Sagittarius Dwarf Irregular Galaxy
The Sagittarius Dwarf Irregular Galaxy (SagDIG) is a dwarf galaxy in the constellation of Sagittarius. (SagDIG should not be confused with the Sagittarius Dwarf Spheroidal Galaxy, SagDEG, a satellite galaxy of the Milky Way discovered decades later in the same constellation.) It lies about 3.4 million light-years away. It was discovered by Cesarsky et al. on a photographic plate taken for the ESO (B) Atlas on 13 June 1977 using the ESO 1 meter Schmidt telescope.
| SagDIG | |
|---|---|
SagDIG by Hubble Space Telescope | |
| Observation data (J2000 epoch) | |
| Constellation | Sagittarius |
| Right ascension | 19h 29m 59.0s |
| Declination | −17° 40′ 41″ |
| Redshift | −79±1 km/s |
| Distance | 3.39±0.23 Mly (1.04±0.07 Mpc) |
| Apparent magnitude (V) | 15.5 |
| Characteristics | |
| Type | IB(s)m V (Dwarf irregular galaxy) |
| Apparent size (V) | 2.9′ × 2.1′ |
| Other designations | |
| Sagittarius Dwarf Irregular, SGR Dwarf, ESO594-G004, PGC 63287, Kowal's Object | |
The SagDIG is thought to be the member of the Local Group most remote from the Local Group's barycenter. It is only slightly outside the zero-velocity surface of the Local Group.
SagDIG is a much more luminous galaxy than the Aquarius Dwarf and it has been through a prolonged period of star formation. This has resulted in it containing a rich intermediate-age population of stars. Twenty-seven candidate carbon stars have been identified inside SagDIG. Analysis shows that the underlying stellar population of SagDIG is metal-poor (at least [Fe/H] ≤ −1.3). Further, the population is young, with the most likely average age between 4 and 8 billion years for the dominant population.