5,793 research outputs found
Determination of the Baryon Density from Large Scale Galaxy Redshift Surveys
We estimate the degree to which the baryon density, , can be
determined from the galaxy power spectrum measured from large scale galaxy
redshift surveys, and in particular, the Sloan Digital Sky Survey. A high
baryon density will cause wiggles to appear in the power spectrum, which should
be observable at the current epoch. We assume linear theory on scales and do not include the effects of redshift distortions, evolution,
or biasing. With an optimum estimate of to ,
the uncertainties in are roughly 0.07 and 0.016 in flat
and open () cosmological models, respectively. This result
suggests that it should be possible to test for consistency with big bang
nucleosynthesis estimates of if we live in an open universe.Comment: 23 Pages, 10 Postscript figure
Using Cluster Abundances and Peculiar Velocities to Test the Gaussianity of the Cosmological Density Field
(Abridged) By comparing the frequency of typical events with that of unusual
events, one can test whether the cosmological density distribution function is
consistent with the normally made assumption of Gaussianity. To this end, we
compare the consistency of the tail-inferred (from clusters) and measured
values (from large-scale flows) of the rms level of mass fluctuations for two
distribution functions: a Gaussian, and a texture (positively-skewed) PDF.
Averaging the recent large-scale flow measurements, we find that observations
of the rms and the tail at the 10 h^-1 Mpc scale disfavor a texture PDF at ~1.5
sigma in all cases. However, taking only the most recent measurement of the
rms, that from Willick et al. (1997b), the comparison disfavors textures for
low Omega_0=0.3, and disfavors Gaussian models if Omega_0=1 (again at ~1.5
sigma). Predictions for evolution of high temperature clusters can also be made
for the models considered, and strongly disfavor Omega_0=1 in Gaussian models
and marginally disfavor Omega_0=1 in texture models. Only Omega_0=0.3 Gaussian
models are consistent with all the data considered.Comment: 34 pg incl. 8 embedded figures, LaTeX, aaspp4.sty, submitted to Ap
3D Spherical Analysis of Baryon Acoustic Oscillations
Baryon Acoustic Oscillations (BAOs) are oscillatory features in the galaxy
power spectrum and are a standard rod to measure the cosmological expansion.
These have been studied in Cartesian space (Fourier or real space) or in
Spherical Harmonic (SH) space in thin shells. Future wide-field surveys will
cover both wide and deep regions of the sky and thus require a simultaneous
treatment of the spherical sky and of an extended radial coverage. The
Spherical Fourier-Bessel (SFB) decomposition is a natural basis for the
analysis of fields in this geometry and facilitates the combination of BAO
surveys with other cosmological probes readily described in this basis. We
present here a new way to analyse BAOs by studying the BAO wiggles from the SFB
power spectrum. In SFB space, the power spectrum generally has both a radial
(k) and tangential (l) dependence and so do the BAOs. In the deep survey limit
and ignoring evolution, the SFB power spectrum becomes radial and reduces to
the Cartesian Fourier power spectrum. In the limit of a thin shell, all the
information is contained in the tangential modes described by the 2D SH power
spectrum. We find that the radialisation of the SFB power spectrum is still a
good approximation even when considering an evolving and biased galaxy field
with a finite selection function. This effect can be observed by all-sky
surveys with depths comparable to current surveys. We find that the BAOs
radialise more rapidly than the full SFB power spectrum. Our results suggest
the first peak of the BAOs in SFB space becomes radial out to l ~ 10 for
all-sky surveys with the same depth as SDSS or 2dF, and out to l ~ 70 for an
all-sky stage IV survey. Subsequent BAO peaks also become radial, but for
shallow surveys these may be in the non-linear regime. For modes that have
become radial, measurements at different l's are useful in practice to reduce
measurement errors.Comment: 6 pages + Appendix. Astro-ph abstract is abridged. Updated with
comments from anonymous referee. Corrected axes of Figure 2. Extended
discussion of radialisation. Accepted for publication in Astronomy &
Astrophysic
IRAS versus POTENT Density Fields on Large Scales: Biasing and Omega
The galaxy density field as extracted from the IRAS 1.2 Jy redshift survey is
compared to the mass density field as reconstructed by the POTENT method from
the Mark III catalog of peculiar velocities. The reconstruction is done with
Gaussian smoothing of radius 12 h^{-1}Mpc, and the comparison is carried out
within volumes of effective radii 31-46 h^{-1}Mpc, containing approximately
10-26 independent samples. Random and systematic errors are estimated from
multiple realizations of mock catalogs drawn from a simulation that mimics the
observed density field in the local universe. The relationship between the two
density fields is found to be consistent with gravitational instability theory
in the mildly nonlinear regime and a linear biasing relation between galaxies
and mass. We measure beta = Omega^{0.6}/b_I = 0.89 \pm 0.12 within a volume of
effective radius 40 h^{-1}Mpc, where b_I is the IRAS galaxy biasing parameter
at 12 h^{-1}Mpc. This result is only weakly dependent on the comparison volume,
suggesting that cosmic scatter is no greater than \pm 0.1. These data are thus
