ABSTRACT We introduce a new project to understand helium reionization using fully coupled N-body, hydrodynamics, and radiative transfer simulations. This project aims to capture correctly the thermal ...history of the intergalactic medium as a result of reionization and make predictions about the Ly forest and baryon temperature-density relation. The dominant sources of radiation for this transition are quasars, so modeling the source population accurately is very important for making reliable predictions. In this first paper, we present a new method for populating dark matter halos with quasars. Our set of quasar models includes two different light curves, a lightbulb (simple on/off) and symmetric exponential model, and luminosity-dependent quasar lifetimes. Our method self-consistently reproduces an input quasar luminosity function given a halo catalog from an N-body simulation, and propagates quasars through the merger history of halo hosts. After calibrating quasar clustering using measurements from the Baryon Oscillation Spectroscopic Survey, we find that the characteristic mass of quasar hosts is for the lightbulb model, and for the exponential model. In the latter model, the peak quasar luminosity for a given halo mass is larger than that in the former, typically by a factor of 1.5-2. The effective lifetime for quasars in the lightbulb model is 59 Myr, and in the exponential case, the effective time constant is about 15 Myr. We include semi-analytic calculations of helium reionization, and discuss how to include these quasars as sources of ionizing radiation for full hydrodynamics with radiative transfer simulations in order to study helium reionization.
We demonstrate the ability of convolutional neural networks (CNNs) to mitigate systematics in the virial scaling relation and produce dynamical mass estimates of galaxy clusters with remarkably low ...bias and scatter. We present two models, CNN1D and CNN2D, which leverage this deep learning tool to infer cluster masses from distributions of member galaxy dynamics. Our first model, CNN1D, infers cluster mass directly from the distribution of member galaxy line-of-sight velocities. Our second model, CNN2D, extends the input space of CNN1D to learn on the joint distribution of galaxy line-of-sight velocities and projected radial distances. We train each model as a regression over cluster mass using a labeled catalog of realistic mock cluster observations generated from the MultiDark simulation and UniverseMachine catalog. We then evaluate the performance of each model on an independent set of mock observations selected from the same simulated catalog. The CNN models produce cluster mass predictions with lognormal residuals of scatter as low as 0.132 dex, greater than a factor of 2 improvement over the classical M- power-law estimator. Furthermore, the CNN model reduces prediction scatter relative to similar machine-learning approaches by up to 17% while executing in drastically shorter training and evaluation times (by a factor of 30) and producing considerably more robust mass predictions (improving prediction stability under variations in galaxy sampling rate by 30%).
The intergalactic medium is expected to clump on scales down to M before the onset of reionization. The impact of these small-scale structures on reionization is poorly understood despite the modern ...understanding that gas clumpiness limits the growth of regions. We use a suite of radiation-hydrodynamics simulations that capture the Jeans mass of unheated gas to study density fluctuations during reionization. Our simulations track the complex ionization and hydrodynamical response of gas in the wake of ionization fronts. The clumping factor of ionized gas (proportional to the recombination rate) rises to a peak value of 5-20 approximately Δt = 10 Myr after ionization front passage, depending on the incident intensity, redshift, and degree to which the gas had been preheated by the first X-ray sources. The clumping factor reaches its relaxed value of 3 by Δt = 300 Myr. The mean free path of Lyman-limit photons evolves in unison, being up to several times shorter in unrelaxed, recently reionized regions compared to those that were reionized much earlier. Assessing the impact of this response on the global reionization process, we find that unrelaxed gaseous structures boost the total number of recombinations by 50% and lead to spatial fluctuations in the mean free path that persist appreciably for several hundred million years after the completion of reionization.
