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Register a new userEvolution of cosmic filaments and of their galaxy population from MHD cosmological simulations
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Despite containing about a half of the total matter in the Universe, at most wavelengths the filamentary structure of the cosmic web is difficult to observe. In this work, we use large unigrid cosmological simulations to investigate how the geometrical, thermodynamical and magnetic properties of cosmological filaments vary with mass and redshift (z $leq 1$). We find that the average temperature, length, volume and magnetic field of filaments are tightly log-log correlated with the underlying total gravitational mass. This reflects the role of self-gravity in shaping their properties and enables statistical predictions of their observational properties based on their mass. We also focus on the properties of the simulated population of galaxy-sized halos within filaments, and compare their properties to the results obtained from the spectroscopic GAMA survey. Simulated and observed filaments with the same length are found to contain an equal number of galaxies, with very similar distribution of halo masses. The total number of galaxies within each filament and the total/average stellar mass in galaxies can now be used to predict also the large-scale properties of the gas in the host filaments across tens or hundreds of Mpc in scale. These results are the first steps towards the future use of galaxy catalogues in order to select the best targets for observations of the warm-hot intergalactic medium.
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We review recent progress in the description of the formation and evolution of galaxy clusters in a cosmological context by using numerical simulations. We focus our presentation on the comparison between simulated and observed X-ray properties, while we will also discuss numerical predictions on properties of the galaxy population in clusters. Many of the salient observed properties of clusters, such as X-ray scaling relations, radial profiles of entropy and density of the intracluster gas, and radial distribution of galaxies are reproduced quite well. In particular, the outer regions of cluster at radii beyond about 10 per cent of the virial radius are quite regular and exhibit scaling with mass remarkably close to that expected in the simplest case in which only the action of gravity determines the evolution of the intra-cluster gas. However, simulations generally fail at reproducing the observed cool-core structure of clusters: simulated clusters generally exhibit a significant excess of gas cooling in their central regions, which causes an overestimate of the star formation and incorrect temperature and entropy profiles. The total baryon fraction in clusters is below the mean universal value, by an amount which depends on the cluster-centric distance and the physics included in the simulations, with interesting tensions between observed stellar and gas fractions in clusters and predictions of simulations. Besides their important implications for the cosmological application of clusters, these puzzles also point towards the important role played by additional physical processes, beyond those already included in the simulations. We review the role played by these processes, along with the difficulty for their implementation, and discuss the outlook for the future progress in numerical modeling of clusters.
We analyse cosmological hydrodynamical simulations of galaxy clusters to study the X-ray scaling relations between total masses and observable quantities such as X-ray luminosity, gas mass, X-ray temperature, and $Y_{X}$. Three sets of simulations are performed with an improved version of the smoothed particle hydrodynamics GADGET-3 code. These consider the following: non-radiative gas, star formation and stellar feedback, and the addition of feedback by active galactic nuclei (AGN). We select clusters with $M_{500} > 10^{14} M_{odot} E(z)^{-1}$, mimicking the typical selection of Sunyaev-Zeldovich samples. This permits to have a mass range large enough to enable robust fitting of the relations even at $z sim 2$. The results of the analysis show a general agreement with observations. The values of the slope of the mass-gas mass and mass-temperature relations at $z=2$ are 10 per cent lower with respect to $z=0$ due to the applied mass selection, in the former case, and to the effect of early merger in the latter. We investigate the impact of the slope variation on the study of the evolution of the normalization. We conclude that cosmological studies through scaling relations should be limited to the redshift range $z=0-1$, where we find that the slope, the scatter, and the covariance matrix of the relations are stable. The scaling between mass and $Y_X$ is confirmed to be the most robust relation, being almost independent of the gas physics. At higher redshifts, the scaling relations are sensitive to the inclusion of AGNs which influences low-mass systems. The detailed study of these objects will be crucial to evaluate the AGN effect on the ICM.
