850 research outputs found
High-Resolution Simulations of Cosmic Microwave Background non-Gaussian Maps in Spherical Coordinates
We describe a new numerical algorithm to obtain high-resolution simulated
maps of the Cosmic Microwave Background (CMB), for a broad class of
non-Gaussian models. The kind of non-Gaussianity we account for is based on the
simple idea that the primordial gravitational potential is obtained by a
non-linear but local mapping from an underlying Gaussian random field, as
resulting from a variety of inflationary models. Our technique, which is based
on a direct realization of the potential in spherical coordinates and fully
accounts for the radiation transfer function, allows to simulate non-Gaussian
CMB maps down to the Planck resolution (), with
reasonable memory storage and computational time.Comment: 9 pages, 5 figures. Submitted to ApJ. A version with higher quality
figures is available at http://www.pd.infn.it/~liguori/content.htm
X-ray and Sunyaev-Zel'dovich scaling relations in galaxy clusters
[Abridged] We present an analysis of the scaling relations between X-ray
properties and Sunyaev-Zel'dovich (SZ) parameters for a sample of 24 X-ray
luminous galaxy clusters observed with Chandra and with measured SZ effect.
These objects are in the redshift range 0.14--0.82 and have X-ray bolometric
luminosity L>10^45 erg/s. We perform a spatially resolved spectral analysis and
recover the density, temperature and pressure profiles of the ICM, just relying
on the spherical symmetry of the cluster and the hydrostatic equilibrium
hypothesis. We observe that the correlations among X-ray quantities only are in
agreement with previous results obtained for samples of high-z X-ray luminous
galaxy clusters. On the relations involving SZ quantities, we obtain that they
correlate with the gas temperature with a logarithmic slope significantly
larger than the predicted value from the self-similar model. The measured
scatter indicates, however, that the central Compton parameter y_0 is a proxy
of the gas temperature at the same level of other X-ray quantities like
luminosity. Our results on the X-ray and SZ scaling relations show a tension
between the quantities more related to the global energy of the system (e.g.
gas temperature, gravitating mass) and the indicators of the structure of the
ICM (e.g. gas density profile, central Compton parameter y_0), showing the most
significant deviations from the values of the slope predicted from the
self-similar model in the L-T, L-M_{tot}, M_{gas}-T, y_0-T relations. When the
slope is fixed to the self-similar value, these relations consistently show a
negative evolution suggesting a scenario in which the ICM at higher redshift
has lower both X-ray luminosity and pressure in the central regions than the
expectations from self-similar model.Comment: MNRAS in press - Minor revision to match published versio
Constraints on extended quintessence from high-redshift Supernovae
We obtain constraints on quintessence models from magnitude-redshift
measurements of 176 type Ia Supernovae. The considered quintessence models are
ordinary quintessence, with Ratra-Peebles and SUGRA potentials, and extended
quintessence with a Ratra-Peebles potential. We compute confidence regions in
the plane and find that for SUGRA potentials it is not
possible to obtain useful constraints on these parameters; for the
Ratra-Peebles case, both for the extended and ordinary quintessence we find
\alpha\mincir 0.8, at the level. We also consider simulated dataset
for the SNAP satellite for the same models: again, for a SUGRA potential it
will not be possible to obtain constraints on , while with a
Ratra-Peebles potential its value will be determined with an error \mincir
0.6. We evaluate the inaccuracy made by approximating the time evolution of
the equation of state with a linear or constant w\diz, instead of using its
exact redshift evolution. Finally we discuss the effects of different
systematic errors in the determination of quintessence parameters.Comment: 8 pages, ApJ in press. We added a discussion of the systematic errors
and we updated the SNe catalogu
The Variance of QSO Counts in Cells
{}From three quasar samples with a total of 1038 objects in the redshift
range we measure the variance of counts in cells of
volume . By a maximum likelihood analysis applied separately on these
samples we obtain estimates of , with .
The analysis from a single catalog for Mpc and from a
suitable average over the three catalogs for and
Mpc, gives , ,
and , respectively, where the
confidence ranges account for both sampling errors and statistical
fluctuations in the counts. This allows a comparison of QSO clustering on large
scales with analogous data recently obtained both for optical and IRAS
galaxies: QSOs seem to be more clustered than these galaxies by a biasing
factor .Comment: 13 pages in plain Tex, 5 figures available in postscript in a
separate file, submitted to ApJ, DAPD-33
Simulated X-ray galaxy clusters at the virial radius: slopes of the gas density, temperature and surface brightness profiles
Using a set of hydrodynamical simulations of 9 galaxy clusters with masses in
the range 1.5 10^{14} M_sun < M_vir < 3.4 10^{15} M_sun, we have studied the
density, temperature and X-ray surface brightness profiles of the intracluster
medium in the regions around the virial radius. We have analyzed the profiles
in the radial range well above the cluster core, the physics of which are still
unclear and matter of tension between simulated and observed properties, and up
to the virial radius and beyond, where present observations are unable to
provide any constraints. We have modeled the radial profiles between 0.3 R_200
and 3 R_200 with power laws with one index, two indexes and a rolling index.
