Deep far-UV observations of the ELAIS N1 field using AstroSat: Source catalogue, spectral energy distribution modelling and star formation

Abstract

We present a far-ultraviolet (FUV) photometric study of the ELAIS N1 deep field using the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat, observed in the F154W filter ($λ_{\rm eff} = 1541$\,Å) with a total on-source exposure time of 30\,ksec. Level 1 data were reduced using CCDLAB v3.0, yielding source catalogues of 1637 objects at $3σ$ and 458 objects at $5σ$, with limiting magnitudes of $25.69\,m_{AB}$ and $25.13\,m_{AB}$ respectively. FUV positions are cross-matched against multiwavelength catalogues spanning optical and infrared wavelengths, with redshifts drawn from spectroscopic and photometric sources. Active galactic nuclei (AGN) are identified and excluded via established multiwavelength criteria, leaving a clean sample of star-forming galaxies (SFGs). Spectral energy distribution (SED) modelling is performed using CIGALE, employing a delayed star formation history with an optional late burst, Bruzual \& Charlot stellar population synthesis, Calzetti dust attenuation, and the SKIRTOR AGN module. From the best-fit models, we derive star formation rates (SFRs), total stellar masses, and young stellar masses as a function of redshift. The SFR increases monotonically with redshift, consistent with the evolution of the Star Formation Main Sequence (SFMS). The ratio of young-to-total stellar mass remains approximately constant across $0 < z \lesssim 0.76$, confirming that the sample consists predominantly of secularly evolving systems undergoing steady, self-regulated star formation rather than starburst-driven episodes.