15689441
Cross-correlation Weak Lensing of SDSS Galaxy Clusters. I. Measurements
This is the first in a series of papers on the weak lensing effect caused by clusters of galaxies in Sloan Digital Sky Survey. The photometrically selected cluster sample, known as MaxBCG, includes ~130,000 objects between redshift 0.1 and 0.3, ranging in size from small groups to massive clusters. We split the clusters into bins of richness and luminosity and stack the surface density contrast to produce mean radial profiles. The mean profiles are detected over a range of scales, from the inner halo (25 kpc h^(–1)) well into the surrounding large-scale structure (30 Mpc h^(–1)), with a significance of 15 to 20 in each bin. The signal over this large range of scales is best interpreted in terms of the cluster-mass cross-correlation function. We pay careful attention to sources of systematic error, correcting for them where possible. The resulting signals are calibrated to the ~10% level, with the dominant remaining uncertainty being the redshift distribution of the background sources. We find that the profiles scale strongly with richness and luminosity. We find that the signal within a given richness bin depends upon luminosity, suggesting that luminosity is more closely correlated with mass than galaxy counts. We split the samples by redshift but detect no significant evolution. The profiles are not well described by power laws. In a subsequent series of papers, we invert the profiles to three-dimensional mass profiles, show that they are well fit by a halo model description, measure mass-to-light ratios, and provide a cosmological interpretation.
16918450
Lensing magnification: implications for counts of submillimetre galaxies and SZ clusters
We study lensing magnification of source galaxies by intervening galaxy groups and clusters using a halo model. Haloes are modelled with truncated NFW profiles with ellipticity added to their lensing potential and propagated to observable lensing statistics. We present the formalism to calculate observable effects due to a distribution of haloes of different masses at different redshifts along the line of sight. We calculate the effects of magnification on the number counts of high-redshift galaxies. Using Balloon-borne Large Aperture Submillimetre Telescope (BLAST) survey data for submillimetre galaxies (SMGs), we find that magnification affects the steep, high flux part of the counts by about 60 per cent. The effect becomes much stronger if the intrinsic distribution is significantly steeper than observed. We also consider the effect of this high-redshift galaxy population on contaminating the Sunyaev-Zel'dovich (SZ) signal of massive clusters using the halo model approach. We find that for the majority of clusters expected to be detected with ongoing SZ surveys, there is significant contamination from the Poisson noise due to background SMGs. This contribution can be comparable to the SZ increment for typical clusters and can also contaminate the SZ decrement of low-mass clusters. Thus, SZ observations, especially for the increment part of the SZ spectrum, need to include careful modelling of this irreducible contamination for mass estimation. Lensing further enhances the contamination, especially close to the cores of massive clusters and for very disturbed clusters with large magnification cross-section.
55870277
Measuring large-scale structure with quasars in narrow-band filter surveys
We show that a large-area imaging survey using narrow-band filters could detect quasars in sufficiently high number densities, and with more than sufficient accuracy in their photometric redshifts, to turn them into suitable tracers of large-scale structure. If a narrow-band optical survey can detect objects as faint as i= 23, it could reach volumetric number densities as high as 10−4 h3 Mpc−3 (comoving) at z∼ 1.5. Such a catalogue would lead to precision measurements of the power spectrum up to z∼ 3–4. We also show that it is possible to employ quasars to measure baryon acoustic oscillations at high redshifts, where the uncertainties from redshift distortions and non-linearities are much smaller than at z≲ 1. As a concrete example we study the future impact of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS), which is a narrow-band imaging survey in the optical over 1/5 of the unobscured sky with 42 filters of ∼100-A full width at half-maximum. We show that J-PAS will be able to take advantage of the broad emission lines of quasars to deliver excellent photometric redshifts, σz≃ 0.002 (1 +z), for millions of objects.
8039374
Photometric Redshift Requirements for Self-Calibration of Cluster Dark Energy Studies
The ability to constrain dark energy from the evolution of galaxy cluster counts is limited by the imperfect knowledge of cluster redshifts. Ongoing and upcoming surveys will mostly rely on redshifts estimated from broadband photometry (photo-z's). For a Gaussian distribution for the cluster photo-z errors and a high cluster yield cosmology defined by the WMAP 1 year results, the photo-z bias, and scatter needs to be known better than 0.003 and 0.03, respectively, in order not to degrade dark energy constrains by more than 10% for a survey with specifications similar to the South Pole Telescope. Smaller surveys and cosmologies with lower cluster yields produce weaker photo-z requirements, though relative to worse baseline constraints. Comparable photo-z requirements are necessary in order to employ self-calibration techniques when solving for dark energy and observable-mass parameters simultaneously. On the other hand, self-calibration in combination with external mass inferences helps reduce photo-z requirements and provides important consistency checks for future cluster surveys. In our fiducial model, training sets with spectroscopic redshifts for ∼5%-15% of the detected clusters are required in order to keep degradations in the dark energy equation of state lower than 20%.
