ESO540-032: a Transition-Type Dwarf in the Sculptor Group

TL;DR

This study presents detailed observations of the dwarf galaxy ESO540-032, revealing its transition-type nature through stellar populations, distance, metallicity, and HI content, confirming its classification within the Sculptor group.

Contribution

The paper provides the first comprehensive analysis of ESO540-032's stellar populations, metallicity, and gas content, establishing it as a transition-type dwarf galaxy in the Sculptor group.

Findings

Dominated by old red giant stars with a small young blue population

Distance estimated at 3.7 Mpc from the red giant branch tip

Contains approximately 10^6 solar masses of HI gas

Abstract

A color-magnitude diagram (CMD) based on HST/ACS data is presented for the Sculptor group dwarf galaxy ESO540-032. The CMD is dominated by an old red giant population but there is a small population of blue stars confined to the central regions of the galaxy as orginally noted by Jerjen and Rejkuba from ground-based data. From the luminosity of the red giant branch tip the distance is determined as 3.7 +/- 0.2 Mpc consistent with previous estimates. The mean metallicity is estimated as [Fe/H] = -1.7 +/- 0.2 from the color of the red giant branch. Isochrone fits indicate an age for the blue star population of ~100 Myr, perhaps less. New HI observations with the Australian Telescope Compact Array confirm that the dwarf contains approximately 10^6 solar masses of HI, centered on the optical image. The HI mass to blue luminosity ratio is 0.15, comparable to the Phoenix dwarf in the Local Group. These properties clearly confirm ESO540-032 as a transition-type dwarf in the Sculptor group.