Paper detail

Primordial magnetic field constraints from the end of reionization

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.