Astronomy:NGC 4945

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NGC 4945
NGC 4945 image take by the MPG/ESO 2.2-metre telescope at La Silla Observatory
Observation data (J2000 epoch)
ConstellationCentaurus
Right ascension 13h 05m 27.279s[1]
Declination−49° 28′ 04.44″[1]
Redshift0.001868±0.00002[2]
Helio radial velocity563±3 km/s[3]
Distance (comoving)0 ± 0 Mly (000 ± 00 Mpc)h−10.73
Distance10.96 ± 0.55 Mly (3.36 ± 0.17 Mpc)[4]
Group or clusterCentaurus A/M83 Group[5]
Apparent magnitude (V)9.3[3]
Characteristics
TypeSB(s)cd?edge[4]
Mass1.4+1.4
−0.7×1011[6] M☉
Size165,185 ly (50.67 kpc) (estimated)[3]
Apparent size (V)20.0′ × 3.8′[3]
Notable featuresSeyfert 2 galaxy[7]
Other designations
ESO 219- G 024, IRAS 13025-4911, PGC 45279[3][8][4]

NGC 4945 is a widely-studied[7] barred spiral galaxy in the constellation Centaurus, visible near the optical double star Xi Centauri.[9] It is also known as Caldwell 83. The galaxy was discovered by Scottish astronomer James Dunlop in 1826.[10] It is located at a distance of approximately 11.0 million light-years (3.36 Mpc) from the Milky Way.[4] NGC 4945 hosts one of the closest active galactic nuclei to Earth and is classified as a Seyfert 2 galaxy.[7]

NGC 4945 is one of the brightest galaxies of the Centaurus A/M83 Group, a large, nearby group of galaxies. The galaxy is the second brightest galaxy in the subgroup centered on Centaurus A.[5] [11]

Observations

The morphological 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 the plane of the sky, which means the galactic plane is being viewed edge-on.[4] NGC 4945 is thought to be similar to the Milky Way Galaxy, although the maximum rotation rate of ~ 180 km/s is lower.[12] It has a combined estimated mass of 1.4+1.4
−0.7×1011 M☉.[6] The stellar mass of the galaxy is 3.8×1010 M☉, or 38 billion times the mass of the Sun.[12]

In 1964, this galaxy was classified as a radio source at the Parkes 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 the IRAS point source catalogue, with most of the emission coming from the core.[15] Most of the Galaxy shows a linear rotation 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 the Very 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 a Seyfert type galaxy and an intense starburst 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 to NGC 4151,[15] and likely harbors a supermassive black hole.[19]

The starburst region is thought to be at least 5×106 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 dense molecular 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 away 1.6 M☉ per year.[25]

NGC 4945 was the first galaxy outside the Local Group to have stars resolved within its galactic halo. The halo mass is relatively large at ~ 3.5×109 M☉ 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 ~ 1.5×109 M☉, which is roughly the same as the Large Magellanic Cloud.[12]

In October 2023, researchers using ALMA discovered an unknown object around 200 light years from the center of the galaxy. This object, named Punctum (Latin for "point" or "dot"), is a highly-polarized millimeter continuum source of synchrotron radiation. Punctum has a high non-visible luminosity, with archive data from Chandra reporting a 1×1037 erg s-1 X-ray luminosity in the 3–6 keV range and ATCA data reporting a radio luminosity of 5×1035 erg s-1 at 23 GHz. In a paper published in July 2025 about the object, the researchers said it most resembles a magnetar due to its polarization of 50%±14%, however the millimeter luminosity of said objects is usually much lower.[26]

Supernovae

Two supernovae have been observed in NGC 4945:

  • SN 2005af (Type II-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 at 25 M☉ and located within a massive stellar cluster.[33]

"NGC 4945" is the title of a song by Brett Domino on the album Funk.

  • The location of NGC 4945 (labelled in red)
    The location of NGC 4945 (labelled in red)

