Infrared photometric study of the massive star forming region S235 using Spitzer-IRAC and JHK observations

TL;DR

This study uses Spitzer-IRAC and JHK observations to analyze star formation in the S235 complex, identifying numerous young stellar objects, their clustering, and evidence of ongoing accretion and shock-excited emissions.

Contribution

It provides a detailed infrared photometric analysis of S235, identifying new YSOs, their classifications, and insights into star formation processes and shock phenomena in the region.

Findings

86 Class 0/I and 144 Class II YSOs identified

High clustering density of YSOs near S235A & B

Evidence of shock-excited H2 emission and ongoing accretion in massive YSOs

Abstract

We present the {\it Spitzer}-IRAC images of the S235 star forming complex that includes the East~1 & 2, Central and S235 A & B regions. In addition, we present the near-infrared images of the S235 A & B regions. The IRAC photometry reveals on-going star formation, with 86 Class 0/I and 144 Class II YSOs in the entire S235 complex. Nearly 73% of these YSOs are present in clusters with a maximum surface density of 120 YSOs/pc$^{2}$ (in the vicinity of S235A & B regions). A few YSOs, possibly in an arc-like formation, are identified towards the south of S235A region, which may be speculated as an evidence for magnetically super-critical collapse. One of the sources in the arc-like formation, namely S235AB-MIR, seems to be a young, massive star that is still accreting matter. SED modeling of some of the newly identified YSOs confirms the classification made on the basis of IRAC colours. The IRAC ratio map of Ch2/Ch4 traces clearly the Br$\alpha$ emission associated with the HII region of S235A within the horse-shoe envelope. Outside the horse-shoe structure, the ratio map indicates shock-excited H$_{2}$ emission. Br$\alpha$ emission is also seen around S235B (from the ratio map). The ratio map of Ch2/Ch4 reveals that the source "e2s3" in the East~2 region may be associated with shock-excited H$_2$ emission outflow or jet. The SED modeling of this new source indicates that it is a very young massive star that is not yet able to drive an HII region.