Nitrogen abundance in the Blue Compact Dwarf galaxies from SDSS

Abstract

We examined all of the galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) to select those with a dete ted [O ΙΙΙ ] λ4363 emission line, whih allows to derive electron temperatures in H װ regions and element abundan es by the diret method. We selected two sub-samples of galaxies: one with detected WR features in their spectra, and the other with the nebular He װ λ4686 emission line. We confirm the increase of the N/O abundance ratio with decrease of the equivalent width EW(Hβ) of the Hβ emission line. This result is explained by gradual nitrogen enrihment of the interstellar medium by ejecta from massive stars in the most recent starburst episode.