Astrophysicist

Category: cosmology

Martizzi et al. (2019)

Baryons in the Cosmic Web of IllustrisTNG – I: gas in knots, filaments, sheets, and voids

by
Martizzi, Davide; Vogelsberger, Mark; Artale, Maria Celeste; Haider, Markus; Torrey, Paul; Marinacci, Federico; Nelson, Dylan; Pillepich, Annalisa; Weinberger, Rainer; Hernquist, Lars; Naiman, Jill; Springel, Volker

abstract
We analyse the IllustrisTNG simulations to study the mass, volume fraction, and phase distribution of gaseous baryons embedded in the knots, filaments, sheets, and voids of the Cosmic Web from redshift z = 8 to redshift z = 0. We find that filaments host more star-forming gas than knots, and that filaments also have a higher relative mass fraction of gas in this phase than knots. We also show that the cool, diffuse intergalactic medium [IGM; T< 10^5 K, n_H< 10^{-4}(1+z) cm^{-3}] and the warm-hot intergalactic medium [WHIM; 10^5 < T< 10^7 K, n_H < 10^{-4}(1+z) cm^{-3}] constitute {̃ } 39 and {̃ } 46{{ per cent}} of the baryons at redshift z = 0, respectively. Our results indicate that the WHIM may constitute the largest reservoir of missing baryons at redshift z = 0. Using our Cosmic Web classification, we predict the WHIM to be the dominant baryon mass contribution in filaments and knots at redshift z = 0, but not in sheets and voids where the cool, diffuse IGM dominates. We also characterize the evolution of WHIM and IGM from redshift z = 4 to redshift z = 0, and find that the mass fraction of WHIM in filaments and knots evolves only by a factor of ̃2 from redshift z = 0 to 1, but declines faster at higher redshift. The WHIM only occupies 4-11 per cent of the volume at redshift 0 ≤ z ≤ 1. We predict the existence of a significant number of currently undetected O VII and Ne IX absorption systems in cosmic filaments, which could be detected by future X-ray telescopes like Athena.

published in
Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 3, p.3766-3787, July 2019

links to paper
[ADS][arXiv]

Villaescusa-Navarro et al. (2018)

Ingredients for 21 cm Intensity Mapping

by
Villaescusa-Navarro, Francisco; Genel, Shy; Castorina, Emanuele; Obuljen, Andrej; Spergel, David N.; Hernquist, Lars; Nelson, Dylan; Carucci, Isabella P.; Pillepich, Annalisa; Marinacci, Federico; Diemer, Benedikt; Vogelsberger, Mark; Weinberger, Rainer; Pakmor, Rüdiger

author
Current and upcoming radio telescopes will map the spatial distribution of cosmic neutral hydrogen (H I) through its 21 cm emission. In order to extract the maximum information from these surveys, accurate theoretical predictions are needed. We study the abundance and clustering properties of H I at redshifts z ≤ 5 using TNG100, a large state-of-the-art magnetohydrodynamic simulation of a 75 h -1Mpc box size, which is part of the IllustrisTNG Project. We show that most of the H I lies within dark matter halos, and we provide fits for the halo H I mass function, i.e., the mean H I mass hosted by a halo of mass M at redshift z. We find that only halos with circular velocities larger than ≃30 km s-1contain H I. While the density profiles of H I exhibit a large halo-to-halo scatter, the mean profiles are universal across mass and redshift. The H I in low-mass halos is mostly located in the central galaxy, while in massive halos the H I is concentrated in the satellites. Our simulation reproduces the bias value of damped Lyα systems from observations. We show that the H I and matter density probability distribution functions differ significantly. Our results point out that for small halos, the H I bulk velocity goes in the same direction and has the same magnitude as the halo peculiar velocity, while in large halos, differences show up. We find that halo H I velocity dispersion follows a power law with halo mass. We find a complicated H I bias, with H I already becoming nonlinear at k = 0.3 h Mpc-1 at z ≳ 3. The clustering of H I can, however, be accurately reproduced by perturbative methods. We find a new secondary bias by showing that the clustering of halos depends not only on mass but also on H I content. We compute the amplitude of the H I shot noise and find that it is small at all redshifts, verifying the robustness of BAO measurements with 21 cm intensity mapping. We study the clustering of H I in redshift space and show that linear theory can explain the ratio between the monopoles in redshift and real space down to 0.3, 0.5, and 1 h Mpc-1 at redshifts 3, 4, and 5, respectively. We find that the amplitude of the Fingers-of-God effect is larger for H I than for matter, since H I is found only in halos above a certain mass. We point out that 21 cm maps can be created from N-body simulations rather than full hydrodynamic simulations. Modeling the one-halo term is crucial for achieving percent accuracy with respect to a full hydrodynamic treatment. Although our results are not converged against resolution, they are, however, very useful as we work at the resolution where the model parameters have been calibrated to reproduce galaxy properties.

published in
The Astrophysical Journal, Volume 866, Issue 2, article id. 135, 41 pp. (October 2018).

links to paper
[ADS][arXiv]

Springel et al. (2018)

First results from the IllustrisTNG simulations: matter and galaxy clustering

by
Springel, Volker; Pakmor, Rüdiger; Pillepich, Annalisa; Weinberger, Rainer; Nelson, Dylan; Hernquist, Lars; Vogelsberger, Mark; Genel, Shy; Torrey, Paul; Marinacci, Federico; Naiman, Jill

abstract
Hydrodynamical simulations of galaxy formation have now reached sufficient volume to make precision predictions for clustering on cosmologically relevant scales. Here, we use our new IllustrisTNG simulations to study the non-linear correlation functions and power spectra of baryons, dark matter, galaxies, and haloes over an exceptionally large range of scales. We find that baryonic effects increase the clustering of dark matter on small scales and damp the total matter power spectrum on scales up to k ̃ 10 h Mpc-1 by 20 per cent. The non-linear two-point correlation function of the stellar mass is close to a power-law over a wide range of scales and approximately invariant in time from very high redshift to the present. The two-point correlation function of the simulated galaxies agrees well with Sloan Digital Sky Survey at its mean redshift z ≃ 0.1, both as a function of stellar mass and when split according to galaxy colour, apart from a mild excess in the clustering of red galaxies in the stellar mass range of109-1010 h-2 M. Given this agreement, the TNG simulations can make valuable theoretical predictions for the clustering bias of different galaxy samples. We find that the clustering length of the galaxy autocorrelation function depends strongly on stellar mass and redshift. Its power-law slope γ is nearly invariant with stellar mass, but declines from γ ̃ 1.8 at redshift z = 0 to γ ̃ 1.6 at redshift z ̃ 1, beyond which the slope steepens again. We detect significant scale dependences in the bias of different observational tracers of large-scale structure, extending well into the range of the baryonic acoustic oscillations and causing nominal (yet fortunately correctable) shifts of the acoustic peaks of around ̃ 5 per cent.

published in
Monthly Notices of the Royal Astronomical Society, Volume 475, Issue 1, p.676-698, March 2018

links to paper
[ADS][arXiv]

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