Probing the thermal state of the intergalactic medium at $z>5$ with the transmission spikes in high-resolution Ly$α$ forest spectra
Prakash Gaikwad, Michael Rauch, Martin G. Haehnelt, Ewald Puchwein, James S. Bolton, Laura C. Keating, Girish Kulkarni, Vid Iršič, Eduardo Bañados, George D. Be… 展开作者
Prakash Gaikwad, Michael Rauch, Martin G. Haehnelt, Ewald Puchwein, James S. Bolton, Laura C. Keating, Girish Kulkarni, Vid Iršič, Eduardo Bañados, George D. Becker, Elisa Boera, Fakhri S. Zahedy, Hsiao-Wen Chen, Robert F. Carswell, Jonathan Chardin, Alberto Rorai
备注：
20 pages (+10 pages appendices), 12 figures (+14 figures appendices); Accepted in MNRAS; Main results are summarized in Fig. 10, Fig. 12 and Table 3
We compare a sample of five high-resolution, high S/N Ly$α$ forest spectra of bright $6<z \lesssim 6.5$ QSOs aimed at spectrally resolving the last remaining transmission spikes at $z>5$ with those obtained from mock absorption spectra from the Sherwood and Sherwood-Relics suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile fitting procedure for the inverted transmitted flux, $1-F$, similar to the widely used Voigt profile fitting of the transmitted flux $F$ at lower redshifts, to characterise the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominant in low temeperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution ($\leq $ 8 km/s) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of $T_0= (11000 \pm 1600,10500\pm 2100,12000 \pm 2200)$ K at $z= (5.4,5.6,5.8)$. This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to $z\sim5.3$, the width distribution of the observed transmission spikes is consistent with the range of $T_0$ caused by spatial fluctuations in the temperature-density relation.
We explore the use of Deep Learning to infer the temperature of the intergalactic medium from the transmitted flux in the high redshift Lyman-alpha forest. We train Neural Networks on sets of simulated spectra from redshift z=2-3 outputs of cosmological hydrodynamic simulations, including high temperature regions added in post-processing to approximate bubbles heated by Helium-II reionization. We evaluate how well the trained networks are able to reconstruct the temperature from the effect of Doppler broadening in the simulated input Lyman-alpha forest absorption spectra. We find that for spec…
A late end to reionisation at redshift $z\simeq 5.3$ is consistent with observed spatial variations in the Ly$α$ forest transmission and the deficit of Ly$α$ emitting galaxies around extended Ly$α$ absorption troughs at $z=5.5$. In this model, large islands of neutral hydrogen should persist in the diffuse intergalactic medium (IGM) until $z\simeq 6$. We use a novel, hybrid approach that combines high resolution cosmological hydrodynamical simulations with radiative transfer to predict the incidence of strong 21 cm forest absorbers with optical depths $τ_{21}>10^{-2}$ from the diffuse IGM in t…
Quasar spectra provide a unique opportunity to investigate the intergalactic medium at high redshifts. The spectral analysis of the Ly$α$ forest allows us to constrain the effective equation of state of the intergalactic medium and its changes during the evolution of the Universe. Based on the Voigt profile fitting of Ly$α$ forest lines in 50 high-resolution QSO spectra obtained at Keck telescope we present new measurements of the power-law index $γ$ of temperature-density relation in IGM for six redshift bins in the range $z=1.6-3.7$. We find that the IGM state is close to isothermal ($γ\appr…
We examine the statistics of the low-redshift Ly-alpha forest in an adaptive mesh refinement hydrodynamic cosmological simulation of sufficient volume to include distinct large-scale environments. We compare our HI column density distribution of absorbers both with recent work and between two highly-refined regions of our simulation: a large-scale overdensity and a large-scale underdensity (on scales of approximately 20 Mpc). We recover the average results presented in Kollmeier et al. (2014) using different simulation methods. We further break down these results as a function of environment t…
