A new Tolman test of a cosmic distance duality relation at 21 cm

TL;DR

This paper proposes using redshifted 21 cm signals from disk galaxies to perform a new Tolman test, potentially providing the most sensitive test of the cosmic distance duality relation with upcoming SKA observations.

Contribution

It introduces a novel method utilizing 21 cm signals from galaxies to test the Etherington relation, with simulated SKA data demonstrating its effectiveness.

Findings

Simulated SKA observations can effectively test the Etherington relation.

The method is sensitive to potential violations of the cosmic distance duality.

Using 21 cm signals offers a new approach to fundamental cosmological tests.

Abstract

Under certain general conditions in an expanding universe, the luminosity distance (d_L) and angular diameter distance (d_A) are connected by the Etherington relation as d_L = d_A (1 + z)^2. The Tolman test suggests the use of objects of known surface brightness, to test this relation. In this letter, we propose the use of redshifted 21 cm signal from disk galaxies, where neutral hydrogen (HI) masses are seen to be almost linearly correlated with surface area, to conduct a new Tolman test. We construct simulated catalogs of galaxies, with the observed size-luminosity relation and realistic redshift evolution of HI mass functions, likely to be detected with the planned Square Kilometer Array (SKA). We demonstrate that these observations may soon provide the best implementation of the Tolman test to detect any violation of the Etherington relation.