Andromeda VIII

RA:

00 : 42.3

Dec:

+ 40 : 37

Type:

dSph pec

RV:

- 500 km/s

Distance:

2700 kly

Apparent Dimension:

45 x 10 arc min

Diameter:

35 x 8 kly

Brightness:

9.1 mag vis

Abs. Mag:

- 15.6 Mag vis

Mass:

And VIII is another dwarf companion of the Andromeda Galaxy M31. This galaxy is so transparent and so vastly extended that it had escaped previous detection despite the fact that it is actually large and of considerable total brightness. It lies within the line of sight from us to the outlayers of the disk of M31, and is projected very close to M32, the brightest elliptical satellite galaxy of the Andromeda Galaxy.

The discoverers found And VIII because of its considerable high relative radial velocity with respect to both M31 and M32: The new galaxy is approaching us at about 500 km/s, which is about 200 km/s more than that of M31, and about 350 km/s more than that of M32. They found 12 candidate planetary nebulae (5 considered safe), and 3 candidate globular cluster members (1 safe), as well as notable amounts of neutral hydrogen gas (H I; about 4*10^5 solar masses) with about this radial velocity. Because of the high differences in radial velocities, it is improbable that this structure is physically associated with either M31 or M32, and gives evidence for its nature as an independent, previously unknown galaxy of low surface brightness.

Apparently, the large extension of this new galaxy comes from tidal gravitational interaction with large M31, which has already almost disrupted this companion. Tidal forces make stars escape from it and spread along its orbit in a tidal stream of stars, which extends far away from the dwarf galaxy.

The image presented here is a representation of And VIII by Nancy Lin over a photo by Robert Gendler; see Case Western Range University Press Release.

Links:

• Case Western Range University Press Release of September 16, 2003 (Local Copy)

• Heather L. Morrison, Paul Harding, Denise Hurley-Keller, and George Jacoby, 2003. Andromeda VIII - a New Tidally Distorted Satellite of M31. [ADS: 2003ApJ...596L.183M] - [Preprint: astro-ph/0309254].

Last Modification: September 18, 2003