Dwarf irregular galaxy Leo A extends even farther, according to HST WFC3 photometry^⋆

¹ Center for Physical Sciences and Technology, Saulėtekio av. 3, 10257 Vilnius, Lithuania
e-mail: vladas.vansevicius@ff.vu.lt
² Vilnius University Observatory, Čiurlionio 29, 03100 Vilnius, Lithuania

Received: 28 August 2017
Accepted: 18 January 2018

Abstract

Context. Leo A is an isolated gas-rich dwarf irregular galaxy of low stellar mass and metallicity residing at the outskirts of the Local Group. Ages of the stellar populations in Leo A range from ~10 Myr to ~10 Gyr. A large stellar halo (up to the deprojected distance of ~1.7 kpc) was discovered based on Subaru wide-field photometry of red giant branch stars.

Aims. We aim to study stellar populations at the very outer region of the Leo A galaxy.

Methods. We analysed HST WFC3 archive observation data in the field that is partly located beyond the previously known limits of the Leo A galaxy. We performed photometry of star-like objects in the F475W and F814W passbands and studied the spatial distribution of the Leo A stars below the horizontal branch.

Results. We report a discovery of stellar halo populations (subgiants and faint red giants) in the Leo A galaxy extending up to ~2.3 kpc deprojected distance from the galaxy centre. Analysis of the colour-magnitude diagram suggests old (>5 Gyr) stellar populations of very low metallicity (Z ~ 0.0001).