MUSE deep-fields: the Ly α luminosity function in the Hubble Deep Field-South at 2.91 < z < 6.64

Abstract

We present the first estimate of the Lyα 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 Lyα emitters covering a flux range of −18.0 < log 10 (F) < −16.3 (erg s −1 cm −2 ), corresponding to luminosities of 41.4 < log 10 (L) < 42.8 (erg s −1 ). As recent studies have shown, Lyα 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 Lyα 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 Lyα luminosity function between redshifts 2.91 < z < 6.64 using the 1/V max 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 1σ 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 Lyα 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 Lyα 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.

The MUSE Hubble Ultra Deep Field Survey

“…With this data we were able to improve the number of known spectroscopic redshifts in this tiny region by an order of magnitude (Bacon et al 2015). This first experiment not only effectively demonstrated the unique capabilities of MUSE in this context, but has also led to new scientific results: the discovery of extended Lyα halos in the circumgalactic medium around high redshift galaxies (Wisotzki et al 2016), the study of gas kinematics (Contini et al 2016), the investigation of the faint-end of the Lyα luminosity function (Drake et al 2017a), the measurement of metallicity gradients (Carton et al 2017) and the properties of galactic winds at high z (Finley et al 2017a).…”

The MUSE Hubble Ultra Deep Field Survey

“…This allows us to draw more solid conclusions than those from our 1 × 1 pilot study of the HDFS field (Drake et al 2017).…”

“…In Drake et al (2017) we discussed the difference in the apparent luminosity function when using different approaches to estimate total Lyα flux. We concluded that using a curve-of-growth analysis provided the most accurate measure of F Lyα although noted that this approach introduced the possibility of a bias in the fraction of the flux recovered according to true total flux.…”

“…photometry (Bacon et al 2015, Drake et al 2017. Given a statistical sample of objects, one can characterise the population by examining the number of objects as a function of their luminosity -the luminosity function, often fit with a Schechter function parametrised by α, φ * and L * (Schechter 1976).…”

“…spectroscopically-confirmed LAEs in a homogeneous manner (Bacon et al 2015, Drake et al 2017 as well as probing the lensed LAE populations behind galaxy clusters (Bina et al 2016, Smit et al 2017. In addition to the ability of MUSE to perform as a 'detection machine' for star-forming galaxies, the deep datacubes allow us to establish reliable total Lyα line fluxes by ensuring we capture the total width of the Lyα line in wavelength, and the full extent of each object on-sky.…”