Spitzer--IRAC Imagery and Photometry of Ultracompact HII Regions With Extended Emission

TL;DR

This study uses Spitzer--IRAC imagery and radio data to analyze the morphology and photometry of ultracompact HII regions with extended emission, revealing their IR characteristics and stellar content.

Contribution

It provides a detailed morphological and photometric analysis of UC HII regions with extended emission, including IR counterparts and stellar classification, based on new Spitzer data.

Findings

Cometary morphology is predominant in extended emission regions.

Most UC sources are classified as Class III in IRAC diagnostics.

Approximately 2%, 10%, and 88% of sources are Class I, II, and III, respectively.

Abstract

We present the results of a morphological study performed to a sample of Ultracompact (UC) HII regions with Extended Emission (EE) using Spitzer--IRAC imagery and 3.6 cm VLA conf. D radio-continuum (RC) maps. Some examples of the comparison between maps and images are presented. Usually there is an IR point source counterpart to the peak(s) of RC emission, at the position of the UC source. We find that the predominant EE morphology is the cometary, and in most cases is coincident with IR emission at 8.0 $\mu$m. Preliminary results of Spitzer--IRAC photometry of a sub-sample of 13 UC HII regions with EE based on GLIMPSE legacy data are also presented. Besides, individual IRAC photometry was performed to 19 UC sources within these 13 regions. We show that UC sources lie on specific locus, both in IRAC color-color and AM-product diagnostic diagrams. Counts of young stellar sources are presented for each region, and we conclude that a proportion of ~ 2%, ~10%, and ~88% of sources in the UC HII regions with EE are, in average, Class I, II, and III, respectively.