Two compact HII regions at the remote outskirts of the Magellanic Clouds

TL;DR

This study investigates the physical properties, stellar content, and star formation activity of two remote, compact H II regions in the Magellanic Clouds using optical and infrared observations.

Contribution

It provides a detailed multi-wavelength analysis of two specific outer Magellanic Cloud H II regions, including their morphology, stellar populations, and young stellar objects, which was previously underexplored.

Findings

Identification of two compact H II regions: LMC N191A and SMC N77A.

Detection of ongoing massive star formation with protostars of 10-20 solar masses.

Characterization of the stellar populations and environmental properties of these regions.

Abstract

The H II regions LMC N191 and SMC N77 are among the outermost massive star-forming regions in the Magellanic Clouds. So far, few works have dealt with these objects despite their interesting characteristics. We aim at studying various physical properties of these objects regarding their morphology (in the optical and Spitzer IRAC wavelengths), ionized gas emission, nebular chemical abundances, exciting sources, stellar content, age, presence or absence of young stellar objects, etc. This study is based mainly on optical ESO NTT observations, both imaging and spectroscopy, coupled with other archive data, notably Spitzer images (IRAC 3.6, 4.5, 5.8, and 8.0 microns) and 2MASS observations. We show the presence of two compact H II regions, a low-excitation blob (LEB) named LMC N191A and a high-excitation blob (HEB) named SMC N77A, and study their properties and those of their exciting massive stars as far as spectral type and mass are concerned. We also analyze the environmental stellar populations and determine their evolutionary stages. Based on Spitzer IRAC data, we characterize the YSO candidates detected in the direction of these regions. Massive star formation is going on in these young regions with protostars of mass about 10 and 20 M_sun in the process of formation.