A large portion of the baryons at low redshifts are still missing from detection. Most of the missing baryons are believed to reside in large scale cosmic filaments. Understanding the distribution of baryons in filaments is crucial for the search for missing baryons. We investigate the properties of cosmic filaments since $z=4.0$ in a cosmological hydrodynamic simulation, focusing on the density and temperature profiles perpendicular to the filament spines. Our quantitative evaluation confirm the rapid growth of thick and prominent filaments after $z=2$. We find that the local linear density of filaments shows correlation with the local diameter since $z=4.0$. The averaged density profiles of both dark matter and baryonic gas in filaments of different width show self-similarity, and can be described by an isothermal single-beta model. The typical gas temperature increases as the filament width increasing, and is hotter than $10^6$ K for filaments with width $D_{fil} gtrsim 4.0 rm{Mpc}$, which would be the optimal targets for the search of missing baryons via thermal Sunyaev-Zeldovich (SZ) effect. The temperature rises significantly from the boundary to the inner core regime in filaments with $D_{fil} gtrsim 4.0 rm{Mpc}$, probably due to heating by accretion shock, while the temperature rise gently in filaments with $D_{fil}< 4.0 rm{Mpc}$.
Cosmological N-body simulations represent an excellent tool to study the formation and evolution of dark matter (DM) halos and the mechanisms that have originated the universal profile at the largest mass scales in the Universe. In particular, the combination of the velocity dispersion $sigma_mathrm{v}$ with the density $rho$ can be used to define the pseudo-entropy $S(r)=sigma_mathrm{v}^2/rho^{,2/3}$, whose profile is well-described by a simple power-law $Spropto,r^{,alpha}$. We analyze a set of cosmological hydrodynamical re-simulations of massive galaxy clusters and study the pseudo-entropy profiles as traced by different collisionless components in simulated galaxy clusters: DM, stars, and substructures. We analyze four sets of simulations, exploring different resolution and physics (N-body and full hydrodynamical simulations) to investigate convergence and the impact of baryons. We find that baryons significantly affect the inner region of pseudo-entropy profiles as traced by substructures, while DM particles profiles are characterized by an almost universal behavior, thus suggesting that the level of pseudo-entropy could represent a potential low-scatter mass-proxy. We compare observed and simulated pseudo-entropy profiles and find good agreement in both normalization and slope. We demonstrate, however, that the method used to derive observed pseudo-entropy profiles could introduce biases and underestimate the impact of mergers. Finally, we investigate the pseudo-entropy traced by the stars focusing our interest in the dynamical distinction between intracluster light (ICL) and the stars bound to the brightest cluster galaxy (BCG): the combination of these two pseudo-entropy profiles is well-described by a single power-law out to almost the entire cluster virial radius.
Bose-Einstein Condensate Dark Matter (BECDM; also known as Fuzzy Dark Matter) is motivated by fundamental physics and has recently received significant attention as a serious alternative to the established Cold Dark Matter (CDM) model. We perform cosmological simulations of BECDM gravitationally coupled to baryons and investigate structure formation at high redshifts ($z gtrsim 5$) for a boson mass $m=2.5cdot 10^{-22}~{rm eV}$, exploring the dynamical effects of its wavelike nature on the cosmic web and the formation of first galaxies. Our BECDM simulations are directly compared to CDM as well as to simulations where the dynamical quantum potential is ignored and only the initial suppression of the power spectrum is considered -- a Warm Dark Matter-like (WDM) model often used as a proxy for BECDM. Our simulations confirm that WDM is a good approximation to BECDM on large cosmological scales even in the presence of the baryonic feedback. Similarities also exist on small scales, with primordial star formation happening both in isolated haloes and continuously along cosmic filaments; the latter effect is not present in CDM. Global star formation and metal enrichment in these first galaxies are delayed in BECDM/WDM compared to the CDM case: in BECDM/WDM first stars form at $zsim 13$/$13.5$ while in CDM star formation starts at $zsim 35$. The signature of BECDM interference, not present in WDM, is seen in the evolved dark matter power spectrum: although the small scale structure is initially suppressed, power on kpc scales is added at lower redshifts. Our simulations lay the groundwork for realistic simulations of galaxy formation in BECDM.
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