Clumpy Starburst in a Local Dwarf Galaxy, NGC 1522

Abstract

To investigate the star-forming process in nearby dwarf galaxies, we present integral field unit observations of the star-forming dwarf galaxy NGC 1522 with the Very Large Telescope/Multi Unit Spectroscopic Explorer as a part of the Dwarf Galaxy Integral Survey. Our observations reveal the presence of a star-forming clumpy ring in its central region. We identify nine distinct star-forming clumps based on an extinction-corrected Hα emission line map, with a total star formation rate of about 0.1 M⊙ yr−1. The nine clumps are considered to be starbursts, which represent an extreme case in the local Universe, without invoking major merging. We investigate the properties of ionized gas using the strong emission lines and “BPT” diagrams, in conjunction with velocity mapping. Our analysis unveils intriguing patterns, including a positive metallicity gradient and low N/O abundance ratio. This peculiar distribution of metallicity may signify external gas accretion. Our results suggest that the ongoing star formation in NGC 1522 might be triggered and sustained by the inflow of external metal-poor gas.