The origin of UV emission in extremely low-mass satellite galaxies: Insights from Leo T

The Leo T Milky Way (MW) satellite is the lowest-mass gas-rich galaxy known to exhibit recent star formation. This highly dark matter-dominated system provides an ideal laboratory for studying star formation in the ultraviolet (UV) regime within an extreme, low-density, and metal-poor environment. We present a far-ultraviolet (FUV) study of Leo T using observations from the Ultraviolet Imaging Telescope (UVIT). Our goals are to characterize the properties of FUV star-forming clusters (SFCs), identify FUV-emitting stars, constrain their physical properties through comparison with existing catalogs, and investigate how star formation proceeds in an extremely low-mass, metal-poor galaxy. We examined the FUV extent of the galaxy and compared it with the H, distribution. We extracted thirty SFCs and derived their properties, including area, luminosity, and star formation rate (SFR), and compared them with previous studies. Far-ultraviolet-emitting stars and their stellar parameters were identified through cross-matching with catalogs from the Hubble Space Telescope and the Multi Unit Spectroscopic Explorer (MUSE). We also estimated the global SFR and star formation efficiencies associated with previously identified CO clouds. i The FUV luminosities of the SFCs confirm the absence of massive O- and B-type stars in Leo T. The FUV-emitting stellar population consists of main-sequence (MS) stars, blue loop (BL) stars, horizontal branch stars, and emission-line (EM) stars. The upper MS and EM stars are concentrated near the optical center, whereas the lower MS and BL stars are more spatially extended. We find that five out of the six FUV-emitting stars with MUSE spectroscopy are extremely metal-poor (mathrm Fe/H łeq -3). The ( - r) color profile indicates that the UV emission is dominated by stellar populations younger than 1 Gyr out to a radius $<$ 185 pc. Despite the recent detection of CO(1-0) emission, no SFCs are associated with the molecular clouds, which exhibit extremely low star formation efficiencies. The spatial distribution of the SFCs is suggestive of a directional interaction with the MW.