| NGC 6872 | |
| Epoch: | J2000 |
| Constellation Name: | Pavo |
| Dist Ly: | 212abbr=onNaNabbr=on |
| Mass: | > |
| Size: | >522abbr=onNaNabbr=on (UV light diameter) 717kly (25.5 mag/arcsec−2 B-band isophote) |
| Appmag V: | 10.69 |
| Absmag V: | −23.29 |
| Size V: | 6.0 × 1.7 |
| Notes: | Interacting galaxy with |
| Names: | ,,,, |
NGC 6872, also known as the Condor Galaxy, is a large barred spiral galaxy of type in the constellation Pavo. It is 212e6ly from Earth. is interacting with the lenticular galaxy, which is less than one twelfth as large. The galaxy has two elongated arms with a diameter based on ultraviolet light of over 522000ly, and a D25.5 isophotal diameter of over 717000ly, making it the largest known spiral galaxy. It was discovered on 27 June 1835 by English astronomer John Herschel.
When observed in the ultraviolet and mid-infrared, the central region and bar of show old stars and low rates of star 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 a stellar 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 young star 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.
IC 4970 is a nearby lenticular galaxy, located only a few arcseconds 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 that approached 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.
An ultraviolet-to-infrared study by Eufrasio, et al. (2013), using data from GALEX, Spitzer, and other resources found that the interaction between the two galaxies appears to have triggered significant star formation in the northeastern arm of beginning about 40kpc from its nucleus. The same appears to have also occurred in the southwestern arm. A bright ultraviolet source was discovered at the end of the northeastern arm, around 90kpc from the nucleus, which may be a tidal dwarf galaxy formed out of the interaction between and . 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. Mihos, et al. (1993), and Eufrasio, et al. (2014), suggest that prior to its interaction with, the galaxy's disk may have been non-uniform with an extended mass distribution.
Machacek, et al. (2005), reported on a 90- X-ray trail that exists between and the nearby elliptical galaxy . is moving away from at 849km/s28km/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 behind as it moves, interstellar medium that was stripped from by ram pressure as it passed through the densest part of the Pavo group, and interstellar medium stripped from by turbulent viscosity as it passes through Pavo. Any or all of these processes may be responsible for the trail. If and did interact in the past, the latter may have affected spiral arms and gas distribution as much as its interaction with .