arXiv subjects

Hurum Maksora Tohfa

Publications and source records attributed to Hurum Maksora Tohfa.

6 recordsLinked to original sources

arXiv2026

An emulator for the ionizing photon mean free path in ultra-high resolution simulations: the implications of mean free path measurements for the reionization history

Measurements of the mean free path of ionizing photons from high-redshift quasar spectra at $z \sim 5$-$6$ constrain the reionization history, but interpreting them requires modeling the kiloparsec-scale clumping that large-volume reionization simulations cannot resolve. We present a deep learning emulator for the mean free path (MFP) trained on high-resolution cosmological radiative transfer simulations of ionization fronts sweeping through small 2 comoving Mpc/h volumes. Using a residual multi-layer perceptron neural network, we predict the MFP at a given redshift as a function of the reionization redshift, photoionization rate, wavelength, and box-scale density, achieving a median relative error of 1.3\% across nearly four orders of magnitude in MFP. Integrating its predictions over box-scale overdensity and an extended reionization history allows the emulator to predict the global MFP. We apply the emulator to extended reionization histories constrained by observed photoionization rates, finding that models prefer late reionization with substantial neutral fractions persisting at $z \lesssim 6$. Fitting a parametric ionization history yields a midpoint of reionization of $z_{\rm re} = 6.58\pm 1.2$ for reionization durations consistent with Planck and kinetic Sunyaev-Zeldovich constraints, and the universe being $10\%$ neutral still at $z < 5.8 ~(6.3)$ at 1~(2)$σ$. Global ionizing emissivity inferences using measurements of the photoionization rate and MFP plus our emulator, which avoids common power-law assumptions, suggest a factor of $2-3$ decline between $z = 6$ and $4.8$, in agreement with previous studies. Our method provides an efficient (and more converged) alternative to large-volume radiative-hydrodynamic simulations of reionization for interpreting MFP measurements, and can also serve as a subgrid prescription for the ionizing opacity within such simulations.

astro-ph.CO↗

arXiv2026

A self-consistent analytical model for both the photoionization rate and reionization history

Recent developments at the intersection of cosmology and astrophysics have highlighted the need for improved analytical models of observables that probe the Epoch of Reionization. With few exceptions, fast analytical treatments of reionization suitable for use in Bayesian inference have been limited to modeling the reionization history, $x_i(z)$. Such models cannot take full advantage of observables that constrain $x_i$ indirectly. One such observable is the photoionization rate of neutral hydrogen, $Γ_{\rm HI}(z)$, which can be inferred from the mean transmission of the Lyman-$α$ forest of high-redshift quasars and galaxies. It has been shown by several prior works that the evolution of $Γ_{\rm HI}$ at $5 \lesssim z \lesssim 6$ is highly sensitive to the tail end of reionization, potentially providing a tight astrophysical constraint on the reionization timeline. We present a new analytical formalism, based on the cosmological radiative transfer equation, that self-consistently predicts $x_i$ and $Γ_{\rm HI}$. We test our model against detailed radiative transfer simulations and find it to be percent-level accurate in $x_i$ and $20-30\%$ accurate in $Γ_{\rm HI}$ at $z \lesssim 6$ - better than or comparable to existing observational uncertainties. Finally, we demonstrate that modest shifts in the ionizing photon output of high-redshift galaxies and/or the endpoint of reionization lead to differences in $Γ_{\rm HI}$ much larger that the model's intrinsic uncertainty, highlighting its utility for interpreting existing data. We explore the origin of modeling uncertainty in $Γ_{\rm HI}$ and comment on future pathways for improvement.

astro-ph.CO↗

arXiv2026

Introducing SAGUARO -- Simulating IGM Evolution and Environments At High Resolution: Setup and First Results

Small-scale physics in the intergalactic medium (IGM) plays a crucial role in shaping the progress of cosmic reionization and several high-redshift observables that probe this period. Several recent studies have characterized the complex, dynamical response of the IGM to reionization down to kilo-parsec scales, including its effect on observables such as the Ly$α$ forest. However, there has been no concentrated attempt to simulate and characterize these effects across the full parameter space of realistic large-scale IGM environments during reionization. To meet this need, we introduce the SAGUARO simulation suite, sub-titled ``Simulating IGM Evolution and Environments At High Resolution''. SAGUARO is a suite of over two hundred high-resolution, coupled radiative-hydrodynamics simulations of IGM gas dynamics during and after reionization. The suite spans a grid of photoionization rates, redshifts of reionization, and box-scale densities. We also simulate other physical effects, such as X-ray pre-heating, recombination radiation, baryon-dark matter free-streaming, and alternative dark matter cosmologies. Our suite includes box sizes of $2$ and $0.25$ $h^{-1}$Mpc, extending to volumes large enough to begin capturing halos above the atomic cooling limit and resolutions high enough to fully resolve the IGM Jeans scale in the cold, neutral universe. We present a detailed description of the setup and first results from SAGUARO, descriptions of the IGM gas dynamics and thermal structure, opacity, self-shielding properties, the effect of the IGM on the reionization photon budget, and the halo mass function, and Ly$α$ transmission properties. SAGUARO will help facilitate detailed studies of small-scale IGM structure and its effects that will help inform the next generation of reionization simulations and data interpretation.

