arXiv subjects

Michele Cappellari

Publications and source records attributed to Michele Cappellari.

At least 19 recordsLinked to original sources

arXiv2026

TDCOSMO XXX: Spatially resolved kinematics of the deflectors in time-delay lens systems B1608+656 and SDSSJ1206+4332 from JWST-NIRSpec observation

We present spatially resolved stellar kinematics of the deflector galaxies in two time-delay lens systems, B1608+656 and SDSS J1206+4332, measured from JWST NIRSpec integral field spectroscopy. B1608+656 is a quadruply imaged quasar lensed by a pair of tidally interacting galaxies, the primary deflector (G1) and a close companion (G2), for which we quantified G2's tidal influence on G1 and define a criterion identifying the region where this perturbation is negligible and standard Jeans-equation modeling remains valid. SDSS J1206+4332 is a doubly imaged quasar whose extended host galaxy is itself quadruply imaged by a foreground massive galaxy (G0), accompanied by a fainter perturber (G1). For both systems, we report the first spectroscopic redshift and velocity dispersion measurements of the perturber galaxies. For G2 in B1608+656, we measure {\sigma}_v = 188 +/- 7 (stat.) +/- 2 (sys.) km/s at z = 0.6307, identical to the redshift of the main deflector G1. For G1 in SDSS J1206+4332, we find {\sigma}_v = 100 +/- 21 (stat.) +/- 2 (sys.) km/s at z = 0.7403, slightly lower than the primary deflector G0. The resolved velocity maps of both primary deflectors show clear rotation signatures and we visually classify them as fast or regular rotators. The data products will be made publicly available and will be combined with time delays, lens models, and line-of-sight convergence to measure cosmological parameters in the upcoming TDCOSMO 2026 milestone publication.

astro-ph.GA↗

arXiv2026

TDCOSMO XXIX: JWST/NIRSpec IFU Spatially Resolved Kinematics of Three Time-delay Lenses

Spatially resolved stellar kinematics are critical to the high precision achieved by cosmological probes utilizing time delays of strongly lensed quasars. Combined with high-resolution imaging and lens modeling, dynamical models of the 2D resolved kinematics of the deflector galaxy tightly constrain the mass profile and break the mass-sheet degeneracy, in turn providing tight constraints on the Hubble constant when the time delays are included. We extract stellar kinematics of the deflector galaxies in the quadruply lensed quasar systems HE0435-1223, PG1115+080, and WFI2033-4723 from James Webb Space Telescope Near-Infrared Spectrograph (JWST-NIRSpec) integral field spectroscopy. The kinematic maps reach average per-bin total (statistical and systematic) uncertainties of 6-11%, with average bin-to-bin correlated errors of only $\sim 1.2\%$. The aperture-integrated velocity dispersions are statistically consistent with the values used in the previous TDCOSMO analysis (all within $0.9\sigma$), with their average uncertainty reduced from 3.7% to 2.4% owing to improvements in the data reduction and kinematic-extraction methodology. We classify PG1115+080 as a fast rotator, HE0435-1223 and WFI2033-4723 as slow rotators within the probed radii, and we refine the source redshifts from the kinematics of the lensed host galaxies. Kinematic maps will be combined with time delays, lens models, and line-of-sight convergence estimates to measure cosmological parameters in the upcoming TDCOSMO 2026 milestone publication.

astro-ph.CO↗

arXiv2026

Supermassive black holes in six triaxial galaxies: Insights from SINFONI and MUSE observations

Dynamical modelling can be used to constrain the masses of central black holes; however, modelling massive galaxies is challenging due to their complexity. In this work, we report six new supermassive black hole mass measurements of massive early-type galaxies from stellar kinematics, which were extracted from adaptive optics-assisted SINFONI and MUSE observations. We combine the stellar kinematics with HST photometry to build DYNAMITE triaxial Schwarzschild orbit-superposition models. Our Schwarzschild models can recover the complex triaxial features of the galaxies and constrain the black hole masses of all six galaxies. We find that strong triaxial kinematic features can bias the mass measurements and correct for this effect. The derived black hole masses are (1.14^{+0.41}_{-0.63}) * 10^9 Msun for NGC 3706, (1.19^{+1.34}_{-0.80}) * 10^9$ Msun for NGC 3923, (1.14^{+1.08}_{-0.95}) * 10^9 Msun for NGC 4261, (4.68^{+2.99}_{-4.26}) * 10^8 Msun for NGC 4636, (3.51^{+3.37}_{-2.57}) * 10^9 Msun for IC 4296, and (2.43^{+1.53}_{-1.65}) * 10^9 Msun for IC 4329 at 3sigma confidence level. We compare our measurements with published results from axisymmetric Schwarzschild modelling and with our Jeans Anisotropic Models (JAM), and obtain mostly consistent black hole masses. Most of our black hole mass estimates can be well constrained using only MUSE observations. All of our mass measurements are in agreement with local black hole scaling relations.