consistent with Omega=1 and b_I\approx 1. If b_I>0.75, as theoretical models of
biasing indicate, then Omega>0.33 at 95% confidence. A comparison with other
estimates of beta suggests scale-dependence in the biasing relation for IRAS
galaxies.Comment: 35 pages including 10 figures, AAS Latex, Submitted to The
Astrophysical Journa
Overweight status and psychological well-being in adolescent boys and girls: a multilevel analysis*
Background: Psychological distress and high body mass index (BMI) are linked in adults, especially in females. Effects of social position and behaviour, and whether obesogenic environments affect adolescents and adults equally are unresolved. The aim was to examine associations between psychological distress and being overweight in adolescents, by sex, accounting for social, lifestyle and contextual factors. Correlation of area-level variation in overweight status in adolescents and adults was investigated. Methods: Height, weight, General Health Questionnaire 12 (GHQ12) of psychological distress, physical activity, smoking, alcohol consumption, area deprivation and social class were available on 635 male and 618 female adolescents (13–15 years) from two cross-sectional population health surveys conducted in Scotland in 1998–99/2003–04. Multilevel logistic regression modelled overweight (including obese) status accounting for intraclass correlation of adolescents in households within postcode sector areas in health board regions. Univariable analysis examined effects of high (4 or more) GHQ12 score; multivariable analysis further allowed for covariates. Adult data were used to assess the importance of correlation between adolescent and adult area-level variation. Results: Univariably, there was significantly increased risk of being overweight associated with high GHQ12 score for girls but not boys; adolescent and adult area-level variation correlation did not impact. Results remained significant for girls in multivariable analyses (OR = 2.44, 95% confidence interval (CI): 1.33–4.50) and non-significant for boys (OR = 1.31, 95% CI: 0.56–3.05). Conclusions: Findings indicate being overweight is associated with psychological distress in adolescent girls, but not boys. Effects are not mediated by social, lifestyle or contextual factors
Cosmic Flows on 100 Mpc/h Scales: Standardized Minimum Variance Bulk Flow, Shear and Octupole Moments
The low order moments, such as the bulk flow and shear, of the large scale
peculiar velocity field are sensitive probes of the matter density fluctuations
on very large scales. In practice, however, peculiar velocity surveys are
usually sparse and noisy, which can lead to the aliasing of small scale power
into what is meant to be a probe of the largest scales. Previously, we
developed an optimal ``minimum variance'' (MV) weighting scheme, designed to
overcome this problem by minimizing the difference between the measured bulk
flow (BF) and that which would be measured by an ideal survey. Here we extend
this MV analysis to include the shear and octupole moments, which are designed
to have almost no correlations between them so that they are virtually
orthogonal. We apply this MV analysis to a compilation of all major peculiar
velocity surveys, consisting of 4536 measurements. Our estimate of the BF on
scales of ~ 100 Mpc/h has a magnitude of |v|= 416 +/- 78 km/s towards Galactic
l = 282 degree +/- 11 degree and b = 6 degree +/- 6 degree. This result is in
disagreement with LCDM with WMAP5 cosmological parameters at a high confidence
level, but is in good agreement with our previous MV result without an
orthogonality constraint, showing that the shear and octupole moments did not
contaminate the previous BF measurement. The shear and octupole moments are
consistent with WMAP5 power spectrum, although the measurement noise is larger
for these moments than for the BF. The relatively low shear moments suggest
that the sources responsible for the BF are at large distances.Comment: 13 Pages, 7 figures, 4 tables. Some changes to reflect the published
versio
Active Galactic Nucleus Pairs from the Sloan Digital Sky Survey. II. Evidence for Tidally Enhanced Star Formation and Black Hole Accretion
Active galactic nuclei (AGNs) are occasionally seen in pairs, suggesting that
tidal encounters are responsible for the accretion of material by both central
supermassive black holes (BHs). In Paper I of this series, we selected a sample
of AGN pairs with projected separations r_p < 100 kpc and velocity offsets <
600 km/s from the SDSS DR7 and quantified their frequency. In this paper, we
address the BH accretion and recent star formation properties in their host
galaxies. AGN pairs experience stronger BH accretion, as measured by their [O
III]5007 luminosities (corrected for contribution from star formation) and
Eddington ratios, than do control samples of single AGNs matched in redshift
and host stellar mass. Their host galaxies have stronger post-starburst
activity and younger mean stellar ages, as indicated by stronger H-delta
absorption and smaller 4000 A break in their spectra. The BH accretion and
recent star formation in the host galaxies both increase with decreasing
projected separation in AGN pairs, for r_p ~< 10-30 kpc. The intensity of BH
accretion, the post-starburst strength, and the mean stellar ages are
correlated between the two AGNs in a pair. The luminosities and Eddington
ratios of AGN pairs are correlated with recent star formation in their host
galaxies, with a scaling relation consistent with that observed in single AGNs.
