X-ray morphology of cluster-mass haloes in self-interacting dark matter
  We perform cosmological zoom-in simulations of $19$ relaxed cluster-mass
haloes with the inclusion of adiabatic gas within the cold dark matter (CDM)
and self-interacting dark matter (SIDM) models. These clusters are selected as
dynamically relaxed clusters from a parent simulation and have typical masses
of $M_{\rm 200} \simeq 1\operatorname{-}3\times 10^{15}\,{\rm M}_{\odot}$. We
find that both the dark matter and the intracluster gas distributions in SIDM
are more spherical than their CDM counterparts, although the difference is
smaller for the gas. Mock X-ray images are generated based on the simulations
and are compared to the real X-ray images of $84$ relaxed clusters selected
from the Chandra and ROSAT archives. We perform ellipse fitting for the
isophotes of mock and real X-ray images and obtain the ellipticities at
cluster-centric radii of $r\simeq 0.1\operatorname{-}0.2\,R_{\rm 200}$. The
X-ray isophotes in SIDM models with increasing cross-sections are rounder than
their CDM counterparts, which manifests as a systematic shift in the
distribution function of ellipticities. Unexpectedly, the X-ray morphology of
the observed "non-peaky" (non-cool-core) clusters agrees better with SIDM
models with cross-section per unit mass $(\sigma/m)= 0.5\operatorname{-}1~{\rm
cm}^2/{\rm g}$ than CDM and SIDM with $(\sigma/m)=0.1\,{\rm cm}^2/{\rm g}$. Our
statistical analysis indicates that the latter two models are disfavored at
least at the $68\%$ confidence level. This conclusion is not altered by
shifting the radial range of measurements or applying temperature selection
criterion. However, the primary uncertainty originates from the lack of
baryonic physics in the adiabatic model, such as gas cooling, star formation
and feedback effects, which have the potential to reconcile CDM simulations
with observations.
