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Draft:HCG 4


  • Comment: No sources listed seem to focus on HCG 4 in particular without being a database. ✶Quxyz✶ (talk) 22:28, 7 August 2026 (UTC)


HCG 4
HCG 4 legacy dr10.jpg
Hickson Compact Group 4 by Legacy Surveys Data Release 10
Observation data (Epoch J2000)
ConstellationCetus
Right ascension00h 34m 15.9s
Declination−21° 26′ 48.0″
Brightest memberESO 540-1
Number of galaxies5
Velocity dispersion338.9 km/s
Redshift0.026915
Distance114.52 Mpc (373.77 Mly)
Other designations
SCG 0031-2143; SCG 05; HIPASS J0034-21

Hickson Compact Group 4[1] is a compact group of galaxies that concludes of 5 members. In Constellation Cetus, HCG 4 was identified by a systematic search by the Palomar Observatory Sky Survey lead by Paul Hickson.[2] HCG 4 is a Compact Galaxy Group along with another 99 Groups detected by Paul Hickson. In HCG 4, HCG 4E is the furthest galaxy, which is 868.36 Million light-year away with a Velocity of 18480 km/s[3], followed by HCG 4C which is 871.56 Mly away. HCG 4B is the closest to Milky Way, followed by HCG 4A and 4D. HCG 4 is a group that is relatively isolated due to it is not connected to any large nearby structures or any clusters.

Properties

HCG 4A has shown a strong infrared radiation from a Far-Infrared (FIR) study by Infrared Astronomy Satellite (IRAS)[4][5], reaching an amount of 10.957 L☉, HCG 4A also has the least B-R (Blue minus Red) and B_T (Total Blue Magnitude)[6][7], indicating to astronomers that HCG 4A has a massive amount of stellar nurseries and is undergoing vigorous star formation. HCG 4A falls under the Luminous Infrared Galaxy (LIRG) category, while HCG 4B, 4C and 4E has not been detected or their infrared radiation is low or weak, they have also high B-R and B_T, hinting that they are not actively forming stars and is likelihood to be dominated by cool and old stars.

HCG 4A is the brightest member of this group, as other studies suggests that HCG 4A has M_B (known as Absolute magnitude) of 21.1, following by HCG 4B, 4C and 4D, which has M_B of 19.3, 19.1 and 19.1 respectively. [8] An analysis of the environment around HCG 4 has been conducted, uncovering that there is a total of 15 background galaxies, 6 foreground stars. The study also a field density of 0.00184 galaxies per square arcminute outside the group. The spiral, elliptical, and lenticular fraction of the background galaxies is 40%, 20%, and 40% respectively. This survey proves that the group members are centrally concentrated with a radius of 3.5 arcminutes and has a Density Contrast of 126[9], while the nearest field galaxy is 14.8 arcminutes away, proving that HCG 4 is truly a compact group.[7] HCG 4 nearby field has a spiral fraction of 40%, which typical for a early type environment.[9]

A study shows that HCG 4D has emission lines, indicating it is undergoing vigorous star formation and is considered as one of the bluest galaxies in the entire HCG catalog and compared to galaxies in similar environments. The Radial velocity [V_rad (km/s)] of HCG 4D is 8005.7 and a Velocity dispersion of the stars in the galaxy [σ (km/s)] of 71.8.[10] In a X-ray study, HCG 4 is dominated by a strong emission from an Active Galactic Nucleus (AGN) within the group, which outshines any diffuse emission from X-ray Emission and is being placed an upper limit of X-ray Luminosity log L_X < 41.11 erg/s[11]. Therefore, HCG 4 is excluded in the ROSAT All Sky Survey (RASS) of Hickson Compact Groups.[12]

