Search

The integrated shear 3-point correlation function $\zeta_{\pm}$ measures the correlation between the local shear 2-point function $\xi_{\pm}$ and the 1-point shear aperture mass in patches of the sky. Unlike other higher-order statistics, $\zeta_{\pm}$ can be efficiently measured from cosmic shear data, and it admits accurate theory predictions on a wide range of scales as a function of cosmological and baryonic feedback parameters. Here, we develop and test a likelihood analysis pipeline for cosmological constraints using $\zeta_{\pm}$. We incorporate treatment of systematic effects from photometric redshift uncertainties, shear calibration bias and galaxy intrinsic alignments. We also develop an accurate neural-network emulator for fast theory predictions in MCMC parameter inference analyses. We test our pipeline using realistic cosmic shear maps based on $N$-body simulations with a DES Y3-like footprint, mask and source tomographic bins, finding unbiased parameter constraints. Relative to $\xi_{\pm}$-only, adding $\zeta_{\pm}$ can lead to $\approx 10-25\%$ improvements on the constraints of parameters like $A_s$ (or $\sigma_8$) and $w_0$. We find no evidence in $\xi_{\pm} + \zeta_{\pm}$ constraints of a significant mitigation of the impact of systematics. We also investigate the impact of the size of the apertures where $\zeta_{\pm}$ is measured, and of the strategy to estimate the covariance matrix ($N$-body vs. lognormal). Our analysis solidifies the strong potential of the $\zeta_{\pm}$ statistic and puts forward a pipeline that can be readily used to improve cosmological constraints using real cosmic shear data., Comment: 21 pages, 11 figures, 3 tables. Comments welcome

We present the integrated 3-point shear correlation function $i\zeta_{\pm}$ -- a higher-order statistic of the cosmic shear field -- which can be directly estimated in wide-area weak lensing surveys without measuring the full 3-point shear correlation function, making this a practical and complementary tool to 2-point statistics for weak lensing cosmology. We define it as the 1-point aperture mass statistic $M_{\mathrm{ap}}$ measured at different locations on the shear field correlated with the corresponding local 2-point shear correlation function $\xi_{\pm}$. Building upon existing work on the integrated bispectrum of the weak lensing convergence field, we present a theoretical framework for computing the integrated 3-point function in real space for any projected field within the flat-sky approximation and apply it to cosmic shear. Using analytical formulae for the non-linear matter power spectrum and bispectrum, we model $i\zeta_{\pm}$ and validate it on N-body simulations within the uncertainties expected from the sixth year cosmic shear data of the Dark Energy Survey. We also explore the Fisher information content of $i\zeta_{\pm}$ and perform a joint analysis with $\xi_{\pm}$ for two tomographic source redshift bins with realistic shape-noise to analyse its power in constraining cosmological parameters. We find that the joint analysis of $\xi_{\pm}$ and $i\zeta_{\pm}$ has the potential to considerably improve parameter constraints from $\xi_{\pm}$ alone, and can be particularly useful in improving the figure of merit of the dynamical dark energy equation of state parameters from cosmic shear data., Comment: Accepted for publication in MNRAS; v2 matches the accepted manuscript; 18 pages + appendix

We present analyses of data augmentation for machine learning redshift estimation. Data augmentation makes a training sample more closely resemble a test sample, if the two base samples differ, in order to improve measured statistics of the test sample. We perform two sets of analyses by selecting 800k (1.7M) SDSS DR8 (DR10) galaxies with spectroscopic redshifts. We construct a base training set by imposing an artificial r band apparent magnitude cut to select only bright galaxies and then augment this base training set by using simulations and by applying the K-correct package to artificially place training set galaxies at a higher redshift. We obtain redshift estimates for the remaining faint galaxy sample, which are not used during training. We find that data augmentation reduces the error on the recovered redshifts by 40% in both sets of analyses, when compared to the difference in error between the ideal case and the non augmented case. The outlier fraction is also reduced by at least 10% and up to 80% using data augmentation. We finally quantify how the recovered redshifts degrade as one probes to deeper magnitudes past the artificial magnitude limit of the bright training sample. We find that at all apparent magnitudes explored, the use of data augmentation with tree based methods provide a estimate of the galaxy redshift with a negligible bias, although the error on the recovered values increases as we probe to deeper magnitudes. These results have applications for surveys which have a spectroscopic training set which forms a biased sample of all photometric galaxies, for example if the spectroscopic detection magnitude limit is shallower than the photometric limit., 13 pages, 4 figures, version accepted by MNRAS, added analysis, results and conclusions unchanged

