NGC 4691 is a barred spiral galaxy in the constellation Virgo. The galaxy lies about 70 million light years away from Earth, which means, given its apparent dimensions, that NGC 4691 is approximately 60,000 light years across.[1] It was discovered by William Herschel on April 17, 1784.[3]

Characteristics

The galaxy has a prominent bar with some bright knots. From the bar emerge two diffuse low-surface-brightness spiral arms which are devoid of knots. The arms form a nearly complete outer ring.[4] Dust is visible across the inner regions of the galaxy. The dust lanes are generally perpendicular to the major axis of the bar.[5] The galaxy is seen face-on. The total molecular gas of the galaxy based on CO emission is estimated to be about 9×108 M☉. Two large molecular clouds are visible along the bar in each side of the nucleus and one more is seen perpendicularly to the bar, located within the inner Lindblad resonance.[6]

The nucleus of the galaxy has been categorised as active, however there is no evidence of it being active in optical wavelengths, but it is a star forming region (HII region) instead.[7][8] A broad H-alpha component has been observed in the central region of the galaxy that is blueshifted by about 500 km/s in respect to the galaxy, indicating it is an outflow that pushes gas away from the plane of the galaxy. It is possible the outflow was created by supernova remnants in the circumnuclear star forming regions.[9]

Supernova

One supernova has been observed in NGC 4691, SN 1997X. It was discovered on 1 February 1997 by Masakatsu Aoki at an apparent magnitude of 13.6.[10] It has been identified spectrographically as a type Ic supernova about one week post maximum.[11][12]

Nearby galaxies

NGC 4691 forms a pair with NGC 4684, which lies 19 arcminutes away. However the difference in redshift is about 470 km/s, indicating that the pairing is likely a projection effect.[5] NGC 4691 is a member of the NGC 4753 Group, along with NGC 4629, NGC 4753, NGC 4771, NGC 4772, NGC 4845, and NGC 4904.[13] It is part of a Virgo II Groups, a chain of groups extending from the Virgo Cluster.[14]

  • NGC 4691 imaged by SDSS
    NGC 4691 imaged by SDSS

References

  1. ^ a b c d e f g h i j "Results for object NGC 4691". NASA/IPAC Extragalactic Database. NASA and Caltech. Retrieved 25 February 2025.
  2. ^ "Revised NGC Data for NGC 4691". spider.seds.org. Retrieved 30 March 2024.
  3. ^ Seligman, Courtney. "NGC 4691 (= PGC 41399)". Celestial Atlas. Retrieved 19 November 2018.
  4. ^ Eskridge, Paul B.; Frogel, Jay A.; Pogge, Richard W.; Quillen, Alice C.; Berlind, Andreas A.; Davies, Roger L.; DePoy, D. L.; Gilbert, Karoline M.; Houdashelt, Mark L.; Kuchinski, Leslie E.; Ramirez, Solange V.; Sellgren, K.; Stutz, Amelia; Terndrup, Donald M.; Tiede, Glenn P. (November 2002). "Near-Infrared and Optical Morphology of Spiral Galaxies". The Astrophysical Journal Supplement Series. 143 (1): 73–111. arXiv:astro-ph/0206320. Bibcode:2002ApJS..143...73E. doi:10.1086/342340.
  5. ^ a b Sandage, A., Bedke, J. (1994), The Carnegie Atlas of Galaxies. Volume I, Carnegie Institution of Washington
  6. ^ Wiklind, T.; Henkel, C.; Sage, L. J. (1 April 1993). "The molecular cloud content of early-type galaxies IV. A molecular bar in NGC 4691". Astronomy and Astrophysics. 271: 71–83. Bibcode:1993A&A...271...71W.
  7. ^ Thomas, Adam D.; Dopita, Michael A.; Shastri, Prajval; Davies, Rebecca; Hampton, Elise; Kewley, Lisa; Banfield, Julie; Groves, Brent; James, Bethan L.; Jin, Chichuan; Juneau, Stéphanie; Kharb, Preeti; Sairam, Lalitha; Scharwächter, Julia; Shalima, P.; Sundar, M. N.; Sutherland, Ralph; Zaw, Ingyin (1 September 2017). "Probing the Physics of Narrow-line Regions in Active Galaxies. IV. Full Data Release of the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7)". The Astrophysical Journal Supplement Series. 232 (1): 11. arXiv:1708.02683. Bibcode:2017ApJS..232...11T. doi:10.3847/1538-4365/aa855a.
  8. ^ Thomas, Adam D.; Dopita, Michael A.; Kewley, Lisa J.; Groves, Brent A.; Sutherland, Ralph S.; Hopkins, Andrew M.; Blanc, Guillermo A. (1 April 2018). "Interrogating Seyferts with NebulaBayes: Spatially Probing the Narrow-line Region Radiation Fields and Chemical Abundances". The Astrophysical Journal. 856 (2): 89. arXiv:1803.00740. Bibcode:2018ApJ...856...89T. doi:10.3847/1538-4357/aab3db.
  9. ^ Garcia-Barreto, J. A.; Franco, J.; Guichard, J.; Carrillo, R. (September 1995). "The Central Regions of NGC 4691: A Remarkable Structure with a Fast Outflow near the Nucleus". The Astrophysical Journal. 451: 156. Bibcode:1995ApJ...451..156G. doi:10.1086/176207.
  10. ^ Nakano, S.; Aoki, M.; Kushida, Y.; Kushida, R.; Suntzeff, N. B.; Clocchiatti, A.; Phillips, M. M.; Kim, D. -W.; Covarrubias, R.; Garnavich, P.; Kirshner, R.; Berlind, P. (4 February 1997). "Supernova 1997X in NGC 4691". International Astronomical Union Circular (6552): 1. ISSN 0081-0304.
  11. ^ Benetti, S.; Turatto, M.; Perez, I.; Wisotzki, L. (4 February 1997). "Supernova 1997X in NGC 4691". International Astronomical Union Circular (6554): 2. ISSN 0081-0304.
  12. ^ Gómez, G.; López, R. (January 2002). "Nebular Spectra of the Type I[CLC]c[/CLC] Supernovae 1997B and 1997X". The Astronomical Journal. 123 (1): 328–336. doi:10.1086/324636.
  13. ^ 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. S2CID 119194025. Retrieved 1 February 2025.
  14. ^ "The Virgo II Groups". www.atlasoftheuniverse.com. Retrieved 25 February 2025.
Allikas: https://en.wikipedia.org/wiki/NGC_4691
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