Dorado Group

The Dorado Group is a loose concentration of galaxies[2] containing both spirals and ellipticals.[3] It is generally considered a 'galaxy group' but may approach the size of a 'galaxy cluster'.[6] It lies primarily in the southern constellation Dorado and is one of the richest galaxy groups of the Southern Hemisphere.[7] Gérard de Vaucouleurs was the first to identify it in 1975 as a large complex nebulae II in the Dorado region,[2] designating it as G16.[3]

Dorado Group
NGC 1566, one of the brightest members of the Dorado Group (Spitzer Space Telescope image)
Observation data (Epoch J2000)
Constellation(s)Dorado
Right ascension04h 17m 03.9s[1]
Declination−56° 07′ 43″[1]
Brightest memberNGC 1566
Number of galaxies46 plus 34 candidate members[2]
Other designations
Shk 18,[2] G16,[2][3] HG3,[2] MC13,[4] and NGC 1566 Group[5]

Characteristics

A rough distance estimate from NGC 1549 (using the Hubble constant as 70) put the cluster at 18.4 megaparsecs (Mpc).[2] The Cepheid distance estimate from Freedman et al. 2001 is 15.3 Mpc.[8] Based upon the 2001 work of Tonry et al.[9] the surface brightness fluctuation (SBF) of six member galaxies was averaged and adjusted to estimate the group's distance at 19.1±0.8 Mpc in 2007.[10]

At the center of the cluster lie interacting galaxies[11] NGC 1549 and NGC 1553. The dominant group members, ordered by luminosity, are: spiral NGC 1566, lenticular NGC 1553, and elliptical NGC 1549.[6] The group spans an area of the sky 10° square, corresponding to an actual area of around 3 Mpc square.[2] The group exhibits a relatively small harmonic mean radius (230 ± 40 kpc) due to the concentration at its core of more luminous galaxies.[6] All together, the group has an overall luminosity of 7.8 ± 1.6 ×1010 L⊙.[6]

The Dorado Group contains three dominant smaller groups within itself, NGC 1672 Group, NGC 1566 Group and the NGC 1433 Group, as evidenced by the H I distribution of the region.[5] The Dorado Group is in the Fornax Wall that connects these three groups.[5] Due to its location in the Fornax Wall, the group is at a similar distance as the Fornax Cluster.[10] The Dorado Group is richer than the Local Group, while still being dominated by disk types of galaxies (i.e. its two brightest members are spiral NGC 1566 and lenticular NGC 1553) and its member galaxies have H I masses on par with non-interacting galaxies of the same morphological type.[10] With the group's apparent crossing time being 12.6 ± 0.6 %[6] of the universe's age, recent analyses deduce that the group is unvirialized, and thus this may explain the abundance of spirals and H I.[10]

Members

The table below lists eighteen galaxies that were identified in 1982 as associated with the Dorado Group by John Peter Huchra and Margaret J. Geller with the ones later dropped struck out.[12] In 1989, the list of members was expanded to 46 by Maia, da Costa, & Latham.[2] In 1990–1991, Henry C. Ferguson and Allan Sandage identified 34 other possible candidate members of the group with magnitudes greater than 19 and eliminated one member from Maia et al. putting the list at 79[6] galaxies.[2][3] Kilborn et al. 2005 confirmed 26 members from the list.[5] In 2006, the list was refined again by Firth et al.[6] Using redshift data, they excluded eleven (as being background galaxies or interloper) from the Ferguson et al. list, confirmed the membership of twenty on the list, and left 48 unconfirmed.[6]

