1,191 research outputs found
Combining spectroscopic and photometric surveys using angular cross-correlations II: Parameter constraints from different physical effects
Future spectroscopic and photometric surveys will measure accurate positions
and shapes of an increasing number of galaxies. In the previous paper of this
series we studied the effects of Redshift Space Distortions (RSD), baryon
acoustic oscillations (BAO) and Weak gravitational Lensing (WL) using angular
cross-correlation. Here, we provide a new forecast that explores the
contribution of including different observables, physical effects (galaxy bias,
WL, RSD, BAO) and approximations (non-linearities, Limber approximation,
covariance between probes). The radial information is included by using the
cross-correlation of separate narrow redshift bins. For the auto correlation
the separation of galaxy pairs is mostly transverse, while the
cross-correlations also includes a radial component. We study how this
information adds to our figure of merit (FoM), which includes the dark energy
equation of state and the growth history, parameterized by . We
show that the Limber approximation and galaxy bias are the most critical
ingredients to the modelling of correlations. Adding WL increases our FoM by
4.8, RSD by 2.1 and BAO by 1.3. We also explore how overlapping surveys perform
under the different assumption and for different figures of merit. Our
qualitative conclusions depend on the survey choices and scales included, but
we find some clear tendencies that highlight the importance of combining
different probes and can be used to guide and optimise survey strategies
Redshift distortions of galaxy correlation functions
To examine how peculiar velocities can affect the 2-, 3-, and 4-point
redshift correlation functions, we evaluate volume-average correlations for
configurations that emphasize and minimize redshift distortions for four
different volume-limited samples from each of the CfA, SSRS, and IRAS redshift
catalogs. We find a characteristic distortion for the 2-point correlation,
\xibar_2: the slope is flatter and the correlation length is larger
in redshift space than in real space; that is, redshift distortions ``move''
correlations from small to large scales. At the largest scales (up to 12
\Mpc), the extra power in the redshift distribution is compatible with
. We estimate to be ,
and for the CfA, SSRS and IRAS catalogs. Higher
order correlations \xibar_3 and \xibar_4 suffer similar redshift
distortions, but in such a way that, within the accuracy of our analysis, the
normalized amplitudes and are insensitive to this effect. The
hierarchical amplitudes and are constant as a function of scale
between 1--12 \Mpc and have similar values in all samples and catalogues,
and , despite the fact that \xibar_2,
\xibar_3, and \xibar_4 differ from one sample to another by large factors
(up to a factor of 4 in \xibar_2, 8 for \xibar_3, and 12 for \xibar_4).
The agreement between the independent estimations of and Comment: 20 pages (12 figues available on request), LaTeX,
FERMILAB-Pub-93-097-
Higher-Order Angular Galaxy Correlations in the SDSS: Redshift and Color Dependence of non-Linear Bias
We present estimates of the N-point galaxy, area-averaged, angular
correlation functions () for = 2,...,7 for
galaxies from the fifth data release of the Sloan Digital Sky Survey. Our
parent sample is selected from galaxies with , and is the
largest ever used to study higher-order correlations. We subdivide this parent
sample into two volume limited samples using photometric redshifts, and these
two samples are further subdivided by magnitude, redshift, and color (producing
early- and late-type galaxy samples) to determine the dependence of
() on luminosity, redshift, and galaxy-type. We
measure () using oversampling techniques and use them
to calculate the projected, . Using models derived from theoretical
power-spectra and perturbation theory, we measure the bias parameters and
, finding that the large differences in both bias parameters ( and
) between early- and late-type galaxies are robust against changes in
redshift, luminosity, and , and that both terms are consistently
smaller for late-type galaxies. By directly comparing their higher-order
correlation measurements, we find large differences in the clustering of
late-type galaxies at redshifts lower than 0.3 and those at redshifts higher
than 0.3, both at large scales ( is larger by at ) and
small scales (large amplitudes are measured at small scales only for ,
suggesting much more merger driven star formation at ). Finally, our
measurements of suggest both that and is negative.Comment: 46 pages, 19 figures, Accepted to Ap
On the CCD Calibration of Zwicky galaxy magnitudes & The Properties of Nearby Field Galaxies
We present CCD photometry for galaxies around 204 bright (m_Z < 15.5) Zwicky
galaxies in the equatorial extension of the APM Galaxy Survey, sampling and
area over 400 square degrees, which extends 6 hours in right ascension. We fit
a best linear relation between the Zwicky magnitude system, m_Z, and the CCD
photometry, B, by doing a likehood analysis that corrects for Malmquist bias.
This fit yields a mean scale error in Zwicky of 0.38 mag per magnitude: ie
Delta m_Z = (0.62 \pm 0.05) Delta B and a mean zero point of = -0.35
\pm 0.15 mag. The scatter around this fit is about 0.4 mag. Correcting the
Zwicky magnitude system with the best fit model results in a 60% lower
normalization and 0.35 mag brighter M_* in the luminosity function. This brings
the CfA2 luminosity function closer to the other low redshift estimations (eg
Stromlo-APM or LCRS). We find a significant positive angular correlation of
magnitudes and position in the sky at scales smaller than about 5 armin, which
corresponds to a mean separation of 120 Kpc/h. We also present colours, sizes
and ellipticities for galaxies in our fields which provides a good local
reference for the studies of galaxy evolution.Comment: Full size figures can be found in
http://www.ieec.fcr.es/cosmo-www/zwicky.ps Version accepted for publication
in MNRAS. Extended discussion on properties of nearby galaxies. References
added. An inconsistency in the R band isophote used has been corrected. Main
results and conclusions are unchange
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