VISION - Vienna survey in Orion. III. Young stellar objects in Orion A
  We have extended and refined the existing young stellar object (YSO) catalogs
for the Orion A molecular cloud, the closest massive star-forming region to
Earth. This updated catalog is driven by the large spatial coverage (18.3
deg$^2$, $\sim$950 pc$^2$), seeing limited resolution ($\sim$0.7$"$), and
sensitivity ($K_s<19$ mag) of the ESO-VISTA near-infrared survey of the Orion A
cloud (VISION). Combined with archival mid- to far-infrared data, the VISTA
data allow for a refined and more robust source selection. We estimate that
among previously known protostars and pre-main-sequence stars with disks,
source contamination levels (false positives) are at least $\sim$6.4% and
$\sim$2.3%, respectively, mostly due to background galaxies and nebulosities.
We identify 274 new YSO candidates using VISTA/Spitzer based selections within
previously analyzed regions, and VISTA/WISE based selections to add sources in
the surroundings, beyond previously analyzed regions. The WISE selection method
recovers about 59% of the known YSOs in Orion A's low-mass star-forming part
L1641, which shows what can be achieved by the all-sky WISE survey in
combination with deep near-infrared data in regions without the influence of
massive stars. The new catalog contains 2980 YSOs, which were classified based
on the de-reddened mid-infrared spectral index into 188 protostars, 185
flat-spectrum sources, and 2607 pre-main-sequence stars with circumstellar
disks. We find a statistically significant difference in the spatial
distribution of the three evolutionary classes with respect to regions of high
dust column-density, confirming that flat-spectrum sources are at a younger
evolutionary phase compared to Class IIs, and are not a sub-sample seen at
particular viewing angles.
