similar redshifts. This is the 24th publication from the Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) imaging survey to search for EoR quasars. The HSC-SSP survey has completed, and this paper is likely the final installment of major (unobscured) quasar discoveries from the SHELLQs project. In addition to the EoR objects, we identified five strong [O III] line emitters at $z < 1$, 30 Galactic brown dwarfs, and 14 passive galaxies at $z \sim 2$, which contaminated our sample of photometric quasar candidates. The present paper focuses on describing the immediate outcome of the spectroscopic observations, while a statistical analysis of the full SHELLQs sample will be presented in our next publication.

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arXiv2025

A PAH deficit in the starburst core of a distant spiral galaxy

We present high-resolution and spatially-matched observations with JWST and ALMA of a starburst galaxy (PACS-830) at $z=1.46$. The NIRCam observations mainly trace the stellar light while the CO ($J$=5--4) observations map the dense molecular gas at kpc scales. Both datasets reveal the morphology to be that of a gas/dust rich bulge with two extending arms, together resembling a grand-design spiral galaxy. The more pronounced arm contributes 21 $\pm$ 6\% of the total CO emission. These results demonstrate that starburst activity at high redshift can be triggered, without undergoing a highly disruptive major merger. We assess the strength and distribution of star formation using two tracers: (1) Polycyclic Aromatic Hydrocarbons (PAHs) emission detected at $8~μ$m ($L_8$) with a MIRI/F1800W image, and (2) $L_\mathrm{IR}$, inferred from the CO ($J$=5--4) map. The spatial profiles of the $L_\mathrm{IR}$ and $L_8$ are dissimilar, thus leading to a significant deficit of mid-IR ($L_8$) emission in the nucleus. We hypothesize that this is due to the destruction of PAH molecules by the intense ionizing radiation field or decreased emission in the photodissociation region, as seen in nearby star-forming regions and consistent with the galaxy-wide properties of distant starbursts. This study reveals spatial variations in the $L_8$ to $L_\mathrm{IR}$ ratio for the first time at $z>1$, in agreement with expectations from theory. Our analysis underscores the pivotal role of joint high-resolution observations with JWST and ALMA in discerning the different phases of the interstellar medium (ISM) and revealing internal physics in galaxy substructures.

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arXiv2025

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.

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arXiv2025

Unveiling Galaxy Structures: Systematic Analysis of Bulge+Disk Decomposition Using Simulated JWST/NIRCam Observations

Characterizing and accurately decomposing galaxies into structural components, such as bulges and disks, is essential for understanding galaxy formation and evolution, particularly at high redshift, where galaxies are compact and faint. Leveraging the unparalleled resolution and sensitivity of JWST and imaging data from CEERs program, we simulate galaxies with bulge+disk components and assess the effectiveness of single and double Sérsic model fittings, respectively. We first evaluate the performance of single Sérsic fits, and find it can recover total magnitudes (i.e., within 0.5 mag), and size (i.e., within 0.2 dex), down to 27 mag. The features that emerged in the residual map can properly reflect the underlying two-component structures. We also show that Sérsic indices can serve as proxies for the bulge-to-total flux ratio (B/T). For double Sérsic models, we find comparable accuracy in recovering bulge and disk magnitudes (i.e., within 0.5 mag), and effective radius (i.e., within 0.2 dex), down to 26 mag. To quantitatively determine whether a double Sérsic model better describes our two-component systems compared to a single Sérsic profile, we evaluate the Bayesian Information Criterion for both model configurations. To extend the applicability of our results to other NIRCam programs, we evaluate the signal-to-noise ratio (SNR) of the simulated galaxies and find that model parameters are reliably reproduced when the SNR exceeds 10. Our work demonstrates the detailed morphological measurement uncertainties using single and double Sérsic models, which provides an essential reference for future JWST/NIRCam-based morphological studies, especially for high-redshift galaxies.

