arXiv subjects

Hengyue Zhang

Publications and source records attributed to Hengyue Zhang.

14 recordsLinked to original sources

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

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.

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arXiv2026

WISDOM Project - XXVII. Giant molecular clouds of the lenticular galaxy NGC 1387: similarities with spiral galaxy clouds

Molecular gas is crucial to understanding star formation and galaxy evolution, but the giant molecular clouds (GMCs) of early-type galaxies (ETGs) have rarely been studied. Here, we present analyses of the spatially resolved GMCs of the lenticular galaxy NGC 1387, exploiting high spatial resolution (0.15" or 14 pc) 12CO(2-1) line observations from the Atacama Large Millimeter/submillimeter Array. We identify 1285 individual GMCs and measure the fundamental properties (radius, velocity dispersion, and molecular gas mass) of each with a modified version of the CPROPStoo package. Unusually for an ETG, the GMCs of NGC 1387 follow scaling relations very similar to those of the Milky Way disc and Local Group galaxy clouds, and most are virialised. GMCs with large masses and radii and/or small galactocentric distances have their angular momenta aligned with the large-scale galactic rotation, while other GMCs do not. These results show that ETGs have more diversified GMC properties than previously thought. We discuss potential reasons for such diversity, and viewing-angle dependency is a plausible candidate.

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arXiv2026

Stellar-mass black holes on the millimetre fundamental plane of black hole accretion

Recent work revealed the existence of a galaxy "millimetre fundamental plane of black hole accretion", a tight correlation between nuclear $1$mm luminosity, intrinsic $2$ - $10$keV X-ray luminosity and supermassive black hole mass, originally discovered for nearby low- and high-luminosity active galactic nuclei. Here we use mm and X-ray data of $5$ X-ray binaries (XRBs) to demonstrate that these stellar-mass black holes also lie on the mm fundamental plane, as they do at radio wavelengths. One source for which we have multi-epoch observations shows evidence of deviations from the plane after a state change, suggesting that the plane only applies to XRBs in the hard state, as is true again at radio wavelengths. We show that both advection-dominated accretion flows and compact jet models predict the existence of the plane across the entire range of black hole masses, although these models vary in their ability to accurately predict the XRB black hole masses.

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arXiv2025

Neural Deprojection of Galaxy Stellar Mass Profiles

We introduce a neural approach to dynamical modeling of galaxies that replaces traditional imaging-based deprojections with a differentiable mapping. Specifically, we train a neural network to translate Nuker profile parameters into analytically deprojectable Multi Gaussian Expansion components, enabling physically realistic stellar mass models without requiring optical observations. We integrate this model into SuperMAGE, a differentiable dynamical modelling pipeline for Bayesian inference of supermassive black hole masses. Applied to ALMA data, our approach finds results consistent with state-of-the-art models while extending applicability to dust-obscured and active galaxies where optical data analysis is challenging.

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arXiv2025

WISDOM Project -- XXVI. Cross-checking supermassive black hole mass estimates from ALMA CO gas kinematics and SINFONI stellar kinematics in the galaxy NGC 4751

We present high angular resolution ($0.19''$ or $\approx24$ pc) ALMA observations of the $^{12}$CO(3-2) line emission of the galaxy NGC 4751. The data provide evidence for the presence of a central SMBH. Assuming a constant mass-to-light ratio ($M/L$), we infer a SMBH mass $M_\text{BH}=3.43^{+0.45}_{-0.44}[\text{stat},3σ]^{+0.22}_{-0.64}[\text{sys}]\times10^9$ M$_\odot$ and a F160W filter stellar $M/L_{F160W}=2.68\pm0.11[\text{stat},3σ]^{+0.10}_{-0.80}[\text{sys}]$ M$_\odot$/L$_{\odot,\text{F160W}}$, where the first uncertainties are statistical and the second systematic. Assuming a linearly spatially-varying $M/L$, we infer $M_\text{BH}=2.79^{+0.75}_{-0.57}[\text{stat},3σ]^{+0.75}_{-0.45}[\text{syst}]\times10^9$ M$_\odot$ and $(M/L_\text{F160W})/(\text{M}_\odot/\text{L}_{\odot,\text{F160W}})=3.07^{+0.27}_{-0.35}[\text{stat},3σ]^{+0.08}_{-1.14}[\text{sys}]-0.09^{+0.08}_{-0.06}[\text{stat},3σ]^{+0.08}_{-0.01}[\text{sys}](R/\text{arcsec})$, where $R$ is the galactocentric radius. We also present SMBH mass estimates using the Jeans Anisotropic Modelling (JAM) method and Very Large Telescope Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) stellar kinematics. Assuming a cylindrically-aligned velocity ellipsoid (JAM$_\text{cyl}$) we infer $M_\text{BH}=(2.52\pm 0.36)\times10^9$ M$_\odot$, while assuming a spherically-aligned velocity ellipsoid (JAM$_\text{sph}$) we infer $M_\text{BH}=(3.24\pm0.87)\times10^9$ M$_\odot$. The SMBH mass assuming a constant $M/L$ is statistically consistent with that of JAM$_\text{sph}$, whereas the mass assuming a linearly-varying $M/L$ is consistent with both JAM$_\text{cyl}$ and JAM$_\text{sph}$ (within the uncertainties). Our derived masses are larger than (and inconsistent with) one previous stellar dynamical measurement using the Schwarzschild orbit-superposition method and the same SINFONI kinematics.

