Lyman alpha Luminosity Functions at Redshift z = 4.5

TL;DR

This study measures the Lyman alpha luminosity function at redshift 4.5 using spectroscopically confirmed galaxies, finding evidence for evolution in luminosity density, while addressing cosmic variance and population III star formation constraints.

Contribution

It provides one of the most precise measurements of the Lyman alpha luminosity function at z=4.5 by combining new and existing data, and investigates its evolution and implications for cosmic star formation.

Findings

L* = 42.83 ± 0.06 and Φ* = -3.48 ± 0.09 for the LF

Tentative evolution in L*Φ* suggests changes in cosmic SFR density

No significant Population III star formation detected in spectra

Abstract

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.