Evidence for the rapid formation of low mass early-type galaxies in
  dense environments
  We explore the environmental dependence of star formation timescales in low
mass galaxies using the [$\alpha$/Fe] abundance ratio as an evolutionary clock.
We present integrated [$\alpha$/Fe] measurements for 11 low mass ($M_\star \sim
10^9~M_\odot$) early-type galaxies (ETGs) with a large range of cluster-centric
distance in the Virgo Cluster. We find a gradient in [$\alpha$/Fe], where the
galaxies closest to the cluster center (the cD galaxy, M87) have the highest
values. This trend is driven by galaxies within a projected radius of 0.4~Mpc
(0.26 times the virial radius of Virgo~A), all of which have super-solar
[$\alpha$/Fe]. Galaxies in this mass range exhibit a large scatter in the
[$\alpha$/Fe]--$\sigma$ diagram, and do not obviously lie on an extension of
the relation defined by massive ETGs. In addition, we find a correlation
between [$\alpha$/Fe] and globular cluster specific frequency ($S_N$),
suggesting that low-mass ETGs that formed their stars over a short period of
time, were also efficient at forming massive star clusters. The innermost
low-mass ETGs in our sample have [$\alpha$/Fe] values comparable to that of
M87, implying that environment is the controlling factor for star formation
timescales in dense regions. These low-mass galaxies could be the surviving
counterparts of the objects that have already been accreted into the halo of
M87, and may be the link between present-day low-mass galaxies and the old,
metal-poor, high-[$\alpha$/Fe], high-$S_N$ stellar populations seen in the
outer halos of massive ETGs.
