AR-2020-21

22 33 rd ANNUAL REPORT 2020-21 LymanContinuumEmittingGalaxies fromAstroSat UVDeep Field One of the significant problems of current observational cosmology is understanding the nature of sources responsible for the reionization of our Universe. These are most likely the first galaxies, perhaps made from the PopIII stars, that formed after the Cosmic DarkAge. Direct detection of these reionization sources is practically infeasible at high redshift (z) due to the steep rise of the opacity of the intergalacticmedium (IGM). Over the last five years, there has been tremendous progress in this field, especially in terms of the detection of the low redshift analogs. For example, several green peas, the compact starburst galaxies at z<0.5, are observed to be emitting Lyman continuum (LyC) photons at 900Å rest-frame. These detections have been possible because of the observations carried out by the HSTCosmic Origins Spectrograph. There are also detections of compact LyC galaxies in the range 2.5 < z < 3.5. The redshift range 0.5 < z < 2.5 has remained barren and has been termed as the LyC desert until the recent discovery of a LyC emitting galaxies at z=1.42 (Saha, et al. NatAst, 2020) based on theAstroSat UVDeep Field (AUDF) data. The AUDF has been made based on the observations carried out by the Ultraviolet ImagingTelescope (UVIT) on AstroSat, India ' s first Space Observatory. It took about two years of constant effort involving running and benchmarking various versions of the pipeline, orbit by orbit analysis of the Figure:AUDFs01 is the newnewly discovered galaxy in the LyC desert UVIT data, accurate astrometry, etc., to produce the first version of the science-ready images of theAUDF in two filters.AUDF is currently the deepest UV deep field, allowing one to study the farthest and faintest sources in the UV passband. In other words, AUDF enables one to study Extreme-UV (EUV) radiation from distant galaxies in the rest frame. The discovery of AUDFs01 is the first such example of the detection of EUV photons at rest-frame. Exciting science results are in the pipeline. We are currently in the process of analyzing multi-epoch far-UV observations on the same field. This work is led by Kanak Saha from IUCAA.