We have discovered a new Galactic satellite galaxy in the constellation of
Sagittarius. The Sagittarius dwarf galaxy is the nearest galaxy known, subtends
an angle of >10 degrees on the sky, lies at a distance of 24 \kpc from the
Sun, \sim 16 \kpc from the centre of the Milky Way. Itis comparable in size
and luminosity to the largest dwarf spheroidal, has a well populated red
horizontal branch with a blue HB extension; a substantial carbon star
population; and a strong intermediate age stellar component with evidence of a
metallicity spread. Isodensity maps show it to be markedly elongated along a
direction pointing towards the Galactic centre and suggest that it has been
tidally distorted. The close proximity to the Galactic centre, the
morphological appearance and the radial velocity of 140 km/s indicate that this
system must have undergone at most very few close orbital encounters with the
Milky Way. It is currently undergoing strong tidal disruption prior to being
integrated into the Galaxy. Probably all of the four globular clusters, M54,
Arp 2, Ter 7 and Ter 8, are associated with the Sagittarius dwarf galaxy, and
will probably share the fate of their progenitor.Comment: MNRAS in press, 22pp uuencoded PS file, 26 printed figures available
on request from [email protected]
