The FLASHES Survey I: Integral Field Spectroscopy of the CGM around 48
  $z=2.3-3.1$ QSOs
  We present the pilot study component of the Fluorescent Lyman-Alpha
Structures in High-z Environments (FLASHES) Survey; the largest integral-field
spectroscopy survey to date of the circumgalactic medium at $z=2.3-3.1$. We
observed 48 quasar fields between 2015 and 2018 with the Palomar Cosmic Web
Imager (Matuszewski et al. 2010). Extended HI Lyman-$\mathrm{\alpha}$ emission
is discovered around 42/48 of the observed quasars, ranging in projected,
flux-weighted radius from 21-71 proper kiloparsecs (pkpc), with 26 nebulae
exceeding $100\mathrm{~pkpc}$ in effective diameter. The circularly averaged
surface brightness radial profile peaks at a maximum of $\mathrm{1\times
10^{-17}~erg~s^{-1}~cm^{-2}~arcsec^{-2}}$
($2\times10^{-15}~\mathrm{erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ adjusted for
cosmological dimming) and luminosities range from
$1.9\times10^{43}~\mathrm{erg~s^{-1}}$ to
$-14.1\times10^{43}~\mathrm{erg~s^{-1}}$. The emission appears to have a highly
eccentric morphology and a maximum covering factor of $50\%$ ($60\%$ for giant
nebulae). On average, the nebular spectra are red-shifted with respect to both
the systemic redshift and Ly$\alpha$ peak of the quasar spectrum. The
integrated spectra of the nebulae mostly have single or double-peaked line
shapes with global dispersions ranging from $167~\mathrm{km~s^{-1}}$ to
$690~\mathrm{km~s^{-1}}$, though the individual (Gaussian) components of lines
with complex shapes mostly appear to have dispersions $\leq 400$
$\mathrm{km~s^{-1}}$, and the flux-weighted velocity centroids of the lines
vary by thousands of $ \mathrm{km~s^{-1}}$ with respect to the systemic QSO
redshifts. Finally, the root-mean-square velocities of the nebulae are found to
be consistent with gravitational motions expected in dark matter halos of mass
$\mathrm{M_h \simeq10^{12.5} M_\odot}$. We compare these results to existing
surveys at both higher and lower redshift.
