NGC 2974

NGC 2974 (also catalogued as NGC 2652) is a lenticular galaxy located in the constellation Sextans. It is located at a distance of circa 90 million light years from Earth, which, given its apparent dimensions, means that NGC 2974 is about 90,000 light years across. It was discovered by William Herschel on January 6, 1785.[4] NGC 2974 is located in the sky about 2 and a half degrees south-south east of Iota Hydrae and more than 6 degrees northeast of Alphard. A 10th magnitude star lies next to the galaxy, thus making it a challenging object at low magnifications. NGC 2974 is part of the Herschel 400 Catalogue.[5]

NGC 2974
Observation data (J2000 epoch)
ConstellationSextans
Right ascension 09h 42m 33s[1]
Declination−03° 41′ 57″[1]
Redshift0.006294 ± 0.000017 [1]
Helio radial velocity1,887 ± 5 km/s[1]
Distance89 ± 29 Mly (27.3 ± 8.8 Mpc)[1]
Apparent magnitude (V)10.9 [2]
Characteristics
TypeE4 [3]
Apparent size (V)3′.5 × 2′.0 [1]
Other designations
NGC 2652, UGCA 172, CGCG 007-022, MCG +00-25-008, PGC 27762[1]

Characteristics
NGC 2974 by GALEX in ultraviolet, where an outer ring becomes visible.

NGC 2974 has been categorised by Gérard de Vaucouleurs as an elliptical galaxy,[3] however there is evidence the galaxy has a disk. A rotating disk of neutral hydrogen with axis similar to that of the optical isophotes of the galaxy was detected in 1988 by Kim et al. They estimated the total HI mass to be 8×108 M☉.[6] The galaxy in ultraviolet, as observed by GALEX, features an outer ring structure that holds about 1% of the total stellar mass of the galaxy and has a population of young stars.[7] The radius of the ring is about 60 arcseconds, while one more, partial, ring has been detected in large radii.[8] The galaxy also features multiple shells, which indicate that it has accreted material, probably by the merger of smaller galaxies.[9]

More detailed observations of the galaxy in HI by the Very Large Array revealed that the HI disk is in fact a ring. The observations also made it possible to measure the rotation curve of HI. The rotation curve rises quickly to a maximal velocity and then declines slowly until it flattens out at a lower velocity. This rotation curve is typical of galaxies with concentrated light distribution and could indicate that while the central part is dominated by visible mass, the outer parts are dominated by dark matter. The mass-to-light ratio is 4.3 M☉/L☉I at one effective radius and increases to 8.5 M☉/L☉I at 5 effective radii, where dark matter comprises at least 55 per cent of the total mass.[10]

Observations of the central area of the galaxy by Hubble Space Telescope revealed the presence of two gaseous spiral features, extending for about 200 parsecs. The kinematics of the central area show significant deviations from circular motions and they have been interpreted as the signature of a bar which is about 540 parsecs in diameter. The bar, although too weak to be detected in visual light is considered strong enough to channel material towards the central parsecs of the nucleus.[11] Observations by SAURON (Spectrographic Areal Unit for Research on Optical Nebulae) confirmed the presence of the inner bar, while it was noted that it is possible that a large-scale bar exists too.[12] The current star formation activity and morphological evolution of NGC 2974 has been attributed to the large bar.[8] A ring observation in O III images may be associated with the inner bar[12] or a nuclear ring.[8]

The nucleus of the galaxy has been found to be active and it has been categorised as a type 2 Seyfert galaxy.[13] The most accepted theory for the energy source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. The mass of the black hole in the centre of NGC 2974 is estimated to be between 140 and 210 million (108.23±0.09) M☉ based on the stellar velocity dispersion.[14]

Nearby galaxies

NGC 2974 is the largest and brightest galaxy in the NGC 2974 group. Other members of the group include the galaxies MCG -01-25-024, UGCA 173, and UGCA 175.[15] Other nearby galaxies include NGC 2967 and UGC 5228 with their groups.[16]

