Lyα Forest Research Articles

Measurements of Effective Optical Depth in the Lyα Forest from the BOSS DR12 Quasar Sample

Abstract We measure the effective optical depth in the Lyα forest using 40,035 quasar spectra from the Twelfth Data Release (DR12) of the Baryon Oscillation Spectroscopic Survey of Sloan Digital Sky Survey IV. A rigorous selection based on spectral index and the equivalent width of the C iv emission line is applied to choose seven uniform samples with minimal intrinsic variations across redshifts. Modeling the redshift evolution of the effective optical depth with a power law, produces and . The 2.2% precision estimate on γ is dominated by systematic errors, likely arising from the bias and uncertainties in spectral index estimates. Even after incorporating the systematic errors, this work provides the most precise estimates of optical depth parameters to date. Finally, using the reconstructed Lyα forest continuum to directly measure the transmitted flux ratio as a function of redshift, we find deviations of less than 2.5% from the predictions from the global model and no convincing evidence for signal associated with He ii reionization.

LATIS: The Lyα Tomography IMACS Survey

Abstract We introduce LATIS, the Lyα Tomography IMACS Survey, a spectroscopic survey at Magellan designed to map the z = 2.2–2.8 intergalactic medium (IGM) in three dimensions by observing the Lyα forest in the spectra of galaxies and QSOs. Within an area of 1.7 deg2, we will observe approximately half of ≳L* galaxies at z = 2.2–3.2 for typically 12 hr, providing a dense network of sightlines piercing the IGM with an average transverse separation of 2.5 h −1 comoving Mpc (1 physical Mpc). At these scales, the opacity of the IGM is expected to be closely related to the dark matter density, and LATIS will therefore map the density field in the z ∼ 2.5 universe at ∼Mpc resolution over the largest volume to date. Ultimately, LATIS will produce approximately 3800 spectra of z = 2.2–3.2 galaxies that probe the IGM within a volume of 4 × 106 h −3 Mpc3, large enough to contain a representative sample of structures from protoclusters to large voids. Observations are already complete over one-third of the survey area. In this paper, we describe the survey design and execution. We present the largest IGM tomographic maps at comparable resolution yet made. We show that the recovered matter overdensities are broadly consistent with cosmological expectations based on realistic mock surveys, that they correspond to galaxy overdensities, and that we can recover structures identified using other tracers. LATIS is conducted in Canada–France–Hawaii Telescope Legacy Survey fields, including COSMOS. Coupling the LATIS tomographic maps with the rich data sets collected in these fields will enable novel studies of environment-dependent galaxy evolution and the galaxy–IGM connection at cosmic noon.

Trend filtering – II. Denoising astronomical signals with varying degrees of smoothness

ABSTRACTTrend filtering – first introduced into the astronomical literature in Paper I of this series – is a state-of-the-art statistical tool for denoising 1D signals that possess varying degrees of smoothness. In this work, we demonstrate the broad utility of trend filtering to observational astronomy by discussing how it can contribute to a variety of spectroscopic and time-domain studies. The observations we discuss are (1) the Lyman-α (Lyα) forest of quasar spectra; (2) more general spectroscopy of quasars, galaxies, and stars; (3) stellar light curves with planetary transits; (4) eclipsing binary light curves; and (5) supernova light curves. We study the Lyα forest in the greatest detail – using trend filtering to map the large-scale structure of the intergalactic medium along quasar-observer lines of sight. The remaining studies share broad themes of: (1) estimating observable parameters of light curves and spectra; and (2) constructing observational spectral/light-curve templates. We also briefly discuss the utility of trend filtering as a tool for 1D data reduction and compression.

