We address the amount of information in the non-Gaussian regime of weak lensing surveys by modelling all relevant covariances of the power spectra and bispectra, using 1000 ray-tracing simulation ...realizations for a Λcold dark matter (ΛCDM) model and an analytical halo model. We develop a formalism to describe the covariance matrices of power spectra and bispectra of all triangle configurations. In addition to the known contributions which extend up to six-point correlation functions, we propose a new contribution 'the halo sample variance (HSV)' arising from the coupling of the lensing Fourier modes with large-scale mass fluctuations on scales comparable with the survey region via halo bias theory. We show that the model predictions are in good agreement with the simulation once we take the HSV into account. The HSV gives a dominant contribution to the covariance matrices at multipoles l 103, which arises from massive haloes with a mass of 1014 M and at relatively low redshifts z 0.4. Since such haloes are easily identified from a multi-colour imaging survey, the effect can be estimated from the data. By adding the bispectrum to the power spectrum, the total information content or the cumulative signal-to-noise ratio up to a certain maximum multipole l
max of a few 103, (S/N)
lmax, is improved by 20-50 per cent, which is equivalent to a factor of 1.4-2.3 larger survey area for the power spectrum measurement alone. However, it is still smaller than the case of a Gaussian field by a factor of 3 mostly due to the HSV. Thus bispectrum measurements are useful for cosmology, but using information from upcoming surveys requires that non-Gaussian covariances are carefully estimated.
Abstract
We measure the small-scale (comoving separation 10 ≲ r
p ≲ 200 h
−1 kpc) two-point correlation function of quasars using a sample of 26 spectroscopically confirmed binary quasars at 0.6 < z ...< 2.2 from the Sloan Digital Sky Survey Quasar Lens Search (SQLS). Thanks to careful candidate selections and extensive follow-up observations of the SQLS, which are aimed at constructing a complete quasar lens sample, our sample of binary quasars is also expected to be nearly complete within a specified range of angular separations and redshifts. The measured small-scale correlation function rises steeply towards smaller scales, which is consistent with earlier studies based on incomplete or smaller binary quasar samples. We find that the quasar correlation function can be fitted by a power law reasonably well over 4 orders of magnitude, with the best-fitting slope of ξ(r) ∝ r
−1.92. We interpret the measured correlation function within the framework of the halo occupation distribution (HOD). We propose a simple model that assumes a constant fraction of quasars that appear as satellites in dark matter haloes, and find that measured small-scale clustering signals constrain the satellite fraction to ƒ
sat = 0.0540.017
−0.016 for a singular isothermal sphere number density profile of satellites. We note that the HOD modelling appears to underpredict clustering signals at the smallest separations of r
p∼ 10 h
−1 kpc unless we assume very steep number density profiles (such as a Navarro-Frenk-White profile with the concentration parameter c
vir≳30), which may be suggestive of enhanced quasar activities by direct interactions.
We provide a new fitting formula of the matter bispectrum in the nonlinear regime calibrated by high-resolution cosmological N-body simulations of 41 cold dark matter (wCDM, w = constant) models ...around the Planck 2015 best-fit parameters. As the parameterization in our fitting function is similar to that in Halofit, our fitting is named BiHalofit. The simulation volume is sufficiently large ( ) to cover almost all measurable triangle bispectrum configurations in the universe. The function is also calibrated using one-loop perturbation theory at large scales ( ). Our formula reproduced the matter bispectrum to within 10% (15%) accuracy in the Planck 2015 model at wavenumber and redshifts z = 0-3. The other 40 wCDM models obtained poorer fits, with accuracy approximating 20% at and (the deviation includes the 10%-level sample variance of the simulations). We also provide a fitting formula that corrects the baryonic effects such as radiative cooling and active galactic nucleus feedback, using the latest hydrodynamical simulation IllustrisTNG. We demonstrate that our new formula more accurately predicts the weak-lensing bispectrum than the existing fitting formulae. This formula will assist current and future weak-lensing surveys and cosmic microwave background lensing experiments. Numerical codes of the formula are available, written in Python (https://toshiyan.github.io/clpdoc/html/basic/basic.html#module-basic.bispec), C, and Fortran (http://cosmo.phys.hirosaki-u.ac.jp/takahasi/codes_e.htm).
