The Physical Properties of Luminous $z\gtrsim8$ Galaxies and
  Implications for the Cosmic Star Formation Rate Density From $\sim$0.35
  deg$^{2}$ of (Pure-)Parallel HST Observations
  We present the largest systematic, HST-based search to date for luminous
$z\gtrsim8$ galaxy candidates using $\sim$1267 arcmin$^{2}$ of (pure-)parallel
observations from a compilation of 288 random sightlines with ACS and WFC3
observations, derived from the SuperBoRG data set and together representing a
factor $\sim1.12\times$ larger than existing space-based data sets. Using NIR
color cuts and careful photo-$z$ analyses, we find 31 $z\gtrsim8$ galaxy
candidates over 29 unique sightlines, and derive global galaxy properties such
as UV magnitudes and continuum slopes, sizes, and rest-frame optical properties
(e.g., SFRs, stellar masses, $A_{\rm v}$). Taking advantage of the
(pure-)parallel nature of our data set - making it one of the most
representative thus far - and derived SFRs, we evaluate the cosmic star
formation rate density for the bright end of the UV luminosity function at
$z\sim8-10$ and test the validity of luminosity function-derived results using
a conversion factor. We find our method yields comparable results to those
derived with luminosity functions. Furthermore, we present follow up
observations of 5 (Super)BoRG targets with Keck/MOSFIRE, finding no evidence of
Ly$\alpha$ in $>3$ hrs of $Y-$band observations in either, consistent with a
largely neutral medium at $z\sim8$. Our results offer a definitive HST legacy
on the bright end of the luminosity function and provide a valuable benchmark
as well as targets for follow up with JWST.
