Spatial distribution of star formation in dwarf galaxies: Merger-driven and secular starburst

Abstract

Galaxy interactions can induce bursts of star formation (SF), while internal or secular processes can also trigger starbursts (SB). Recent studies of the spatial distribution of SF in high-mass (M$_{*}>10^{10}M_{\odot}$) SB galaxies show that SF is centrally concentrated in merger-driven SBs, whereas in secularly driven SB systems, SF is uniformly enhanced across the system. However, it is not clear whether such distinct spatial signatures are present in low-mass (M$_{*} < 10^{10} M_{\odot}$) SB galaxies. In this context, we studied the SF properties of a sample of 272 isolated SB (i.e., with no massive galaxy, within a 1 Mpc$^3$ volume) dwarf galaxies consisting of 17 post-merger and 255 non-interacting SB galaxies, spanning a stellar mass range of $10^{7}-10^{9.6} M_{\odot}$ and a redshift range of 0.01-0.12. For this study, we utilise FUV imaging data from GALEX to estimate the star formation rates of our sample galaxies. We investigated the spatial variation of SB activity by comparing star formation rate surface density (SFRD) across radial bins for post-merger and non-interacting samples of dwarfs. We find an enhancement in SFRD across all radial bins for both samples, and that the enhancement is more or less uniform across the galaxy, within uncertainties. This indicates that SF in low-mass SB galaxies is uniformly enhanced throughout the galaxy, regardless of the mechanism that triggers the SB. This contrasts with observations in massive galaxies, where SF is centrally concentrated in merger-driven SB systems. The lack of central concentration of SF in low-mass merger systems could be due to their shallow gravitational potentials and the compression of extended gaseous envelopes during interactions, which trigger SF across these galaxies. Deeper, higher-spatial-resolution observations are essential for better understanding the spatial distribution of SF in low-mass galaxies.