View source for NGC 4631

{{Short description|Galaxy in the constellation Canes Venatici}}
{{Infobox Galaxy
| name = [[New General Catalogue|NGC]] 4631
| image = NGC 4631 HST.jpg
|caption = An image of NGC 4631 taken with [[Hubble Space Telescope]]
| constellation name = [[Canes Venatici]]<ref name="sinnott1988">{{cite book 
  | editor=R. W. Sinnott
  | title= The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer
  | date=1988
  | publisher=Sky Publishing Corporation and Cambridge University Press
  | isbn=978-0-933346-51-2}}</ref>
| epoch = [[J2000]]
| type = SB(s)d<ref name="ned">{{cite web
  | title=NASA/IPAC Extragalactic Database
  | work=Results for NGC 4631
  | url=http://nedwww.ipac.caltech.edu/
  | access-date=2006-11-21}}</ref>
| ra = {{RA|12|42|08.0}}<ref name="ned" />
| dec = {{DEC|+32|32|29}}<ref name="ned" />
| dist_ly = 30 [[Light-year|Mly]]
| z = 606 ± 3 km/[[second|s]]<ref name="ned" />
| appmag_v = 9.8<ref name="ned" />
| size_v = 15′.5 × 2′.7<ref name="ned" />
| notes = edge-on
| names = Whale Galaxy,<ref name="simbad" /> {{odlist | UGC= 7865 | PGC= 42637 | Arp= 281}},<ref name="ned" /> [[Caldwell catalogue|Caldwell]]&nbsp;32
}}

'''NGC 4631''' (also known as the '''Whale Galaxy''' or '''Caldwell 32''') is a  [[barred spiral galaxy]] in the [[constellation]] [[Canes Venatici]] about 30 million light years away from Earth. It was discovered on 20 March 1787 by [[Germany|German-British]] astronomer [[William Herschel]].<ref name="selig">{{cite web | url = https://cseligman.com/text/atlas/ngc46.htm#4631 | title = New General Catalogue Objects: NGC{{nbsp}}4631 | last = Seligman | first = Courtney | website = Celestial Atlas | access-date = 4 September 2024 }}</ref> This galaxy's slightly distorted wedge shape gives it the appearance of a herring or a whale, hence its nickname.<ref name="simbad">{{cite simbad
  | title=NGC 4631
  | access-date=2006-08-22}}</ref>  Because this nearby galaxy is seen edge-on from [[Earth]], professional astronomers observe this galaxy to better understand the gas and stars located outside the plane of the galaxy.

