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We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 5 and Cycle 6 observations of CO (2 -1) and CO (3-2) emission at 0"2-0"3 resolution in two radio-bright, brightest group/cluster early-type galaxies, NGC 315 and NGC 4261. The data resolve CO emission that extends within their black hole (BH) spheres of influence (rg), tracing regular Keplerian rotation down to just tens of parsecs from the BHs. The projected molecular gas speeds in the highly inclined (i ≥ 60°) disks rise at least to 500 km s-1 near their galaxy centers. We fit dynamical models of thin-disk rotation directly to the ALMA data cubes and account for the extended stellar mass distributions by constructing galaxy surface brightness profiles corrected for a range of plausible dust extinction values. The best-fit models yield (MBH/109 M⊙)= 2.08 ± 0.01(stat)+0.32-0.14 (sys) for NGC315 and (MBH/109 M⊙) = 1.67 ± 0.10(stat)+0.39-0.24(sys) for NGC 4261, the latter of which is larger than previous estimates by a factor of ~3. The BH masses are broadly consistent with the relations between BH masses and host galaxy properties. These are among the first ALMA observations to map dynamically cold gas kinematics well within the BH-dominated regions of radio galaxies, resolving the respective rg by factors of ~5-10. The observations demonstrate ALMA's ability to precisely measure BH masses in active galaxies, which will enable more confident probes of accretion physics for the most massive galaxies.

We present 0.″14 resolution Atacama Large Millimeter/submillimeter Array (ALMA) CO(2âˆ'1) observations of the circumnuclear gas disk in UGC 2698, a local compact galaxy. The disk exhibits regular rotation with projected velocities rising to 450 km sâˆ'1 near the galaxy center. We fit gas-dynamical models to the ALMA data cube, assuming the CO emission originates from a dynamically cold, thin disk, and measured the mass of the supermassive black hole (BH) in UGC 2698 to be M BH = (2.46 ± 0.07 [1 σ statistical] âˆ' 0.78 + 0.70 [systematic]) Ă— 109 M ⊙. UGC 2698 is part of a sample of nearby early-type galaxies that are plausible z ∼ 2 red nugget relics. Previous stellar-dynamical modeling for three galaxies in the sample found BH masses consistent with the BH massâˆ'stellar velocity dispersion (M BH âˆ' σ ⋆) relation but over-massive relative to the BH massâˆ'bulge luminosity (M BH âˆ' L bul) correlation, suggesting that BHs may gain the majority of their mass before their host galaxies. However, UGC 2698 is consistent with both M BH âˆ' σ ⋆ and M BH âˆ' L bul. As UGC 2698 has the largest stellar mass and effective radius in the local compact galaxy sample, it may have undergone more recent mergers that brought it in line with the BH scaling relations. Alternatively, given that the three previously measured compact galaxies are outliers from M BH âˆ' L bul, while UGC 2698 is not, there may be significant scatter at the poorly sampled high-mass end of the relation. Additional gas-dynamical M BH measurements for the compact galaxy sample will improve our understanding of BHâˆ'galaxy co-evolution. [ABSTRACT FROM AUTHOR]