119117607
Simulations of Galileon modified gravity: Clustering statistics in real and redshift space
We use N-body simulations to study the statistics of massive halos and redshift space distortions for theories with a standard \Lambda CDM expansion history and a galileon-type scalar field. The extra scalar field increases the gravitational force, leading to enhanced structure formation. We compare our measurements of the real space matter power spectrum and halo properties with fitting formula for estimating these quantities analytically. We find that a model for power spectrum, halo mass-function and halo bias, derived from \Lambda CDM simulations can fit the results from our simulations of modified gravity when \sigma_8 is appropriately adjusted. We also study the redshift space distortions in the two point correlation function measured from these simulations, finding a difference in the ratio of the redshift space to real space clustering amplitude relative to standard gravity on all scales. We find enhanced clustering on scales r>10 Mpc/h and increased damping of the correlation function for scales r<9 Mpc/h. The boost in the clustering on large scales due to the enhanced gravitational forces cannot be mimicked in a standard gravity model by simply changing \sigma_8. This result illustrates the usefulness of redshift space distortion measurements as a probe of modifications to General Relativity.
21813819
Magnification Effects on Source Counts and Fluxes
We consider the effect of lensing magnification on high redshift sources in the case that magnification varies on the sky, as expected in wide fields of view or within observed galaxy clusters. We give expressions for number counts, flux and flux variance as integrals over the probability distribution of the magnification. We obtain these through a simple mapping between averages over the observed sky and over the magnification probability distribution in the source plane. Our results clarify conflicting expressions in the literature and can be used to calculate a variety of magnification effects. We highlight two applications: 1. Lensing of high-z galaxies by galaxy clusters can provide the dominant source of scatter in SZ observations at frequencies larger than the SZ null. 2. The number counts of high-z galaxies with a Schechter-like luminosity function will be changed at high luminosities to a power law, with significant enhancement of the observed counts at L >
118387259
Energy conditions bounds and their confrontation with supernovae data
The energy conditions play an important role in the understanding of several properties of the Universe, including the current accelerating expansion phase and the possible existence of the so-called phantom fields. We show that the integrated bounds provided by the energy conditions on cosmological observables such as the distance modulus {mu}(z) and the lookback time t{sub L}(z) are not sufficient (or necessary) to ensure the local fulfillment of the energy conditions, making explicit the limitation of these bounds in the confrontation with observational data. We recast the energy conditions as bounds on the deceleration and normalized Hubble parameters, obtaining new bounds which are necessary and sufficient for the local fulfillment of the energy conditions. A statistical confrontation, with 1{sigma}-3{sigma} confidence levels, between our bounds and supernovae data from the gold and combined samples is made for the recent past. Our analyses indicate, with 3{sigma} confidence levels, the fulfillment of both the weak energy condition (WEC) and dominant energy condition (DEC) for z{<=}1 and z < or approx. 0.8, respectively. In addition, they suggest a possible recent violation of the null energy condition (NEC) with 3{sigma}, i.e. a very recent phase of superacceleration. Our analyses also show the possibility of violationmore » of the strong energy condition (SEC) with 3{sigma} in the recent past (z{<=}1), but interestingly the q(z)-best-fit curve crosses the SEC--fulfillment divider at z{approx_equal}0.67, which is a value very close to the beginning of the epoch of cosmic acceleration predicted by the standard concordance flat {lambda}CDM scenario.« less
119272920
REVISITING THE CONFRONTATION OF THE ENERGY CONDITIONS WITH SUPERNOVAE DATA
In the standard Friedmann–Lemaˆotre–Robertson–Walker (FLRW) approach to model the Universe the violation of the so-called energy conditions is related to some important properties of the Universe as, for example, the current and the inflationary accelerating expansion phases. The energy conditions are also necessary in the formulation and proofs of Hawking-Penrose singularity theorems. In two recent articles we have derived bounds from energy conditions and made confrontations of these bounds with supernovae data. Here, we extend these results in following way: first, by using our most recent statistical procedure for calculating new q(z) estimates from the gold and combined type Ia supernovae samples; second, we use these estimates to obtain a new picture of the energy conditions fulfillment and violation for the recent past (z ≤ 1) in the context of the standard cosmology.