The ACCELERATION programme: I. Cosmology with the redshift drift

ABSTRACT Detecting the change of a cosmological object’s redshift due to the time evolution of the Universal expansion rate is an ambitious experiment that will be attempted with future telescope facilities. In this paper, we describe the ACCELERATION programme, which aims to study the properties of the most underdense regions of the Universe. One of the highlight goals of this programme is to prepare for the redshift drift measurement. Using the EAGLE cosmological hydrodynamic simulations, we estimate the peculiar acceleration of gas in galaxies and the Lyα forest. We find that star-forming ‘cold neutral gas’ exhibits large peculiar acceleration due to the high local density of baryons near star-forming regions. We conclude that absorption by cold neutral gas is unlikely to yield a detection of the cosmological redshift drift. On the other hand, we find that the peculiar accelerations of Lyα forest absorbers are more than an order of magnitude below the expected cosmological signal. We also highlight that the numerous low H i column density systems display lower peculiar acceleration. Finally, we propose a new ‘Lyα cell’ technique that applies a small correction to the wavelength calibration to secure a relative measurement of the cosmic drift between two unrelated cosmological sources at different redshifts. For suitable combinations of absorption lines, the cosmological signal can be more than doubled, while the affect of the observer peculiar acceleration is mitigated. Using current data of four suitable Lyα cells, we infer a limit on the cosmological redshift drift to be $\dot{v}_{\rm obs}\lt 65~{\rm m~s}^{-1}~{\rm yr}^{-1}$ (2σ).

TARDIS. I. A Constrained Reconstruction Approach to Modeling the z ∼ 2.5 Cosmic Web Probed by Lyα Forest Tomography

Abstract Recent Lyα forest tomography measurements of the intergalactic medium (IGM) have revealed a wealth of cosmic structures at high redshift (z ∼ 2.5). In this work, we present the Tomographic Absorption Reconstruction and Density Inference Scheme (TARDIS), a new chronocosmographic analysis tool for understanding the formation and evolution of these observed structures. We use maximum likelihood techniques with a fast nonlinear gravitational model to reconstruct the initial density field of the observed regions. We find that TARDIS allows accurate reconstruction of smaller-scale structures than standard Wiener-filtering techniques. Applying this technique to mock Lyα forest data sets that simulate ongoing and future surveys such as CLAMATO, Subaru PFS, or the ELTs, we are able to infer the underlying matter density field at observed redshift and classify the cosmic web structures. We find good agreement with the underlying truth in both the characteristic eigenvalues and eigenvectors of the pseudo-deformation tensor, with the eigenvalues inferred from 30 m class telescopes correlated at r = 0.95 relative to the truth. As an output of this method, we are able to further evolve the inferred structures to late time (z = 0) and also track the trajectories of coeval z = 2.5 galaxies to their z = 0 cosmic web environments.

The influence of metagalactic ultraviolet background fluctuations on the high-redshift Lyα forest

ABSTRACT Under the assumption that galaxies and quasi-stellar objects (QSOs) dominate the metagalactic ultraviolet (UV) background, it is shown that at high redshifts, fluctuations in the UV background are dominated by QSO shot noise and have an autocorrelation length of a few to several comoving Mpcs, depending on the bright end of the QSO luminosity function. The correlations create long-range spatial coherence in the neutral hydrogen fraction. Using a semi-analytic model, it is demonstrated that the coherence may account for the broad distribution in effective optical depths measured in the Lyα forest spectra of background QSOs, for line-of-sight segments of comoving length $50\, h^{-1}$ Mpc at redshifts 5 < z < 6. Capturing the fluctuations in a numerical simulation requires a comoving box size of ∼1 Gpc, although a box half this size may be adequate if sufficient random realizations of the QSO population are performed.

The COS CGM Compendium. III. Metallicity and Physical Properties of the Cool Circumgalactic Medium at z ≲ 1