== Starburst and superwind ==
[[File:NGC 4631 Hubble mosaic.jpg|thumb|left|300px|NGC 4631 mosaic of two [[Hubble Space Telescope|HST]] images; 7.2′x2′ view]]
NGC 4631 contains a central [[starburst (astronomy)|starburst]], which is a region of intense [[star formation]].  The strong star formation is evident in the emission from [[ion]]ized [[hydrogen]]<ref name="randetal1992">{{cite journal
  | author=R. J. Rand | author2=S. R. Kulkarni | author3=J. J. Hester
  | title=Warm ionized gas in the edge-on galaxies NGC 4565 and NGC 4631
  | journal=Astrophysical Journal
  | date=1992
  | volume=396
  | pages=97–103
  | bibcode=1992ApJ...396...97R  | doi=10.1086/171699
| doi-access=free
  }}</ref> and [[interstellar dust]] heated by the stars formed in the starburst.<ref name="bendoetal2006">{{cite journal
  | author=G. J. Bendo | display-authors= 4 | author2= D. A. Dale | author3= B. T. Draine | author4= C. W. Engelbracht | author5= R. C. Kennicutt, Jr. | author6=D. Calzetti | author7=K. D. Gordon | author8=G. Helou | author9=D. Hollenbach | author10=A. Li | author11=E. J. Murphy | author12=M. K. M. Prescott | author13=J.-D. T. Smith
  | title=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
  | journal=Astrophysical Journal
  | date=2006
  | volume=652
  | issue=1
  | pages=283–305
  | bibcode=2006ApJ...652..283B  | doi=10.1086/508057
|arxiv = astro-ph/0607669 | s2cid= 119419587 }}</ref>  The most massive stars that form in star formation regions only burn hydrogen gas through [[Nuclear fusion|fusion]] for a short period of time, after which they explode as [[supernovae]].  So many supernovae have exploded in the center of NGC 4631 that they are blowing gas out of the plane of the galaxy. This [[galactic superwind|superwind]] can be seen in [[X-ray]]s<ref name="wangetal1994">{{cite journal
  | author=Q. D. Wang | display-authors=4 | author2=R. A. S. Walterbos | author3=M. F. Steakley | author4=C. A. Norman | author5= R. Braun
  | title=ROSAT detection of diffuse hot gas in the edge-on galaxy NGC 4631
  | journal=Astrophysical Journal
  | date=1994
  | volume=439
  | pages=176–184
  | bibcode=1995ApJ...439..176W
  | doi=10.1086/175162| hdl=2060/19950011081 | s2cid=121407361 | hdl-access=free}}</ref> and in [[spectral line]] emission.<ref name="randetal1992" />  The gas from this superwind has produced a giant, diffuse corona of hot, X-ray emitting gas around the whole galaxy.<ref name="wangetal1">{{cite journal
  | author=Q. D. Wang | display-authors= 4 | author2= S. Immler | author3= R. Walterbos | author4= J. T. Lauroesch | author5= D. Breitschwerdt
  | title=Chandra Detection of a Hot Gaseous Corona around the Edge-on Galaxy NGC 4631
  | journal=Astrophysical Journal
  | date=2001
  | volume=555
  | issue=2
  | pages=L99–L102
  | bibcode=2001ApJ...555L..99W  | doi=10.1086/323179
|arxiv = astro-ph/0105541 | s2cid= 15558867 }}</ref>

Although no supernovae have been observed in NGC 4631 yet, a [[luminous red nova]], designated AT{{nbsp}}2021biy, was discovered on 29 January 2021 (type LRN, mag. 18.1).<ref>[https://www.wis-tns.org/object/2021biy Transient Name Server entry for AT 2021biy.] Retrieved 10 November 2023.</ref> This transient was studied in detail. The progenitor was either a luminous [[yellow supergiant]] or, most likely, a [[Binary star|binary]] with a primary that had a mass of 17-24 {{Solar mass|link=true}}. Luminous red novae have two peaks, with the second peak resembling a plateau. The plateau for AT 2021biy had the longest plateau observed to date, with a duration of 210 days.<ref>{{Cite journal |last=Cai |first=Y.-Z. |last2=Pastorello |first2=A. |last3=Fraser |first3=M. |last4=Wang |first4=X.-F. |last5=Filippenko |first5=A. V. |last6=Reguitti |first6=A. |last7=Patra |first7=K. C. |last8=Goranskij |first8=V. P. |last9=Barsukova |first9=E. A. |last10=Brink |first10=T. G. |last11=Elias-Rosa |first11=N. |last12=Stevance |first12=H. F. |last13=Zheng |first13=W. |last14=Yang |first14=Y. |last15=Atapin |first15=K. E. |date=November 2022 |title=Forbidden hugs in pandemic times. III. Observations of the luminous red nova AT 2021biy in the nearby galaxy NGC 4631 |url=https://ui.adsabs.harvard.edu/abs/2022A&A...667A...4C/abstract |journal=Astronomy and Astrophysics |language=en |volume=667 |pages=A4 |arxiv=2207.00734 |bibcode=2022A&A...667A...4C |doi=10.1051/0004-6361/202244393 |issn=0004-6361}}</ref>