astro-ph.GA↗

arXiv2026

TDCOSMO XXV: A "soup-to-nuts" 6.5% $H_0$ measurement $-$ strong lensing and dynamics with a maximally flexible mass sheet

We present a blind time-delay cosmography measurement of the Hubble constant $H_0$ based on the quadruply imaged quasar SDSSJ1433+6007. Our analysis combines deep Hubble Space Telescope imaging, extended time-delay monitoring from the Wendelstein and Maidanak Observatories, and spatially resolved stellar kinematics from the Keck Cosmic Web Imager and Reionization Mapper. We build a robust lens model to reconstruct the mass distribution and high-signal-to-noise kinematic maps to break the mass-sheet degeneracy (MSD), explicitly accounting for the lens galaxy's oblateness, rotation, and anisotropy. Furthermore, we constrain the external convergence ($\kappa_{\rm ext}$) by characterizing the line-of-sight environment using wide-field photometry from the Dark Energy Spectroscopic Instrument (DESI) Legacy Survey data release 10. We incorporate these constraints into our joint lensing and dynamical model, running multiple iterations to estimate random and systematic uncertainties. Accounting for maximal flexibility of the mass-sheet transformation, and assuming a flat $\Lambda$CDM cosmology and an $\Omega_{\rm m, 0}$ prior from DESI data release 2, we infer $H_0 = 73.2^{+4.8}_{-4.7}$ km s$^{-1}$ Mpc$^{-1}$ (a $6.5\%$ precision), and an internal mass-sheet parameter $\lambda_{\rm int}=1.12^{+0.05}_{-0.06}$. Notably, $\lambda_{\rm int}$ is $2\sigma$ away from unity for this system, highlighting the importance of treating it as a free parameter. Our $H_0$ measurement is consistent with the result from our 2025 milestone paper, and it will be included in our next hierarchical analysis to improve the overall precision. Moving forward, the comprehensive pipeline demonstrated herein establishes a robust framework that can be readily applied to future strongly lensed systems to further refine cosmological constraints.

astro-ph.CO↗

arXiv2026

Spatially Resolved Kinematics of SLACS Lens Galaxies. II: Breaking Degeneracies with Lensing and Dynamical Models

We model the dynamical mass density profiles of 14 strong gravitational lens galaxies from the Sloan Lens ACS (SLACS) sample using spatially resolved kinematics obtained from Keck KCWI integral-field spectroscopy. We use the Jeans Anisotropic Modeling (JAM) method, combining 2D kinematic maps with joint constraints from lens models from Hubble Space Telescope imaging. We use informative priors on the anisotropy and intrinsic shape from local galaxies to help break the residual mass-anisotropy degeneracy (MAD). We find nearly isothermal power-law total mass density slopes ($ρ_{\rm tot}\propto r^{-γ}$) for the sample with a mean of $γ= 2.04\pm0.02$ with intrinsic scatter of $0.08^{+0.03}_{-0.02}$. We fit explicitly for deviations from the pure power-law form that are fully sensitive to the mass-sheet degeneracy (MSD) and constrain the value of the mass-sheet parameter $\rm λ_{int}$ for each individual galaxy to an average precision of 5.8%. The mean value of $\rm λ_{int}$ for the sample is $1.01\pm0.03$, with intrinsic scatter of $0.11\pm0.03$. Values of $\rm λ_{int}$ for individual objects and the scatter in the sample are consistent to $1σ$ uncertainty with those found by the Time-Delay COSMOgraphy collaboration's 2025 milestone analysis, which used a spherical analysis of the same dataset, but azimuthally averaged. We thus conclude that on average power-law mass profiles are a good first-order description of the SLACS sample and do not introduce measureable bias in time-delay cosmography. However, our analysis indicates that more flexible mass models should be able to reproduce the highly detailed kinematic datasets more accurately.