The post-reionization thermal state of the intergalactic medium is characterized by a power-law relationship between temperature and density, with a slope determined by the parameter $γ$. We describe a new method to measure $γ$ using the ratio of flux curvature in the Lyman-$α$ and $β$ forests. At a given redshift, this curvature ratio incorporates information from the different gas densities traced by Lyman-$α$ and $β$ absorption. It is relatively simple and fast to compute and appears robust against several observational uncertainties. We apply this technique to a sample of 27 high-resolutio…
In this article, the temperature-density relation of the intergalactic medium was studied in the region $1.6 \leq z < 2.0$ divided into two bins. For this purpose, the Ly-$α$ forest decomposition into individual absorption profiles was used for the study of 35 publicly available quasar spectra obtained by the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (ESO) and by the High Resolution Echelle Spectrometer (HIRES) on the Keck Telescope. For the determination of the thermal state sensitive cut-off position in the $b - N_{HI}$ distribution, the iterative fitting…
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 sp…
We present a set of ultra-large particle-mesh simulations of the LyA forest targeted at understanding the imprint of baryon acoustic oscillations (BAO) in the inter-galactic medium. We use 9 dark matter only simulations which can, for the first time, simultaneously resolve the Jeans scale of the intergalactic gas while covering the large volumes required to adequately sample the acoustic feature. Mock absorption spectra are generated using the fluctuating Gunn-Peterson approximation which have approximately correct flux probability density functions (PDFs) and small-scale power spectra. On lar…
We examine the column density distribution function (CDDF) and Doppler parameter distribution from hydrodynamical simulations and Cosmic Origins Spectrograph (COS) observations of the Lyman-alpha forest at redshift $0\leq z\leq 0.2$. Allowing for a factor of two uncertainty in the metagalactic HI photoionisation rate, our hydrodynamical simulations are in good agreement ($1$-$1.5σ$) with the shape and amplitude of the observed CDDF at HI column densities $10^{13.3}\rm\,cm^{-2}\leq N_{\rm HI}\leq 10^{14.5}\rm\,cm^{-2}$. However, the Doppler widths of the simulated lines remain too narrow with r…
We compare cosmological hydrodynamical simulations combined with the homogeneous metagalactic UV background (UVB) of Haardt & Madau (2012) (HM2012) to observations of the Lyman-alpha forest that are sensitive to the thermal and ionization state of the intergalactic medium (IGM). The transition from optically thick to thin photoheating predicted by the simple one-zone, radiative transfer model implemented by HM2012 predicts a thermal history that is in remarkably good agreement with the observed rise of the IGM temperature at z~3 if we account for the expected evolution of the volume filling fa…
Cosmic reionization was the last major phase transition of hydrogen from neutral to highly ionized in the intergalactic medium (IGM). Current observations show that the IGM is significantly neutral at $z>7$, and largely ionized by $z\sim5.5$. However, most methods to measure the IGM neutral fraction are highly model-dependent, and are limited to when the volume-averaged neutral fraction of the IGM is either relatively low ($\bar{x}_{\rm HI} \lesssim 10^{-3}$) or close to unity ($\bar{x}_{\rm HI}\sim 1$). In particular, the neutral fraction evolution of the IGM at the critical redshift range of…
Maps of the large-scale structure of the Universe at redshifts 2-4 can be made with the Lyman-alpha forest which are complementary to low redshift galaxy surveys. We apply the Wiener interpolation method of Caucci et al. to construct three-dimensional maps from sets of Lyman-alpha forest spectra taken from cosmological hydrodynamic simulations. We mimic some current and future quasar redshift surveys (BOSS, eBOSS and MS-DESI) by choosing similar sightline densities. We use these appropriate subsets of the Lyman-alpha absorption sightlines to reconstruct the full three dimensional Lyman-alpha f…
