A gallery of bubbles - The nature of the bubbles observed by Spitzer and what ATLASGAL tells us about the surrounding neutral material

TL;DR

This study investigates the nature of Spitzer-observed galactic bubbles, their association with massive stars, and their role in triggering star formation, using multi-wavelength data including ATLASGAL to analyze surrounding neutral material.

Contribution

It provides a detailed analysis of the physical properties and star formation activity around galactic bubbles, highlighting their potential in triggering massive star formation.

Findings

86% of bubbles contain ionized gas from HII regions.

98% of bubbles show central 24 micron emission.

40% of resolved bubbles are surrounded by cold dust.

Abstract

We attempt to determine the nature of the bubbles observed by Spitzer in the Galactic plane, mainly to establish if possible their association with massive stars. We take advantage of the very simple morphology of these objects to search for star formation triggered by HII regions, and to estimate the importance of this mode of star formation. We consider a sample of 102 bubbles detected by Spitzer-GLIMPSE, and catalogued by Churchwell et al.(2006). We use mid-infrared and radio-continuum public data to discuss their nature. We use the ATLASGAL survey at 870 micron to search for dense neutral material collected on their borders. Results: We find that 86% of the bubbles contain ionized gas detected by means of its radio-continuum emission at 20-cm. Thus, most of the bubbles observed at 8.0 micron enclose HII regions ionized by O-B2 stars. Ninety-eight percent of the bubbles exhibit 24 micron emission in their central regions. The ionized regions at the center of the 8.0 micron bubbles seem to be devoid of PAHs but contain hot dust. Among the 65 regions for which the angular resolution of the observations is high enough to resolve the spatial distribution of cold dust at 870 micron, we find that 40% are surrounded by cold dust, and that another 28% contain interacting condensations. The former are good candidates for the collect and collapse process, as they display an accumulation of dense material at their borders. The latter are good candidates for the compression of pre-existing condensations by the ionized gas. Eighteen bubbles exhibit associated ultracompact HII regions and/or methanol masers in the direction of dust condensations adjacent to their ionization fronts. Our results suggest that more than a quarter of the bubbles may have triggered the formation of massive objects.