The PdBI Arcsecond Whirlpool Survey (PAWS). The Role of Spiral Arms in Cloud and Star Formation

Abstract

The process that leads to the formation of the bright star forming sites observed along prominent spiral arms remains elusive. We present results of a multi-wavelength study of a spiral arm segment in the nearby grand-design spiral galaxy M51 that belongs to a spiral density wave and exhibits nine gas spurs. The combined observations of the(ionized, atomic, molecular, dusty) interstellar medium (ISM) with star formation tracers (HII regions, young <10Myr stellar clusters) suggest (1) no variation in giant molecular cloud (GMC) properties between arm and gas spurs, (2) gas spurs and extinction feathers arising from the same structure with a close spatial relation between gas spurs and ongoing/recent star formation (despite higher gas surface densities in the spiral arm), (3) no trend in star formation age either along the arm or along a spur, (4) evidence for strong star formation feedback in gas spurs: (5) tentative evidence for star formation triggered by stellar feedback for one spur, and (6) GMC associations (GMAs) being no special entities but the result of blending of gas arm/spur cross-sections in lower resolution observations. We conclude that there is no evidence for a coherent star formation onset mechanism that can be solely associated to the presence of the spiral density wave. This suggests that other (more localized) mechanisms are important to delay star formation such that it occurs in spurs. The evidence of star formation proceeding over several million years within individual spurs implies that the mechanism that leads to star formation acts or is sustained over a longer time-scale.

52 pages, 9 figures, 8 tables, accepted to ApJ

References in corpus (12)

• Bias-free Measurement of Giant Molecular Cloud Properties
• Dynamically Driven Evolution of the Interstellar Medium in M51
• Formation of Spiral-Arm Spurs and Bound Clouds in Vertically Stratified Galactic Gas Disks
• A complete 12CO 2-1 map of M51 with HERA: I. Radial averages of CO, HI, and radio continuum
• GMC formation by agglomeration and self gravity
• The Blueshifting and Baldwin effects for the [OIII] 5007 Emission Line in Type 1 Active Galactic Nuclei
• Geometrically Derived Timescales for Star Formation in Spiral Galaxies
• Using H-alpha Morphology and Surface Brightness Fluctuations to Age-Date Star Clusters in M83
• Analysis of spiral arms using anisotropic wavelets: gas, dust and magnetic fields in M51
• An HST Archival Survey of Feathers in Spiral Galaxies
• Radial Dependence of the Pattern Speed of M51
• Detection of Dense Molecular Gas in Inter-Arm Spurs in M51

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• The recent star formation history of NGC 628 on resolved scales
• Molecular clouds in M51 from high-resolution extinction mapping
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