arXiv subjects

Jose Oñorbe

Publications and source records attributed to Jose Oñorbe.

At least 19 recordsLinked to original sources

arXiv2025

Gaseous Dynamical Friction: a Numerical Study of Extended Perturbers

The process of momentum and energy transfer between a massive body and a background medium it is moving through is known as dynamical friction (DF). It is key to our understanding of many astrophysical systems. We present a series of high-resolution simulations of gaseous DF using Lagrangian meshless finite mass hydrodynamics solver, the moving-mesh MUSCL scheme, and the piecewise parabolic method (PPM) solver. We use a set of simulations of massive bodies, modelled as Plummer spheres, moving with Mach $0.2 \leq \mathcal{M} \leq 3$. We investigate at which radial distances from the perturber these solvers recover the linear point mass solution for gaseous DF. We analyse the drag force and the structure and time evolution of the wake. The different solvers agree closely. Numerical convergence is reached when the initial spatial resolution is $0.2r_s$, where $r_s$ is the softening scale of the Plummer sphere. We find that the wake structure and drag force are recovered, at the $5\%$ level, when compared beyond $4r_\mathrm{s}$. Our results predict that models using the standard linear point mass DF solution will overestimate the drag force on extended perturbers by as much as 25\%, for Mach$\sim$1. Finally, we consider DF in the context of galaxy clusters, where dark matter subhaloes move through circumgalactic media. We show that DF is typically in the linear regime for most subhaloes in hosting haloes $<10^{11}$ M$_{\odot}$ but non-linear in more massive host haloes.

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arXiv2024

Measurements of the Thermal and Ionization State of the Intergalactic Medium during the Cosmic Afternoon

We perform the first measurement of the thermal and ionization state of the intergalactic medium (IGM) across 0.9 < z < 1.5 using 301 \lya absorption lines fitted from 12 HST STIS quasar spectra, with a total pathlength of Δz=2.1. We employ the machine-learning-based inference method that uses joint b-N distributions obtained from \lyaf decomposition. Our results show that the HI photoionization rates, Γ, are in good agreement with the recent UV background synthesis models, with \log (Γ/s^{-1})={-11.79}^{0.18}_{-0.15}, -11.98}^{0.09}_{-0.09}, and {-12.32}^{0.10}_{-0.12} at z=1.4, 1.2, and 1 respectively. We obtain the IGM temperature at the mean density, T_0, and the adiabatic index, γ, as [\log (T_0/K), γ]= [{4.13}^{+0.12}_{-0.10}, {1.34}^{+0.10}_{-0.15}], [{3.79}^{+0.11}_{-0.11}, {1.70}^{+0.09}_{-0.09}] and [{4.12}^{+0.15}_{-0.25}, {1.34}^{+0.21}_{-0.26}] at z=1.4, 1.2 and 1 respectively. Our measurements of T_0 at z=1.4 and 1.2 are consistent with the expected trend from z<3 temperature measurements as well as theoretical expectations that, in the absence of any non-standard heating, the IGM should cool down after HeII reionization. Whereas, our T_0 measurements at z=1 show unexpectedly high IGM temperature. However, because of the relatively large uncertainty in these measurements of the order of ΔT_0~5000 K, mostly emanating from the limited redshift path length of available data in these bins, we can not definitively conclude whether the IGM cools down at z<1.5. Lastly, we generate a mock dataset to test the constraining power of future measurement with larger datasets. The results demonstrate that, with redshift pathlength Δz \sim 2 for each redshift bin, three times the current dataset, we can constrain the T_0 of IGM within 1500K. Such precision would be sufficient to conclusively constrain the history of IGM thermal evolution at z < 1.5.

astro-ph.CO↗

arXiv2023

The impact of varying inhomogeneous reionization histories on metrics of Ly$α$ opacity

