Work

Atacama Large Millimeter/submillimeter Array (ALMA) 12 CO(2–1) Gas Dynamics in NGC 315: A Multimethod Benchmark for Supermassive Black Hole Mass Measurement

Year: 2026

Type: article

Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 7 12 CO(2−1) observations of the circumnuclear disk in NGC 315 at an angular resolution of 0 . ″ 230 × 0 . ″ 175 , improving on past measurements and resolving the sphere of influence (SOI) of the supermassive black hole (SMBH), whose mass has been estimated previously as M BH = 2.0 8 − 0.15 + 0.33 × 1 0 9 M ⊙ . 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 Markov chain Monte Carlo (MCMC) and nested sampling approaches, as well as a frequentist code to the same data set, 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 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 BH / 1 0 9 M ⊙ = 2.0 2 − 0.05 + 0.04 (stat) − 0.04 + 0.05 (sys), where the comparable contributions to the full error budget arise from modeling systematics rather than formal fitting uncertainties. Our M BH is consistent with the empirical M BH – σ ⋆ and M BH – L 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 BH systematic uncertainties and for future cross-comparisons of gaseous and stellar dynamical approaches.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/aea151