Abstract We characterize the metallicities and physical properties of cool, photoionized gas in a sample of 152 z ≲ 1 strong Lyα forest systems (SLFSs, absorbers with 15 < log N H i < 16.2). The sample is drawn from our Cosmic Origins Spectrograph (COS) circumgalactic medium compendium (CCC), an ultraviolet survey of H i-selected circumgalactic gas around z ≲ 1 galaxies that targets 261 absorbers with 15 < log N H i < 19. We show that the metallicity probability distribution function of the SLFSs at z ≲ 1 is unimodal, skewed to low metallicities with a mean and median of [X/H] = −1.47 and −1.18 dex. Very metal-poor gas with [X/H] < −1.4 represents about half of the population of absorbers with 15 < log N H i ≲ 18, while it is rare at higher N H i . Thus, there are important reservoirs of primitive (though not pristine) diffuse ionized gas around z ≲ 1 galaxies. The photoionized gas around z ≲ 1 galaxies is highly inhomogeneous based on the wide range of metallicities observed (−3 ≲ [X/H] ≲ +0.4) and the fact that there are large metallicity variations (factors of 2 to 25) for most of the closely spaced absorbers (Δv ≲ 300 km s−1) along the same sightlines. These absorbers show a complex evolution with redshift and H i column density, and we identify subtle cosmic evolution effects that affect the interpretation of metallicity distributions and comparison with other absorber samples. We discuss the physical conditions and cosmic baryon and metal budgets of the CCC absorbers. Finally, we compare the CCC results to recent cosmological zoom simulations and explore the origins of the 15 < log N H i < 19 absorbers within the Evolution and Assembly of GaLaxies and their Environments (EAGLE) high-resolution simulations.

Simulating MOS science on the ELT: Lyα forest tomography

Mapping the large-scale structure through cosmic time has numerous applications in studies of cosmology and galaxy evolution. At z ≳ 2, the structure can be traced by the neutral intergalactic medium (IGM) by way of observing the Lyα forest towards densely sampled lines of sight of bright background sources, such as quasars and star-forming galaxies. We investigate the scientific potential of MOSAIC, a planned multi-object spectrograph on the European Extremely Large Telescope (ELT), for the 3D mapping of the IGM at z ≳ 3. We simulated a survey of 3 ≲ z ≲ 4 galaxies down to a limiting magnitude of mr ∼ 25.5 mag in an area of 1 degree2 in the sky. Galaxies and their spectra (including the line-of-sight Lyα absorption) were taken from the lightcone extracted from the Horizon-AGN cosmological hydrodynamical simulation. The quality of the reconstruction of the original density field was studied for different spectral resolutions (R = 1000 and R = 2000, corresponding to the transverse typical scales of 2.5 and 4 Mpc) and signal-to-noise ratios (S/N) of the spectra. We demonstrate that the minimum S/N (per resolution element) of the faintest galaxies that a survey like this has to reach is S/N = 4. We show that a survey with this sensitivity enables a robust extraction of cosmic filaments and the detection of the theoretically predicted galaxy stellar mass and star-formation rate gradients towards filaments. By simulating the realistic performance of MOSAIC, we obtain S/N(Tobs, R, mr) scaling relations. We estimate that ≲35 (65) nights of observation time are required to carry out the survey with the instrument’s high multiplex mode and with a spectral resolution of R = 1000 (2000). A survey with a MOSAIC-concept instrument on the ELT is found to enable the mapping of the IGM at z > 3 on Mpc scales, and as such will be complementary to and competitive with other planned IGM tomography surveys.

Three- and two-point spatial correlations of intergalactic medium at z ∼ 2 using projected quasar triplets

ABSTRACT We present analysis of two- and three-point correlation functions of Lyα forest (at 2 ≤ z ≤ 2.5) using X-Shooter spectra of three background quasar triplets probing transverse separations of 0.5–1.6 pMpc. We present statistics based on transmitted flux and clouds identified using Voigt profile fitting. We show that the observed two-, three-point correlation functions and reduced three-point correlation (i.e. Q) are well reproduced by our simulations. We assign probabilities for realizing all the observed correlation properties simultaneously using our simulations. Our simulations suggest an increase in correlation amplitudes and Q with increasing NH i. We roughly see this trend in the observations too. We identify a concurrent gap of 17Å (i.e. 14.2 h−1 cMpc, one of the longest reported) wide along one of the triplets. Such gap is realized only in 14.2 per cent of our simulated sightlines and most of the time belongs to a void in the matter distribution. In the second triplet, we detect Damped Lyα systems (DLAs) along all three sightlines (with spatial separations 0.64 to 1.6 pMpc) within a narrow redshift interval (i.e. Δz = 0.088). Detection of a foreground quasar (∼1 pMpc from the triplet sightlines) and excess partial Lyman Limit systems (with NH i in the range $10^{16-17.2} \, \mathrm{cm}^{-2}$) around these DLAs suggest that we may be probing a large overdense region. We also report positive C iv–C iv correlations up to ∼500 km s−1 only in the longitudinal direction. Additionally, we conclude a positive C iv–Lyα correlations for higher NH i thresholds (${\gt}10^{15}\, \mathrm{cm}^{-2}$) up to a scale of ∼1000 km s−1 both in transverse and longitudinal directions.