Far-Infrared observations (FIR) found that HCG 4A is a strong emitter (60 μm = 3.85 Jy, 100 μm = 8.08 Jy), supporting that it is undergoing vigorous star formation. HCG 4D have also been detected, but it is only detected at 60 μm Flux of only 0.21 Jy, suggesting it has very little amount of stardust to fuel the formation of stars. For HCG 4B, 4C and 4E, no FIR have been detected, suggesting it has no significant emission.[13] The observed neutral hydrogen gas (log[M(HI)_obs]) is 10.31 and the predicted neutral hydrogen gas log[M(HI)_pred] is 10.34, the difference between the observed amount and the predicted amount is 0.03. Therefore, HCG 4 is not significantly deficient in Hydrogen gas (HI).[14]

HCG 4 has a Crossing time (H0tc) of 0.0126, median galaxy separation of 57 kpc (186,000 light-years), radial velocity dispersion of 338.9 km/s , and a Mass to light ratio (M☉/L☉) of 229.1.[15] This indicates that HCG 4 is a moderately massive compact group, contains a large amount of dark matter, and is predicted that each member will merge quickly.[15] HCG 4A is a face-on spiral galaxy, which has a major axis diameter(") of 41.10 and a minor axis diameter of 33.50, which has an axis ratio (a/b) of 0.82, indicating it is almost fully face-on.[15]

Morphology

Studies has shown that HCG 4C has a disturbed morphology, often due to gravitational interaction with other galaxies that may be a sign of a pre-merger. Other than that, HCG 4D also has a disturbed morphology, has emission lines and is too blue, indicating a sign of a post merger and has high star formation.[5] HCG 4 has an angular diameter of 409.75 arcseconds and a mean surface brightness of 26.52 mag/arcsec².[16] Early studies shown that HCG 4 may just be a chance alignment in a loose group[17], but The Monte Carlo simulations show that finding a group like HCG 4 is significantly low (log P ≈ -1.6), confirming that it is a genuine compact group rather than a chance projection[18] A study found that HCG's velocity dispersion is correlated to their elongation, suggesting that their members rotate around the group's gravitational center.[19] Numerical simulations show that compact groups can last up to 10 Billion years without merging, supporting the idea that HCG 4 is a stable, long-lived system.[20]

Another study suggests that out of 5 galaxies in HCG 4 group, there are a total of 3 galaxies are spirals.[21] Therefore, the spiral fraction (FSP) for this galaxy group is 0.6 or 60%.[21] There 1 Lenticular and Elliptical in this group, but for HCG 4B and 4E, previously identified by Paul Hickson as lenticular and elliptical, both are actually spirals that is being corrected by Barbara Ann Williams.[22] In HCG 4, there are 2 galaxy pairs, which are HCG 4A and 4D, HCG 4C and 4E, while HCG 4B seems to be a foreground galaxy due to the velocity differences[23]. HCG 4A is a late type spiral galaxy, has a Star formation rate [SFR (M☉/yr)] of 16.4 M☉ per year, has an Infrared luminosity [log L_IR (L☉)] of 11.22 or 1.7 × 10¹¹ L☉, suggesting it is undergoing very active star formation, and is considered as a luminous infrared galaxy (LIRG). However, HCG 4B is a Late Type spiral and 4D is a Early Type spiral, both has much lower rates of Star formation compared to HCG 4A, which are 0.54 and 0.70. HCG 4A, 4B and 4D is dynamically old.[24] HCG 4D is classified as a dusty elliptical galaxy. Its dusty disk is (34"), which is much larger than its stellar disk (18"), suggesting it is interacting with another galaxy in its group.[24]

HCG 4A has a diameter (kpc) of 65.83 (about 215,000 light-years), it is significantly larger than the Milky Way (30 kpc) and may be comparable to the largest galaxies in the universe.[25]

Members

Hickson Compact Group 4 consists of 5 members, HCG 4A to 4E, where their details are stated in the table below.

