Young Stellar Populations in MYStIX Star Forming Regions: Candidate Protostars

TL;DR

This study identifies 1,109 candidate protostars in 14 star-forming regions using infrared and X-ray data from the MYStIX project, revealing their spatial correlation with molecular structures and highlighting the sample's reliability and incompleteness.

Contribution

It provides a new catalog of candidate protostars combining infrared and X-ray data, with improved selection criteria and spatial analysis, enhancing understanding of early star formation stages.

Findings

Most candidates are associated with molecular cores and filaments.

Two-thirds of candidates are newly reported.

The sample has high reliability but is incomplete.

Abstract

The Massive Young Star Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog (MIRES) and Chandra-based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1,109 MYStIX Candidate Protostars (MCPs) are found in 14 star forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few 'false positives' from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many 'false negatives'. Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be eludicated.