Mapping Quasar Light Echoes in 3D with Lyα Forest Tomography

Abstract The intense radiation emitted by luminous quasars dramatically alters the ionization state of their surrounding IGM. This so-called proximity effect extends out to tens of Mpc, and manifests as large coherent regions of enhanced Lyα (Lyα) forest transmission in absorption spectra of background sightlines. Here, we present a novel method based on Lyα forest tomography, which is capable of mapping these quasar “light echoes” in three dimensions. Using a dense grid (10–100) of faint ( ) background galaxies as absorption probes, one can measure the ionization state of the IGM in the vicinity of a foreground quasar, yielding detailed information about the quasar’s radiative history and emission geometry. An end-to-end analysis—combining cosmological hydrodynamical simulations post-processed with a quasar emission model, realistic estimates of galaxy number densities, and instrument + telescope throughput—is conducted to explore the feasibility of detecting quasar light echoes. We present a new, fully Bayesian statistical method that allows one to reconstruct quasar light echoes from thousands of individual low-S/N transmission measurements. Armed with this tool, we undertake an exhaustive parameter study and show that light echoes can be convincingly detected for luminous (M 1450 < −27.5 mag, corresponding to m 1450 < 18.4 mag at ) quasars at redshifts 3 < z QSO < 5, and that a relative precision better than 20% on the quasar age can be achieved for individual objects in the expected range of ages between 1 and 100 Myr. The observational requirements are relatively modest: moderate-resolution (R ≳ 750), multiobject spectroscopy at a low signal-to-noise ratio (S/N > 5) is sufficient, requiring three-hour integrations using existing instruments on 8 m class telescopes.

A search for cosmological anisotropy using the Lyman alpha forest from SDSS quasar spectra

ABSTRACT The cosmological principle, the combined assumptions of cosmological isotropy and homogeneity, underpins the standard model of big bang cosmology with which we interpret astronomical observations. A new test of isotropy over the redshift range 2 < z < 4 and across large angular scales on the sky is presented. We use the cosmological distribution of neutral hydrogen, as probed by the Ly α forest seen towards distant quasars. The Sloan Digital Sky Survey provides the largest data set of quasar spectra available to date. We use combined information from Data Releases 12 and 14 to select a sample of 142 661 quasars most suitable for this purpose. The scales covered by the data extend beyond post-inflation causality scales, thus probing initial conditions in the early Universe. We identify significant spatially correlated systematic effects that can emulate cosmological anisotropy. Once these systematics have been accounted for, the data are found to be consistent with isotropy, providing an important independent check on the standard model, consistent with results from cosmic microwave background data.

