The OH line contamination of 21 cm intensity fluctuation measurements for z=1~4

TL;DR

This paper investigates how the 18 cm OH line can contaminate 21 cm intensity fluctuation measurements used to study large-scale cosmic structures at redshifts 1 to 4, finding contamination levels up to 1%.

Contribution

It provides the first detailed estimate of OH line contamination on 21 cm intensity power spectrum measurements across redshifts 1 to 4.

Findings

OH contamination can reach 0.1% to 1% of 21 cm fluctuations at z=1-3.

Contamination declines rapidly for z>3, becoming negligible.

The study uses simulations to estimate OH signal and its impact on 21 cm measurements.

Abstract

The large-scale structure of the Universe can be mapped with unresolved intensity fluctuations of the 21 cm line. The power spectrum of the intensity fluctuations has been proposed as a probe of the baryon acoustic oscillations at low to moderate redshifts with interferometric experiments now under consideration. We discuss the contamination to the low-redshift 21 cm intensity power spectrum generated by the 18 cm OH line since the intensity fluctuations of the OH line generated at a slightly higher redshift contribute to the intensity fluctuations observed in an experiment. We assume the OH megamaser luminosity is correlated with the star formation rate, and use the simulation to estimate the OH signal and the spatial anisotropies. We also use a semi-analytic simulation to predict the 21 cm power spectrum. At z=1 to 3, we find that the OH contamination could reach 0.1% to 1% of the 21 cm rms fluctuations at the scale of the first peak of the baryon acoustic oscillation. When z>3 the OH signal declines quickly, so that the contamination on the 21-cm becomes negligible at high redshifts.