Influence of ~7 keV sterile neutrino dark matter on the process of reionization

TL;DR

This study explores how ~7 keV sterile neutrino dark matter, potentially linked to an unidentified X-ray line, influences the reionization process, predicting sharper reionization and lower redshift compared to cold dark matter models.

Contribution

First to analyze the impact of sterile neutrino dark matter capable of producing the 3.5 keV line on reionization using an extended semi-analytical model.

Findings

Sterile neutrino dark matter leads to sharper reionization.

It predicts a lower redshift of reionization and reduced electron scattering optical depth.

Differences are below current model uncertainties.

Abstract

Recent reports of a weak unidentified emission line at ~3.5 keV found in spectra of several matter-dominated objects may give a clue to resolve the long-standing problem of dark matter. One of the best physically motivated particle candidate able to produce such an extra line is sterile neutrino with the mass of ~7 keV. Previous works show that sterile neutrino dark matter with parameters consistent with the new line measurement modestly affects structure formation compared to conventional cold dark matter scenario. In this work, we concentrate for the first time on contribution of the sterile neutrino dark matter able to produce the observed line at ~3.5 keV, to the process of reionization. By incorporating dark matter power spectra for ~7 keV sterile neutrinos into extended semi-analytical 'bubble' model of reionization we obtain that such sterile neutrino dark matter would produce significantly sharper reionization compared to widely used cold dark matter models, impossible to 'imitate' within the cold dark matter scenario under any reasonable choice of our model parameters, and would have a clear tendency of lowering both the redshift of reionization and the electron scattering optical depth (although the difference is still below the existing model uncertainties). Further dedicated studies of reionization (such as 21 cm measurements or studies of kinetic Sunyaev-Zeldovich effect) will thus be essential for reconstruction of particle candidate responsible the ~3.5 keV line.