The observational features of the massive galaxy cluster “ El Gordo ” ( ACT-CL J0102–4915 ) , such as the X-ray emission , the Sunyaev-Zel ’ dovich ( SZ ) effect , and the surface mass density distribution , indicate that they are caused by an exceptional ongoing high-speed collision of two galaxy clusters , similar to the well-known Bullet Cluster .
We perform a series of hydrodynamical simulations to investigate the merging scenario and identify the initial conditions for the collision in ACT-CL J0102–4915 .
By surveying the parameter space of the various physical quantities that describe the two colliding clusters , including their total mass ( M ) , mass ratio ( \xi ) , gas fractions ( f _ { b } ) , initial relative velocity ( V ) , and impact parameter ( P ) , we find out an off-axis merger with P \sim 800 h _ { 70 } ^ { -1 } { kpc } , V \sim 2500 { km s ^ { -1 } } , M \sim 3 \times 10 ^ { 15 } { M _ { \odot } } , and \xi = 3.6 that can lead to most of the main observational features of ACT-CL J0102–4915 .
Those features include the morphology of the X-ray emission with a remarkable wake-like substructure trailing after the secondary cluster , the X-ray luminosity and the temperature distributions , and also the SZ temperature decrement .
The initial relative velocity required for the merger is extremely high and rare compared to that inferred from currently available \Lambda cold dark matter ( \Lambda CDM ) cosmological simulations , which raises a potential challenge to the \Lambda CDM model , in addition to the case of the Bullet Cluster .