MUSE Deep-Fields: The Lya Luminosity Function in the Hubble Deep Field South at 2.91 < z < 6.64

TL;DR

This study estimates the Lyα luminosity function in the Hubble Deep Field South at redshifts 2.91 to 6.64 using MUSE spectroscopy, revealing higher number densities than previous reports and emphasizing the importance of accurate flux measurements.

Contribution

First to estimate the Lyα luminosity function in this redshift range with blind MUSE spectroscopy, accounting for extended emission and flux underestimation, providing a benchmark for future deep-field studies.

Findings

Luminosity function is 2-3 times higher than previous estimates.

No strong evolution observed in the luminosity function across the studied redshift range.

Accurate flux estimation significantly impacts the derived luminosity function.

Abstract

We present the first estimate of the Ly{\alpha} luminosity function using blind spectroscopy from the Multi Unit Spectroscopic Explorer, MUSE, in the Hubble Deep Field South. Using automatic source-detection software, we assemble a homogeneously-detected sample of 59 Ly{\alpha} emitters covering a flux range of -18.0 < log10 (F) < -16.3 (erg s^-1 cm^-2), corresponding to luminosities of 41.4 < log10 (L) < 42.8 (erg s^-1). As recent studies have shown, Ly{\alpha} fluxes can be underestimated by a factor of two or more via traditional methods, and so we undertake a careful assessment of each object's Ly{\alpha} flux using a curve-of-growth analysis to account for extended emission. We describe our self-consistent method for determining the completeness of the sample, and present an estimate of the global Ly{\alpha} luminosity function between redshifts 2.91 < z < 6.64 using the 1/Vmax estimator. We find the luminosity function is higher than many number densities reported in the literature by a factor of 2 - 3, although our result is consistent at the 1{\sigma} level with most of these studies. Our observed luminosity function is also in good agreement with predictions from semi-analytic models, and shows no evidence for strong evolution between the high- and low-redshift halves of the data. We demonstrate that one's approach to Ly{\alpha} flux estimation does alter the observed luminosity function, and caution that accurate flux assessments will be crucial in measurements of the faint end slope. This is a pilot study for the Ly{\alpha} luminosity function in the MUSE deep-fields, to be built on with data from the Hubble Ultra Deep Field which will increase the size of our sample by almost a factor of 10.