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References
  1. "NASA/IPAC Extragalactic Database". Results for NGC 2974. Retrieved 2019-01-18.
  2. "Revised NGC Data for NGC 2974". spider.seds.org. Retrieved 25 November 2018.
  3. de Vaucouleurs, G.; et al. (1991). "Third reference catalogue of bright galaxies". 9. New York: Springer-Verlag. Cite journal requires |journal= (help)
  4. Seligman, Courtney. "NGC 2974". Celestial Atlas. Retrieved 19 November 2018.
  5. O'Meara, Steve (2007). Herschel 400 Observing Guide. Cambridge University Press. pp. 85–86. ISBN 9780521858939.
  6. Kim, D.-W.; Jura, M.; Guhathakurta, P.; Knapp, G. R.; van Gorkom, J. H. (July 1988). "H I observations of the elliptical galaxies NGC 2974 and NGC 5018". The Astrophysical Journal. 330: 684. doi:10.1086/166504.
  7. Marino, Antonietta; Bianchi, Luciana; Rampazzo, Roberto; Thilker, David A.; Annibali, Francesca; Bressan, Alessandro; Buson, Lucio Maria (1 August 2011). "TRACING REJUVENATION EVENTS IN NEARBY S0 GALAXIES". The Astrophysical Journal. 736 (2): 154. arXiv:1105.3812. doi:10.1088/0004-637X/736/2/154.
  8. Jeong, H.; Bureau, M.; Yi, S. K.; Krajnovic, D.; Davies, R. L. (11 April 2007). "Star formation and figure rotation in the early-type galaxy NGC 2974". Monthly Notices of the Royal Astronomical Society. 376 (3): 1021–1032. arXiv:astro-ph/0608212. doi:10.1111/j.1365-2966.2007.11535.x.
  9. Tal, Tomer; van Dokkum, Pieter G.; Nelan, Jenica; Bezanson, Rachel (1 November 2009). "The Frequency of Tidal Features Associated with Nearby Luminous Elliptical Galaxies From a Statistically Complete Sample". The Astronomical Journal. 138 (5): 1417–1427. arXiv:0908.1382. Bibcode:2009AJ....138.1417T. doi:10.1088/0004-6256/138/5/1417.
  10. Weijmans, Anne-Marie; Krajnović, Davor; Van De Ven, Glenn; Oosterloo, Tom A.; Morganti, Raffaella; De Zeeuw, P. T. (4 January 2008). "The shape of the dark matter halo in the early-type galaxy NGC 2974". Monthly Notices of the Royal Astronomical Society. 383 (4): 1343–1358. doi:10.1111/j.1365-2966.2007.12680.x.
  11. Emsellem, E.; Goudfrooij, P.; Ferruit, P. (11 November 2003). "A two-arm gaseous spiral in the inner 200 pc of the early-type galaxy NGC 2974: signature of an inner bar". Monthly Notices of the Royal Astronomical Society. 345 (4): 1297–1312. doi:10.1046/j.1365-2966.2003.07050.x.
  12. Krajnovic, D.; Cappellari, M.; Emsellem, E.; McDermid, R. M.; De Zeeuw, P. T. (11 March 2005). "Dynamical modelling of stars and gas in NGC 2974: determination of mass-to-light ratio, inclination and orbital structure using the Schwarzschild method". Monthly Notices of the Royal Astronomical Society. 357 (4): 1113–1133. doi:10.1111/j.1365-2966.2005.08715.x.
  13. Maia, Marcio A. G.; Machado, Rodolfo S.; Willmer, Christopher N. A. (October 2003). "The Seyfert Population in the Local Universe". The Astronomical Journal. 126 (4): 1750–1762. doi:10.1086/378360.
  14. Bosch, Remco C. E. van den (2 November 2016). "Unification of the fundamental plane and Super Massive Black Hole Masses". The Astrophysical Journal. 831 (2): 134. arXiv:1606.01246. doi:10.3847/0004-637X/831/2/134.
  15. Garcia, A. M. (1993). "General study of group membership. II - Determination of nearby groups". Astronomy and Astrophysics Supplement Series. 100 (1): 47–90. Bibcode:1993A&AS..100...47G. ISSN 0365-0138.
  16. Makarov, Dmitry; Karachentsev, Igor (21 April 2011). "Galaxy groups and clouds in the local (z∼ 0.01) Universe". Monthly Notices of the Royal Astronomical Society. 412 (4): 2498–2520. arXiv:1011.6277. Bibcode:2011MNRAS.412.2498M. doi:10.1111/j.1365-2966.2010.18071.x.


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