Spitzer Mid-infrared Study of Compact HII Regions in the Magellanic Clouds

TL;DR

This study analyzes the mid-infrared properties of compact HII regions in the Magellanic Clouds using Spitzer data, revealing similarities with typical HII regions despite their youth and metallicity differences.

Contribution

It provides the first detailed mid-infrared analysis of a rare class of compact HII regions in the Magellanic Clouds, highlighting their dust content and excitation properties.

Findings

Higher excitation HII regions show stronger 8 micron emission.

Mid-infrared colors are similar across different excitation levels.

Compact HII regions have sizes of about 1.5-3 parsecs.

Abstract

We present a study of the mid-infrared properties and dust content of a sample of 27 HII ``blobs'', a rare class of compact HII regions in the Magellanic Clouds. A unique feature of this sample is that even though these HII regions are of high and low excitation they have nearly the same physical sizes ~1.5-3 pc. We base our analysis on archival 3-8 microns infrared imagery obtained with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope. We find that despite their youth, sub-solar metallicity and varied degrees of excitation, the mid-infrared colors of these regions are similar to those of typical HII regions. Higher excitation ``blobs'' (HEBs) display stronger 8 micron emission and redder colors than their low-excitation counterparts (LEBs).