Young Stellar Populations in MYStIX Star Forming Regions: Candidate
  Protostars
  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.