Number Other Names Right

ascension

Declination Distance Type B-R B_T Velocity (km/s)[3] Redshift
4A[26] ESO 540-1 00h 34m 13.8212s -21° 26' 20.578″ 114.21 Mpc

(372.75 Mly)

(R')SB(r)bc 1.01 13.78 8097 0.026845
4B[27] ESO 540-2 00h 34m 14.0381s -21° 21' 1.645" 98.51 Mpc

(321.51 Mly)

(R')SB(r)b? pec 1.03 15.52 7065 0.023293
4C[28] PGC 2051 00h 34m 15.5165s -21° 25' 03.128" 267.04 Mpc

(871.56 Mly)

S0? 1.51 15.90 18410 0.061409
4D[29] PGC 2057 00h 34m 16.8280s -21° 28' 39.880" 117.07 Mpc

(382.09 Mly)

E? 1.19 15.68 8215 0.027492
4E[30] PGC 2040 00h34m08.3089s -21° 26' 07.719" 266.06 Mpc

(868.36 Mly)

S? 1.31 16.37 18480 0.061186

References

  1. ^ "NED results for HCG 4". NASA/IPAC Extragalactic Database. National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 2026-07-14.
  2. ^ Hickson, P. (1982). "Systematic properties of compact groups of galaxies". The Astrophysical Journal. 255: 382. Bibcode:1982ApJ...255..382H. doi:10.1086/159838.
  3. ^ a b Hickson, P.; Mendes de Oliveira, C.; Huchra, J. P.; Palumbo, G. G. C. (1992). "Dynamical Properties of Compact Groups of Galaxies". The Astrophysical Journal. 399: 353. Bibcode:1992ApJ...399..353H. doi:10.1086/171932.
  4. ^ Verdes-Montenegro, L.; Yun, M. S.; Perea, J.; del Olmo, A.; Ho, P. T. P. (1998-04-10). "Effects of Interaction-Induced Activities in Hickson Compact Groups: CO and Far-Infrared Study". The Astrophysical Journal. 497: 89–107. Bibcode:1998ApJ...497...89V. doi:10.1086/305456.
  5. ^ a b Mendes de Oliveira, C.; Hickson, P. (1994). "Morphology of Galaxies in Compact Groups". The Astrophysical Journal. 427: 684. Bibcode:1994ApJ...427..684M. doi:10.1086/174176.
  6. ^ Hickson, P.; Kindl, E.; Auman, J. R. (1989). "A photometric catalog of compact groups of galaxies". The Astrophysical Journal Supplement Series. 70: 687. Bibcode:1989ApJS...70..687H. doi:10.1086/191354.
  7. ^ a b Kindl, Enrico (1991). A photometric and morphological study of compact groups of galaxies and their environments (Ph.D. thesis). University of British Columbia.
  8. ^ Mendes de Oliveira, C.; Hickson, P. (1991). "The Luminosity Function of Compact Groups of Galaxies". The Astrophysical Journal. 380: 30. Bibcode:1991ApJ...380...30M. doi:10.1086/170564.
  9. ^ a b Palumbo, G. G. C.; Saracco, P.; Hickson, P.; Mendes de Oliveira, C. (1995). "Environment of Compact Groups of Galaxies". The Astronomical Journal. 109 (4): 1476. Bibcode:1995AJ....109.1476P. doi:10.1086/117379.
  10. ^ Mendes de Oliveira, C.; Coelho, P.; González, J. J.; Barbuy, B. (2005). "Ages, Metallicities, and α-Element Enhancement for Galaxies in Hickson Compact Groups". The Astronomical Journal. 130 (1): 55–64. Bibcode:2005AJ....130...55M. doi:10.1086/430280.
  11. ^ Mulchaey, John S.; Davis, David S.; Mushotzky, Richard F.; Burstein, David (2003). "An X-Ray Atlas of Groups of Galaxies". The Astrophysical Journal Supplement Series. 145 (1): 39–53. Bibcode:2003ApJS..145...39M. doi:10.1086/345736.
  12. ^ Ponman, T. J.; Bourner, P. D. J.; Ebeling, H. (1996). "X-ray properties of compact galaxy groups". In Zimmermann, H. U.; Trümper, J. E.; Yorke, H. (eds.). MPE Report 263: Proceedings of the Röntgenstrahlung from the Universe Conference. pp. 357–360. Bibcode:1996rftu.proc..357P.