== Nearby galaxies and galaxy group ==
[[File:NGC4631.jpg|thumb|left|300px|NGC 4631 (magnitude 10) + [[NGC 4627]] (magnitude 13)]]
NGC 4631 has a nearby companion [[dwarf elliptical galaxy]], [[NGC 4627]].  NGC 4627 and NGC 4631 together were listed in the ''[[Atlas of Peculiar Galaxies]]'' as an example of a "double galaxy" or a galaxy pair.<ref name="arp1966">{{cite journal
  | author=H. Arp
  | title=Atlas of Peculiar Galaxies
  | journal=Astrophysical Journal Supplement
  | date=1966
  | volume=14
  | pages=1–20
  | bibcode=1966ApJS...14....1A  | doi=10.1086/190147
}}</ref>

NGC 4631 and NGC 4627 are part of the [[NGC 4631 Group]], a group of galaxies that also includes the interacting galaxies [[NGC 4656]] and [[NGC 4657]].<ref name="nbg">{{cite book 
  | author=R. B. Tully
  | date=1988
  | title=Nearby Galaxies Catalog
  | publisher=Cambridge University Press
  | location=Cambridge
  | isbn=978-0-521-35299-4}}</ref><ref name="fouqueetal1992">{{cite journal
  | author=P. Fouque | author2=E. Gourgoulhon | author3=P. Chamaraux | author4=G. Paturel
  | title=Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
  | journal=Astronomy and Astrophysics Supplement
  | date=1992
  | volume=93
  | pages=211–233
  | bibcode=1992A&AS...93..211F}}</ref><ref name="garcia1993">{{cite journal
  | author=A. M. Garcia
  | title=General study of group membership. II - Determination of nearby groups
  | journal=Astronomy and Astrophysics Supplement
  | date=1993
  | volume=100
  | pages=47–90
  | bibcode=1993A&AS..100...47G}}</ref><ref name="giuricinetal2002">{{cite journal
  | author=G. Giuricin | author2=C. Marinoni | author3= L. Ceriani | author4= A. Pisani
  | title=Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
  | journal=Astrophysical Journal
  | date=2000
  | volume=543
  | issue=1
  | pages=178–194
  | bibcode=2000ApJ...543..178G  | doi=10.1086/317070
|arxiv = astro-ph/0001140 | s2cid=9618325 }}</ref>  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<ref name="nbg" /> to 27,<ref name="giuricinetal2002" /> and all studies identify very different member galaxies for this group.

{{clear left}}

== See also ==
*[[NGC 253]], a similar edge-on spiral galaxy
*[[NGC 891]], a similar edge-on spiral galaxy
*[[NGC 4565]], a similar edge-on spiral galaxy
*[[NGC 5907]], a similar edge-on spiral galaxy
* [[List of NGC objects (4001–5000)]]

== References ==
{{reflist}}

== External links ==
{{commonscat}}
*[http://antwrp.gsfc.nasa.gov/apod/ap040123.html APOD (2004-01-23)] – The Whale Galaxy
*[http://apod.nasa.gov/apod/ap100517.html APOD (2010-05-17)] – The Whale Galaxy (a better image)
*{{WikiSky}}
*{{CelestialRefEx|siblings=show}}
* [http://messier.seds.org/xtra/ngc/n4631.html SEDS] – NGC 4631

{{Sky|12|42|08|+|32|32|29|30000000}}
{{Catalogs|NGC=4631|UGC=7865|PGC=42637|Arp=281|C=32}}
{{Caldwell catalogue}}
{{Ngc50}}
{{Canes Venatici}}
{{Authority control}}

{{DEFAULTSORT:NGC 4631}}
[[Category:Barred spiral galaxies]]
[[Category:NGC 4631 Group]]
[[Category:Canes Venatici]]
[[Category:NGC objects|4631]]
[[Category:UGC objects|07865]]
[[Category:Principal Galaxies Catalogue objects|042637]]
[[Category:Arp objects|281]]
[[Category:Caldwell objects|032b]]
[[Category:Astronomical objects discovered in 1787|17870320]]
[[Category:Discoveries by William Herschel]]