Our results suggest that galaxy tidal interactions enhance both BH accretion
and star formation in AGN pairs, even though the majority of low redshift AGNs
is not coincident with on-going interactions.Comment: 16 pages, 12 figures; to appear in Ap
Binary Quasars in the Sloan Digital Sky Survey: Evidence for Excess Clustering on Small Scales
We present a sample of 218 new quasar pairs with proper transverse
separations R_prop < 1 Mpc/h over the redshift range 0.5 < z < 3.0, discovered
from an extensive follow up campaign to find companions around the Sloan
Digital Sky Survey and 2dF Quasar Redshift Survey quasars. This sample includes
26 new binary quasars with separations R_prop < 50 kpc/h (theta < 10
arcseconds), more than doubling the number of such systems known. We define a
statistical sample of binaries selected with homogeneous criteria and compute
its selection function, taking into account sources of incompleteness. The
first measurement of the quasar correlation function on scales 10 kpc/h <
R_prop < 400 kpc/h is presented. For R_prop < 40 kpc/h, we detect an order of
magnitude excess clustering over the expectation from the large scale R_prop >
3 Mpc/h quasar correlation function, extrapolated down as a power law to the
separations probed by our binaries. The excess grows to ~ 30 at R_prop ~ 10
kpc/h, and provides compelling evidence that the quasar autocorrelation
function gets progressively steeper on sub-Mpc scales. This small scale excess
can likely be attributed to dissipative interaction events which trigger quasar
activity in rich environments. Recent small scale measurements of galaxy
clustering and quasar-galaxy clustering are reviewed and discussed in relation
to our measurement of small scale quasar clustering.Comment: 25 pages, 12 figures, 9 tables. Submitted to the Astronomical Journa
Cosmological Constraints from the Clustering of the Sloan Digital Sky Survey DR7 Luminous Red Galaxies
We present the power spectrum of the reconstructed halo density field derived
from a sample of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey
Seventh Data Release (DR7). The halo power spectrum has a direct connection to
the underlying dark matter power for k <= 0.2 h/Mpc, well into the quasi-linear
regime. This enables us to use a factor of ~8 more modes in the cosmological
analysis than an analysis with kmax = 0.1 h/Mpc, as was adopted in the SDSS
team analysis of the DR4 LRG sample (Tegmark et al. 2006). The observed halo
power spectrum for 0.02 < k < 0.2 h/Mpc is well-fit by our model: chi^2 = 39.6
for 40 degrees of freedom for the best fit LCDM model. We find \Omega_m h^2 *
(n_s/0.96)^0.13 = 0.141^{+0.009}_{-0.012} for a power law primordial power
spectrum with spectral index n_s and \Omega_b h^2 = 0.02265 fixed, consistent
with CMB measurements. The halo power spectrum also constrains the ratio of the
comoving sound horizon at the baryon-drag epoch to an effective distance to
z=0.35: r_s/D_V(0.35) = 0.1097^{+0.0039}_{-0.0042}. Combining the halo power
spectrum measurement with the WMAP 5 year results, for the flat LCDM model we
find \Omega_m = 0.289 +/- 0.019 and H_0 = 69.4 +/- 1.6 km/s/Mpc. Allowing for
massive neutrinos in LCDM, we find \sum m_{\nu} < 0.62 eV at the 95% confidence
level. If we instead consider the effective number of relativistic species Neff
as a free parameter, we find Neff = 4.8^{+1.8}_{-1.7}. Combining also with the
Kowalski et al. (2008) supernova sample, we find \Omega_{tot} = 1.011 +/- 0.009
and w = -0.99 +/- 0.11 for an open cosmology with constant dark energy equation
of state w.Comment: 26 pages, 19 figures, submitted to MNRAS. The power spectrum and a
module to calculate the likelihoods is publicly available at
http://lambda.gsfc.nasa.gov/toolbox/lrgdr/ . v2 fixes abstract formatting
issu
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