The cosmological analysis of X-ray cluster surveys: IV. Testing ASpiX
  with template-based cosmological simulations
  Following extensive tests on analytical toy-catalogues (paper III), we
present the results of a more realistic study over a 711 deg2 template-based
cosmological simulation. Dark matter halos from the Aardvark simulation have
been ascribed luminosities, temperatures and core-radii, using local scaling
relations and assuming self-similar evolution. Predicted X-ray sky-maps are
converted into XMM event lists using an instrumental simulator. The XXL
pipeline run on the resulting sky images, produces an 'observed' cluster
catalogue over which the tests have been performed. This allowed us to
investigate the relative power of various combinations of count-rate,
hardness-ratio, apparent-size and redshift information. Two fitting methods
were used : a traditional MCMC approach and a simple minimisation procedure
(Amoeba) whose mean uncertainties are a posteriori evaluated by means of
synthetic catalogues. Results were analysed and compared to the predictions
from a Fisher analysis (FA). For this particular catalogue realisation,
assuming perfectly known scaling relations, the CR-HR combination gives
$\sigma_8$ and $\Omega_m$ at the 10% level, while CR-HR-r$_c$-z improves this
to $\leq$ 3%. Adding a second hardness ratio improves results from the
CR-HR1-r$_c$ combination, but to a lesser extent than adding redshift
information. When all coefficients of the M-T relation (including scatter) are
also fitted, cosmological parameters are constrained to within 5-10%, and
larger for the M-T coefficients (up to a factor of two for the scatter). Errors
returned by the MCMC, by Amoeba, and by FA predictions, are in most cases in
excellent agreement and always within a factor of two. We also study the impact
of the scatter of the M-Rc relation on the number of detected clusters: for the
cluster typical sizes usually assumed, the larger the scatter, the lower the
number of detected objects.
