The Dust Properties of Bubble HII Regions as seen by Herschel

TL;DR

This study uses Herschel FIR data to analyze dust properties in bubble HII regions, revealing consistent dust temperatures, mass estimates of swept-up material, and insights into their three-dimensional structure and star formation implications.

Contribution

It provides the first detailed FIR analysis of dust temperatures, masses, and structure in bubble HII regions, enhancing understanding of their role in star formation.

Findings

Average dust temperature in PDRs is 26K.

Mass of swept-up material ranges from 300 to 10,000 solar masses.

Bubbles are three-dimensional structures with emission from both PDR sides.

Abstract

Because of their relatively simple morphology, "bubble" HII regions have been instrumental to our understanding of star formation triggered by HII regions. With the far-infrared (FIR) spectral coverage of the Herschel satellite, we can access the wavelengths where these regions emit the majority of their energy through their dust emission. At Herschel wavelengths 70 micron to 500 micron, the emission associated with HII regions is dominated by the cool dust in their photodissociation regions (PDRs). We find average dust temperatures of 26K along the PDRs, with little variation between the HII regions in the sample, while local filaments and infrared dark clouds average 19K and 15K respectively. Higher temperatures lead to higher values of the Jeans mass, which may affect future star formation. The mass of the material in the PDR, collected through the expansion of the HII region, is between ~300 and ~10,000 Solar masses for the HII regions studied here. These masses are in rough agreement with the expected masses swept up during the expansion of the \hii\ regions. Approximately 20% of the total FIR emission is from the direction of the bubble central regions. This suggests that we are detecting emission from the "near-side" and "far-side" PDRs along the line of sight and that bubbles are three-dimensional structures. We find only weak support for a relationship between dust temperature and beta, of a form similar to that caused by noise and calibration uncertainties alone.