NGC 6946

NGC 6946
A image of NGC 6946, the fireworks galaxy.
Observation data (J2000 epoch)
ConstellationCepheus & Cygnus
Right ascension20h 34m 52.3s[1]
Declination+60° 09′ 14″[1]
Redshift0.000133[1]
Heliocentric radial velocity48 ± 2 km/s[1]
Distance25.2 ± 1.0 Mly
7.72± 0.32 Mpc)[2]
Apparent magnitude (V)+9.6[1]
Characteristics
TypeSAB(rs)cd[1]
Size26.77 kpc (87,300 ly)
(diameter; 25.0 mag/arcsec2 B-band isophote)[1][3]
Apparent size (V)16.0 x 11.2 arcmin[4]
Other designations
UGC 11597, PGC 65001, Arp 29,[1] Caldwell 12
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NGC 6946, sometimes referred to as the Fireworks Galaxy, is a face-on intermediate spiral galaxy with a small bright nucleus, whose location in the sky straddles the boundary between the northern constellations of Cepheus and Cygnus. Its distance from Earth is about 25.2 million light-years or 7.72 megaparsecs,[2] similar to the distance of M101 (NGC 5457) in the constellation Ursa Major.[5] Both were once considered to be part of the Local Group,[6] but are now known to be among the dozen bright spiral galaxies near the Milky Way but beyond the confines of the Local Group.[7] NGC 6946 lies within the Virgo Supercluster.[8]

The galaxy was discovered by William Herschel on 9 September 1798. Based on an estimation by the Third Reference Catalogue of Bright Galaxies (RC3) in 1991, the galaxy has a D25 B-band isophotal diameter of 26.77 kiloparsecs (87,300 light-years).[1][3] It is heavily obscured by interstellar matter due to its location close to the galactic plane of the Milky Way.[9] Due to its prodigious star formation it has been classified as an active starburst galaxy.[7] NGC 6946 has also been classified as a double-barred spiral galaxy, with the inner, smaller bar presumably responsible for funneling gas into its center.[10][11]

Various unusual celestial objects have been observed within NGC 6946. This includes the so-called 'Red Ellipse' along one of the northern arms that looks like a super-bubble or very large supernova remnant, and which may have been formed by an open cluster containing massive stars. There are also two regions of unusual dark lanes of nebulosity, while within the spiral arms several regions appear devoid of stars and gaseous hydrogen, some spanning up to two kiloparsecs across.[7][dubious – discuss] A third peculiar object, discovered in 1967, is now known as "Hodge's Complex".[12] This was once thought to be a young supergiant cluster, but in 2017 it was conjectured to be an interacting dwarf galaxy superimposed on NGC 6946.[7]

  1. ^ a b c d e f g h i Cite error: The named reference ned was invoked but never defined (see the help page).
  2. ^ a b Eldridge, J J; Xiao, Lin (2 March 2019). "The distance, supernova rate, and supernova progenitors of NGC 6946". Monthly Notices of the Royal Astronomical Society: Letters. 485 (1): L58–L61. arXiv:1903.00173. Bibcode:2019MNRAS.485L..58E. doi:10.1093/mnrasl/slz030. S2CID 118831398.
  3. ^ a b Cite error: The named reference RC3 was invoked but never defined (see the help page).
  4. ^ Jarrett, T. H.; Chester, T.; Cutri, R.; Schneider, S. E.; Huchra, J. P. (2003). "The 2MASS Large Galaxy Atlas". The Astronomical Journal. 125 (2): 525–554. Bibcode:2003AJ....125..525J. doi:10.1086/345794. S2CID 117784410.
  5. ^ Cite error: The named reference CAG1994 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference SEDS2013 was invoked but never defined (see the help page).
  7. ^ a b c d Cite error: The named reference Efremov2017 was invoked but never defined (see the help page).
  8. ^ "Nearby Groups of Galaxies". ned.ipac.caltech.edu. Retrieved 3 May 2018.
  9. ^ "NED data for some important Non-Messier Galaxies".
  10. ^ Schinnerer, Eva; et, al (2006). "Molecular Gas Dynamics in NGC 6946: A Bar-driven Nuclear Starburst Caught in the Act". The Astrophysical Journal. 649 (1): 181–200. arXiv:astro-ph/0605702. Bibcode:2006ApJ...649..181S. doi:10.1086/506265. S2CID 14717998.
  11. ^ Eibensteiner, Cosima; et, al (2022). "A 2-3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946". Astronomy & Astrophysics. 659 (A173): 37. arXiv:2201.02209. Bibcode:2022A&A...659A.173E. doi:10.1051/0004-6361/202142624.
  12. ^ Cite error: The named reference Hodge1967 was invoked but never defined (see the help page).