Аннотация
We search for evidence of diffuse Ly-alpha emission from extended neutral
hydrogen surrounding Ly-alpha emitting galaxies (LAEs) using deep narrow-band
images of the Extended Chandra Deep Field South. By stacking the profiles of
187 LAEs at z = 2.06, 241 LAEs at z = 3.10, and 179 LAEs at z = 3.12, and
carefully performing low-surface brightness photometry, we obtain mean surface
brightness maps that reach 9.9, 8.7, and 6.2 x 10^-19 ergs cm^-2 s^-1
arcsec^-2 in the emission line. We undertake a thorough investigation of
systematic uncertainties in our surface brightness measurements, and find that
our limits are 5-10 times larger than would be expected from Poisson background
fluctuations; these uncertainties are often underestimated in the literature.
At z ~ 3.1, we find marginal evidence for extended halos with scale lengths of
5-8 kpc, and demonstrate that sub-samples of galaxies with low equivalent
widths and brighter continuum magnitudes are more likely to possess such halos.
At z ~ 2.1, we find no evidence of extended Ly-alpha emission down to our
detection limits. We compare these findings to other measurements in the
literature, and discuss possible instrumental and astrophysical reasons for the
discrepancies, including possible evolution of Ly-alpha halo properties from z
~ 3.1 to z ~ 2.1.
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