We present the SPHINX suite of cosmological adaptive mesh refinement simulations, the first radiation-hydrodynamical simulations to simultaneously capture large-scale reionization and the escape of ...ionizing radiation from thousands of resolved galaxies. Our 5 and 10 co-moving Mpc volumes resolve haloes down to the atomic cooling limit and model the interstellar medium with better than ≈10 pc resolution. The project has numerous goals in improving our understanding of reionization and making predictions for future observations. In this first paper, we study how the inclusion of binary stars in computing stellar luminosities impacts reionization, compared to a model that includes only single stars. Owing to the suppression of galaxy growth via strong feedback, our galaxies are in good agreement with observational estimates of the galaxy luminosity function. We find that binaries have a significant impact on the timing of reionization: with binaries, our boxes are 99.9 percent ionized by volume at z ≈ 7, while without them our volumes fail to reionize by z = 6. These results are robust to changes in volume size, resolution, and feedback efficiency. The escape of ionizing radiation from individual galaxies varies strongly and frequently. On average, binaries lead to escape fractions of ≈7-10 percent, about three times higher than with single stars only. The higher escape fraction is a result of a shallower decline in ionizing luminosity with age, and is the primary reason for earlier reionization, although the higher integrated luminosity with binaries also plays a subdominant role.
ABSTRACT
We use the SPHINX suite of high-resolution cosmological radiation hydrodynamics simulations to study how spatially and temporally inhomogeneous reionization impacts the baryonic content of ...dwarf galaxies and cosmic filaments. We compare simulations with and without stellar radiation to isolate the effects of radiation feedback from that of supernova, cosmic expansion, and numerical resolution. We find that the gas content of cosmic filaments can be reduced by more than 80 per cent following reionization. The gas inflow rates into haloes with ${M_{\rm vir}\lesssim 10^8\, \mathrm{M}_{\odot }}$ are strongly affected and are reduced by more than an order of magnitude compared to the simulation without reionization. A significant increase in gas outflow rates is found for halo masses ${M_{\rm vir}\lesssim 7\times 10^7\, \mathrm{M}_{\odot }}$. Our simulations show that inflow suppression (i.e. starvation), rather than photoevaporation, is the dominant mechanism by which the baryonic content of high-redshift dwarf galaxies is regulated. At fixed redshift and halo mass, there is a large scatter in the halo baryon fractions that is entirely dictated by the timing of reionization in the local region surrounding a halo which can change by Δz ≳ 3 at fixed mass. Finally, although the gas content of high-redshift dwarf galaxies is significantly impacted by reionization, we find that most haloes with ${M_{\rm vir}\lesssim 10^8\, \mathrm{M}_{\odot }}$ can remain self-shielded and form stars long after reionization, until their local gas reservoir is depleted, suggesting that Local Group dwarf galaxies do not necessarily exhibit star formation histories that peak prior to z = 6. Significantly larger simulation boxes will be required to capture the full process of reionization and understand how our results translate to environments not probed by our current work.
ABSTRACT
We measure escape fractions, fesc, of ionizing radiation from galaxies in the sphinx suite of cosmological radiation-hydrodynamical simulations of reionization, resolving haloes with $M_{\rm ...vir}\gtrsim 7.5 \times 10^7 \ {\rm {M}_{\odot }}$ with a minimum cell width of ≈10 pc. Our new and largest 20 co-moving Mpc wide volume contains tens of thousands of star-forming galaxies with halo masses up to a few times 1011 M⊙. The simulated galaxies agree well with observational constraints of the ultraviolet (UV) luminosity function in the Epoch of Reionization. The escape fraction fluctuates strongly in individual galaxies over time-scales of a few Myr, due to its regulation by supernova and radiation feedback, and at any given time a tiny fraction of star-forming galaxies emits a large fraction of the ionizing radiation escaping into the intergalactic medium. Statistically, fesc peaks in intermediate-mass, intermediate-brightness, and low-metallicity galaxies (M* ≈ 107 M⊙, M1500 ≈ −17, Z ≲ 5 × 10−3 Z⊙), dropping strongly for lower and higher masses, brighter and dimmer galaxies, and more metal-rich galaxies. The escape fraction correlates positively with both the short-term and long-term specific star formation rate. According to sphinx, galaxies too dim to be yet observed, with ${M_{1500}}\gtrsim -17$, provide about 55 per cent of the photons contributing to reionization. The global averaged fesc naturally decreases with decreasing redshift, as predicted by UV background models and low-redshift observations. This evolution is driven by decreasing specific star formation rates over cosmic time.
