Galaxy NGC 3631 (Arp 27)

NGC 3631
NGC 3631: Galaxy in Ursa Major; 500 mm Cassegrain 3625 mm f/7.2; SBIG STL11K; 280-120-120-120 min LRGB; Berner Oberland; © 2015 Radek Chromik


This galaxy was discovered on 14 April 1789 by the famous German-British astronomer William Herschel using his selfmade reflecting telescope of 20 foot focal length (aperture 18.7 inch) in Slough near Windsor in Great Britain. He cataloged it as «bright nebula» (class I) with the designation I 226. He noted: «considerably bright, round, small bright resolvable nucleus and very faint chevelure, 4' diameter.» [465] His son John listed it as h 858 (GC 2379) and noted in his catalog of 1833: «pretty bright, large, round, suddenly much brighter in the middle, 2' diameter.» [466] In his catalogue of 1864 John Herschel describes it as «pretty bright, large, round, suddenly very brighter in the middle, barely resolvable nucleus.» [467] John L. E. Dreyer listed this galaxy as NGC 3631 in his «New General Catalogue», published in 1888. [313]

Halton Arp divided his «Atlas of Peculiar Galaxies», published in 1966, into groups based on purely morphological criteria. The galaxy here received the designation Arp 27 (APG 27) as a galaxy with «one heavy arm». He also noted: «Note straight arms, absorption tube crossing from inside to outside of S arm.» [199]

NGC 3631
NGC 3631: Image taken with Hubble Space Telescope. © ESA/Hubble & NASA [525]

Physical Properties

NGC 3631 is a grand-design spiral galaxy of type SAc. The inclination angle of the disc is about 17°, so we see it nearly face-on. The two-armed spiral structure seems to be well defined in optical light, but it has a number of irregularities, especially in the outer parts of the disc. The two-armed spiral structure of NGC 3631 has a wave nature. The observed vertical gas motions represent motions in a spiral density wave. The radius of corotation is about 42 arcsec, or 3.2 kpc. There is evidence of two anticyclonic and four cyclonic vortices near corotation in a frame of reference rotating with the spiral pattern. The centres of the anticyclones lie between the observed spiral arms. The cyclones lie close to the observed spirals, but their centres are shifted from the maxima in brightness. [523, 524]

Revised+Historic NGC/IC, Version 22/9, © Dr. Wolfgang Steinicke [277]
DesignationNGC 3631
TypeGx (Sc)
Right Ascension11h 21m 02.7s
Declination+53° 10' 11"
Diameter5 × 3.7 arcmin
Photographic (blue) magnitude11.0 mag
Visual magnitude10.4 mag
Surface brightness13.7 mag·arcmin-2
Position angle114°
Distance derived from z16.29 Mpc
Metric Distance21.600 Mpc
Dreyer DescriptionpB, L, R, svmbMrN
Identification, RemarksUGC 6360, MCG 9-19-47, CGCG 268-21, Arp 27, VV 363, IRAS 11181+5326

Finder Chart

The galaxy NGC 3631 is located in the constellation Ursa Major. The constellation is circumpolar, but is highest at night from November to July, which is best for observing.

Chart Galaxy NGC 3631 (Arp 27)
Galaxy NGC 3631 (Arp 27) in constellation Ursa Maior. Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

More Objects Nearby (±15°)


149SkySafari 6 Pro, Simulation Curriculum;
160The STScI Digitized Sky Survey;
199«Atlas Of Peculiar Galaxies», Halton Arp, 1966; Astrophysical Journal Supplement, vol. 14, p.1 (1966); DOI:10.1086/190147; Bibcode:1966ApJS...14....1A
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)
313«A New General Catalogue of Nebulae and Clusters of Stars, being the Catalogue of the late Sir John F.W. Herschel, Bart., revised, corrected, and enlarged» Dreyer, J. L. E. (1888); Memoirs of the Royal Astronomical Society. 49: 1–237; Bibcode:1888MmRAS..49....1D
465«Catalogue of 500 new nebulae, nebulous stars, planetary nebula:, and clusters of stars; with remarks on the construction of the heavens» William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1802; DOI:10.1098/rstl.1802.0021
466«Observations of nebulæ and clusters of stars, made at Slough, with a twenty-feet reflector, between the years 1825 and 1833» John Frederick William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1833, Pages: 359-505; DOI:10.1098/rstl.1833.0021
467«Catalogue of nebulae and clusters of stars» John Frederick William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1864; DOI:10.1098/rstl.1864.0001
523«Vertical motions in the gaseous disk of the spiral galaxy NGC 3631» Fridman, A. M.; Koruzhii, O. V.; Zasov, A. V.; Sil'chenko, O. K.; Moiseev, A. V.; Burlak, A. N.; Afanas'ev, V. L.; Dodonov, S. N.; Knapen, J.; Astronomy Letters, Volume 24, Issue 6, November 1998, pp.764-773; Pis'ma v Astronomicheskii Zhurnal, Vol. 24, p. 883; Bibcode:1998AstL...24..764F
524«Gas motions in the plane of the spiral galaxy NGC 3631» A. M. Fridman, O. V. Khoruzhii, E. V. Polyachenko, A. V. Zasov, O. K. Sil'Chenko, A. V. Moiseev, A. N. Burlak, V. L. Afanasiev, S. N. Dodonov, J. H. Knapen; Monthly Notices of the Royal Astronomical Society, Volume 323, Issue 3, May 2001, Pages 651–662; DOI:10.1046/j.1365-8711.2001.04218.x
525Hubble Looks at a Face-On Grand Spiral; (2022-07-10)