Giant Halos in Dwarf Irregular Galaxies vs. Dwarf Elliptical Galaxies

Abstract

We present a discovery of a giant stellar halo in NGC 6822, a dwarf irregular galaxy in the Local Group. This halo is mostly made of old red giants, showing striking features: 1) it is several times larger than the main body of the galaxy seen in the optical images, and 2) it is elongated in the direction almost perpendicular to the HI disk of NGC 6822. The structure of this stellar halo looks similar to the shape of dwarf elliptical galaxies, indicating that the halos of dwarf irregular galaxies share the same origin with those of the dwarf elliptical galaxies.Comment: 4 pages, 3 figures, proceedings of IAU Colloquium 198, "Near-Field Cosmology With Dwarf Elliptical Galaxies", editors H. Jerjen and B. Binggeli, Cambridge University Pres