arXiv subjects

Matteo Viel

Publications and source records attributed to Matteo Viel.

At least 73 records · Page 4Linked to original sources

arXiv2021

Constraining beyond $Λ$CDM models with 21cm intensity mapping forecast observations combined with latest CMB data

We explore constraints on dark energy and modified gravity with forecast 21cm intensity mapping measurements using the Effective Field Theory approach. We construct a realistic mock data set forecasting a low redshift 21cm signal power spectrum $P_{21}(z,k)$ measurement from the MeerKAT radio-telescope. We compute constraints on cosmological and model parameters through Monte Carlo Markov chain techniques, testing both the constraining power of $P_{21}(k)$ alone and its effect when combined with the latest Planck 2018 CMB data. We complement our analysis by testing the effects of tomography from an ideal mock data set of observations in multiple redshift bins. We conduct our analysis numerically with the codes EFTCAMB/EFTCosmoMC, which we extend by implementing a likelihood module fully integrated with original codes. We find that adding $P_{21}(k)$ to CMB data provides significantly tighter constraints on $Ω_ch^2$ and $H_0$, with a reduction of the error with respect to Planck results at the level of more than $60\%$. For the parameters describing beyond $Λ$CDM theories, we observe a reduction in the error with respect to the Planck constraints at the level of $\lesssim 10\%$. The improvement increases up to $\sim 35\%$ when we constrain the parameters using ideal, tomographic mock observations. We conclude that the power spectrum of the 21cm signal is sensitive to variations of the parameters describing the examined beyond $Λ$CDM models and, thus, $P_{21}(k)$ observations could help to constrain dark energy. The constraining power on such theories is improved significantly by tomography.

astro-ph.CO↗

arXiv2021

The Quijote simulations

The Quijote simulations are a set of 44,100 full N-body simulations spanning more than 7,000 cosmological models in the $\{Ω_{\rm m}, Ω_{\rm b}, h, n_s, σ_8, M_ν, w \}$ hyperplane. At a single redshift the simulations contain more than 8.5 trillions of particles over a combined volume of 44,100 $(h^{-1}{\rm Gpc})^3$; each simulation follow the evolution of $256^3$, $512^3$ or $1024^3$ particles in a box of $1~h^{-1}{\rm Gpc}$ length. Billions of dark matter halos and cosmic voids have been identified in the simulations, whose runs required more than 35 million core hours. The Quijote simulations have been designed for two main purposes: 1) to quantify the information content on cosmological observables, and 2) to provide enough data to train machine learning algorithms. In this paper we describe the simulations and show a few of their applications. We also release the Petabyte of data generated, comprising hundreds of thousands of simulation snapshots at multiple redshifts, halo and void catalogs, together with millions of summary statistics such as power spectra, bispectra, correlation functions, marked power spectra, and estimated probability density functions.

astro-ph.CO↗

arXiv2021

Joint constraints on thermal relic dark matter from strong gravitational lensing, the Lyman-$α$ forest, and Milky Way satellites

We derive joint constraints on the warm dark matter (WDM) half-mode scale by combining the analyses of a selection of astrophysical probes: strong gravitational lensing with extended sources, the Lyman-$α$ forest, and the number of luminous satellites in the Milky Way. We derive an upper limit of $λ_{\rm hm}=0.089{\rm~Mpc~h^{-1} }$ at the 95 per cent confidence level, which we show to be stable for a broad range of prior choices. Assuming a Planck cosmology and that WDM particles are thermal relics, this corresponds to an upper limit on the half-mode mass of $M_{\rm hm }< 3 \times 10^{7} {\rm~M_{\odot}~h^{-1}}$, and a lower limit on the particle mass of $m_{\rm th }> 6.048 {\rm~keV}$, both at the 95 per cent confidence level. We find that models with $λ_{\rm hm}> 0.223 {\rm~Mpc~h^{-1} }$ (corresponding to $m_{\rm th }> 2.552 {\rm~keV}$ and $M_{\rm hm }< 4.8 \times 10^{8} {\rm~M_{\odot}~h^{-1}}$) are ruled out with respect to the maximum likelihood model by a factor $\leq 1/20$. For lepton asymmetries $L_6>10$, we rule out the $7.1 {\rm~keV}$ sterile neutrino dark matter model, which presents a possible explanation to the unidentified $3.55 {\rm~keV}$ line in the Milky Way and clusters of galaxies. The inferred 95 percentiles suggest that we further rule out the ETHOS-4 model of self-interacting DM. Our results highlight the importance of extending the current constraints to lower half-mode scales. We address important sources of systematic errors and provide prospects for how the constraints of these probes can be improved upon in the future.