astro-ph.CO↗

arXiv2024

A cosmic microwave background search for fine-structure constant evolution

In some extensions of the standard model of particle physics, the values of the fundamental coupling constants vary in space and time. Some observations of quasars hint at time and spatial variation of the fine structure constant $α$. Here, the Bekenstein-Sandvik-Barrow-Magueijo (BSBM) model (which posits the existence of a scalar field driving evolution in the fundamental electric charge $e$) is tested against quasar and Planck satellite cosmic microwave background (CMB) data. In this model, variations in $e$ are coupled to the matter density through a factor $ζ_{\rm m}/ω$, which is related to electromagnetic contributions to nucleon masses, and {the energy} scale of new physics. Simulations conducted here do not support claims that the electrostatic contribution to $ζ_{m}$ is completely shielded. Other common approximations used in BSBM field evolution are found to be adequate. Principal components of the CMB data with respect to variations in $α$ are used to obtain constraints of $ζ_{\rm m}/ω\lesssim 9.3 \times 10^{-9}$ for a massless field. A forecast anticipating the promise of the Simons Observatory (SO) CMB experiment shows that SO will be sensitive to values of $ζ_{\rm m}/ω\geq 2.2 \times 10^{-9}$.

astro-ph.CO↗

arXiv2024

Forecast Cosmological Constraints with the 1D Wavelet Scattering Transform and the Lyman-$α$ forest

We make forecasts for the constraining power of the 1D Wavelet Scattering Transform (WST) when used with a Lyman-$α$ forest cosmology survey. Using mock simulations and a Fisher matrix, we show that there is considerable cosmological information in the scattering transform coefficients not captured by the flux power spectrum. We estimate mock covariance matrices assuming uncorrelated Gaussian pixel noise for each quasar, at a level drawn from a simple lognormal model. The extra information comes from a smaller estimated covariance in the first-order wavelet power, and from second-order wavelet coefficients which probe non-Gaussian information in the forest. Forecast constraints on cosmological parameters from the WST are more than an order of magnitude tighter than for the power spectrum, shrinking a $4D$ parameter space by a factor of $10^6$. Should these improvements be realised with DESI, inflationary running would be constrained to test common inflationary models predicting $α_s = - 6\times 10^{-4}$ and neutrino mass constraints would be improved enough for a $5-σ$ detection of the minimal neutrino mass.

astro-ph.CO↗

arXiv2023

SN 2023ixf in Messier 101: Photo-ionization of Dense, Close-in Circumstellar Material in a Nearby Type II Supernova

We present UV/optical observations and models of supernova (SN) 2023ixf, a type II SN located in Messier 101 at 6.9 Mpc. Early-time ("flash") spectroscopy of SN 2023ixf, obtained primarily at Lick Observatory, reveals emission lines of H I, He I/II, C IV, and N III/IV/V with a narrow core and broad, symmetric wings arising from the photo-ionization of dense, close-in circumstellar material (CSM) located around the progenitor star prior to shock breakout. These electron-scattering broadened line profiles persist for $\sim$8 days with respect to first light, at which time Doppler broadened features from the fastest SN ejecta form, suggesting a reduction in CSM density at $r \gtrsim 10^{15}$ cm. The early-time light curve of SN2023ixf shows peak absolute magnitudes (e.g., $M_{u} = -18.6$ mag, $M_{g} = -18.4$ mag) that are $\gtrsim 2$ mag brighter than typical type II supernovae, this photometric boost also being consistent with the shock power supplied from CSM interaction. Comparison of SN 2023ixf to a grid of light curve and multi-epoch spectral models from the non-LTE radiative transfer code CMFGEN and the radiation-hydrodynamics code HERACLES suggests dense, solar-metallicity, CSM confined to $r = (0.5-1) \times 10^{15}$ cm and a progenitor mass-loss rate of $\dot{M} = 10^{-2}$ M$_{\odot}$yr$^{-1}$. For the assumed progenitor wind velocity of $v_w = 50$ km s$^{-1}$, this corresponds to enhanced mass-loss (i.e., ``super-wind'' phase) during the last $\sim$3-6 years before explosion.

astro-ph.HE↗