Abstract
Understanding the origin of strong galactic outflows and the suppression of star formation in dwarf galaxies is a key problem in galaxy formation. Using a set of radiation-hydrodynamic ...simulations of an isolated dwarf galaxy embedded in a 1010 M⊙ halo, we show that the momentum transferred from resonantly scattered Lyman-α (Lyα) photons is an important source of stellar feedback which can shape the evolution of galaxies. We find that Lyα feedback suppresses star formation by a factor of two in metal-poor galaxies by regulating the dynamics of star-forming clouds before the onset of supernova explosions (SNe). This is possible because each Lyα photon resonantly scatters and imparts ∼10–300 times greater momentum than in the single scattering limit. Consequently, the number of star clusters predicted in the simulations is reduced by a factor of ∼5, compared to the model without the early feedback. More importantly, we find that galactic outflows become weaker in the presence of strong Lyα radiation feedback, as star formation and associated SNe become less bursty. We also examine a model in which radiation field is arbitrarily enhanced by a factor of up to 10, and reach the same conclusion. The typical mass-loading factors in our metal-poor dwarf system are estimated to be ∼5–10 near the mid-plane, while it is reduced to ∼1 at larger radii. Finally, we find that the escape of ionizing radiation and hence the reionization history of the Universe is unlikely to be strongly affected by Lyα feedback.
ABSTRACT
The Ly α emission line is one of the most promising probes of cosmic reionization but isolating the signature of a change in the ionization state of the intergalactic medium (IGM) is ...challenging because of intrinsic evolution and internal radiation transfer effects. We present the first study of the evolution of Ly α emitters (LAE) during the epoch of reionization based on a full radiation-hydrodynamics cosmological simulation that is able to capture both the large-scale process of reionization and the small-scale properties of galaxies. We predict the Ly α emission of galaxies in the 103 cMpc3sphinx simulation at 6 ≤ z ≤ 9 by computing the full Ly α radiation transfer from interstellar medium (ISM) to IGM scales. sphinx is able to reproduce many observational constraints such as the UV/Ly α luminosity functions and stellar mass functions at z ≳ 6 for the dynamical range probed by our simulation (M1500 ≳ −18, LLy α ≲ 1042 erg s−1, M⋆ ≲ 109 M⊙). As intrinsic Ly α emission and internal Ly α escape fractions barely evolve from z = 6–9, the observed suppression of Ly α luminosities with increasing redshift is fully attributed to IGM absorption. For most observable galaxies (M1500 ≲ −16), the Ly α line profiles are slightly shifted to the red due to internal radiative transfer effects that mitigates the effect of IGM absorption. Overall, the enhanced Ly α suppression during reionization traces the IGM neutral fraction $x_{{\rm H\, {i}}}$ well, but the predicted amplitude of this reduction is a strong function of the Ly α peak shift, which is set at ISM/circumgalactic medium scales. We find that a large number of LAEs could be detectable in very deep surveys during reionization when $x_{{\rm H\, {i}}}$ is still $\approx 50{{\ \rm per\ cent}}$.
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 multifrequency, 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 $(5\, \text{cMpc})^3$ 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 $\scriptstyle{n_B \gt -0.562\log _{10}\left(\frac{B_0}{1{\rm n}G}\right) - 3.35}$ 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 Ly α forest due to PMFs will be challenging because photoionization and photoheating efficiently smooth the density field. However, we find that the first absorption feature in the global 21-cm 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 ${\rm \mathit{ M}_{UV,1500\,\mathring{\rm A}}=-13}$ can probe the sources that provide the majority of photons for reionization out to z = 12.
