ALMA detection of [ C II ] 158 μ m emission from a strongly lensed z = 2 . 013 star - forming galaxy ?

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 ] 158 μm emission line, one of the main coolants of the ISM. Results. Emission of the [C ] 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 ] luminosity is L[CII] = 1.2 × 108 L . The observed ratio of [C ]-to-IR emission, L[CII]/LFIR ≈ (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]/LCO= 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 (LIR ∼ (1.1−1.3) × 1011 L ) 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.