arXiv subjects

Mathieu Langer

Publications and source records attributed to Mathieu Langer.

At least 19 recordsLinked to original sources

arXiv2025

Velocity fields and turbulence from cosmic filaments to galaxy clusters

Galaxy clusters are currently the endpoint of the hierarchical structure formation; they form via the accretion of dark matter and cosmic gas from their local environment. In particular, filaments contribute grandly by accreting gas from cosmic matter sheets and underdense regions and feeding it to the galaxy clusters. Along the way, the gas in filaments is shocked and heated, which, together with the velocity structure within the filament, induces swirling and, thus, turbulence. In this work, we study a constrained hydrodynamical simulation replica of the Virgo cluster to characterise the velocity field in the two cosmic filaments connected to the cluster with unprecedented high resolution. First, we conduct a qualitative examination of slices extracted from the simulation. We study the temperature, the velocity field, and derived quantities in longitudinal cuts to study the general structure of the filaments and in transverse cuts to study their inner organisation and connection to cosmic matter sheets and underdense regions. Then, we conduct a quantitative study of velocities in Virgo's filaments by computing the 2D energy spectrum from 1 and 5~Mpc square maps extracted from the slices and centred on the core of the filaments. We show that the velocity field goes from mostly compressive far in the filaments to mostly solenoidal in Virgo's core. Moreover, we observe that the total energy spectrum in the filaments gains in amplitude and steepens towards Virgo.

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arXiv2021

On the relative effect of nodes and filaments of the cosmic web on the quenching of galaxies and the orientation of their spin

Filaments and clusters of the cosmic web have an impact on the properties of galaxies, switching off their star-formation, contributing to the build-up of their stellar mass, and influencing the acquisition of their angular momentum. In this work we make use of the IllustrisTNG simulation, coupled with the DisPerSE cosmic web extraction algorithm, to test which is the galaxy property most affected by the cosmic web and, conversely, to assess the differential impact of the various cosmic web features on a given galaxy property. Our aim is to use this information to better understand galaxy evolution and to identify on which galaxy property future efforts should focus to detect the cosmic web from the galaxy distribution. We provide a comprehensive analysis of the relation between galaxy properties and cosmic web features. We also perform extensive tests in which we try to disentangle the effect of local overdensities of galaxies on their properties from the effect of the large scale structure environment. Our results show that star-formation is the quantity that shows the strongest variation with the distances from the cosmic web features, but it is also the one that shows the strongest relation to the local environment of galaxies. On the other hand, the direction of the angular momentum of galaxies is the property that shows the weakest trends with distance from cosmic web features, while also being more independent from the local environment of galaxies. We conclude that the direction of the angular momentum of galaxies and its use to improve our detection of the cosmic web features could be the focus of futures studies benefiting from larger statistical samples.

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arXiv2021

Relative distribution of dark matter, gas, and stars around cosmic filaments in the IllustrisTNG simulation

We present a comprehensive study of the distribution of matter around different populations of large-scale cosmic filaments, using the IllustrisTNG simulation at z=0. We computed the dark matter (DM), gas, and stellar radial density profiles of filaments, and we characterise the distribution of the baryon fraction in these structures. We find that baryons exactly follow the underlying DM distribution only down to r~7 Mpc to the filament spines. At shorter distances (r<7 Mpc), the baryon fraction profile of filaments departs from the cosmic value $\Omega_\mathrm{b} / \Omega_\mathrm{m}$. While in the r~0.7-7 Mpc radial domain this departure is due to the radial accretion of the warm-hot intergalactic medium (WHIM) towards the filament cores (creating an excess of baryons with respect to the cosmic fraction), the cores of filaments (r<0.7 Mpc) show a clear baryon depletion instead. The analysis of the efficiency of active galactic nuclei (AGN) feedback events in filaments reveals that they are potentially powerful enough to eject gas outside of the gravitational potential wells of filaments. We show that the large-scale environment (i.e. denser versus less dense, hotter versus colder regions) has a non-negligible effect on the absolute values of the DM, gas, and stellar densities around filaments. Nevertheless, the relative distribution of baryons with respect to the underlying DM density field is found to be independent of the filament population. Finally, we provide scaling relations between the gas density, temperature, and pressure for the different populations of cosmic filaments. We compare these relations to those pertaining to clusters of galaxies, and find that these cosmic structures occupy separate regions of the density-temperature and density-pressure planes.

