NGC 2976

NGC 2976
Observation data (J2000 epoch)
ConstellationUrsa Major
Right ascension09h 47m 15.458s[1]
Declination+67° 54′ 58.97″[1]
Distance11.6 ± 1.2 Mly (3.56 ± 0.38 Mpc)[2][3]
Group or clusterM81 Group[4]
Apparent magnitude (V)10.8[5]
Absolute magnitude (B)16.90[6]
Characteristics
TypeSAa[7]
Size6 kpc[4]
Apparent size (V)5.89′ × 3.02′[8]
Notable featuresPeculiar
Other designations
IRAS 09431+6809, UGC 5221,[9] H I.285, PGC 28120[5]
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NGC 2976 is a peculiar dwarf galaxy[4] in the northern circumpolar constellation of Ursa Major. It was discovered by German-born astronomer William 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 the M81 Group[4] and lies 1° 20′ to the southwest of Messier 81.[11] The projected separation of this galaxy from the M81 Group is 190 kpc.[6]

The morphological classification of this galaxy is SAa,[7] which matches an unbarred spiral galaxy (SA) with very tightly-wound spiral 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 the Large and Small 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 the line of sight from the Earth.[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 strong H II regions, one to each side.[6] The overall star formation rate is 0.2 M☉ y−1.[4] The outer disk shows a history of steady star 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 of neutral hydrogen with a mass of (2.67±0.65)×107 M☉ located 27 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 extended tidal tail of neutral hydrogen. The last significant interaction took place around one billion years ago.[6]

Closeup of NGC 2976 by the Hubble Space Telescope
  1. ^ a b Cite error: The named reference Skrutskie2006 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference karachentsevetal2004 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference Karachentsevetal2006 was invoked but never defined (see the help page).
  4. ^ a b c d e f g Cite error: The named reference Drzazga2016 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference ned was invoked but never defined (see the help page).
  6. ^ a b c d e Cite error: The named reference Valenzuela2014 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Paturel2002 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Paturel2003 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Seligman was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference SEDS was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Williams2010 was invoked but never defined (see the help page).