Huchra et al. 1982 Members of the Dorado Group
(with strikeouts for ones dropped by Maia et al. in 1989)
Name Type[1] R.A. (J2000)[1] Dec. (J2000)[1] Redshift (km/s)[1] Apparent Magnitude[1]
NGC 2082 SAB(rs+)c 05h 41m 51.1s −64° 18′ 04″ 1184 ± 6 12.6
NGC 1947 S0− pec 05h 26m 47.6s −63° 45′ 36″ 1100 ± 24 11.7
NGC 1796 (R)SB(r)dm: 05h 02m 42.5s −61° 08′ 24″ 1014 ± 9 12.9
NGC 1688 SB(rs)dm 04h 48m 23.8s −59° 48′ 01″ 1228 ± 6 12.6
NGC 1672 (R'_1:)SB(r)bc Sy2 04h 45m 42.5s −59° 14′ 50″ 1331 ± 3 10.3
IC 2056 SAB(r)b 04h 16m 24.5s −60° 12′ 25″ 1133 ± 10 12.5
NGC 1559 SB(s)cd 04h 17m 35.8s −62° 47′ 01″ 1304 ± 4 11.0
NGC 1543 (R)SB(l)00 04h 12m 43.2s −57° 44′ 17″ 1176 ± 7 11.5
NGC 1574 SA0− 04h 21m 58.8s −56° 58′ 29″ 1050 ± 25 11.4
NGC 1533 (L)SB(rs)00 04h 09m 51.8s −56° 07′ 06″ 790 ± 5 11.7
NGC 1546 SA0+? 04h 14m 36.5s −56° 03′ 39″ 1284 ± 14 11.8
NGC 1553 SA(rl)00 04h 16m 10.5s −55° 46′ 49″ 1080 ± 11 10.3
NGC 1549 E0−1 04h 15m 45.1s −55° 35′ 32″ 1220 ± 15 10.7
NGC 1566 (R'_1)SAB(rs)bcSy1 04h 20m 00.4s −54° 56′ 16″ 1504 ± 2 10.3
NGC 1617 (R')SAB(rs)a 04h 31m 39.5s −54° 36′ 08″ 1063 ± 21 11.4
NGC 1515 SAB(s)bc 04h 04m 02.7s −54° 06′ 00″ 1175 ± 7 12.1
NGC 1705 SA0− pec 04h 54m 13.5s −53° 21′ 40″ 633 ± 6 12.8
NGC 1596 SA0: sp 04h 27m 38.1s −55° 01′ 40″ 1510 ± 8 12.1
Peculiar galaxy NGC 1487 is located about 30 million light-years away in the constellation of Eridanus.[13]

The Maia et al. 1989 thirty-four added members were: IC 2049, NGC 1536, IC 2058, IC 2032, NGC 1602, NGC 1581, IC 2085, NGC 1522, PGC 15149, NGC 1556, NGC 1527, NGC 1494, NGC 1493, PGC 14416, IC 2000, NGC 1483, NGC 1433, PGC 14078, NGC 1495, NGC 1510, NGC 1510, NGC 1512, IC 1959, IC 1986, NGC 1448, NGC 1487, IC 1933, NGC 1311, IC 1954, IC 1914, NGC 1411, IC 1970, PGC 13818, NGC 1249, and PGC 11139.[4] And the six dropped from the 1982 list were: NGC 2082, NGC 1947, NGC 1796, NGC 1688, NGC 1672, and NGC 1559.[4] In 2007, a study of ultracompact dwarfs (UCD) identified one definite and two possible UCD members of the group.[8] The thirty-four added by Ferguson et al. 1990 included IC 2038 and IC 2039.[3]

The NGC 1566 Group of Dorado contains H I with MHI = 3.5×1010 M⊙ of which 40% alone comes from the NGC 1566 galaxy.[5] More than half of its members are outside its virial radius of 580 kpc which suggests this group is a young non-virialized group. The 2005 Kilborn et al. set of confirmed NGC 1566 Group members (within the Dorado Group) is:[5]

