Spitzer and NIR observations of Massive star forming regions W5-east, NGC7538, S235, S252, and S254-S258.
Lori Allen, Joseph Hora, Chris Brunt, Giovanni Fazio
We present Spitzer-IRAC observations of the massive star forming regions W5-east, NGC7538, S235, and S252. The region S254-S258 is also included in our analysis using a more recent distance estimate. Spitzer data is combined with near-IR observations to identify and classify the young stellar objects (YSOs) in each region. We detect in total 3045 YSO candidates. Of those, 565 were classified as Class 0/I, and 1184 as Class II sources. Minimum spanning tree (MST) algorithm is used to detect embedded clusters of YSOs. We identify 39 embedded clusters, 15 of those detected for the first time. The percentage of YSOs found in clusters range between 52% and 73%. The structure of the molecular cloud is examined using 12CO and 13CO, as well as a near-IR extinction maps. Spatial distribution of Class 0/I and Class II sources is compared using Q parameter and Kolmogorov-Smirnov (K-S) tests. We found that Class 0/I sources are distributed in general more hierarchically than Class II and associated with the more dense molecular material. This is in agreement with both classes evolutionary stage and supports the idea that star formation occurs along hierarchically distributed dust filaments. The same statistical tools are used to compare physical characteristics of massive and low-mass embedded clusters. We find that the properties of embedded clusters harboring massive stars are a scaled-up version of the low-mass case.