Lyα Forest Research Articles

Covariance matrices for the Lyman-α forest using the lognormal approximation

We investigate the nature of correlations in the small-scale flux statistics of the Lyman-α (Lyα) forest across redshift bins. Understanding and characterising these correlations is important for unbiased cosmological and astrophysical parameter inference using the Lyα forest. We focus on the 1-dimensional flux power spectrum (FPS) and mean flux (F̅) simulated using the semi-numerical lognormal model we developed in earlier work. The lognormal model can capture the effects of long wavelength modes with relative ease as compared to full smoothed particle hydrodynamical (SPH) simulations that are limited by box volume. For a single redshift bin of size Δz ≃ 0.1, we show that the lognormal model predicts positive cross-correlations between k-bins in the FPS, and a negative correlation for F̅ × FPS, in qualitative agreement with SPH simulations and theoretical expectations. For measurements across two neighbouring redshift bins of width Δ z each (using long flux skewers of length 2Δ z that are 'split' in half), the lognormal model predicts an anti-correlation for FPS × FPS and a positive correlation for F̅ × FPS, caused by modes with the longest wavelengths. This is in contrast to SPH simulations which predict a negligible magnitude for cross-redshift correlations derived from such `split' skewers, and we discuss possible reasons for this difference. Finally, we perform a preliminary test of the impact of neglecting long wavelength modes on parameter inference, finding that whereas the correlation structure of neighbouring redshift bins has relatively little impact, the absence of long wavelength modes in the model can lead to ≳ 2 - σ biases in the inference of astrophysical parameters. Our results motivate a more careful treatment of long wavelength modes in analyses that rely on the small-scale Lyα forest for parameter inference.

The long-lasting effect of X-ray pre-heating in the post-reionization intergalactic medium

ABSTRACT X-ray photons can penetrate deep into the intergalactic medium (IGM), leading to pre-heating of the IGM prior to cosmic reionization. X-ray pre-heating wipes out some of the small-scale structures that would otherwise be present prior to the passage of an ionization front. Accurate modelling of the small-scale structure is vital to the post-reionization IGM, since the small-scale structure is ultimately the dominant source of long-lasting relics from hydrogen reionization. However, the precise impact of X-ray pre-heating in the fossils from hydrogen reionization is highly uncertain. In this work, we explore and establish for the first time, the long-lasting impact of X-ray pre-heating in the post-reionization IGM via hydrodynamic simulations with high-mass resolution. We find that the addition of X-ray pre-heating astrophysics leads to an overall lesser impact of the effect of inhomogeneous reionization in the Lyα forest – depending on specific X-ray prescription – at low redshifts (z ∼ 2) with respect to a model with no X-ray pre-heating. However, at high redshifts (z ∼ 4), our results indicate a strengthening of the relics of reionization in the Lyα forest because the IGM becomes more transparent compared to the scenario with no pre-heating. Thus, the absence of X-ray pre-heating in Lyα modelling can lead to a biased inference of cosmological parameters. Nevertheless, optimistically, the inclusion of X-ray pre-heating emerges as a promising novel avenue to probe the astrophysics of cosmic dawn.

Large-scale excess H i absorption around z ≈ 4 galaxies detected in a background galaxy spectrum in the MUSE eXtremely deep field

ABSTRACT Observationally mapping the relation between galaxies and the intergalactic medium (IGM) is of key interest for studies of cosmic reionization. Diffuse hydrogen gas has typically been observed in H i Lyman-α (Lyα) absorption in the spectra of bright background quasars. However, it is important to extend these measurements to background galaxies as quasars become increasingly rare at high redshift and rarely probe closely separated sight lines. Here, we use deep integral field spectroscopy in the MUSE eXtremely Deep Field to demonstrate the measurement of the Lyα transmission at z ≈ 4 in absorption to a background galaxy at z = 4.77. The H i transmission is consistent with independent quasar sight lines at similar redshifts. Exploiting the high number of spectroscopic redshifts of faint galaxies (500 between z = 4.0–4.7 within a radius of 8 arcmin) that are tracers of the density field, we show that Lyα transmission is inversely correlated with galaxy density, i.e. transparent regions in the Lyα forest mark underdense regions at z ≈ 4. Due to large-scale clustering, galaxies are surrounded by excess H i absorption over the cosmic mean out to 4 cMpc/h70. We also find that redshifts from the peak of the Lyα line are typically offset from the systemic redshift by +170 km s−1. This work extends results from z ≈ 2–3 to higher redshifts and demonstrates the power of deep integral field spectroscopy to simultaneously measure the ionization structure of the IGM and the large-scale density field in the early Universe.

