122 research outputs found
Colour matters: the effects of lensing on the positional offsets between optical and submillimetre galaxies in Herschel★-ATLAS
No full textWe report an unexpected variation in the positional offset distributions between Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) submillimetre (submm) sources and their optical associations, depending on both 250-mu m signal-to-noise ratio and 250/350-mu m colour. We show that redder and brighter submm sources have optical associations with a broader distribution of positional offsets than would be expected if these offsets were due to random positional errors in the source extraction. The observation can be explained by two possible effects: either red submm sources trace a more clustered population than blue ones, and their positional errors are increased by confusion, or red submm sources are generally at high redshifts and are frequently associated with low-redshift lensing structures which are identified as false counterparts. We perform various analyses of the data, including the multiplicity of optical associations, the redshift and magnitude distributions in H-ATLAS in comparison to HerMES, and simulations of weak lensing, and we conclude that the effects are most likely to be explained by widespread weak lensing of Herschel-SPIRE sources by foreground structures. This has important consequences for counterpart identification and derived redshift distributions and luminosity functions of submm surveys.</p
Constraining f (R) Gravity Theory Using Weak Lensing Peak Statistics from the Canada-France-Hawaii-Telescope Lensing Survey
No full textIn this Letter, we report the observational constraints on the Hu-Sawicki f (R) theory derived from weak lensing peak abundances, which are closely related to the mass function of massive halos. In comparison with studies using optical or x-ray clusters of galaxies, weak lensing peak analyses have the advantages of not relying on mass-baryonic observable calibrations. With observations from the Canada-France-Hawaii-Telescope Lensing Survey, our peak analyses give rise to a tight constraint on the model parameter vertical bar f(R0)vertical bar for n = 1. The 95% C.L. is log(10) vertical bar f(R0)vertical bar < -4.82 given WMAP9 priors on (Omega(m), A(s)). With Planck15 priors, the corresponding result is log(10) vertical bar f(R0)vertical bar < -5.16.BIS National E-infrastructure Capital Grant [ST/K00042X/1]; STFC Capital Grants [ST/H008519/1, ST/K00087X/1]; STFC DIRAC Operations Grant [ST/K003267/1]; Durham University; Ministry of Finance of People's Republic of China [ZDYZ2008-2]; NSFC of China [11333001, 11173001, 11033005]; NSFC [11103012, 1143303, 1143304]; Shanghai Research Grant of STCSM [13JC1404400, 16ZR1424800]; Shanghai Normal University [DYL201603]; 1000 Young Talents program in China; Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences Grant [XDB09000000]; U.K. STFC Consolidated Grants [ST/L00075X/1, RF040335]; China Postdoctoral Science Foundation [2016M591006]SCI(E)[email protected]
Neutrino masses, dark energy and the gravitational lensing of pre-galactic H i
No full textWe study the constraints which the next generation of radio telescopes could place on the mass and number of neutrino species by studying the gravitational lensing of high-redshift 21-cm emission in combination with wide-angle surveys of galaxy lensing. We use simple characterizations of reionization history and of proposed telescope designs to forecast the constraints and detectability threshold for neutrinos. It is found that the degeneracy between neutrino parameters and dark energy parameters is significantly reduced by incorporating 21-cm lensing. The combination of galaxy and 21-cm lensing could constrain the sum of the neutrino masses to within ∼0.04 eV and the number of species to within ∼0.1. This is an improvement of a factor of 2.6 in mass and 1.4 in number over a galaxy lensing survey alone. This includes marginalizing over an 11-parameter cosmological model with a two-parameter model for the dark energy equation of state. If the dark energy equation of state is held fixed at w ≡ p/ρ = -1, the constraints improve to ∼0.025 eV and 0.04. These forecasted errors depend critically on the fraction of sky that can be surveyed in redshifted 21-cm emission (25 per cent is assumed here) and the redshift of reionization (z = 7 is assumed here). It is also found that neutrinos with masses too small to be detected in the data could none the less cause a significant bias in the measured dark energy equation of state. © 2009 The Author. Journal compilation. © 2009 RAS
NOISY WEAK-LENSING CONVERGENCE PEAK STATISTICS NEAR CLUSTERS OF GALAXIES AND BEYOND
No full textTaking into account noise from intrinsic ellipticities of source galaxies, in this paper, we study the peak statistics in weak-lensing convergence maps around clusters of galaxies and beyond. We emphasize how the noise peak statistics is affected by the density distribution of nearby clusters, and also how cluster-peak signals are changed by the existence of noise. These are the important aspects to be thoroughly understood in weak-lensing analyses for individual clusters as well as in cosmological applications of weak-lensing cluster statistics. We adopt Gaussian smoothing with the smoothing scale theta(G) = 0.5 arcmin in our analyses. It is found that the noise peak distribution near a cluster of galaxies sensitively depends on the density profile of the cluster. For a cored isothermal cluster with the core radius R-c, the inner region with R <= R-c appears noisy containing on average similar to 2.4 peaks with nu >= 5 for R-c = 1.7 arcmin and the true peak height of the cluster nu = 5.6, where nu denotes the convergence signal-to-noise ratio. For a Navarro-Frenk-White (NFW) cluster of the same mass and the same central nu, the average number of peaks with nu >= 5 within R <= R-c is similar to 1.6. Thus a high peak corresponding to the main cluster can be identified more cleanly in the NFW case. In the outer region with R-c < R <= 5R(c), the number of high noise peaks is considerably enhanced in comparison with that of the pure noise case without the nearby cluster. For nu >= 4, depending on the treatment of the mass-sheet degeneracy in weak-lensing analyses, the enhancement factor f is in the range of similar to 5 to similar to 55 for both clusters as their outer density profiles are similar. The properties of the main-cluster-peak identified in convergence maps are also significantly affected by the presence of noise. Scatters as well as a systematic shift for the peak height are present. The height distribution is peaked at nu similar to 6.6, rather than at nu = 5.6, corresponding to a shift of Delta nu similar to 1, for the isothermal cluster. For the NFW cluster, Delta nu similar to 0.8. The existence of noise also causes a location offset for the weak-lensing identified main-cluster-peak with respect to the true center of the cluster. The offset distribution is very broad and extends to R similar to R-c for the isothermal case. For the NFW cluster, it is relatively narrow and peaked at R similar to 0.2R(c). We also analyze NFW clusters of different concentrations. It is found that the more centrally concentrated the mass distribution of a cluster is, the less its weak-lensing signal is affected by noise. Incorporating these important effects and the mass function of NFW dark matter halos, we further present a model calculating the statistical abundances of total convergence peaks, true and false ones, over a large field beyond individual clusters. The results are in good agreement with those from numerical simulations. The model then allows us to probe cosmologies with the convergence peaks directly without the need of expensive follow-up observations to differentiate true and false peaks.Astronomy & AstrophysicsSCI(E)16ARTICLE21408-142071
Direct probe of dark energy through gravitational lensing effect
No full textWe show that gravitational lensing can provide a direct method to probe the nature of dark energy at astrophysical scales. For lensing system as an isolated astrophysical object, we derive the dark energy contribution to gravitational potential as a repulsive power law term, containing a generic equation of state parameter w. We find that it generates w-dependent and position-dependent modification to the conventional light orbital equation of w = -1. With post-Newtonian approximation, we compute its direct effect for an isolated lensing system at astrophysical scales and find that the dark energy force can deflect the path of incident light rays. We demonstrate that the dark-energy-induced deflection angle Delta alpha(DE) alpha M(1+1/3w) (with1+1/3w > 0), which increases with the lensing mass M and consistently approaches zero in the limit M -> 0. This effect is distinctive because dark energy tends to diffuse the rays and generates concave lensing effect. This is in contrast to the conventional convex lensing effect caused by both visible and dark matter. Measuring such concave lensing effect can directly probe the existence and nature of dark energy. We estimate this effect and show that the current gravitational lensing experiments are sensitive to the direct probe of dark energy at astrophysical scales. For the special case w = -1, our independent study favors the previous works that the cosmological constant can affect light bending, but our prediction qualitatively and quantitatively differ from the literature, including our consistent realization of Delta alpha(DE) -> 0 (under M -> 0) at the leading order.National NSF of China [11275101, 11135003, 11675086]SCI(E)ARTICLE
Moderate galaxy-galaxy lensing
No full textWe study moderate gravitational lensing where a background galaxy is magnified substantially, but not multiply imaged, by an intervening galaxy. We focus on the case where both the lens and source are elliptical galaxies. The signatures of moderate lensing include isophotal distortions and systematic shifts in the Fundamental Plane and Kormendy relation, which can potentially be used to statistically determine the galaxy mass profiles. These effects are illustrated using Monte Carlo simulations of galaxy pairs where the foreground galaxy is modelled as a singular isothermal sphere model and observational parameters appropriate for the Large Synoptic Survey Telescope. The range in radius probed by moderate lensing will be larger than that by strong lensing, and is in the interesting regime where the density slope may be changing. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS
Galaxy-Galaxy Weak-lensing Measurements from SDSS. I. Image Processing and Lensing Signals
No full textWe present our image processing pipeline that corrects the systematics introduced by the point-spread function (PSF). Using this pipeline, we processed Sloan Digital Sky Survey (SDSS) DR7 imaging data in r band and generated a galaxy catalog containing the shape information. Based on our shape measurements of the galaxy images from SDSS DR7, we extract the galaxy-galaxy (GG) lensing signals around foreground spectroscopic galaxies binned in different luminosities and stellar masses. We estimated the systematics, e. g., selection bias, PSF reconstruction bias, PSF dilution bias, shear responsivity bias, and noise rectification bias, which in total is between -9.1% and 20.8% at 2 sigma levels. The overall GG lensing signals we measured are in good agreement with Mandelbaum et al. The reduced chi(2) between the two measurements in different luminosity bins are from 0.43 