Evidence for the Accretion of Gas in Star-forming Galaxies: High N/O Abundances in Regions of Anomalously Low Metallicity

While all models for the evolution of galaxies require accretion gas to sustain their growth via on-going star formation, it has proven difficult directly detect this inflowing material. In paper we use data nearby star-forming in SDSS IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey search evidence imprinted chemical composition interstellar medium. We measure both O/H and N/O abundance ratios regions previously identified as having anomalously low values O/H. show that unusual locations these vs. plane indicate they have been created through mixing disk higher metallicity with accreted lower metallicity. Taken together previous analysis on low-metallicity regions, results imply metal-poor can probably formation present-day late-type galaxies.