  A recently-discovered class of outflows, extremely high-velocity outflows
(EHVOs), may be key to understanding feedback processes as it is likely the
most powerful in terms of mass-energy. These EHVOs have been observed at
redshifts 1.052 < z_em < 7.641, but the potential connection with outflows in
emission had not been studied. We find that EHVOs, albeit their small numbers
at the moment, appear to show distinct CIV and HeII properties. In particular,
EHVOs are more predominant in quasars with large blueshifts of the CIV emission
line, suggesting a connection between emission and absorption outflowing
signatures for these extreme outflows. We also find incipient trends with the
maximum velocity of the outflows, which is similar to what has been previously
found in BALQSOs, but now extending previous studies to speeds up to ~0.2c. We
find the bolometric luminosities, Eddington ratios, and black hole masses of
our sample are overall very similar from the general quasar population upon
considering their CIV emission properties. This is close to the case for HeII
EW as we observe a tentative upper limit to the HeII strength for a quasar to
host an EHVO. This study shows that extreme outflows such as EHVOs appear in
quasars that are clearly a distinct class from the overall BALQSO population,
and solidify the relation between outflows observed in emission and in
absorption.