References

  1. ↑ 1.0 1.1 Skrutskie, Michael F. et al. (February 1, 2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal 131 (2): 1163–1183. doi:10.1086/498708. ISSN 0004-6256. Bibcode: 2006AJ....131.1163S. 
  2. ↑ de Vaucouleurs, G. et al. (2016). Third Reference Catalogue of Bright Galaxies. New York: Springer-Verlag. https://heasarc.gsfc.nasa.gov/W3Browse/all/rc3.html. Retrieved 2025-03-08. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 "NASA/IPAC Extragalactic Database". Results for NGC 4945. http://nedwww.ipac.caltech.edu/. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Crowther, Paul A. (January 2013). "On the association between core-collapse supernovae and H II regions". Monthly Notices of the Royal Astronomical Society 428 (3): 1927–1943. doi:10.1093/mnras/sts145. Bibcode: 2013MNRAS.428.1927C. 
  5. ↑ 5.0 5.1 Karachentsev, I. D.; Sharina, M. E.; Dolphin, A. E.; Grebel, E. K. et al. (2002). "New distances to galaxies in the Centaurus A group". Astronomy and Astrophysics 385 (1): 21–31. doi:10.1051/0004-6361:20020042. Bibcode: 2002A&A...385...21K. 
  6. ↑ 6.0 6.1 Graham, 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. doi:10.1071/AS08013. Bibcode: 2008PASA...25..167G. 
  7. ↑ 7.0 7.1 7.2 7.3 Gaspar, G. et al. (May 2022). "An Infrared View of the Obscured AGN Environment in NGC 4945". The Astronomical Journal 163 (5): id. 230. doi:10.3847/1538-3881/ac5ea4. Bibcode: 2022AJ....163..230G. 
  8. ↑ "NGC 4945". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+4945. 
  9. ↑ "NGC 4945". DOCdb :Deep Sky Observer's Companion – the online database. http://www.docdb.net/show_object.php?id=ngc_4945. 
  10. ↑ "Caldwell 83". NASA. 10 September 2020. https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-caldwell-catalog/caldwell-83/. 
  11. ↑ Karachentsev, I. D. (2005). "The Local Group and Other Neighboring Galaxy Groups". Astronomical Journal 129 (1): 178–188. doi:10.1086/426368. Bibcode: 2005AJ....129..178K. 
  12. ↑ 12.0 12.1 12.2 Beltrand, 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. doi:10.1051/0004-6361/202450626. Bibcode: 2024A&A...690A.115B. 
  13. ↑ 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. doi:10.1071/PH640340. Bibcode: 1964AuJPh..17..340B. 
  14. ↑ 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. 
  15. ↑ 15.0 15.1 Done, C. et al. (June 1996). "NGC 4945: The brightest Seyfert 2 galaxy at 100 keV". Astrophysical Journal Letters 463 (2): L63. doi:10.1086/310056. Bibcode: 1996ApJ...463L..63D. 
  16. ↑ 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. doi:10.1086/130685. Bibcode: 1980PASP...92..397P. 
  17. ↑ 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. 
  18. ↑ Whiteoak, J. B. (1986). "NGC 4945 – a galaxy with a nucleus full of surprises". Astronomical Society of Australia, Proceedings 6 (4): 467–471. doi:10.1017/S1323358000018403. Bibcode: 1986PASA....6..467W. 
  19. ↑ "Milky Way's Not-So-Distant Cousin Likely Harbors Supermassive Black Hole". Science Daily. https://www.sciencedaily.com/releases/2009/09/090902112111.htm. 
  20. ↑ Spoon, H. W. W. et al. (May 2000). "Mid-infrared ISO spectroscopy of NGC 4945". Astronomy and Astrophysics 357: 898–908. Bibcode: 2000A&A...357..898S. 
  21. ↑ Wang, M. et al. (August 2004). "Dense gas in nearby galaxies. XVI. The nuclear starburst environment in NGC 4945". Astronomy and Astrophysics 422 (3): 883–905. doi:10.1051/0004-6361:20035722. Bibcode: 2004A&A...422..883W. 
  22. ↑ Cunningham, M. R.; Whiteoak, J. B. (November 2005). "The nuclear molecular clouds of NGC4945". Monthly Notices of the Royal Astronomical Society 364 (1): 37–46. doi:10.1111/j.1365-2966.2005.09502.x. Bibcode: 2005MNRAS.364...37C. 
  23. ↑ Gaspar, G. et al. (2022). "An Infrared View of the Obscured AGN Environment in NGC 4945". The Astronomical Journal 163 (5): 230. doi:10.3847/1538-3881/ac5ea4. Bibcode: 2022AJ....163..230G. 
  24. ↑ Emig, Kimberly L. et al. (November 2020). "Super star clusters in the central starburst of NGC 4945". The Astrophysical Journal 903 (1): id. 50. doi:10.3847/1538-4357/abb67d. Bibcode: 2020ApJ...903...50E. 
  25. ↑ Porraz Barrera, Natalia et al. (June 2024). "Hot Gas Outflow Properties of the Starburst Galaxy NGC 4945". The Astrophysical Journal 968 (2): id. 54. doi:10.3847/1538-4357/ad4606. Bibcode: 2024ApJ...968...54P. 
  26. ↑ 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)
  27. ↑ Jacques, C.; Pimentel, E. (2005). "Possible Supernova in NGC 4945". International Astronomical Union Circular (8482): 1. Bibcode: 2005IAUC.8482....1J. 
  28. ↑ "SN 2005af". IAU. https://www.wis-tns.org/object/2005af. 
  29. ↑ Pereyra, A. et al. (August 2006). "Optical polarimetric monitoring of the type II-plateau SN 2005af". Astronomy and Astrophysics 454 (3): 827–831. doi:10.1051/0004-6361:20065207. Bibcode: 2006A&A...454..827P. 
  30. ↑ 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. 
  31. ↑ Bishop, David. "Supernova 2011ja in NGC 4945". https://www.rochesterastronomy.org/sn2011/sn2011ja.html. 
  32. ↑ "SN 2011ja". IAU. https://www.wis-tns.org/object/2011ja. 
  33. ↑ Andrews, J. E. et al. (April 2016). "Early dust formation and a massive progenitor for SN 2011ja?". Monthly Notices of the Royal Astronomical Society 457 (3): 3241–3253. doi:10.1093/mnras/stw164. Bibcode: 2016MNRAS.457.3241A. 

Further reading

Coordinates: Sky map 13h 05m 27.5s, −49° 28′ 06″



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