arXiv subjects

Long Q. T. Nguyen

Publications and source records attributed to Long Q. T. Nguyen.

3 recordsLinked to original sources

arXiv2026

Probing the Variation of the Inner Surface-Brightness Profile of Nuclear Star Clusters on the Intermediate-Mass Black Hole Mass Measurements Using Mock Observations of ELT/MICADO and HARMONI

Simulations of intermediate-mass black holes (IMBH) in dwarf galaxies within 10 Mpc that host bright nuclear star clusters (NSCs), prime candidates for IMBH formation, using the High Angular Resolution Monolithic Optical and Near-infrared Integral (HARMONI) field spectrograph on the Extremely Large Telescope, probe black hole formation in the early Universe. Our approach combines observed surface brightness profiles from the Hubble Space Telescope (HST), synthetic stellar population spectra, and Jeans Anisotropic Modeling (JAM) for stellar dynamics. Mock HARMONI observations were generated with the HSIM simulator and analyzed in a Bayesian framework to infer IMBH masses down to 0.5% of the NSC mass. In this work, we extend these simulations by constructing improved stellar-mass models using SimCADO to simulate imaging with the Multi-AO Imaging Camera for Deep Observations (MICADO). The MICADO data are jointly analyzed with HARMONI kinematics via JAM to reassess IMBH masses and uncertainties. This combined framework enables us to examine how variations in the NSC inner surface-brightness slope influence IMBH mass estimates, providing tighter constraints on low-mass black holes and advancing models for IMBH detection in NSCs.

astro-ph.GA↗

arXiv2026

Dynamical Evidence for a Billion Solar Mass Black Hole in Galaxy NGC 4061 from ALMA $^{12}$CO(2-1) Kinematics

We present the first robust dynamical measurement of the supermassive black hole (SMBH) mass in the massive early-type galaxy NGC 4061 using high-spatial-resolution ALMA observations of the $^{12}$CO(2-1) emission. By combining archival Cycle 6 data with new Cycle 7 observations, we achieve a synthesized beam of $0''.16 \times 0''.13$, comparable to the expected sphere of influence of the central black hole. The molecular gas forms a regularly rotating circumnuclear disk aligned with the prominent dust lane seen in HST imaging. We model the full three-dimensional ALMA data cube using the KinMS forward-modeling framework, exploring both data-driven and analytic prescriptions for the gas surface brightness distribution. Our Bayesian analysis yields a best-fitting SMBH mass of $M_{\rm BH} = (1.17^{+0.08}_{-0.10}\,[{\rm stat.}] \pm 0.43\,[{\rm syst.}]) \times 10^{9}$ M$_\odot$ and an $I$-band stellar mass-to-light ratio of $M/L_{\rm F814W} = 3.46^{+0.07}_{-0.06}\,[{\rm stat.}] \pm 0.10\,[{\rm syst.}]$ M$_\odot$/L$_\odot$. The inferred black hole mass is fully consistent across different modeling assumptions and remains insensitive to plausible radial variations in the $M/L_{\rm F814W}$ profile. Our results resolve the long-standing discrepancy between previous indirect mass estimates based on conflicting stellar velocity dispersion measurements and demonstrate that the exceptionally large dispersion reported in the literature is likely spurious. This study highlights the power of high-resolution ALMA molecular gas kinematics for precision SMBH mass measurements at the high-mass end of the local black hole mass function.

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↗