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]

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

References

  1. 1 2 Skrutskie, Michael F.; Cutri, Roc M.; Stiening, Rae; Weinberg, Martin D.; Schneider, Stephen E.; Carpenter, John M.; Beichman, Charles A.; Capps, Richard W.; Chester, Thomas; Elias, Jonathan H.; Huchra, John P.; Liebert, James W.; Lonsdale, Carol J.; Monet, David G.; Price, Stephan; Seitzer, Patrick; Jarrett, Thomas H.; Kirkpatrick, J. Davy; Gizis, John E.; Howard, Elizabeth V.; Evans, Tracey E.; Fowler, John W.; Fullmer, Linda; Hurt, Robert L.; Light, Robert M.; Kopan, Eugene L.; Marsh, Kenneth A.; McCallon, Howard L.; Tam, Robert; Van Dyk, Schuyler D.; Wheelock, Sherry L. (1 February 2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal. 131 (2): 1163–1183. Bibcode:2006AJ....131.1163S. doi:10.1086/498708. ISSN 0004-6256. S2CID 18913331.
  2. ↑ Karachentsev, I. D.; et al. (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.
  3. ↑ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. S2CID 120973010.
  4. 1 2 3 4 5 6 7 Drzazga, R. T.; et al. (May 2016). "Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976". Astronomy & Astrophysics. 589: 16. arXiv:1603.00482. Bibcode:2016A&A...589A..12D. doi:10.1051/0004-6361/201527236. S2CID 119193441. A12.
  5. 1 2 "NASA/IPAC Extragalactic Database". Results for NGC 2976. Retrieved 2006-11-25.
  6. 1 2 3 4 5 Valenzuela, Octavio; et al. (February 2014). "Non-axisymmetric Structure in the Satellite Dwarf Galaxy NGC 2976: Implications for its Dark/Bright Mass Distribution and Evolution". The Astronomical Journal. 147 (2): 8. arXiv:1310.7021. Bibcode:2014AJ....147...27V. doi:10.1088/0004-6256/147/2/27. S2CID 119246641. 27.
  7. 1 2 Paturel, G.; et al. (2002). "Comparison LEDA/SIMBAD octobre 2002. Catalogue to be published in 2003". LEDA. Bibcode:2002LEDA.........0P.
  8. ↑ Paturel, G.; et al. (December 2003). "HYPERLEDA. I. Identification and designation of galaxies". Astronomy and Astrophysics. 412: 45–55. Bibcode:2003A&A...412...45P. doi:10.1051/0004-6361:20031411.
  9. ↑ "NGC 2976". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-09-15.
  10. ↑ Seligman, Courtney. "NGC Objects: NGC 2950 - 2999". Celestial Atlas. Retrieved 2016-03-01.
  11. ↑ Frommert, Hartmut; Kronberg, Christine (March 29, 1998). "NGC 2976". Students for the Exploration and Development of Space. Retrieved 2020-09-14.
  12. ↑ Williams, Benjamin F.; et al. (January 2010). "The Advanced Camera for Surveys Nearby Galaxy Survey Treasury. IV. The Star Formation History of NGC 2976". The Astrophysical Journal. 709 (1): 135–148. arXiv:0911.4121. Bibcode:2010ApJ...709..135W. doi:10.1088/0004-637X/709/1/135. S2CID 56054888.
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