arXiv subjects

Eduardo Rozo

Publications and source records attributed to Eduardo Rozo.

At least 91 records · Page 5Linked to original sources

arXiv2013

Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion

The quantity and quality of cosmic structure observations have greatly accelerated in recent years. Further leaps forward will be facilitated by imminent projects, which will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to the nature of dark matter and dark energy. Dark energy and gravity both affect how rapidly structure grows; the greater the acceleration, the more suppressed the growth of structure, while the greater the gravity, the more enhanced the growth. While distance measurements also constrain dark energy, the comparison of growth and distance data tests whether General Relativity describes the laws of physics accurately on large scales. Modified gravity models are able to reproduce the distance measurements but at the cost of altering the growth of structure (these signatures are described in more detail in the accompanying paper on Novel Probes of Gravity and Dark Energy). Upcoming surveys will exploit these differences to determine whether the acceleration of the Universe is due to dark energy or to modified gravity. To realize this potential, both wide field imaging and spectroscopic redshift surveys play crucial roles. Projects including DES, eBOSS, DESI, PFS, LSST, Euclid, and WFIRST are in line to map more than a 1000 cubic-billion-light-year volume of the Universe. These will map the cosmic structure growth rate to 1% in the redshift range 0<z<2, over the last 3/4 of the age of the Universe.

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arXiv2013

redMaPPer II: X-ray and SZ Performance Benchmarks for the SDSS Catalog

We evaluate the performance of the SDSS DR8 redMaPPer photometric cluster catalog by comparing it to overlapping X-ray and SZ selected catalogs from the literature. We confirm the redMaPPer photometric redshifts are nearly unbiased (<Δz> < 0.005), have low scatter (σ_z ~ 0.006-0.02, depending on redshift), and have a low catastrophic failure rate (~ 1%). Both the T_X-λ and Mgas-λ scaling relations are consistent with a mass scatter of σ_{\ln M|λ} ~ 25%, albeit with a ~ 1% outlier rate due to projection effects. This failure rate is somewhat lower than that expected for the full cluster sample, but is consistent with the additional selection effects introduced by our reliance on X-ray and SZ selected reference cluster samples. Where the redMaPPer DR8 catalog is volume limited (z < 0.35), the catalog is 100% complete above T_X > 3.5 keV, and L_X > 2\times 10^{44} erg/s, decreasing to 90% completeness at L_X ~ 10^{43} erg/s. All rich (λ> 100), low redshift (z < 0.25) redMaPPer clusters are X-ray detected in the ROSAT All Sky Survey (RASS), and 86% of the clusters are correctly centered. Compared to other SDSS photometric cluster catalogs, redMaPPer has the highest completeness and purity, and the best photometric redshift performance, though some algorithms do achieve comparable performance to redMaPPer in subsets of the above categories and/or in limited redshift ranges. The redMaPPer richness is clearly the one that best correlates with X-ray temperature and gas mass. Most algorithms (including redMaPPer) have very similar centering performance, with only one exception which performs worse.

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arXiv2013

Observational Probes of Cosmic Acceleration

The accelerating expansion of the universe is the most surprising cosmological discovery in many decades, implying that the universe is dominated by some form of "dark energy" with exotic physical properties, or that Einstein's theory of gravity breaks down on cosmological scales. The profound implications of cosmic acceleration have inspired ambitious experimental efforts to measure the history of expansion and growth of structure with percent-level precision or higher. We review in detail the four most well established methods for making such measurements: Type Ia supernovae, baryon acoustic oscillations (BAO), weak gravitational lensing, and galaxy clusters. We pay particular attention to the systematic uncertainties in these techniques and to strategies for controlling them at the level needed to exploit "Stage IV" dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST. We briefly review a number of other approaches including redshift-space distortions, the Alcock-Paczynski test, and direct measurements of H_0. We present extensive forecasts for constraints on the dark energy equation of state and parameterized deviations from GR, achievable with Stage III and Stage IV experimental programs that incorporate supernovae, BAO, weak lensing, and CMB data. We also show the level of precision required for other methods to provide constraints competitive with those of these fiducial programs. We emphasize the value of a balanced program that employs several of the most powerful methods in combination, both to cross-check systematic uncertainties and to take advantage of complementary information. Surveys to probe cosmic acceleration produce data sets with broad applications, and they continue the longstanding astronomical tradition of mapping the universe in ever greater detail over ever larger scales.

