High-velocity outflows in massive post-starburst galaxies at z > 1
  We investigate the prevalence of galactic-scale outflows in post-starburst
(PSB) galaxies at high redshift ($1 < z < 1.4$), using the deep optical spectra
available in the UKIDSS Ultra Deep Survey (UDS). We use a sample of $\sim40$
spectroscopically confirmed PSBs, recently identified in the UDS field, and
perform a stacking analysis in order to analyse the structure of strong
interstellar absorption features such as Mg ii ($\lambda2800$ Ang.). We find
that for massive ($M_* > 10^{10}\rm\,M_{\odot}$) PSBs at $z > 1$, there is
clear evidence for a strong blue-shifted component to the Mg ii absorption
feature, indicative of high-velocity outflows ($v_{\rm
out}\sim1150\pm160\rm\,km\,s^{-1}$) in the interstellar medium. We conclude
that such outflows are typical in massive PSBs at this epoch, and potentially
represent the residual signature of a feedback process that quenched these
galaxies. Using full spectral fitting, we also obtain a typical stellar
velocity dispersion $\sigma_*$ for these PSBs of $\sim200\rm\,km\,s^{-1}$,
which confirms they are intrinsically massive in nature (dynamical mass $M_{\rm
d}\sim10^{11}\rm\,M_{\odot}$). Given that these high-$z$ PSBs are also
exceptionally compact ($r_{\rm e}\sim1$--$2\rm\,kpc$) and spheroidal (Sersic
index $n\sim3$), we propose that the outflowing winds may have been launched
during a recent compaction event (e.g. major merger or disc collapse) that
triggered either a centralised starburst or active galactic nuclei (AGN)
activity. Finally, we find no evidence for AGN signatures in the optical
spectra of these PSBs, suggesting they were either quenched by stellar feedback
from the starburst itself, or that if AGN feedback is responsible, the AGN
episode that triggered quenching does not linger into the post-starburst phase.
