Dorado Group | |
---|---|
Observation data (Epoch J2000) | |
Constellation(s) | Dorado |
Right ascension | 04h17m 03.9s[1] |
Declination | −56° 07′ 43″[1] |
Brightest member | NGC 1566 |
Number of galaxies | 46 plus 34 candidate members[2] |
Other designations | |
Shk 18,[2] G16,[2][3] HG3,[2] MC13,[4] and NGC 1566 Group[5] | |
See also: Galaxy group, Galaxy cluster, List of galaxy groups and clusters |
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]
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]
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]
Name | Type[1] | R.A. (J2000)[1] | Dec. (J2000)[1] | Redshift (km/s)[1] | Apparent Magnitude[1] |
---|---|---|---|---|---|
SAB(rs+)c | 05h41m 51.1s | −64° 18′ 04″ | 1184 ± 6 | 12.6 | |
S0− pec | 05h26m 47.6s | −63° 45′ 36″ | 1100 ± 24 | 11.7 | |
(R)SB(r)dm: | 05h02m 42.5s | −61° 08′ 24″ | 1014 ± 9 | 12.9 | |
SB(rs)dm | 04h48m 23.8s | −59° 48′ 01″ | 1228 ± 6 | 12.6 | |
(R'_1:)SB(r)bc Sy2 | 04h45m 42.5s | −59° 14′ 50″ | 1331 ± 3 | 10.3 | |
IC 2056 | SAB(r)b | 04h16m 24.5s | −60° 12′ 25″ | 1133 ± 10 | 12.5 |
SB(s)cd | 04h17m 35.8s | −62° 47′ 01″ | 1304 ± 4 | 11.0 | |
NGC 1543 | (R)SB(l)00 | 04h12m 43.2s | −57° 44′ 17″ | 1176 ± 7 | 11.5 |
NGC 1574 | SA0− | 04h21m 58.8s | −56° 58′ 29″ | 1050 ± 25 | 11.4 |
NGC 1533 | (L)SB(rs)00 | 04h09m 51.8s | −56° 07′ 06″ | 790 ± 5 | 11.7 |
NGC 1546 | SA0+? | 04h14m 36.5s | −56° 03′ 39″ | 1284 ± 14 | 11.8 |
NGC 1553 | SA(rl)00 | 04h16m 10.5s | −55° 46′ 49″ | 1080 ± 11 | 10.3 |
NGC 1549 | E0−1 | 04h15m 45.1s | −55° 35′ 32″ | 1220 ± 15 | 10.7 |
NGC 1566 | (R'_1)SAB(rs)bcSy1 | 04h20m 00.4s | −54° 56′ 16″ | 1504 ± 2 | 10.3 |
NGC 1617 | (R')SAB(rs)a | 04h31m 39.5s | −54° 36′ 08″ | 1063 ± 21 | 11.4 |
NGC 1515 | SAB(s)bc | 04h04m 02.7s | −54° 06′ 00″ | 1175 ± 7 | 12.1 |
NGC 1705 | SA0− pec | 04h54m 13.5s | −53° 21′ 40″ | 633 ± 6 | 12.8 |
NGC 1596 | SA0: sp | 04h27m 38.1s | −55° 01′ 40″ | 1510 ± 8 | 12.1 |
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]
Name | Type[1] | R.A. (J2000)[1] | Dec. (J2000)[1] | Redshift (km/s)[1] | Apparent Magnitude[1] |
---|---|---|---|---|---|
IC 2049 | SAB(s)d? | 04h12m 04.3s | −58° 33′ 25″ | 1469 ± 7 | 14.5 |
NGC 1536 | SB(s)c pec | 04h10m 59.8s | −56° 28′ 50″ | 1217 ± 13 | 13.2 |
NGC 1543 | (R)SB(l)00 | 04h12m 43.2s | −57° 44′ 17″ | 1176 ± 7 | 11.5 |
LSBG F157-081 | Irregular | 04h27m 13.7s | −57° 25′ 42″ | 1215 ± 7 | 16.7 |
NGC 1533 | (L)SB(rs)00 | 04h09m 51.8s | −56° 07′ 06″ | 790 ± 5 | 11.7 |
IC 2038 | Sd pec | 04h08m 53.7s | −55° 59′ 22″ | 712 ± 52 | 15.5 |
APMBGC 157+016+068 | Irregular | 04h22m 51.7s | −56° 13′ 39″ | 1350 ± 4 | 16.3 |
NGC 1546 | SA0+? | 04h14m 36.5s | −56° 03′ 39″ | 1284 ± 14 | 11.8 |
IC 2058 | Sc | 04h17m 54.3s | −55° 55′ 58″ | 1379 ± 1 | 13.9 |
IC 2032 | IAB(s)m pec | 04h07m 03.0s | −55° 19′ 26″ | 1068 ± 7 | 14.7 |
NGC 1566 | (R'_1)SAB(rs)bcSy1 | 04h20m 00.4s | −54° 56′ 16″ | 1504 ± 2 | 10.3 |
NGC 1596 | SA0: sp | 04h27m 38.1s | −55° 01′ 40″ | 1510 ± 8 | 12.1 |
NGC 1602 | IB(s)m pec | 04h27m 55.0s | −55° 03′ 28″ | 1568 ± 8 | 13.3 |
NGC 1515 | SAB(s)bc | 04h04m 02.7s | −54° 06′ 00″ | 1175 ± 7 | 12.1 |
NGC 1522 | (R')S00: pec | 04h06m 07.9s | −52° 40′ 06″ | 898 ± 7 | 13.9 |
ESO 118-019 | S00 pec | 04h18m 59.5s | −58° 15′ 27″ | 1239 | 14.9 |
ESO 157-030 | E4 | 04h27m 32.6s | −54° 11′ 48″ | 1471 ± 28 | 14.7 |
ESO 157-047 | S0/a? pec sp | 04h39m 19.1s | −54° 12′ 41″ | 1655 ± 10 | 15.5 |
ESO 157-049 | S? | 04h39m 36.9s | −53° 00′ 46″ | 1678 ± 5 | 14.3 |
IC 2085 | S00 pec sp | 04h31m 24.2s | −54° 25′ 01″ | 982 ± 10 | 13.9 |
NGC 1549 | E0−1 | 04h15m 45.1s | −55° 35′ 32″ | 1220 ± 15 | 10.7 |
NGC 1553 | SA(rl)00 | 04h16m 10.5s | −55° 46′ 49″ | 1080 ± 11 | 10.3 |
NGC 1574 | SA0− | 04h21m 58.8s | −56° 58′ 29″ | 1050 ± 25 | 11.4 |
NGC 1581 | S0− | 04h24m 44.9s | −54° 56′ 31″ | 1600 ± 27 | 13.6 |
NGC 1617 | (R')SAB(rs)a | 04h31m 39.5s | −54° 36′ 08″ | 1063 ± 21 | 11.4 |
Abell 3202 | Irregular | 04h01m 15.2s | −53° 29′ 23″ | 1135 ± 40 | 16.9 |