Using a set of cosmological hydro-dynamical simulations , we constrained the properties of primordial magnetic fields by studying their impact on the formation and evolution of dwarf galaxies .
We performed a large set of simulations ( 8 dark matter only and 72 chemo-hydrodynamical ) including primordial magnetic fields through the extra density fluctuations they induce at small length scales ( k \geq 10 h { Mpc ^ { -1 } } ) in the matter power spectrum .
Our sample of dwarfs include 9 systems selected out of the initial ( 3.4 \textrm { Mpc } / h ) ^ { 3 } parent box , re-simulated from z = 200 to z = 0 using a zoom-in technique and including the physics of baryons .
We explored a large variety of primordial magnetic fields with strength B _ { \lambda } ranging from 0.05 to 0.50 \textrm { nG } and magnetic energy spectrum slopes n _ { B } from -2.9 to -2.1 .
Strong magnetic fields characterized by a high amplitude ( B _ { \lambda } = 0.50 , 0.20 \textrm { nG } with n _ { B } = -2.9 ) or by a steep initial power spectrum slope ( n _ { B } = -2.1 , -2.4 , with B _ { \lambda } = 0.05 \textrm { nG } ) induce perturbations in the mass scales from 10 ^ { 7 } to 10 ^ { 9 } M _ { \odot } .
In this context emerging galaxies see their star formation rate strongly boosted .
They become more luminous and metal rich than their counterparts without primordial magnetic fields .
Such strong fields are ruled out by their inability to reproduce the observed scaling relations of dwarf galaxies .
They predict dwarf galaxies to be at the origin of an unrealistically early reionization of the Universe and also overproduce luminous satellites in the Local Group .
Weaker magnetic fields impacting the primordial density field at corresponding masses \lesssim 10 ^ { 6 } M _ { \odot } , produce a large number of mini dark halos orbiting the dwarfs , however out of reach for current lensing observations .
This study allows for the first time to constrain the properties of primordial magnetic fields based on realistic cosmological simulations of dwarf galaxies .