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Abstract
Investigating the spin parameter distribution of subhaloes in two high resolution isolated halo simulations, re- cent work by Onions et al. suggested that typical subhalo spins are consistently lower than the spin distribution found for field haloes. To further examine this puzzle, we have analyzed simulations of a cosmological volume with sufficient resolution to resolve a significant subhalo population. We confirm the result of Onions et al. and show that the typical spin of a subhalo decreases with decreasing mass and increasing proximity to the host halo center. We interpret this as the growing influence of tidal stripping in removing the outer layers, and hence the higher angular momentum particles, of the subhaloes as they move within the host potential. Investigating the redshift dependence of this effect, we find that the typical subhalo spin is smaller with decreasing redshift. This indicates a temporal evolution as expected in the tidal stripping scenario.
Highlights
In the standard model of structure formation, the rotation velocities of disc galaxies are correlated with the spin properties of their surrounding dark matter halos (Fall & Efstathiou 1980)
The halo spin is an important parameter in many semianalytic models of galaxy formation (Kauffmann et al 1993, 1997; Frenk et al 1997; Cole et al 2000; Benson et al 2001; Bower et al 2006; Croton et al 2006; Bertone et al 2007; De Lucia & Blaizot 2007; Font et al 2008; Benson 2012) and a number of studies have investigated the spin of individual dark matter halos in cosmological simulations (Peebles 1969; Bullock et al 2001; Hetznecker & Burkert 2006; Bett et al 2007; Gottlöber & Yepes 2007; Maccio et al 2007; Knebe & Power 2008; Antonuccio-Delogu et al 2010; Wang et al 2011; Lacerna & Padilla 2012; Bryan et al 2013; Trowland et al 2013)
To understand further whether tidal stripping of high angular momentum material could cause the lower subhalo spin distribution, we investigate the radial dependence of the subhalo spins
Summary
In the standard model of structure formation, the rotation velocities of disc galaxies are correlated with the spin properties of their surrounding dark matter halos (Fall & Efstathiou 1980). Onions et al (2013) investigated the spin distribution of subhalos in two high-resolution simulations of a Milky Waylike halo (the Aquarius simulation Springel et al 2008 and the GHALO simulation Stadel et al 2009) analyzed by a variety of subhalo finders They suggested that subhalo spins are significantly offset to lower values than those seen in typical distribution functions fitted to halos (Bullock et al 2001; Bett et al 2007). Colín et al (2004) found the spin parameter distribution of isolated dwarf dark matter halos to be perfectly consistent with that of larger halos This suggests that the consistently lower spin of substructure is not due to the generally smaller mass of subhalos, but is more likely related to tidal stripping of high angular momentum material.
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