Rhapsody. II. Subhalo Properties and the Impact of Tidal Stripping From a Statistical Sample of Cluster-Size Halos

TL;DR

This study analyzes the properties of subhalos in cluster-sized halos using high-resolution simulations, highlighting how selection criteria influence observed correlations and the effects of tidal stripping on subhalo characteristics.

Contribution

It demonstrates that subhalo selection based on peak maximum circular velocity reveals different correlations than current velocity-based selection, emphasizing the importance of selection criteria.

Findings

Subhalo number uncorrelated with halo formation time when selected by peak maximum circular velocity.

Tidal stripping affects the correlation between subhalo properties and halo formation history.

Main halo dominance and subhalo mass fraction are linked to halo concentration and formation history.

Abstract

We discuss the properties of subhalos in cluster-size halos, using a high-resolution statistical sample: the Rhapsody simulations introduced in Wu et al. (2012). We demonstrate that the criteria applied to select subhalos have significant impact on the inferred properties of the sample, including the scatter in the number of subhalos, the correlation between the subhalo number and formation time, and the shape of subhalos' spatial distribution and velocity structure. We find that the number of subhalos, when selected using the peak maximum circular velocity in their histories (a property expected to be closely related to the galaxy luminosity), is uncorrelated with the formation time of the main halo. This is in contrast to the previously reported correlation from studies where subhalos are selected by the current maximum circular velocity; we show that this difference is a result of the tidal stripping of the subhalos. We also find that the dominance of the main halo and the subhalo mass fraction are strongly correlated with halo concentration and formation history. These correlations are important to take into account when interpreting results from cluster samples selected with different criteria. Our sample also includes a fossil cluster, which is presented separately and placed in the context of the rest of the sample.