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arXiv2020

Properties of gas phases around cosmic filaments at z=0 in the Illustris-TNG simulation

We present the study of gas phases around cosmic-web filaments detected in the TNG300-1 hydro-dynamical simulation at redshift z=0. We separate the gas in five different phases according to temperature and density. We show that filaments are essentially dominated by gas in the warm-hot intergalactic medium (WHIM), which accounts for more than 80% of the baryon budget at $r \sim 1$ Mpc. Apart from WHIM gas, cores of filaments ($r<1$ Mpc) also host large contributions other hotter and denser gas phases, whose fractions depend on the filament population. By building temperature and pressure profiles, we find that gas in filaments is isothermal up to $r \sim 1.5$ Mpc, with average temperatures of T_core = $4-13 \times 10^5$ K, depending on the large scale environment. Pressure at cores of filaments is on average P_core = $4-12 \times 10^{-7}$ keV/cm^3, which is ~1000 times lower than pressure measured in observed clusters. We also estimate that the observed Sunyaev-Zel'dovich (SZ) signal from cores of filaments should range between $0.5 < y < 4.1 \times 10^{-8}$, and these results are compared with recent observations. Our findings show that the state of the gas in filaments depend on the presence of haloes, and on the large scale environment.

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arXiv2020

Improved constraints on reionisation from CMB observations: A parameterisation of the kSZ effect

We show that, in the context of patchy reionisation, an accurate description of the angular power spectrum of the kinetic Sunyaev-Zel'dovich (kSZ) effect is not possible with simple scaling relations between the amplitude of the spectrum and global parameters, such as the reionisation midpoint and its duration. We introduce a new parameterisation of this spectrum, based on a novel description of the power spectrum of the free electrons density contrast Pee (k,z) in terms of the reionisation global history and morphology. We directly relate features of the spectrum to the typical ionised bubble size at different stages in the process and, subsequently, to the angular scale at which the patchy kSZ power spectrum reaches its maximum. We successfully calibrated our results on a custom set of advanced radiative hydrodynamical simulations and later found our parameterisation to be a valid description of a wide range of other simulations and, therefore, reionisation physics. In the end, and as long as the global reionisation history is known, two parameters are sufficient to derive the angular power spectrum. Such an innovative framework applied to cosmic microwave background data and combined with 21cm intensity mapping will allow a first consistent detection of the amplitude and shape of the patchy kSZ signal, giving in turn access to the physics of early light sources.

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arXiv2020

Populations of filaments from the distribution of galaxies in numerical simulations

We present a statistical study of the filamentary structures of the cosmic web in the large hydro-dynamical simulations Illustris-TNG, Illustris, and Magneticum at redshift z=0. We focus on the radial distribution of the galaxy density around filaments detected using the Discrete Persistent Structure Extractor (DisPerSE). We show that the average profile of filaments presents an excess of galaxy density (> 5 sigma) up to radial distances of 27 Mpc from the core. The relation between galaxy density and the length of filaments is further investigated showing that short (L_f < 9 Mpc) and long (L_f > 20 Mpc) filaments are two statistically different populations. Short filaments are puffier, denser, and more connected to massive objects, whereas long filaments are thinner, less dense, and more connected to less massive structures. These two populations trace different environments and may correspond to bridges of matter between over-dense structures (short filaments), and to cosmic filaments shaping the skeleton of the cosmic web (long filaments). Through Markov Chain Monte Carlo (MCMC) explorations, we find that the density profiles of both short and long filaments can be described by the same empirical models (generalised Navarro, Frenk and White, beta-model, a single and a double power law) with different and distinct sets of parameters.