We present the largest M31 near-infrared (F110W (close to J band), F160W (H band)) Cepheid sample so far. The sample consists of 371 Cepheids with photometry obtained from the HST PHAT program. The sample of 319 fundamental mode Cepheids, 16 first overtone Cepheids and 36 type II Cepheids, was identified using the median absolute deviation (MAD) outlier rejection method we develop here. This method does not rely on priors and allows us to obtain this clean Cepheid sample without rejecting a large fraction of Cepheids. The obtained Period-Luminosity relations (PLRs) have a very small dispersion, i.e. 0.155 mag in F160W, despite using random phased observations. This remarkably small dispersion allows us to determine that the PLRs are significantly better described by a broken slope at ten days than a linear slope. The use of our sample as an anchor to determine the Hubble constant gives a $3.2\%$ larger Hubble constant compared to the Riess et al. (2012) sample., Accepted for publication in ApJ. Note that the estimate of the Hubble constant changed from the first to the second version. The estimation is now using the difference in the anchor galaxy and therefore the magnitude difference gives an increased Hubble constant

We describe the construction of a template set of spectral energy distributions (SEDs) for the estimation of photometric redshifts of luminous red galaxies (LRGs) with a Bayesian template fitting method. By examining the color properties of several publicly available SED sets within a redshift range of 00.15) of 0.12%. We show that templates that optimally describe the brightest galaxies (-24.5, Comment: 21 pages, 25 figures, accepted for publication in the Astrophysical Journal (ApJ)

We study the SLACS strong lensing system SDSSJ1430+4105 at z=0.285. The lensed source (z=0.575) of this system has a complex morphology with several subcomponents. Its subcomponents span a radial range from 4 to 10kpc in the lens plane. Therefore we can constrain the slope of the total projected mass profile around the Einstein radius (R_E) from lensing alone. We measure a density profile that is slightly but not significantly shallower than isothermal at R_E. We decompose the mass of the lensing galaxy into a de Vaucouleurs (deV) component to trace the stars and an additional dark component. The spread of multiple image components over a large radial range also allows us to determine the amplitude of the deV and dark matter components separately. We get a mass to light ratio of M_deV/L_B~5.5\pm1.5M/L_sun,B and a dark matter fraction within R_E of ~20 to 40%. Modelling the star formation history assuming composite stellar populations at solar metallicity to the galaxy's photometry yields a mass to light ratio of M_star,salp/L_B~4.0_{-1.3}^{+0.6}M/L_sun,B and M_star,chab/L_B~2.3_{-0.8}^{+0.3}M/L_sun,B for Salpeter and Chabrier IMFs, respectively. Hence, the mass to light ratio derived from lensing is more Salpeter-like, in agreement with results for massive Coma galaxies and other nearby massive early type galaxies. We examine the consequences of the galaxy group in which the lensing galaxy is embedded, showing that it has little influence on the mass to light ratio obtained for the deV component of the lensing galaxy. Finally, we decompose the projected, azimuthally averaged 2D density distribution of the deV and dark matter component of the lensing signal into spherically averaged 3D density profiles. We can show that the 3D dark and luminous matter density within R_E~0.6R_eff of this SLACS galaxy is similar to the values of Coma galaxies with the same velocity dispersions., 24 pages, 21 figures, 11 tables, accepted for publication by MNRAS

The early Universe at redshift z\sim6-11 marks the reionization of the intergalactic medium, following the formation of the first generation of stars. However, those young galaxies at a cosmic age of \lesssim 500 million years (Myr, at z \gtrsim 10) remain largely unexplored as they are at or beyond the sensitivity limits of current large telescopes. Gravitational lensing by galaxy clusters enables the detection of high-redshift galaxies that are fainter than what otherwise could be found in the deepest images of the sky. We report the discovery of an object found in the multi-band observations of the cluster MACS1149+22 that has a high probability of being a gravitationally magnified object from the early universe. The object is firmly detected (12 sigma) in the two reddest bands of HST/WFC3, and not detected below 1.2 {\mu}m, matching the characteristics of z\sim9 objects. We derive a robust photometric redshift of z = 9.6 \pm 0.2, corresponding to a cosmic age of 490 \pm 15Myr (i.e., 3.6% of the age of the Universe). The large number of bands used to derive the redshift estimate make it one of the most accurate estimates ever obtained for such a distant object. The significant magnification by cluster lensing (a factor of \sim15) allows us to analyze the object's ultra-violet and optical luminosity in its rest-frame, thus enabling us to constrain on its stellar mass, star-formation rate and age. If the galaxy is indeed at such a large redshift, then its age is less than 200 Myr (at the 95% confidence level), implying a formation redshift of zf \lesssim 14. The object is the first z>9 candidate that is bright enough for detailed spectroscopic studies with JWST, demonstrating the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts., Comment: Submitted to the Nature Journal. 39 Pages, 13 figures