The simulated temperature and [0.5-2] keV surface brightness profiles well
reproduce the observed behaviours outside the core. The shape of all these
profiles in the radial range considered depends mainly on the activity of the
gravitational collapse, with no significant difference among models including
extraphysics. The profiles steepen in the outskirts, with the slope of the
power-law fit that changes from -2.5 to -3.4 in the gas density, from -0.5 to
-1.8 in the gas temperature, and from -3.5 to -5.0 in the X-ray soft surface
brightness. We predict that the gas density, temperature and [0.5-2] keV
surface brightness values at R_200 are, on average, 0.05, 0.60, 0.008 times the
measured values at 0.3 R_200. At 2 R_200, these values decrease by an order of
magnitude in the gas density and surface brightness, by a factor of 2 in the
temperature, putting stringent limits on the detectable properties of the
intracluster-medium (ICM) in the virial regions.Comment: 13 pages, 6 figures; added reference and other minor change
Large-scale inhomogeneities of the intracluster medium: improving mass estimates using the observed azimuthal scatter
Using a set of hydrodynamical simulations of 62 galaxy clusters and groups we
study the ICM of inhomogeneities, focusing on the ones on the large scale that,
unlike clumps, are the most difficult to identify. To this purpose we introduce
the concept of residual clumpiness, C_R, that quantifies the large-scale
inhomogeneity of the ICM. After showing that this quantity can be robustly
defined for relaxed systems, we characterize how it varies with radius, mass
and dynamical state of the halo. Most importantly, we observe that it
introduces an overestimate in the determination of the density profile from the
X-ray emission, which translates into a systematic overestimate of 6 (12)% in
the measurement of M_gas at R_200 for our relaxed (perturbed) cluster sample.
At the same time, the increase of C_R with radius introduces also a ~2%
systematic underestimate in the measurement of the hydrostatic-equilibrium mass
(M_he), which adds to the previous one generating a systematic ~8.5%
overestimate in f_gas in our relaxed sample. Since the residual clumpiness of
the ICM is not directly observable, we study its correlation with the azimuthal
scatter in the X-ray surface brightness of the halo and in the y-parameter
profiles. We find that their correlation is highly significant (r_S = 0.6-0.7),
allowing to define the azimuthal scatter measured in the X-ray surface
brightness profile and in the y-parameter as robust proxies of C_R. After
providing a function that connects the two quantities, we obtain that
correcting the observed gas density profiles using the azimuthal scatter
eliminates the bias in the measurement of M_gas for relaxed objects, which
becomes (0+/-2)% up to 2R_200, and reduces it by a factor of 3 for perturbed
ones. This method allows also to eliminate the systematics on the measurements
of M_he and f_gas, although a significant halo to halo scatter remains.
(abridged)Comment: 18 pages, 17 figures, 3 tables. Submitted to MNRAS, revised after
referee's comment
Velocity Fields in Non--Gaussian Cold Dark Matter Models
We analyse the large--scale velocity field obtained by N--body simulations of
cold dark matter (CDM) models with non--Gaussian primordial density
fluctuations, considering models with both positive and negative primordial
skewness in the density fluctuation distribution. We study the velocity
probability distribution and calculate the dependence of the bulk flow,
one--point velocity dispersion and Cosmic Mach Number on the filtering size. We
find that the sign of the primordial skewness of the density field provides
poor discriminatory power on the evolved velocity field. All non--Gaussian
models here considered tend to have lower velocity dispersion and bulk flow
than the standard Gaussian CDM model, while the Cosmic Mach Number turns out to
be a poor statistic in characterizing the models. Next, we compare the
large--scale velocity field of a composite sample of optically selected
galaxies as described by the Local Group properties, bulk flow, velocity
correlation function and Cosmic Mach Number, with the velocity field of mock
catalogues extracted from the N--body simulations. The comparison does not
clearly permit to single out a best model: the standard Gaussian model is
however marginally preferred by the maximum likelihood analysis.Comment: 10 pages in Latex with mn.sty (available at the end of the paper
The Cluster Distribution as a Test of Dark Matter Models. IV: Topology and Geometry
We study the geometry and topology of the large-scale structure traced by
galaxy clusters in numerical simulations of a box of side 320 Mpc, and
compare them with available data on real clusters. The simulations we use are
generated by the Zel'dovich approximation, using the same methods as we have
used in the first three papers in this series. We consider the following models
to see if there are measurable differences in the topology and geometry of the
superclustering they produce: (i) the standard CDM model (SCDM); (ii) a CDM
model with (OCDM); (iii) a CDM model with a `tilted' power
spectrum having (TCDM); (iv) a CDM model with a very low Hubble
constant, (LOWH); (v) a model with mixed CDM and HDM (CHDM); (vi) a
flat low-density CDM model with and a non-zero cosmological
term (CDM). We analyse these models using a variety of
statistical tests based on the analysis of: (i) the Euler-Poincar\'{e}
characteristic; (ii) percolation properties; (iii) the Minimal Spanning Tree
construction. Taking all these tests together we find that the best fitting
model is CDM and, indeed, the others do not appear to be consistent
with the data. Our results demonstrate that despite their biased and extremely
sparse sampling of the cosmological density field, it is possible to use
clusters to probe subtle statistical diagnostics of models which go far beyond
the low-order correlation functions usually applied to study superclustering.Comment: 17 pages, 7 postscript figures, uses mn.sty, MNRAS in pres
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