A Detection of Cosmological 21 cm Emission from CHIME in Cross-correlation with eBOSS Measurements of the Lyα Forest

We report the detection of 21 cm emission at an average redshift z¯=2.3 in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements of the Lyα forest from eBOSS. Data collected by CHIME over 88 days in the 400–500 MHz frequency band (1.8 < z < 2.5) are formed into maps of the sky and high-pass delay filtered to suppress the foreground power, corresponding to removing cosmological scales with k ∥ ≲ 0.13 Mpc−1 at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Lyα forest flux transmission spectra to estimate the 21 cm–Lyα cross-correlation function. Fitting a simulation-derived template function to this measurement results in a 9σ detection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals ∼6–10 times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of 21 cm emission to date, and they set the stage for future 21 cm intensity mapping analyses at z > 1.8.

Unveiling dark matter free streaming at the smallest scales with the high redshift Lyman-alpha forest

This study introduces novel constraints on the free streaming of thermal relic warm dark matter (WDM) from Lyman-α forest flux power spectra. Our analysis utilizes a high resolution, high redshift sample of quasar spectra observed using the HIRES and UVES spectrographs (z=4.2–5.0). We employ a Bayesian inference framework and a simulation-based likelihood that encompasses various parameters including the free streaming of dark matter, cosmological parameters, the thermal history of the intergalactic medium, and inhomogeneous reionization to establish lower limits on the mass of a thermal relic WDM particle of 5.7 keV (at 95% CL). This result surpasses previous limits from the Lyman-α forest through reduction of the measured uncertainties due to a larger statistical sample and by measuring clustering to smaller scales (kmax=0.2 km−1 s). The approximately two-fold improvement due to the expanded statistical sample suggests that the effectiveness of Lyman-α forest constraints on WDM models at high redshifts are limited by the availability of high quality quasar spectra. Restricting the analysis to comparable scales and thermal history priors as in prior studies (kmax&lt;0.1 km−1 s) lowers the bound on the WDM mass to 4.1 keV. As the precision of the measurements increases, it becomes crucial to examine the instrumental and modeling systematics. On the modeling front, we argue that the impact of the thermal history uncertainty on the WDM particle mass constraint has diminished due to improved independent observations. At the smallest scales, the primary source of modeling systematic arises from the structure in the peculiar velocity of the intergalactic medium and inhomogeneous reionization. Published by the American Physical Society 2024

Field-level Lyman-α forest modeling in redshift space via augmented nonlocal Fluctuating Gunn-Peterson Approximation

