A multi-wavelength investigation of RCW175: an HII region harboring spinning dust emission

TL;DR

This study investigates the HII region RCW175 across multiple wavelengths, revealing its structure, star formation activity, dust properties, and the nature of its anomalous microwave emission, highlighting the role of the radiation field in spinning dust emission.

Contribution

It provides a detailed multi-wavelength analysis of RCW175, clarifies the origin of its anomalous microwave emission, and emphasizes the influence of the radiation field on spinning dust models.

Findings

RCW175 consists of two separate HII regions with different evolutionary stages.

The anomalous microwave emission correlates with the radiation field, not small dust grains.

The study suggests the importance of gas ions in spinning dust emission models.

Abstract

Using infrared, radio continuum and spectral observations, we performed a detailed investigation of the HII region RCW175. We determined that RCW175, which actually consists of two separate HII regions, G29.1-0.7 and G29.0-0.6, is located at a distance of 3.2+/-0.2 kpc. Based on the observations we infer that the more compact G29.0-0.6 is less evolved than G29.1-0.7 and was possibly produced as a result of the expansion of G29.1-0.7 into the surrounding interstellar medium. We compute a star formation rate for RCW175 of (12.6+/-1.9)x10^{-5} M_{\sun}/yr, and identified 6 possible young stellar object candidates within its vicinity. Additionally, we estimate that RCW175 contains a total dust mass of 215+/-53 M_{\sun}. RCW175 has previously been identified as a source of anomalous microwave emission (AME), an excess of emission at cm wavelengths often attributed to electric dipole radiation from the smallest dust grains. We find that the AME previously detected in RCW175 is not correlated with the smallest dust grains (polycyclic aromatic hydrocarbons or small carbonaceous dust grains), but rather with the exciting radiation field within the region. This is a similar result to that found in the Perseus molecular cloud, another region which harbors AME, suggesting that the radiation field may play a pivotal role in the production of this new Galactic emission mechanism. Finally, we suggest that these observations may hint at the importance of understanding the role played by the major gas ions in spinning dust models.