The filamentary network of intergalactic medium (IGM) gas that gives origin to the Lyman-alpha forest in the spectra of distant quasars encodes information on the physics of structure formation and the early thermodynamics of diffuse baryonic material. Here, we use a massive suite of more than 400 high-resolution cosmological hydrodynamical simulations run with the Graphics Processing Unit-accelerated code Cholla to study the IGM at high spatial resolution maintained over the entire computational volume. The simulations capture a wide range of possible thermal histories of intergalactic gas by…
Using high redshift radio sources as background, the 21cm forest observations probe the neutral hydrogen absorption signatures of early structures along the lines of sight. Directly sensitive to the spin temperature, it complements the 21cm tomography observations, and provides information on the temperature as well as the ionization state of the intergalactic medium (IGM). We use a radiative transfer simulation to investigate the 21cm forest signals during the epoch of reionization. We first confirmed that the optical depth and equivalent width (EW) are good representations of the ionization …
Measurements of the Ly$α$ forest based on large numbers of quasar spectra from sky surveys such as SDSS/eBOSS accurately probe the distribution of matter on small scales and thus provide important constraints on several ingredients of the cosmological model. A main summary statistic derived from those measurements is the one-dimensional power spectrum, P1D, of the Ly$α$ absorption. However, model predictions for P1D rely on expensive hydrodynamical simulations of the intergalactic medium, which was the limiting factor in previous analyses. Datasets from upcoming surveys such as DESI will push …
Ringing of the Reionization: A first direct measurement of the intergalactic pressure smoothing scale at redshift z>4.2 as imprinted onto small-scale peculiar velocities in the Lyman-alpha forest
University of Hertfordshire（赫特福德大学）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；SISSA- International School for Advanced Studies（国际高等研究学院）；INFN – National Institute for Nuclear Physics（意大利国家核物理研究所）；IFPU, Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；INAF, Osservatorio Astronomico di Trieste（的里雅斯特天文台）；ICSC - Centro Nazionale di Ricerca in High Performance Computing, Big Data e Quantum Computing（高性能计算、大数据与量子计算国家研究中心）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）
Spectroscopy of the Ly$α$ forest in quasar spectra proved to be a useful tool for probing the intergalactic gas. We developed the automatic program for Voigt profile fitting of Ly$α$ forest lines. We run this code on 9 high resolution ($\sim 50000$) quasars spectra with a high signal-to-noise ratio ($\sim 50 -100$) from the Keck telescope archive and obtained the sample of single well-fitted Ly$α$ lines. Fitting the joint 2d distribution of column density and Doppler parameter from this sample by physically reasonable model we estimate a power law index $γ$ of the equation of state of the inte…
We investigate the thermal history of the intergalactic medium (IGM) in the redshift interval z=1.7--3.2 by studying the small-scale fluctuations in the Lyman alpha forest transmitted flux. We apply a wavelet filtering technique to eighteen high resolution quasar spectra obtained with the Ultraviolet and Visual Echelle Spectrograph (UVES), and compare these data to synthetic spectra drawn from a suite of hydrodynamical simulations in which the IGM thermal state and cosmological parameters are varied. From the wavelet analysis we obtain estimates of the IGM thermal state that are in good agreem…
We present a 30h integration Very Large Telescope X-shooter spectrum of the Lyman series forest towards the $z = 7.084$ quasar ULAS J1120+0641. The only detected transmission at ${\rm S/N}>5$ is confined to seven narrow spikes in the Ly$α$ forest, over the redshift range $5.858<z<6.122$, just longward of the wavelength of the onset of the Ly$β$ forest. There is also a possible detection of one further unresolved spike in the Ly$β$ forest at $z=6.854$, with ${\rm S/N}=4.5$. We also present revised Hubble Space Telescope F814W photometry of the source. The summed flux from the transmission spike…
