The starburst galaxy NGC 7714

Narrowband Hα imaging and long-slit optical and near-infrared spectroscopy are analyzed in a study of the starburst galaxy NGC 7714. The data indicate that the galaxy as a whole is experiencing intense star formation activity; this is more conspicuous in the nucleus, where the star formation rate and the star formation rate per unit area are higher than in the rest of the galaxy. Evidence for this intense star formation activity comes from the detection of broad emission He II λ4686, attributed to WN stars; this suggests an age of the present burst between 3 and 5 Myr. Evidence of the existence of previous bursts come from the detection of the infrared Ca II triplet in absorption, which indicates the presence of red giant or supergiant stars. Spectroscopic data are taken at two position angles (P.A. = 110° and 216°) across the nucleus and comprise also three giant H II regions located in the circumnuclear region and in the spiral arms. The physical conditions and chemical composition of the gas are derived. Abundances are moderately low, with an excess of N in and around the nucleus. The velocity curve at P.A. = 216° is very distorted, indicating large departures from circular motion. Higher velocity dispersion of the gas in the circumnuclear region has also been found and could be related to enhanced star formation.