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arXiv2025

COSMOS-Web: Unraveling the Evolution of Galaxy Size and Related Properties at $2<z<10$

We measure galaxy sizes from $2 < z < 10$ using COSMOS-Web, the largest-area JWST imaging survey to date, covering $\sim$0.54 deg$^2$. We analyze the rest-frame optical (~5000A) size evolution and its scaling relation with stellar mass ($R_e\propto M_*^α$) for star-forming and quiescent galaxies. For star-forming galaxies, the slope $α$ remains approximately 0.20 at $2 < z < 8$, showing no significant evolution over this redshift range. At higher redshifts, the slopes are $-0.13 \pm 0.15$ and $0.37 \pm 0.36$ for $8 < z < 9$ and $9 < z < 10$, respectively. At fixed galaxy mass, the size evolution for star-forming galaxies follows $R_e \propto (1+z)^{-β}$, with $β= 1.21 \pm 0.05$. For quiescent galaxies, the slope is steeper $α\sim 0.5$-$0.8$ at $2 < z < 5$, and $β=0.81\pm0.26$. We find that the size-mass relation is consistent between UV and optical at $z < 8$ for star-forming galaxies. However, we observe a decrease in the slope from UV to optical at $z > 8$, with a tentative negative slope in the optical at $8 < z < 9$, suggesting a complex interplay between intrinsic galaxy properties and observational effects such as dust attenuation. We discuss the ratio between galaxies' half-light radius, and underlying halos' virial radius, $R_{vir}$, and find the median value of $R_e/R_{vir}=2.7\%$. The star formation rate surface density evolves as $\logΣ_\text{SFR} = (0.20\pm0.08)\,z+(-0.65\pm0.51)$, and the $Σ_\text{SFR}$-$M_*$ relation remains flat at $2 3$ provides new insights into galaxy size and related properties in the rest-frame optical.

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arXiv2025

Near-IR clumps and their properties in high-z galaxies with JWST/NIRCam

Resolved stellar morphology of $z>1$ galaxies was inaccessible before JWST. This limitation, due to the impact of dust on rest-frame UV light, had withheld major observational conclusions required to understand the importance of clumps in galaxy evolution. Essentially independent of this issue, we use the rest-frame near-IR for a stellar-mass dependent clump detection method and determine reliable estimations of selection effects. We exploit publicly available JWST/NIRCam and HST/ACS imaging data from CEERS, to create a stellar-mass based picture of clumps in a mass-complete sample of 418 galaxies within a wide wavelength coverage of $0.5-4.6\,μ$m and a redshift window of $1 < z < 2$. We find that a near-IR detection gives access to a larger, and possibly different, set of clumps within galaxies, with those also detected in UV making up only $28\%$. Whereas, $85\%$ of the UV clumps are found to have a near-IR counterpart. These near-IR clumps closely follow the UVJ classification of their respective host galaxies, with these hosts mainly populating the star-forming regime besides a fraction of them ($16\%$) that can be considered quiescent. The mass of the detected clumps are found to be within the range of $10^{7.5-9.5}\,\rm M_{\odot}$, therefore expected to drive gas into galaxy cores through tidal torques. The clump stellar mass function is found to have a slope of $-1.50 \pm 0.14$, indicating a hierarchical nature similar to that of star-forming regions in the local Universe. Finally, we observe a radial gradient of increasing clump mass towards the centre of galaxies.

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arXiv2025

A multi-wavelength investigation of spiral structures in $z > 1$ galaxies with JWST

Recent JWST observations have revealed the prevalence of spiral structures at $z > 1$. Unlike in the local Universe, the origin and the consequence of spirals at this epoch remain unexplored. We use public JWST/NIRCam data from the COSMOS-Web survey to map spiral structures in eight massive ($> 10^{10.5}\,\rm M_{\odot}$) star-forming galaxies at $z_{\rm spec} \sim 1.5$. We present a method for systematically quantifying spiral arms at $z>1$, enabling direct measurements of flux distributions. Using rest-frame near-IR images, we construct morphological models accurately tracing spiral arms. We detect offsets ($\sim 0.2 - 0.8\,\rm kpc$) between the rest-frame optical and near-IR flux distributions across most arms. Drawing parallels to the local Universe, we conclude that these offsets reflect the presence of density waves. For nine out of eighteen arms, the offsets indicate spiral shocks triggered by density waves. Five arms have offsets in the opposite direction and are likely associated with tidal interactions. For the remaining cases with no detected offsets, we suggest that stochastic 'clumpy' star formation is the primary driver of their formation. In conclusion, we find a multi-faceted nature of spiral arms at $z > 1$, similar to that in the local Universe.

