Abstract:
In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken
with an aim to explore its hidden young stellar population as well as to understand the
structure and star formation history for the first time. This complex is composed of five
prominent embedded clusters associated with the subregions A, C, E, NGC 2175s and Teu
136. We used Two Micron All Sky Survey-near-infrared and Spitzer-Infrared Array Camera,
Multiband Imaging Photometer for Spitzer photometry to identify and classify the young stellar
objects (YSOs) by their infrared (IR) excess emission. Using the IR colour–colour criteria,
we identified 577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are transition disc
YSOs, suggesting a moderately rich number of YSOs in this complex. Spatial distribution of
the candidate YSOs shows that they are mostly clustered around the subregions in the western
half of the complex, suggesting enhanced star formation activity towards its west. Using the
spectral energy distribution and optical colour–magnitude diagram-based age analyses, we
derived probable evolutionary status of the subregions of Sh2-252. Our analysis shows that
the region A is the youngest (∼0.5 Myr), the regions B, C and E are of similar evolutionary
stage (∼1–2 Myr) and the clusters NGC 2175s and Teu 136 are slightly evolved (∼2–3 Myr).
Morphology of the region in the 1.1 mm map shows a semicircular shaped molecular shell
composed of several clumps and YSOs bordering the western ionization front of Sh2-252.
Our analyses suggest that next generation star formation is currently under way along this
border and that possibly fragmentation of the matter collected during the expansion of the H II
region as one of the major processes is responsible for such stars. We observed the densest
concentration of YSOs (mostly Class I, ∼0.5 Myr) at the western outskirts of the complex,
within a molecular clump associated with water and methanol masers and we suggest that it is
indeed a site of cluster formation at a very early evolutionary stage, sandwiched between the
two relatively evolved CH II regions A and B.