astro-ph.CO↗

arXiv2021

The impact of massive neutrinos on halo assembly bias

Using the publicly available Quijote simulations, we present the first measurements of the assembly bias of dark matter halos in N-body simulations which include massive neutrinos. We focus on the dependence of the linear bias $b_1$ on three halo properties: 1) concentration $c$, 2) spin $λ$, and 3) ellipticity $s$. Although these simulations cover a large volume, superior to any future surveys, we do not detect any effect of neutrinos on the relations $b_1(c)$, $b_1(λ)$ and $b_1(s)$ at fixed halo mass. We further study the dependence of halo properties and environment on neutrinos, finding these quantities to be impacted by neutrino masses at the same level as assembly bias. We find that the effect of neutrinos on spin and shape can be largely attributed to the change in the cold dark matter $σ_8$ in neutrinos simulations, which is not the case for concentration.

astro-ph.CO↗

arXiv2021

Quantifying the impact of baryon-CDM perturbations on halo clustering and baryon fraction

Baryons and cold dark matter (CDM) did not comove prior to recombination. This leads to differences in the local baryon and CDM densities, the so-called baryon-CDM isocurvature perturbations $δ_{bc}$. These perturbations are usually neglected in the analysis of Large-Scale Structure data but taking them into account might become important in the era of high precision cosmology. Using gravity-only 2-fluid simulations we assess the impact of such perturbations on the dark matter halos distribution. In particular, we focus on the baryon fraction in halos as a function of mass and large-scale $δ_{bc}$, which also allows us to study details of the nontrivial numerical setup required for such simulations. We further measure the cross-power spectrum between the halo field and $δ_{bc}$ over a wide range of mass. This cross-correlation is nonzero and negative which shows that halo formation is impacted by $δ_{bc}$. We measure the associated bias parameter $b_{δ_{bc}}$ and compare it to recent results, finding good agreement. Finally we quantify the impact of such perturbations on the halo-halo power spectrum and show that this effect can be degenerate with the one of massive neutrinos for surveys like DESI.

astro-ph.CO↗

arXiv2021

Reionization and galaxy inference from the high-redshift Lyα forest

The transmission of Lyman-α (Lyα) in the spectra of distant quasars depends on the density, temperature, and ionization state of the intergalactic medium (IGM). Therefore, high-redshift (z > 5) Lyα forests could be invaluable in studying the late stages of the epoch of reionization (EoR), as well as properties of the sources that drive it. Indeed, high-quality quasar spectra have now firmly established the existence of large-scale opacity fluctuations at z > 5, whose physical origins are still debated. Here we introduce a Bayesian framework capable of constraining the EoR and galaxy properties by forward-modelling the high-z Lyα forest. Using priors from galaxy and CMB observations, we demonstrate that the final overlap stages of the EoR (when >95% of the volume was ionized) should occur at z < 5.6, in order to reproduce the large-scale opacity fluctuations seen in forest spectra. However, it is the combination of patchy reionization and the inhomogeneous UV background that produces the longest Gunn-Peterson troughs. Lyα forest observations tighten existing constraints on the characteristic ionizing escape fraction of galaxies, with the combined observations suggesting f_{\rm esc} \approx 7^4_3%, and disfavoring a strong evolution with the galaxy's halo (or stellar) mass.