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arXiv2025

WISDOM Project -- XXV. Improving the CO-dynamical supermassive black hole mass measurement in the galaxy NGC 1574 using high spatial resolution ALMA observations

We present a molecular gas dynamical supermassive black hole (SMBH) mass measurement in the nearby barred lenticular galaxy NGC 1574, using Atacama Large Millimeter/sub-millimeter Array observations of the $^{12}$CO(2-1) emission line with synthesised beam full-widths at half-maximum of $0.''078\times0.''070$ ($\approx7.5\times6.7$ pc$^2$). The observations are the first to spatially resolve the SMBH's sphere of influence (SoI), resulting in an unambiguous detection of the Keplerian velocity increase due to the SMBH towards the centre of the gas disc. We also detect a previously known large-scale kinematic twist of the CO velocity map, due to a position angle (PA) warp and possible mild non-circular motions, and we resolve a PA warp within the central $0.''2\times0.''2$ of the galaxy, larger than that inferred from previous intermediate-resolution data. By forward modelling the data cube, we infer a SMBH mass of $(6.2\pm1.2)\times10^7$ M$_\odot$ ($1σ$ confidence interval), slightly smaller than but statistically consistent with the SMBH mass derived from the previous intermediate-resolution data that did not resolve the SoI, and slightly outside the $1σ$ scatter of the SMBH mass -- stellar velocity dispersion relation. Our measurement thus emphasises the importance of observations that spatially resolve the SMBH SoI for accurate SMBH mass measurements and gas dynamical modelling.

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arXiv2025

WISDOM project -- XXIII. Star-formation efficiencies of eight early-type galaxies and bulges observed with SITELLE and ALMA

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars with scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. These gas-rich ETGs have properties similar to those of bulges at the centres of spiral galaxies. We use spatially-resolved observations (~ 100 pc resolution) of warm ionised-gas emission lines (Hbeta, [O III], [N II], Halpha and [S II]) from the imaging Fourier transform spectrograph SITELLE at the Canada-France-Hawaii Telescope and cold molecular gas (12CO(2-1) or 12CO(3-2)) from the Atacama Large Millimeter/submillimeter Array (ALMA) to study the SF properties of 8 ETGs and bulges. We use the ionised-gas emission lines to classify the ionisation mechanisms and demonstrate a complete absence of regions dominated by SF ionisation in these ETGs and bulges, despite abundant cold molecular gas. The ionisation classifications also show that our ETGs and bulges are dominated by old stellar populations. We use the molecular gas surface densities and Halpha-derived SF rates (in spiral galaxies outside of the bulges) or upper limits (in ETGs and bulges) to constrain the depletion times (inverse of the SF efficiencies), suggesting again suppressed SF in our ETGs and bulges. Finally, we use the molecular gas velocity fields to measure the gas kinematics, and show that bulge dynamics, particularly the strong shear due to the deep and steep gravitational potential wells, is an important SF-regulation mechanism for at least half of our sample galaxies.

astro-ph.GA↗

arXiv2025

WISDOM Project -- XXII. A 5% precision CO-dynamical supermassive black hole mass measurement in the galaxy NGC 383