Context. Devising fast and accurate methods of predicting the Lyman-α forest at the field level, avoiding the computational burden of running large-volume cosmological hydrodynamic simulations, is of fundamental importance to quickly generate the massive set of simulations needed by the state-of-the-art galaxy and Lyα forest spectroscopic surveys. Aims. We present an improved analytical model to predict the Lyα forest at the field level in redshift space from the dark matter field, expanding upon the widely used Fluctuating Gunn-Peterson Approximation (FGPA). Instead of assuming a unique universal relation over the whole considered cosmic volume, we introduce a dependence on the cosmic web environment (knots, filaments, sheets, and voids) in the model, thereby effectively accounting for nonlocal bias. Furthermore, we include a detailed treatment of velocity bias in the redshift space distortion modeling, allowing the velocity bias to be cosmic-web-dependent. Methods. We first mapped the dark matter field from real to redshift space through a particle-based relation including velocity bias, depending on the cosmic web classification of the dark matter field in real space. We then formalized an appropriate functional form for our model, building upon the traditional FGPA and including a cutoff and a boosting factor mimicking a threshold and inverse-threshold bias effect, respectively, with model parameters depending on the cosmic web classification in redshift space. Eventually, we fit the coefficients of the model via an efficient Markov chain Monte Carlo scheme. Results. We find evidence for a significant difference between the same model parameters in different environments, suggesting that for the investigated setup the simple standard FGPA is not able to adequately predict the Lyα forest in the different cosmic web regimes. We reproduce the summary statistics of the reference cosmological hydrodynamic simulation that we use for comparison, yielding an accurate mean transmitted flux, probability distribution function, 3D power spectrum, and bispectrum. In particular, we achieve maximum deviation and average deviation accuracy in the Lyα forest 3D power spectrum of ∼3% and ∼0.1% up to k ∼ 0.4 h Mpc−1, and ∼5% and ∼1.8% up to k ∼ 1.4 h Mpc−1. Conclusions. Our new model outperforms previous analytical efforts to predict the Lyα forest at the field level in all the probed summary statistics, and has the potential to become instrumental in the generation of fast accurate mocks for covariance matrices estimation in the context of current and forthcoming Lyα forest surveys.

Optimal 1D Ly α forest power spectrum estimation – III. DESI early data

ABSTRACT The 1D power spectrum P1D of the Ly α forest provides important information about cosmological and astrophysical parameters, including constraints on warm dark matter models, the sum of the masses of the three neutrino species, and the thermal state of the intergalactic medium. We present the first measurement of P1D with the quadratic maximum likelihood estimator (QMLE) from the Dark Energy Spectroscopic Instrument (DESI) survey early data sample. This early sample of 54 600 quasars is already comparable in size to the largest previous studies, and we conduct a thorough investigation of numerous instrumental and analysis systematic errors to evaluate their impact on DESI data with QMLE. We demonstrate the excellent performance of the spectroscopic pipeline noise estimation and the impressive accuracy of the spectrograph resolution matrix with 2D image simulations of raw DESI images that we processed with the DESI spectroscopic pipeline. We also study metal line contamination and noise calibration systematics with quasar spectra on the red side of the Ly α emission line. In a companion paper, we present a similar analysis based on the Fast Fourier Transform estimate of the power spectrum. We conclude with a comparison of these two approaches and discuss the key sources of systematic error that we need to address with the upcoming DESI Year 1 analysis.

Analysis of the Lyman-Alpha Forest and Reionization Based on THESAN

Analysis of the Lyman-Alpha Forest and Reionization Based on THESAN

Canonical Hubble-Tension-Resolving Early Dark Energy Cosmologies Are Inconsistent with the Lyman-α Forest.

Current cosmological data exhibit discordance between indirect and some direct inferences of the present-day expansion rate H_{0}. Early dark energy (EDE), which briefly increases the cosmic expansion rate prior to recombination, is a leading scenario for resolving this "Hubble tension" while preserving a good fit to cosmic microwave background (CMB) data. However, this comes at the cost of changes in parameters that affect structure formation in the late-time universe, including the spectral index of scalar perturbations n_{s}. Here, we present the first constraints on axionlike EDE using data from the Lyman-α forest, i.e., absorption lines imprinted in background quasar spectra by neutral hydrogen gas along the line of sight. We consider two independent measurements of the one-dimensional Lyα forest flux power spectrum from the Sloan Digital Sky Survey (SDSS eBOSS) and from the MIKE/HIRES and X-Shooter spectrographs. We combine these with a baseline dataset comprised of Planck CMB data and baryon acoustic oscillation (BAO) measurements. Combining the eBOSS Lyα data with the CMB and BAO dataset reduces the 95% confidence level (C.L.) upper bound on the maximum fractional contribution of EDE to the cosmic energy budget f_{EDE} from 0.07 to 0.03 and constrains H_{0}=67.9_{-0.4}^{+0.4} km/s/Mpc (68% C.L.), with maximum aposteriori value H_{0}=67.9 km/s/Mpc. Similar results are obtained for the MIKE/HIRES and X-Shooter Lyα data. Our Lyα-based EDE constraints yield H_{0} values that are in >4σ tension with the SH0ES distance-ladder measurement and are driven by the preference of the Lyα forest data for n_{s} values lower than those required by EDE cosmologies that fit Planck CMB data. Taken at face value, the Lyα forest severely constrains canonical EDE models that could resolve the Hubble tension.

