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Astron. Astrophys. 358, 471-480 (2000)

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2. The Local Group of galaxies

Reviews of the LG membership have been given by van den Bergh (1994a), Grebel (1997), Mateo (1998) and Courteau & van den Bergh (1999). Here we use the membership list of Courteau & van den Bergh (1999).

Within the Local Group, galaxies can be divided into three main subgroups. The first consists of the Milky Way and its satellites. This includes the Large and Small Magellanic Clouds, Fornax, and Sagittarius as well as 9 other small dwarf galaxies. The second group consists of M31 and its satellites, the largest of which is M33, a spiral galaxy. The compact elliptical galaxy M32, the irregular galaxy IC 1613 and numerous dwarf galaxies including NGC 147, NGC 185 and NGC 205 are also in the M31 subgroup. Recently, two independent groups (Armandroff et al. 1998a,b and Karachentsev & Karachentseva 1999) have found three new dwarf satellites of M31 named And V, Pegasus II (And VI) and Cassiopeia (And VII) which are included in our LG list. The third group is known as the Local Group Cloud (LGC), which is a large cloud of mainly dwarf galaxies extending throughout the Local Group. All of the galaxies in the Courteau & van den Bergh (1999) list are included in a subgroup, with 2 galaxies having somewhat uncertain assignments (Mateo 1998).

Galaxies that have at some point been associated with the Local Group but are not on the Courteau & van den Bergh (1999) list have not been included here. Notable examples of these are the galaxies in the NGC 3109 (or Antlia-Sextans) subgroup (NGC 3109, Antlia, Sextans A and Sextans B in Mateo 1998). Of these galaxies NGC 3109 is the only one with evidence of a globular cluster system - Demers et al. (1985) found ten globular cluster candidates. NGC 55 is another example of a galaxy we have not included. This had been associated with the LGC subgroup (Mateo 1998) but seems more likely to actually belong in the Sculptor (South Polar) Group (Courteau & van den Bergh 1999). NGC 55 has an estimated total GC population of 25[FORMULA]15 (Liller & Alcaino 1983) but only 3 with any information (Da Costa & Graham 1982; Beasley & Sharples 1999). Other galaxies that have been removed by Courteau & van den Bergh (1999) include IC 5152 (which has 10 unconfirmed candidate GCs suggested in Zijlstra & Minniti 1999), GR 8 which has no known GCs, and various other dwarf galaxies with no known GCs.

Simulations (e.g. Valtonen & Wiren 1994) have suggested that the IC 342/Maffei Group of galaxies (which consists of IC 342, Maffei 1 and 2, Dwingloo 1 and 2, NGC 1569, NGC 1560, UGCA 105, UGCA 92, UGCA 86, Cassiopeia 1 and MB 1; see Krismer et al. 1995) might once have been part of the LG but was thrown out by interaction with M31. Courteau & van den Bergh (1999) do not include this group in the LG based on their criteria for membership and we follow this assignment. It appears that no study has been carried out of the GC systems of galaxies in this group, although several galaxies might be expected to have some based on their luminosity. We also mention the Sab spiral M81 (NGC3031) in passing. Although not in the LG, at [FORMULA] 3 Mpc it is sufficiently close for a detailed spectroscopic study. A recent spectroscopic study using the Keck 10m telescope by Schroder et al. (2000) finds that the GCs have similar spectra and line indices to Milky Way halo GCs.

Our final list of LG galaxies is summarised in Table 1. We give galaxy names, Hubble type, subgroup, distance, absolute V band luminosity and number of GCs. Most properties come directly from Courteau & van den Bergh (1999), except the number of GCs which is the result of our investigation (see Sect. 3). The table is ordered by subgrouping within the Local Group.


[TABLE]

Table 1. Local Group Galaxy Properties. Subgrouping is given by MW = Milky Way, M31 = Andromeda, LGC = Local Group Cloud. Most quantities in this table are from Courteau & van den Bergh (1999). Distance is in kpc. See text for the number of globular clusters. A dash in the last column means that no reliable mention of globular clusters in this galaxy could be found in the literature.


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© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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