Spectral Distortion of the CMB by the Cumulative CO Emission from Galaxies throughout Cosmic History

TL;DR

This paper predicts that the cumulative CO emission from galaxies causes a detectable spectral distortion in the CMB, primarily from redshifts 2-5, which future instruments like PIXIE could observe.

Contribution

It models the CO emission's impact on the CMB spectrum and identifies the redshift range and frequency band where the distortion is most prominent.

Findings

CO emission causes a spectral bump at 100-200 GHz.

Peak intensity of the CO-induced distortion is approximately 2×10^{-23} W m^{-2} Hz^{-1} sr^{-1}.

Most CO foreground originates from redshifts 2-5.

Abstract

We show that the cumulative CO emission from galaxies throughout cosmic history distorts the spectrum of the cosmic microwave background (CMB) at a level that is well above the detection limit of future instruments, such as the Primordial Inflation Explorer (PIXIE). The modeled CO signal has a prominent bump in the frequency interval 100-200 GHz, with a characteristic peak intensity of ~ 2$\times$10$^{-23}$ W m$^{-2}$ Hz$^{-1}$ sr$^{-1}$. Most of the CO foreground originates from modest redshifts, z ~ 2-5, and needs to be efficiently removed for more subtle distortions from the earlier universe to be detected.