We discuss the feasibility of the detection of the 21cm forest in the diffuse IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been derived using simulations of reionization which include detailed radiative transfer of ionizing photons. We find that the spectra from reionization models with similar total comoving hydrogen ionizing emissivity but different frequency distribution look remarkably similar. Thus, unless the reionization histories are very different from each other (e.g. a predominance of UV vs. x-ray heating) we do not expect to distinguish them by means o…
We investigate Lyman-$α$ transmission spikes at $z > 5$ in synthetic quasar spectra, and discuss their connection to the properties of the intergalactic medium and their ability to constrain reionization models. We use state-of-the-art radiation-hydrodynamic simulations from the Cosmic Reionization On Computers series to predict the number of transmission spikes as a function of redshift, both in the ideal case of infinite spectral resolution and in a realistic observational setting. Transmission spikes are produced in highly-ionized underdense regions located in the vicinity of UV sources. We…
High-signal to noise observations of the Ly$α$ forest transmissivity in the z = 7.085 QSO ULAS J1120+0641 show seven narrow transmission spikes followed by a long 240 cMpc/h trough. Here we use radiative transfer simulations of cosmic reionization previously calibrated to match a wider range of Ly$α$ forest data to show that the occurrence of seven transmission spikes in the narrow redshift range z = 5.85 - 6.1 is very sensitive to the exact timing of reionization. Occurrence of the spikes requires the most under dense regions of the IGM to be already fully ionised. The rapid onset of a long t…
We present new measurements of the temperature of the intergalactic medium (IGM) derived from the Lyman-alpha forest over 2.0 < z < 4.8. The small-scale structure in the forest of 61 high-resolution QSO spectra is quantified using a new statistic, the curvature, and the conversion to temperature calibrated using a suite of hydrodynamic simulations. At each redshift we focus on obtaining the temperature at an optimal overdensity probed by the Lyman-alpha forest, T(Delta), where the temperature is nearly a one-to-one function of the curvature regardless of the slope of the temperature-density re…
We present new measurements of the thermal state of the intergalactic medium (IGM) at $z\sim2.4$ derived from absorption line profiles in the Ly$α$ forest. We use a large set of high-resolution hydrodynamical simulations to calibrate the relationship between the temperature-density ($T$--$Δ$) relation in the IGM and the distribution of HI column densities, $N_{\rm HI}$, and velocity widths, $b_{\rm HI}$, of discrete Ly$α$ forest absorbers. This calibration is then applied to the measurement of the lower cut-off of the $b_{\rm HI}$--$N_{\rm HI}$ distribution recently presented by Rudie et al. (…
The burgeoning rise of the 21-cm forest I: constraints on the optical depth of the intergalactic medium at $5.38 < z < 5.84$
University of Bologna（博洛尼亚大学）；INAF – Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）；Rhodes University（罗德岛大学）；South African Radio Astronomy Observatory（南非射电天文台）；University of Catania（卡塔尼亚大学）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）
The thermal state of the post-reionization IGM is sensitive to the timing of reionization and the nature of the ionizing sources. We have modelled here the thermal state of the IGM in cosmological radiative transfer simulations of a realistic, extended, spatially inhomogeneous hydrogen reionization process, carefully calibrated with Ly-alpha forest data. We compare these with cosmological simulations run using a spatially homogeneous ionizing background. The simulations with a realistic growth of ionized regions and a realistic spread in reionization redshifts show, as expected, significant sp…
We re-analyse high redshift and high resolution Lyman-$α$ forest spectra considered in (Viel et al 2013), seeking to constrain the properties of warm dark matter particles. Compared to this previous work, we consider a wider range of thermal histories of the intergalactic medium. We find that both warm and cold dark matter models can explain the cut-off observed in the flux power spectra of high-resolution observations equally well. This implies, however, very different thermal histories and underlying re-ionisation models. We discuss how to remove this degeneracy.