Probing inhomogeneity in the helium ionizing UV background

ABSTRACT We present an analysis combining the simultaneous measurement of intergalactic absorption by hydrogen (${\rm {H\,\small {I}}}$), helium (${\rm {He\,\small {II}}}$), and oxygen (${\rm {O\,\small {VI}}}$) in UV and optical quasar spectra. The combination of the ${\rm {H\,\small {I}}}$ and ${\rm {He\,\small {II}}}$ Lyman-alpha forests through η (the ratio of column densities of singly ionized helium to neutral hydrogen) is thought to be sensitive to large-scale inhomogeneities in the extragalactic UV background. We test this assertion by measuring associated five-times-ionized oxygen (${\rm {O\,\small {VI}}}$) absorption, which is also sensitive to the UV background. We apply the pixel optical depth technique to ${\rm {O\,\small {VI}}}$ absorption in high and low η samples filtered on various scales. This filtering scale is intended to represent the scale of any coherent oxygen excess/deficit. We find a 2σ detection of an ${\rm {O\,\small {VI}}}$ opacity excess in the low η sample on scales of ∼10 cMpc for HE 2347-4342 at $\bar{z}\approx 2.6$, consistent with a large-scale excess in hard UV photons. However, for HS 1700 + 6416 at $\bar{z}\approx 2.5$ we find that the measured ${\rm {O\,\small {VI}}}$ absorption is not sensitive to differences in η. HS 1700 + 6416 also shows a relative absence of ${\rm {O\,\small {VI}}}$ overall, which is 6σ inconsistent with that of HE 2347-4342. This implies UV background inhomogeneities on ≳200 cMpc scales, hard UV regions having internal ionization structure on ∼10 cMpc scales, and soft UV regions showing no such structure. Furthermore, we perform the pixel optical depth search for oxygen on the ${\rm {He\,\small {II}}}$ Gunn-Peterson trough of HE 2347-4342 and find results consistent with post-${\rm {He\,\small {II}}}$-reionization conditions.

Power spectrum of the flux in the Lyman-alpha forest from high-resolution spectra of 87 QSOs

Abstract We measure and calibrate the power spectrum of the flux in the Ly α forest at 1.8 < z < 4.6 for wavenumbers 0.003 ≤ k ≤ 0.1 s km−1 from the spectra of 87 QSOs obtained with HIRES on the Keck-I telescope. This is the largest sample using high-resolution spectra, yielding the smallest statistical errors, and we have applied calibrations to reduce new systematic errors. We fit Voigt profiles to the damped Ly α absorbers and we remove them. We subtract metal lines statistically based on metal absorption on the red side of the Ly α emission peak. We find that when performing a statistical subtraction of metal lines, a systematic offset due to the blending of metal and hydrogen lines must be taken into account. This offset was not accounted for in previous analyses, and requires up to a $3 {{\ \rm per\ cent}}$ reduction in the BOSS Ly α forest flux power spectrum, increasing the allowed neutrino mass. For the first time in a Ly α forest power spectrum measurement from high-resolution spectra, we correct for spectral leakage by applying Welch’s window function. Our treatment of metal line removal as well as our elimination of errors due to spectral leakage leads to a more accurate measurement of the Ly α forest power spectrum at the smallest scales. We find evidence that previously published values of the power are systematically too high at scales log k ≥ −1.3 (k ≥ 0.05) s km−1, which implies that the intergalactic medium is hotter than previously deduced from the Ly α forest flux power spectrum.

Anomaly in the Opacity of the Post-reionization Intergalactic Medium in the Lyα and Lyβ Forest

Abstract We measure the intergalactic medium (IGM) opacity in the Lyα as well as in the Lyβ forest along 19 quasar sightlines between 5.5 ≲ z abs ≲ 6.1, probing the end stages of the reionization epoch. Owing to its lower oscillator strength, the Lyβ transition is sensitive to different gas temperatures and densities than Lyα, 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 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 that come close to reproducing the distribution of Lyα effective optical depths nevertheless underpredict the Lyβ 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 ≳ 5.8.

