Random Primordial Magnetic Fields and the Gas Content of Dark Matter Halos

TL;DR

This paper explores how random primordial magnetic fields influence early galaxy formation, particularly affecting the baryon gas content and filtering mass, with implications for understanding the magnetic field's properties through high-redshift observations.

Contribution

It introduces models of primordial magnetic fields with various geometries and demonstrates their significant impact on galaxy formation metrics like filtering mass and gas fraction.

Findings

RPMF can significantly depress baryon gas fraction in small halos.

The effect depends on magnetic field strength and cell size.

Observations of high-redshift halos can constrain primordial magnetic field properties.

Abstract

We recently predicted the existence of random primordial magnetic fields (RPMF) in the form of randomly oriented cells with dipole-like structure with a cell size $L_0$ and an average magnetic field $B_0$. Here we investigate models for primordial magnetic field with a similar web-like structure, and other geometries, differing perhaps in $L_0$ and $B_0$. The effect of RPMF on the formation of the first galaxies is investigated. The filtering mass, $M_F$, is the halo mass below which baryon accretion is severely depressed. We show that these RPMF could influence the formation of galaxies by altering the filtering mass and the baryon gas fraction of a halo, $f_g$. The effect is particularly strong in small galaxies. We find, for example, for a comoving $B_0=0.1\muG$, and a reionization epoch that starts at $z_s=11$ and ends at $z_e=8$, for $L_0=100\,\text{pc}$ at $z=12$, the $f_g$ becomes severely depressed for $M<10^7\msun$, whereas for $B_0=0$ the $f_g$ becomes severely depressed only for much smaller masses, $M<10^5\msun$. We suggest that the observation of $M_F$ and $f_g$ at high redshifts can give information on the intensity and structure of primordial magnetic fields.