  13. ^ Allam, S.; Assendorp, R.; Longo, G.; Braun, M.; Richter, G. (1996). "Far infrared properties of Hickson compact groups of galaxies. I. High resolution IRAS maps and fluxes" (PDF). Astronomy & Astrophysics Supplement Series. 117: 39–82. Bibcode:1996A&AS..117...39A. doi:10.1051/aas:1996159.
  14. ^ Verdes-Montenegro, L.; Yun, M. S.; Williams, B. A.; Huchtmeier, W. K.; Del Olmo, A.; Perea, J. (2001). "Where is the neutral atomic gas in Hickson groups?" (PDF). Astronomy & Astrophysics. 377: 812–826. Bibcode:2001A&A...377..812V. doi:10.1051/0004-6361:20011127.
  15. ^ a b c Hickson, P. (1993). "Atlas of Compact Groups of Galaxies". Astrophysical Letters and Communications. 29: 1. Bibcode:1993ApL&C..29....1H.
  16. ^ de Carvalho, R. R.; Ribeiro, A. L. B.; Zepf, Stephen E. (1994). "Structural Properties of Compact Groups of Galaxies". The Astrophysical Journal. 420: 41. Bibcode:1994ApJ...420...41D. doi:10.1086/173543.
  17. ^ Mamon, G. A. (1986). "Are Compact Groups of Galaxies Physically Bound?". The Astrophysical Journal. 307: 426. Bibcode:1986ApJ...307..426M. doi:10.1086/164429.
  18. ^ Hickson, P.; Rood, H. J. (1988). "The Nature of Compact Groups of Galaxies". The Astrophysical Journal. 331: L69. Bibcode:1988ApJ...331L..69H. doi:10.1086/185248.
  19. ^ Tovmassian, H. M.; Chavushyan, V. H.; Martinez, O.; Yam, O.; Tiersch, H. (2002). "Dynamics of Hickson Compact Groups of Galaxies". In Rosado, M.; Binette, L.; Arias, L. (eds.). Galaxies: The Third Dimension. ASP Conference Series. Vol. 282. Astronomical Society of the Pacific. pp. 262–268. Bibcode:2002ASPC..282..262T.
  20. ^ Aceves, H.; Velázquez, H. (2002). "N-Body Simulations of Small Galaxy Groups". Revista Mexicana de Astronomía y Astrofísica. 38: 199–214. Bibcode:2002RMxAA..38..199A.
  21. ^ a b Kindl, E. (1990). A Study of the Environments of Compact Groups of Galaxies (Ph.D. thesis). University of British Columbia. Bibcode:1990PhDT........20K.
  22. ^ Williams, B. A.; Rood, Herbert J. (1987). "Neutral Hydrogen in Compact Groups of Galaxies". The Astrophysical Journal Supplement Series. 63: 265–294. Bibcode:1987ApJS...63..265W. doi:10.1086/191166.
  23. ^ Seligman, Courtney. "Hickson Compact Group 4". Celestial Atlas. Retrieved 2026-08-08.
  24. ^ a b Bitsakis, T.; Charmandaris, V.; Appleton, P. N.; Diaz-Santos, T.; Le Floc'h, E.; da Cunha, E.; Alatalo, K.; Cluver, M. (2014). "Herschel observations of Hickson compact groups of galaxies: Unveiling the properties of cold dust" (PDF). Astronomy & Astrophysics. 565: A25. Bibcode:2014A&A...565A..25B. doi:10.1051/0004-6361/201323349.
  25. ^ "NED results for object ESO 540-G001". NASA/IPAC Extragalactic Database (NED). California Institute of Technology. Retrieved 2026-08-08.
  26. ^ "NED results for HCG 4A". NASA/IPAC Extragalactic Database. National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 2026-07-14.
  27. ^ "NED results for HCG 4B". NASA/IPAC Extragalactic Database (NED). National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 2026-07-14.
  28. ^ "NED results for HCG 4C". NASA/IPAC Extragalactic Database (NED). National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 2026-07-14.
  29. ^ "NED results for HCG 4D". NASA/IPAC Extragalactic Database (NED). National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 2026-07-14.
  30. ^ "NED results for HCG 4E". NASA/IPAC Extragalactic Database (NED). National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 2026-07-14.

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