Dorado Group

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Template:Short description

Template:Galaxy cluster The Dorado Group is a loose concentration of galaxies[1] containing both spirals and ellipticals.[2] It is generally considered a 'galaxy group' but may approach the size of a 'galaxy cluster'.[3] It lies primarily in the southern constellation Dorado and is one of the richest galaxy groups of the Southern Hemisphere.[4] Gérard de Vaucouleurs was the first to identify it in 1975 as a large complex nebulae II in the Dorado region,[1] designating it as G16.[2]

Characteristics

A rough distance estimate from NGC 1549 (using the Hubble constant as 70) put the cluster at 18.4 megaparsecs (Mpc).[1] The Cepheid distance estimate from Freedman et al. 2001 is 15.3 Mpc.[5] Based upon the 2001 work of Tonry et al.[6] the surface brightness fluctuation (SBF) of six member galaxies was averaged and adjusted to estimate the group's distance at Script error: No such module "val". in 2007.[7]

At the center of the cluster lie interacting galaxies[8] NGC 1549 and NGC 1553. The dominant group members, ordered by luminosity, are: spiral NGC 1566, lenticular NGC 1553, and elliptical NGC 1549.[3] The group spans an area of the sky 10° square, corresponding to an actual area of around 3 Mpc square.[1] The group exhibits a relatively small harmonic mean radius (230 ± 40 kpc) due to the concentration at its core of more luminous galaxies.[3] All together, the group has an overall luminosity of 7.8 ± 1.6 Template:E L⊙.[3]

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.[9] The Dorado Group is in the Fornax Wall that connects these three groups.[9] Due to its location in the Fornax Wall, the group is at a similar distance as the Fornax Cluster.[7] 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.[7] With the group's apparent crossing time being 12.6 ± 0.6 %[3] 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.[7]

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.[10] In 1989, the list of members was expanded to 46 by Maia, da Costa, & Latham.[1] 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[3] galaxies.[1][2] Kilborn et al. 2005 confirmed 26 members from the list.[9] In 2006, the list was refined again by Firth et al.[3] 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.[3]

Huchra et al. 1982 Members of the Dorado Group
(with strikeouts for ones dropped by Maia et al. in 1989)
Name Type[11] R.A. (J2000)[11] Dec. (J2000)[11] Redshift (km/s)[11] Apparent Magnitude[11]
NGC 2082 SAB(rs+)c Template:RA Template:DEC 1184 ± 6 12.6
NGC 1947 S0− pec Template:RA Template:DEC 1100 ± 24 11.7
NGC 1796 (R)SB(r)dm: Template:RA Template:DEC 1014 ± 9 12.9
NGC 1688 SB(rs)dm Template:RA Template:DEC 1228 ± 6 12.6
NGC 1672 (R'_1:)SB(r)bc Sy2 Template:RA Template:DEC 1331 ± 3 10.3
IC 2056 SAB(r)b Template:RA Template:DEC 1133 ± 10 12.5
NGC 1559 SB(s)cd Template:RA Template:DEC 1304 ± 4 11.0
NGC 1543 (R)SB(l)00 Template:RA Template:DEC 1176 ± 7 11.5
NGC 1574 SA0− Template:RA Template:DEC 1050 ± 25 11.4
NGC 1533 (L)SB(rs)00 Template:RA Template:DEC 790 ± 5 11.7
NGC 1546 SA0+? Template:RA Template:DEC 1284 ± 14 11.8
NGC 1553 SA(rl)00 Template:RA Template:DEC 1080 ± 11 10.3
NGC 1549 E0−1 Template:RA Template:DEC 1220 ± 15 10.7
NGC 1566 (R'_1)SAB(rs)bcSy1 Template:RA Template:DEC 1504 ± 2 10.3
NGC 1617 (R')SAB(rs)a Template:RA Template:DEC 1063 ± 21 11.4
NGC 1515 SAB(s)bc Template:RA Template:DEC 1175 ± 7 12.1
NGC 1705 SA0− pec Template:RA Template:DEC 633 ± 6 12.8
NGC 1596 SA0: sp Template:RA Template:DEC 1510 ± 8 12.1
File:NGC 1487 HST.jpg
Peculiar galaxy NGC 1487 is located about 30 million light-years away in the constellation of Eridanus.[12]

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 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.[13] And the six dropped from the 1982 list were: NGC 2082, NGC 1947, NGC 1796, NGC 1688, NGC 1672, and NGC 1559.[13] In 2007, a study of ultracompact dwarfs (UCD) identified one definite and two possible UCD members of the group.[5] The thirty-four added by Ferguson et al. 1990 included IC 2038 and IC 2039.[2]

The NGC 1566 Group of Dorado contains H I with MHI = 3.5Template:E M⊙ of which 40% alone comes from the NGC 1566 galaxy.[9] 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:[9]

Kilborn et al. 2005 Members of the NGC 1566 Group
Name Type[11] R.A. (J2000)[11] Dec. (J2000)[11] Redshift (km/s)[11] Apparent Magnitude[11]
IC 2049 SAB(s)d? Template:RA Template:DEC 1469 ± 7 14.5
NGC 1536 SB(s)c pec Template:RA Template:DEC 1217 ± 13 13.2
NGC 1543 (R)SB(l)00 Template:RA Template:DEC 1176 ± 7 11.5
LSBG F157-081 Irregular Template:RA Template:DEC 1215 ± 7 16.7
NGC 1533 (L)SB(rs)00 Template:RA Template:DEC 790 ± 5 11.7
IC 2038 Sd pec Template:RA Template:DEC 712 ± 52 15.5
APMBGC 157+016+068 Irregular Template:RA Template:DEC 1350 ± 4 16.3
NGC 1546 SA0+? Template:RA Template:DEC 1284 ± 14 11.8
IC 2058 Sc Template:RA Template:DEC 1379 ± 1 13.9
IC 2032 IAB(s)m pec Template:RA Template:DEC 1068 ± 7 14.7
NGC 1566 (R'_1)SAB(rs)bcSy1 Template:RA Template:DEC 1504 ± 2 10.3
NGC 1596 SA0: sp Template:RA Template:DEC 1510 ± 8 12.1
NGC 1602 IB(s)m pec Template:RA Template:DEC 1568 ± 8 13.3
NGC 1515 SAB(s)bc Template:RA Template:DEC 1175 ± 7 12.1
NGC 1522 (R')S00: pec Template:RA Template:DEC 898 ± 7 13.9
ESO 118-019 S00 pec Template:RA Template:DEC 1239 14.9
ESO 157-030 E4 Template:RA Template:DEC 1471 ± 28 14.7
ESO 157-047 S0/a? pec sp Template:RA Template:DEC 1655 ± 10 15.5
ESO 157-049 S? Template:RA Template:DEC 1678 ± 5 14.3
IC 2085 S00 pec sp Template:RA Template:DEC 982 ± 10 13.9
NGC 1549 E0−1 Template:RA Template:DEC 1220 ± 15 10.7
NGC 1553 SA(rl)00 Template:RA Template:DEC 1080 ± 11 10.3
NGC 1574 SA0− Template:RA Template:DEC 1050 ± 25 11.4
NGC 1581 S0− Template:RA Template:DEC 1600 ± 27 13.6
NGC 1617 (R')SAB(rs)a Template:RA Template:DEC 1063 ± 21 11.4
Abell 3202 Irregular Template:RA Template:DEC 1135 ± 40 16.9

External links

References

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Template:Stars of Dorado

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