Millimeter observations of HCM 6A, a gravitationally lensed Lyα emitting galaxy at z = 6.56 ^*

¹ LERMA, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France e-mail: frederic.boone@obspm.fr
² Max-Planck-Institut für Radioastronomie, auf dem Hügel 69, 53121 Bonn, Germany
³ Geneva Observatory, Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
⁴ Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique, UMR 5572, 14 avenue E. Belin, 31400 Toulouse, France
⁵ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

Received: 11 July 2007
Accepted: 21 September 2007

Abstract

The gravitationally lensed Lyα emitting galaxy, HCM 6A, detected by Hu et al. (2002) at behind the Abell 370 cluster was observed with the MAMBO-2 array of bolometers at 1.2 mm wavelength. The galaxy was not detected down to 1.08 mJy (), but the depth of the observations and the lens amplification allow us to improve by approximately one order of magnitude previously published upper limits on far infrared emission of Lyα emitting galaxies at this redshift. The following upper limits are derived from our observations, assuming typical dust parameters: dust mass <5.310⁷ , IR luminosity <2.110¹¹ , and star formation rate <35  yr^-1. The observed restframe UV-optical-IR spectral energy distribution (SED) of this galaxy is compatible with that of normal spiral galaxies or blue compact dwarf galaxies. SEDs of prototypical ULIRGs, such as Arp 220, are clearly excluded. Finally, we obtain an upper limit of 2.110^-2  yr^-1 Mpc^-3 for the dust-obscured SFR density of Lyα selected galaxies at z ~ 6.6.