Subhalo demographics in the Illustris simulation: effects of baryons and halo-to-halo variation

Abstract

We study the abundance of subhaloes in the hydrodynamical cosmological simulation Illustris, which includes both baryons and dark matter in a ΛCDM volume 106.5 Mpc a side. We compare Illustris to its dark matter-only (DMO) analog, Illustris-Dark, and quantify the effects of baryonic processes on the demographics of subhaloes in the host mass range 10 11 to 3 × 10 14 M . We focus on both the evolved (z = 0) subhalo cumulative mass functions (SHMF) and the statistics of subhaloes ever accreted, i.e. infall subhalo mass function. We quantify the variance in subhalo abundance at fixed host mass and investigate the physical reasons responsible for such scatter. We find that in Illustris, baryonic physics impacts both the infall and z = 0 subhalo abundance by tilting the DMO function and suppressing the abundance of low-mass subhaloes. The breaking of self-similarity in the subhalo abundance at z = 0 is enhanced by the inclusion of baryonic physics. The non-monotonic alteration of the evolved subhalo abundances can be explained by the modification of the concentration-mass relation of Illustris hosts compared to Illustris-Dark. Interestingly, the baryonic implementation in Illustris does not lead to an increase in the halo-to-halo variation compared to Illustris-Dark. In both cases, the fractional intrinsic scatter today is larger for Milky Way-like haloes than for cluster-sized objects. For Milky Way-like haloes, it increases from about eight per cent at infall to about 25 per cent at the current epoch. In both runs, haloes of fixed mass formed later host more subhaloes than early formers.

Disruption of satellite galaxies in simulated groups and clusters: the roles of accretion time, baryons, and pre-processing

“…To 9 This threshold is not fully equivalent to M z = 0 tot > 5 × 10 8 M in the DMonly (DMO) version, because the DM particles in the DMO simulations also account for the mass contributed by baryons and are therefore more massive, by a factor of (1 − Ω b /Ω m ) −1 = 1.19. 10 Note that the absolute survival fractions in the DM-only simulation of Chua et al (2017) are significantly higher than in our Fig. 4, because they do not explicitly include the pre-processing phase.…”

“…The small net influence of baryons is also is at odds with the recent study of Chua et al (2017), who found that, in the Illustris simulation, the inclusion of baryons reduces the survival fraction by ≈ 5-20 per cent, at all masses. It is plausible that these differences reflect different sub-grid physics implementations, so that a destabilizing effect of gas stripping dominates in Illustris, while it is approximately cancelled by the cohesive effect of star formation in Hydrangea 10 .…”

“…Because of its complexity, this problem needs to be addressed with numerical simulations (see, e.g., van den Bosch & Ogiya 2018). Since the late 1990s, these have achieved sufficiently high resolution to avoid ubiquitous numerical dissolution of satellite galaxies (or 'subhaloes'; e.g., Ghigna et al 1998;Moore et al 1999;Springel et al 2001Springel et al , 2008Gao et al 2012), which prompted a multitude of studies that analysed their evolution and survival in detail (e.g., Tormen et al 1998;De Lucia et al 2004;Gao et al 2004;Weinberg et al 2008;Dolag et al 2009;Xie & Gao 2015;Chua et al 2017;. The qualitatively consistent conclusion from these studies is that subhaloes survive for a limited amount of time, with the lowest survival rate (i.e., fastest disruption) at both the highest and lowest ends of the subhalo mass range.…”

“…An inherent limitation in all numerical studies is that limited resolution precludes the identification of subhaloes below a limiting mass, even if they are physically not completely disrupted. If survival is defined as the subhalo retaining at least a given number of particles (e.g., Gao et al 2004;Xie & Gao 2015; van den Bosch 2017) or a minimum mass set by the resolution of the simulation (e.g., Chua et al 2017), simulations with higher resolution predict higher survival fractions: for example, Xie & Gao (2015) found that in the Phoenix dark matter only galaxy cluster simulations (Gao et al 2012), which resolve each cluster with ∼10 8 particles, more than half of all subhaloes with mass above 10 10 M accreted at z = 2 survive to the present day.…”

Enhanced cluster lensing models with measured galaxy kinematics

“…Limousin et al 2009, Munari et al 2016, 2017. Such a comparison can shed light on baryionic processes shaping cluster substructure, dynamical processes leading to halo stripping in different environments, and indirectly on the nature of dark matter (Despali & Vegetti 2017;Chua et al 2017;Nipoti et al 2018;Niemiec et al 2019).…”