astro-ph.CO↗

arXiv2020

Sources of $H_0$-tensions in dark energy scenarios

By focusing on the simple $w\neq-1$ extension to $Λ$CDM, we assess which epoch(s) possibly source the $H_0$-tension. We consider Cosmic Microwave Background (CMB) data in three possible ways: $i)$ complete CMB data; $ii)$ excluding the $l<30$ temperature and polarization likelihoods; $iii)$ imposing early universe priors, that disentangle early and late time physics. Through a joint analysis with low-redshift supernovae type-Ia and gravitationally lensed time delay datasets, {and neglecting galaxy clustering Baryonic Acoustic Oscillation (BAO) data}, we find that the inclusion of early universe CMB priors is consistent with the local estimate of $H_0$ while excluding the low-$l$+lowE likelihoods mildly relaxes the tension. This is in contrast to joint analyses with the complete CMB data. Our simple implementation of contrasting the effect of different CMB priors on the $H_0$ estimate shows that the early universe information from the CMB data when decoupled from late-times physics could be in agreement with a higher value of $H_0$. {We also find no evidence for the early dark energy model using only the early universe physics within the CMB data. Finally using the BAO data in different redshift ranges to perform inverse distance ladder analysis, we find that the early universe modifications, while being perfectly capable of alleviating the $H_0$-tension when including the BAO galaxy clustering data, would be at odds with the Ly-$α$ BAO data due to the difference in $r_{\rm d}\, vs.\, H_0$ correlation between the two BAO datasets.} We therefore infer and speculate that source for the $H_0$-tension between CMB and local estimates could possibly originate in the modeling of late-time physics within the CMB analysis. This in turn recasts the $H_0$-tension as an effect of late-time physics in CMB, instead of the current early-time CMB vs. local late-time physics perspective.

astro-ph.CO↗

arXiv2020

The evolution of the low-density HI intergalactic medium from z=3.6 to 0: Data, transmitted flux and HI column density

We present a new, uniform analysis of the HI transmitted flux (F) and HI column density (N(HI)) distribution in the low-density IGM as a function of redshift z for 0<z<3.6 using 55 HST/COS FUV (Delta(z)=7.2 at z<0.5), five HST/STIS+COS NUV (Delta(z)=1.3 at z~1) and 24 VLT/UVES and Keck/HIRES (Delta(z)=11.6 at 1.7<z<3.6) AGN spectra. We performed a consistent, uniform Voigt profile analysis to combine spectra taken with different instruments, to reduce systematics and to remove metal-line contamination. We confirm previously known conclusions on firmer quantitative grounds in particular by improving the measurements at z~1. Two flux statistics at 0<F<1, the mean HI flux and the flux probability distribution function (PDF), show that considerable evolution occurs from z=3.6 to z=1.5, after which it slows down to become effectively stable for z<0.5. However, there are large sightline variations. For the HI column density distribution function (CDDF, f proptional to N(HI)^(-beta)) at log (N(HI)/1cm^-2)=[13.5, 16.0], beta increases as z decreases from beta~1.60 at z~3.4 to beta~1.82 at z~0.1. The CDDF shape at lower redshifts can be reproduced by a small amount of clockwise rotation of a higher-z CDDF with a slightly larger CDDF normalisation. The absorption line number per z (dn/dz) shows a similar evolutionary break at z~1.5 as seen in the flux statistics. High-N(HI) absorbers evolve more rapidly than low-N(HI) absorbers to decrease in number or cross-section with time. The individual dn/dz shows a large scatter at a given z. The scatter increases toward lower z, possibly caused by a stronger clustering at lower z.

astro-ph.CO↗

arXiv2020

Exploring galaxies-gravitational waves cross-correlations as an astrophysical probe

Gravitational waves astronomy has opened a new opportunity to study the Universe. Full exploitation of this window can especially be provided by combining data coming from gravitational waves experiments with luminous tracers of the Large Scale Structure, like galaxies. In this work we investigate the cross-correlation signal between gravitational waves resolved events, as detected by the Einstein Telescope, and actively star-forming galaxies. The galaxies distribution is computed through their UV and IR luminosity functions and the gravitational waves events, assumed to be of stellar origin, are self-consistently computed from the aforementioned galaxies distribution. We provide a state-of-the-art treatment both on the astrophysical side, taking into account the impact of the star formation and chemical evolution histories of galaxies, and in computing the cross-correlation signal, for which we include lensing and relativistic effects. We find that the measured cross-correlation signal can be sufficiently strong to overcome the noise and provide a clear signal. As a possible application of this methodology, we consider a proof-of-concept case in which we aim at discriminating a metallicity dependence on the compact objects merger efficiency against a reference case with no metallicity dependence. When considering galaxies with a Star Formation Rate $ψ> 10 \: M_{\odot} /\rm{yr}$, a Signal-to-Noise ratio around a value of 2-4 is gained after a decade of observation time, depending on the observed fraction of the sky. This formalism can be exploited as an astrophysical probe and could potentially allow to test and compare different astrophysical scenarios.