The epoch of hydrogen reionization is complete by $z=5$, but its progression at higher redshifts is uncertain. Measurements of Ly$α$ forest opacity show large scatter at $z<6$, suggestive of spatial fluctuations in neutral fraction ($x_\mathrm{HI}$), temperature, or ionizing background, either individually or in combination. However, these effects are degenerate, necessitating modeling these physics in tandem in order to properly interpret the observations. We begin this process by developing a framework for modeling the reionization history and associated temperature fluctuations, with the intention of incorporating ionizing background fluctuations at a later time. To do this, we generate several reionization histories using semi-numerical code AMBER, selecting histories with volume-weighted neutral fractions that adhere to the observed CMB optical depth and dark pixel fractions. Implementing these histories in the \texttt{Nyx} cosmological hydrodynamics code, we examine the evolution of gas within the simulation, and the associated metrics of the Ly$α$ forest opacity. We find that the pressure smoothing scale within the IGM is strongly correlated with the adiabatic index of the temperature-density relation. We find that while models with 20,000 K photoheating at reionization are better able to reproduce the shape of the observed $z=5$ 1D flux power spectrum than those with 10,000 K, they fail to match the highest wavenumbers. The simulated autocorrelation function and optical depth distributions are systematically low and narrow, respectively, compared to the observed values, but are in better agreement when the reionization history is longer in duration, more symmetric in its distribution of reionization redshifts, or if there are remaining neutral regions at $z<6$. The systematically low variance likely requires the addition of a fluctuating UVB.

astro-ph.CO↗

arXiv2023

Forecasting constraints on the high-z IGM thermal state from the Lyman-$α$ forest flux auto-correlation function

The auto-correlation function of the Lyman-$α$ (Ly$α$) forest flux from high-z quasars can statistically probe all scales of the intergalactic medium (IGM) just after the epoch of reionization. The thermal state of the IGM, which is determined by the physics of reionization, sets the amount of small-scale power seen in the \lya forest. To study the sensitivity of the auto-correlation function to the thermal state of the IGM, we compute the auto-correlation function from cosmological hydrodynamical simulations with semi-numerical models of the thermal state of the IGM. We create mock data sets of 20 quasars to forecast constraints on $T_0$ and $γ$, which characterize a tight temperature-density relation in the IGM, at $5.4 \leq z \leq 6$. At $z = 5.4$ we find that an ideal data set constrains $T_0$ to 29\% and $γ$ to 9\%. In addition, we investigate four realistic reionization scenarios that combine temperature and ultra-violet background (UVB) fluctuations at $z = 5.8$. We find that, when using mock data generated from a model that includes temperature and UVB fluctuations, we can rule out a model with no temperature or UVB fluctuations at $>1σ$ level 50.5\% of the time.

astro-ph.CO↗

arXiv2023

First measurement of the Mg II forest correlation function in the Epoch of Reionization

In the process of producing the roughly three ionizing photons per atom required to reionize the IGM, the same massive stars explode and eject metals into their surroundings. While the overly sensitive Lya transition makes Gunn-Peterson absorption of background quasar light an ineffective probe of reionization at z > 6, strong low-ionization transitions like the MgII doublet will give rise to a detectable "metal-line forest", if metals pollute the neutral IGM. We measure the auto-correlation of the MgII forest transmission using a sample of ten ground based z >= 6.80 quasar spectra probing the redshift range 5.96 < z_MgII < 7.42 (z_MgII,median = 6.47). The correlation function exhibits strong small-scale clustering and a pronounced peak at the doublet velocity (768 km/s) arising from strong absorbers in the CGM of galaxies. After these strong absorbers are identified and masked the signal is consistent with noise. Our measurements are compared to a suite of models generated by combining a large hydrodynamical simulation with a semi-numerical reionization topology, assuming a simple uniform enrichment model. We obtain a 95% credibility upper limit of [Mg/H] < -3.73 at z_MgII,median = 6.47, assuming uninformative priors on [Mg/H] and the IGM neutral fraction x_HI. Splitting the data into low-z (5.96 < z_MgII < 6.47; z_MgII,median = 6.235) and high-z (6.47 < z_MgII < 7.42; z_MgII,median = 6.72) subsamples again yields null-detections and 95% upper limits of [Mg/H] < -3.75 and [Mg/H] < -3.45, respectively. These first measurements set the stage for an approved JWST Cycle 2 program (GO 3526) targeting a similar number of quasars that will be an order of magnitude more sensitive, making the Mgii forest an emerging powerful tool to deliver precision constraints on the reionization and enrichment history of the Universe.

