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

TL;DR

This study investigates how dwarf-dwarf mergers affect star formation by analyzing 6,155 isolated dwarfs (194 post-merger, 5,961 non-interacting) in the local universe using GALEX FUV data to derive instantaneous SFRs. An automated pipeline measures total and central/outer SFRs, validating post-merger galaxies against mass- and redshift-matched controls and examining the spatial distribution of SF. The results show a median SFR enhancement of $0.24$ dex ($\sim1.73\times$) with $67\%$ of post-mergers enhanced, and both central and outer regions experience SF elevation, indicating a broad, galaxy-wide response to interactions. About $33\%$ of post-mergers are quenched, suggesting a range of post-merger evolutionary stages; overall, dwarf-dwarf mergers can influence SF in the local universe, though more extensive and higher-resolution studies are needed to fully understand the mechanisms and timescales involved.

Abstract

Dwarf galaxies dominate the galaxy population across all redshifts, and majority of mergers are expected to occur between them. However, the impact of dwarf-dwarf mergers on star formation (SF) is less understood. In this context, we study SF in 6,155 isolated dwarf galaxies (no massive galaxy, $M_{*} > 10^{10} M_{\odot}$, within 1 Mpc$^3$), including 194 post-mergers and 5,961 non-interacting galaxies, spanning stellar masses of $10^7$ - $10^{9.6}$ M$_{\odot}$ and redshifts of 0.01 - 0.12. Post-mergers sample is from a previous study, which used deep optical images to identify dwarf galaxies with merger signatures. Using GALEX FUV data, we estimate star formation rates (SFRs) and find difference in log(SFR) between a post-merger galaxy and the median of its corresponding control sample, matched in stellar mass and redshift. SFR offsets range from -2 to +2 dex, indicating both enhancement and suppression of SF in our sample with 67% of post-mergers showing enhancement. The median SFR is found to be elevated by 0.24 dex ($\sim$1.73 times) in post-mergers, comparable to enhancements seen in massive galaxies. SF is found to be similarly enhanced in both the central (6" diameter region) and outer regions of post-mergers with respect to their non-interacting counterparts. This is in contrast to what is observed in massive galaxies, where the merger-triggered SF is more significant in the central regions. In the given small range of redshift, post-merger dwarfs exhibit a higher median specific SFR compared to their non-interacting counterparts. About 33% of post-mergers are quenched, possibly reflecting 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 SF in the local universe. A more comprehensive study of post-merger dwarfs is required to understand their evolution.

Figures (9)

• Figure 1: Flowchart showing the automated analysis of sample dwarfs step by step. For available data, we downloaded the FUV image containing the dwarf galaxy along with the corresponding background image. (*)-If multiple FUV datasets are available, then we download the image having maximum exposure. The subsequent analysis steps are detailed in Section \ref{['3']}.
• Figure 2: Left panel image displays the entire field of view 1.2$^{\circ}$ of GALEX with a red circle highlighting the location of the dwarf galaxy LEDA 1148477. The right panel image shows a zoomed-in view of the dwarf galaxy.
• Figure 3: Histogram displaying the distribution of target galaxies corresponding to stellar mass (top) and redshift (bottom). The blue bars represent post-mergers, while the orange bars represent the non-interacting dwarfs. Stellar mass is given in units of Solar mass.
• Figure 4: Trunk structure (white boundary) of dwarf galaxy plotted on background galaxy cutout, and green colored circular region signifies the central region as defined in section \ref{['3.2']}.
• Figure 5: SFR vs Stellar mass with density contours plotted over it for non-interacting dwarfs, while individual scatter points denote post-merger dwarfs. The figure indicates that post-merger dwarfs tend to exhibit slightly elevated SFRs compared to their non-interacting counterparts at a given stellar mass.