Abstract
Understanding the escape of Lyman continuum (LyC) and Ly
α
photons from giant molecular clouds (GMCs) is crucial if we are to study the reionization of the universe and to interpret spectra ...of observed galaxies at high redshift. To this end, we perform high-resolution, radiation-magnetohydrodynamic simulations of GMCs with self-consistent star formation and stellar feedback. We find that a significant fraction (15%–70%) of ionizing radiation escapes from the simulated GMCs with different masses (10
5
and 10
6
M
⊙
), as the clouds are dispersed within about 2–5 Myr from the onset of star formation. The fraction of LyC photons leaked is larger when the GMCs are less massive, metal poor, less turbulent, and less dense. The most efficient leakage of LyC radiation occurs when the total star formation efficiency of a GMC is about 20%. The escape of Ly
α
shows a trend similar to that of LyC photons, except that the fraction of Ly
α
photons escaping from the GMCs is larger (
f
Ly
α
≈
f
900
0.27
) and that a GMC with strong turbulence shows larger
f
Ly
α
. The simulated GMCs show a characteristic velocity separation of Δ
v
≈ 120 km s
−1
in the time-averaged emergent Ly
α
spectra, suggesting that Ly
α
could be useful to infer the kinematics of the interstellar and circumgalactic medium. We show that Ly
α
luminosities are a useful indicator of the LyC escape, provided the number of LyC photons can be deduced through stellar population modeling. Finally, we find that the correlations between the escape fractions of Ly
α
, ultraviolet photons at 1500 Å, and the Balmer
α
line are weak.
Abstract
We analyse the properties of circumgalactic gas around simulated galaxies in the redshift range z ≥ 3, utilizing a new sample of cosmological zoom simulations. These simulations are intended ...to be representative of the observed samples of Lyman α (Ly α) emitters recently obtained with the multi unit spectroscopic explorer (MUSE) instrument (halo masses ∼1010–1011 M⊙). We show that supernova feedback has a significant impact on both the inflowing and outflowing circumgalactic medium (CGM) by driving outflows, reducing diffuse inflow rates, and by increasing the neutral fraction of inflowing gas. By temporally stacking simulation outputs, we find that significant net mass exchange occurs between inflowing and outflowing phases: none of the phases are mass-conserving. In particular, we find that the mass in neutral outflowing hydrogen declines exponentially with radius as gas flows outwards from the halo centre. This is likely caused by a combination of both fountain-like cycling processes and gradual photoionization/collisional ionization of outflowing gas. Our simulations do not predict the presence of fast-moving neutral outflows in the CGM. Neutral outflows instead move with modest radial velocities (∼50 km s−1), and the majority of the kinetic energy is associated with tangential rather than radial motion.
ABSTRACT
Limited constraints on the evolution of the Lyman Continuum (LyC) escape fraction represent one of the primary uncertainties in the theoretical determination of the reionization history. Due ...to the intervening intergalactic medium, the possibility of observing LyC photons directly in the epoch of reionization is highly unlikely. For this reason, multiple indirect probes of LyC escape have been identified, some of which are used to identify low-redshift LyC leakers (e.g. O32), while others are primarily useful at z > 6 (e.g. O iii/C iii far-infrared emission). The flux ratio of the resonant Mg ii doublet emission at 2796$\mathring{\rm A}$ and 2803$\mathring{\rm A}$ as well as the Mg ii optical depth have recently been proposed as ideal diagnostics of LyC leakage that can be employed at z > 6 with JWST. Using state-of-the-art cosmological radiation hydrodynamics simulations post-processed with CLOUDY and resonant-line radiative transfer, we test whether Mg ii is indeed a useful probe of LyC leakage. Our simulations indicate that the majority of bright, star-forming galaxies with high LyC escape fractions are expected to be Mg ii emitters rather than absorbers at z = 6. However, we find that the Mg ii doublet flux ratio is a more sensitive indicator of dust rather than neutral hydrogen, limiting its use as a LyC leakage indicator to only galaxies in the optically thin regime. Given its resonant nature, we show that Mg ii will be an exciting probe of the complex kinematics in high-redshift galaxies in upcoming JWST observations.
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