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arXiv2013

Cluster Cosmology at a Crossroads: Neutrino Masses

Galaxy clusters --- in combination with CMB and BAO data --- can provide precise constraints on the sum of neutrino masses. However, these constraints depend on the calibration of the mass--observable relation. For instance, the mass calibration employed in Planck Collaboration (2011a,b) rules out the minimal 6-parameter ΛCDM model at 3.7σ, and implies a sum of neutrino masses \sum m_ν= 0.39 \pm 0.10. By contrast, the mass calibration favored by Rozo et al. (2012b) from a self-consistent analysis of X-ray, SZ, and optical scaling relations is consistent with a minimal flat ΛCDM model with no massive neutrinos (1.7σ), and is a better fit to additional data (e.g. H0). We discuss these results in light of the recent SPT and ACT analysis, noting that the Rozo et al. (2012b) model suggests the current mild "tension" (<2σ) between CMB and BAO+H_0 data will decrease as the uncertainties in these measurements decrease.

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arXiv2012

Spatial Anisotropy of Galaxy Kinematics in Sloan Digital Sky Survey Galaxy Clusters

Measurements of galaxy cluster kinematics are important in understanding the dynamical state and evolution of clusters of galaxies, as well as constraining cosmological models. While it is well established that clusters exhibit non-spherical geometries, evident in the distribution of galaxies on the sky, azimuthal variations of galaxy kinematics within clusters have yet to be observed. Here we measure the azimuthal dependence of the line-of-sight velocity dispersion profile in a stacked sample of 1743 galaxy clusters from the Sloan Digital Sky Survey (SDSS). The clusters are drawn from the SDSS DR8 redMaPPer catalog. We find that the line-of-sight velocity dispersion of galaxies lying along the major axis of the central galaxy is larger than those that lie along the minor axis. This is the first observational detection of anisotropic kinematics of galaxies in clusters. We show that the result is consistent with predictions from numerical simulations. Furthermore we find that the degree of projected anisotropy is strongly dependent on the line-of-sight orientation of the galaxy cluster, opening new possibilities for assessing systematics in optical cluster finding.

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arXiv2012

Cosmological Constraints from the Large Scale Weak Lensing of SDSS MaxBCG Clusters

We derive constraints on the matter density \Om and the amplitude of matter clustering \sig8 from measurements of large scale weak lensing (projected separation R=5-30\hmpc) by clusters in the Sloan Digital Sky Survey MaxBCG catalog. The weak lensing signal is proportional to the product of \Om and the cluster-mass correlation function \xicm. With the relation between optical richness and cluster mass constrained by the observed cluster number counts, the predicted lensing signal increases with increasing \Om or \sig8, with mild additional dependence on the assumed scatter between richness and mass. The dependence of the signal on scale and richness partly breaks the degeneracies among these parameters. We incorporate external priors on the richness-mass scatter from comparisons to X-ray data and on the shape of the matter power spectrum from galaxy clustering, and we test our adopted model for \xicm against N-body simulations. Using a Bayesian approach with minimal restrictive priors, we find \sig8(\Om/0.325)^{0.501}=0.828 +/- 0.049, with marginalized constraints of \Om=0.325_{-0.067}^{+0.086} and \sig8=0.828_{-0.097}^{+0.111}, consistent with constraints from other MaxBCG studies that use weak lensing measurements on small scales (R<=2\hmpc). The (\Om,\sig8) constraint is consistent with and orthogonal to the one inferred from WMAP CMB data, reflecting agreement with the structure growth predicted by GR for an LCDM cosmological model. A joint constraint assuming LCDM yields \Om=0.298 +/- 0.020 and \sig8=0.831 +/- 0.020. Our cosmological parameter errors are dominated by the statistical uncertainties of the large scale weak lensing measurements, which should shrink sharply with current and future imaging surveys.

