Cristiano De Boni - February 26, 2016

The mass accretion rate of galaxy clusters: a measurable quantity

The mass accretion rate of galaxy clusters has been the topic of numerous 
detailed numerical and theoretical investigations, but so far it has remained 
inaccessible to measurements in the real Universe.
I will explore the possibility of measuring the mass accretion rate of galaxy 
clusters from their mass profile beyond the virial radius.
I derive the accretion rate from the mass of a spherical shell whose infall 
velocity is extracted from N-body simulations.
This approximation is rather crude in hierarchical clustering scenarios, where 
both smooth accretion and aggregation of smaller dark matter haloes contribute 
to the mass accretion of clusters.
Nevertheless, in the redshift range z=[0,2], my prescription returns an average
 mass accretion rate within 20-40 % of the average rate derived from the merger 
trees of dark matter haloes extracted from N-body simulations.
Since the measurement of the mass profile of clusters beyond their virial 
radius can be performed with the caustic technique applied to dense redshift 
surveys of the cluster outer regions, my result suggests that measuring the 
mean mass accretion rate of a sample of galaxy clusters is actually feasible.
I thus provide a new potential observational test of the cosmological and 
structure formation models.