astro-ph.GA↗

arXiv2026

TDCOSMO. XXIII. Measurement of the Hubble constant from the doubly lensed quasar HE1104-1805

Time-delay cosmography leverages strongly lensed quasars to measure the Universe's current expansion rate, H_0, independently from other methods. While the latest TDCOSMO results relied mainly on quadruply lensed quasars, doubly lensed systems are far more common and offer precise time delays, potentially enlarging the usable sample by a factor of five and enabling percent-level constraints on H_0. We present the first TDCOSMO analysis of a doubly imaged source, HE1104-1805, including the measurement of the four necessary ingredients. First, by combining 17 years of data from the SMARTS, Euler and WFI telescopes, we measure a time delay of 176.3\pm 10.8 days. Second, using MUSE data, we extract stellar velocity dispersion measurements in three radial bins with up to 5% precision. Third, employing F160W HST imaging for lens modelling and marginalising over various modelling choices, we measure the Fermat potential difference between the images. Fourth, using wide-field imaging, we measure the convergence added by objects not included in the lens modelling. Hence, we measure the time delay distance and the angular diameter distance to the deflector, favouring a power-law mass model over a baryonic and dark matter composite model. The measurement was performed blindly and yielded H_0 = 64.2^{+5.8}_{-5.0} x $λ_{int} km s^{-1} Mpc^{-1}, where λ_{int} is the internal mass sheet degeneracy parameter. This is in agreement with the TDCOSMO-2025 milestone and its precision for λ_{int}=1 is comparable to that obtained with the best-observed quadruply lensed quasars (4-6%). This work is a stepping stone towards a precise measurement of H_0 using a large sample of doubly lensed quasars, supplementing the current sample. The next TDCOSMO milestone paper will include this system in its hierarchical analysis, constraining λ_{int} and H_0 jointly with multiple lenses.

astro-ph.GA↗

arXiv2026

WISDOM Project -- XXVIII. Molecular gas measurement of the supermassive black hole mass of the galaxy NGC 1387

Supermassive black hole (SMBH) masses can be measured using molecular gas kinematics. Here we present high angular resolution ($0.12$ arcsec or $\approx11$ pc) Atacama Large Millimeter/submillimeter Array observations of the $^{12}$CO(2-1) line emission of the early-type galaxy NGC 1387. The observations reveal a face-on, regularly-rotating central molecular gas disc with a diameter of $\approx18$ arcsec ($\approx1.7$ kpc) and a central depression slightly larger than the SMBH sphere of influence. We forward model the CO data cube in a Bayesian framework with the \textsc{Kinematic Molecular Simulation} code, and use \textit{Hubble Space Telescope} data to constrain the stellar gravitational potential contribution to the molecular gas kinematics. We infer a SMBH mass of $1.10^{+1.71}_{-0.95}[\text{stat},3σ]^{+2.45}_{-1.09}[\text{sys}]\times10^8$ M$_\odot$ and a F160W-filter stellar mass-to-light ratio of $0.90^{+0.44}_{-0.35}[\text{stat}, 3σ]^{+0.46}_{-0.36}[\text{sys}]$ M$_\odot$/L$_{\odot,\text{F160W}}$. This SMBH mass is consistent with the SMBH mass -- stellar velocity dispersion relation.

astro-ph.GA↗

arXiv2026

TDCOSMO XXIV. First spatially resolved kinematics of the lens galaxy obtained using JWST-NIRSpec to improve time-delay cosmography

