Populations of Young Stellar Objects in Nearby Molecular Clouds
  We develop a new method to identify YSOs from star-forming regions using the
photometry data from Spitzer's c2d Legacy Project. The aim is to obtain YSO
lists as complete as possible for studying the statistical properties, such as
Star Formation Rate (SFR) and lifetimes of YSOs in different evolutionary
stages. The largest obstacle for identifying YSOs comes from background
galaxies with similar SEDs to YSOs. Traditionally, selected color-color and
color-magnitude criteria are used to separate YSOs and galaxies. However, since
there is no obvious boundary between YSOs and galaxies in Color-Color Diagrams
(CCDs) and Color-Magnitude Diagrams (CMDs), those criteria may exclude faint
YSOs near the boundary. In this paper, we separate the YSOs and galaxies in
multi-dimensional (Multi-D) magnitude space, which is equivalent to using all
variations of CMDs simultaneously. Comparing sources from molecular clouds to
Spitzer's SWIRE data, which have negligible amount of YSOs, we can naturally
identify YSO candidates locating outside of the galaxy populated regions in the
Multi-D space. In the five c2d-surveyed clouds, we select 322 new YSO
candidates (YSOc), miss/exclude 33 YSOc compared to Evans et al. 2009 and
result in 1313 YSOc in total. As a result, SFR increases 28% correspondingly,
but the lifetimes of YSOs in different evolutionary stages remain unchanged.
Comparing to theories Krumholz & McKee 2005, our derived SFR suggests that star
formation in large scale is dominated by supersonic turbulence rather than
magnetic fields. Furthermore, we identify 7 new Very Low Luminosity Objects.
