In the Pegasus I Cluster with NGC 7615, NGC 7619, NGC 7623, NGC 7626,
and NGC 7631.
S0 (de Vaucouleurs)
Companion 1.5, 4, 0.6 x 0.1
In the Pegasus I Cluster.
Ap. J., 51, 304, 1920.
Dynamics and Mass:
Ap. J., 134, 262, 1961.
A.J., 66, 545, 1961.
4. NGC 7619 Group
This is a group of five galaxies which form part of the Pegasus cluster (Hubble
and Humason 1931; Edson and Zwicky 1941); they are the brightest members of it.
The group has been studied by Hodge (1961). The types and velocities are
NGC 7611 (S0), +3579 km/sec; NGC 7617 (S0), +5068 km/sec; NGC 7619 (E3), +3953
km/sec; NGC 7623 (E4), +3659 km/sec; and NGC 7626 (E1), +3553 km/sec. The group
has an approximate diameter of 3.5 X 10^5^ pc and the separations between the
galaxies are on the average greater than 220 kpc. Consequently, Hodge finds that
the virial theorem is satisfied only for galactic masses in the range
10^12^-10^13^ M_sun_ and mass-to-light ratios of the order of 300. There is some
difficulty in estimating the total population of the cluster containing the
brightest galaxies listed by Hodge. Probably the estimate by Zwicky (1959, p.
63) of about 60 members is the best. If the five that have been measured form a
good sample of the whole, and if the cluster has little central concentration,
as seems to be the case, then we may conclude that probably the whole group is
unstable, unless a considerable amount of dark material is present.