Evidence for C ii diffuse line emission at redshift z ∼ 2.6

Abstract

C is one of the brightest emission lines from star-forming galaxies and is an excellent tracer for star formation. Recent work measured the C emission line amplitude for redshifts 2 < z < 3.2 by cross-correlating Planck High Frequency Instrument emission maps with tracers of overdensity from the Baryon Oscillation Spectroscopic Sky Survey, finding I C = 6.6 +5.0 −4.8 × 10 4 Jy/sr at 95% confidence. In this paper, we present a refinement of this earlier work by improving the mask weighting in each of the Planck bands and the precision in the covariance matrix. We report a detection of excess emission in the 545 GHz Planck band separate from the cosmic infrared background (CIB) present in the 353-857 GHz Planck bands. This excess is consistent with redshifted C emission, in which case we report b C I C = 2.0 +1.2 −1.1 × 10 5 Jy/sr at 95% confidence, which strongly favors many collisional excitation models of C emission. Our detection shows strong evidence for a model with a non-zero C parameter, though line intensity mapping observations at high spectral resolution will be needed to confirm this result.

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