ALBERT

Description: We present a spectroscopically confirmed sample of Lyman α 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 previous narrow-band surveys from the Large Area Lyman Alpha (LALA) survey to build a unified Lyα luminosity function. We spectroscopically observed 64 candidate LAEs in the ECDFS, confirming 46 objects as z  ~ 4.5 LAEs based on single-line detections with no continuum emission bluewards of the line, resulting in a Lyα confirmation rate of ~70 per cent. We did not detect significant flux from neither the C iv 1549 Å emission line nor the He ii 1640 Å 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 Lyα 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 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 Lyα luminosity functions in our two deepest narrow-band filters in the ECDFS differ at greater than 2 significance, and the product L ** 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 Lyα luminosity functions to date, with our sample of over 200 spectroscopically confirmed Lyα galaxies yielding log 10 ( L *) = 42.83 ± 0.06 (erg s –1 ) and log 10 (*) = –3.48 ± 0.09 (Mpc –3 ). We compare our new luminosity function to others from the literature to study the evolution of the Lyα luminosity density at 0 〈 z  〈 7. We find tentative evidence for evolution in the product L **, 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.