3 research outputs found
Measuring cosmological bulk flows via the kinematic Sunyaev-Zeldovich effect in the upcoming cosmic microwave background maps
We propose a new method to measure the possible large-scale bulk flows in the
Universe from the cosmic microwave background (CMB) maps from the upcoming
missions, MAP and Planck. This can be done by studying the statistical
properties of the CMB temperature field at many X-ray cluster positions. At
each cluster position, the CMB temperature fluctuation will be a combination of
the Sunyaev-Zeldovich (SZ) kinematic and thermal components, the cosmological
fluctuations and the instrument noise term. When averaged over many such
clusters the last three will integrate down, whereas the first one will be
dominated by a possible bulk flow component. In particular, we propose to use
all-sky X-ray cluster catalogs that should (or could) be available soon from
X-ray satellites, and then to evaluate the dipole component of the CMB field at
the cluster positions. We show that for the MAP and Planck mission parameters
the dominant contributions to the dipole will be from the terms due to the SZ
kinematic effect produced by the bulk flow (the signal we seek) and the
instrument noise (the noise in our signal). Computing then the expected
signal-to-noise ratio for such measurement, we get that at the 95 % confidence
level the bulk flows on scales >100h^{-1} Mpc can be probed down to the
amplitude of km/sec with the MAP data and down to only 30 km/sec with
the Planck mission.Comment: Astrophysical Journal Letters, in pres
Reconstructing the spectrum of the pregalactic density field from astronomical data
In this paper we evaluate the spectrum of the pregalactic density field on
scales Mpc from a variety of astronomical data. APM
data on in six narrow magnitude is used, after correcting to
possible evolutionary effects, to constrain the spectrum of galaxy clustering
on scales . Fitting power spectra of CDM
models to the data at all depths requires if the primordial
index and if the spectrum is tilted with . Then we
compare the peculiar velocity field predicted by the APM spectrum of galaxy
(light) distribution with the actual velocity data. The two fields are
consistent and the comparison suggests that the bias factor is scale
independent with (0.2-0.3). The next dataset used comes
from the cluster correlation data. We calculate in detail the amplification of
the cluster correlation function due to gravitational clustering and use the
data on both the slope of the cluster correlation function and its
amplitude-richness dependence. Cluster masses are normalized using the Coma
cluster. We find that CDM models are hard to reconcile with all the three
datasets: APM data on , the data on cluster correlation function,
and the data on the latter's amplitude-richness dependence. We show that the
data on the amplitude-richness dependence can be used directly to obtain the
spectrum of the pregalactic density field. Applying the method to the data, we
recover the density field on scales between 5 and 25Mpc whose slope is
in good agreement with the APM data on the same scales. Requiring the two
amplitudes to be the same, fixes the value of to be 0.3 in agreement
with observations of the dynamics of the Coma cluster. Finally we use the dataComment: to be published in Ap.J - minor revision + typos correcte