Letter to the Editor

The H-alpha luminosity function at redshift 2.2^*

A new determination using VLT/HAWK-I

¹ Geneva Observatory, University of Geneva, 51 chemin des Maillettes, 1290 Sauverny, Switzerland e-mail: matthew.hayes@unige.ch
² Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 Avenue E. Belin, 31400 Toulouse, France
³ Oskar Klein Center for Cosmoparticle physics, Department of Astronomy, Stockholm University, 10691 Stockholm, Sweden

Received: 31 August 2009
Accepted: 7 December 2009

Abstract

We aim to place new, strengthened constraints on the luminosity function (LF) of H-alpha (Hα) emitting galaxies at redshift , and to further constrain the instantaneous star-formation rate density of the universe (). We have used the new HAWK-I instrument at ESO-VLT to obtain extremely deep narrow-band (line; NB2090) and broad-band (continuum; ) imaging observations. The target field is in the GOODS-South, providing us with a rich multi-wavelength auxiliary data set, which we utilise for redshift confirmation and to estimate dust content. We use this new data to measure the faint-end slope (α) of LF(H with unprecedented precision. The data are well fit by a Schechter function and also a single power-law, yielding and , respectively. Thus we are able to confirm the steepening of α from low- to high-z predicted by a number of authors and observed at other wavelengths. We combine our LF data-points with those from a much shallower but wider survey at (Geach et al. 2008), constructing a LF spanning a factor of 50 in luminosity. Re-fitting the Schechter parameters, we obtain  erg s^-1;  Mpc^-3; . We integrate over LF(H and apply a correction for dust attenuation to determine the instantaneous cosmic star-formation rate density at without assuming α or extrapolating it from lower-z. Our measurement of  is   yr^-1 Mpc^-3, integrated over a range of .