| NGC 2976 | |
|---|---|
 | |
| Observation data (J2000epoch) | |
| Constellation | Ursa Major |
| Right ascension | 09h 47m 15.458s[1] |
| Declination | +67° 54′ 58.97″[1] |
| Distance | 11.6 ± 1.2 Mly (3.56 ± 0.38 Mpc)[2][3] |
| Group orcluster | M81 Group[4] |
| Apparent magnitude (V) | 10.8[5] |
| Absolute magnitude (B) | 16.90[6] |
| Characteristics | |
| Type | SAa[7] |
| Size | 6 kpc[4] |
| Apparent size (V) | 5.89′ × 3.02′[8] |
| Notable features | Peculiar |
| Other designations | |
| IRAS 09431+6809,UGC 5221,[9] H I.285,PGC 28120[5] | |
NGC 2976 is a peculiardwarf galaxy[4] in the northerncircumpolar constellation ofUrsa Major. It was discovered by German-born astronomerWilliam Herschel on November 8, 1801, and catalogued as H I.285.J. L. E. Dreyer described it as, "bright, very large, much extended 152°, star involved".[10] It is a member of theM81 Group[4] and lies 1° 20′ to the southwest ofMessier 81.[11] The projected separation of this galaxy from the M81 Group is190 kpc.[6]
Themorphological classification of this galaxy is SAa,[7] which matches anunbarred spiral galaxy (SA) with very tightly-woundspiral arms (a). The actual visual form of the galaxy is a pure disk with no spiral arms or bulge. The luminosity and size of this galaxy is mid-way between theLarge andSmall Magellanic Clouds.[4]De Vaucouleurs and associates classed it as type SAc, suggesting more loosely wound arms. It is inclined at an angle of 65° to theline of sight from theEarth.[4]
Although appearing as a disk, there is evidence for a non-axisymmetric form of gas distribution, with a suggestion of central bar plus large-scale spiral arms.[6] The inner structure contains many dark lanes and stellar condensations in its disk. There are two strongH II regions, one to each side.[6] The overall star formation rate is0.2 M☉ y−1.[4] The outer disk shows a history of steadystar formation, although the formation rate has declined significantly over the last billion years and the population is now dominated by older stars. Within a~3 kpc radius of the center, star formation has been steady, having not undergone a recent decline.[12]
There is a cloud ofneutral hydrogen with a mass of(2.67±0.65)×107 M☉ located27 kpc to the northeast of this galaxy, which may be interacting gravitationally with NGC 2976. The galaxy also shows evidence of tidal stripping, with an extendedtidal tail of neutral hydrogen. The last significant interaction took place around one billion years ago.[6]
Media related toNGC 2976 at Wikimedia Commons