Towards a Solution for the Ca II Triplet Puzzle : Results from Dwarf Elliptical Galaxies

TL;DR

This study provides new age and metallicity estimates for dwarf elliptical galaxies using optical spectroscopy, revealing they are more metal-rich and younger than previously thought, and addresses the Calcium puzzle.

Contribution

It offers updated metallicity and age measurements for dE galaxies, resolving discrepancies in Calcium absorption strengths and advancing understanding of their star formation history.

Findings

dE galaxies are more metal-rich and younger than earlier estimates

Some dE's show recent star formation and self-enrichment

Results support the Calcium puzzle solution with consistent absorption strengths

Abstract

We present new estimates of ages and metallicities, based on FORS/VLT optical (4400-5500A) spectroscopy, of 16 dwarf elliptical galaxies (dE's) in the Fornax Cluster and in Southern Groups. These dE's are more metal-rich and younger than previous estimates based on narrow-band photometry and low-resolution spectroscopy. For our sample we find a mean metallicity [Z/H] = -0.33 dex and mean age 3.5 Gyr, consistent with similar samples of dE's in other environments (Local Group, Virgo). Three dE's in our sample show emission lines and very young ages. This suggests that some dE's formed stars until a very recent epoch and were self-enriched by a long star formation history. Previous observations of large near-infrared (~8500A) Ca II absorption strengths in these dE's are in good agreement with the new metallicity estimates, solving part of the so-called Calcium puzzle.