952 research outputs found
Deciphering cosmological information from redshift surveys of high-z objects - the cosmological light-cone effect and redshift-space distortion -
The three-dimensional distribution of astronomical objects observed in
redshift space significantly differs from the true distribution since the
distance to each object cannot be determined by its redshift only; for the peculiar velocity field contaminates the true recession velocity of
the Hubble flow, while the true distance for objects at sensitively
depends on the (unknown and thus assumed) cosmological parameters. This hampers
the effort to understand the true distribution of large-scale structure of the
universe. In addition, all cosmological observations are carried out on a
light-cone, the null hypersurface of an observer at . This implies that
their intrinsic properties and clustering statistics should change even within
the survey volume. Therefore a proper comparison taking account of the
light-cone effect is important to extract any cosmological information from
redshift catalogues, especially for . We present recent theoretical
development on the two effects -- the cosmological light-cone effect and the
cosmological redshift-space distortion -- which should play key roles in
observational cosmology in the 21st century.Comment: 28pages, 20 figures, minor revision to match the final version to
appear in Progress of Theoretical Physics Supplement, vol. 133 (1999
Modeling peculiar velocities of dark matter halos
We present a simple model that accurately describes various statistical
properties of peculiar velocities of dark matter halos. We pay particular
attention to the following two effects; first, the evolution of the halo
peculiar velocity depends on the local matter density, instead of the global
density. Second, dark matter halos are biased tracers of the underlying mass
distribution, thus halos tend to be located preferentially at high density
regions. For the former, we develop an empirical model calibrated with N-body
simulations, while for the latter, we use a conventional halo bias models based
on the extended Press-Schechter model combined with an empirical log-normal
probability distribution function of the mass density distribution. We find
that compared with linear theory, the present model significantly improves the
accuracy of predictions of statistical properties of the halo peculiar velocity
field including the velocity dispersion, the probability distribution function,
and the pairwise velocity dispersion at large separations. Thus our model
predictions may be useful in analyzing future observations of the peculiar
velocities of galaxy clusters.Comment: This paper was published in MNRAS, 343, 1312 (2003). Owing to an
error in numerical computations, some incorrect results were presented there.
Erratum is to be published in MNRAS. Conclusions of the original version are
unaffected by the correction. This version supersedes the original versio
Confronting cold dark matter cosmologies with strong clustering of Lyman break galaxies at
We perform a detailed analysis of the statistical significance of a
concentration of Lyman break galaxies at recently discovered by
Steidel et al. (1997), using a series of N-body simulations with
particles in a (100\himpc)^3 comoving box. While the observed number density
of Lyman break galaxies at implies that they correspond to systems
with dark matter halos of \simlt 10^{12}M_\odot, the resulting clustering of
such objects on average is not strong enough to be reconciled with the
concentration if it is fairly common; we predict one similar concentration
approximately per () fields in three representative cold dark matter
models. Considering the current observational uncertainty of the frequency of
such clustering at , it would be premature to rule out the models, but
the future spectroscopic surveys in a dozen fields could definitely challenge
all the existing cosmological models a posteriori fitted to the universe.Comment: the final version which matchs that published in ApJ Letters (Feb
1998); compared with the previous versions, the predictions for the SCDM
model are slightly changed; Latex, 11 pages, including 3 ps figure
Where Are the Baryons? II: Feedback Effects
Numerical simulations of the intergalactic medium have shown that at the
present epoch a significant fraction (40-50%) of the baryonic component should
be found in the (T~10^6K) Warm-Hot Intergalactic Medium (WHIM) - with several
recent observational lines of evidence indicating the validity of the
prediction. We here recompute the evolution of the WHIM with the following
major improvements: (1) galactic superwind feedback processes from galaxy/star
formation are explicitly included; (2) major metal species (O V to O IX) are
computed explicitly in a non-equilibrium way; (3) mass and spatial dynamic
ranges are larger by a factor of 8 and 2, respectively, than in our previous
simulations. Here are the major findings: (1) galactic superwinds have dramatic
effects, increasing the WHIM mass fraction by about 20%, primarily through
heating up warm gas near galaxies with density 10^{1.5}-10^4 times the mean
density. (2) the fraction of baryons in WHIM is increased modestly from the
earlier work but is ~40-50%. (3) the gas density of the WHIM is broadly peaked
at a density 10-20 times the mean density, ranging from underdense regions to
regions that are overdense by 10^3-10^4. (4) the median metallicity of the WHIM
is 0.18 Zsun for oxygen with 50% and 90% intervals being (0.040,0.38) and
(0.0017,0.83).Comment: 44 pages, 17 figures, high res version at
http://www.astro.princeton.edu/~cen/baryonII.ps.g
Slow relative motion of IRAS galaxies at small separations: implications for galaxy formation models
We report on the measurement of the two-point correlation function and the
pairwise peculiar velocity of galaxies in the IRAS PSCz survey. The real space
two-point correlation function can be fitted to a power law with and r_0=3.70 \mpc. The pairwise peculiar
velocity dispersion is close to 400 \kms at r_p=3\mpc
and decreases to about 150 \kms at r_p \approx 0.2 \mpc. These values are
significantly lower than those obtained from the Las Campanas Redshift Survey,
but agree very well with the results of blue galaxies reported by the SDSS team
later on. We have constructed mock samples from N-body simulations with a
cluster-weighted bias and from the theoretically constructed GIF catalog. We
find that the two-point correlation function of the mock galaxies can be
brought into agreemnt with the observed result, but the model does not reduce
the velocity dispersions of galaxies to the level measured in the PSCz data.
Thus we conclude that the peculiar velocity dispersions of the PSCz galaxies
require a biasing model which substantially reduces the peculiar velocity
dispersion on small scales relative to their spatial clustering. The results
imply that either the cosmogony model needs to be revised or the velocity bias
is important for the velocity dispersion of the IRAS galaxies.Comment: 4 pages, contribution to the proceedings "A New Era in Cosmology",
ASP conference series, eds. T. Shanks and N. Metcalf
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