astro-ph.CO↗

arXiv2023

Convergence of small scale Ly$α$ structure at high-$z$ under different reionization scenarios

The Ly$α$ forest (LAF) at $z>5$ probes the thermal and reionization history of the intergalactic medium (IGM) and the nature of dark matter, but its interpretation requires comparison to cosmological hydrodynamical simulations. At high-$z$, convergence of these simulations is more exacting since transmission is dominated by underdense voids that are challenging to resolve. With evidence mounting for a late end to reionization, small structures down to the sub-kpc level may survive to later times than conventionally thought due to the reduced time for pressure smoothing to impact the gas, further tightening simulation resolution requirements. We perform a suite of simulations using the Eulerian cosmological hydrodynamics code Nyx, spanning domain sizes of 1.25-10 $h^{-1}$ Mpc and 5-80 $h^{-1}$ kpc cells, and explore the interaction of these variables with the timing of reionization on the properties of the matter distribution and the simulated LAF at $z=5.5$. In observable Ly$α$ power, convergence within 10% is achieved for $k< 0.1$ s/km, but larger $k$ shows deviation of up to 20 percent. While a later reionization retains more small structure in the density field, because of the greater thermal broadening there is little difference in the convergence of LAF power between early ($z=9$) and later ($z=6$) reionizations. We conclude that at $z\sim5.5$, resolutions of 10 kpc are necessary for convergence of LAF power at $k<0.1$ s/km, while higher-$k$ modes require higher resolution, and that the timing of reionization does not significantly impact convergence given realistic photoheating.

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arXiv2023

Modelling the cosmological Lyman-Werner background radiation field in the Early Universe

The Lyman-Werner (LW) radiation field is a key ingredient in the chemo-thermal evolution of gas in the Early Universe, as it dissociates H2 molecules, the primary cooling channel in an environment devoid of metals and dust. Despite its important role, it is still not implemented in cosmological simulations on a regular basis, in contrast to the ionising UV background. This is in part due to uncertainty in the source modelling, their spectra and abundance, as well as the detailed physics involved in the propagation of the photons and their interactions with the molecules. The goal of this work is to produce an accurate model of the LW radiation field at $z\geq6$, by post-processing the physics-rich high-resolution FiBY simulation. Our novelties include updated cross sections for H$_2$, H$^-$ and H$^+_2$ chemical species, IGM absorption by neutral Hydrogen and various spectral models for Population III and Population II stars. With our fiducial set of parameters, we show that the mean LW intensity steadily increases by three orders of magnitude from $z\sim23$ to $z\sim6$, while spatial inhomogeneities originate from massive star-forming galaxies that dominate the photon budget up to a distance of $\sim100$ proper kpc. Our model can be easily applied to other simulations or semi-analytical models as an external radiation field that regulates the formation of stars and massive black hole seeds in high-$z$ low-mass halos.

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arXiv2023

Forecasting constraints on the mean free path of ionizing photons at $z \geq 5.4$ from the Lyman-$α$ forest flux auto-correlation function

