Global photometric analysis of galactic HII regions

TL;DR

This study analyzes infrared fluxes from 99 galactic HII regions to assess dust composition and radiation fields, revealing lower PAH fractions and comparable UV intensities to extragalactic regions, aiding in distinguishing ionized regions.

Contribution

It provides a comprehensive infrared photometric analysis of galactic HII regions, highlighting PAH destruction and comparing color indices with extragalactic objects for better classification.

Findings

PAH mass fraction is significantly lower than the Galactic average.

Radiation field intensities are similar to those in extragalactic HII regions.

Color indices can distinguish ionized hydrogen regions from planetary nebulae.

Abstract

Total infrared fluxes are estimated for 99 HII regions around massive stars. The following wavebands have been used for the analysis: 8 and 24 $\mu$m, based on data from Spitzer space telescope (IRAC and MIPS, respectively); 70, 160, 250, 350, and 500 $\mu$m, based on data from Herschel Space Observatory (PACS and SPIRE). The estimated fluxes are used to evaluate the mass fraction of polycyclic aromatic hydrocarbons ($q_{\rm PAH}$) and the intensity of the ultraviolet emission in the studied objects. It is shown that the PAH mass fraction, $q_{\rm PAH}$, is much lower in these objects than the average Galactic value, implying effective destruction of aromatic particles in HII regions. Estimated radiation field intensities ($U$) are close to those derived for extragalactic HII complexes. Color indices [$F_{24}$/$F_{8}$], [$F_{70}$/$F_{24}$], [$F_{160}$/$F_{24}$], [$F_{160}$/$F_{70}$] are compared to criteria proposed to distinguish between regions of ionized hydrogen and planetary nebulae. Also, we relate our results to analogous color indices for extragalactic complexes of ionized hydrogen.