Effects of dark matter pressure on the ellipticity of cosmic voids

TL;DR

This work explores how nonzero dark matter pressure, encoded in a pseudo-isothermal EOS $P_{\mathrm{DM}}(\rho_{\mathrm{DM}})$, impacts the ellipticity of cosmic voids. It derives the linear growth factor $D(z)$ and the transfer function $T_{\mathrm{NZPDM}}(k)$ in the presence of DM pressure and propagates these into the void-ellipticity distribution $p(\varepsilon;R_L,z)$, using a universal EOS with parameters from galaxy U5750. The key result is that DM pressure reduces small-scale power and slows density growth, leading to a shift of the void-ellipticity distribution toward more spherical shapes and a lower mean ellipticity $\langle\varepsilon\rangle$, with stronger effects at higher redshift and in the $\Lambda$CDM model, highlighting void statistics as a potential probe of DM pressure.

Abstract

The dark matter in or around the cosmic voids affects their shapes. The thermodynamical properties of dark matter can alter the ellipticity of cosmic voids. Here, applying the dark matter equation of state from the pseudo-isothermal density profile of galaxies, we explore the shapes of cosmic voids with the non zero pressure dark matter in different cosmological models. For this purpose, the linear growth of density perturbation in the presence of dark matter pressure is calculated. In addition, the matter transfer function considering the dark matter pressure, as well as the linear matter power spectrum in the presence of the dark matter pressure are presented. Employing these results, the probability density distribution for the ellipticity of cosmic voids with the non zero pressure dark matter is calculated. Our calculations verify that the dark matter pressure leads to more spherical shapes for the cosmic voids.

Figures (6)

• Figure 1: Dark matter EOS related to the galaxy U5750 with the parameters ${\rho}_0=0.31\ GeV/cm^3$ and $p_0=1.1\times 10^{-8} \ GeV/cm^3$ and $\chi^2_{min}/d.o.f.=0.01$Barranco.
• Figure 2: Linear growth factor, $D(z)$, as a function of the redshift, $z$, for two cases of zero pressure DM (ZPDM) and non zero pressure DM (NZPDM), applying different cosmological models.
• Figure 3: Matter transfer function in the cases of ZPDM and NZPDM.
• Figure 4: Probability density distribution of the void ellipticity at different values of the redshift, $z$, in the cases of zero pressure DM (ZPDM) and non zero pressure DM (NZPDM) considering different values of the Lagrangian void scale, $R_L$, in different cosmological models.
• Figure 5: Redshift dependency of $\varepsilon_{max}$ for cosmic voids with zero pressure DM (ZPDM) and non zero pressure DM (NZPDM) at different values of the Lagrangian void scale, $R_L$, applying different cosmological models.