Probing the Metal Enrichment of the Intergalactic Medium at $z=5-6$
  Using the Hubble Space Telescope
  We test the galactic outflow model by probing associated galaxies of four
strong intergalactic CIV absorbers at $z=5$--6 using the Hubble Space Telescope
(HST) ACS ramp narrowband filters. The four strong CIV absorbers reside at
$z=5.74$, $5.52$, $4.95$, and $4.87$, with column densities ranging from
$N_{\rm{CIV}}=10^{13.8}$ cm$^{-2}$ to $10^{14.8}$ cm$^{-2}$. At $z=5.74$, we
detect an i-dropout Ly$\alpha$ emitter (LAE) candidate with a projected impact
parameter of 42 physical kpc from the CIV absorber. This LAE candidate has a
Ly$\alpha$-based star formation rate (SFR$_{\rm{Ly\alpha}}$) of 2 $M_\odot$
yr$^{-1}$ and a UV-based SFR of 4 $M_\odot$ yr$^{-1}$. Although we cannot
completely rule out that this $i$-dropout emitter may be an [OII] interloper,
its measured properties are consistent with the CIV powering galaxy at
$z=5.74$. For CIV absorbers at $z=4.95$ and $z=4.87$, although we detect two
LAE candidates with impact parameters of 160 kpc and 200 kpc, such distances
are larger than that predicted from the simulations. Therefore we treat them as
non-detections. For the system at $z=5.52$, we do not detect LAE candidates,
placing a 3-$\sigma$ upper limit of SFR$_{\rm{Ly\alpha}}\approx 1.5\ M_\odot$
yr$^{-1}$. In summary, in these four cases, we only detect one plausible CIV
source at $z=5.74$. Combining the modest SFR of the one detection and the three
non-detections, our HST observations strongly support that smaller galaxies
(SFR$_{\rm{Ly\alpha}} \lesssim 2\ M_\odot$ yr$^{-1}$) are main sources of
intergalactic CIV absorbers, and such small galaxies play a major role in the
metal enrichment of the intergalactic medium at $z\gtrsim5$.