Can the low-redshift Lyman alpha forest constrain AGN feedback models?

ABSTRACT We investigate the potential of low-redshift Lyman alpha (Lyα) forest for constraining active galactic nuclei (AGNs) feedback models by analysing the Illustris and IllustrisTNG simulation at z = 0.1. These simulations are ideal for studying the impact of AGN feedback on the intergalactic medium (IGM) as they share initial conditions with significant differences in the feedback prescriptions. Both simulations reveal that the IGM is significantly impacted by AGN feedback. Specifically, feedback is stronger in Illustris and results in reducing cool baryon fraction to 23 per cent relative to 39 per cent in IllustrisTNG. However, when comparing various statistics of Lyα forest such as 2D and marginalized distributions of Doppler widths and H i column density, line density, and flux power spectrum with real data, we find that most of these statistics are largely insensitive to the differences in feedback models. This lack of sensitivity arises because of the fundamental degeneracy between the fraction of cool baryons and the H i photoionization rate (ΓHI) as their product determines the optical depth of the Lyα forest. Since the ΓHI cannot be precisely predicted from first principles, it needs to be treated as a nuisance parameter adjusted to match the observed Lyα line density. After adjusting ΓHI, the distinctions in the considered statistics essentially fade away. Only the Lyα flux power spectrum at small spatial scales exhibits potentially observable differences, although this may be specific to the relatively extreme feedback model employed in Illustris. Without independent constraints on either ΓHI or cool baryon fraction, constraining AGN feedback with low-redshift Lyα forest will be very challenging.

An Exploration of AGN and Stellar Feedback Effects in the Intergalactic Medium via the Low-redshift Lyα Forest

We explore the role of galactic feedback on the low-redshift Lyα (Lyα) forest (z ≲ 2) statistics and its potential to alter the thermal state of the intergalactic medium. Using the Cosmology and Astrophysics with Machine Learning Simulations (CAMELS) suite, we explore variations of the AGN and stellar feedback models in the IllustrisTNG and Simba subgrid models. We find that both AGN and stellar feedback in Simba play a role in setting the Lyα forest column density distribution function (CDD) and the Doppler width (b-value) distribution. The Simba AGN jet feedback mode is able to efficiently transport energy out to the diffuse IGM, causing changes in the shape and normalization of the CDD and a broadening of the b-value distribution. We find that stellar feedback plays a prominent role in regulating supermassive black hole growth and feedback, highlighting the importance of constraining stellar and AGN feedback simultaneously. In IllustrisTNG, the AGN feedback variations explored in CAMELS do not affect the Lyα forest, but varying the stellar feedback model does produce subtle changes. Our results imply that the low-z Lyα forest can be sensitive to changes in the ultraviolet background, stellar and black hole feedback, and that AGN jet feedback in particular can have a strong effect on the thermal state of the IGM.

Quasar Factor Analysis—An Unsupervised and Probabilistic Quasar Continuum Prediction Algorithm with Latent Factor Analysis

Since their first discovery, quasars have been essential probes of the distant Universe. However, due to our limited knowledge of its nature, predicting the intrinsic quasar continua has bottlenecked their usage. Existing methods of quasar continuum recovery often rely on a limited number of high-quality quasar spectra, which might not capture the full diversity of the quasar population. In this study, we propose an unsupervised probabilistic model, quasar factor analysis (QFA), which combines factor analysis with physical priors of the intergalactic medium to overcome these limitations. QFA captures the posterior distribution of quasar continua through generatively modeling quasar spectra. We demonstrate that QFA can achieve the state-of-the-art performance, ∼2% relative error, for continuum prediction in the Lyα forest region compared to previous methods. We further fit 90,678 2 < z < 3.5, signal-to-noise ratio >2 quasar spectra from Sloan Digital Sky Survey Data Release 16 and found that for ∼30% quasar spectra where the continua were ill-determined with previous methods, QFA yields visually more plausible continua. QFA also attains ≲1% error in the 1D Lyα power spectrum measurements at z ∼ 3 and ∼4% in z ∼ 2.4. In addition, QFA determines latent factors representing more physical motivation than principal component analysis. We investigate the evolution of the latent factors and report no significant redshift or luminosity dependency except for the Baldwin effect. The generative nature of QFA also enables outlier detection robustly; we showed that QFA is effective in selecting outlying quasar spectra, including damped Lyα systems and potential Type II quasar spectra.

