ALMA detection of [C ii] 158 μm emission from a strongly lensed z = 2.013 star-forming galaxy^⋆

¹ Observatoire de Genève, Département d’Astronomie, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
e-mail: daniel.schaerer@unige.ch
² CNRS, IRAP, 14 Avenue E. Belin, 31400 Toulouse, France
³ Department of Physics, University of California, Santa Barbara, CA 93106, USA
⁴ CRAL, Observatoire de Lyon, Université de Lyon 1, 9 avenue Ch. André, 69561 Saint-Genis Laval, France
⁵ Department of Astronomy, California Institute of Technology, MS 249-17, Pasadena, CA 91125, USA
⁶ ESAC, ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
⁷ Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
⁸ Observatoire de Paris, LERMA, 61 Av. de l’Observatoire, 75014 Paris, France

Received: 18 December 2014
Accepted: 11 February 2015

Abstract

Aims. Our objectives are to determine the properties of the interstellar medium (ISM) and of star formation in typical star-forming galaxies at high redshift.

Methods. Following up on our previous multi-wavelength observations with HST, Spitzer, Herschel, and the Plateau de Bure Interferometer (PdBI), we have studied a strongly lensed z = 2.013 galaxy, the arc behind the galaxy cluster MACS J0451+0006, with ALMA to measure the [C ii] 158 μm emission line, one of the main coolants of the ISM.

Results. Emission of the [C ii] line from the southern part of this galaxy is detected at 10σ. Taking strong gravitational lensing into account, which provides a magnification of μ = 49, the intrinsic lensing-corrected [C ii] luminosity is L_[CII] = 1.2 × 10⁸L_⊙. The observed ratio of [C ii]-to-IR emission, L_[CII]/L_FIR ≈ (1.2−2.4) × 10^-3, is found to be similar to that in nearby galaxies. The same also holds for the observed ratio L_[CII]/L_CO= 2.3 × 10³, which is comparable to that of star-forming galaxies and active galaxy nuclei (AGN) at low redshift.

Conclusions. We utilize strong gravitational lensing to extend diagnostic studies of the cold ISM to an order of magnitude lower luminosity (L_IR ~ (1.1−1.3) × 10¹¹L_⊙) and SFR than previous work at high redshift. While larger samples are needed, our results provide evidence that the cold ISM of typical high-redshift galaxies has physical characteristics similar to normal star-forming galaxies in the local Universe.