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arXiv2018

Magnetizing the Cosmic Web during Reionization

Increasing evidence suggests that cosmological sheets, filaments, and voids may be substantially magnetized today. The origin of magnetic fields in the intergalactic medium (IGM) is, however, currently uncertain. It seems well known that non-standard extensions to the physics of the standard model can provide mechanisms susceptible of magnetizing the universe at large. Perhaps less well known is the fact that standard, classical physics of matter--radiation interactions actually possesses the same potential. We discuss a magnetogenesis mechanism based on the exchange of momentum between hard photons and electrons in an inhomogeneous IGM. Operating in the neighborhood of ionizing sources during the epoch of reionization, this mechanism is capable of generating magnetic seeds of relevant strengths over scales comparable to the distance between ionizing sources. In addition, summing up the contributions of all ionizing sources and taking into account the distribution of gas inhomogeneities, we show that this mechanism leaves the IGM, at the end of reionization, with a level of magnetization that might account, when amplification mechanisms take over, for the magnetic fields strengths in the current cosmic web.

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arXiv2018

Magnetising the Cosmic Web during Reionisation

Evidence repeatedly suggests that cosmological sheets, filaments and voids may be substantially magnetised today. The origin of magnetic fields in the intergalactic medium is however currently uncertain. We discuss a magnetogenesis mechanism based on the exchange of momentum between hard photons and electrons in an inhomogeneous intergalactic medium. Operating near ionising sources during the epoch of reionisation, it is capable of generating magnetic seeds of relevant strengths over scales comparable to the distance between ionising sources. Furthermore, when the contributions of all ionising sources and the distribution of gas inhomogeneities are taken into account, it leads, by the end of reionisation, to a level of magnetisation that may account for the current magnetic fields strengths in the cosmic web.

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arXiv2018

Analytic growth rate of gravitational instability in self-gravitating planar polytropes

Gravitational instability is a key process that may lead to fragmentation of gaseous structures (sheets, filaments, haloes) in astrophysics and cosmology. We introduce here a method to derive analytic expressions for the growth rate of gravitational instability in a plane stratified medium. We consider a pressure-confined, static, self-gravitating fluid of arbitrary polytropic exponent, with both free and rigid boundary conditions. The method we detail here can naturally be generalised to analyse the stability of more complex systems. Our analytical results are in excellent agreement with numerical resolutions.

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arXiv2017

Mean Energy Density of Photogenerated Magnetic Fields Throughout the Epoch of Reionization

Magnetic fields are ubiquitous in the Universe. They seem to be present at virtually all scales and all epochs. Yet, whether the fields on cosmological scales are of astrophysical or cosmological origin remains an open major problem. Here we focus on an astrophysical mechanism based on the photoionization of the intergalactic medium during the Epoch of Reionization. Building upon previous studies that depicted the physical mechanism around isolated sources of ionization, we present here an analytic model to estimate the level at which this mechanism contributed to the magnetization of the whole Universe, thanks to the distribution of sources, before and alongside early luminous structure formation. This model suggests that the Universe may be globally magnetized to the order of, at least, a few $10^{-20}$~G comoving (i.e. several $10^{-18}$~G during the Epoch of Reionization) by this mechanism, prior to any amplification process.