astro-ph.GA↗

arXiv2025

Clumps as multiscale structures in cosmic noon galaxies

Star-forming clumps have been found to significantly influence the star formation of gas-rich $z>1$ galaxies. Using public data from JWST/NIRCam (COSMOS-Web) and ALMA (FMOS-COSMOS), we study a sample of 32 massive ($>10^{10.5}\,\rm M_{\odot}$) main-sequence galaxies at $z_{\rm spec}\sim1.5$ with $\sim0.3\,\rm kpc$ resolution. We create composite morphological models consisting of bulge, disk, and clumps to fully 'deconstruct' the galaxy images. With the resulting measurements of the flux and size of these components, we find the following: (I)The combined contribution of clumps is $1-30\%$ towards the net star formation rate (SFR) of the host while contributing $1-20\%$ to its stellar mass. The clumps show a correlation between their stellar mass and SFR, but have an increased specific-SFR (sSFR) relative to the star-forming main sequence, with offsets ranging from $0\lesssimΔ\log\rm sSFR\lesssim 0.4$. They feature star formation surface densities of $10^{-2}-10^{2}\,\rm M_{\odot}/yr/kpc^{2}$, consistent with values observed in local star-forming and starburst galaxies. (II)The clumps span a large range of characteristic sizes ($r_{e}\sim0.1-1\,\rm kpc$) and stellar masses ($\sim 10^{8.0-9.5}\,\rm M_{\odot}$). We estimate a mass-size relation ($r_{e}\propto\rm M_{\star}^{\,0.52\pm0.07}$) along with a stellar mass function (slope, $α=-1.85\pm 0.19$), both suggesting a hierarchical nature similar to that expected in star-forming regions in local galaxies. (III)Our measurements agree with the properties of stellar clumps in $z\gtrsim1$ lensed systems, bridging the gap between lensed and unlensed studies by detecting structures at sub-kpc scales.(IV)Clumps are found to be preferentially located along spiral features visible primarily in the residual rest-frame near-IR images. In conclusion, we present an observation-based, coherent picture of star-forming clumps at $z>1$.

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arXiv2024

A new approach to constraining properties of AGN host galaxies by combining image and SED decomposition: testing upon the MBH-M* relation

The outshining light from active galactic nuclei (AGNs) poses significant challenges in studying the properties of AGN host galaxies. To address this issue, we propose a novel approach which combines image decomposition and spectral energy distribution (SED) decomposition to constrain properties of AGN host galaxies. Image decomposition allows us to disentangle optical flux into AGN and stellar components, thereby providing additional constraints on the SED models to derive more refined stellar mass. To test the viability of this approach, we obtained a sample of 24 X-ray selected type-I AGNs with redshifts ranging from 0.73 to 2.47. We estimated the stellar masses for our sample and found that our results are generally consistent with earlier estimates based on different methods. Through examining the posterior distribution of stellar masses, we find that our method could derive better constrained results compared to previous SED decomposition methods. With the derived stellar masses, we further studied the MBH-M* relation of our sample, finding a higher intrinsic scatter in the correlation for our entire sample compared to the local quiescent correlation, which could be caused by a few black hole monsters in our sample. We propose that based on our method, future works could extend to larger samples of high-redshift AGN host galaxies, thereby enhancing our understanding of their properties.

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arXiv2024

Combining Direct Black Hole Mass Measurements and Spatially Resolved Stellar Kinematics to Calibrate the $M_{\rm BH}$-$σ_\star$ 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 $σ_\star$, 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 $σ_\star$ measured across the bulge. Accounting for the different $M_{\rm BH}$ distributions, we demonstrate - for the first time - that AGNs follow the same $M_{\rm BH}$-$σ_\star$ 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.