to 0.83. Larger reduced chi(2) from 0.60 to 1.87 are seen for different stellar mass bins, which is mainly caused by the different stellar mass estimator. The results in this paper with higher signal-to-noise ratio are due to the larger survey area than SDSS DR4, confirming that more luminous/massive galaxies bear stronger GG lensing signals. We divide the foreground galaxies into red/blue and star-forming/quenched subsamples and measure their GG lensing signals. We find that, at a specific stellar mass/luminosity, the red/quenched galaxies have stronger GG lensing signals than their counterparts, especially at large radii. These GG lensing signals can be used to probe the galaxy-halo mass relations and their environmental dependences in the halo occupation or conditional luminosity function framework.973 Program [2015CB857002]; NSFC [11128306, 11121062, 11233005, 11503064, 11333001, 11673018, 11303033]; Strategic Priority Research Program "The Emergence of Cosmological Structures" of the Chinese Academy of Sciences [XDB09000000]; Office of Science and Technology, Shanghai Municipal Government [11DZ2260700]; Chinese Scholarship Council [201504910477]; Shanghai Natural Science Foundation [15ZR1446700]; STCSM grant [13JC1404400, 16R1424800]; SHNU grant [DYL201603]; Klaus Tschira Foundation; U.S. National Science Foundation [AST 1516962]; Youth Innovation Promotion Association of CAS; High Performance Computing Resource in the Core Facility for Advanced Research Computing at Shanghai Astronomical ObservatorySCI(E)ARTICLE183
No evidence for the evolution of mass density power-law index gamma from strong gravitational lensing observation
No full textIn this paper, we consider the singular isothermal sphere lensing model that has a spherically symmetric power-law mass distribution rho(tot)(r) similar to r(-gamma). We investigate whether the mass density power-law index gamma is cosmologically evolutionary by using the strong gravitational lensing (SGL) observation, in combination with other cosmological observations. We also check whether the constraint result of gamma is affected by the cosmological model, by considering several simple dynamical dark energy models. We find that the constraint on gamma is mainly decided by the SGL observation and independent of the cosmological model, and we find no evidence for the evolution of gamma from the SGL observation.National Natural Science Foundation of China [11522540, 11690021]; Top-Notch Young Talents Program of China; Provincial Department of Education of Liaoning [L2012087]SCI(E)ARTICLE86
Constraining modified gravity with weak-lensing peaks
No full text\ua9 2024 The Author(s)It is well established that maximizing the information extracted from upcoming and ongoing stage-IV weak-lensing surveys requires higher order summary statistics that complement the standard two-point statistics. In this work, we focus on weak-lensing peak statistics to test two popular modified gravity models, f(R) and nDGP, using the FORGE and BRIDGE weak-lensing simulations, respectively. From these simulations, we measure the peak statistics as a function of both cosmological and modified gravity parameters simultaneously. Our findings indicate that the peak abundance is sensitive to the strength of modified gravity, while the peak two-point correlation function is sensitive to the nature of the screening mechanism in a modified gravity model. We combine these simulated statistics with a Gaussian Process Regression emulator and a Gaussian likelihood to generate stage-IV forecast posterior distributions for the modified gravity models. We demonstrate that, assuming small scales can be correctly modelled, peak statistics can be used to distinguish general relativity from f(R) and nDGP models at the 2σ level with a stage-IV survey area of 300 and 1000 deg2, respectively. Finally, we show that peak statistics can constrain log10 (|fR0|) = −6 per cent to 2 per cent precision, and log10(H0rc) = 0.5 per cent to 25 per cent precision
Measuring the deviation from the linear and deterministic bias through cosmic gravitational lensing effects
No full textSince gravitational lensing effects directly probe inhomogeneities of dark matter, lensing-galaxy cross-correlations can provide us important information on the relation between dark matter and galaxy distributions, i.e., the bias. In this paper, we propose a method to measure the stochasticity/nonlinearity of the galaxy bias through correlation studies of the cosmic shear and galaxy number fluctuations. Specifically, we employ the aperture mass statistics M-ap to describe the cosmic shear. We divide the foreground-galaxy redshift z(f) < z(s) into several bins, where z(s) is the redshift of the source galaxies, and calculate the quantity (MapNg(z(f)))(2)/(hN(g)(2)(z(f))) for each redshift bin. Then, the ratio of the summation of (MapNg(z(f)))(2)/(N-g(2)(z(f))) over the bins to (M-ap(2)) gives a measure of the nonlinear/stochastic bias. Here, N-g(z(f)) is the projected surface number density fluctuation of foreground galaxies at redshift z(f), and M-ap is the aperture mass from the cosmic-shear analysis. We estimate that for a moderately deep weak-lensing survey with z(s) = 1, source galaxy surface number density n(b) = 30 galaxies arcmin(-2), and a survey area of 25 deg(2), the effective r-parameter that represents the deviation from the linear and deterministic bias is detectable in the angular range of 1'-10' if \r - 1\ greater than or similar to 10%. For shallow, wide surveys such as the Sloan Digital Sky Survey with z(s) = 0: 5, n(b) = 5 galaxies arcmin(-2), and a survey area of 10(4) deg(2), a 10% detection of r is possible over the angular range 1'-100'.Astronomy & AstrophysicsSCI(E)7ARTICLE133-4159
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