Lyα luminosity functions at redshift z ≈ 4.5

We present a spectroscopically confirmed sample of Lyman alpha emitting galaxies (LAEs) at z similar to 4.5 in the Extended Chandra Deep Field-South (ECDFS), which we combine with a sample of z similar to 4.5 LAEs from previous narrow-band surveys from the Large Area Lyman Alpha (LALA) survey to build a unified Ly alpha luminosity function. We spectroscopically observed 64 candidate LAEs in the ECDFS, confirming 46 objects as z similar to 4.5 LAEs based on single-line detections with no continuum emission bluewards of the line, resulting in a Ly alpha confirmation rate of similar to 70 per cent. We did not detect significant flux from neither the C IV lambda 1549 angstrom emission line nor the He II lambda 1640 angstrom emission line in individual LAE spectra. These lines were also undetected in a co-added spectrum, with the co-added line ratio of He II to Ly alpha constraining the Population III star formation rate (SFR) to be <0.3 per cent of the total SFR and <1.25 per cent of the observed SFR (both at the 2 sigma level). We combine the optical spectra with deep X-ray and radio images to constrain the AGN fraction in the sample. Only LAE was detected in both the X-ray and radio, while the other objects remained undetected, even when stacked. The Ly alpha luminosity functions in our two deepest narrow-band filters in the ECDFS differ at greater than 2s significance, and the product L*Phi* differs by a factor of >3. Similar luminosity function 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 narrow-band surveys at z = 4.5, we obtain one of the best measured Ly alpha luminosity functions to date, with our sample of over 200 spectroscopically confirmed Ly alpha galaxies yielding log(10)(L*) = 42.83 +/- 0.06 (erg s(-1)) and log10(Phi*) = -3.48 +/- 0.09 (Mpc(-3)). We compare our new luminosity function to others from the literature to study the evolution of the Ly alpha 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.