Spatially resolved stellar kinematics has become a key ingredient in time-delay cosmography to break the mass-sheet degeneracy in the mass profile and in turn provide a precise constraint on the Hubble constant and other cosmological parameters. In this paper, we present the first measurements of 2D resolved stellar kinematics for the lens galaxy in the quadruply lensed quasar system RXJ1131$-$1231 using integral field spectroscopy from JWST's Near-Infrared Spectrograph (NIRSpec), marking the first such measurement conducted with JWST. In extracting robust kinematic measurements from this first-of-its-kind dataset, we have made methodological improvements both in the data reduction and kinematic extraction. In our kinematic extraction procedure, we performed joint modeling of the lens galaxy, the quasar, and its host galaxy's contributions in the spectra to deblend the lens galaxy component and robustly constrain its stellar kinematics. Our improved methodological frameworks are released as software pipelines for future use: squirrel, for extracting stellar kinematics, and RegalJumper, for JWST-NIRSpec data reduction. We incorporated additional artifact cleaning beyond the standard JWST pipeline. We compared our measured stellar kinematics from the JWST NIRSpec with previously obtained ground-based measurements from the Keck Cosmic Web Imager integral field unit and find that the two datasets are statistically consistent at a $\sim$1.1$σ$ confidence level. Our measured kinematics will be used in a future study to improve the precision of the Hubble constant measurement.

astro-ph.GA↗

arXiv2026

A general spectral solver for the axisymmetric Jeans equations: fast dynamical modelling of galaxies with arbitrary anisotropy

Axisymmetric Jeans modelling is widely used to infer galaxy mass profiles from integral-field kinematics, but existing implementations maintain tractability by adopting highly restricted anisotropy prescriptions. I present a new spectral method that solves the axisymmetric Jeans equations as a two-dimensional boundary-value problem. Remarkably, this breaks the traditional trade-off between model flexibility and computational cost, accommodating completely general anisotropy distributions $β(r,θ)$ while executing significantly faster than standard restrictive techniques. The method relies on three key choices: (i) solving for the intrinsic dispersion $\overline{v_r^2}$ rather than the rapidly varying pressure $ν\overline{v_r^2}$ to improve numerical conditioning; (ii) working in logarithmic radius to efficiently resolve the large dynamic range of galaxies, uniquely matching scale-free (power-law) regimes; and (iii) imposing a Robin outer boundary condition that enforces the correct asymptotic decay on a finite computational domain. Orbit integrations in realistic galaxy potentials motivate spherical alignment of the velocity ellipsoid as a physically plausible default, though the framework easily adapts to other alignments. Validated against exact analytic benchmarks -- including new analytic Jeans solutions derived herein -- the solver recovers intrinsic second moments with high accuracy, showing radially uniform residuals for power-law tests. In practice, it delivers orders-of-magnitude speed-ups over high-accuracy quadrature schemes and is naturally suited to massive GPU parallelization. Released in the public JamPy package, this enables the routine application of highly general Jeans models to large surveys and the extensive parameter-space exploration required for rigorous uncertainty quantification.

astro-ph.GA↗

arXiv2026

Dynamical Modelling of Galactic Kinematics using Neural Networks

The advent of integral field data has revolutionised the study of galaxy evolution. A key component of this is dynamical modelling methods which have allowed for crucial insights to be made from kinematic data. Despite this importance, most dynamical models make a number of key assumptions which do not hold for real galaxies. These include assumptions about the geometry (axisymmetry or triaxiality), the shape of the velocity ellipsoid, and the shape of the underlying stellar distribution. At the same time, machine learning methods are becoming increasingly powerful, with many applications appearing in astronomy. As a first step towards building new dynamical modelling methods with machine learning, it is important to understand the types of machine learning architectures that are best fit for dynamical modelling. To investigate this, we construct a training set of dynamical models of early-type galaxies using Jeans Anisotropic Modelling (JAM). We then train a neural network on this data using the parameters of JAM and mock photometry as the input. We are able to accurately model JAM galaxies with relatively simple machine learning architectures, leading to a significant speed increase over traditional JAM modelling.

astro-ph.GA↗

arXiv2026

WISDOM project -- XVIII. Molecular gas distributions and kinematics of three megamaser galaxies