astro-ph.CO↗

arXiv2020

Constraints on the Spacetime Dynamics of an Early Dark Energy Component

We consider an Early Dark Energy (EDE) cosmological model, and perform an analysis which takes into account both background and perturbation effects via the parameters $c^{2}_{\rm eff}$ and $c^{2}_{\rm vis}$, representing effective sound speed and viscosity, respectively. By using the latest available data we derive constraints on the amount of dark energy at early times and the present value of the equation of state. Our focus is on the effect that early dark energy has on the Cosmic Microwave Background (CMB) data, including polarization and lensing, in a generalized parameter space including a varying total neutrino mass, and tensor to scalar ratio, besides the 6 standard parameters of the minimal cosmological model. We find that the inclusion of Baryonic Acoustic Oscillations (BAO) data and CMB lensing significantly improves the constraints on the EDE parameters, while other high redshift data like the Quasar Hubble diagram and the Lyman-$α$ forest BAO have instead a negligible impact. We find $Ω_{\rm eDE} < 0.00391 $ and $w_{0} < -0.9500 $ at the $95 \%$ C.L. for EDE accounting for its clustering through the inclusion of perturbation dynamics. This limit becomes weaker $Ω_{\rm eDE} < 0.00337$ if perturbations are neglected. The constraints on the EDE parameters are remarkably stable even when $Σm_ν$, and $r$ parameters are varied, with weak degeneracies between $Ω_{\rm eDE}$ and $r$ or $Σm_ν$. Perturbation parameters are not constrained with current data sets, and tensions between the CMB derived $H_0$ and $σ_8$ values and those measured with local probes are not eased. This work demonstrates the capability of CMB probes to constrain the total amount of EDE well below the percent level.

astro-ph.CO↗

arXiv2020

Impact of dark matter models on the EoR 21-cm signal bispectrum

The nature of dark matter sets the timeline for the formation of first collapsed halos and thus affects the sources of reionization. Here, we consider two different models of dark matter: cold dark matter (CDM) and thermal warm dark matter (WDM), and study how they impact the epoch of reionization (EoR) and its 21-cm observables. Using a suite of simulations, we find that in the WDM scenarios, the structure formation on small scales gets suppressed resulting in a smaller number of low mass dark matter halos compared to the CDM scenario. Assuming that the efficiency of sources in producing ionizing photons remain the same, this leads to a lower number of total ionizing photons produced at any given cosmic time and thus in a delay in the reionization process. We also find visual differences in the neutral hydrogen (HI) topology and in 21-cm maps in case of the WDM compared to the CDM. However, differences in the 21-cm power spectra, at the same neutral fraction, are found to be small. Thus, we focus on the non-Gaussianity in the EoR 21-cm signal, quantified through its bispectrum. We find that the 21-cm bispectra (driven by the HI topology) are significantly different in WDM models when compared with CDM, even for same mass averaged neutral fractions. This establishes that the 21-cm bispectrum is a unique and promising way to differentiate between different dark matter models, and can be used to constrain the nature of the dark matter in the future EoR observations.

astro-ph.CO↗

arXiv2020

Non-linear damping of superimposed primordial oscillations on the matter power spectrum in galaxy surveys

Galaxy surveys are an important probe for superimposed oscillations on the primordial power spectrum of curvature perturbations, which are predicted in several theoretical models of inflation and its alternatives. In order to exploit the full cosmological information in galaxy surveys it is necessary to study the matter power spectrum to fully non-linear scales. We therefore study the non-linear clustering in models with superimposed linear and logarithmic oscillations to the primordial power spectrum by running high-resolution dark-matter-only N-body simulations. We fit a Gaussian envelope for the non-linear damping of superimposed oscillations in the matter power spectrum to the results of the N-body simulations for $k \lesssim 0.6\ h/$Mpc at $0 \leq z \leq 5$ with an accuracy below the percent. We finally use this fitting formula to forecast the capabilities of future galaxy surveys, such as Euclid and Subaru, to probe primordial oscillation down to non-linear scales alone and in combination with the information contained in CMB anisotropies.

astro-ph.CO↗

arXiv2020

Late-time decaying dark matter: constraints and implications for the $H_0$-tension

