A submillimeter study of the IR dust bubble S 21 and its environs

TL;DR

This study uses submillimeter and infrared observations to analyze the gas and dust structure of the IR dust bubble S 21, revealing a dense molecular shell, warm interior dust, and potential star formation activity triggered by the bubble's expansion.

Contribution

It provides detailed physical characterization of S 21's molecular and dust environment, and investigates star formation triggered by the bubble's expansion, which is a novel comprehensive multi-wavelength analysis.

Findings

Molecular shell with 2900 solar masses and 1.4 pc radius encircles S 21.

Detection of warm dust inside the bubble and cold dust in the outskirts.

Identification of YSO candidates suggesting triggered star formation.

Abstract

Based on the molecular emission in the $^{12}$CO(2-1) and $^{13}$CO(2-1) lines, and the continuum emission in the MIR and FIR towards the S21 IR dust bubble, we analyze the physical characteristics of the gas and dust linked to the nebula and the presence of young stellar objects (YSOs) in its environs. The line emission reveals a clumpy molecular shell, 1.4 pc in radius, encircling S21. The total molecular mass in the shell amounts to 2900 solar masses and the original ambient density, 2.1 x 10$^3$ cm$^{-3}$, indicating that the bubble is evolving in a high density interstellar medium. The image at 24 $\mu$m shows warm dust inside the bubble, while the emission in the range 250 to 870 $\mu$m reveal cold dust in its outskirts, coincident with the molecular gas. The detection of radio continuun emission indicates that the bubble is a compact HII region. A search for YSOs using photometric criteria allowed to identify many candidates projected onto the molecular clumps. We analize if the collect and collapse process has triggered a new generation of stars.