| NGC 6872 | |
|---|---|
 NGC 6872 (center) withIC 4970 (above) | |
| Observation data (J2000epoch) | |
| Constellation | Pavo |
| Right ascension | 20h 16m 56.558s[1] |
| Declination | −70° 46′ 04.60″[1] |
| Redshift | 0.015194±0.0001[1] |
| Heliocentric radial velocity | 4555±30 km/s[1] |
| Galactocentric velocity | 4443±30 km/s[1] |
| Distance | 212 Mly (65 Mpc)[2] |
| Apparent magnitude (V) | 10.69[1] |
| Absolute magnitude (V) | −23.29[1] |
| Characteristics | |
| Type | SB(s)b pec[1] |
| Mass | >1011[3] M☉ |
| Size | 219.63kiloparsecs (716,000light-years)(diameter;25.0 mag/arcsec2 B-band isophote)[1] |
| Apparent size (V) | 6.0′ × 1.7′[1] |
| Notable features | Interacting galaxy withIC 4970 |
| Other designations | |
| ESO 73-32,JB a 28-1,LEDA 64413,2MASX J20165648-7046057,2E 2011.7-7055 | |
NGC 6872, also known as theCondor Galaxy,[3] is a largebarredspiral galaxy oftypeSB(s)b pec in the constellationPavo. It is 212 millionlight-years (65 Mpc) from Earth.[3]NGC 6872 isinteracting with the lenticular galaxyIC 4970, which is less than one twelfth as large.[2][3] The galaxy has two elongated arms with a diameter based on ultraviolet light of over 522,000light-years (160,000 pc), and a D25.5isophotal diameter of over 717,000light-years (220,000 pc), making it thelargest known spiral galaxy.[2][a][b] The galaxy contains a centralblack hole with a mass of 269 millionM☉[4]. It was discovered on 27 June 1835 by English astronomerJohn Herschel.[5]
When observed in theultraviolet and mid-infrared, the central region and bar ofNGC 6872 showold stars and low rates ofstar formation, with rates increasing along the spiral arms as distance from the core increases. The most active region of star formation, located in the northeast arm, shows astellar flux around 1,000 times higher than in the central region, though this may be affected by the density of stellar dust in the core. The extended portions of both arms exhibit youngstar cluster formations with ages ranging from one to one hundred million years. Star formation rates in the northeast extended arm are twice that of the southwest extended arm, and five times the formation rate in the sections of the arms closer to the central region.[3]
IC 4970 is a nearbylenticular galaxy, located only a fewarcseconds away, and is known to be interacting with NGC 6872. Horrelou and Koribalski (2007), using a computer simulation to determine how the two galaxies were interacting, reported thatIC 4970 approachedNGC 6872 nearly along the plane of its spiral disk, making its closest approach approximately 130 million years ago and resulting in the latter's current highly elongated shape.[6]
An ultraviolet-to-infrared study by Eufrasio,et al. (2013), using data fromGALEX,Spitzer, and other resources found that the interaction between the two galaxies appears to have triggered significant star formation in the northeastern arm ofNGC 6872 beginning about 130 thousand light-years (40 kpc) from its nucleus.[7] The same appears to have also occurred in the southwestern arm.[2] A bright ultraviolet source was discovered at the end of the northeastern arm, around 290 thousand light-years (90 kpc) from the nucleus, which may be atidal dwarf galaxy formed out of the interaction betweenIC 4970 andNGC 6872.[7] The bright ultraviolet nature of this cluster indicates that it contains stars less than 200 million years old, which roughly coincides with the timeframe of the collision.[2] Mihos,et al. (1993), and Eufrasio,et al. (2014), suggest that prior to its interaction withIC 4970, the galaxy's disk may have been non-uniform with an extended mass distribution.[3][8]
Machacek,et al. (2005), reported on a 290–330-thousand-light-year (90–100 kpc)X-ray trail that exists betweenNGC 6872 and the nearby elliptical galaxyNGC 6876.NGC 6872 is moving away fromNGC 6876 at 849 ± 28 km/s (528 ± 17 mi/s) in approximately the same trajectory as the X-ray trail, suggesting a link between the two galaxies. Four possibilities for the trail's existence were given: gas stripped from the two galaxies during a close fly-by,intergalactic medium that has been gravitationally focused behindNGC 6872 as it moves,interstellar medium that was stripped fromNGC 6872 byram pressure as it passed through the densest part of the Pavo group, and interstellar medium stripped fromNGC 6872 by turbulentviscosity as it passes through Pavo. Any or all of these processes may be responsible for the trail. IfNGC 6872 andNGC 6876 did interact in the past, the latter may have affectedNGC 6872's arms and gas distribution as much as its interaction withIC 4970.[9]