Fluctuations in Lyman-$α$ (Ly$α$) forest transmission towards high-$z$ quasars are partially sourced from spatial fluctuations in the ultraviolet background (UVB), the level of which are set by the mean free path of ionizing photons ($λ_{\text{mfp}}$). The auto-correlation function of Ly$α$ forest flux characterizes the strength and scale of transmission fluctuations and, as we show, is thus sensitive to $λ_{\text{mfp}}$. Recent measurements at $z \sim 6$ suggest a rapid evolution of $λ_{\text{mfp}}$ at $z>5.0$ which would leave a signature in the evolution of the auto-correlation function. For this forecast, we model mock Ly$α$ forest data with properties similar to the XQR-30 extended data set at $5.4 \leq z \leq 6.0$. At each $z$ we investigate 100 mock data sets and an ideal case where mock data matches model values of the auto-correlation function. For ideal data with $λ_{\text{mfp}}=9.0$ cMpc at $z=6.0$, we recover $λ_{\text{mfp}}=12^{+6}_{-3}$ cMpc. This precision is comparable to direct measurements of $λ_{\text{mfp}}$ from the stacking of quasar spectra beyond the Lyman limit. Hypothetical high-resolution data leads to a $\sim40\%$ reduction in the error bars over all $z$. The distribution of mock values of the auto-correlation function in this work is highly non-Gaussian for high-$z$, which should caution work with other statistics of the high-$z$ Ly$α$ forest against making this assumption. We use a rigorous statistical method to pass an inference test, however future work on non-Gaussian methods will enable higher precision measurements.

astro-ph.CO↗

arXiv2022

Measuring the thermal and ionization state of the low-$z$ IGM using likelihood free inference

We present a new approach to measure the power-law temperature density relationship $T=T_0 (ρ/ \barρ)^{γ-1}$ and the UV background photoionization rate $Γ_{\rm HI}$ of the IGM based on the Voigt profile decomposition of the Ly$α$ forest into a set of discrete absorption lines with Doppler parameter $b$ and the neutral hydrogen column density $N_{\rm HI}$. Previous work demonstrated that the shape of the $b$-$N_{\rm HI}$ distribution is sensitive to the IGM thermal parameters $T_0$ and $γ$, whereas our new inference algorithm also takes into account the normalization of the distribution, i.e. the line-density d$N$/d$z$, and we demonstrate that precise constraints can also be obtained on $Γ_{\rm HI}$. We use density-estimation likelihood-free inference (DELFI) to emulate the dependence of the $b$-$N_{\rm HI}$ distribution on IGM parameters trained on an ensemble of 624 Nyx hydrodynamical simulations at $z = 0.1$, which we combine with a Gaussian process emulator of the normalization. To demonstrate the efficacy of this approach, we generate hundreds of realizations of realistic mock HST/COS datasets, each comprising 34 quasar sightlines, and forward model the noise and resolution to match the real data. We use this large ensemble of mocks to extensively test our inference and empirically demonstrate that our posterior distributions are robust. Our analysis shows that by applying our new approach to existing Ly$α$ forest spectra at $z\simeq 0.1$, one can measure the thermal and ionization state of the IGM with very high precision ($σ_{\log T_0} \sim 0.08$ dex, $σ_γ\sim 0.06$, and $σ_{\log Γ_{\rm HI}} \sim 0.07$ dex).

astro-ph.CO↗

arXiv2022

Forecasts for WEAVE-QSO: 3D clustering and connectivity of critical points with Lyman-$α$ tomography

The upcoming WEAVE-QSO survey will target a high density of quasars over a large area, enabling the reconstruction of the 3D density field through Lyman-$α$ tomography over unprecedented volumes smoothed on intermediate scales ($\approx$ 16 Mpc/$h$). We produce mocks of the Lyman-$α$ forest using LyMAS, and reconstruct the 3D density field between sightlines through Wiener filtering in a configuration compatible with the future WEAVE-QSO observations. The fidelity of the reconstruction is assessed by measuring one- and two-point statistics from the distribution of critical points in the cosmic web. In addition, initial Lagrangian statistics are predicted from first principles, and measurements of the connectivity of the cosmic web are performed. The reconstruction captures well the expected features in the auto- and cross-correlations of the critical points. This remains true after a realistic noise is added to the synthetic spectra, even though sparsity of sightlines introduces systematics, especially in the cross-correlations of points with mixed signature. Specifically, for walls and filaments, the most striking clustering features could be measured with up to 4 sigma of significance with a WEAVE-QSO-like survey. Moreover, the connectivity of each peak identified in the reconstructed field is globally consistent with its counterpart in the original field, indicating that the reconstruction preserves the geometry of the density field not only statistically, but also locally. Hence the critical points relative positions within the tomographic reconstruction could be used as standard rulers for dark energy by WEAVE-QSO and similar surveys.

