The substructure of the Perseus star forming region: A survey with Gaia
  DR2
  We use photometric and kinematic data from Gaia DR2 to explore the structure
of the star forming region associated with the molecular cloud of Perseus.
Apart from the two well known clusters, IC 348 and NGC 1333, we present five
new clustered groups of young stars, which contain between 30 and 300 members,
named Autochthe, Alcaeus, Heleus, Electryon and Mestor. We demonstrate these
are co-moving groups of young stars, based on how the candidate members are
distributed in position, proper motion, parallax and colour-magnitude space. By
comparing their colour-magnitude diagrams to isochrones we show that they have
ages between 1 and 5 Myr. Using 2MASS and WISE colours we find that the
fraction of stars with discs in each group ranges from 10 to 50 percent. The
youngest of the new groups is also associated with a reservoir of cold dust,
according to the Planck map at 353 GHz. We compare the ages and proper motions
of the five new groups to those of IC 348 and NGC 1333. Autochthe is clearly
linked with NGC 1333 and may have formed in the same star formation event. The
seven groups separate roughly into two sets which share proper motion, parallax
and age: Heleus, Electryon, Mestor as the older set, and NGC 1333, Autochthe as
the younger set. Alcaeus is kinematically related to the younger set, but at a
more advanced age, while the properties of IC 348 overlap with both sets. All
older groups in this star forming region are located at higher galactic
latitude.
