Abstract
Abstract We present PHANGS–ALMA, the first survey to map CO J = 2 → 1 line emission at ∼1″ ∼100 pc 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, 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, Atacama Large Millimeter/submillimeter Array (ALMA) observations, and characteristics of the delivered data and derived data products. As the ALMA sample serves as the parent sample for parallel surveys with MUSE on the Very Large Telescope, the Hubble Space Telescope, AstroSat, the Very Large Array, 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.
Highlights
This paper presents PHANGS–ALMA, an Atacama Large Millimeter/submillimeter Array (ALMA) survey aimed at studying the physics of molecular gas across the nearby galaxy population
Though the data are suitable for many scientific applications, the survey was designed with the broad goals of quantifying the physics of star formation and feedback at the scale of individual giant molecular clouds (GMCs) and connecting these measurements to galaxy-scale properties and processes
The sample selection (Section 3) and observing strategy (Section 5) for PHANGS–ALMA were designed to address five core science goals: 1. Measure the demographics of molecular clouds, and measure how GMC populations depend on host galaxy and location in a galaxy
Summary
This paper presents PHANGS–ALMA, an Atacama Large Millimeter/submillimeter Array (ALMA) survey aimed at studying the physics of molecular gas across the nearby galaxy population. The resulting CO(2−1) data have high spatial and spectral resolution, good surface brightness sensitivity, full flux recovery, and good coverage of the area of active star formation in each target These characteristics make PHANGS–ALMA the first “cloud scale,” ∼100 pc, survey of molecular gas across a local galaxy sample that is representative of where stars form in the z = 0 universe. Though the data are suitable for many scientific applications, the survey was designed with the broad goals of quantifying the physics of star formation and feedback at the scale of individual giant molecular clouds (GMCs) and connecting these measurements to galaxy-scale properties and processes With these goals in mind, the PHANGS team has followed up PHANGS–ALMA with a suite of multiwavelength programs that span the spectrum from the far-UV to radio, aiming to sample all stages of the star formation and feedback cycle.
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