ALMA CO(2-1) Gas Dynamics in NGC 315: A Multi-Method Benchmark for Supermassive Black Hole Mass Measurement
Dieu D. Nguyen, Benjamin D. Boizelle, Hai N. Ngo, Elena Gallo, Tuan N. Le, Sabine Thater, Tien H. T. Ho, Tinh Q. T. Le, Que T. Le, Sam Norcross, Xueyi Li, Huy G. Tong, Nghi K. N. Le, Huy M. B. Tran
arXiv:2608.31015v1 Announce Type: new
Abstract: We present ALMA Cycle~7 cotwo observations of the circumnuclear disk in NGC~315 at an angular resolution of $0farcs230times0farcs175$, improving on past measurements and resolving the sphere of influence (SOI) of the supermassive black hole (SMBH), whose mass has previously been estimated of $M_{rm BH}= left(2.08^{+0.33}_{-0.15}right) times 10^9$~M$_odot$ The high spatial resolution and sensitivity enable robust full-cube forward modeling of the molecular gas kinematics and a direct comparison of multiple independent gas-based dynamical modeling techniques. We apply standard Bayesian codes using both MCMC and nested sampling approaches, as well as a frequentist code to the same dataset, exploring systematic uncertainties associated with the stellar mass distribution, gas surface-brightness parameterization, and disk geometry. All methods yield consistent black hole masses, indicating that the inferred $M_{rm BH}$ is not strongly method-dependent. Combining the ensemble of independent molecular-gas-based models, we derive an ensemble median black hole mass of $M_{rm BH}/10^9,mathrm{M_odot} = 2.02^{+0.04}_{-0.05}$(stat)$^{+0.05}_{-0.04}$(sys), where the comparable contributions to the full error budget arise from modeling systematics rather than formal fitting uncertainties. Our $M_{rm BH}$ is consistent with the empirical $M_{rm BH}$–$sigma_star$ and $M_{rm BH}$–$L_{rm bulge}$ scaling relations, and lies 32% below an independent stellar-dynamical measurement, a discrepancy we discuss in the context of systematic differences between gas- and stellar-based methods. NGC~315 serves as a benchmark for quantifying molecular gas-dynamical $M_{rm BH}$ systematic uncertainties and for future cross-comparisons of gaseous and stellar dynamical approaches.arXiv:2608.31015v1 Announce Type: new
Abstract: We present ALMA Cycle~7 cotwo observations of the circumnuclear disk in NGC~315 at an angular resolution of $0farcs230times0farcs175$, improving on past measurements and resolving the sphere of influence (SOI) of the supermassive black hole (SMBH), whose mass has previously been estimated of $M_{rm BH}= left(2.08^{+0.33}_{-0.15}right) times 10^9$~M$_odot$ The high spatial resolution and sensitivity enable robust full-cube forward modeling of the molecular gas kinematics and a direct comparison of multiple independent gas-based dynamical modeling techniques. We apply standard Bayesian codes using both MCMC and nested sampling approaches, as well as a frequentist code to the same dataset, exploring systematic uncertainties associated with the stellar mass distribution, gas surface-brightness parameterization, and disk geometry. All methods yield consistent black hole masses, indicating that the inferred $M_{rm BH}$ is not strongly method-dependent. Combining the ensemble of independent molecular-gas-based models, we derive an ensemble median black hole mass of $M_{rm BH}/10^9,mathrm{M_odot} = 2.02^{+0.04}_{-0.05}$(stat)$^{+0.05}_{-0.04}$(sys), where the comparable contributions to the full error budget arise from modeling systematics rather than formal fitting uncertainties. Our $M_{rm BH}$ is consistent with the empirical $M_{rm BH}$–$sigma_star$ and $M_{rm BH}$–$L_{rm bulge}$ scaling relations, and lies 32% below an independent stellar-dynamical measurement, a discrepancy we discuss in the context of systematic differences between gas- and stellar-based methods. NGC~315 serves as a benchmark for quantifying molecular gas-dynamical $M_{rm BH}$ systematic uncertainties and for future cross-comparisons of gaseous and stellar dynamical approaches.

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