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 its demographics in the nearby dwarf irregular galaxy WLM using the Ultra-Violet Imaging Telescope (UVIT) multi band 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 > 17500 K which are likely to be the 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 south western part of the galaxy shows many hot star forming regions, high level of Hα emission and low column density of H I which altogether denote a vigorous recent star formation. WLM is likely to have a large fraction of low mass compact star forming regions with mass M < 10 3 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, which is similar to the average value measured for nearby dwarf irregular galaxies.

The volumetric star formation law for nearby galaxies

“…The profile of the SFR surface density also seems reliable, as it is similar to other estimates in the literature obtained from FUV emission (e.g. Mondal et al 2018). Our Σ SFR does not take into account the possible contribution of dustobscured star formation, which is instead included in Leroy et al (2008) profiles.…”

Joint gas and stellar dynamical models of WLM: an isolated dwarf galaxy within a cored, prolate DM halo

“…For example, the resultant decrease in central density and gas concentration may be extremely important for evolutionary changes of dwarf satel- lites, as demonstrated by Brooks & Zolotov (2014). Finding present day observational signatures which can trace the rapidity and strength of the potential fluctuations may provide further insight into the timescales, and mechanisms with which the DM core is growing, and can potentially differentiate feedback driven or particle scattering processes (e.g., gas and stellar spatial distributions; Mondal, Subramaniam & George 2018). This will be discussed in the subsequent section, however to first order the DM halo density profile we derive is in excellent agreement with the predictions from simulations which incorporate the effect of feedback driven halo expansion in a CDM framework.…”

A tale of two nearby dwarf irregular galaxies WLM and IC 2574 -- as revealed by UVIT

“…Our analysis shows that the clumps detected in IC 2574 do not show any distinct mode in their orientation, whereas in WLM we noticed the majority of the clumps are aligned along south-west to north-east direction. Earlier studies by Kepley et al (2007); Mondal et al (2018) have shown the possibility of propagating star formation in the hook-like H I structure around the centre in WLM. The specific mode of orientation of the star-forming clumps may have a connection with this.…”

“…The clumps with bluer colour are seen between radii 0.4 -0.8 kpc. These clumps are mostly located in the regions R1, R2, and R3, as shown in Mondal et al (2018). The clumps identified in the central and the outer part of the galaxy are relatively redder in colour.…”

“…Melena et al (2009) have performed a photometric study of star-forming knots in WLM using GALEX data. Mondal et al (2018) studied the (FUV−NUV) colour demographics of young star-forming regions with multi-band imaging observations from the Ultra-Violet Imaging Telescope (UVIT). The galaxy IC 2574 has been studied by to understand the connection between expanding H I holes and the triggered star formation using UVIT FUV observations.…”