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

• Published in: Monthly notices of the Royal Astronomical Society. Letters Vol. 489; no. 1; pp. L53 - L57
• Main Authors: Yang, Shengqi, Pullen, Anthony R, Switzer, Eric R
• Format: Journal Article
• Language: English
• Published: United Kingdom Oxford University Press 01-10-2019
• ISSN: 1745-3925; 1745-3933
• DOI: 10.1093/mnrasl/slz126

C ii is one of the brightest emission lines from star-forming galaxies and is an excellent tracer for star formation. Recent work measured the C ii 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 ${I}_{{\text C}\,\rm {\small II}}=6.6^{+5.0}_{-4.8}\times {10}^{4}$ Jy sr−1 at $95\,{\text{per cent}}$ confidence level. 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 ii emission, in which case we report $b_{{\text C} \,\rm {\small II}}I_{{\text C} \,\rm {\small II}} =2.0^{+1.2}_{-1.1}\times 10^5$ Jy sr−1 at $95\ {\text {per cent}}$ confidence level, which strongly favours many collisional excitation models of C ii emission. Our detection shows strong evidence for a model with a non-zero C ii parameter, though line intensity mapping observations at high spectral resolution will be needed to confirm this result.