The thermal evolution of the intergalactic medium (IGM) can serve as a sensitive probe of cosmological heat sources and sinks. We employ it to limit interactions between dark matter and baryons. After reionization the IGM temperature is set by the balance between photoheating and adiabatic cooling. We use measurements of the IGM temperature from Lyman-$α$-forest data to constrain the cross-section $σ$ between dark matter and baryons, finding $σ< 10^{-20}$ cm$^2$ for dark-matter masses $m_χ\leq 1$ GeV. This provides the first direct constraint on scattering between dark matter and baryons at re…
The inhomogeneous cosmological reionization process leaves tangible imprints in the intergalactic medium down to z=4-5. The Lyman-alpha forest flux power spectrum provides a potentially powerful probe of the epoch of reionization. With the existing SDSS I/II quasar sample we show that two cosmological reionization scenarios, one completing reionization at z=6 and the other at z=9, can be distinguished at ~7 sigma level by utilizing Lyman alpha forest absorption spectra at z=4.5+-0.5, in the absence of other physical processes that may also affect the Lyman alpha flux power spectrum. The redshi…
We present a new method to infer parameters of the temperature-density relation in the intergalactic medium in the post-reionization epoch at $z\sim 2-4$. This method is based on the analysis of the Ly$α$ absorbers distribution over column densities and Doppler parameters by the model joint probability density function. This approach allows us to measure the power-law index $γ$ of the temperature-density relation and a certain combination of the temperature at the mean density $T_0$ and hydrogen photoionization rate $Γ$. To estimate $T_0$ and $Γ$ separately, we employ measurements of the Ly$α$…
We present the Sherwood-Relics simulations, a new suite of large cosmological hydrodynamical simulations aimed at modelling the intergalactic medium (IGM) during and after the cosmic reionization of hydrogen. The suite consists of over 200 simulations that cover a wide range of astrophysical and cosmological parameters. It also includes simulations that use a new lightweight hybrid scheme for treating radiative transfer effects. This scheme follows the spatial variations in the ionizing radiation field, as well as the associated fluctuations in IGM temperature and pressure smoothing. It is com…
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…
The distribution of diffuse gas in the intergalactic medium (IGM) imprints a series of hydrogen absorption lines on the spectra of distant background quasars known as the Lyman-$α$ forest. Cosmological hydrodynamical simulations predict that IGM density fluctuations are suppressed below a characteristic scale where thermal pressure balances gravity. We measured this pressure-smoothing scale by quantifying absorption correlations in a sample of close quasar pairs. We compared our measurements to hydrodynamical simulations, where pressure smoothing is determined by the integrated thermal history…
The majority of cosmic rays (CRs) generated by star-forming galaxies escape them and enter the intergalactic medium (IGM). Galactic wind termination shocks might also accelerate CRs. I show that the mean pressure of these CRs can reach to within an order of magnitude of the mean Lyman-alpha forest thermal pressure. At z >~ 1, their pressure may have even been dominant. I also demonstrate that, whichever IGM phase the CRs reside in, they contribute significantly to its pressure if its temperature is ~$10^4$ K, as long as pionic and Coulomb losses are negligible. Where CRs end up depends on the …
According to the photo-heating model of the intergalactic medium (IGM), He II reionization is expected to affect its thermal evolution. Evidence for additional energy injection into the IGM has been found at $3\lesssim z\lesssim4$, though the evidence for the subsequent fall-off below $z\sim2.8$ is weaker and depends on the slope of the temperature--density relation, $γ$. Here we present, for the first time, an extension of the IGM temperature measurements down to the atmospheric cut-off of the H I Lyman-$α$ forest at $z\simeq1.5$. Applying the curvature method on a sample of 60 UVES spectra w…
The reionization of the second electron of helium shapes the physical state of intergalactic gas at redshifts between 2 < z < 5. Because performing full in situ radiative transfer in hydrodynamic simulations is computationally expensive for large volumes, the physics of HeII reionization is often approximated by a uniform UV background model that does not capture the patchiness of reionization. We have devised a model that implements the effects of HeII reionization using semi-analytic calculations of the thermal state of intergalactic gas-- a way to bypass a full radiative transfer simulation…
A long (110 cMpc/$h$) and deep absorption trough in the Ly$α$ forest has been observed extending down to redshift 5.5 in the spectrum of ULAS J0148+0600. Although no Ly$α$ transmission is detected, Ly$β$ spikes are present which has led to claims that the gas along this trough must be ionized. Using high resolution cosmological radiative transfer simulations in large volumes, we show that in a scenario where reionization ends late ($z \sim 5.2$), our simulations can reproduce troughs as long as observed. In this model, we find that the troughs are caused by islands of neutral hydrogen. Small i…
We investigate a contribution of the Jeans smoothing to the minimal width of Ly$α$ forest lines and discuss how the accounting for this additional broadening affects the inferred parameters of the intergalactic matter equation of state. We estimate a power-law index $γ$ of the equation of state, a temperature at the mean density $T_0$ and a hydrogen photoionization rate $Γ$ within 4 redshift bins. Furthermore, in each bin we obtain an upper limit on the scale-parameter $f_{\rm J}$, which sets the relation between the Jeans length and the characteristic physical size of the absorber clouds.