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arXiv2017

Observational constraints on key-parameters of cosmic reionisation history

We discuss constraints on cosmic reionisation and their implications on a cosmic SFR density $\rho_\mathrm{SFR}$ model; we study the influence of key-parameters such as the clumping factor of ionised hydrogen in the intergalactic medium (IGM) $C_{H_{II}}$ and the fraction of ionising photons escaping star-forming galaxies to reionise the IGM $f_\mathrm{esc}$. Our analysis uses SFR history data coming from luminosity functions, assuming that star-forming galaxies were sufficient to lead the reionisation process at high redshift. We add two other sets of constraints: measurements of the IGM ionised fraction and the most recent result from Planck Satellite about the integrated Thomson optical depth of the Cosmic Microwave Background (CMB) $\tau_\mathrm{Planck}$. We also consider various possibilities for the evolution of these two parameters with redshift, and confront them with observational data cited above. We conclude that, if the model of a constant clumping factor is chosen, the fiducial value of $3$ often used in papers is consistent with observations; even if a redshift-dependent model is considered, the resulting optical depth is strongly correlated to $C_{H_{II}}$ mean value at $z>7$, an additional argument in favour of the use of a constant clumping factor. Besides, the escape fraction is related to too many astrophysical parameters to allow us to use a complete and fully satisfactory model. A constant value with redshift seems again to be the most likely expression: considering it as a fit parameter, we get from the maximum likelihood (ML) model $f_\mathrm{esc}=0.24\pm0.08$; with a redshift-dependent model, we find an almost constant evolution, slightly increasing with $z$, around $f_\mathrm{esc}=0.23$. Last, our analysis shows that a reionisation beginning as early as $z\geq14$ and persisting until $z\sim6$ is a likely storyline.

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arXiv2016

ATCA observations of the MACS-Planck Radio Halo Cluster Project - I. New detection of a radio halo in PLCK G285.0-23.7

We investigate the possible presence of diffuse radio emission in the intermediate redshift, massive cluster PLCK G285.0-23.7 (z=0.39, M_500 = 8.39 x 10^(14) M_Sun). Our 16cm-band ATCA observations of PLCK G285.0-23.7 allow us to reach a rms noise level of ~11 microJy/beam on the wide-band (1.1-3.1 GHz), full-resolution (~5 arcsec) image of the cluster, making it one of the deepest ATCA images yet published. We also re-image visibilities at lower resolution in order to achieve a better sensitivity to low-surface-brightness extended radio sources. We detect one of the lowest luminosity radio halos known at z>0.35, characterised by a slight offset from the well-studied 1.4 GHz radio power vs. cluster mass correlation. Similarly to most known radio-loud clusters (i.e. those hosting diffuse non-thermal sources), PLCK G285.0-23.7 has a disturbed dynamical state. Our analysis reveals a similarly elongated X-ray and radio morphology. While the size of the radio halo in PLCK G285.0-23.7 is smaller than lower redshift radio-loud clusters in the same mass range, it shows a similar correlation with the cluster virial radius, as expected in the framework of hierarchical structure formation.

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arXiv2015

A new parameterization of the reionisation history

Motivated by the current constraints on the epoch of reionisation from recent cosmic microwave background observations, ionising background measurements of star-forming galaxies, and low redshifts line-of-sight probes, we propose a new data-motivated parameterisation of the history of the average ionisation fraction. This parameterisation describes a flexible redshift-asymmetric reionisation process in two regimes that is capable of fitting all the current constraints.

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arXiv2015

Intergalactic Magnetogenesis at Cosmic Dawn by Photoionization

We present a detailed analysis of an astrophysical mechanism that generates cosmological magnetic fields during the Epoch of Reionization. It is based on the photoionization of the Intergalactic Medium by the first sources formed in the Universe. First the induction equation is derived, then the characteristic length and time scales of the mechanism are identified, and finally numerical applications are carried out for first stars, primordial galaxies and distant powerful quasars. In these simple examples, the strength of the generated magnetic fields varies between the order of $10^{-23}$ G on hundreds of kiloparsecs to $10^{-19}$ G on hundreds of parsecs in the neutral Intergalactic Medium between the Str\"omgren spheres of the sources. Thus this mechanism contributes to the premagnetization of the whole Universe before large scale structures are in place. It operates with any ionizing source, at any time during the Epoch of Reionization. Finally, the generated fields possess a characteristic spatial configuration which may help discriminate these seeds from those produced by different mechanisms.

