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Researchers used ALMA telescope observations to measure the mass of the supermassive black hole in galaxy NGC 315 by analyzing molecular gas movements in its circumnuclear disk. By applying multiple independent analytical methods (Bayesian and frequentist approaches) to the same high-resolution data, they obtained a consistent black hole mass estimate of approximately 2.02 billion solar masses. The study demonstrates that different gas-based measurement techniques yield similar results, with systematic uncertainties from modeling choices contributing as much to the error budget as statistical uncertainties.
Why it matters
This work establishes a methodological benchmark for measuring supermassive black hole masses using molecular gas dynamics, helping astronomers understand the reliability and limitations of different measurement techniques. The cross-validation of multiple methods and comparison with stellar dynamics measurements provides crucial quality control for future black hole mass studies across the universe.
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⚠️ Preprint – Noch nicht peer-reviewed
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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.