NGC 7217
Spiral Galaxy NGC 7217 by HST, 1.62′ view
Observation data (J2000 epoch)
ConstellationPegasus
Right ascension22h 07m 52.4s[1]
Declination+31° 21′ 33″[1]
Redshift952 ± 2 km/s[1]
Distance50.0 Mly
Apparent magnitude (V)11.0[1]
Characteristics
Type(R)SA(r)ab[1]
Apparent size (V)3.9′ × 3.2′[1]
Other designations
UGC 11914,[1] PGC 68096[1]

NGC 7217 is an unbarred spiral galaxy in the constellation Pegasus.

Features

NGC 7217 is a gas-poor system[2] whose main features are the presence of several rings of stars concentric to its nucleus: three main ones –the outermost one being of the most prominent and the one that features most of the gas and star formation of this galaxy –[2] plus several others inside the innermost one discovered with the help of the Hubble Space Telescope; a feature that suggests NGC 7217's central regions have suffered several starbursts.[3] There is also a very large and massive spheroid that extends beyond its disk.[4]

Other noteworthy features this galaxy has are the presence of a number of stars rotating in the opposite direction around the galaxy's center to most of them[5] and two distinct stellar populations: one of intermediate age on its innermost regions and a younger, metal-poor version on its outermost ones.[6]

It has been suggested these features were caused by a merger with another galaxy[7] and, in fact, computer simulations show that NGC 7217 could have been a large lenticular galaxy that merged with one or two smaller gas-rich ones of late Hubble type becoming the spiral galaxy we see today;[6] however right now this galaxy is isolated in space, with no nearby major companions.[6] More recent research, however, presents a somewhat different scenario in which NGC 7217's massive bulge and halo would have been formed in a merger and the disk formed later (and is still growing) either accreting gas from the intergalactic medium or smaller gas-rich galaxies, or most likely from a previously existing reserve.[8]

Wide field view of the galaxy

See also

References

  1. 1 2 3 4 5 6 7 8 "NASA/IPAC Extragalactic Database". Results for NGC 7217. Retrieved 2006-11-25.
  2. 1 2 Verdes-Montenegro, L.; Bosma, A. (1995). "The three rings of the isolated galaxy NGC 7217". Astronomy and Astrophysics. 300: 65. Bibcode:1995A&A...300...65V.
  3. ↑ Combes, F.; García-Burillo, S.; Boone, F.; Hunt, L.K.; et al. (2004). "Molecular gas in NUclei of GAlaxies (NUGA). II. The ringed LINER NGC 7217". Astronomy and Astrophysics. 414 (3): 857–872. arXiv:astro-ph/0310652. Bibcode:2004A&A...414..857C. doi:10.1051/0004-6361:20031664. S2CID 12941641.
  4. ↑ Buta, R.; van Driel, W.; Braine, J.; Combes, F.; et al. (1995). "NGC 7217: A Spheroid-dominated, Early-Type Resonance Ring Spiral Galaxy". The Astrophysical Journal. 450: 593. Bibcode:1995ApJ...450..593B. doi:10.1086/176169.
  5. ↑ Merrifield, M.R.; Kuijken, K. (1994). "Counterrotating stars in the disk of the SAB galaxy NGC 7217". Astrophysical Journal. 432 (2): 575–589. Bibcode:1994ApJ...432..575M. doi:10.1086/174596. hdl:1887/92276.
  6. 1 2 3 Sil'Chenko, O.K.; Chillingarian, I.V.; Sotnikova, N.Y.; Afanasiev, Victor L. (2011). "Large-scale nested stellar discs in NGC 7217". Monthly Notices of the Royal Astronomical Society. 414 (4): 3645–3655. arXiv:1103.1692. Bibcode:2011MNRAS.414.3645S. doi:10.1111/j.1365-2966.2011.18665.x. S2CID 119299160.
  7. ↑ Sil'Chenko, O.K.; Moiseev, A.V. (2006). "Nature of Nuclear Rings in Unbarred Galaxies: NGC 7742 and NGC 7217". The Astronomical Journal. 131 (6): 1336–1346. arXiv:astro-ph/0512431. Bibcode:2006AJ....131.1336S. doi:10.1086/499945. S2CID 14589261.
  8. ↑ Fabricius, M. H.; Coccato, Lodovico; Bender, R.; Drory, N.; Gössl, C.; Landriau, M.; Saglia, R. P.; Thomas, J.; Williams, M. J. (2009). "Regrowth of stellar discs in mature galaxies: the two-component nature of NGC 7217 revisited with VIRUS-W". Monthly Notices of the Royal Astronomical Society. 441 (3): 2212–2229. arXiv:1404.2272. Bibcode:2014MNRAS.441.2212F. doi:10.1093/mnras/stu694. S2CID 119269888.
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