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

## TL;DR

This study investigates how spiral arms influence cloud and star formation in galaxy M51, finding no clear evidence that spiral density waves directly trigger star formation, highlighting the importance of local processes.

## Contribution

It provides a detailed multi-wavelength analysis showing that star formation in spiral arms and spurs is not solely driven by spiral density waves, emphasizing the role of local mechanisms.

## Key findings

- GMC properties are consistent between arm and spurs.
- Gas spurs are closely related to star formation regions.
- Star formation feedback is evident in gas spurs.

## 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.