UVIT imaging of WLM: demographics of star-forming regions in the nearby dwarf irregular galaxy

Abstract

We present a study of star-forming regions and their demographics in the nearby dwarf irregular galaxy WLM using Ultraviolet Imaging Telescope (UVIT) multiband observations in three filters, F148W, N245M, and N263M. We find that the UV emission is extended at least up to 1.7 kpc, with the NUV emission more extended than the FUV. We create UV color maps ((F148W − N245M) and (F148W − N263M)) to study the temperature morphology of young stellar complexes with the help of theoretical models. We identify several complexes with temperature T > 17,500 K, which are likely to be OB associations present in the galaxy. These complexes show good spatial correlation with the Hα-emitting regions, H i distribution, and HST-detected hot stars. The hot star-forming regions are found to be clumpy in nature and show a hierarchical structure, with sizes in the range of 4–50 pc, with a large number with sizes <10 pc. The southwestern part of the galaxy shows many hot star-forming regions, high levels of Hα emission, and low column density of H i, which altogether denote vigorous recent star formation. WLM is likely to have a large fraction of low-mass compact star-forming regions with mass M < 103 M ⊙, in agreement with the size and mass of the CO clouds. We estimate the star formation rate of WLM to be ~0.008 M ⊙ yr−1, which is similar to the average value measured for nearby dwarf irregular galaxies.