Tidal interaction, star formation and chemical evolution in blue compact dwarf galaxy Mrk 22

Abstract

The optical spectroscopic and radio interferometric HI 21 cm-line observations of the blue compact dwarf galaxy Mrk 22 are presented. The Wolf-Rayet (WR) emission line features corresponding to high ionization lines of HeII $\lambda$4686 and CIV $\lambda$5808 from young massive stars are detected. The ages of two prominent star forming regions in the galaxy are estimated as $\sim$10 Myr and $\sim$ 4 Myr. The galaxy has non-thermal radio deficiency, which also indicates a young star-burst and lack of supernovae events from the current star formation activities, consistent with the detection of WR emission lines features. A significant N/O enrichment is seen in the fainter star forming region. The gas-phase metallicities [12 + log(O/H)] for the bright and faint regions are estimated as 7.98$\pm$0.07 and 7.46$\pm$0.09 respectively. The galaxy has a large diffuse HI envelop. The HI images reveal disturbed gas kinematics and HI clouds outside the optical extent of the galaxy, indicating recent tidal interaction or merger in the system. The results strongly indicate that Mrk 22 is undergoing a chemical and morphological evolution due to ongoing star formation, most likely triggered by a merger.