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Arp 4
This image shows two galaxies side by side. The galaxy on the top left is smaller in size, and appears as a bright glowing spiral with clearly-defined arms. A larger blue galaxy dominates the full right field of the image. This galaxy is more irregularly shaped, with a glowing central bar, and varying regions of concentrated hues of blue. The background is black with various stars and galaxies in the distance.
Arp 4 (right) with PGC 6629 (left) imaged by the Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationCetus
Right ascension01h 48m 25.7565s[1]
Declination−12° 22′ 52.392″[1]
Redshift0.005384±0.0000100[1]
Heliocentric radial velocity1,614±3 km/s[1]
Distance64.7 ± 4.6 Mly (19.83 ± 1.42 Mpc)[1]
Group or clusterNGC 720 Group (LGG 38)
Apparent magnitude (V)13.71[1]
Characteristics
TypeIAB(rs)m[1]
Size~52,900 ly (16.23 kpc) (estimated)[1]
Apparent size (V)2.8′ × 2.3′[1]
Other designations
DDO 14, Arp 4, MCG -02-05-050, PGC 6626[1]

Arp 4 is an irregular galaxy in the constellation of Cetus. Its velocity with respect to the cosmic microwave background is 1,345±19 km/s, which corresponds to a Hubble distance of 64.7 ± 4.6 Mly (19.83 ± 1.42 Mpc).[1] Additionally, one non-redshift measurement gives a similar distance estimate of 65 Mly (19.8 Mpc).[2] It was discovered by Dutch-Canadian astronomer Sidney van den Bergh in 1959, who listed it in the David Dunlap Observatory Catalogue as dwarf galaxy DDO 14.[3]

Arp 4 is the fourth object in Halton Arp's Atlas of Peculiar Galaxies, and one of six Arp objects in the 'Low Surface Brightness Galaxies' section. The other five low surface brightness galaxies are Arp 1 (NGC 2857), Arp 2 (UGC 10310), Arp 3, Arp 5 (NGC 3664), and Arp 6 (NGC 2537).[4]

Arp 4 with PGC 6629 imaged by Legacy Surveys

Arp 4 has a possible active galactic nucleus, i.e. it has a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars.[5][6]

Arp 4 and the galaxy PGC 6629 are visually very close to each other, but the alignment is purely optical, as the Hubble distance to PGC 6629 is 675.0 ± 47.3 Mly (206.96 ± 14.50 Mpc), which is about 10 times further away than Arp 4.[7]

NGC 720 group

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Arp 4 is a member of the NGC 720 galaxy group (also known as LGG 38). The other galaxies in the group are NGC 720, MCG -02-05-056, MCG -02-05-072, MCG -02-05-074, DDO 15, KUG 0150-138, KUG 0151-140, PGC 87900, PGC 87906, and UGCA 22.[8][9][10]

See also

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References

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  1. ^ a b c d e f g h i j k "Results for object ARP 004". NASA/IPAC Extragalactic Database. NASA and Caltech. Retrieved 17 December 2025.
  2. ^ "Distance Results for ARP 004". NASA/IPAC Extragalactic Database. NASA. Retrieved 17 December 2025.
  3. ^ Van Den Bergh, Sidney (1959). "A Catalogue of Dwarf Galaxies". Publications of the David Dunlap Observatory. 2 (5): 147. Bibcode:1959PDDO....2..147V.
  4. ^ Arp, Halton (1966). "Atlas of Peculiar Galaxies". Bibcode:1966apg..book.....A. Retrieved 17 December 2025.
  5. ^ Asmus, D.; Greenwell, C. L.; Gandhi, P.; Boorman, P. G.; Aird, J.; Alexander, D. M.; Assef, R. J.; Baldi, R. D.; Davies, R. I.; Hönig, S. F.; Ricci, C.; Rosario, D. J.; Salvato, M.; Shankar, F.; Stern, D. (2020). "Local AGN survey (LASr): I. Galaxy sample, infrared colour selection, and predictions for AGN within 100 MPC". Monthly Notices of the Royal Astronomical Society. 494 (2): 1784. arXiv:2003.05959. Bibcode:2020MNRAS.494.1784A. doi:10.1093/mnras/staa766.
  6. ^ "MCG-02-05-050". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 December 2025.
  7. ^ "Results for object MCG -02-05-050a". NASA/IPAC Extragalactic Database. NASA and Caltech. Retrieved 17 December 2025.
  8. ^ Garcia, A. M. (1993). "General study of group membership. II. Determination of nearby groups". Astronomy and Astrophysics Supplement Series. 100: 47. Bibcode:1993A&AS..100...47G.
  9. ^ Madore, Barry F.; Freedman, Wendy L.; Bothun, Gregory D. (2004). "Companions to Isolated Elliptical Galaxies: Revisiting the Bothun-Sullivan Sample". The Astrophysical Journal. 607 (2): 810. arXiv:0802.1354. Bibcode:2004ApJ...607..810M. doi:10.1086/383486.
  10. ^ "LGG 38". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 December 2025.
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  • Media related to Arp 4 at Wikimedia Commons
  • Arp 4 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images