Abstract
ABSTRACT At high redshift, the cosmic web is widely expected to have a significant impact on the morphologies, dynamics, and star formation rates of the galaxies embedded within it, underscoring the need for a comprehensive study of the properties of such a filamentary network. With this goal in mind, we perform an analysis of high-z gas and dark matter (DM) filaments around a Milky Way-like progenitor simulated with the ramses adaptive mesh refinement (AMR) code from cosmic scales (∼1 Mpc) down to the virial radius of its DM halo host (∼20 kpc at z = 4). Radial density profiles of both gas and DM filaments are found to have the same functional form, namely a plummer-like profile modified to take into account the wall within which these filaments are embedded. Measurements of the typical filament core radius r0 from the simulation are consistent with that of isothermal cylinders in hydrostatic equilibrium. Such an analytic model also predicts a redshift evolution for the core radius of filaments in fair agreement with the measured value for DM [r0∝ (1 + z)−3.18 ± 0.28]. Gas filament cores grow as [r0∝ (1 + z)−2.72 ± 0.26]. In both gas and DM, temperature and vorticity sharply drop at the edge of filaments, providing an excellent way to constrain the outer filament radius. When feedback is included, the gas temperature and vorticity fields are strongly perturbed, hindering such a measurement in the vicinity of the galaxy. However, the core radius of the filaments as measured from the gas density field is largely unaffected by feedback; and the median central density is only reduced by about 20 per cent.
Highlights
Galactic surveys have revealed the presence of anisotropic structure on scales of Mpc, made up of nodes, voids, sheets and filaments (e.g. Davis et al 1982; de Lapparent et al 1986; Geller & Huchra 1989)
The collisionless fluid in this high resolution region consists of dark matter (DM) particles each with mass 5.6 × 104 M, whereas the gas evolution equations are solved on the adaptive mesh refinement (AMR) grid by means of a Godunov method (HLLC Riemann solver) with a MinMod limiter to reconstruct variables at cell interfaces
As the DM velocity dispersion for the particular filament we study is comparable to the gas sound speed (i.e. ∼ 10 km/s or 104K which corresponds the bottom temperature of the cooling curve for atomic hydrogen, see Fig. 7) we expect a core radius for the gas similar to that of the DM, i.e. r0 ∼ 8kpc, and this seems to be within a factor of 2 of the measured value
Summary
Galactic surveys have revealed the presence of anisotropic structure on scales of Mpc, made up of nodes, voids, sheets and filaments (e.g. Davis et al 1982; de Lapparent et al 1986; Geller & Huchra 1989). Katz et al 2003; Kereš et al 2005; Woods et al 2014; Stewart et al 2017) The erosion of these small-scale gas filaments at lower redshifts is argued to be at least partly responsible for the bimodal distribution in colour, star formation rates and morphology of galaxies (Dekel & Birnboim 2006) (though quenching of the largest galaxies are dependent on AGN feedback, see e.g. Croton et al (2006)). As gas depletion timescales are estimated to be on the order of a few Gyrs for local disk galaxies (e.g. Bigiel et al 2011; Leroy et al 2013; Rahman et al 2012), replenishment by inflow of pristine gas is required to match the observations This finding is supported by observations of extended gas disks around galaxies (co-rotating with the stellar disk), either directly in emission (e.g. from Lyman-α, Prescott et al 2015) or indirectly in absorption (e.g. from galaxy-quasar pairs, as studied in Zabl et al 2019; Ho & Martin 2019), all suggesting filamentary accretion from the cosmic web
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