We precisely constrain the inner mass profile of Abell 2261 (z=0.225) for the first time and determine this cluster is not "over-concentrated" as found previously, implying a formation time in agreement with {\Lambda}CDM expectations. These results are based on strong lensing analyses of new 16-band HST imaging obtained as part of the Cluster Lensing and Supernova survey with Hubble (CLASH). Combining this with revised weak lensing analyses of Subaru wide field imaging with 5-band Subaru + KPNO photometry, we place tight new constraints on the halo virial mass M_vir = 2.2\pm0.2\times10^15 M\odot/h70 (within r \approx 3 Mpc/h70) and concentration c = 6.2 \pm 0.3 when assuming a spherical halo. This agrees broadly with average c(M,z) predictions from recent {\Lambda}CDM simulations which span 5, Comment: Submitted to the Astrophysical Journal. 19 pages, 14 figures

Weak lensing measurements of cluster masses are necessary for calibrating mass-observable relations (MORs) to investigate the growth of structure and the properties of dark energy. However, the measured cluster shear signal varies at fixed mass M_200m due to inherent ellipticity of background galaxies, intervening structures along the line of sight, and variations in the cluster structure due to scatter in concentrations, asphericity and substructure. We use N-body simulated halos to derive and evaluate a weak lensing circular aperture mass measurement M_ap that minimizes the mass estimate variance in the presence of all these forms of variability. Depending on halo mass and observational conditions, the resulting mass estimator improves on M_ap filters optimized for circular NFW-profile clusters in the presence of uncorrelated large scale structure (LSS) about as much as the latter improve on an estimator that only minimizes the influence of shape noise. Optimizing for uncorrelated LSS while ignoring the variation of internal cluster structure puts too much weight on the profile near the cores of halos, and under some circumstances can even be worse than not accounting for LSS at all. We briefly discuss the impact of variability in cluster structure and correlated structures on the design and performance of weak lensing surveys intended to calibrate cluster MORs., Comment: 11 pages, 5 figures; accepted by MNRAS

The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit multi-cycle treasury program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the cluster cores, a key prediction of CDM. The CLASH cluster sample is larger and less biased than current samples of space-based imaging studies of clusters to similar depth, as we have minimized lensing-based selection that favors systems with overly dense cores. Specifically, twenty CLASH clusters are solely X-ray selected. The X-ray selected clusters are massive (kT > 5 keV; 5 - 30 x 10^14 M_solar) and, in most cases, dynamically relaxed. Five additional clusters are included for their lensing strength (Einstein radii > 35 arcsec at z_source = 2) to further quantify the lensing bias on concentration, to yield high resolution dark matter maps, and to optimize the likelihood of finding highly magnified high-redshift (z > 7) galaxies. The high magnification, in some cases, provides angular resolutions unobtainable with any current UVOIR facility and can yield z > 7 candidates bright enough for spectroscopic follow-up. A total of 16 broadband filters, spanning the near-UV to near-IR, are employed for each 20-orbit campaign on each cluster. These data are used to measure precise (sigma_phz < 0.02(1+z)) photometric redshifts for dozens of newly discovered multiply-lensed images per cluster. Observations of each cluster are spread over 8 epochs to enable a search, primarily in the parallel fields, for Type Ia supernovae at z > 1 to improve constraints on the time dependence of the dark energy equation of state and the evolution of such supernovae in an epoch when the universe is matter dominated., Accepted for publication in the Astrophysical Journal Supplements, 22 pages, 16 figures. Updated Tables 3,4,8 and figures 6 and 8 to reflect replacement of Abell 963 with Abell 1423 in CLASH survey. A963 cannot be observed with WFC3 due to the lack of usable guide stars

We want to derive bias free, accurate photometric redshifts for those fields of the CFHTLS-Wide data which are covered in the u*, g', r', i' and z' filters and are public on January 2008. These are 37 square degrees in the W1, W3 and W4 fields with photometric data for a total of 2.597.239 galaxies. We use the photometric redshift code PHOTO-z of Bender et al. (2001). We compare our redshifts for the W1, W3 and W4 fields to about 7500 spectroscopic redshifts from the VVDS therein. For galaxies with 17.5, 20 pages, 20 figures, full resolution pdf-file available at http://www.usm.uni-muenchen.de/people/mike/CFHTLS_photoz.pdf First referee report obtained 107 days after submission. Comments & suggestions of the referee are included. Paper resubmitted. photozs can be obtained on request, shortened abstract

We present a new method for reconstructing two-dimensional mass maps of galaxy clusters from the image distortion of background galaxies. In contrast to most previous approaches, which directly convert locally averaged image ellipticities to mass maps (direct methods), our entropy-regularized maximum-likelihood method is an inverse approach. Albeit somewhat more expensive computationally, our method allows high spatial resolution in those parts of the cluster where the lensing signal is strong enough. Furthermore, it allows to straightforwardly incorporate additional constraints, such as magnification information or strong-lensing features. Using synthetic data, we compare our new approach to direct methods and find indeed a substantial improvement especially in the reconstruction of mass peaks. The main differences to previously published inverse methods are discussed., Comment: 19 pages including 7 postscript figures; submitted to Astronomy and Astrophysics

