Spectroscopic confirmation of a gravitationally lensed Lyman-break galaxy at z[C II] = 6.827 using NOEMA
Schaerer, D.; Zitrin, A.; van der Werf, P.; Bouwens, R. J.; Hodge, J. A.; Longmore, S. N.; Smit, R.; Bradley, L.; Schouws, S.; Molyneux, S. J.; Phillips, S.
United Kingdom, Germany, Switzerland, France, Netherlands, United States, Israel
Abstract
We present the spectroscopic confirmation of the brightest known gravitationally lensed Lyman-break galaxy in the Epoch of Reionization (EoR), A1703-zD1, through the detection of [C II] 158 $\mu$m at a redshift of z = 6.8269 ± 0.0004. This source was selected behind the strong lensing cluster Abell 1703, with an intrinsic luminosity and a very blue Spitzer/Infrared Array Camera (IRAC) [3.6]-[4.5] colour, implying high equivalent width line emission of [O III] + Hβ. [C II] is reliably detected at 6.1σ cospatial with the rest-frame ultraviolet (UV) counterpart, showing similar spatial extent. Correcting for the lensing magnification, the [C II] luminosity in A1703-zD1 is broadly consistent with the local $L_{\rm [C\, {\small II}]}$-star formation rate (SFR) relation. We find a clear velocity gradient of 103 ± 22 km $\rm s^{-1}$ across the source that possibly indicates rotation or an ongoing merger. We furthermore present spectral scans with no detected [C II] above 4.6σ in two unlensed Lyman-break galaxies in the Extended Groth Strip (EGS)-Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field at z ~ 6.6-6.9. This is the first time that the Northern Extended Millimeter Array (NOEMA) has been successfully used to observe [C II] in a 'normal' star-forming galaxy at z > 6, and our results demonstrate its capability to complement the Atacama Large Millimeter/submillimeter Array (ALMA) in confirming galaxies in the EoR.