Measuring the photoionization rate, neutral fraction, and mean free path of H i ionizing photons at 4.9 ≤ z ≤ 6.0 from a large sample of XShooter and ESI spectra

ABSTRACT We measure the mean free path ($\lambda _{\rm mfp,H\, \small {I}}$), photoionization rate ($\langle \Gamma _{\rm H\, \small {I}} \rangle$), and neutral fraction ($\langle f_{\rm H\, \small {I}} \rangle$) of hydrogen in 12 redshift bins at 4.85 &amp;lt; z &amp;lt; 6.05 from a large sample of moderate resolution XShooter and ESI QSO absorption spectra. The fluctuations in ionizing radiation field are modelled by post-processing simulations from the Sherwood suite using our new code ‘EXtended reionization based on the Code for Ionization and Temperature Evolution’ (ex-cite). ex-cite uses efficient Octree summation for computing intergalactic medium attenuation and can generate large number of high resolution $\Gamma _{\rm H\, \small {I}}$ fluctuation models. Our simulation with ex-cite shows remarkable agreement with simulations performed with the radiative transfer code Aton and can recover the simulated parameters within 1σ uncertainty. We measure the three parameters by forward-modelling the Lyα forest and comparing the effective optical depth ($\tau _{\rm eff, H\, \small {I}}$) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modelling parameters, observational systematics, and cosmic variance. Our best-fitting parameters show significant evolution with redshift such that $\lambda _{\rm mfp,H\, \small {I}}$ and $\langle f_{\rm H\, \small {I}} \rangle$ decreases and increases by a factor ∼6 and ∼104, respectively from z ∼ 5 to z ∼ 6. By comparing our $\lambda _{\rm mfp,H\, \small {I}}$, $\langle \Gamma _{\rm H\, \small {I}} \rangle$ and $\langle f_{\rm H\, \small {I}} \rangle$ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best-fitting parameter evolution is consistent with a model in which reionization completes by z ∼ 5.2. Our best-fitting model that matches the $\tau _{\rm eff, H\, \small {I}}$ distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters.

The scale of homogeneity in the Rh = ct universe

ABSTRACT Studies of the Universe’s transition to smoothness in the context of Lambda cold dark matter (ΛCDM) have all pointed to a transition radius no larger than ∼300 Mpc. These are based on a broad array of tracers for the matter power spectrum, including galaxies, clusters, quasars, the Ly-α forest, and anisotropies in the cosmic microwave background. It is therefore surprising, if not anomalous, to find many structures extending out over scales as large as ∼2 Gpc, roughly an order of magnitude greater than expected. Such a disparity suggests that new physics may be contributing to the formation of large-scale structure, warranting a consideration of the alternative Friedmann–Lemaître–Robertson–Walker cosmology known as the Rh = ct universe. This model has successfully eliminated many other problems in ΛCDM. In this paper, we calculate the fractal (or Hausdorff) dimension in this cosmology as a function of distance, showing a transition to smoothness at ∼2.2 Gpc, fully accommodating all of the giant structures seen thus far. This outcome adds further observational support for Rh = ct over the standard model.

