Absorption by Spinning Dust: a Contaminant for High-Redshift 21 cm Observations

TL;DR

This paper investigates how spinning dust grains in our galaxy could create weak absorption signals that contaminate high-redshift 21 cm observations, especially near 80 MHz, and discusses their potential impact on measurements like EDGES.

Contribution

It introduces the possibility that spinning dust absorption may affect high-redshift 21 cm measurements and evaluates its potential significance and uncertainties.

Findings

Spinning dust can produce weak absorption signals near 80 MHz.

The strength of absorption depends on grain abundance and dipole moments.

The broad spectrum of spinning dust limits its interference with narrow 21 cm features.

Abstract

Spinning dust grains in front of the bright Galactic synchrotron background can produce a weak absorption signal that could affect measurements of high redshift 21 cm absorption. At frequencies near 80 MHz where the EDGES experiment has reported 21\,cm absorption at $z \approx 17$, absorption could be produced by interstellar nanoparticles with radii $a \approx 50\AA$ in the cold interstellar medium at temperature $T \approx 50$ K. Atmospheric aerosols could contribute additional absorption. The strength of the absorption depends on the abundance of such grains and on their dipole moments, which are uncertain. The breadth of the absorption spectrum of spinning dust limits its possible impact on measurement of a relatively narrow 21 cm absorption feature.