Search for CII Emission on Cosmological Scales at Redshift Z~2.6

TL;DR

This study searches for large-scale CII emission at redshift z~2.6 using Planck data cross-correlated with SDSS-III objects, finding potential signals but requiring more sensitive measurements for confirmation.

Contribution

First attempt to detect high-redshift CII emission on cosmological scales using Planck intensity maps cross-correlated with galaxy surveys.

Findings

Detected an anomalous emission possibly due to CII at high redshift.

Bayesian analysis shows CII and CIB+SZ models are statistically indistinguishable.

Future surveys could significantly improve CII detection sensitivity.

Abstract

We present a search for CII emission over cosmological scales at high-redshifts. The CII line is a prime candidate to be a tracer of star formation over large-scale structure since it is one of the brightest emission lines from galaxies. Redshifted CII emission appears in the submillimeter regime, meaning it could potentially be present in the higher frequency intensity data from the Planck satellite used to measure the cosmic infrared background (CIB). We search for CII emission over redshifts z=2-3.2 in the Planck 545 GHz intensity map by cross-correlating the 3 highest frequency Planck maps with spectroscopic quasars and CMASS galaxies from the Sloan Digital Sky Survey III (SDSS-III), which we then use to jointly fit for CII intensity, CIB parameters, and thermal Sunyaev-Zeldovich (SZ) emission. We report a measurement of an anomalous emission $\mathrm{I_\nu}=6.6^{+5.0}_{-4.8}\times10^4$ Jy/sr at 95% confidence, which could be explained by CII emission, favoring collisional excitation models of CII emission that tend to be more optimistic than models based on CII luminosity scaling relations from local measurements; however, a comparison of Bayesian information criteria reveal that this model and the CIB & SZ only model are equally plausible. Thus, more sensitive measurements will be needed to confirm the existence of large-scale CII emission at high redshifts. Finally, we forecast that intensity maps from Planck cross-correlated with quasars from the Dark Energy Spectroscopic Instrument (DESI) would increase our sensitivity to CII emission by a factor of 5, while the proposed Primordial Inflation Explorer (PIXIE) could increase the sensitivity further.