The co-evolution of galaxies and supermassive black holes (SMBHs) underpins our understanding of galaxy evolution, but different methods to measure SMBH masses have only infrequently been cross-checked. We attempt to identify targets to cross-check two of the most accurate methods, megamaser and cold molecular gas dynamics. Three promising galaxies are selected from all those with existing megamaser SMBH mass measurements. We present Atacama Large Millimeter/sub-millimeter Array (ALMA) 12CO(2-1) and 230-GHz continuum observations with angular resolutions of about 0.5". Every galaxy has an extended rotating molecular gas disc and 230-GHz continuum source(s), but all also have irregularities and/or non-axisymmetric features: NGC1194 is highly inclined and has disturbed and lopsided central 12CO(2-1) emission; NGC3393 has a nuclear disc with fairly regular but patchy 12CO(2-1) emission with little gas near the kinematic major axis, faint emission in the very centre and two brighter structures reminiscent of a nuclear ring and/or spiral; NGC5765B has a strong bar and very bright 12CO(2-1) emission concentrated along two bisymmetric offset dust lanes and two bisymmetric nuclear spiral arms. 12CO(2-1) and 12CO(3-2) observations with the James Clerk Maxwell Telescope are compared with the ALMA observations. Because of the disturbed gas kinematics and the impractically long integration times required for higher angular resolution observations, none of the three galaxies is suitable for a future SMBH mass measurement. Nonetheless, increasing the number of molecular gas observations of megamaser galaxies is valuable, and the ubiquitous disturbances suggest a link between large-scale gas properties and the existence of megamasers.

astro-ph.GA↗

arXiv2026

MAGNUS III: Mild evolution of the total density slope in massive early-type galaxies since z$\sim$1 from dynamical modeling of MUSE integral-field stellar kinematics

We investigate the total mass density slope evolution in massive early-type galaxies (ETGs) over the last 6.5 billion years ($0 < z < 0.75$). We perform a detailed dynamical analysis of approximately 200 ETGs spanning the redshift range $0.24 < z < 0.75$, utilizing spatially resolved stellar kinematics derived from high signal-to-noise ratio (S/N) MUSE-DEEP spectroscopy and surface brightness models from high-resolution HST imaging. We constrain mass distributions using the Jeans Anisotropic Modeling (JAM) technique coupled with Multi-Gaussian Expansion (MGE) method. To rigorously constrain evolutionary trends, we combine this intermediate-redshift dataset with a local ETG sample ($z \sim 0.05$) from the MaNGA survey. We adopt dynamical constraints for the local sample derived using an identical homogeneous methodology, ensuring a strictly consistent comparison. We found that the total density profiles of the intermediate-redshift ETG sample are approximately isothermal and exhibit a median mass-weighted total density slope, $<γ_{\rm T}>=2.19 \pm 0.01$ at $ =0.44$, which is shallower than the local baseline of $<γ_{\rm T}> = 2.26 \pm 0.01$ at $ =0.04$. This structural shift corresponds to a redshift gradient of $\mathrm{d} γ_{\rm T}/\mathrm{d} z \approx -0.20 \pm 0.03$, detected at $\sim$5-$σ$ significance. We demonstrate that this trend is robust against model assumptions and persists even when restricting the analysis to high-velocity dispersion systems ($σ_e > 150$ km/s). Our findings are consistent with previous lensing-based studies and in tension with cosmological simulations. The observed steepening suggests that dissipative processes, such as gas-rich accretion and mergers, must play a non-negligible role in the late-stage assembly of massive ETGs.

astro-ph.GA↗

arXiv2026

Extending the Frontier of Spatially-Resolved Supermassive Black Hole Mass Measurements to at $1\lesssim z\lesssim2$: Simulations with ELT/MICADO High-Resolution Mass Models and HARMONI Integral-Field Stellar Kinematics

Current spatially resolved kinematic measurements of supermassive black hole (SMBH) masses are largely confined to the local Universe (distances $\lesssim100$ Mpc). We investigate the potential of the Extremely Large Telescope's (ELT) first-light instruments, MICADO and HARMONI, to extend these dynamical measurements to galaxies at redshift $1\lesssim z\lesssim2$. We select a sample of five bright, massive, quiescent galaxies at these redshifts, adopting their Sérsic profiles from HST photometry as their intrinsic surface brightness distributions. Based on these intrinsic models, we generate mock MICADO images using SimCADO and mock HARMONI integral-field spectroscopic data cubes using HSIM. The HARMONI simulations utilize input stellar kinematics derived from Jeans Anisotropic Models (JAM). We then process these mock observations: the simulated MICADO images are fitted with Multi-Gaussian Expansion to derive stellar mass models, and stellar kinematics are extracted from mock HARMONI cubes with pPXF. Finally, these derived stellar mass models and kinematics are used to constrain JAM dynamical models within a Bayesian framework. Our analysis demonstrates that SMBH masses can be recovered with an accuracy of $\sim$10%. We find that MICADO can provide detailed stellar mass models with $\sim$1 hour of on-source exposure. HARMONI requires longer minimum integrations for reliable stellar kinematic measurements of SMBHs. The required on-source time scales with apparent brightness, ranging from 5-7.5 hours for galaxies at $z\approx1$ (F814W, 20-20.5 mag) to 5 hours for galaxies at $1<z\lesssim2$ (F160W, 20.8 mag). These findings highlight the ELT's capability to push the frontier of SMBH mass measurements to $z\approx2$, enabling crucial tests of SMBH-galaxy co-evolution at the top end of the galaxy mass function.

