Introducing SPHINX-MHD: The Impact of Primordial Magnetic Fields on the First Galaxies, Reionization, and the Global 21cm Signal

Abstract

We present the first results from SPHINX-MHD, a suite of cosmological radiation-magnetohydrodynamics simulations designed to study the impact of primordial magnetic fields (PMFs) on galaxy formation and the evolution of the intergalactic medium (IGM) during the epoch of reionization. The simulations are among the first to employ multi-frequency, on-the-fly radiation transfer and constrained transport ideal MHD in a cosmological context to simultaneously model the inhomogeneous process of reionization as well as the growth of primordial magnetic fields. We run a series of (5 Mpc) 3 cosmological volumes, varying both the strength of the seed magnetic field and its spectral index. We find that PMFs with a spectral index (𝑛 𝐵 ) and a comoving amplitude (𝐵 0 ) that have 𝑛 𝐵 > −0.562 log 10 𝐵 0 1n𝐺 − 3.35 produce electron optical depths (𝜏 𝑒 ) that are inconsistent with CMB constraints due to the unrealistically early collapse of low-mass dwarf galaxies. For 𝑛 𝐵 ≥ −2.9, our constraints are considerably tighter than the ∼ n𝐺 constraints from Planck. PMFs that do not satisfy our constraints have little impact on the reionization history or the shape of the UV luminosity function. Likewise, detecting changes in the Ly𝛼 forest due to PMFs will be challenging because photoionisation and photoheating efficiently smooth the density field. However, we find that the first absorption feature in the global 21cm signal is a particularly sensitive indicator of the properties of the PMFs, even for those that satisfy our 𝜏 𝑒 constraint. Furthermore, strong PMFs can marginally increase the escape of LyC photons by up to 25% and shrink the effective radii of galaxies by ∼ 44% which could increase the completeness fraction of galaxy surveys. Finally, our simulations show that surveys with a magnitude limit of M UV,1500Å = −13 can probe the sources that provide the majority of photons for reionization out to 𝑧 = 12.

Gravitational waves from the remnants of the first stars in nuclear star clusters

“…The escape fractions adopted here are within the typical range fesc ∼ 0.1 − 0.7 seen in simulations and semi-analytical models (e.g. So et al 2014;Paardekooper et al 2015;Inayoshi et al 2016;Visbal et al 2020;Katz et al 2021).…”

Distribution function of nuclei from $e^\pm$ scattering in the presence of a strong primordial magnetic field

“…These small-scale PMFs, however, undergo dissipation during the later cosmic evolution [22,[24][25][26]. This PMF evolution depends upon the helicity and homogeneity of the magnetic fields [24,27], and its behavior in the late non-linear structure formation phase has been investigated in a number of recent three-dimensional simulations [28][29][30][31]. Ultimately, what we can observe with current measurements are signatures of large-scale PMFs which could have been generated in the inflationary epoch before the big bang [32].…”

“…Ultimately, what we can observe with current measurements are signatures of large-scale PMFs which could have been generated in the inflationary epoch before the big bang [32]. Constraints on the PMF [26] have been deduced from various astronomical observations such as the CMB temperature and polarization from gravitational [33][34][35][36][37][38][39] and heating effects [40], redshifted 21 cm signal from heating effects [31,[41][42][43], ultra-faint dwarf galaxies from gravitational effects [44], and gravitational waves (at very small scales) [45].…”

RAMSES-RTZ: Non-Equilibrium Metal Chemistry and Cooling Coupled to On-The-Fly Radiation Hydrodynamics

“…In this work, we build upon these previous approaches by coupling non-equilibrium metal chemistry and cooling to the radiation hydrodynamics code RAMSES-RT (Teyssier 2002;Rosdahl et al 2013;. Our goals are to more accurately model gas cooling as well as emission and absorption lines from individual metals efficiently enough for use in cosmological simulations, thus significantly improving on the approach we have recently used to compare simulations with observations (Katz et al 2017(Katz et al , 2019(Katz et al , 2021.…”

“…Furthermore, the code makes use of the variable-speed-of-light approximation (Katz et al 2017), which is particularly useful for reionization simulations and is able to run with both RT and ideal magnetohydrodynamics (MHD) simultaneously (e.g. Katz et al 2021;Kimm et al 2021), which are important for studies of the CGM (e.g. Mitchell et al 2021;van de Voort et al 2021;Buie et al 2022).…”