Published online by Cambridge University Press: 10 November 2010
The star formation history in the nuclei of late-type 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 selected 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 populations 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 samples, do not substantially affect 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 6 HDS and 2 CS galaxies it was possible to determine Oxygen (O/H) and Nitrogen (N/H) abundances. The samples present similar (O/H) values, but in the CS galaxies the (N/O) ratio is lower at equal galaxy luminosity.
Evidence of several environmental effects that affect galaxy properties have been reported recently: (a) the morphology-density relation (fractional increase of early-type galaxies towards regions of high concentration, Dressier 1980; Postman & Geller 1984; Giovanelli, Haynes & Chincarini 1986; Maia & da Costa 1990); (b) the morphology-clustercentric radius relation (Whitmore, Gilmore & Jones 1993).