Triggered Star Formation and Dust around Mid-Infrared-Identified Bubbles

TL;DR

This study investigates the distribution of young stellar objects and dust around mid-infrared bubbles, finding limited evidence for triggered star formation and revealing unexpected dust temperature profiles.

Contribution

It provides new insights into star formation processes at bubble boundaries and challenges existing models of dust temperature gradients.

Findings

Only 20% of HII regions show YSOs associated with PDRs.

Dust temperature gradients are shallower than predicted by models.

Possible explanations include variable grain sizes and non-equilibrium processes.

Abstract

We use Two Micron All Sky Survey, GLIMPSE, and MIPSGAL survey data to analyze the young stellar object (YSO) and warm dust distribution around several mid-infrared-identified bubbles. We identify YSOs using J-band to 8 um photometry and correlate their distribution relative to the PDR (as traced by diffuse 8 um emission) which we assume to be associated with and surround a HII region. We find that only 20% of the sample HII regions appear to have a significant number of YSOs associated with their PDRs, implying that triggered star formation mechanisms acting on the boundary of the expanding HII region do not dominate in this sample. We also measure the temperature of dust inside 20 HII regions using 24 um and 70 um MIPSGAL images. In eight circularly symmetric sources we analyze the temperature distribution and find shallower temperature gradients than is predicted by an analytic model. Possible explanations of this shallow temperature gradient are a radially dependent grain-size distribution and/or non-equilibrium radiative processes.