2 research outputs found
Neutral hydrogen surveys for high redshift galaxy clusters and proto-clusters
We discuss the possibility of performing blind surveys to detect large-scale
features of the universe using 21cm emission. Using instruments with approx.
5'-10' resolution currently in the planning stage, it should be possible to
detect virialized galaxy clusters at intermediate redshifts using the combined
emission from their constituent galaxies, as well as less overdense structures,
such as proto-clusters and the `cosmic web', at higher redshifts. Using
semi-analytic methods we compute the number of virialized objects and those at
turnaround which might be detected by such surveys. We find a surprisingly
large number of objects might be detected even using small (approx. 5%)
bandwidths and elaborate on some issues pertinent to optimising the design of
the instrument and the survey strategy. The main uncertainty is the fraction of
neutral gas relative to the total dark matter within the object. We discuss
this issue in the context of the observations which are currently available.Comment: 10 pages, 6 figure
Cluster abundances and S-Z power spectra: effects of non-Gaussianity and early dark energy
In the standard Lambda CDM cosmological model with a Gaussian primordial
density fluctuation field, the relatively low value of the mass variance
parameter (sigma_8=0.74{+0.05}{-0.06}, obtained from the WMAP 3-year data)
results in a reduced likelihood that the measured level of CMB anisotropy on
the scales of clusters is due to the Sunyaev-Zeldovich (S-Z) effect. To assess
the feasibility of producing higher levels of S-Z power, we explore two
alternative models which predict higher cluster abundance. In the first model
the primordial density field has a chi^2_1 distribution, whereas in the second
an early dark energy component gives rise to the desired higher cluster
abundance. We carry out the necessary detailed calculations of the levels of
S-Z power spectra, cluster number counts, and angular 2-point correlation
function of clusters, and compare (in a self-consistent way) their predicted
redshift distributions. Our results provide a sufficient basis upon which the
viability of the three models may be tested by future high quality
measurements.Comment: 12 pages, 5 figures, accepted for publication in MNRA