AstroSat detection of Lyman continuum emission from a z=1.42 galaxy

TL;DR

This paper reports the first detection of Lyman continuum emission from a galaxy at z=1.42 using AstroSat, providing new insights into sources of cosmic reionization during peak star formation.

Contribution

It presents the first detection of extreme ultraviolet radiation from a distant galaxy at z=1.42, expanding the observational window for studying ionizing sources during Cosmic Noon.

Findings

Detected Lyman continuum emission with >20% escape fraction.

First observation of EUV radiation at 600 Angstrom from a galaxy at z=1.42.

Opens new avenues to study reionization sources at intermediate redshifts.

Abstract

One of the outstanding problems of current observational cosmology is to understand the nature of sources that produced the bulk of the ionizing radiation after the Cosmic Dark Age. Direct detection of these reionization sources is practically infeasible at high redshift due to the steep decline of intergalactic medium transmission. However, a number of low-redshift analogs emitting Lyman continuum at~900 Angstrom ~restframe are now detected at $z< 0.4$ and there are detections in the range $ 2.5< z< 3.5$ also. Here, we report the detection of Lyman continuum emission with a high escape fraction (>20%) from a low-mass clumpy galaxy at z=1.42, in the middle of the redshift range where no detection has been made before and near the peak of the Cosmic Star-formation history. The observation was made in the Hubble Extreme Deep field by the wide-field Ultra-Violet-Imaging Telescope onboard AstroSat. This is the first detection of Extreme Ultraviolet radiation from a distant galaxy at a rest-frame wavelength of 600 Angstrom, and it opens up a new window to constrain the shape of the ionization spectrum. Further observations with AstroSat should significantly increase the sample of Lyman continuum leaking galaxies at Cosmic Noon.