Assembling a RELIC at Redshift 1: Spectroscopic Observations of Galaxies
  in the RELICS Cluster SPT-CLJ0615-5746
  We present a catalog of spectroscopic redshifts for SPT-CLJ0615$-$5746, the
most distant cluster in the Reionization Lensing Cluster Survey (RELICS). Using
Nod & Shuffle multi-slit observations with LDSS-3 on Magellan, we identify
${\sim}50$ cluster members and derive a cluster redshift of $z_c = 0.972$, with
a velocity dispersion of $\sigma = 1235 \pm 170\ \textrm{km}\ \textrm{s}^{-1}$.
We calculate a cluster mass using a $\sigma_{200}-M_{200}$ scaling relation of
$M_{200} = (9.4 \pm 3.6) \times 10^{14}\ M_\odot$, in agreement with previous,
independent mass measurements of this cluster. In addition, we examine the
kinematic state of SPT-CLJ0615$-$5746, taking into consideration prior
investigations of this system. With an elongated profile in lensing mass and
X-ray emission, a non-Gaussian velocity dispersion that increases with
clustercentric radius, and a brightest cluster galaxy not at rest with the bulk
of the system, there are multiple cluster properties that, while not
individually compelling, combine to paint a picture that SPT-CLJ0615$-$5746 is
currently being assembled.