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arXiv2024

Crimson Behemoth: a Massive Clumpy Structure Hosting a Dusty AGN at $z=4.91$

The current paradigm for the co-evolution of galaxies and their supermassive black holes postulates that dust-obscured active galactic nuclei (AGNs) represent a transitional phase towards a more luminous and unobscured state. However, our understanding of dusty AGNs and their host galaxies at early cosmic times is inadequate due to observational limitations. Here, we present JWST observations of CID-931, an X-ray-detected AGN at a spectroscopic redshift of $z_{\rm spec}=4.91$. Multiband NIRCam imaging from the COSMOS-Web program reveals an unresolved red core, similar to JWST-discovered dusty AGNs. Strikingly, the red core is surrounded by at least eight massive star-forming clumps spread over $1.\!\!^{\prime\prime}6 \approx 10~{\rm kpc}$, each of which has a stellar mass of $10^9-10^{10}M_\odot$ and $\sim0.1-1~{\rm kpc}$ in radius. The whole system amounts to $10^{11}M_\odot$ in stellar mass, higher than typical star-forming galaxies at the same epoch. In this system, gas inflows and/or complex merger events may trigger clump formation and AGN activity thus leading to the rapid formation of a massive galaxy hosting a supermassive black hole. Future follow-up observations will provide new insights into the evolution of the galaxy-black hole relationship during such transitional phases in the early universe.

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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 ($σ_μ=0.30^{+0.14}_{-0.13}$), 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.

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arXiv2024

Strong gravitational lensing by AGNs as a probe of the quasar-host relations in the distant Universe

The tight correlations found between masses of supermassive black holes (SMBHs) and the luminosities, total stellar masses, and velocity dispersions of their host galaxies are often interpreted as a sign of their co-evolution. Studying these correlations across redshift provides a powerful insight into the evolutionary path followed by the quasar and its host galaxy. While the mass of the black hole is accessible from single-epoch spectra, measuring the mass of its host galaxy is challenging as the active nucleus largely overshines its host. Here, we present a technique to probe quasar-host relations beyond the local universe with strong gravitational lensing, hence overcoming the use of stellar population models or velocity dispersion measurements, both prone to degeneracies. We study in detail one of the three known cases of strong lensing by a quasar to accurately measure the mass of its host and to infer a total lensing mass of $\log_{10}(M_{\rm Tot, h}/M_{\odot}) = 10.27^{+0.06}_{-0.07}~$ within the Einstein radius of 1.2 kpc. The lensing measurement is more precise than any other alternative technique and compatible with the local $M_{BH}$-$M_{\star, h}$ scaling relation. The sample of such quasar-galaxy or quasar-quasar lensing systems should reach a few hundreds with Euclid and Rubin-LSST, thus enabling the application of such a method with statistically significant sample sizes.

astro-ph.GA↗

arXiv2024

A Robust Bayesian Meta-Analysis for Estimating the Hubble Constant via Time Delay Cosmography

We propose a Bayesian meta-analysis to infer the current expansion rate of the Universe, called the Hubble constant ($H_0$), via time delay cosmography. Inputs of the meta-analysis are estimates of two properties for each pair of gravitationally lensed images; time delay and Fermat potential difference estimates with their standard errors. A meta-analysis can be appealing in practice because obtaining each estimate from even a single lens system involves substantial human efforts, and thus estimates are often separately obtained and published. Moreover, numerous estimates are expected to be available once the Rubin Observatory starts monitoring thousands of strong gravitational lens systems. This work focuses on combining these estimates from independent studies to infer $H_0$ in a robust manner. The robustness is crucial because currently up to eight lens systems are used to infer $H_0$, and thus any biased input can severely affect the resulting $H_0$ estimate. For this purpose, we adopt Student's $t$ error for the input estimates. We investigate properties of the resulting $H_0$ estimate via two simulation studies with realistic imaging data. It turns out that the meta-analysis can infer $H_0$ with sub-percent bias and about 1% level of coefficient of variation, even when 30% of inputs are manipulated to be outliers. We also apply the meta-analysis to three gravitationally lensed systems to obtain an $H_0$ estimate and compare it with existing estimates. An R package, h0, is publicly available for fitting the proposed meta-analysis.

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