Spectroscopic study of blue compact galaxies III. Empirical population synthesis

TL;DR

This study analyzes the stellar populations of 73 blue compact galaxies using empirical population synthesis, revealing they are typically old, with complex star formation histories involving multiple stellar generations and varying metallicities.

Contribution

First application of empirical population synthesis to a large sample of blue compact galaxies, providing detailed insights into their stellar content and star formation histories.

Findings

BCGs are age-composite stellar systems with multiple stellar populations.

Star formation episodes in BCGs typically started less than a billion years ago.

Older stars can contribute up to half of the optical emission in BCGs.

Abstract

This is the third paper of a series dedicated to the study of the star formation rates, star formation histories, metallicities and dust contents of a sample of blue compact galaxies (BCGs). We constrain the stellar contents of 73 blue compact galaxies by analyzing their continuum spectra and the equivalent widths of strong stellar absorption features using a technique of empirical population synthesis based on a library of observed star-cluster spectra. Our results indicate that blue compact galaxies are typically age-composite stellar systems; in addition to young stars, intermediate-age and old stars contribute significantly to the 5870 A continuum emission of most galaxies in our sample. The stellar populations of blue compact galaxies also span a variety of metallicities. The ongoing episodes of star formation started typically less than a billion years ago. Some galaxies may be undergoing their first global episode of star formation, while for most galaxies in our sample, older stars are found to contribute up to half the optical emission. Our results suggest that BCGs are primarily old galaxies with discontinuous star formation histories. The absorption equivalent widths measured in the synthetic spectra range from typically 1.5 A for Halpha, to 2 -- 5 A for Hbeta, Hgamma, and Hdelta. The implied accurate measurements of emission-line intensities will be used in a later study to constrain the star formation rates and gas-phase chemical element abundances of blue compact galaxies.