The Spectroscopic Signature of Variability in High-redshift Quasars

Abstract Using 16,421 spectra from a sample of 340 quasars (1.62 < z < 3.30) from the Sloan Digital Sky Survey (SDSS) Reverberation Mapping Project, we present an analysis of quasar spectral variability. We confirm the intrinsic Baldwin effect (BE) and brighter-means-bluer trends in which emission line strength and color are associated with changes in luminosity. We then create a composite differential spectrum that captures the wavelength dependence of quasar variability as a function of change in luminosity. When using a bandpass around 1740 Å to describe the luminosity, the differential spectrum follows a power law at longer wavelengths that breaks blueward of 1700 Å. However, the shape of the differential spectrum, the location of the power-law break, and the slope of the intrinsic BE all vary with the choice of bandpass used to define the change in quasar luminosity. We propose that the observed behavior can be explained by inhomogeneous accretion or slim accretion disk models where delays in the reprocessing of incident light on the accretion disk cause local deviations in temperature from the thin-disk model. Finally, we quantify the effects on cosmology studies that are due to the variations in the quasar spectrum in the Lyα forest wavelength range. Using the observed spectroscopic signatures to predict the quasar continuum over the interval 1040 < λ < 1200 Å, we find that the derived spectral templates can reduce the uncertainty of the Lyα forest continuum level in individual epochs from 17.2% to 7.7%, near the level where systematic errors in SDSS flux calibration are expected to dominate.

Classification of Broad Absorption Line Quasars with a Convolutional Neural Network

Abstract Quasars that exhibit blueshifted, broad absorption lines (BAL QSOs) are an important probe of black hole feedback on galaxy evolution. Yet the presence of BALs is also a complication for large spectroscopic surveys that use quasars as cosmological probes because the BAL features can affect redshift measurements and contaminate information about the matter distribution in the Lyα forest. We present a new BAL QSO catalog for quasars in the Sloan Digital Sky Survey (SDSS) Data Release 14 (DR14). As the SDSS DR14 quasar catalog has over 500,000 quasars, we have developed an automated BAL classifier with a Convolutional Neural Network (CNN). We trained our CNN classifier on the C iv λ 1549 region of a sample of quasars with reliable human classifications, and compared the results to both a dedicated test sample and visual classifications from the earlier SDSS DR12 quasar catalog. Our CNN classifier correctly classifies over 98% of the BAL quasars in the DR12 catalog, which demonstrates comparable reliability to human classification. The disagreements are generally for quasars with lower signal-to-noise ratio spectra and/or weaker BAL features. Our new catalog includes the probability that each quasar is a BAL, the strength, blueshifts and velocity widths of the troughs, and similar information for any Si iv λ 1398 BAL troughs that may be present. We find significant BAL features in 16.8% of all quasars with 1.57 < z < 5.56 in the SDSS DR14 quasar catalog.

The one-dimensional power spectrum from the SDSS DR14 Lyα forests

We present a measurement of the 1D Lyα forest flux power spectrum, using the complete Baryon Oscillation Spectroscopic Survey (BOSS) and first extended-BOSS (eBOSS) quasars at zqso > 2.1, corresponding to the fourteenth data release (DR14) of the Sloan Digital Sky Survey (SDSS). Our results cover thirteen bins in redshift from zLyα = 2.2 to 4.6, and scales up to k = 0.02 (km/s)−1. From a parent sample of 180,413 visually inspected spectra, we selected the 43,751 quasars with the best quality; this data set improves the previous result from the ninth data release (DR9), both in statistical precision (achieving a reduction by a factor of two) and in redshift coverage. We also present a thorough investigation of identified sources of systematic uncertainties that affect the measurement. The resulting 1D power spectrum of this work is in excellent agreement with the one from the BOSS DR9 data.

UV background fluctuations and three-point correlations in the large-scale clustering of the Lyman α forest

