A multiwavelength study of star formation in the vicinity of galactic H II region Sh 2-100

Abstract

We present multiwavelength investigation of morphology, physical-environment, stellar contents, and star formation activity in the vicinity of star-forming region Sh 2-100. It is found that the Sh 2-100 region contains seven H II regions of ultracompact and compact nature. The present estimation of distance for three H II regions, along with the kinematic distance for others, suggests that all of them belong to the same molecular cloud complex. Using near-infrared photometry, we identified the most probable ionizing sources of six H II regions. Their approximate photometric spectral type estimates suggest that they are massive early-B to mid-O zero-age-main-sequence stars and agree well with radio continuum observations at 1280 MHz, for sources whose emissions are optically thin at this frequency. The morphology of the complex shows a non-uniform distribution of warm and hot dust, well mixed with the ionized gas, which correlates well with the variation of average visual extinction (~4.2-97 mag) across the region. We estimated the physical parameters of ionized gas with the help of radio continuum observations. We detected an optically visible compact nebula located to the south of the 850 µm emission associated with one of the H II regions and the diagnostic of the optical emission line ratios gives electron density and electron temperature of ~0.67 ×10³ cm^-3 and ~10⁴ K, respectively. The physical parameters suggest that all the H II regions are in different stages of evolution, which correlate well with the probable ages in the range ~0.01-2 Myr of the ionizing sources. The spatial distribution of infrared excess stars, selected from near-infrared and Infrared Array Camera color-color diagrams, correlates well with the association of gas and dust. The positions of infrared excess stars, ultracompact and compact H II regions at the periphery of an H I shell, possibly created by a WR star, indicate that star formation in Sh 2-100 region might have been induced by an expanding H I shell.