The prevalence of star formation as a function of Galactocentric radius

TL;DR

This study analyzes the distribution of star-forming objects across the Galaxy, revealing that the fraction of star-forming sources decreases with Galactocentric radius and is unaffected by spiral arm locations, suggesting environmental influences on star formation.

Contribution

It introduces the star-forming fraction (SFF) as a new metric to quantify star formation prevalence and examines its variation with Galactocentric radius using Hi-GAL survey data.

Findings

SFF is about 25% in the inner Galaxy.

SFF declines with Galactocentric radius at -0.026 per kpc.

Spiral arms do not significantly influence star formation activity.

Abstract

We present large-scale trends in the distribution of star-forming objects revealed by the Hi-GAL survey. As a simple metric probing the prevalence of star formation in Hi-GAL sources, we define the fraction of the total number of Hi-GAL sources with a 70-micron counterpart as the "star-forming fraction" or SFF. The mean SFF in the inner galactic disc (3.1 kpc < R_GC < 8.6 kpc) is 25%. Despite an apparent pile-up of source numbers at radii associated with spiral arms, the SFF shows no significant deviations at these radii, indicating that the arms do not affect the star-forming productivity of dense clumps either via physical triggering processes or through the statistical effects of larger source samples associated with the arms. Within this range of Galactocentric radii, we find that the SFF declines with R_GC at a rate of -0.026 +/- 0.002 per kiloparsec, despite the dense gas mass fraction having been observed to be constant in the inner Galaxy. This suggests that the SFF may be weakly dependent on one or more large-scale physical properties of the Galaxy, such as metallicity, radiation field, pressure or shear, such that the dense sub-structures of molecular clouds acquire some internal properties inherited from their environment.