Primordial magnetic field constraints from the end of reionization

TL;DR

This paper uses reionization data and galaxy luminosity functions to place upper limits on primordial magnetic fields, showing that fields stronger than 2-3 nG are inconsistent with observations at redshift 7.

Contribution

It introduces a simplified reionization model that incorporates magnetic pressure effects and systematically analyzes uncertainties to constrain primordial magnetic field strength.

Findings

Upper limit on primordial magnetic field strength B_0 ≤ 2-3 nG at z≈7.

Magnetic pressure affects low-mass halo collapse, influencing reionization.

Stronger constraints possible with future high-ionization measurements at z>7.

Abstract

Primordial magnetic fields generated in the early universe are subject of considerable investigation, and observational limits on their strength are required to constrain the theory. Due to their impact on the reionization process, the strength of primordial fields can be limited using the latest data on reionization and the observed UV-luminosity function of high-redshift galaxies. Given the steep faint-end slope of the luminosity function, faint galaxies contribute substantial ionizing photons, and the low-luminosity cutoff has an impact on the total budget thereof. Magnetic pressure from primordial fields affects such cutoff by preventing collapse in halos with mass below 10^{10} M_solar (B_0 / 3 nG)^3, with B_0 the co-moving field strength. In this letter, the implications of these effects are consistently incorporated in a simplified model for reionization, and the uncertainties due to the cosmological parameters, the reionization parameters and the observed UV luminosity function are addressed. We show that the observed ionization degree at z\sim7 leads to the strongest upper limit of B_0\lsim 2-3nG. Stronger limits could follow from measurements of high ionization degree at z>7.