The Dynamical State of the Frontier Fields Galaxy Cluster Abell 370
  We study the dynamics of Abell 370 (A370), a highly massive Hubble Frontier
Fields galaxy cluster, using self-consistent three-dimensional
N-body/hydrodynamical simulations. Our simulations are constrained by X-ray,
optical spectroscopic and gravitational lensing, and Sunyaev-Zel'dovich (SZ)
effect observations. Analyzing archival Chandra observations of A370 and
comparing the X-ray morphology to the latest gravitational lensing mass
reconstruction, we find offsets of ~30 kpc and ~100 kpc between the two X-ray
surface brightness peaks and their nearest mass surface density peaks,
suggesting that it is a merging system, in agreement with previous studies.
Based on our dedicated binary cluster merger simulations, we find that initial
conditions of the two progenitors with virial masses of 1.7 x 10^(15) M_sun and
1.6 x 10^(15) M_sun, an infall velocity of 3500 km/s, and an impact parameter
of 100 kpc can explain the positions and the offsets between the peaks of the
X-ray emission and mass surface density, the amplitude of the integrated SZ
signal, and the observed relative line-of-sight velocity. Moreover, our best
model reproduces the observed velocity dispersion of cluster member galaxies,
which supports the large total mass of A370 derived from weak lensing. Our
simulations suggest that A370 is a major merger after the second core passage
in the infalling phase, just before the third core passage. In this phase, the
gas has not settled down in the gravitational potential well of the cluster,
which explains why A370 does not follow closely the galaxy cluster scaling
relations.
