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

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).

Photometric data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A144