AstroSat-UVIT observations of a possibly interacting pair of galaxies in HCG 77

¹ Indian Institute of Science Education and Research, Mohali, SAS Nagar Punjab, 140306, India
² Thapar Institute of Engineering and Technology, Patiala, Punjab, 147004, India
³ Tata Institute of Fundamental Research, Mumbai, 400005, India

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Received: 20 September 2025
Accepted: 22 December 2025

Abstract

Context. Interactions and mergers possibly enhance the star formation in dwarf galaxies in a group environment.

Aims. We aim to study star-forming regions and the spectral energy distribution of two possibly interacting galaxies, PGC 56121 and PGC 56125, in the Hickson Compact Group 77.

Methods. We utilized the far-ultraviolet (FUV) channel of the Ultra Violet Imaging Telescope (UVIT) on board AstroSat to observe and produce FUV images of the galaxies. Our FUV images are at a much higher resolution in comparison to those obtained from previous galaxy surveys by GALEX in the near-UV and those from PS-1, DSS.

Results. We have identified several star-forming regions in the two possibly interacting galaxies, PGC 56121 and PGC 56125. These two galaxies form a pair widely separated in redshift and are seen in projection. We also report the presence of a candidate tidal dwarf galaxy at the end of one of the tidal tails located to the east of the pair, and we identified three major star-forming regions in the tidal dwarf. The spectral energy distribution of three galaxies in the system is presented and analyzed to investigate the key physical properties, such as stellar mass, dust mass, total luminosity, and star formation history, of the three galaxies. Based on these observations and on a comparison with observations in radio, these three galaxies are probably part of a small group of interacting galaxies.