Abstract
In this work we investigate in detail the effects local environment (groups
and pairs) has on galaxies with stellar mass similar to the Milky-Way (L*
galaxies). A volume limited sample of 6,150 galaxies is classified to determine
emission features, morphological type and presence of a disk. This sample
allows for characteristics of galaxies to be isolated (e.g. stellar mass and
group halo mass), and their codependencies determined.
We observe that galaxy-galaxy interactions play the most important role in
shaping the evolution within a group halo, the main role of halo mass is in
gathering the galaxies together to encourage such interactions. Dominant pair
galaxies find their overall star formation enhanced when the pair's mass ratio
is close to 1, otherwise we observe the same galaxies as we would in an
unpaired system. The minor galaxy in a pair is greatly affected by its
companion galaxy, and whilst the star forming fraction is always suppressed
relative to equivalent stellar mass unpaired galaxies, it becomes lower still
when the mass ratio of a pair system increases.
We find that, in general, the close galaxy-galaxy interaction rate drops as a
function of halo mass for a given amount of stellar mass. We find evidence of a
local peak of interactions for Milky-Way stellar mass galaxies in Milky-Way
halo mass groups. Low mass halos, and in particular Local Group mass halos, are
an important environment for understanding the typical evolutionary path of a
unit of stellar mass.
We find compelling evidence for galaxy conformity in both groups and pairs,
where morphological type conformity is dominant in groups, and emission class
conformity is dominant in pairs. This suggests that group scale conformity is
the result of many galaxy encounters over an extended period of time, whilst
pair conformity is a fairly instantaneous response to a transitory interaction.
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