THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS). I. A CLOUD-SCALE/MULTI-WAVELENGTH VIEW OF THE INTERSTELLAR MEDIUM IN A GRAND-DESIGN SPIRAL GALAXY

Abstract

The PdBI (Plateau de Bure Interferometer) Arcsecond Whirlpool Survey (PAWS)\nhas mapped the molecular gas in the central ~9kpc of M51 in its 12CO(1-0) line\nemission at cloud-scale resolution of ~40pc using both IRAM telescopes. We\nutilize this dataset to quantitatively characterize the relation of molecular\ngas (or CO emission) to other tracers of the interstellar medium (ISM), star\nformation and stellar populations of varying ages. Using 2-dimensional maps, a\npolar cross-correlation technique and pixel-by-pixel diagrams, we find: (a)\nthat (as expected) the distribution of the molecular gas can be linked to\ndifferent components of the gravitational potential, (b) evidence for a\nphysical link between CO line emission and radio continuum that seems not to be\ncaused by massive stars, but rather depend on the gas density, (c) a close\nspatial relation between the PAH and molecular gas emission, but no predictive\npower of PAH emission for the molecular gas mass,(d) that the I-H color map is\nan excellent predictor of the distribution (and to a lesser degree the\nbrightness) of CO emission, and (e) that the impact of massive (UV-intense)\nyoung star-forming regions on the bulk of the molecular gas in central ~9kpc\ncan not be significant due to a complex spatial relation between molecular gas\nand star-forming regions that ranges from co-spatial to spatially offset to\nabsent. The last point, in particular, highlights the importance of galactic\nenvironment -- and thus the underlying gravitational potential -- for the\ndistribution of molecular gas and star formation.\n