Paper detail

The size and structure of the spheroid of IC 1613

Nearby galaxies, spirals as well as irregulars, have been found to be much larger than previously believed. The structure of the huge spheroid surrounding dwarf galaxies could give clues to their past gravitational history. Thanks to wide field imagers, nearby galaxies with diameter of dozens of arcmin can be effectively surveyed. We obtain, from the CFHT archives, a series of i' and g' MegaCam images of IC 1613 in order to determine the stellar surface density of the field and determine the shape of its spheroid. From the colour magnitude diagram we select some 36,000 stars, in the first three magnitudes of the red giant branch. The spatial distribution of these stars is used to establish the structure of the spheroid. The position angle of the major axis of the stellar spheroid is found to be $\approx 90^\circ$, some 30$^\circ$ from the major axis of the HI cloud surrounding IC 1613. The surface density profile of the spheroid is not exponential over all the length of the major axis. A King profile, with a core radius of 4.5' and a tidal radius of 24' fits the data. The tidal truncation of the spheroid suggests that IC 1613 is indeed a satellite of M31.