We present a measurement of the supermassive black hole (SMBH) mass of the nearby lenticular galaxy NGC 383, based on Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the $^{12}$CO(2-1) emission line with an angular resolution of $0.''050\times0.''024$ ($\approx16\times8$ pc$^2$). These observations spatially resolve the nuclear molecular gas disc down to $\approx41,300$ Schwarzschild radii and the SMBH sphere of influence by a factor of $\approx24$ radially, better than any other SMBH mass measurement using molecular gas to date. The high resolution enables us to probe material with a maximum circular velocity of $\approx1040$ km/s, even higher than those of the highest-resolution SMBH mass measurements using megamasers. We detect a clear Keplerian increase (from the outside in) of the line-of-sight rotation velocities, a slight offset between the gas disc kinematic (i.e. the position of the SMBH) and morphological (i.e. the centre of the molecular gas emission) centres, an asymmetry of the innermost rotation velocity peaks and evidence for a mild position angle warp and/or non-circular motions within the central $\approx0.''3$. By forward modelling the mass distribution and ALMA data cube, we infer a SMBH mass of $(3.58\pm0.19)\times10^9$ M$_\odot$ ($1σ$ confidence interval), more precise ($5\%$) but consistent within $\approx1.4σ$ with the previous measurement using lower-resolution molecular gas data. Our measurement emphasises the importance of high spatial resolution observations for precise SMBH mass determinations.

astro-ph.GA↗

arXiv2024

WISDOM Project -- XIX. Figures of merit for supermassive black hole mass measurements using molecular gas and/or megamaser kinematics

The mass ($M_\mathrm{BH}$) of a supermassive black hole (SMBH) can be measured using spatially-resolved kinematics of the region where the SMBH dominates gravitationally. The most reliable measurements are those that resolve the smallest physical scales around the SMBHs. We consider here three metrics to compare the physical scales probed by kinematic tracers dominated by rotation: the radius of the innermost detected kinematic tracer $R_\mathrm{min}$ normalised by respectively the SMBH's Schwarzschild radius ($R_\mathrm{Schw}\equiv 2GM_\mathrm{BH}/c^2$, where $G$ is the gravitational constant and $c$ the speed of light), sphere-of-influence (SOI) radius ($R_\mathrm{SOI}\equiv GM_\mathrm{BH}/σ_\mathrm{e}^2$, where $σ_\mathrm{e}$ is the stellar velocity dispersion within the galaxy's effective radius) and equality radius [the radius $R_\mathrm{eq}$ at which the SMBH mass equals the enclosed stellar mass, $M_\mathrm{BH}=M_*(R_\mathrm{eq})$, where $M_*(R)$ is the stellar mass enclosed within the radius $R$]. All metrics lead to analogous simple relations between $R_\mathrm{min}$ and the highest circular velocity probed $V_\mathrm{c}$. Adopting these metrics to compare the SMBH mass measurements using molecular gas kinematics to those using megamaser kinematics, we demonstrate that the best molecular gas measurements resolve material that is physically closer to the SMBHs in terms of $R_\mathrm{Schw}$ but is slightly farther in terms of $R_\mathrm{SOI}$ and $R_\mathrm{eq}$. However, molecular gas observations of nearby galaxies using the most extended configurations of the Atacama Large Millimeter/sub-millimeter Array can resolve the SOI comparably well and thus enable SMBH mass measurements as precise as the best megamaser measurements.

astro-ph.GA↗

arXiv2023

A fundamental plane of black hole accretion at millimetre wavelengths

We report the discovery of the ``mm fundamental plane of black-hole accretion'', which is a tight correlation between the nuclear 1 mm luminosity ($L_{\rm ν, mm}$), the intrinsic $2$ -- $10$~keV X-ray luminosity ($L_{\rm X,2-10}$) and the supermassive black hole (SMBH) mass ($M_{\rm BH}$) with an intrinsic scatter ($σ_{\rm int}$) of $0.40$ dex. The plane is found for a sample of 48 nearby galaxies, most of which are low-luminosity active galactic nuclei (LLAGN). Combining these sources with a sample of high-luminosity (quasar-like) nearby AGN, we find that the plane still holds. We also find that $M_{\rm BH}$ correlates with $L_{\rm ν, mm}$ at a highly significant level, although such correlation is less tight than the mm fundamental plane ($σ_{\rm int}=0.51$ dex). Crucially, we show that spectral energy distribution (SED) models for both advection-dominated accretion flows (ADAFs) and compact jets can explain the existence of these relations, which are not reproduced by the standard torus-thin accretion disc models usually associated to quasar-like AGN. The ADAF models reproduces the observed relations somewhat better than those for compact jets, although neither provides a perfect prediction. Our findings thus suggest that radiatively-inefficient accretion processes such as those in ADAFs or compact (and thus possibly young) jets may play a key role in both low- and high-luminosity AGN. This mm fundamental plane also offers a new, rapid method to (indirectly) estimate SMBH masses.