astro-ph.GA↗

arXiv2026

When relics were made: vigorous stellar rotation and low dark matter content in the massive ultra-compact galaxy GS-9209 at z=4.66

JWST uncovered a large number of massive quiescent galaxies (MQGs) at $z>3$, which theoretical models struggle to reproduce. Explaining the number density of such objects requires extremely high conversion efficiency of baryons into stars in early dark matter halos. Using stellar kinematics, we can investigate the processes shaping the mass assembly histories of MQGs. We present high-resolution JWST/NIRSpec integral field spectroscopy of GS-9209, a massive, compact quiescent galaxy at $z=4.66$ ($\log (M_{\ast}/M_{\odot})=10.52 \pm 0.06$, $R_{eff}=220 \pm 20$ pc). Full spectral fitting of the spatially resolved stellar continuum reveals a clear rotational pattern, yielding a spin parameter of $λ_{2R_{eff}}=0.85 \pm 0.10$. This study suggests that at least a fraction of the earliest quiescent galaxies were fast rotators and that quenching was a dynamically gentle process, preserving the stellar disc even in highly compact objects. Using Jeans anisotropic modelling and assuming a NFW profile, we measure a dark matter fraction of $f_{DM} (<2R_{eff}) = 14.5^{+6.0}_{-4.2} \% $. Our findings use stellar kinematics to confirm the massive nature of early quiescent galaxies, previously inferred from stellar population modelling. We suggest that GS-9209 has a similar structure to low-redshift `relic' galaxies. However, unlike relic galaxies which have bottom-heavy initial mass functions (IMF), the dynamically inferred mass-to-light ratio of GS-9209 is consistent with a Milky-Way like IMF. The kinematical properties of GS-9209 are different from those of $z<1$ early-type galaxies and more similar to those of recently quenched post-starburst galaxies at $z>2$.

astro-ph.GA↗

arXiv2026

The Supermassive Black Hole in the Nearby Spiral Galaxy M81: A Robust Mass from JWST/NIRSpec Stellar Dynamics

Despite its proximity, the mass of the supermassive black hole (SMBH) in the spiral galaxy M81 (NGC~3031) has remained uncertain, with previous dynamical measurements being unreliable. We present the first robust stellar-dynamical measurement of its mass using high-resolution, two-dimensional kinematics from JWST/NIRSpec observations of the central $3''\times3''$. By tracing stellar motions in the near-infrared, our data penetrate the obscuring nuclear dust and allow for the separation of stellar light from the non-thermal AGN continuum. We modeled the kinematics using JAM within a Bayesian framework, exploring a comprehensive suite of models that systematically account for uncertainties in the point-spread function, orbital anisotropy, and stellar mass-to-light ratio. This ensemble modeling approach demonstrates that a central dark mass unambiguously drives the central rise in velocity dispersion. The models yield a robust SMBH mass of $M_{\rm BH} = (4.78^{+0.07}_{-0.10})\times10^7$ M$_\odot$. This result resolves a long-standing uncertainty in the mass of M81's black hole and provides a crucial, reliable anchor point for SMBH-galaxy scaling relations.

