NGC 3945

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

{{Infobox galaxy

| image = NGC 3945 lenticular Galaxy 13024680373 e2ca77db8d o.png

| alt =

| caption = NGC 3945 imaged by the Hubble Space Telescope

| epoch = J2000

| constellation name = Ursa Major

| ra = {{RA|11|53|13.726}}{{cite journal |doi=10.1086/498708 |last1=Skrutskie |first1=Michael F. |last2=Cutri |first2=Roc M. |last3=Stiening |first3=Rae |last4=Weinberg |first4=Martin D. |last5=Schneider |first5=Stephen E. |last6=Carpenter |first6=John M. |last7=Beichman |first7=Charles A. |last8=Capps |first8=Richard W. |last9=Chester |first9=Thomas |last10=Elias |first10=Jonathan H. |last11=Huchra |first11=John P. |last12=Liebert |first12=James W. |last13=Lonsdale |first13=Carol J. |last14=Monet |first14=David G. |last15=Price |first15=Stephan |last16=Seitzer |first16=Patrick |last17=Jarrett |first17=Thomas H. |last18=Kirkpatrick |first18=J. Davy |last19=Gizis |first19=John E. |last20=Howard |first20=Elizabeth V. |last21=Evans |first21=Tracey E. |last22=Fowler |first22=John W. |last23=Fullmer |first23=Linda |last24=Hurt |first24=Robert L. |last25=Light |first25=Robert M. |last26=Kopan |first26=Eugene L. |last27=Marsh |first27=Kenneth A. |last28=McCallon |first28=Howard L. |last29=Tam |first29=Robert |last30=Van Dyk |first30=Schuyler D. |last31=Wheelock |first31=Sherry L. |title=The Two Micron All Sky Survey (2MASS) |journal=The Astronomical Journal |date=1 February 2006 |volume=131 |issue=2 |pages=1163–1183 |bibcode=2006AJ....131.1163S |s2cid=18913331 |issn=0004-6256 |doi-access=free }}

| dec = {{DEC|+60|40|32.02}}

| h_radial_v = 1242 ± 22 km/s

| z = 0.004153

| dist_ly = {{cvt|19.4|Mpc|Mly|lk=on|order=flip}}{{cite journal|doi=10.1093/mnras/stw1868|title=Complex central structures suggest complex evolutionary paths for barred S0 galaxies|year=2016|last1=Dullo|first1=Bililign T.|last2=Martínez-Lombilla|first2=Cristina|last3=Knapen|first3=Johan H.|journal=Monthly Notices of the Royal Astronomical Society|volume=462|issue=4|pages=3800–3811|doi-access=free |arxiv=1608.03539}}

| group_cluster = NGC 4036 Group (LGG 266)

| type = (R)SB(rs)0⁺

| size = ~{{convert|39.48|kpc|ly|abbr=on|lk=on|order=flip}} (estimated){{cite web

| website = NASA/IPAC Extragalactic Database

| publisher = NASA and Caltech

| title=Results for object NGC 3945

| url = https://ned.ipac.caltech.edu/byname?objname=NGC+3945

| access-date = 26 May 2025}}

| appmag_v = 10.75{{cite web|url=http://leda.univ-lyon1.fr/ledacat.cgi?o=NGC%203945|title=Search specification: NGC 3945|work=HyperLeda|publisher=Université Claude Bernard Lyon 1|accessdate=2021-05-18}}

| appmag_b = 11.70

| absmag_v =

| size_v = {{Val|5.2|×|3.5|u=arcminute}}{{r|ned}}

| names = {{odlist | IRAS= 11506+6056 | CGCG= 292-042 | UGC= 6860 | MCG= +10-17-096 | PGC= 37258}}{{cite simbad|title=NGC 3945|accessdate=2021-05-18}}{{r|ned}}

}}

NGC 3945 is a barred lenticular galaxy in the constellation Ursa Major. It was discovered by German-British astronomer William Herschel on March 19, 1790.{{cite web|url=http://cseligman.com/text/atlas/ngc39.htm#3945|title=New General Catalogue objects: NGC 3900 - 3949|author=Seligman, Courtney|website=cseligman.com|accessdate=2021-05-18}}

NGC 3945 has a complex structure, with two concentric bars and a pseudobulge. Unlike classical bulges which are like miniature elliptical galaxies, pseudobulges have features similar to disk galaxies, including a flattened structure and significant rotation.{{cite journal|doi=10.1088/0004-6256/136/2/773|title=The Structure of Classical Bulges and Pseudobulges: The Link Between Pseudobulges and Sérsic Index|year=2008|last1=Fisher|first1=David B.|last2=Drory|first2=Niv|journal=The Astronomical Journal|volume=136|issue=2|pages=773–839|arxiv=0805.4206|bibcode=2008AJ....136..773F|s2cid=16126374}} It is classified as a LINER galaxy. The formation history of NGC 3945 is likely quite complex, with the pseudo-bulge being formed gradually from disk material, while bulges (spheroidal components) would have formed from violent merger events.

Unlike galaxies with similar velocity dispersions and luminosities, the central black hole of NGC 3945 has an unusually low mass, estimated to be around {{solar mass|{{val|9e6}}|link=y}}. However, it is also possible that NGC 3945 has no central black hole at all.{{cite journal|doi=10.1088/0004-637X/695/2/1577|title=A Quintet of Black Hole Mass Determinations|year=2009|last1=Gültekin|first1=Kayhan|last2=Richstone|first2=Douglas O.|last3=Gebhardt|first3=Karl|last4=Lauer|first4=Tod R.|last5=Pinkney|first5=Jason|last6=Aller|first6=M. C.|last7=Bender|first7=Ralf|last8=Dressler|first8=Alan|last9=Faber|first9=S. M.|last10=Filippenko|first10=Alexei V.|last11=Green|first11=Richard|last12=Ho|first12=Luis C.|last13=Kormendy|first13=John|last14=Siopis|first14=Christos|journal=The Astrophysical Journal|volume=695|issue=2|pages=1577–1590|arxiv=0901.4162|bibcode=2009ApJ...695.1577G|s2cid=14365610}}