astro-ph.CO↗

arXiv2021

Improving IGM temperature constraints using wavelet analysis on high-redshift quasars

The thermal state of the intergalactic medium (IGM) contains vital information about the epoch of reionization, one of the most transformative yet poorly understood periods in the young universe. This thermal state is encoded in the small-scale structure of Lyman-$α$ (Ly$α$) absorption in quasar spectra. The 1D flux power spectrum measures the average small-scale structure along quasar sightlines. At high redshifts, where the opacity is large, averaging mixes high signal-to-noise ratio transmission spikes with noisy absorption troughs. Wavelet amplitudes are an alternate statistic that maintains spatial information while quantifying fluctuations at the same spatial frequencies as the power spectrum, giving them the potential to more sensitively measure the small-scale structure. Previous Ly$α$ forest studies using wavelet amplitude probability density functions (PDFs) used limited spatial frequencies and neglected strong correlations between PDF bins and across wavelets scales, resulting in sub-optimal and unreliable parameter inference. Here we present a novel method for performing statistical inference using wavelet amplitude PDFs that spans the full range of spatial frequencies probed by the power spectrum and that fully accounts for these correlations. We applied this procedure to realistic mock data drawn from a simple thermal model parameterized by the temperature at mean density, $T_0$, and find that wavelets deliver 1$σ$ constraints on $T_0$ that are on average 7% more sensitive at $z=5$ (12% at $z=6$) than those from the power spectrum. We consider the possibility of combing wavelet PDFs with the power, but find that this does not lead to improved sensitivity.

astro-ph.CO↗

arXiv2021

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

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 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 PMFs. We run a series of $(5\,\text{cMpc})^3$ cosmological volumes, varying both the strength of the seed magnetic field ($B_0$) and its spectral index ($n_B$). We find that PMFs that have $n_B > -0.562\log_{10}\left(\frac{B_0}{1{\rm n}G}\right) - 3.35$ produce electron optical depths ($τ_e$) that are inconsistent with CMB constraints due to the unrealistically early collapse of low-mass dwarf galaxies. For $n_B\geq-2.9$, our constraints are considerably tighter than the $\sim{\rm n}G$ 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 Lya 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 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 $\sim44\%$ which could increase the completeness fraction of galaxy surveys. Finally, our simulations show that surveys with a magnitude limit of ${\rm M_{UV,1500}=-13}$ can probe the sources that provide the majority of photons for reionization out to $z=12$.

astro-ph.CO↗

arXiv2020

Probing Reionization and Early Cosmic Enrichment with the MgII Forest

Because the same massive stars that reionized the intergalactic medium (IGM) inevitably exploded as supernovae that polluted the Universe with metals, the history of cosmic reionization and enrichment are intimately intertwined. While the overly sensitive Ly-alpha transition completely saturates in a neutral IGM, strong low-ionization metal lines like the MgII 2796,2804 doublet will give rise to a detectable `metal-line forest' if the metals produced during reionization (Z ~ 10^{-3}Z_sol) permeate the neutral IGM. We simulate the MgII forest for the first time by combining a large hydrodynamical simulation with a semi-numerical reionization topology, assuming a simple enrichment model where the IGM is uniformly suffused with metals. In contrast to the traditional approach of identifying discrete absorbers, we treat the absorption as a continuous random field and measure its two-point correlation function, leveraging techniques from precision cosmology. We show that a realistic mock dataset of 10 JWST spectra can simultaneously determine the Mg abundance, [Mg/H], with a 1sigma precision of 0.02 dex and measure the global neutral fraction to 5% for a Universe with = 0.74 and [Mg/H] = -3.7. Alternatively, if the IGM is pristine, a null-detection of the MgII forest would set a stringent upper limit on the IGM metallicity of [Mg/H] < -4.4 at 95% credibility, assuming > 0.5 from another probe. Concentrations of metals in the circumgalactic environs of galaxies can significantly contaminate the IGM signal, but we demonstrate how these discrete absorbers can be easily identified and masked such that their impact on the correlation function is negligible. The MgII forest thus has tremendous potential to precisely constrain the reionization and enrichment history of the Universe.

