Carbon monoxide line emission as a CMB foreground: tomography of the star-forming universe with different spectral resolutions

TL;DR

This paper investigates how carbon monoxide and other line emissions from star-forming galaxies act as foregrounds in CMB observations, proposing spectral resolution variation as a method to map the universe's star formation history.

Contribution

It introduces a model for CO line foregrounds in CMB data and demonstrates how spectral resolution changes can enhance the detection and separation of these signals.

Findings

CO line emission significantly contaminates CMB at 20-60 GHz and small angular scales.

Varying spectral resolution can increase the line signal amplitude by up to two orders of magnitude.

Spectral bandwidth variation enables tomography of the star-forming universe across different redshifts.

Abstract

The rotational lines of carbon monoxide and the fine structure lines of CII and of the most abundant metals, emitted during the epoch of enhanced star formation in the universe, are redshifted in the frequency channels where the present-day and future CMB experiments are sensitive. We estimate the contribution to the CMB angular power spectrum by the emission in such lines in merging star-forming galaxies. We used the Lacey-Cole approach to characterize the distribution of the merging halos, together with a parametrization for the star formation rate in each of them. Using observational data from a sample of local, low-redshift, and high-redshift objects, we calibrated the luminosity in each line as a function of the star formation rate. We show that the correlation term arising from CO line emission is a significant source of foreground for CMB in a broad range of frequencies (in particular in the 20-60 GHz band) and for 1000<l<8000, corresponding to angular scales smaller than 10 arcminutes. Moreover, we demonstrate that observing with different spectral resolutions will give the possibility of increasing the amplitude of the signal up to two orders of magnitude in C_l and will help separate the line contribution from practically all other foreground sources and from the primary fluctuations themselves, since these show no significant dependence on the spectral resolution. We propose to perform observations with varying spectral bandwidths as a new tool to construct a tomography of the universe, by probing different redshift slices with varying thickness. (abridged)