Evolution of Mass and Velocity Field in the Cosmic Web: Comparison Between Baryonic and Dark Matter

Abstract

We investigate the evolution of cosmic web since z = 5 in grid based cosmological hydrodynamical simulations, focusing on the mass and velocity field of both baryonic and cold dark matter. The tidal tensor of density is used as the main method for web identification, with λ th = 0.2 − 1.2. The evolution trends in baryonic and dark matter are similar, while moderate differences are observed. Sheets appeared early and their large scale pattern may have been set up by z = 3. In term of mass, filaments superseded sheets as the primary collapsing structures at z ∼ 2 − 3. Tenuous filaments assembled with each other to form prominent ones at z < 2. In accordance with the construction of the frame of sheets, the cosmic divergence velocity, v div , had been well developed above 2-3 Mpc by z=3. Afterwards, curl velocity, v curl , grown dramatically along with the rising of filaments, become comparable to v div , for < 2 − 3M pc at z = 0. The scaling of v curl can be described by the hierarchical turbulence model. The alignment between vorticity and eigenvectors of shear tensor in baryonic matter field resembles dark matter, and is even moderately stronger between ω and e 1 , and e 3 . Compared with dark matter, mildly less baryonic matter is found residing in filaments and clusters, and its vorticity has been developed more significantly below 2 − 3M pc. These differences may be underestimated due to the limited resolution and lack of star formation in our simulation. The impact of the change of dominant structures in over-dense regions at z ∼ 2 − 3 on galaxy formation and evolution is shortly discussed.

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

“…For the same classification threshold λ th and smoothing length RG (see Subsection 2.2), comparison to Forero-Romero et al (2009) indicates that the mass fraction of knots at redshift z = 0 in Illus-trisTNG is higher by a factor ∼ 2 with respect to that in dark matter only simulations. On the other hand, the mass fraction of filaments in IllustrisTNG is similar to that of the dark matter simulations of Zhu & Feng (2017) show the evolution of mass and volume fractions of the four cosmic structures identified with the same method with λ th = 0.2 and 0.4, which bracket our fiducial value λ th = 0.3, but they adopt smaller smoothing lengths RG 390 kpc/h. Furthermore, the simulations of Zhu & Feng (2017) include baryons, but they use a different set of cosmological parameters (WMAP5).…”

“…On the other hand, the mass fraction of filaments in IllustrisTNG is similar to that of the dark matter simulations of Zhu & Feng (2017) show the evolution of mass and volume fractions of the four cosmic structures identified with the same method with λ th = 0.2 and 0.4, which bracket our fiducial value λ th = 0.3, but they adopt smaller smoothing lengths RG 390 kpc/h. Furthermore, the simulations of Zhu & Feng (2017) include baryons, but they use a different set of cosmological parameters (WMAP5). These differences influence the exact values of the mass and volume fractions of each structure.…”

Baryons in the Cosmic Web of IllustrisTNG – II. The connection among galaxies, haloes, their formation time, and their location in the Cosmic Web

“…These results were based on our own Cosmic Web classification tool based on the deformation tensor of the density field (i.e. its Hessian matrix; Aragón-Calvo et al 2007;Hahn et al 2007;Sousbie et al 2009;Forero-Romero et al 2009;Zhu & Feng 2017;Cui et al 2018). This method assigns a physically-based web class to each region of the simulation at each redshift.…”

Preheating of the Intergalactic Medium by Gravitational Collapse and Ultraviolet Background

“…In addition, the fraction of halos with t cool,cir > t H is relatively higher in filaments than other morphological types of cosmic structures. The rapid growth of this fraction since z = 2 is actually in accordance to the dramatic rising of filaments during the same epoch (e.g., Zhu & Feng 2017). Low mass halos in the filaments may witness relatively stronger reduction of gas accretion due to preheating.…”

“…The threshold of eigenvalues is set to 0.8. The same method and threshold were applied in Zhu & Feng(2017), which showed that the dominant structures measured by mass fraction had transited from sheets to filaments at z ∼ 2 − 3.…”