  The recently discovered z=10 galaxy (Pello et al 2004) has a strong Lyman
alpha emission line that is consistent with being surprisingly symmetric, even
given the relatively poor quality of its spectrum. The blue wing of a Lyman
alpha line originating at high redshift should be strongly suppressed by
resonant hydrogen absorption along the line of sight, an expectation borne out
by the observed asymmetric shapes of the existing sample of Lyman alpha
emitting sources at lower redshifts (3< z < 6.7). Absorption on the blue side
of the line of the Pello et al. source could be reduced if the intergalactic
medium (IGM) in the vicinity of the galaxy is highly ionized, but we show that
this requires an unrealistically high ionizing emissivity. We suggest instead
that the Lyman alpha emitting gas be receding relative to the surrounding gas
with a velocity of >= 35km/s, a large velocity that is plausible only if the
galaxy is part of a larger system (group of galaxies) with a velocity
dispersion >= 35km/s. We find that with this velocity shift, the observed
strength and shape of the line is still consistent with the galaxy being
surrounded by its own Stromgren sphere embedded in a fully neutral IGM. More
generally, we predict that at any given redshift, the bright Lyman alpha
emitters with broader lines would exhibit stronger asymmetry than fainter ones.
Bright galaxies with symmetric Lyman alpha lines may be signposts for groups
and clusters of galaxies, within which they can acquire random velocities
comparable to or larger than their linewidths.