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arXiv2015

SKA Deep Polarization and Cosmic Magnetism

Deep surveys with the SKA1-MID array offer for the first time the opportunity to systematically explore the polarization properties of the microJy source population. Our knowledge of the polarized sky approaching these levels is still very limited. In total intensity the population will be dominated by star-forming and normal galaxies to intermediate redshifts ($z \sim1-2$), and low-luminosity AGN to high redshift. The polarized emission from these objects is a powerful probe of their intrinsic magnetic fields and of their magnetic environments. For redshift of order 1 and above the broad bandwidth of the mid-bands span the Faraday thick and thin regimes allowing study of the intrinsic polarization properties of these objects as well as depolarization from embedded and foreground plasmas. The deep field polarization images will provide Rotation Measures data with very high solid angle density allowing a sensitive statistical analysis of the angular variation of RM on critical arc-minute scales from a magnetic component of Large Scale Structure of the Universe.

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arXiv2011

Second order cross-correlation between kSZ and 21 cm fluctuations from the EoR

The measurement of the brightness temperature fluctuations of neutral hydrogen 21 cm lines from the Epoch of Reionisation (EoR) is expected to be a powerful tool for revealing the reionisation process. We study the 21 cm cross-correlation with Cosmic Microwave Background (CMB) temperature anisotropies, focusing on the effect of the patchy reionisation. We calculate, up to second order, the angular power spectrum of the cross-correlation between 21 cm fluctuations and the CMB kinetic Sunyaev-Zel'dovich effect (kSZ) from the EoR, using an analytical reionisation model. We show that the kSZ and the 21 cm fluctuations are anti-correlated on the scale corresponding to the typical size of an ionised bubble at the observed redshift of the 21 cm fluctuations. The amplitude of the angular power spectrum of the cross-correlation depends on the fluctuations of the ionised fraction. Especially, in a highly inhomogeneous reionisation model, the amplitude reaches the order of $100 μK^2$ at $\ell \sim 3000$. We also show that second order terms may help in distinguishing between reionisation histories.

astro-ph.CO↗

arXiv2009

Detectability of the 21 cm-CMB cross-correlation from the EoR

The 21-cm line fluctuations and the cosmic microwave background (CMB) are powerful probes of the epoch of reionisation of the universe. We study the potential of the cross-correlation between 21-cm line fluctuations and CMB anisotropy to obtain further constraints on the reionisation history. We compute analytically the 21-cm cross-correlation with the CMB temperature anisotropy and polarisation, and we calculate the signal-to-noise (SN) ratio for its detection with Planck together with LOFAR, MWA and SKA. We find, on the one hand, that the 21-cm cross-correlation signal with CMB polarisation from the instant reionisation can be detected with an SN ratio of $\sim 1$ for LOFAR and $\sim 10$ for SKA. On the other hand, we confirm that the detection of the 21-cm cross-correlation with CMB polarisation is practically infeasible.

astro-ph.CO↗

arXiv2009

Cross-correlation Study between the Cosmological 21-cm Signal and the kinetic Sunyaev-Zel'dovich effect

The Universe's Epoch of Reionization (EoR) can be studied using a number of observational probes that provide complementary or corroborating information. Each of these probes suffers from its own systematic and statistical uncertainties. It is therefore useful to consider the mutual information that these data sets contain. In this paper we present a cross-correlation study between the kinetic Sunyaev-Zel'dovich effect (kSZ) -- produced by the scattering of CMB photons off free electrons produced during the reionization process -- and the cosmological 21cm signal -- which reflects the neutral hydrogen content of the Universe, as a function of redshift. The study is carried out using a simulated reionization history in 100Mpc/h scale N-body simulations with radiative transfer. In essence we find that the two probes anti-correlate. The significance of the anti-correlation signal depends on the extent of the reionization process, wherein extended histories result in a much stronger signal compared to instantaneous cases. Unfortunately however, once the primary CMB fluctuations are included into our simulation they serve as a source of large correlated noise that renders the cross-correlation signal insignificant, regardless of the reionization scenario.

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