The cross-correlation of galaxies in absorption with the Lyman α forest

ABSTRACT We present the first clustering measurement of Strong Blended Lyman α (SBLA) absorption systems by measuring their cross-correlation with the Lyman α forest. SBLAs are a new population of absorbers detected within the Lyman α forest. We find a bias of 2.329 ± 0.057, consistent with that of Damped Lyman α absorbers (DLAs). For DLAs, we recover a bias of 2.331 ± 0.057 larger than previously reported. We also find a redshift space distortion parameter β = 0.417 ± 0.010, also consistent with the recovered value for DLAs (β = 0.416 ± 0.010). This is consistent with SBLA and DLA systems tracing different portions of the circumgalactic medium of a broadly common population of galaxies. Given these common clustering properties, we combined them to perform a cross-correlation of galaxies in absorption with the Lyα forest. We find that the BAO scale uncertainty of this new measurement is 1.75 × that of Lyα autocorrelation and 1.6 × that of the quasar cross-correlation with the Lyα forest. We note that the current preferred metal contamination model for fitting the correlation functions with respect to the Lyα forest is not realistic enough for SBLA systems, likely due to their status as high redshift precision sites of high metal enrichment. Mock spectra including SBLA systems and their associated metal absorption are required to understand this sample fully. We conclude that SBLAs have the potential to complement the standard Lyα cosmological analyses in future surveys.

Cosmological-scale Lyα Forest Absorption around Galaxies and AGNs Probed with the HETDEX and SDSS Spectroscopic Data

We present cosmological-scale three-dimensional neutral hydrogen (H i) tomographic maps at z = 2–3 over a total of 837 deg2 in two blank fields that are developed with Lyα forest absorptions of 14,736 background Sloan Digital Sky Survey (SDSS) quasars at z = 2.08–3.67. Using the tomographic maps, we investigate the large-scale (≳10 h −1 cMpc) average H i radial profiles and two-direction profiles of the line-of-sight (LOS) and transverse directions around galaxies and active galactic nuclei (AGNs) at z = 2–3 identified by the Hobby–Eberly Telescope Dark Energy eXperiment survey and SDSS, respectively. The peak of the H i radial profile around galaxies is lower than the one around AGNs, suggesting that the dark matter halos of galaxies are less massive on average than those of AGNs. The LOS profile of AGNs is narrower than the transverse profile, indicating the Kaiser effect. There exist weak absorption outskirts at ≳30 h −1 cMpc beyond H i structures of galaxies and AGNs found in the LOS profiles that can be explained by the H i gas at ≳30 h −1 cMpc falling toward the source position. Our findings indicate that the H i radial profile of AGNs has transitions from proximity zones (≲a few h −1 cMpc) to the H i structures (∼1–30 h −1 cMpc) and the weak absorption outskirts (≳30 h −1 cMpc). Although there is no significant dependence of AGN types (type 1 vs. type 2) on the H i profiles, the peaks of the radial profiles anticorrelate with AGN luminosities, suggesting that AGNs’ ionization effects are stronger than the gas mass differences.

Planting a Lyman alpha forest on AbacusSummit

ABSTRACT The full-shape correlations of the Lyman alpha (Ly α) forest contain a wealth of cosmological information through the Alcock–Paczyński effect. However, these measurements are challenging to model without robustly testing and verifying the theoretical framework used for analysing them. Here, we leverage the accuracy and volume of the N-body simulation suite AbacusSummit to generate high-resolution Ly α skewers and quasi-stellar object (QSO) catalogues. One of the main goals of our mocks is to aid in the full-shape Ly α analysis planned by the Dark Energy Spectroscopic Instrument (DESI) team. We provide optical depth skewers for six of the fiducial cosmology base-resolution simulations ($L_{\rm box} = 2\, h^{-1}\, {\rm Gpc}$, N = 69123) at z = 2.5. We adopt a simple recipe based on the Fluctuating Gunn–Peterson Approximation (FGPA) for constructing these skewers from the matter density in an N-body simulation and calibrate it against the 1D and 3D Ly α power spectra extracted from the hydrodynamical simulation IllustrisTNG (TNG; $L_{\rm box} = 205\, h^{-1}\, {\rm Mpc}$, N = 25003). As an important application, we study the non-linear broadening of the baryon acoustic oscillation (BAO) peak and show the cross-correlation between DESI-like QSOs and our Ly α forest skewers. We find differences on small scales between the Kaiser approximation prediction and our mock measurements of the Ly α × QSO cross-correlation, which would be important to account for in upcoming analyses. The AbacusSummit Ly α forest mocks open up the possibility for improved modelling of cross-correlations between Ly α and cosmic microwave background (CMB) lensing and Ly α and QSOs, and for forecasts of the 3-point Ly α correlation function. Our catalogues and skewers are publicly available on Globus via the National Energy Research Scientific Computing Center (NERSC) (full link under the section ‘Data Availability’).

