Dwarf-dwarf interactions and their influence on star formation: Insights from post-merger galaxies

¹ Indian Institute of Astrophysics, Koramangala II Block, Bangalore 560034, India
² Pondicherry University, R.V. Nagar, Kalapet, 605014 Puducherry, India
³ Leibniz-Institut fur Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
⁴ Indian Institute of Science Education and Research, Mohanpur, Haringhata Farm, West Bengal, 741246, India

^⋆ Corresponding author: rakshit.chauhan@iiap.res.in

Received: 9 March 2025
Accepted: 18 July 2025

Abstract

Interactions and mergers play a crucial role in shaping the physical properties of galaxies. Dwarf galaxies are the dominant galaxy population at all redshifts, and the majority of mergers are expected to occur between them. The effect of dwarf-dwarf mergers on star formation in these systems is not yet fully understood. In this context, we studied the star formation properties of a sample of 6155 isolated (i.e., with no massive galaxy, M_* > 10¹⁰ M_⊙, within a 1 Mpc³ volume) dwarf galaxies consisting of 194 post-merger and 5961 non-interacting galaxies, spanning a stellar mass range of 10⁷ − 10^9.6 M_⊙ and a redshift range of 0.01–0.12. The post-merger galaxies studied here were identified in a past study in the literature, which found galaxies with signatures of recent merger activity (in the form of tidal features) in deep optical images. We used the far-ultraviolet imaging data from the GALEX mission and estimated the star formation rate (SFR) of our sample galaxies. To investigate the impact of interactions on star formation, we estimated the difference in log(SFR) between a post-merger galaxy and the median of its corresponding control sample matched in stellar mass and redshift. The offset in our sample has a range of −2 to +2 dex, indicating both enhancement and suppression of star formation in these recent merger galaxies. Around 67% of the sample (130 galaxies) shows an enhancement in SFR. The median offset (enhancement) of the sample is 0.24 dex (1.73 times), indicating an ∼70% increase in the SFR of recent merger galaxies compared to their non-interacting counterparts. Out of 194 post-merger dwarfs, around 44%, 20%, and 9% show twofold, fivefold, and tenfold enhancements in SFR, respectively. Overall, we found a moderate enhancement in the median SFR of the post-merger sample, compared to that of the non-interacting dwarfs, by a factor of nearly two. This factor is comparable to the average enhancement factor observed in massive post-merger galaxies. However, we observed widespread star formation across the sample of dwarf galaxies. Star formation is found to be enhanced in both the central (6″diameter region at the centre) and outer regions of the post-merger galaxies compared to their non-interacting counterparts, and the factor of enhancement was found to be similar. This is in contrast to what is observed in massive galaxies, where the merger-triggered star formation is more significant in the central regions. Furthermore, we did not observe any significant dependence of the enhancement factor on stellar mass across the sample. Additionally, we found that in the given small redshift range, post-merger dwarfs exhibit a higher median specific star formation rate compared to their non-interacting counterparts. About 33% of the galaxies in our post-merger dwarf sample are quenched. These galaxies could be at a later stage of the post-merger regime, where quenching can happen as observed in massive galaxies. This study suggests that dwarf-dwarf mergers can affect star formation in the local Universe. A more comprehensive study of post-merger dwarfs is required to understand their evolution.