HI Imaging of a Blueberry Galaxy Suggests a Merger Origin

Abstract: Blueberry galaxies (BBs) are fainter, less massive, and lower redshift counterparts of the Green pea galaxies. They are thought to be the nearest analogues of the high redshift Lyman Alpha (Ly$\alpha$) emitters. We report the interferometric imaging of HI 21 cm emission from a Blueberry galaxy, J1509+3731, at redshift, z = 0.03259, using the Giant Metrewave Radio Telescope (GMRT). We find that this Blueberry galaxy has an HI mass of $M_{\text{HI}} \approx 3\times 10^8 \, M_{\odot}$ and an HI-to-stellar mass ratio $M_{\text{HI}}/M_* \approx$ 2.4. Using SFR estimates from the H$\beta$ emission line, we find that it has a short HI depletion time scale of $\approx 0.2$ Gyr, which indicates a significantly higher star-formation efficiency compared to typical star-forming galaxies at the present epoch. Interestingly, we find an offset of $\approx 2$ kpc between the peak of the HI 21 cm emission and the optical centre which suggests a merger event in the past. Our study highlights the important role of mergers in triggering the starburst in BBs and their role in the possible leakage of Lyman-$\alpha$ and Lyman-continuum photons which is consistent with the previous studies on BB galaxies.