Letter to the Editor

Enhanced [CII] emission in a z = 4.76 submillimetre galaxy

¹ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
e-mail: cdebreuc@eso.org
² INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
³ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁴ Department of Physics, McGill University, Ernest Rutherford Building, 3600 Rue University, Montréal, Québec, H3A 2T8, Canada
⁵ Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
⁶ Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan

Received: 11 March 2011
Accepted: 27 April 2011

Abstract

We present the detection of bright [CII] emission in the z = 4.76 submillimetre galaxy LESS J033229.4-275619 using the Atacama Pathfinder EXperiment. This represents the highest redshift [CII] detection in a submm selected, star-formation dominated system. The AGN contributions to the [CII] and far-infrared (FIR) luminosities are small. We find an atomic mass derived from [CII] comparable to the molecular mass derived from CO. The ratio of the [CII], CO and FIR luminosities imply a radiation field strength G₀ ~ 10³ and a density  ~ 10⁴ cm^-3 in a kpc-scale starburst, as seen in local and high redshift starbursts. The high L _[CII] /L_FIR = 2.4 × 10^-3 and the very high L _[CII] /L_{CO(1 − 0)} ≈ 10⁴ are reminiscent of low metallicity dwarf galaxies, suggesting that the highest redshift star-forming galaxies may also be characterised by lower metallicities. We discuss the implications of a reduced metallicity on studies of the gas reservoirs, and conclude that especially at very high redshift, [CII] may be a more powerful and reliable tracer of the interstellar matter than CO.