The distribution of the absorption line broadening observed in the Ly$α$ forest carries information about the temperature and widths of the filaments in the intergalactic medium (IGM). In this work, we present and test a new method for inferring the temperature of the IGM, the size of the absorbing filaments and the photo-ionization rate of hydrogen from the properties of absorption line broadening in the Ly$α$ forest. We apply our method to mock spectra from the reference model of the EAGLE cosmological simulation, and we demonstrate that we are able to reconstruct the IGM properties. Our met…
We introduce a new set of large scale, high resolution hydrodynamical simulations of the intergalactic medium: the Sherwood simulation suite. These are performed in volumes 10^3-160^3 h^-3 comoving Mpc^{3}, span almost four orders of magnitude in mass resolution with up to 17.2 billion particles, and employ a variety of physics variations including warm dark matter and galactic outflows. We undertake a detailed comparison of the simulations to high resolution, high signal-to-noise observations of the Lyman-alpha forest over the redshift range 2 < z < 5. The simulations are in very good agreeme…
The temperature of the low-density intergalactic medium (IGM) at high redshift is sensitive to the timing and nature of hydrogen and HeII reionization, and can be measured from Lyman-alpha forest absorption spectra. Since the memory of intergalactic gas to heating during reionization gradually fades, measurements as close as possible to reionization are desirable. In addition, measuring the IGM temperature at sufficiently high redshifts should help to isolate the effects of hydrogen reionization since HeII reionization starts later, at lower redshift. Motivated by this, we model the IGM temper…
We study the properties of self-shielding intergalactic absorption systems and their implications for the ionizing background. We find that cosmological simulations post-processed with detailed radiative transfer calculations generally are able to reproduce the observed abundance of Lyman-limit systems, and we highlight possible discrepancies between the observations and simulations. This comparison tests cosmological simulations at overdensities of ~100. Furthermore, we show that the properties of Lyman-limit systems in these simulations, in simple semi-analytic arguments, and as suggested by…
The thermal state of the intergalactic medium (IGM) at z < 6 constrains the nature and timing of cosmic reionization events, but its inference from the Ly-alpha forest is degenerate with the 3-D structure of the IGM on ~100 kpc scales, where, analogous to the classical Jeans argument, the pressure of the T~$10^4$ K gas supports it against gravity. We simulate the IGM using smoothed particle hydrodynamics, and find that, at z < 6, the gas density power spectrum does not exhibit the expected Jeans filtering cutoff, because dense gas in collapsed halos dominates the small-scale power masking pres…
We present an updated version of the so-called Madau model for the attenuation by the intergalactic neutral hydrogen against the radiation from distant objects. First, we derive a distribution function of the intergalactic absorbers from the latest observational statistics of the Ly$α$ forest, Lyman limit systems, and damped Ly$α$ systems. The distribution function excellently reproduces the observed redshift evolutions of the Ly$α$ depression and of the mean-free-path of the Lyman continuum simultaneously. Then, we derive a set of the analytic functions which describe the mean intergalactic a…