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arXiv2012

A Comparative Study of Local Galaxy Clusters: II: X-ray and SZ Scaling Relations

We compare cluster scaling relations published for three different samples selected via X-ray and Sunyaev-Zel'dovich (SZ) signatures. We find tensions driven mainly by two factors: i) systematic differences in the X-ray cluster observables used to derive the scaling relations, and ii) uncertainty in the modeling of how the gas mass of galaxy clusters scales with total mass. All scaling relations are in agreement after accounting for these two effects. We describe a multivariate scaling model that enables a fully self-consistent treatment of multiple observational catalogs in the presence of property covariance, and apply this formalism when interpreting published results. The corrections due to scatter and observable covariance can be significant. For instance, our predicted Ysz-Lx scaling relation differs from that derived using the naive "plug in" method by \approx 25%. Finally, we test the mass normalization for each of the X-ray data sets we consider by applying a space density consistency test: we compare the observed REFLEX luminosity function to expectations from published Lx-M relations convolved with the mass function for a WMAP7 flat ΛCDM model.

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arXiv2012

Closing the Loop: A Self-Consistent Model of Optical, X-ray, and SZ Scaling Relations for Clusters of Galaxies

We demonstrate that optical data from SDSS, X-ray data from ROSAT and Chandra, and SZ data from Planck, can be modeled in a fully self-consistent manner. After accounting for systematic errors and allowing for property covariance, we find that scaling relations derived from optical and X-ray selected cluster samples are consistent with one another. Moreover, these clusters scaling relations satisfy several non-trivial spatial abundance constraints and closure relations. Given the good agreement between optical and X-ray samples, we combine the two and derive a joint set of LX-M and YSZ-M relations. Our best fit YSZ-M relation is in good agreement with the observed amplitude of the thermal SZ power spectrum for a WMAP7 cosmology, and is consistent with the masses for the two CLASH galaxy clusters published thus far. We predict the halo masses of the remaining z \leq 0.4 CLASH clusters, and use our scaling relations to compare our results with a variety of X-ray and weak lensing cluster masses from the literature.

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arXiv2012

A Comparative Study of Local Galaxy Clusters: I. Derived X-ray Observables

We examine systematic differences in the derived X-ray properties of galaxy clusters as reported by three different groups: Vikhlinin et al. (2009a), Mantz et al. (2010b), and Planck Collaboration (2011b). The sample overlap between any two pairs of works ranges between 16 to 28 galaxy clusters in common. We find systematic differences in most reported properties, including the total cluster mass, M500. The most extreme case is an average 45% \pm 5% difference in cluster mass between the Planck Collaboration (2011b) and Mantz et al. (2010b), for clusters at z > 0.13 (averaged over 16 clusters). These mass differences induce differences in cluster observables defined within an R500 aperture. After accounting for aperture differences, we find very good agreement in gas mass estimates between the different groups. However, the soft-band X-ray luminosity, LX, core-excised spectroscopic temperature, TX, and gas thermal energy, YX = MgasTX display mean differences at the 5%-15% level. We also find that the low (z \leq 0.13) and high (z \geq 0.13) galaxy cluster samples in Planck Collaboration (2011b) appear to be systematically different: the YSZ/YX ratio for these two sub- samples is ln(YSZ/YX) = -0.06 \pm 0.04 and ln(YSZ/YX) = 0.08 \pm 0.04 for the low and high redshift sub-samples respectively.

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arXiv2012

The Ysz--Yx Scaling Relation as Determined from Planck and Chandra

SZ clusters surveys like Planck, the South Pole Telescope, and the Atacama Cosmology Telescope, will soon be publishing several hundred SZ-selected systems. The key ingredient required to transport the mass calibration from current X-ray selected cluster samples to these SZ systems is the Ysz--Yx scaling relation. We constrain the amplitude, slope, and scatter of the Ysz--Yx scaling relation using SZ data from Planck, and X-ray data from Chandra. We find a best fit amplitude of \ln (D_A^2\Ysz/CY_X) = -0.202 \pm 0.024 at the pivot point CY_X=8\times 10^{-5} Mpc^2. This corresponds to a Ysz/Yx-ratio of 0.82\pm 0.024, in good agreement with X-ray expectations after including the effects of gas clumping. The slope of the relation is α=0.916\pm 0.032, consistent with unity at \approx 2.3σ. We are unable to detect intrinsic scatter, and find no evidence that the scaling relation depends on cluster dynamical state.