The image distortions of high-redshift galaxies caused by gravitational light deflection of foreground clusters of galaxies can be used to reconstruct the two-dimensional surface mass density of these clusters. We apply an unbiased parameter-free reconstruction technique to the cluster CL0939+4713 (Abell 851), observed with the WFPC2 on board of the HST. We demonstrate that a single deep WFPC2 observation can be used for cluster mass reconstruction despite its small field of view and the irregular shape of the data field (especially for distant clusters). For CL0939, we find a strong correlation between the reconstructed mass distribution and the bright cluster galaxies indicating that mass follows light on average. The detected anti-correlation between the faint galaxies and the reconstructed mass is most likely an effect of the magnification (anti) bias, which was detected previously in the cluster A1689. Because of the high redshift of CL0939 (z_d=0.41), the redshift distribution of the lensed, faint galaxies has to be accounted for in the reconstruction technique. We derive an approximate global transformation for the surface mass density which leaves the mean image ellipticities invariant, resulting in an uncertainty in the normalization of the mass. From the non-negativity of the surface mass density, we derive lower limits on the mass inside the observed field. We can break the invariance transformation for the mass using the magnification effect on the observed number density of the background galaxies. Assuming a mean redshift of 0.8 and a fraction of 15 % (20 %) of cluster galaxies in the observed galaxy sample with 23, Comment: 23 pages, Plain-Tex, no macros needed, including 13 figures, three figures not included; a gzipped uuencoded postscript file can be obtained via anonymous ftp at ftp//ftp.mpa-garching.mpg.de/incoming/caro/cl0939.uu , submitted to Astronomy and Astrophysics

Gravitational light deflection can distort the images of distant sources by its tidal effects. The population of faint blue galaxies is at sufficiently high redshift so that their images are distorted near foreground clusters, with giant luminous arcs being the most spectacular evidence for this effect. Much weaker distortions, however, can observationally be detected by a statistical analysis of the numerous faint galaxy images, as first demonstrated by Tyson, Valdes \& Wenk. This distortion effect can be used as a {\it quantitativetool} for the reconstruction of the surface mass density of galaxy clusters with appropriate redshifts, as was demonstrated by Kaiser \&Squires. They have derived an explicit equation for this surface mass density in terms of its tidal field. The reconstruction formula by Kaiser \& Squires must be modified because of two effects: in its original form it applies only to weak lenses, and hence must be generalized to account for stronger lensing effects. Second, due to the nature of the inversion formula, it produces boundary artefacts (or biases) if applied to real data which are confined to a finite field on the sky. We discuss several possibilities to obtain inversion formulae which are exact for ideal data on a finite data field (CCD). We demonstrate that there exists an infinite number of such finite-field inversion formulae, which differ in their sensitivity to observational effects (such as noise, intrinsic ellipticities of the sources, etc.). We show that, using two simple conditions, one can uniquely specify a finite-field formula which in a well-defined sense minimizes the sensitivity to observational effects. We then use synthetic data to compare the quality of our new reconstruction method with that of previous, uuenc.ps-file, Fig.1,4,10 are in a second file (uuenc.ps) The new inversion kernel is easy to program but can also be obtained from the Authors (stella@mpa-garching.mpg.de)

In a recent paper by Rodrigues-Williams \& Hogan (RH94), a correlation between high-redshift, optically-selected QSOs and Zwicky clusters was reported at a very high significance level. Due to the fairly bright flux threshold of the cluster sample, these correlations cannot be interpreted as being due to an environmental effect of the clusters on the quasar activity. The most likely interpretation employed in RH94 was the effect of gravitational lensing by the foreground clusters, though the required magnification to explain the observed correlations has to be considerably higher than obtained from simple mass models for the clusters. We have repeated the analysis of RH94 using a different QSO sample, namely radio quasars and radio galaxies from the 1-Jy sample. In accordance with RH, we detect a statistically significant correlation between Zwicky clusters and 1-Jy sources with intermediate redshift ($z\approx 1$), but fail to detect significant effects for higher-redshift sources. In addition, we detect a highly significant underdensity of low-redshift radio sources around Zwicky clusters, for which an environmental interpretation seems to be most reasonable. Our result for the overdensity of $z\sim 1$ sources is in good agreement with previous results and can possibly be interpreted as a lensing effect, though we have not tried to quantitatively investigate a lensing model. Other interpretations, such as patchy dust obscuration, can not explain the observed effect and its tendency with redshift., 21 pages, uudecoded postscriptfile, figures included, MPA preprint number 828