A Precision Measurement of the Mass of the Black Hole in NGC 3258 from
  High-Resolution ALMA Observations of its Circumnuclear Disk
  We present $\sim0.10^{\prime\prime}-$resolution Atacama Large
Millimeter/submillimeter Array (ALMA) CO(2$-$1) imaging of the arcsecond-scale
($r \approx 150$ pc) dusty molecular disk in the giant elliptical galaxy NGC
3258. The data provide unprecedented resolution of cold gas disk kinematics
within the dynamical sphere of influence of a supermassive black hole,
revealing a quasi-Keplerian central increase in projected rotation speed rising
from 280 km s$^{-1}$ at the disk's outer edge to $>400$ km s$^{-1}$ near the
disk center. We construct dynamical models for the rotating disk and fit
beam-smeared model CO line profiles directly to the ALMA data cube. Our models
incorporate both flat disks and tilted-ring disks that provide a better fit of
the mildly warped structure in NGC 3258. We show that the exceptional angular
resolution of the ALMA data makes it possible to infer the host galaxy's mass
profile within $r=150$ pc solely from the ALMA CO kinematics, without relying
on optical or near-infrared imaging data to determine the stellar mass profile.
Our model therefore circumvents any uncertainty in the black hole mass that
would result from the substantial dust extinction in the galaxy's central
region. The best model fit yields $M_\mathrm{BH} = 2.249\times10^9$ $M_\odot$
with a statistical model-fitting uncertainty of just 0.18\%, and systematic
uncertainties of 0.62\% from various aspects of the model construction and 12\%
from uncertainty in the distance to NGC 3258. This observation demonstrates the
full potential of ALMA for carrying out highly precise measurements of
$M_\mathrm{BH}$ in early-type galaxies containing circumnuclear gas disks