astro-ph.CO↗

arXiv2019

Anomaly in the Opacity of the Post-Reionization Intergalactic Medium in the Ly$α$ and Ly$β$ Forest

We measure the intergalactic medium (IGM) opacity in the Ly$α$ as well as in the Ly$β$ forest along $19$ quasar sightlines between $5.5\lesssim z_{\rm abs}\lesssim 6.1$, probing the end stages of the reionization epoch. Owing to its lower oscillator strength the Ly$β$ transition is sensitive to different gas temperatures and densities than Ly$α$, providing additional constraints on the ionization and thermal state of the IGM. A comparison of our measurements to different inhomogeneous reionization models, derived from post-processing the Nyx cosmological hydrodynamical simulation to include spatial fluctuations in the ultraviolet background (UVB) or the gas temperature field, as well as to a uniform reionization model with varying thermal states of the IGM, leads to two primary conclusions: First, we find that including the effects of spectral noise is key for a proper data to model comparison. Noise effectively reduces the sensitivity to high opacity regions, and thus even stronger spatial inhomogeneities are required to match the observed scatter in the observations than previously inferred. Second, we find that models which come close to reproducing the distribution of Ly$α$ effective optical depths nevertheless underpredict the Ly$β$ opacity at the same spatial locations. The origin of this disagreement is not entirely clear but models with an inversion in the temperature-density relation of the IGM just after reionization is completed match our measurements best, although they still do not fully capture the observations at $z\gtrsim 5.8$.

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arXiv2019

Inhomogeneous Reionization Models in Cosmological Hydrodynamical Simulations

In this work we present a new hybrid method to simulate the thermal effects of the reionization in cosmological hydrodynamical simulations. The method improves upon the standard approach used in simulations of the intergalactic medium (IGM) and galaxy formation without a significant increase of the computational cost allowing for efficient exploration of the parameter space. The method uses a small set of phenomenological input parameters and combines a semi-numerical reionization model to solve for the topology of reionization and an approximate model of how reionization heats the IGM, with the massively parallel \texttt{Nyx} hydrodynamics code, specifically designed to solve for the structure of diffuse IGM gas. We have produced several large-scale high resolution cosmological hydrodynamical simulations ($2048^3$, $L_{\rm box} = 40$ Mpc/h) with different instantaneous and inhomogeneous HI reionization models that use this new methodology. We study the IGM thermal properties of these models and find that large scale temperature fluctuations extend well beyond the end of reionization. Analyzing the 1D flux power spectrum of these models, we find up to $\sim 50\%$ differences in the large scale properties (low modes, $k\lesssim0.01$ s/km) of the post-reionization power spectrum due to the thermal fluctuations. We show that these differences could allow one to distinguish between different reionization scenarios already with existing Ly$α$ forest measurements. Finally, we explore the differences in the small-scale cutoff of the power spectrum and we find that, for the same heat input, models show very good agreement provided that the reionization redshift of the instantaneous reionization model happens at the midpoint of the inhomogeneous model.

astro-ph.CO↗

arXiv2019

The Power Spectrum of the Lyman-$α$ Forest at z < 0.5

We present new measurements of the flux power-spectrum P(k) of the $z<0.5$ HI Lyman-$α$ forest spanning scales k ~ 0.001-0.1 s/km. These results were derived from 65 far ultraviolet quasar spectra (resolution R~18000) observed with the Cosmic Origin Spectrograph (COS) on board the Hubble Space Telescope. The analysis required careful masking of all contaminating, coincident absorption from HI and metal-line transitions of the Galactic interstellar medium and intervening absorbers as well as proper treatment of the complex COS line-spread function. From the P(k) measurements, we estimate the HI photoionization rate ($Γ_{\rm HI}$) in the z<0.5 intergalactic medium. Our results confirm most of the previous $Γ_{\rm HI}$ estimates. We conclude that previous concerns of a photon underproduction crisis are now resolved by demonstrating that the measured $Γ_{\rm HI}$ can be accounted for by ultraviolet emission from quasars alone. In a companion paper, we will present constraints on the thermal state of the $z<0.5$ intergalactic medium from the P(k) measurements presented here.