Kilborn et al. 2005 Members of the NGC 1566 Group
Name Type[1] R.A. (J2000)[1] Dec. (J2000)[1] Redshift (km/s)[1] Apparent Magnitude[1]
IC 2049 SAB(s)d? 04h 12m 04.3s −58° 33′ 25″ 1469 ± 7 14.5
NGC 1536 SB(s)c pec 04h 10m 59.8s −56° 28′ 50″ 1217 ± 13 13.2
NGC 1543 (R)SB(l)00 04h 12m 43.2s −57° 44′ 17″ 1176 ± 7 11.5
LSBG F157-081 Irregular 04h 27m 13.7s −57° 25′ 42″ 1215 ± 7 16.7
NGC 1533 (L)SB(rs)00 04h 09m 51.8s −56° 07′ 06″ 790 ± 5 11.7
IC 2038 Sd pec 04h 08m 53.7s −55° 59′ 22″ 712 ± 52 15.5
APMBGC 157+016+068 Irregular 04h 22m 51.7s −56° 13′ 39″ 1350 ± 4 16.3
NGC 1546 SA0+? 04h 14m 36.5s −56° 03′ 39″ 1284 ± 14 11.8
IC 2058 Sc 04h 17m 54.3s −55° 55′ 58″ 1379 ± 1 13.9
IC 2032 IAB(s)m pec 04h 07m 03.0s −55° 19′ 26″ 1068 ± 7 14.7
NGC 1566 (R'_1)SAB(rs)bcSy1 04h 20m 00.4s −54° 56′ 16″ 1504 ± 2 10.3
NGC 1596 SA0: sp 04h 27m 38.1s −55° 01′ 40″ 1510 ± 8 12.1
NGC 1602 IB(s)m pec 04h 27m 55.0s −55° 03′ 28″ 1568 ± 8 13.3
NGC 1515 SAB(s)bc 04h 04m 02.7s −54° 06′ 00″ 1175 ± 7 12.1
NGC 1522 (R')S00: pec 04h 06m 07.9s −52° 40′ 06″ 898 ± 7 13.9
ESO 118-019 S00 pec 04h 18m 59.5s −58° 15′ 27″ 1239 14.9
ESO 157-030 E4 04h 27m 32.6s −54° 11′ 48″ 1471 ± 28 14.7
ESO 157-047 S0/a? pec sp 04h 39m 19.1s −54° 12′ 41″ 1655 ± 10 15.5
ESO 157-049 S? 04h 39m 36.9s −53° 00′ 46″ 1678 ± 5 14.3
IC 2085 S00 pec sp 04h 31m 24.2s −54° 25′ 01″ 982 ± 10 13.9
NGC 1549 E0−1 04h 15m 45.1s −55° 35′ 32″ 1220 ± 15 10.7
NGC 1553 SA(rl)00 04h 16m 10.5s −55° 46′ 49″ 1080 ± 11 10.3
NGC 1574 SA0− 04h 21m 58.8s −56° 58′ 29″ 1050 ± 25 11.4
NGC 1581 S0− 04h 24m 44.9s −54° 56′ 31″ 1600 ± 27 13.6
NGC 1617 (R')SAB(rs)a 04h 31m 39.5s −54° 36′ 08″ 1063 ± 21 11.4
Abell 3202 Irregular 04h 01m 15.2s −53° 29′ 23″ 1135 ± 40 16.9

