Tests of Chemical Enrichment Scenarios in Ellipticals Using Continuum Colors and Spectroscopy

TL;DR

This study combines spectroscopic and photometric data to analyze metallicity distributions in early-type galaxies, revealing the prevalence of the G-dwarf problem and proposing a simple model consistent with observations and inhomogeneous enrichment theories.

Contribution

It introduces a simple analytic model that better fits galaxy color data by reducing metal-poor stars, aligning with inhomogeneous chemical enrichment scenarios.

Findings

G-dwarf problem is common in early-type galaxies.

Simple infall models predict colors too blue compared to observations.

Proposed model reduces metal-poor stars, matching data and inhomogeneous enrichment predictions.

Abstract

We combine spectroscopic metallicity values with integrated narrowband continuum colors to explore the internal metallicity distribution in early-type galaxies. The different techniques for determining metallicity (indices versus colors) allows for an estimate of the contribution from metal-poor stars in a predominantly metal-rich population which, in turn, places constraints on the shape and width of a galaxy's metallicity distribution function (MDF). The color-spectroscopic data is compared to the closed box, infall and inhomogeneous chemical evolution models. The G-dwarf problem, a deficiency in metal-poor stars as compared to closed box models, is evident in the dataset and indicates this deficiency is common to all early-type galaxies. However, even simple infall models predict galaxy colors which are too blue compared to the observations. A simple analytic model is proposed which matches the elliptical data and recent HST observations of M31 (Worthey et al 2005) and NGC 5128 (Harris & Harris 2000) by reducing the number of metal-poor stars in a systematic fashion. While without physical justification, the shape of these models are similar to predictions of inhomogeneous enrichment scenarios.