clusively with GMOS observations to obtain
dynamical masses for a clean sub-sample of
clusters (Sifón et al., in preparation).
Figure 3.
Constraints on
cosmological parameters
when dynamical masses
from ACT are included.
The black contours show
the best-fit parameters
obtained from WMAP-7
observations, and the
green contours show the
results when combining
WMAP-7 with ACT
clusters, including the
dynamical masses of
the southern sample.
The blue dashed and
black dotted contours
show the results when
combining information
from WMAP, baryon
acoustic oscillations and
the Hubble constant
from measurements of
the distance ladder, with
and without ACT cluster
information, respectively.
In Hasselfield et al. (2013), we have used this
“equatorial sample” to obtain cosmological
constraints from cluster number counts. As
has been shown before, we find that the calibration of the SZE-mass relation is the critical
missing ingredient that will allow us to fully
understand the cosmological implications of
this sample.
Figure 3 shows the constraining power of the
ACT sample when the dynamical masses are
included in the fit (Hasselfield et al., 2013),
specifically for the characteristic amplitude
of matter fluctuations, s8, and the density
of matter, Wm. The black contours show the
best-fit parameters obtained from Sevenyear Wilkinson Microwave Anisotropy Probe
(WMAP-7) observations, and the green contours show the results when combining
WMAP-7 with ACT clusters, including the dynamical masses of the southern sample. The
blue dashed and black dotted contours show
the results when combining information
from WMAP, baryon acoustic oscillations and
the Hubble constant from measurements of
the distance ladder, with and without ACT
cluster information, respectively.
The dynamical masses provide improvements
on cosmological parameter constraints because they impose strong restrictions on the
scaling relations. (In statistical terminology,
they are “tight priors.”) Our ongoing analysis of
recent GMOS observations for the equatorial
sample will provide a firmer basis for using galaxy clusters as precision probes of cosmology.
This work constituted the bulk of C. Sifón’s MSc
thesis at Pontificia Universidad Católica de
Chile, which was completed in January 2012.
Cristóbal Sifón is a PhD student at Leiden Observatory. He can be reached at:
[email protected]
Felipe Menanteau is a research associate at Rutgers University. He