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arXiv2011

The Sunyaev-Zeldovich Signal of the maxBCG SDSS Galaxy Clusters in WMAP

The Planck Collaboration measured the Sunyaev-Zel'dovich (SZ) decrement of optically selected clusters from the Sloan Digital Sky Survey, finding that it falls significantly below expectations based on existing mass calibration of the maxBCG galaxy clusters. Resolving this tension requires either the data to go up, or the theoretical expectations to come down. Here, we use data from the Wilkinson Microwave Anisotropy Probe (WMAP) to perform an independent estimate of the SZ decrement of maxBCG clusters. The recovered signal is consistent with that obtained using Planck, though with larger error bars due to WMAP's larger beam size and smaller frequency range. Nevertheless, this detection serves as an independent confirmation of the magnitude of the effect, and demonstrates that the observed discrepancy must be theoretical in origin.

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arXiv2011

Extrinsic Sources of Scatter in the Richness-Mass Relation of Galaxy Clusters

Maximizing the utility of upcoming photometric cluster surveys requires a thorough understanding of the richness-mass relation of galaxy clusters. We use Monte Carlo simulations to study the impact of various sources of observational scatter on this relation. Cluster ellipticity, photometric errors, photometric redshift errors, and cluster-to-cluster variations in the properties of red-sequence galaxies contribute negligible noise. Miscentering, however, can be important, and likely contributes to the scatter in the richness-mass relation of galaxy maxBCG clusters at the low mass end, where centering is more difficult. We also investigate the impact of projection effects under several empirically motivated assumptions about cluster environments. Using SDSS data and the maxBCG cluster catalog, we demonstrate that variations in cluster environments can rarely (\approx 1% - 5% of the time) result in significant richness boosts. Due to the steepness of the mass/richness function, the corresponding fraction of optically selected clusters that suffer from these projection effects is \approx 5% - 15%. We expect these numbers to be generic in magnitude, but a precise determination requires detailed, survey-specific modeling.

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arXiv2011

Cosmological Constraints from Galaxy Clustering and the Mass-to-Number Ratio of Galaxy Clusters

We place constraints on the average density (Omega_m) and clustering amplitude (sigma_8) of matter using a combination of two measurements from the Sloan Digital Sky Survey: the galaxy two-point correlation function, w_p, and the mass-to-galaxy-number ratio within galaxy clusters, M/N, analogous to cluster M/L ratios. Our w_p measurements are obtained from DR7 while the sample of clusters is the maxBCG sample, with cluster masses derived from weak gravitational lensing. We construct non-linear galaxy bias models using the Halo Occupation Distribution (HOD) to fit both w_p and M/N for different cosmological parameters. HOD models that match the same two-point clustering predict different numbers of galaxies in massive halos when Omega_m or sigma_8 is varied, thereby breaking the degeneracy between cosmology and bias. We demonstrate that this technique yields constraints that are consistent and competitive with current results from cluster abundance studies, even though this technique does not use abundance information. Using w_p and M/N alone, we find Omega_m^0.5*sigma_8=0.465+/-0.026, with individual constraints of Omega_m=0.29+/-0.03 and sigma_8=0.85+/-0.06. Combined with current CMB data, these constraints are Omega_m=0.290+/-0.016 and sigma_8=0.826+/-0.020. All errors are 1-sigma. The systematic uncertainties that the M/N technique are most sensitive to are the amplitude of the bias function of dark matter halos and the possibility of redshift evolution between the SDSS Main sample and the maxBCG sample. Our derived constraints are insensitive to the current level of uncertainties in the halo mass function and in the mass-richness relation of clusters and its scatter, making the M/N technique complementary to cluster abundances as a method for constraining cosmology with future galaxy surveys.

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arXiv2010

A GMBCG Galaxy Cluster Catalog of 55,424 Rich Clusters from SDSS DR7

We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.