We constrain and update the bounds on the life-time of a decaying dark matter model with a warm massive daughter particle using the most recent low-redshift probes. We use Supernovae Type-Ia, Baryon Acoustic Oscillations and the time delay measurements of gravitationally lensed quasars. These data sets are complemented by the early universe priors taken from the Cosmic Microwave background. For the maximum allowed fraction of the relativistic daughter particle, the updated bounds on the life-time are found to be $τ> 9\, \rm{Gyr}$ and $τ>11\,\rm{Gyr}$ at $95\%$ C.L., for the two-body and many-body decay scenarios, respectively. We also comment on the recent proposal that the current two-body decaying dark matter model can provide resolution for the $H_0$-tension, by contrasting against the standard $Λ$CDM model. We infer that the current dark matter decaying scenario is unlikely to alleviate the $H_0$-tension. We find that the decaying dark matter is able to reduce the trend of the decreasing $H_0$ values with increasing lens redshifts observed in the strong lensing dataset.

astro-ph.CO↗

arXiv2020

The impact of relativistic effects on the 3D Quasar-Lyman-$α$ cross-correlation

We study the impact of relativistic effects in the 3-dimensional cross-correlation between Lyman-$α$ forest and quasars. Apart from the relativistic effects, which are dominated by the Doppler contribution, several systematic effects are also included in our analysis (intervening metals, unidentified high column density systems, transverse proximity effect and effect of the UV fluctuations). We compute the signal-to-noise ratio for the Baryonic Oscillation Spectroscopic Survey (BOSS), the extended Baryonic Oscillation Spectroscopic Survey (eBOSS) and the Dark Energy Spectroscopic Instrument (DESI) surveys, showing that DESI will be able to detect the Doppler contribution in a Large Scale Structure (LSS) survey for the first time, with a S/N $>7$ for $r_{\rm min} > 10$ Mpc$/h$, where r$_{\rm min}$ denotes the minimum comoving separation between sources. We demonstrate that several physical parameters, introduced to provide a full modelling of the cross-correlation function, are affected by the Doppler contribution. By using a Fisher matrix approach, we establish that if the Doppler contribution is neglected in the data analysis, the derived parameters will be shifted by a non-negligible amount for the upcoming surveys.

astro-ph.CO↗

arXiv2020

$H_0$ Reconstruction with Type Ia Supernovae, Baryon Acoustic Oscillation and Gravitational Lensing Time-Delay

There is a persistent $H_0$-tension, now at more than $\gtrsim 4σ$ level, between the local distance ladder value and the \emph{Planck} cosmic microwave background measurement, in the context of flat $Λ$CDM model. We reconstruct $H(z)$ in a cosmological-model-independent way using three low-redshift distance probes including the latest data from baryon acoustic oscillation, Type Ia supernova and four gravitational lensing Time-Delay observations. We adopt general parametric models of $H(z)$ and assume a Gaussian prior on the sound horizon at drag epoch, $r_{\mathrm s}$, from \emph{Planck} measurement. The reconstructed $H_0$ using Pantheon SN Ia and BAO data are consistent with the \emph{Planck} flat $Λ$CDM value. When including the GLTD data, $H_0$ increases mildly, yet remaining discrepant with the local measurement at $\sim 2.5σ$ level. Our reconstructions being blind to the dark sectors at low redshift, we reaffirm the earlier claims that the Hubble tension is not likely to be solved by modifying the energy budget of the low-redshift universe. We further forecast the constraining ability of future realistic mock BAO data from DESI and GLTD data from LSST, combining which, we anticipate that the uncertainty of the inferred $H_0$ would be improved by $\sim 38\%$, reaching $σ_{H_0} \approx 0.56$ uncertainty level.

astro-ph.CO↗

arXiv2019

Beyond two-point statistics: using the minimum spanning tree as a tool for cosmology

