PHANGS-ALMA: Arcsecond CO(2-1) Imaging of Nearby Star-Forming Galaxies
  We present PHANGS-ALMA, the first survey to map CO J=2-1 line emission at ~1"
~ 100pc spatial resolution from a representative sample of 90 nearby (d<~20
Mpc) galaxies that lie on or near the z=0 "main sequence" of star-forming
galaxies. CO line emission traces the bulk distribution of molecular gas, which
is the cold, star-forming phase of the interstellar medium. At the resolution
achieved by PHANGS-ALMA, each beam reaches the size of a typical individual
giant molecular cloud (GMC), so that these data can be used to measure the
demographics, life-cycle, and physical state of molecular clouds across the
population of galaxies where the majority of stars form at z=0. This paper
describes the scientific motivation and background for the survey, sample
selection, global properties of the targets, ALMA observations, and
characteristics of the delivered ALMA data and derived data products. As the
ALMA sample serves as the parent sample for parallel surveys with VLT/MUSE,
HST, AstroSat, VLA, and other facilities, we include a detailed discussion of
the sample selection. We detail the estimation of galaxy mass, size, star
formation rate, CO luminosity, and other properties, compare estimates using
different systems and provide best-estimate integrated measurements for each
target. We also report the design and execution of the ALMA observations, which
combine a Cycle~5 Large Program, a series of smaller programs, and archival
observations. Finally, we present the first 1" resolution atlas of CO emission
from nearby galaxies and describe the properties and contents of the first
PHANGS-ALMA public data release.
