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IC 342/Maffei Group

The IC 342/Maffei Group (also known as the IC 342 Group or the Maffei 1 Group) is the nearest group of galaxies to the Local Group. The group can be described as a binary group; the member galaxies are mostly concentrated around either IC 342 or Maffei 1, both of which are the brightest galaxies within the group. The group is one of many located within the Virgo Supercluster (i.e. the Local Supercluster).

Members

The table below lists galaxies that have been identified as associated with the IC342/Maffei 1 Group by I. D. Karachentsev. Note that Karachentsev divides this group into two subgroups centered around IC 342 and Maffei 1.

Members of the IC 342 Subgroup
Name Type R.A. (J2000) Dec. (J2000) Redshift (km/s) Apparent Magnitude
Camelopardalis A Irr -46 ± 1 14.8
Camelopardalis B Irr 77 16.1
Cassiopeia 1 dIrr 35 16.4
IC 342 SAB(rs)cd 31 ± 3 9.1
KK 35 Irr 105 ± 1 17.2
NGC 1560 SA(s)d -36 ± 5 12.2
UGCA 86 Im 67 ± 4 13.5
UGCA 105 Im 111 ± 5 13.9

Members of the Maffei 1 Subgroup
Name Type R.A. (J2000) Dec. (J2000) Redshift (km/s) Apparent Magnitude
Dwingeloo 1 SB(s)cd 110 8.3
Dwingeloo 2 Im 94 ± 1 20.5
KKH 11 dE 310 16.2
KKH 12 Irr 70 17.8
Maffei 1 S0 pec 02|36|35.4} 13 ± 22 11.4
Maffei 2 SAB(rs)bc -17 ± 5 16.0
MB 1 SAB(s)d 20.5 190 ± 1
MB 3 dSph 59 ± 1 19.8

Additionally, KKH 37 is listed as possibly being a members of the IC 342 Subgroup, and KKH 6 is listed as possibly being members of the Maffei 1 Subgroup.

Foreground dust obscuration

As seen from Earth, the group lies near the plane of the Milky Way (a region sometimes called the zone of avoidance). Consequently, the light from many of the galaxies is severely affected by dust obscuration within the Milky Way. This complicates observational studies of the group, as uncertainties in the dust obscuration also affect measurements of the galaxies' luminosities and distances as well as other related quantities.

Moreover, the galaxies within the group have historically been difficult to identify. Many galaxies have only been discovered using late 20th century astronomical instrumentation. For example, while many fainter, more distant galaxies, such as the galaxies in the New General Catalogue, were already identified visually by the end of the nineteenth century, Maffei 1 and Maffei 2 were only discovered in 1968 using infrared photographic images of the region. Furthermore, it is difficult to determine whether some objects near IC 342 or Maffei 1 are galaxies associated with the IC 342/Maffei Group or diffuse foreground objects within the Milky Way that merely look like galaxies. For example, the objects MB 2 and Camelopardalis C were once thought to be dwarf galaxies in the IC 342/Maffei Group but are now known to be objects within the Milky Way.

Group formation and possible interactions with the Local Group

Since the IC 342/Maffei Group and the Local Group are located physically close to each other, the two groups may have influenced each other's evolution during the early stages of galaxy formation. An analysis of the velocities and distances to the IC 342/Maffei Group as measured by M. J. Valtonen and collaborators suggested that IC 342 and Maffei 1 were moving faster than what could be accounted for in the expansion of the universe. They therefore suggested that IC 342 and Maffei 1 were ejected from the Local Group after a violent gravitational interaction with the Andromeda Galaxy during the early stages of the formation of the two groups.

However, this interpretation is dependent on the distances measured to the galaxies in the group, which in turn is dependent on accurately measuring the degree to which interstellar dust in the Milky Way obscures the group. More recent observations have demonstrated that the dust obscuration may have been previously overestimated, so the distances may have been underestimated. If these new distance measurements are correct, then the galaxies in the IC 342/Maffei Group appear to be moving at the rate expected from the expansion of the universe, and the scenario of a collision between the IC 342/Maffei Group and the Local Group would be implausible.

References

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