ABSTRACT Using the Lyman α (Lyα) Mass Association Scheme, we make theoretical predictions for the three-dimensional three-point correlation function (3PCF) of the Lyα forest at redshift z = 2.3. We bootstrap results from the (100 h−1 Mpc)3 Horizon hydrodynamic simulation to a (1 h−1 Gpc)3N-body simulation, considering both a uniform ultraviolet background (UVB) and a fluctuating UVB sourced by quasars with a comoving nq ≈ 10−5h3 Mpc−3 placed either in massive haloes or randomly. On scales of 10–30 h−1 Mpc, the flux 3PCF displays hierarchical scaling with the square of the two-point correlation function (2PCF), but with an unusual value of Q ≡ ζ123/(ξ12ξ13 + ξ12ξ23 + ξ13ξ23) ≈ −4.5 that reflects the low bias of the Lyα forest and the anticorrelation between mass density and transmitted flux. For halo-based quasars and an ionizing photon mean free path of λ = 300 h−1 Mpc comoving, UVB fluctuations moderately depress the 2PCF and 3PCF, with cancelling effects on Q. For λ = 100 or 50 h−1 Mpc, UVB fluctuations substantially boost the 2PCF and 3PCF on large scales, shifting the hierarchical ratio to Q ≈ −3. We scale our simulation results to derive rough estimate of the detectability of the 3PCF in current and future observational data sets for the redshift range z = 2.1–2.6. At r = 10 and 20 h−1 Mpc, we predict a signal-to-noise ratio (SNR) of ∼9 and ∼7, respectively, for both Baryon Oscillation Spectroscopic Survey (BOSS) and extended BOSS (eBOSS), and ∼37 and ∼25 for Dark Energy Spectroscopic Instrument (DESI). At r = 40 h−1 Mpc the predicted SNR is lower by a factor of ∼3–5. Measuring the flux 3PCF would provide a novel test of the conventional paradigm of the Lyα forest and help separate the contributions of UVB fluctuations and density fluctuations to Lyα forest clustering, thereby solidifying its foundation as a tool of precision cosmology.

Ruling out 3 keV warm dark matter using 21 cm EDGES data

Weakly interacting cold dark matter (CDM) particles, which are otherwise extremely successful in explaining various cosmological observations, exhibit a number of problems on small scales. One possible way of solving these problems is to invoke (so-called) warm dark matter (WDM) particles with masses $m_x \sim$ keV. Since the formation of structure is delayed in such WDM models, it is natural to expect that they can be constrained using observations related to the first stars, e.g., the 21 cm signal from cosmic dawn. In this work, we use a detailed galaxy formation model, Delphi, to calculate the 21 cm signal at high-redshifts and compare this to the recent EDGES observations. We find that while CDM and 5 keV WDM models can obtain a 21 cm signal within the observed redshift range, reproducing the amplitude of the observations requires the introduction of an excess radio background. On the other hand, WDM models with $m_x \leq 3$ keV can be ruled out since they are unable to match either the redshift range or the amplitude of the EDGES signal, irrespective of the parameters used. Comparable to values obtained from the low-redshift Lyman Alpha forest, our results extend constraints on the WDM particle to an era inaccessible by any other means; additional forthcoming 21 cm data from the era of cosmic dawn will be crucial in refining such constraints.

Impact of inhomogeneous reionization on the Lyman-α forest

The \lya forest at high redshifts is a powerful probe of reionization. Modeling and observing this imprint comes with significant technical challenges: inhomogeneous reionization must be taken into account while simultaneously being able to resolve the web-like small-scale structure prior to reionization. In this work we quantify the impact of inhomogeneous reionization on the \lya forest at lower redshifts ($2 < z < 4$), where upcoming surveys such as DESI will enable precision measurements of the flux power spectrum. We use both small box simulations capable of handling the small-scale structure of the \lya forest and semi-numerical large box simulations capable of representing the effects of inhomogeneous reionization. We find that inhomogeneous reionization could produce a measurable effect on the \lya forest power spectrum. The deviation in the 3D power spectrum at $z_{\rm obs} = 4$ and $k = 0.14 \ \rm{Mpc}^{-1}$ ranges from $19 - 36\%$, with a larger effect for later reionization. The corrections decrease to $2.0 - 4.1\%$ by $z_{\rm obs} = 2$. The impact on the 1D power spectrum is smaller, and ranges from $3.3 - 6.5\%$ at $z_{\rm obs}=4$ to $0.35 - 0.75\%$ at $z_{\rm obs}=2$, values which are comparable to the statistical uncertainties in current and upcoming surveys. Furthermore, we study how can this systematic be constrained with the help of the quadrupole of the 21 cm power spectrum.