Themorphological classification of NGC 4945 is SB(s)cd?edge,[4] indicating this is a barred spiral galaxy (SB) with no inner ring structure (s) and possibly loosely-wound spiral arms (cd?). It is inclined at an angle of 90° to theplane of the sky, which means thegalactic plane is being viewed edge-on.[4] NGC 4945 is thought to be similar to theMilky Way Galaxy, although the maximum rotation rate of~ 180 km/s is lower.[12] It has a combined estimated mass of1.4+1.4 −0.7×1011M☉.[6] The stellar mass of the galaxy is3.8×1010M☉, or 38 billion times the mass of the Sun.[12]
In 1964, this galaxy was classified as a radio source at theParkes Observatory.[13] The nucleus was obscured in the optical band but was found to be a quite prominent source of infrared emission.[14] It is the third brightest galaxy in theIRAS point source catalogue, with most of the emission coming from the core.[15] Most of the Galaxy shows a linearrotation curve, although the southwest region showed an infall suggestive of a bar.[16]
Detailed study of the supermassive black hole at the center of the galaxy, created with the help of theVery Large Telescope
In 1979, strong H2O maser emission was detected from the central region.[17] The properties of the nuclear region are suggestive of both aSeyfert type galaxy and an intensestarburst region with a complex structure.[18] The active nucleus is heavily obscured by dust. These dust lanes approach the nucleus, forming a tightly-wound structure in the inner 650 ly (200 pc).[7]X-ray emission from the nuclear region indicates a Type 2 Seyfert galaxy. It is a strong emitter of hard X-rays, second only toNGC 4151,[15] and likely harbors asupermassive black hole.[19]
The starburst region is thought to be at least5×106 years old and contributes at least half of the luminosity coming from the core.[20] It is concentrated in the central 330 ly (100 pc) and includes a conical cavity likely produced by supernovae-driven winds.[21] This is taking place in a region of densemolecular clouds,[22] forming a disk of dust and gas, along with many rich star clusters.[23][24] A hot wind of gas from the nuclear region is carrying away1.6 M☉ per year.[25]
NGC 4945 was the first galaxy outside theLocal Group to have stars resolved within its galactic halo. The halo mass is relatively large at~ 3.5×109M☉ and it is metal-rich, both of which are typical for a Milky Way-like galaxy. It appears to be counter-rotating compared to the main disk, suggesting the halo has been accreted. The mass of the dominant satellite accreted into the halo is~ 1.5×109M☉, which is roughly the same as theLarge Magellanic Cloud.[12]
In October 2023, researchers usingALMA discovered an unknown object around 200 light years from the center of the galaxy. This object, namedPunctum (Latin for "point" or "dot"), is ahighly-polarizedmillimeter continuum source ofsynchrotron radiation.Punctum has a high non-visible luminosity, with archive data fromChandra reporting a1×1037 erg s-1 X-ray luminosity in the 3–6keV range andATCA data reporting a radio luminosity of5×1035 erg s-1 at 23 GHz. In a paper published in July 2025 about the object, the researchers said it most resembles amagnetar due to its polarization of50%±14%, however the millimeter luminosity of said objects is usually much lower.[26]
SN 2005af (TypeII-P, mag. 12.8) was discovered by CEAMIG/REA Supernovae Search on 8 February 2005, reaching a peak magnitude of 12.5 on 12 February.[27][28][29]
SN 2011ja (Type II-P, mag. 14) was discovered by Libert "Berto" Monard on 18 December 2011, and achieved a maximum magnitude of 11.7 on 9 January 2012.[30][31][32] The progenitor star for 2011ja may have been massive at25 M☉ and located within a massivestellar cluster.[33]
^abGraham, Alister W. (November 2008). "Populating the Galaxy Velocity Dispersion – Supermassive Black Hole Mass Diagram: A Catalogue of (Mbh, σ) Values".Publications of the Astronomical Society of Australia.25 (4):167–175.arXiv:0807.2549.Bibcode:2008PASA...25..167G.doi:10.1071/AS08013.S2CID89905.
^abcBeltrand, Camila; et al. (October 2024). "First resolved stellar halo kinematics of a Milky Way-mass galaxy outside the Local Group: The flat counter-rotating halo in NGC 4945".Astronomy & Astrophysics.690. id. A115.arXiv:2406.17533.Bibcode:2024A&A...690A.115B.doi:10.1051/0004-6361/202450626.
^Bolton, J. G.; et al. (September 1964). "The Parkes catalogue of radio sources, declination zone −20° to −60°".Australian Journal of Physics.17 (3): 340.Bibcode:1964AuJPh..17..340B.doi:10.1071/PH640340.
^Shobbrook, R. R.; Shaver, P. A. (August 1967). "The nucleus of the southern spiral NGC 4945".The Observatory.87:169–170.Bibcode:1967Obs....87..169S.
^Peterson, C. J. (August 1980). "Observations of the kinematics of the excited gas in the late-type spiral galaxy NGC 4945".Publications of the Astronomical Society of the Pacific.92:397–408.Bibcode:1980PASP...92..397P.doi:10.1086/130685.
^Moorwood, A. F. M.; Glass, I. S. (June 1984). "Infrared activity in Circinus and NGC 4945 : two galaxies containing luminous H2 O masers".Astronomy and Astrophysics.135:281–288.Bibcode:1984A&A...135..281M.
^E., Shablovinskaia; C., Ricci; C-S., Chang; R., Paladino; Y., Diaz; D., Belfiori; S., Aalto; M., Koss; T., Kawamuro; E., Lopez-Rodriguez; R., Mushotzky; C., Privon, G. (2025). "ALMA discovery of Punctum – a highly polarized mm source in nuclear starburst galaxy NGC 4945".arXiv:2507.13014 [astro-ph.HE].{{cite arXiv}}: CS1 maint: multiple names: authors list (link)
^Jacques, C.; Pimentel, E. (2005). "Possible Supernova in NGC 4945".International Astronomical Union Circular (8482): 1.Bibcode:2005IAUC.8482....1J.
^"SN 2005af".Transient Name Server.IAU. Retrieved8 December 2024.
^Monard, L. A. G.; et al. (2011). "Supernova 2011ja in NGC 4945 = PSN J13051112-4931270".Central Bureau Electronic Telegrams (2946): 1.Bibcode:2011CBET.2946....1M.
Henkel, C.; et al. (April 1994). "Dense gas in nearby galaxies. VII. The active nucleus of NGC 4945".Astronomy and Astrophysics.284:17–27.Bibcode:1994A&A...284...17H.
Dahlem, M.; et al. (March 1993). "The distribution of CO in NGC 4945".Astronomy and Astrophysics.270:29–42.Bibcode:1993A&A...270...29D.
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