Introducing SPHINX-MHD: the impact of primordial magnetic fields on the first galaxies, reionization, and the global 21-cm 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 cMpc)3 cosmological volumes, varying both the strength of the seed magnetic field and its spectral index. We find that PMFs with a spectral index (nB) and a comoving amplitude (B0) that have $n_B > -0.562\log _{10}\left(\frac{B_0}{1{\rm n}G}\right) - 3.35$ produce electron optical depths (τe) that are inconsistent with CMB constraints due to the unrealistically early collapse of low-mass dwarf galaxies. For nB ≥ −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 τe constraint. Furthermore, strong PMFs can marginally increase the escape of LyC photons by up to 25 per cent and shrink the effective radii of galaxies by $\sim 44{{\ \rm per\ cent}}$ which could increase the completeness fraction of galaxy surveys. Finally, our simulations show that surveys with a magnitude limit of ${\rm M_{UV,1500\mathring{\rm A}}=-13}$ can probe the sources that provide the majority of photons for reionization out to z = 12.

Momentum deposition of supernovae with cosmic rays

“…The second type is a tangled magnetic field that follows a magnetic energy spectrum with spectral index 𝑛 𝐵 . The tangled magnetic initial conditions (ICs; Martin-Alvarez et al in prep.; but also similar to those employed in Katz et al 2021) are produced by modulating the spectrum of the vector potential at each Fourier wavelength 𝑘 and requiring the magnetic energy spectra produced by its curl to have a spectral slope 𝑛 𝐵 . All our magnetic ICs assume 𝑛 𝐵 = 3/2 to reproduce a Kazantsev spectrum (Kazantsev 1968) corresponding to the magnetic inversecascade characteristic of a tangled ISM (Bhat & Subramanian 2013; 1 https://bitbucket.org/rteyssie/ramses/src/master/ Martin-Alvarez et al 2018).…”

Limit on intergalactic magnetic field from ultra-high-energy cosmic ray hotspot in Perseus-Pisces region

“…The UHECR bound on large correlation length cosmological magnetic field (that would originate from Inflation) is stronger than the limit from non-observation of magnetic field induced excess optical depth of CMB signal [29] and is somewhat weaker than the limit imposed by non-observation of faster recombination [30]. Closeness of the bounds from three different techniques indicates that improvement of the sensitivity of these techniques may result in a "multi-messenger" detection of inflationary cosmological magnetic field, if it has scale-invariant power spectrum and the field strength close to B ∼ 10 −10 G.…”

“…The bound from Faraday rotation is from [28]. The "CMB scattering" bound is from [29]. The "CMB clumping" bound is from [30].…”

“…This in turn leads to earlier formation of the first stars and modification of dynamics of the reionisation. Non-observation of excess scattering of the CMB photons by free electrons generated by early reionisation [29] imposes a bound on the cosmological IGMF at the level of the solid lines in Fig. 2.…”

Towards convergence of turbulent dynamo amplification in cosmological simulations of galaxies

“…Current observational constraints cannot rule out strong PMFs, but provide a conservative comoving magnetic field strength upper limit of 𝐵 0 < 10 −9 G, obtained by Planck Collaboration (2015) 1 . Numerical studies offer a promising avenue to further understand the origin and evolution of galactic magnetic fields, for example, by studying the evolution of magnetic fields with different origins (Martin-Alvarez et al 2021;Garaldi et al 2021) and predicting observables upon which strong PMFs may have an impact on, such as galactic properties (Martin-Alvarez et al 2020), supermassive black hole masses (Pillepich et al 2018), the population of galaxies or cosmic reionization (Sanati et al 2020;Katz et al 2021).…”