Abstract
Using the novel semi-numerical code for reionization AMBER, we model the patchy kinetic Sunyaev–Zel’dovich (kSZ) effect by directly specifying the reionization history with the redshift ...midpoint
z
mid
, duration Δ
z
, and asymmetry
A
z
. We further control the ionizing sources and radiation through the minimum halo mass
M
h
and the radiation mean free path
λ
mfp
. AMBER reproduces the free-electron number density and the patchy kSZ power spectrum of radiation–hydrodynamic simulations at the target resolution (1 Mpc
h
−1
) with matched reionization parameters. With a suite of (2 Gpc/
h
)
3
simulations using AMBER, we first constrain the redshift midpoint 6.0 <
z
mid
< 8.9 using the Planck 2018 Thomson optical depth result (95% CL). Then, assuming
z
mid
= 8, we find that the amplitude of
D
ℓ
=
3000
pkSZ
scales linearly with the duration of reionization Δ
z
and is consistent with the 1
σ
upper limit from South Pole Telescope (SPT) results up to Δ
z
< 5.1 (Δ
z
encloses 5%–95% ionization). Moreover, a shorter
λ
mfp
can lead to a ∼10% lower
D
ℓ
=
3000
pkSZ
and a flatter slope in the
D
ℓ
=
3000
pkSZ
−
Δ
z
scaling relation, thereby affecting the constraints on Δ
z
at
ℓ
= 3000. Allowing
z
mid
and
λ
mfp
to vary simultaneously, we get spectra consistent with the SPT result (95% CL) up to Δ
z
= 12.8 (but
A
z
> 8 is needed to ensure the end of reionization before
z
= 5.5). We show that constraints on the asymmetry require ∼0.1
μ
k
2
measurement accuracy at multipoles other than
ℓ
= 3000. Finally, we find that the amplitude and shape of the kSZ spectrum are only weakly sensitive to
M
h
under a fixed reionization history and radiation mean free path.
ABSTRACT
Cold dark matter model predicts that the large-scale structure grows hierarchically. Small dark matter haloes form first. Then, they grow gradually via continuous merger and accretion. These ...haloes host the majority of baryonic matter in the Universe in the form of hot gas and cold stellar phase. Determining how baryons are partitioned into these phases requires detailed modelling of galaxy formation and their assembly history. It is speculated that formation time of the same mass haloes might be correlated with their baryonic content. To evaluate this hypothesis, we employ haloes of mass above $10^{14}\, \mathrm{M}_{\odot }$ realized by TNG300 solution of the IllustrisTNG project. Formation time is not directly observable. Hence, we rely on the magnitude gap between the brightest and the fourth brightest halo galaxy member, which is shown that traces formation time of the host halo. We compute the conditional statistics of the stellar and gas content of haloes conditioned on their total mass and magnitude gap. We find a strong correlation between magnitude gap and gas mass, BCG stellar mass, and satellite galaxies stellar mass, but not the total stellar mass of halo. Conditioning on the magnitude gap can reduce the scatter about halo property–halo mass relation and has a significant impact on the conditional covariance. Reduction in the scatter can be as significant as 30 per cent, which implies more accurate halo mass prediction. Incorporating the magnitude gap has a potential to improve cosmological constraints using halo abundance and allows us to gain insight into the baryon evolution within these systems.
We present a new hybrid code for large-volume, high-resolution simulations of cosmic reionization, which utilizes an N-body algorithm for dark matter, physically motivated prescriptions for baryons ...and star formation, and an adaptive ray-tracing algorithm for radiative transfer of ionizing photons. Two test simulations, each with 3 billion particles and 400 million rays in a 50 Mpc h super(-1) box, have been run to give Initial results. Halos are resolved down to virial temperatures of 10 super(4) K for the redshift range of interest in order to robustly model star formation and clumping factors. This is essential to correctly account for ionization and recombination processes. We find that the halos and sources are strongly biased with respect to the underlying dark matter, re-enforcing the requirement of large simulation boxes to minimize cosmic variance and to obtain a qualitatively correct picture of reionization. We model the stellar initial mass function (IMF) by following the spatially dependent gas metallicity evolution, and distinguish between the first generation, Population III (PopIII) stars and the second generation, Population II (PopII) stars. The PopIII stars with a top-heavy IMF produce an order of magnitude more ionizing photons at high redshlfts z unk 10, resulting in a more extended reionization. In our simulations, complete overlap of H II regions occurs at z approximately 6.5, and the computed mass- and volume-weighted residual H I fractions at 5 unk approximately unk 6.5 are both in good agreement with high-redshift quasar absorption measurements from the Sloan Digital Sky Survey (SDSS). The values for the Thomson optical depth are consistent within 1 - sigma of the current best-fit value from third-year Wilkinson Microwave Anisotropy Probe (WMAP) results.
