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

¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany e-mail: chm@mpa-garching.mpg.de
² Space Research Institute (IKI), Profsoyuznaya 84/32, Moscow 117810, Russia

Received: 14 May 2008
Accepted: 25 June 2008

Abstract

Context. 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.

Aims. We estimate the contribution to the CMB angular power spectrum by the emission in such lines in merging star-forming galaxies.

Methods. 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.

Results. 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  GHz band) and for , corresponding to angular scales smaller than 10 arcmin. 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.

Conclusions. 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. This should yield new constraints on the regions responsible for the metal enrichment in the universe and on their clustering pattern and will lead to new hints about the reionization epoch and the cosmological parameters, including .