astro-ph.GA↗

arXiv2023

WISDOM Project -- XVII. Beam-by-beam Properties of the Molecular Gas in Early-type Galaxies

We present a study of the molecular gas of seven early-type galaxies with high angular resolution data obtained as part of the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) project with the Atacama Large Millimeter/submillimeter Array. Using a fixed spatial scale approach, we study the mass surface density ($Σ$) and velocity dispersion ($σ$) of the molecular gas on spatial scales ranging from $60$ to $120$pc. Given the spatial resolution of our data ($20$ - $70$pc), we characterise these properties across many thousands of individual sight lines ($\approx50,000$ at our highest physical resolution). The molecular gas along these sight lines has a large range ($\approx2$dex) of mass surface densities and velocity dispersions $\approx40\%$ higher than those of star-forming spiral galaxies. It has virial parameters $α_\mathrm{vir}$ that depend weakly on the physical scale observed, likely due to beam smearing of the bulk galactic rotation, and is generally super-virial. Comparing the internal turbulent pressure ($P_\mathrm{turb}$) to the pressure required for dynamic equilibrium ($P_\mathrm{DE}$), the ratio $P_\mathrm{turb}$/$P_\mathrm{DE}$ is significantly less than unity in all galaxies, indicating that the gas is not in dynamic equilibrium and is strongly compressed, in apparent contradiction to the virial parameters. This may be due to our neglect of shear and tidal forces, and/or the combination of three-dimensional and vertical diagnostics. Both $α_\mathrm{vir}$ and $P_\mathrm{turb}$ anti-correlate with the global star-formation rate of our galaxies. We therefore conclude that the molecular gas in early-type galaxies is likely unbound, and that large-scale dynamics likely plays a critical role in its regulation. This contrasts to the giant molecular clouds in the discs of late-type galaxies, that are much closer to dynamical equilibrium.

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arXiv2023

Dynamical Masses and Ages of Sirius-like Systems

We measure precise orbits and dynamical masses and derive age constraints for six confirmed and one candidate Sirius-like systems, including the Hyades member HD 27483. Our orbital analysis incorporates radial velocities, relative astrometry, and Hipparcos-Gaia astrometric accelerations. We constrain the main-sequence lifetime of a white dwarf's progenitor from the remnant's dynamical mass and semi-empirical initial-final mass relations and infer the cooling age from mass and effective temperature. We present new relative astrometry of HD 27483 B from Keck/NIRC2 observations and archival HST data, and obtain the first dynamical mass of ${0.798}_{-0.041}^{+0.10}$ $M_{\odot}$, and an age of ${450}_{-180}^{+570}$ Myr, consistent with previous age estimates of Hyades. We also measure precise dynamical masses for HD 114174 B ($0.591 \pm 0.011$ $M_{\odot}$) and HD 169889 B (${0.526}_{-0.037}^{+0.039}$ $M_{\odot}$), but their age precisions are limited by their uncertain temperatures. For HD 27786 B, the unusually small mass of $0.443 \pm 0.012$ $M_{\odot}$ suggests a history of rapid mass loss, possibly due to binary interaction in its progenitor's AGB phase. The orbits of HD 118475 and HD 136138 from our RV fitting are overall in good agreement with Gaia DR3 astrometric two-body solutions, despite moderate differences in the eccentricity and period of HD 136138. The mass of ${0.580}_{-0.039}^{+0.052}$ $M_{\odot}$ for HD 118475 B and a speckle imaging non-detection confirms that the companion is a white dwarf. Our analysis shows examples of a rich number of precise WD dynamical mass measurements enabled by Gaia DR3 and later releases, which will improve empirical calibrations of the white dwarf initial-final mass relation.

astro-ph.SR↗

arXiv2021

Cleaning Images with Gaussian Process Regression

Many approaches to astronomical data reduction and analysis cannot tolerate missing data: corrupted pixels must first have their values imputed. This paper presents astrofix, a robust and flexible image imputation algorithm based on Gaussian Process Regression (GPR). Through an optimization process, astrofix chooses and applies a different interpolation kernel to each image, using a training set extracted automatically from that image. It naturally handles clusters of bad pixels and image edges and adapts to various instruments and image types. For bright pixels, the mean absolute error of astrofix is several times smaller than that of median replacement and interpolation by a Gaussian kernel. We demonstrate good performance on both imaging and spectroscopic data, including the SBIG 6303 0.4m telescope and the FLOYDS spectrograph of Las Cumbres Observatory and the CHARIS integral-field spectrograph on the Subaru Telescope.

astro-ph.IM↗