During reionization, the intergalactic medium is heated impulsively by supersonic ionization fronts (I-fronts). The peak gas temperatures behind the I-fronts, , are a key uncertainty in models of the ...thermal history after reionization. Here we use high-resolution radiative transfer (RT) simulations to study the parameter space of . We show that is only mildly sensitive to the spectrum of incident radiation over most of the parameter space, with temperatures set primarily by I-front speeds. We also explore what current models of reionization predict for by measuring I-front speeds in cosmological RT simulations. We find that the post-I-front temperatures evolve toward hotter values as reionization progresses. Temperatures of = 17,000-22,000 K are typical during the first half of reionization, but = 25,000-30,000 K may be achieved near the end of this process if I-front speeds reach ∼104 km s−1, as found in our simulations. Shorter reionization epochs lead to hotter . We discuss implications for z > 5 Ly forest observations, which potentially include sight lines through hot, recently reionized patches of the universe. Interpolation tables from our parameter space study are made publicly available, along with a simple fit for the dependence of on the I-front speed.
We compare the predictions of four different algorithms for the distribution of ionized gas during the Epoch of Reionization. These algorithms are all used to run a 100 Mpc h
−1 simulation of ...reionization with the same initial conditions. Two of the algorithms are state-of-the-art ray-tracing radiative transfer codes that use disparate methods to calculate the ionization history. The other two algorithms are fast but more approximate schemes based on iterative applications of a smoothing filter on the underlying source and density fields. We compare these algorithms' resulting ionization and 21-cm fields using several different statistical measures. The two radiative transfer schemes are in excellent agreement judging by the power spectra of both the ionization fields and the 21-cm emission fields (agreeing to better than 10 per cent) and are in good agreement with the analytic schemes (better than 50 per cent) over the range of ionized fractions and wavevectors we compare (
Mpc−1).
This agreement suggests that the different approximations involved in the ray-tracing algorithms are sensible and that seminumerical schemes provide a numerically inexpensive, yet fairly accurate, description of the reionization process.
We examine the impact of baryon-dark matter relative velocities on intergalactic small-scale structure and the 21 cm signal during reionization. Streaming velocities reduced clumping in the ...intergalactic medium on mass scales of ∼104-108 M . This effect produced a distinct baryon acoustic oscillation (BAO) feature in the 21 cm power spectrum at wavenumbers k ∼ 0.1 h/Mpc, near which forthcoming surveys will be most sensitive. In contrast to the highly uncertain impact of streaming velocities on star formation, the effect on clumping is better constrained because it is set mainly by cosmology and straightforward gas dynamics. We quantify the latter using coupled radiation-hydrodynamic simulations that capture the Jeans scale of pre-reionization gas. The clumping factor of ionized gas is reduced by 5%-10% in regions with rms streaming velocities. The suppression peaks 5 Myr after a region is reionized, but disappears within 200 Myr due to pressure smoothing. We model the corresponding impact on the 21 cm signal and find that the BAO feature is most likely to appear at 10% ionization. During this phase, the feature may appear at the 1% (5%) level at k ∼ 0.1 (0.06) h/Mpc with an amplitude that varies by a factor of <10 across a range of reionization histories. We also provide a model for the signal originating from streaming velocity's impact on ionizing sources, which can vary by 4 orders of magnitude depending on highly uncertain source properties. We find that the clumping signal probably dominates the source one unless Population III star formation in 106-108 M halos contributed significantly to the first 10% of reionization.
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