Ionizing stellar population in the disk of NGC 3310 $-$ I. The impact of a minor merger on galaxy evolution

Abstract

Numerical simulations of minor mergers predict little enhancement in the global star formation activity. However, it is still unclear the impact they have on the chemical state of the whole galaxy and on the mass build-up in the galaxy bulge and disc. We present a two-dimensional analysis of NCG 3310, currently undergoing an intense starburst likely caused by a recent minor interaction, using data from the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey (PINGS). With data from a large sample of about a hundred HII regions identified throughout the disc and spiral arms we derive, using strong-line metallicity indicators and direct derivations, a rather flat gaseous abundance gradient. Thus, metal mixing processes occurred, as in observed galaxy interactions. Spectra from PINGS data and additional multiwavelength imaging were used to perform a spectral energy distribution fitting to the stellar emission and a photoionization modelling of the nebulae. The ionizing stellar population is characterized by single populations with a narrow age range (2.5-5 Myr) and a broad range of masses ($10^4-6\times10^6 M_\odot$). The effect of dust grains in the nebulae is important, indicating that 25-70% of the ultraviolet photons can be absorbed by dust. The ionizing stellar population within the HII regions represents typically a few percent of the total stellar mass. This ratio, a proxy to the specific star formation rate, presents a flat or negative radial gradient. Therefore, minor interactions may indeed play an important role in the mass build-up of the bulge.