astro-ph.GA↗

arXiv2026

Measuring the Central Dark Mass in NGC 4258 with JWST/NIRSpec Stellar Kinematics

We present a new stellar dynamical measurement of the supermassive black hole (SMBH) mass in the nearby spiral galaxy NGC 4258, a critical benchmark for extragalactic mass measurements. We use archival JWST/NIRSpec IFU data (G235H/F170LP grating) to extract high-resolution two-dimensional stellar kinematics from the CO bandhead absorption features within the central $3'' \times 3''$. We extract the stellar kinematics after correcting for instrumental artifacts and separating the stellar light from the non-thermal AGN continuum. We employ Jeans Anisotropic Models (JAM) to fit the observed kinematics, exploring a grid of 12 models to systematically test the impact of different assumptions for the point-spread function, stellar mass-to-light ratio ($M/L$) profile, and orbital anisotropy. All 12 models provide broadly acceptable fits, albeit with minor differences. The ensemble median and 68% (1$σ$) bootstrap confidence intervals of our 12 models yield a black hole mass of $M_{\rm BH} = (4.08^{+0.19}_{-0.33}) \times 10^7$ M$_\odot$. This paper showcases the utility of using the full model ensemble to robustly account for systematic uncertainties, rather than relying on formal errors from a single preferred model, as has been common practice. Our result is just 5% larger than, and consistent with, the benchmark SMBH mass derived from water maser dynamics, validating the use of NIRSpec stellar kinematics for robust SMBH mass determination. Our analysis demonstrates JWST's capability to resolve the SMBH's sphere of influence and deliver precise dynamical masses, even in the presence of significant AGN continuum emission.

astro-ph.GA↗

arXiv2026

TDCOSMO XIX. Measuring stellar velocity dispersion with sub-percent accuracy for cosmography

The stellar velocity dispersion ($σ$) of massive elliptical galaxies is a key ingredient in breaking the mass-sheet degeneracy and obtaining precise and accurate cosmography from gravitational time delays. The relative uncertainty on the Hubble constant H$_0$ is double the relative error on $σ$. Therefore, time-delay cosmography imposes much more demanding requirements on the precision and accuracy of $σ$ than galaxy studies. While precision can be achieved with an adequate signal-to-noise ratio (S/N), the accuracy critically depends on key factors such as the elemental abundance and temperature of stellar templates, flux calibration, and wavelength ranges. We carried out a detailed study of the problem using multiple sets of galaxy spectra of massive elliptical galaxies with S/N$\sim$30--160 Å$^{-1}$, along with state-of-the-art empirical and semi-empirical stellar libraries and stellar population synthesis templates. We show that the choice of stellar library is generally the dominant source of residual systematic errors. We propose a general recipe for mitigating and accounting for residual uncertainties. We show that a sub-percent level of accuracy can be achieved on individual spectra with our data quality, which we subsequently validated with simulated mock datasets. The covariance between velocity dispersions measured for a sample of spectra can also be reduced to sub-percent levels. We recommend this recipe for all applications that require high precision and accurate stellar kinematics. Thus, we have made all the software publicly available to facilitate its implementation. This recipe will also be used in future TDCOSMO collaboration papers.

astro-ph.GA↗

arXiv2026

TDCOSMO XXI. Accurate stellar velocity dispersions of the SL2S lens sample and the fundamental plane of the lensing mass

We reanalyzed spectra that were taken as part of the SL2S lens galaxy survey with the goal to obtain the stellar velocity dispersion with a precision and accuracy sufficient for time-delay cosmography. In order to achieve this goal, we imposed stringent cuts on the signal-to-noise ratio (S/N), and employed recently developed methods to mitigate and quantify residual systematic errors that are transferred from template libraries and fitting process. We also quantified the covariance across the sample. For galaxy spectra with S/N $>20/$Å, our new measurements have an average random uncertainty of 3-4\%, an average systematic uncertainty of 2\%, and a covariance across the sample of 1\%. We find a negligible covariance between spectra taken with different instruments. The systematic uncertainty and covariance need to be included when the sample is used as an external dataset in time-delay cosmography. We revisited empirical scaling relations of lens galaxies based on the improved kinematics. We show that the SL2S sample, the TDCOSMO time-delay lens sample, and the lower-redshift SLACS sample follow the same correlation of the effective radius, stellar velocity dispersion, and lensing mass, known as the lensing-mass fundamental plane, as the previously derived correlation that assumed isothermal mass profiles for the deflectors. We also derived for the first time the lensing-mass fundamental plane assuming free power-law mass density profiles, and we show that the three samples also follow the same correlation. This is consistent with a scenario in which massive galaxies evolve by growing their radii and mass, but stay within the plane.

astro-ph.GA↗