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arXiv2010

Precision Measurements of the Cluster Red Sequence using an Error Corrected Gaussian Mixture Model

The red sequence is an important feature of galaxy clusters and plays a crucial role in optical cluster detection. Measurement of the slope and scatter of the red sequence are affected both by selection of red sequence galaxies and measurement errors. In this paper, we describe a new error corrected Gaussian Mixture Model for red sequence galaxy identification. Using this technique, we can remove the effects of measurement error and extract unbiased information about the intrinsic properties of the red sequence. We use this method to select red sequence galaxies in each of the 13,823 clusters in the maxBCG catalog, and measure the red sequence ridgeline location and scatter of each. These measurements provide precise constraints on the variation of the average red galaxy populations in the observed frame with redshift. We find that the scatter of the red sequence ridgeline increases mildly with redshift, and that the slope decreases with redshift. We also observe that the slope does not strongly depend on cluster richness. Using similar methods, we show that this behavior is mirrored in a spectroscopic sample of field galaxies, further emphasizing that ridgeline properties are independent of environment.

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arXiv2010

Weak Lensing Mass Calibration with Shear and Magnification

We study how joint shear and magnification measurements improve the statistical precision of weak lensing mass calibration experiments, relative to standard shear-only analysis. For our magnification measurements, we consider not only the impact of lensing on the source density of galaxies, but also the apparent increase in source sizes. The combination of all three lensing probes - density, size, and shear - can improve the statistical precision of mass estimates by as much as 40% - 50%. This number is insensitive to survey assumptions, though it depends on the degree of knowledge of the parameters controlling the magnification measurements, and on the value of the parameter q that characterizes the response of the source population to magnification. Furthermore, the combination of magnification and shear allows for powerful cross-checks on residual systematics (such as point spread function corrections) at the few percent level.

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arXiv2010

Stacked Weak Lensing Mass Calibration: Estimators, Systematics, and Impact on Cosmological Parameter Constraints

When extracting the weak lensing shear signal, one may employ either locally normalized or globally normalized shear estimators. The former is the standard approach when estimating cluster masses, while the latter is the more common method among peak finding efforts. While both approaches have identical signal-to-noise in the weak lensing limit, it is possible that higher order corrections or systematics considerations make one estimator preferable over the other. In this paper, we consider the efficacy of both estimators within the context of stacked weak lensing mass estimation in the Dark Energy Survey (DES). We find the two estimators have nearly identical statistical precision, even after including higher order corrections, but that these corrections must be incorporated into the analysis to avoid observationally relevant biases in the recovered masses. We also demonstrate that finite bin-width effects may be significant if not properly accounted for, and that the two estimators exhibit different systematics, particularly with respect to contamination of the source catalog by foreground galaxies. Thus, the two estimators may be employed as a systematics cross-check of each other. Stacked weak lensing in the DES should allow for the mean mass of galaxy clusters to be calibrated to about 2% precision (statistical only), which can improve the figure of merit of the DES cluster abundance experiment by a factor of ~3 relative to the self-calibration expectation. A companion paper (Schmidt & Rozo, 2010) investigates how the two types of estimators considered here impact weak lensing peak finding efforts.

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arXiv2010

Weak Lensing Peak Finding: Estimators, Filters, and Biases

Large catalogs of shear-selected peaks have recently become a reality. In order to properly interpret the abundance and properties of these peaks, it is necessary to take into account the effects of the clustering of source galaxies, among themselves and with the lens. In addition, the preferred selection of lensed galaxies in a flux- and size-limited sample leads to fluctuations in the apparent source density which correlate with the lensing field (lensing bias). In this paper, we investigate these issues for two different choices of shear estimators which are commonly in use today: globally-normalized and locally-normalized estimators. While in principle equivalent, in practice these estimators respond differently to systematic effects such as lensing bias and cluster member dilution. Furthermore, we find that which estimator is statistically superior depends on the specific shape of the filter employed for peak finding; suboptimal choices of the estimator+filter combination can result in a suppression of the number of high peaks by orders of magnitude. Lensing bias generally acts to increase the signal-to-noise νof shear peaks; for high peaks the boost can be as large as Δν~ 1-2. Due to the steepness of the peak abundance function, these boosts can result in a significant increase in the abundance of shear peaks. A companion paper (Rozo et al., 2010) investigates these same issues within the context of stacked weak lensing mass estimates.

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