ALMA detection of [CII] 158 micron emission from a strongly lensed z=2 star-forming galaxy

TL;DR

This study uses ALMA to detect [CII] 158 micron emission from a strongly lensed galaxy at z=2, revealing that its interstellar medium properties are similar to those of local star-forming galaxies, extending diagnostics to lower luminosities.

Contribution

First detection of [CII] emission in a strongly lensed z=2 galaxy, enabling ISM analysis at lower luminosities than previously possible.

Findings

[CII] emission detected at 10 sigma with lensing correction

[CII]-to-IR and [CII]-to-CO ratios similar to local galaxies

ISM properties of high-z galaxies resemble those of local star-forming galaxies

Abstract

Our objectives are to determine the properties of the interstellar medium (ISM) and of star-formation in typical star-forming galaxies at high redshift. 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 [CII] 158 micron emission line, one of the main coolants of the ISM. [CII] emission from the southern part of this galaxy is detected at 10 $\sigma$. Taking into account strong gravitational lensing, which provides a magnification of $\mu=49$, the intrinsic lensing-corrected [CII]158 micron luminosity is $L(CII)=1.2 \times 10^8 L_\odot$. The observed ratio of [CII]-to-IR emission, $L(CII)/L(FIR) \approx (1.2-2.4) \times 10^{-3}$, is found to be similar to that in nearby galaxies. The same also holds for the observed ratio $L(CII)/L(CO)=2.3 \times 10^3$, which is comparable to that of star-forming galaxies and active galaxy nuclei (AGN) at low redshift. We utilize strong gravitational lensing to extend diagnostic studies of the cold ISM to an order of magnitude lower luminosity ($L(IR) \sim (1.1-1.3) \times 10^{11} L_\odot$) 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.