NGC 4631 (also known as theWhale Galaxy orCaldwell 32) is abarred spiral galaxy in theconstellationCanes Venatici about 30 million light years away from Earth. It was discovered on 20 March 1787 byGerman-British astronomerWilliam Herschel.[4] This galaxy's slightly distorted wedge shape gives it the appearance of a herring or a whale, hence its nickname.[3] Because this nearby galaxy is seen edge-on fromEarth, professional astronomers observe this galaxy to better understand the gas and stars located outside the plane of the galaxy.
NGC 4631 contains a centralstarburst, which is a region of intensestar formation. The strong star formation is evident in the emission fromionizedhydrogen[5] andinterstellar dust heated by the stars formed in the starburst.[6] The most massive stars that form in star formation regions only burn hydrogen gas throughfusion for a short period of time, after which they explode assupernovae. So many supernovae have exploded in the center of NGC 4631 that they are blowing gas out of the plane of the galaxy. Thissuperwind can be seen inX-rays[7] and inspectral line emission.[5] The gas from this superwind has produced a giant, diffuse corona of hot, X-ray emitting gas around the whole galaxy.[8]
Although no supernovae have been observed in NGC 4631 yet, aluminous red nova, designated AT2021biy, was discovered on 29 January 2021 (type LRN, mag. 18.1).[9]
NGC 4631 and NGC 4627 are part of theNGC 4631 Group, a group of galaxies that also includes the interacting galaxiesNGC 4656 andNGC 4657.[11][12][13][14] However, exact group identification is problematic because this galaxy and others lie in a part of the sky that is relatively crowded. Estimates of the number of galaxies in this group range from 5[11] to 27,[14] and all studies identify very different member galaxies for this group.
^R. W. Sinnott, ed. (1988).The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press.ISBN978-0-933346-51-2.
^G. J. Bendo; D. A. Dale; B. T. Draine; C. W. Engelbracht; et al. (2006). "The Spectral Energy Distribution of Dust Emission in the Edge-on Spiral Galaxy NGC 4631 as Seen with Spitzer and the James Clerk Maxwell Telescope".Astrophysical Journal.652 (1):283–305.arXiv:astro-ph/0607669.Bibcode:2006ApJ...652..283B.doi:10.1086/508057.S2CID119419587.
^abR. B. Tully (1988).Nearby Galaxies Catalog. Cambridge: Cambridge University Press.ISBN978-0-521-35299-4.
^P. Fouque; E. Gourgoulhon; P. Chamaraux; G. Paturel (1992). "Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members".Astronomy and Astrophysics Supplement.93:211–233.Bibcode:1992A&AS...93..211F.
^A. M. Garcia (1993). "General study of group membership. II - Determination of nearby groups".Astronomy and Astrophysics Supplement.100:47–90.Bibcode:1993A&AS..100...47G.
