Misc,
The Lyman-alpha luminosity function at z=5.7-6.6 and the steep drop of the faint end: implications for reionization
(2016)cite arxiv:1606.07435Comment: 16 pages, 7 figures. Submitted to MNRAS.
Abstract
We present new results from the widest narrow band survey search for
Lyman-alpha (Lya) emitters at z=5.7, just after reionization. We survey a total
of 7 deg$^2$ spread over the COSMOS, UDS and SA22 fields. We find over 11,000
line emitters, out of which 514 are robust Lya candidates at z=5.7 within a
volume of 6.3x10$^6$ Mpc$^3$. Our Lya emitters span a wide range in Lya
luminosities, from faint to bright (L$_Ly\alpha\sim10^42.5-44$ erg
s$^-1$) and rest-frame equivalent widths (EW$_0$~25-1000 \AA) in a single,
homogeneous data-set. By combining all our fields we find that the faint end
slope of the z=5.7 Lya luminosity function is very steep, with
$\alpha=-2.3^+0.4_-0.3$. We also present an updated z=6.6 Lya luminosity
function, based on comparable volumes and obtained with the same methods, which
we directly compare with that at z=5.7. We find a significant decline of the
number density of faint Lya emitters from z=5.7 to z=6.6 (by $0.5\pm0.1$ dex),
but no evolution at the bright end/no evolution in L*. Faint Lya emitters at
z=6.6 show much more extended haloes than those at z=5.7, suggesting that
neutral Hydrogen plays an important role, increasing the scattering and leading
to observations missing faint Lya emission within the epoch of reionization.
All together, our results indicate that we are observing patchy reionization
which happens first around the brightest Lya emitters, allowing the number
densities of those sources to remain unaffected by the increase of neutral
Hydrogen fraction from z~5 to z~7.