We use hydrodynamic cosmological simulations in a (600 Mpc)^3 volume to study the observability of baryon acoustic oscillations (BAO) in the intergalactic medium as probed by Lyman alpha forest (LAF) absorption. The large scale separation between the wavelength of the BAO mode (~150 Mpc) and the size of LAF absorbers (~100 kpc) makes this a numerically challenging problem. We report on several 2048^3 simulations of the LAF using the ENZO code. We adopt WMAP5 concordance cosmological parameters and power spectrum including BAO perturbations. 5000 synthetic HI absorption line spectra are generat…
We use the Sherwood-Relics suite of hybrid hydrodynamical and radiative transfer simulations to model the effect of inhomogeneous reionisation on the 1D power spectrum of the \Lya forest transmitted flux at redshifts $4.2\leq z \leq 5$. Relative to models that assume a homogeneous UV background, reionisation suppresses the power spectrum at small scales, $k \sim 0.1\rm\,km^{-1}\,s$ by $\sim 10$ per cent because of spatial variations in the thermal broadening kernel and the divergent peculiar velocity field associated with over-pressurised intergalactic gas. On larger scales, $k<0.03\rm\,km^{-1…
A unified description is provided for the 21cm signatures arising from minihaloes against a bright background radio source and against the Cosmic Microwave Background (CMB), within the context of a dynamical collapsing cosmological spherical halo model. The equivalent width distribution of the resulting 21cm forest is computed for LCDM cosmologies, along with the brightness temperature differential relative to the CMB. The effects of an ambient Ly-alpha radiation field and heating of the IGM on the signatures are included. It is shown that the dynamical effects of heating substantially suppres…
We present new high-resolution (R~14,000) spectra of the two brightest HeII-transparent quasars in the far-UV (FUV) at z>3.5, HE2QSJ2311-1417 (z=3.70) and HE2QSJ1630+0435 (z=3.81), obtained with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). In the predominantly saturated HeII absorption spectra, both sightlines show several isolated resolved (full width at half maximum FWHM>50 km/s) transmission spikes in HeII Ly$α$ and HeII Ly$β$. The incidence of such spikes decreases with increasing redshift, but both sightlines show significant spikes at z>3.5, signaling the pr…
For low-redshift cosmology and galaxy formation rates, it is important to account for all the baryons synthesized in the Big Bang. Although galaxies and clusters contain 10% of the baryons, many more reside in the photoionized Lyman-alpha forest and shocked-heated warm-hot intergalactic medium (WHIM) at T = 10^5 to 10^7 K. Current tracers of WHIM at 10^5 to 10^6 K include the O VI 1032, 1038 absorption lines, together with broad Lyman-alpha absorbers (BLAs) and EUV/X-ray absorption lines from Ne VIII, O VII, and O VIII. We improve the O VI baryon surveys with corrections for oxygen metallicity…
The amplitude of the ionizing background that pervades the intergalactic medium (IGM) at the end of the epoch of reionization provides a valuable constraint on the emissivity of the sources which reionized the Universe. While measurements of the ionizing background at lower redshifts rely on a simulation-calibrated mapping between the photoionization rate and the mean transmission of the Ly$α$ forest, at $z\gtrsim6$ the IGM becomes increasingly opaque, and transmission arises solely in narrow spikes separated by saturated Gunn-Peterson troughs. In this regime, the traditional approach of measu…
We use a large set of cosmological smoothed particle hydrodynamics (SPH) simulations to examine the effect of mass resolution and box size on synthetic Lya forest spectra at 2 \leq z \leq 5. The mass resolution requirements for the convergence of the mean Lya flux and flux power spectrum at z=5 are significantly stricter than at lower redshift. This is because transmission in the high redshift Lya forest is primarily due to underdense regions in the intergalactic medium (IGM), and these are less well resolved compared to the moderately overdense regions which dominate the Lya forest opacity at…
