Properties of galaxies at the faint end of the Hα luminosity function at z ~ 0.62^⋆

¹ Departamento de Astrofísica y CC. de la AtmósferaFacultad de CC. Físicas, Universidad Complutense de Madrid, Av. Complutense s/n, 28040 Madrid, Spain
e-mail: cgguijarro@ucm.es
² Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
³ European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴ Dipartimento di Fisica e Astronomia “G. Galilei”, Universitá di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁵ CRAL, Observatoire de Lyon, Université Lyon 1, 9 Avenue Ch. André, 69561 Saint-Genis Laval Cedex, France
⁶ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France

Received: 15 June 2015
Accepted: 14 April 2016

Abstract

Context. Studies measuring the star formation rate density, luminosity function, and properties of star-forming galaxies are numerous. However, it exists a gap at 0.5 < z < 0.8 in Hα-based studies.

Aims. Our main goal is to study the properties of a sample of faint Hα emitters at z ~ 0.62. We focus on their contribution to the faint end of the luminosity function and derived star formation rate density, characterising their morphologies and basic photometric and spectroscopic properties.

Methods. We use a narrow-band technique in the near-infrared, with a filter centred at 1.06 μm. The data come from ultra-deep VLT/HAWK-I observations in the GOODS-S field with a total of 31.9 h in the narrow-band filter. In addition to our survey, we mainly make use of ancillary data coming from the CANDELS and Rainbow Cosmological Surveys Database, from the 3D-HST for comparison, and also spectra from the literature. We perform a visual classification of the sample and study their morphologies from structural parameters available in CANDELS. In order to obtain the luminosity function, we apply a traditional V/V_max method and perform individual extinction corrections for each object to accurately trace the shape of the function.

Results. Our 28 Hα-selected sample of faint star-forming galaxies reveals a robust faint-end slope of the luminosity function α = - 1.46_-0.08^+0.16 . The derived star formation rate density at z ~ 0.62 is ρ_SFR = 0.036_-0.008^+0.012 M_⊙ yr^-1 Mpc^-3 . The sample is mainly composed of disks, but an important contribution of compact galaxies with Sérsic indexes n ~ 2 display the highest specific star formation rates.

Conclusions. The luminosity function at z ~ 0.62 from our ultra-deep data points towards a steeper α when an individual extinction correction for each object is applied. Compact galaxies are low-mass, low-luminosity, and starburst-dominated objects with a light profile in an intermediate stage from early to late types.