astro-ph.CO↗

arXiv2018

New Constraints on IGM Thermal Evolution from the Lyα Forest Power Spectrum

We determine the thermal evolution of the intergalactic medium (IGM) over $3\, \mathrm{Gyr}$ of cosmic time $1.8<z<5.4$ by comparing measurements of the Lyα forest power spectrum to a suite of $\sim70$ hydrodynamical simulations. We conduct Bayesian inference of IGM thermal parameters using an end-to-end forward modeling framework whereby mock spectra generated from our simulation grid are used to build a custom emulator which interpolates the power spectrum between thermal grid points. The temperature at mean density $T_0$ rises steadily from $T_0\sim 6000\, \mathrm{K}$ at $z=5.4$, peaks at $14000\, \mathrm{K}$ for $z\sim 3.4$, and decreases at lower redshift reaching $T_0\sim 7000\, \mathrm{K}$ by $z\sim1.8$. This evolution provides conclusive evidence for photoionization heating resulting from the reionization of He II, as well as the subsequent cooling of the IGM due to the expansion of the Universe after all reionization events are complete. Our results are broadly consistent with previous measurements of thermal evolution based on a variety of approaches, but the sensitivity of the power spectrum, the combination of high precision BOSS measurements of large-scale modes ($k\lesssim 0.02\, \mathrm{s/km}$) with our recent determination of the small-scale power, our large grid of models, and our careful statistical analysis allow us to break the well known degeneracy between the temperature at mean density $T_0$ and the slope of the temperature density relation $γ$ that has plagued previous analyses. At the highest redshifts $z\geq5$ we infer lower temperatures than expected from the standard picture of IGM thermal evolution leaving little room for additional smoothing of the Lyα forest by free streaming of warm dark matter.

astro-ph.CO↗

arXiv2018

QSO MUSEUM I: A sample of 61 extended Ly$α$-emission nebulae surrounding $z\sim3$ quasars

Motivated by the recent discovery of rare Enormous Lyman-Alpha Nebulae (ELAN) around z~2 quasars, we have initiated a long-term observational campaign with the MUSE instrument to directly uncover the astrophysics of the gas around quasars. We present here the first 61 targets of our effort under the acronym QSO MUSEUM (Quasar Snapshot Observations with MUse: Search for Extended Ultraviolet eMission). These quasars have a median redshfit of z=3.17, absolute $i$ magnitude in the range $-29.67\leq M_i(z=2)\leq-27.03$, and different levels of radio-loudness. This sample unveils diverse specimens of Ly$α$ nebulosities extending for tens of kiloparsecs around these quasars (on average out to a maximum projected distance of 80 kpc) above a surface brightness SB$>8.8\times10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ ($2σ$). The bulk of the extended Ly$α$ emission is within R<50 kpc, and is characterized by relatively quiescent kinematics, with average velocity dispersions of $\langle σ_{\rm Lyα}\rangle < 400$~km~s$^{-1}$. Therefore, the motions within all these Ly$α$ nebulosities have amplitudes consistent with gravitational motions expected in dark matter halos hosting quasars at these redshifts, possibly reflecting the complexity in propagating a fast wind on large scales. Our current data suggest a combination of photoionization and resonant scattering as powering mechanisms of the Ly$α$ emission. We discover the first $z\sim3$ ELAN, which confirms a very low probability ($\sim1\%$) of occurrence of such extreme systems at these cosmic epochs. Finally, we discuss the redshift evolution currently seen in extended Ly$α$ emission around radio-quiet quasars from $z\sim3$ to $z\sim2$, concluding that it is possibly linked to a decrease of cool gas mass within the quasars' CGM from $z\sim3$ to $z\sim2$, and thus to the balance of cool vs hot media.

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