Star formation history of KDG 61 and KDG 64 from spectroscopy and colour-magnitude diagrams

TL;DR

This study combines spectroscopy and colour-magnitude diagrams to analyze the star formation history of KDG 61 and KDG 64, revealing predominantly old, low-metallicity populations with some intermediate-age stars, and no significant gradients.

Contribution

It provides a comprehensive star formation history of KDG 61 and KDG 64 using combined spectroscopic and photometric data, highlighting their old populations and marginal metallic enrichment.

Findings

Galaxies dominated by old (12-14 Gyr) low-metallicity populations.

Detection of stars aged 1 to 4 Gyr with marginal metal enrichment.

No significant radial gradients in age or metallicity.

Abstract

A study of two dE/dSph members of the nearby M 81 group of galaxies, KDG 61 and UGC 5442 = KDG 64, has been made. Direct Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images and integrated-light spectra of 6 m telescope of Special Astrophysical Observatory of Russian Academy of Sciences have been used for quantitative star formation history analysis. The spectroscopic and colour-magnitude diagrams analysis gives consistent results. These galaxies appear to be dominated by an old population (12-14 Gyr) of low metallicity ([Fe/H]~-1.5). Stars of ages about 1 to 4 Gyr have been detected in both galaxies. The later population shows marginal metal enrichment. We do not detect any significant radial gradients in age or metallicity in these galaxies. Our radial velocity measurement suggests that the HII knot on the line-of-sight of KDG 61 is not gravitationally attached to the galaxy.