References
  1. "NASA/IPAC Extragalactic Database", Results for Dorado Group and various galaxies, retrieved 2008-06-26
  2. Carrasco, Eleazar R.; Mendes de Oliveira, Cláudia; Infante, Leopoldo; Bolte, Michael (January 2001), "The Dwarf Galaxy Population of the Dorado Group Down to MV~−11", The Astronomical Journal, 121 (1): 148–168, arXiv:astro-ph/0010076, Bibcode:2001AJ....121..148C, doi:10.1086/318035, S2CID 1348985
  3. Ferguson, Henry C.; Sandage, Allan (July 1990), "Population studies in groups and clusters of galaxies. III – A catalog of galaxies in five nearby groups", Astronomical Journal, 100: 1–31, Bibcode:1990AJ....100....1F, doi:10.1086/115486, ISSN 0004-6256
  4. Maia, M. A. G.; da Costa, L. N.; Latham, David W. (April 1989), "A catalog of southern groups of galaxies", Astrophysical Journal Supplement Series, 69: 809–829, Bibcode:1989ApJS...69..809M, doi:10.1086/191328, ISSN 0067-0049
  5. Virginia A. Kilborn; Bärbel S. Koribalski; Duncan A. Forbes; David G. Barnes; Ruth C. Musgrave (January 2005), "A Wide-Field Hi Study of the NGC 1566 Group", Monthly Notices of the Royal Astronomical Society, 356 (1): 77–88, arXiv:astro-ph/0409743, Bibcode:2005MNRAS.356...77K, doi:10.1111/j.1365-2966.2004.08450.x
  6. Firth, P.; Evstigneeva, E. A.; Jones, J. B.; Drinkwater, M. J.; Phillipps, S.; Gregg, M. D. (November 2006), "Kinematics, substructure and luminosity-weighted dynamics of six nearby galaxy groups", Monthly Notices of the Royal Astronomical Society, 372 (4): 1856–1868, arXiv:astro-ph/0608584, Bibcode:2006MNRAS.372.1856F, doi:10.1111/j.1365-2966.2006.10993.x, S2CID 18646500
  7. Laurikainen, Eija; Salo, Heikki; Buta, Ronald; Knapen, Johan; Speltincx, Tom; Block, David (December 2006), "The Near-infrared S0 Survey III: Morphology of 15 Southern Early-Type Disk Galaxies", The Astronomical Journal, 132 (6): 2634–2652, arXiv:astro-ph/0609343, Bibcode:2006AJ....132.2634L, doi:10.1086/508810, S2CID 16856632
  8. Evstigneeva, E. A.; Drinkwater, M. J.; Jurek, R.; Firth, P.; Jones, J. B.; Gregg, M. D.; Phillipps, S. (July 2007), "Searches for ultracompact dwarf galaxies in galaxy groups", Monthly Notices of the Royal Astronomical Society, 378 (3): 1036–1042, arXiv:0704.1750, Bibcode:2007MNRAS.378.1036E, doi:10.1111/j.1365-2966.2007.11856.x, S2CID 15880069
  9. J. L. Tonry; A. Dressler; J. P. Blakeslee; E. A. Ajhar; A. B. Fletcher; G. A. Luppino; M. R. Metzger; C. B. Moore (2001), "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances", Astrophysical Journal, 546 (2): 681–693, arXiv:astro-ph/0011223, Bibcode:2001ApJ...546..681T, doi:10.1086/318301, S2CID 17628238
  10. DeGraaff, Regina Barber; Blakeslee, John P.; Meurer, Gerhardt R.; Putman, Mary E. (December 2007), "A Galaxy in Transition: Structure, Globular Clusters, and Distance of the Star-Forming S0 Galaxy NGC 1533 in Dorado", The Astrophysical Journal, 671 (2): 1624–1639, arXiv:0710.0893, Bibcode:2007ApJ...671.1624D, doi:10.1086/523640, S2CID 14312626
  11. Bridges, Terry J.; Hanes, David A. (April 1990), "Globular clusters in the interacting galaxies NGC 1549 and NGC 1553", Astronomical Journal, 99: 1100–1107, 1340, 1341, Bibcode:1990AJ.....99.1100B, doi:10.1086/115399, ISSN 0004-6256
  12. Huchra, John Peter; Geller, Margaret J. (June 15, 1982), "Groups of galaxies. I – Nearby groups", Astrophysical Journal, 257 (Part 1): 423–437, Bibcode:1982ApJ...257..423H, doi:10.1086/160000
  13. "One from many". Retrieved 1 February 2016.
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