Kinematic Properties and Stellar Populations of Faint Early-Type Galaxies: II. Line-Strength Measurements of Central Coma Galaxies

TL;DR

This study measures line-strengths of 74 early-type galaxies in the Coma cluster, revealing how their stellar populations and kinematic properties vary with galaxy velocity dispersion, especially at low sigma values.

Contribution

It provides new measurements of line-strengths for faint galaxies down to sigma of 30 km/s and analyzes their stellar populations and index-sigma relations, extending previous work to lower velocity dispersions.

Findings

Low-sigma galaxies are younger, less metal-rich, and have lower alpha/Fe ratios.

Index-sigma relations differ depending on the index used, with some showing a break around 100 km/s.

Relations are tighter for indices unaffected by stellar atmosphere micro-turbulence.

Abstract

We present line-strength measurements for 74 early-type galaxies in the core of the Coma cluster reaching down to velocity dispersions, sigma, of 30 km/s. The index-sigma relations for our sample, including galaxies with sigma<100 km/s (low-sigma), differ in shape depending on which index is used. We notice two types of relations for the metallic indices: one showing a break in the slope around ~100 km/s, and another group with strong linear relations between an index and log sigma. We find no connection between the behavior of index-sigma relations with either alpha- or Fe-peak elements. However, we find indications that the relations are tighter for indices which do not depend on the micro-turbulent velocities of stellar atmospheres. We confirm previous results that low-sigma galaxies including dE/dS0s are on average younger, less metal rich, and have lower [alpha/Fe] in comparison to E/S0s. Our data show that these trends derived for high-sigma galaxies extend down to dE/dS0s. This is a factor of ~2 lower in sigma than previously published work. We confirm that the observed anti-correlation between age and metallicity for high-sigma galaxies is consistent with the effects of correlated errors. Low-sigma galaxies also show a similar relation between age and metallicity as a result of correlated errors. However, they are offset from this relationship so that, on average, they are less metal rich and younger than their high-sigma counterparts.