Cosmological studies of large-scale structure have relied on two-point statistics, not fully exploiting the rich structure of the cosmic web. In this paper we show how to capture some of this cosmic web information by using the minimum spanning tree (MST), for the first time using it to estimate cosmological parameters in simulations. Discrete tracers of dark matter such as galaxies, $N$-body particles or haloes are used as nodes to construct a unique graph, the MST, that traces skeletal structure. We study the dependence of the MST on cosmological parameters using haloes from a suite of COLA simulations with a box size of $250\ h^{-1}{\rm Mpc}$, varying the amplitude of scalar fluctuations $\left(A_{\rm s}\right)$, matter density $\left(Ω_{\rm m}\right)$, and neutrino mass $\left(\sum m_ν\right)$. The power spectrum $P$ and bispectrum $B$ are measured for wavenumbers between $0.125$ and $0.5$ $h{\rm Mpc}^{-1}$, while a corresponding lower cut of $\sim12.6$ $h^{-1}{\rm Mpc}$ is applied to the MST. The constraints from the individual methods are fairly similar but when combined we see improved $1σ$ constraints of $\sim 17\%$ ($\sim 12\%$) on $Ω_{\rm m}$ and $\sim 12\%$ ($\sim 10\%$) on $A_{\rm s}$ with respect to $P$ ($P+B$) thus showing the MST is providing additional information. The MST can be applied to current and future spectroscopic surveys (BOSS, DESI, Euclid, PSF, WFIRST, and 4MOST) in 3D and photometric surveys (DES and LSST) in tomographic shells to constrain parameters and/or test systematics.

astro-ph.CO↗

arXiv2019

The atomic Hydrogen content of the post-reionization Universe

We present a comprehensive analysis of atomic hydrogen (HI) properties using a semi-analytical model of galaxy formation and N-body simulations covering a large cosmological volume at high resolution. We examine the HI mass function and the HI density, characterizing both their redshift evolution and their dependence on hosting halo mass. We analyze the HI content of dark matter haloes in the local Universe and up to redshift $z=5$, discussing the contribution of different galaxy properties. We find that different assembly history plays a crucial role in the scatter of this relation. We propose new fitting functions useful for constructing mock HI maps with HOD techniques. We investigate the HI clustering properties relevant for future $21$~cm Intensity Mapping (IM) experiments, including the HI bias and the shot noise level. The HI bias increases with redshift and it is roughly flat on the largest scales probed. The scale dependency is found at progressively larger scales with increasing redshift, apart from a dip feature at $z=0$. The shot-noise values are consistent with the ones inferred by independent studies, confirming that shot-noise will not be a limiting factor for IM experiments. We detail the contribution from various galaxy properties on the HI power spectrum and their relation to the halo bias. We find that HI poor satellite galaxies play an important role at the scales of the 1-halo term. Finally, we present the $21$~cm signal in redshift space, a fundamental prediction to be tested against data from future radio telescopes such as SKA.

astro-ph.CO↗

arXiv2019

Neutrino masses and cosmology with Lyman-alpha forest power spectrum

We present constraints on neutrino masses, the primordial fluctuation spectrum from inflation, and other parameters of the $Λ$CDM model, using the one-dimensional Ly$α$-forest power spectrum measured by Palanque-Delabrouille et al. (2013) from SDSS-III/BOSS, complemented by Planck 2015 cosmic microwave background (CMB) data and other cosmological probes. This paper improves on the previous analysis by Palanque-Delabrouille et al. (2015) by using a more powerful set of calibrating hydrodynamical simulations that reduces uncertainties associated with resolution and box size, by adopting a more flexible set of nuisance parameters for describing the evolution of the intergalactic medium, by including additional freedom to account for systematic uncertainties, and by using Planck 2015 constraints in place of Planck 2013. Fitting Ly$α$ data alone leads to cosmological parameters in excellent agreement with the values derived independently from CMB data, except for a weak tension on the scalar index $n_s$. Combining BOSS Ly$α$ with Planck CMB constrains the sum of neutrino masses to $\sum m_ν< 0.12$ eV (95\% C.L.) including all identified systematic uncertainties, tighter than our previous limit (0.15 eV) and more robust. Adding Ly$α$ data to CMB data reduces the uncertainties on the optical depth to reionization $τ$, through the correlation of $τ$ with $σ_8$. Similarly, correlations between cosmological parameters help in constraining the tensor-to-scalar ratio of primordial fluctuations $r$. The tension on $n_s$ can be accommodated by allowing for a running ${\mathrm d}n_s/{\mathrm d}\ln k$. Allowing running as a free parameter in the fits does not change the limit on $\sum m_ν$. We discuss possible interpretations of these results in the context of slow-roll inflation.

astro-ph.CO↗