The Near-ir Ca Ii Triplet - Σ Relation for Bulges of Spiral Galaxies

We present measurements of the near-infrared Calcium II triplet (CaT, CaT), Paschen (PaT) and Magnesium (Mg I) indices for a well-studied sample of 19 bulges of early to intermediate spiral galaxies. We find that both the CaT and CaT indices decrease with central velocity dispersion σ with small scatter. This dependence is similar to that recently found by Cenarro (2002) for elliptical galaxies, implying an uniform CaT – σ relation that applies to galaxies from ellipticals to intermediate-type spirals. The decrease of CaT and CaT with σ contrasts with the well-known increase of another α-element index, Mg2, with σ. We discuss the role of Ca underabundance ([Ca/Fe]<0) and IMF variations in the onset of the observed relations. Subject headings: galaxies: bulges — galaxies: fundamental parameters — galaxies: abundances