Lyman alpha Luminosity Functions at Redshift z = 4.5
  We present a spectroscopically confirmed sample of Lyman alpha emitting
galaxies (LAEs) at z ~ 4.5 in the Extended Chandra Deep Field South (ECDFS),
which we combine with a sample of z ~ 4.5 LAEs from the Large Area Lyman Alpha
(LALA) survey to build a unified Lya luminosity function (LF). We
spectroscopically observed 64 candidate LAEs in the ECDFS, confirming 46
objects as z~4.5 LAEs. We did not detect significant flux from neither C_iv
1549\AA\ nor the He_ii 1640\AA\ emission in individual LAE spectra, even with a
coadded spectrum. With the coadded line ratio of He_ii to Lya constraining the
Population III star formation rate (SFR) to be <0.3% of the total SFR, and
<1.25% of the observed SFR (both at the 2-$\sigma$ level). Only one LAE was
detected in both the X-ray and radio, while the other objects remained
undetected, even when stacked. The Lya LF in our two deepest narrowband filters
in the ECDFS differ at >2$\sigma$ significance, and the product $L^*\Phi^*$
differs by a factor of >3. Similar LF differences have been used to infer
evolution in the neutral gas fraction in the intergalactic medium at z>6, yet
here the difference is likely due to cosmic variance, given that the two
samples are from adjoining line-of-sight volumes. Combining our new sample of
LAEs with those from previous LALA narrowband surveys at z = 4.5, we obtain one
of the best measured Lya LFs to date of L* = 42.83 $\pm$ 0.06 and $\Phi^*$ =
-3.48 $\pm$ 0.09. We compare our new LF to others from the literature to study
the evolution of the Lya luminosity density at 0 < z < 7. We find tentative
evidence for evolution in the product $L^* \Phi^*$, which approximately tracks
the cosmic SFR density, but since field-to-field and survey-to-survey
variations are in some cases as large as the possible evolution, some caution
is needed in interpreting this trend.
