Discovery of a Double-core Dwarf Galaxy in a Major Wet Merger: MCG+08-16-005

Abstract I present the discovery of a dwarf galaxy with double cores, MCG+08-16-005, observed by an Integral Field Unit. Based on photometric and spatially resolved spectroscopic analyses, the galaxy is suggested as an ongoing dwarf-dwarf merger. MCG+08-16-005 is a galaxy pair embedded in a large-scale filament, located at a distance of 31.2 Mpc, with M r = − 17.39 mag, g − r = 0.37 mag, and a stellar mass of 8.3 × 10 8 M ⊙ . The double cores are clearly shown in grz -band images, with a projected separation of about 6″ (902 pc). The cores exhibit blue colors, while the outer regions appear red, consistent with the colors of dwarf elliptical galaxies found in the Virgo cluster. The estimated mass ratio of the expected progenitors is about 1.75, suggesting that this is a major dwarf-dwarf merger. Spatially resolved spectroscopy reveals rotational motions in both the stellar and gaseous components. The star-formation rates of the cores are 0.046 and 0.029 M ⊙ yr −1 , indicating that the galaxy is undergoing a gas-rich wet merger. The gas-phase abundances in the cores are characterized by lower O/H and higher N/O ratios compared to the surrounding regions, suggesting that pristine gas is processed during the merger. The cores are expected to be merged in about 81 Myr. Through this wet major dwarf-dwarf merger, MCG+08-16-005 exhibits properties consistent with those of a quiescent blue compact dwarf galaxy in terms of HI content and star-formation activity. MCG+08-16-005 is likely in a transitional phase in its internal kinematics, between Sm and dE galaxies.