NGC 5557 is an elliptical galaxy in the constellation Boötes. It was discovered by William Herschel on May 1, 1785.[4] The distance to NGC 5557 is not well known, but it is estimated to be about 127 million light-years (38.8 megaparsecs) away.[3]
| NGC 5557 | |
|---|---|
 SDSS image of NGC 5557 | |
| Observation data (J2000 epoch) | |
| Constellation | Boötes |
| Right ascension | 14h 18m 25.708s[1] |
| Declination | +36° 29′ 37.28″[1] |
| Redshift | 0.010764[2] |
| Heliocentric radial velocity | 3210 ± 28 km/s[2] |
| Distance | 127 Mly (38.8 Mpc)[3] |
| Apparent magnitude (V) | 12.2[4] |
| Absolute magnitude (V) | −22.39[5] |
| Characteristics | |
| Type | E1[3] |
| Other designations | |
| UGC 9161, MCG +06-31-093, PGC 51104[2] | |
NGC 5557 is quite massive, with a K-band absolute magnitude of −24.8, and is a slow rotator,[3] which suggests it gained mass through dry mergers (galaxy mergers involving galaxies significant amounts of gas).[5] However, it has a faint tidal tail to its east, as well as a more complex structure to the west. This structure, if found to be connected to NGC 5557, would one of the largest around a galaxy, spanning about 1.1 million light-years (350,000 parsecs).[3] This filamentary structure suggests that NGC 5557 may have formed from a more gas-rich galaxy merger a couple billion years ago.[3] This implies that the galaxy merger would need to have a low impact parameter.[5]
NGC 5557 is part of a galaxy group,[3][4] and is the largest such galaxy in the group by far.[3] Surrounding the galaxy near the eastern filament are several small bluish objects, which are possibly tidal dwarf galaxies.[3]
Two supernovae have been observed in NGC 5557: SN 1996aa (type Ia, mag. 17),[6] and SN 2013gn (type Ia, mag. 15.3).[7]
References
External links
Media related to NGC 5557 at Wikimedia Commons
