Spitzer-IRAC GLIMPSE of High Mass Protostellar Objects

TL;DR

This study uses Spitzer-IRAC data to analyze 50 high-mass protostellar objects, revealing that envelope accretion dominates their growth and that their infrared nebulae resemble ultra-compact HII regions, shedding light on massive star formation stages.

Contribution

It provides a detailed analysis of IRAC data and SED fitting for high-mass protostars, highlighting the role of envelope accretion and the morphology of their infrared nebulae.

Findings

Envelope accretion dominates in massive star formation.

Infrared nebulae resemble ultra-compact HII regions.

Ionised accretion flows may be significant.

Abstract

The Spitzer-GLIMPSE point source catalog and images have been used to study a sample of 381 massive protostellar candidates. IRAC-Point source photometry was used to analyse colours, magnitudes and spectral indicies of the infrared counterparts (IRCs) of massive protostellar objects and a bonafide sample of 50 point sources was obtained. Spectral energy distributions (SEDs) of these 50 sources was extended to the near-infrared and millimeter range by using 2MASS and millimeter data from the literature. An online SED fitter tool based on Monte-Carlo radiative transfer of an accretion model involving star,disk and envelope was used to fit the SEDs of the 50 sources. The IRCs to massive protostellar objects are found to successfully imitate the SEDs of evolutionary phases similar to low mass star formation. Envelope accretion, rather than disk accretion is found to be dominant in building the most massive stars. Unresolved centimeter continuum emission is associated with 27 IRCs classified as massive protostars suggesting that ionised accretion flows may play an important role along with the molecular component. The morphology of the infrared nebulae surrounding the IRCs have an unusual resemblance to the morphologies of ultra-compact HII regions suggesting that these infrared nebulae are possible precursors to the UCHII regions.