Close companions to two high-redshift quasars
  We report the serendipitous discoveries of companion galaxies to two
high-redshift quasars. SDSS J025617.7+001904 is a z=4.79 quasar included in our
recent survey of faint quasars in the SDSS Stripe 82 region. The initial MMT
slit spectroscopy shows excess Lyman alpha emission extending well beyond the
quasar's light profile. Further imaging and spectroscopy with LBT/MODS1
confirms the presence of a bright galaxy (i_AB = 23.6) located 2arcsec (12 kpc
projected) from the quasar with strong Lyman alpha emission (EW_0 ~ 100Ang) at
the redshift of the quasar, as well as faint continuum. The second quasar,
CFHQS J005006.6+344522 (z=6.25), is included in our recent HST SNAP survey of
z~6 quasars searching for evidence of gravitational lensing. Deep imaging with
ACS and WFC3 confirms an optical dropout ~4.5 mag fainter than the quasar
(Y_AB=25) at a separation of 0.9 arcsec. The red i_775-Y_105 color of the
galaxy and its proximity to the quasar (5 kpc projected if at the quasar
redshift) strongly favor an association with the quasar. Although it is much
fainter than the quasar it is remarkably bright when compared to field galaxies
at this redshift, while showing no evidence for lensing. Both systems may
represent late-stage mergers of two massive galaxies, with the observed light
for one dominated by powerful ongoing star formation and for the other by rapid
black hole growth. Observations of close companions are rare; if major mergers
are primarily responsible for high-redshift quasar fueling then the phase when
progenitor galaxies can be observed as bright companions is relatively short.