Boosting line intensity map signal-to-noise ratio with the Ly-α forest cross-correlation

ABSTRACT We forecast the prospects for cross-correlating future line intensity mapping (LIM) surveys with the current and future Ly-α forest measurements. Using large cosmological hydrodynamic simulations, we model the emission from the CO rotational transition in the CO Mapping Array Project LIM experiment at the 5-yr benchmark and the Ly-α forest absorption signal for extended Baryon Acoustic Oscillations (BOSS), Dark energy survey instrument (DESI), and Prime Focus multiplex Spectroscopy survey (PFS). We show that CO × Ly-α forest significantly enhances the detection signal-to-noise ratio (S/N) of CO, with up to $300{{\ \rm per\, cent}}$ improvement when correlated with the PFS Ly-α forest survey and a 50–75 per cent enhancement with the available eBOSS or the upcoming DESI observations. This is competitive with even CO × spectroscopic galaxy surveys. Furthermore, our study suggests that the clustering of CO emission is tightly constrained by CO × Ly-α forest due to the increased sensitivity and the simplicity of Ly-α absorption modelling. Foreground contamination or systematics are expected not to be shared between LIM and Ly-α forest observations, providing an unbiased inference. Ly-α forest will aid in detecting the first LIM signals. We also estimate that [C ii] × Ly-α forest measurements from Experiment for Cryogenic Large-Aperture Intensity Mapping and DESI/eBOSS should have a larger S/N than planned [C ii] × quasar observations by about an order of magnitude.

Constraining the Temperature-density Relation of the Inter-galactic Medium from Analytically Modeling Lyα Forest Absorbers

The absorption by neutral hydrogen in the intergalactic medium (IGM) produces the Lyα forest in the spectra of quasars. The Lyα forest absorbers have a broad distribution of neutral hydrogen column density N H I and Doppler b parameter. The narrowest Lyα absorption lines (of lowest b) with neutral hydrogen column density above ∼1013cm−2 are dominated by thermal broadening, which can be used to constrain the thermal state of the IGM. Here we constrain the temperature-density relation of the IGM at 1.6 < z < 3.6 by using N H I and b parameters measured from 24 high-resolution and high-signal-to-noise quasar spectra and by employing an analytic model to model the N H I-dependent low-b cutoff in the b distribution. In each N H I bin, the b cutoff is estimated using two methods, one non-parametric method from computing the cumulative b distribution and a parametric method from fitting the full b distribution. We find that the IGM temperature T 0 at the mean gas density shows a peak of ∼1.5 × 104 K at z ∼ 2.7–2.9. At redshift higher than this, the index γ approximately remains constant, and it starts to increase toward lower redshifts. The evolution in both parameters is in good agreement with constraints from completely different approaches, which signals that He ii reionization completes around z ∼ 3.

Lyman-Alpha Forest: Features, Detection Scenarios and Simulations

The Epoch of Reionization (Eop) is a very important period which helps understand the evolution and formation of our universe. The Lyman alpha emission from the highly red shift quasars provides us information of the universe during the Epoch of Reionization. The Lyman alpha forest is the spectra of the Lyman alpha emission in the spectra of quasars with high red-shift. Intergalactic medium (IGM) causes the absorption lines in the spectra. The study of Lyman-alpha forest and the Epoch of Reionization has been an been a important topic in cosmology since Gun and Peterson first detected the absorb line in the spectra of quasars. This passage wil first discuss about the formation of Lyman-alpha forest and discusses the features Lyman alpha forest and the information indicated by these features about the universe during the Eop. In the last part, this paper summarizes the detection approach of Lyman alpha forest and the simulation of IGM in EoP. These results shed light on guiding further exploration of Lyman Alpha Forest.