Abstract
We present the results of a study of stellar population properties at large galactocentric radii of 14 low-mass early-type galaxies in the Fornax and Virgo clusters. We derive radial profiles of age, total metallicity [Z/H] and [alpha/Fe] abundance ratios out to similar to 1-3 effective radii by using nearly all of the Lick/IDS absorption-line indices in comparison to recent single stellar population models. We extend our study to higher galaxy mass via a novel literature compilation of 37 early-type galaxies, which provides stellar population properties out to one effective radius. We find that metallicity gradients correlate with galactic mass, and the relationship shows a sharp change in slope at a dynamical mass of similar to 3.5 x 10(10) M-circle dot. The central and mean values of the stellar population parameters (measured in r <= r(e)/8 and at r = r(e), respectively) define positive mass trends. We suggest that the low metallicities, almost solar [alpha/Fe] ratios and the tight mass-metallicity gradient relation displayed by the low-mass galaxies are indicative of an early star-forming collapse with extended (i.e. >= 1 Gyr), low-efficiency star formation, and mass-dependent galactic outflows of metal-enriched gas. The flattening of metallicity gradients in high-mass galaxies and the broad scatter of the relationship are attributed to merger events. The high metallicities and supersolar abundances shown by these galaxies imply a rapid, high efficiency star formation. The observed [Z/H]-mass and [alpha/Fe]-mass relationships can be interpreted as a natural outcome of an early star-forming collapse. However, we find that hierarchical galaxy formation models implementing mass-dependent star formation efficiency, varying initial mass function, energy feedback via active galactic nucleus and the effects due to merger-induced starbursts can also reproduce both our observed relationships.
Original language | English |
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Pages (from-to) | 272-292 |
Number of pages | 21 |
Journal | Monthly Notices of the Royal Astronomical Society (MNRAS) |
Volume | 408 |
Issue number | 1 |
DOIs | |
Publication status | Published - 11 Oct 2010 |
Keywords
- galaxies: abundances
- galaxies: dwarf
- galaxies: elliptical and lenticular, cD
- galaxies: evolution
- galaxies: formation
- galaxies: stellar content
- STELLAR POPULATION-MODELS
- SPATIALLY-RESOLVED SPECTROSCOPY
- SURFACE BRIGHTNESS FLUCTUATIONS
- SPH CHEMODYNAMICAL SIMULATION
- ABSORPTION-LINE STRENGTHS
- STAR-FORMATION HISTORIES
- FUNDAMENTAL-PLANE-SURVEY
- ACTIVE GALACTIC NUCLEI
- RED-SEQUENCE GALAXIES
- ELLIPTIC GALAXIES