# Hydrogen Molecules in the Dark Ages Halos: Thermal Emission vs. Resonant Scattering

## TL;DR

This paper analyzes the thermal emission and resonant scattering of hydrogen molecules in dark ages halos, predicting extremely faint signals that could be detectable with future advanced telescopes.

## Contribution

It provides a detailed modeling of hydrogen molecule emission in dark ages halos, including both thermal and resonant scattering processes, under cosmological conditions.

## Key findings

- Maximal differential brightness temperatures are in the nanokelvin range for warm halos.
- Thermal emission dominates in hot halos, reaching microkelvin levels.
- Signals are below current telescope sensitivities but may be detectable with next-generation instruments.

## Abstract

The emission from dark ages halos in the lines of transitions between lowest rotational levels of hydrogen and hydrogen deuteride molecules is analyzed. It is assumed molecules to be excited by CMB and collisions with hydrogen atoms. The physical parameters of halos and number density of molecules are precalculated in assumption that halos are homogeneous top-hat spheres formed from the cosmological density perturbations in the four-component Universe with post-Planck cosmological parameters. The differential brightness temperatures and differential spectral fluxes in the rotational lines of H$_2$-HD molecules are computed for two phenomena: thermal luminescence and resonant scattering of CMB radiation. The results show that expected maximal values of differential brightness temperature of warm halos ($T_K\sim$200-800 K) are at the level of nanokelvins, are comparable for both phenomena, and are below sensitivity of modern sub-millimeter radio telescopes. For hot halos ($T_K\sim$2000-5000 K) the thermal emission of H2-ortho molecules dominates and the differential brightness temperatures are predicted to be of a few microkelvins at the frequencies 300-600 GHz, that could be detectable with telescopes of a new generation.