Black Hole Mass Measurements of Early-type Galaxies NGC 1380 and NGC 6861 through ALMA and HST Observations and Gas-dynamical Modeling*

Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of CO(2–1) emission from the circumnuclear disks in two early-type galaxies, NGC 1380 and 6861. The disk each galaxy is highly inclined ( i ∼ 75°), projected velocities molecular gas near centers are ∼300 km s −1 ∼500 fit thin dynamical models to ALMA data cubes constrain masses central black holes (BHs). created host using Hubble Space Telescope images for extended stellar mass distributions incorporated a range plausible dust extinction values. For 1380, our best-fit model yields M BH = 1.47 × 10 8 ⊙ with ∼40% uncertainty. 6861, lack tracers within BH’s sphere influence due hole distribution precludes precise measurement . However, fits require value (1–3) 9 6861 reproduce observations. generally consistent predictions local BH–host scaling relations. Systematic uncertainties associated light choice dominate error budget both measurements. Despite these limitations, measurements demonstrate ALMA’s ability provide constraints on cases where radius marginally resolved or has hole.