NGC 3994

{{Short description|Galaxy in the constellation Ursa Major}}

{{Infobox galaxy

| name = NGC 3994

| image = NGC 3994 hst o4rl03010 sx2-1-.png

| caption = NGC 3994 by Hubble Space Telescope

| epoch = J2000

| type = SA(r)c pec {{cite web

| title=NASA/IPAC Extragalactic Database

| work=Results for NGC 3994

| url=http://ned.ipac.caltech.edu/cgi-bin/nph-objsearch?objname=NGC+3994

| access-date=2024-03-26 }}

| ra = {{RA|11|57|36.9}}

| dec = {{DEC|+32|16|40}}

| dist_ly = 161 ± 11.4 Mly (49.4 ± 3.5 Mpc)

| z = 0.010279 ± 0.000009

| h_radial_v = 3,082 ± 3 km/s

| appmag_v = 12.7{{cite web |title=Revised NGC Data for NGC 3994 |url=https://spider.seds.org/ngc/revngcic.cgi?NGC3994 |website=spider.seds.org |access-date=30 March 2024}}

| size_v = 1.30{{prime}} × 0.64{{prime}}

| constellation name = Ursa Major

| notes = Interacting galaxy

| names = UGC 6936, Arp 313, VV 249b, MCG +06-26-059, PGC 37616, HOLM 309B

}}

NGC 3994 is an unbarred spiral galaxy in the constellation Ursa Major. The galaxy lies about 160 million light years away from Earth, which means, given its apparent dimensions, that NGC 3994 is approximately 70,000 light years across. It was discovered by Heinrich d'Arrest on April 6, 1864.{{cite web |last1=Seligman |first1=Courtney |title=NGC 3994 |url=https://cseligman.com/text/atlas/ngc39a.htm#3994 |website=Celestial Atlas |access-date=19 November 2018}}

NGC 3994 forms a triplet of galaxies with NGC 3995, which lies 1.9 arcminutes, and NGC 3991, which lies 3.7 arcminutes away. The triplet has been included in Halton Arp's Atlas of Peculiar Galaxies as Arp 313. Both NGC 3995 and NGC 3991 have a disturbed appearance while NGC 3994 does not.Sandage, A., Bedke, J. (1994), The Carnegie Atlas of Galaxies. Volume I, Carnegie Institution of Washington The triplet is part of the NGC 3966 Group or LGG 259. Other members include NGC 3966, NGC 3935, NGC 3986, IC 2973, UGC 6892, IC 2978, and IC 2979.{{cite journal |last1=Garcia |first1=A. M. |title=General study of group membership. II. Determination of nearby groups. |journal=Astronomy and Astrophysics Supplement Series |date=1 July 1993 |volume=100 |pages=47–90 |url=https://cdsarc.cds.unistra.fr/ftp/J/A+AS/100/47/table2.dat |bibcode= 1993A&AS..100...47G |issn=0365-0138}}{{cite journal|last1=Makarov|first1=Dmitry|last2=Karachentsev|first2=Igor|title=Galaxy groups and clouds in the local (z~ 0.01) Universe|journal=Monthly Notices of the Royal Astronomical Society|date=21 April 2011|volume=412|issue=4|pages=2498–2520|doi=10.1111/j.1365-2966.2010.18071.x|doi-access=free |bibcode=2011MNRAS.412.2498M|arxiv=1011.6277|s2cid=119194025}}

The nucleus of the galaxy has been found to be active, and based on its spectral lines it is a composite object with LINER and HII region characteristics.{{cite journal |last1=Gonçalves |first1=A. C. |last2=Véron-Cetty |first2=M.-P. |last3=Véron |first3=P. |title=AGNs with composite spectra: II. Additional data |journal=Astronomy and Astrophysics Supplement Series |date=March 1999 |volume=135 |issue=3 |pages=437–466 |doi=10.1051/aas:1999183|arxiv=astro-ph/9811342 |bibcode=1999A&AS..135..437G }} The nucleus lacks central ultraviolet emission when observed by the Hubble Space Telescope. Star formation knots are visible along the spiral arms, most of them with ages less than 20 million years, with no correlation between location and age.{{cite journal |last1=Eggers |first1=D. |last2=Weistrop |first2=D. |last3=Stone |first3=A. |last4=Nelson |first4=C. H. |last5=Hancock |first5=M. |title=Hubble Space Telescope Observations of Star-forming Regions in NGC 3994/3995 |journal=The Astronomical Journal |date=January 2005 |volume=129 |issue=1 |pages=136–147 |doi=10.1086/426358|bibcode=2005AJ....129..136E }} The star formation rate of NGC 3995 is estimated to be {{val|2.9|0.6|ul=M_solar}} per year, with higher rates observed near the centre of the galaxy.{{cite journal |last1=Logroño-García |first1=R. |last2=Vilella-Rojo |first2=G. |last3=López-Sanjuan |first3=C. |last4=Varela |first4=J. |last5=Viironen |first5=K. |last6=Muniesa |first6=D. J. |last7=Cenarro |first7=A. J. |last8=Cristóbal-Hornillos |first8=D. |last9=Ederoclite |first9=A. |last10=Marín-Franch |first10=A. |last11=Moles |first11=M. |last12=Vázquez Ramió |first12=H. |last13=Bonoli |first13=S. |last14=Díaz-García |first14=L. A. |last15=Orsi |first15=A. |last16=San Roman |first16=I. |last17=Akras |first17=S. |last18=Chies-Santos |first18=A. L. |last19=Coelho |first19=P. R. T. |last20=Daflon |first20=S. |last21=Costa-Duarte |first21=M. V. |last22=Dupke |first22=R. |last23=Galbany |first23=L. |last24=González Delgado |first24=R. M. |last25=Hernandez-Jimenez |first25=J. A. |last26=Lopes de Oliveira |first26=R. |last27=Mendes de Oliveira |first27=C. |last28=Oteo |first28=I. |last29=Gonçalves |first29=D. R. |last30=Sánchez-Portal |first30=M. |last31=Schmidtobreick |first31=L. |last32=Sodré |first32=L. |title=J-PLUS: Measuring H α emission line fluxes in the nearby universe |journal=Astronomy & Astrophysics |date=February 2019 |volume=622 |pages=A180 |doi=10.1051/0004-6361/201732487|arxiv=1804.04039 |bibcode=2019A&A...622A.180L }}