Galaxy properties in different environments. II. Star formation in bulges of late-type spirals

Abstract

The star formation history in the nucleus of late spiral galaxies is compared between a sample in a high galaxy density medium (HDS) and a control sample (CS) of isolated galaxies. We have observed 20 HDS and 18 CS galaxies from a larger list generated by the application of a group-finding algorithm to the SSRS survey. Using equivalent widths of absorption lines and the continuum distribution, we determined the nuclear stellar population types, from those dominated by old population to those containing star formation bursts of different ages and intensities. The HDS and CS stellar population type histograms are similar, suggesting that environmental influences, at least for the present sample, do not affect substantially the nuclear stellar population. However, the nuclear emission lines indicate that, in the BPT diagnostic diagrams, there is an excess of HDS galaxies located within or close to the AGN loci. For six HDS and two CS galaxies, it was possible to determine oxygen (0/H) and nitrogen (N/H) abundances. The samples present similar 0/H values, but in the CS galaxies the N/0 ratio is lower at equal galaxy luminosity.