Abstract
Galaxy clusters contain a large population of low mass dwarf elliptical
galaxies whose exact origin is unclear: their colors, structural properties and
kinematics differ substantially from those of dwarf irregulars in the field. We
use the Illustris cosmological simulation to study differences in the assembly
paths of dwarf galaxies (3e8 < M_*/M_sun < 1e10) according to their
environment. We find that cluster dwarfs achieve their maximum total and
stellar mass on average ~ 8 and ~ 4.5 Gyr ago, respectively, around the time of
infall into the clusters. In contrast, field dwarfs not subjected to
environmental stripping, reach their maximum mass at redshift z = 0. This
different assembly history naturally produces a color bimodality, with blue
isolated dwarfs and redder cluster dwarfs exhibiting negligible star-formation
today. The cessation of star formation happens over median times 3.5-5 Gyr
depending on stellar mass, and shows a large scatter (~ 1-8 Gyr), with the
lower values associated with starburst events that occur at infall through the
virial radius or pericentric passages. We argue that such starbursts together
with the early assembly of cluster dwarfs can provide a natural explanation for
the higher specific frequency of globular clusters (GCs) in cluster dwarfs, as
found observationally. We present a simple model for the formation and
stripping of GCs that supports this interpretation. The origin of dwarf
ellipticals in clusters is, therefore, consistent with an
environmentally-driven evolution of field dwarf irregulars. However the z = 0
field analogs of cluster dwarf progenitors have today stellar masses a factor ~
3 larger --a difference arising from the early truncation of star formation in
cluster dwarfs.
Description
[1509.00030] On the Assembly of Dwarf Galaxies in Clusters and their Efficient Formation of Globular Clusters
Links and resources
Tags