Upcoming wide-area weak lensing surveys are expensive both in time and cost and require an optimal survey design in order to attain maximum scientific returns from a fixed amount of available ...telescope time. The supersample covariance (SSC), which arises from unobservable modes that are larger than the survey size, significantly degrades the statistical precision of weak lensing power spectrum measurement even for a wide-area survey. Using the 1000 mock realizations of the lognormal model, which approximates the weak lensing field for a Λ-dominated cold dark matter model, we study an optimal survey geometry to minimize the impact of SSC contamination. For a continuous survey geometry with a fixed survey area, a more elongated geometry such as a rectangular shape of 1:400 side length ratio reduces the SSC effect and allows for a factor of 2 improvement in the cumulative signal-to-noise ratio (S/N) of power spectrum measurement up to ℓmax ≃ a few 103, compared to compact geometries such as squares or circles. When we allow the survey geometry to be disconnected but with a fixed total area, assuming 1 × 1 deg2 patches as the fundamental building blocks of survey footprints, the best strategy is to locate the patches with ∼15 deg separation. This separation angle corresponds to the scale at which the two-point correlation function has a negative minimum. The best configuration allows for a factor of 100 gain in the effective area coverage as well as a factor of 2.5 improvement in the S/N at high multipoles, yielding a much wider coverage of multipoles than in the compact geometry.
ABSTRACT
We report the largest sample of candidate strong gravitational lenses belonging to the Survey of Gravitationally lensed Objects in HSC Imaging for group-to-cluster scale (SuGOHI-c) systems. ...These candidates are compiled from the S18A data release of the Hyper Suprime-Cam Subaru Strategic Program (HSC–SSP) Survey. We visually inspect ∼39 500 galaxy clusters, selected from several catalogues, overlapping with the Wide, Deep, and UltraDeep fields, spanning the cluster redshift range of 0.05 < zcl < 1.38. We discover 641 candidate lens systems, of which 536 are new. From the full sample, 47 are almost certainly bona fide lenses, 181 of them are highly probable lenses, and 413 are possible lens systems. Additionally, we present 131 lens candidates at galaxy scale serendipitously discovered during the inspection. We obtained spectroscopic follow-up of 10 candidates using the X-shooter. With this follow-up, we confirm eight systems as strong gravitational lenses. Of the remaining two, one of the sources is too faint to detect any emission, and the other has a tentative redshift close to the lens redshift, but additional arcs in this system are yet to be observed spectroscopically. Since the HSC–SSP is an ongoing survey, we expect to find ∼600 definite or probable lenses using this procedure and even more if combined with other lens finding methods.
The unique combination of superb spatial resolution, wide-area coverage, and deep depth of the optical imaging from the Hyper Suprime-Cam (HSC) Subaru Strategic Program is utilized to search for dual ...quasar candidates. Using an automated image analysis routine on 34,476 known Sloan Digital Sky Survey quasars, we identify those with two (or more) distinct optical point sources in HSC images covering 796 deg2. We find 421 candidates out to a redshift of 4.5 of which one hundred or so are more likely after filtering out contaminating stars. Angular separations of 0 6-4 0 correspond to projected separations of 3-30 kpc, a range relatively unexplored for population studies of luminous dual quasars. Using Keck I/Low Resolution Imaging Spectrometer and Gemini-N/Near-Infrared Integral Field Spectrometer, we spectroscopically confirm three dual quasar systems at z < 1, two of which are previously unknown out of eight observed, based on the presence of characteristic broad emission lines in each component, while highlighting that the continuum of one object in one of the pairs is reddened. In all cases, the O iiiλ5007 emission lines have mild velocity offsets, thus the joint O iii line profile is not double-peaked. We find a dual quasar fraction of 0.26 0.18% and no evidence for evolution. A comparison with the Horizon-AGN simulation seems to support the case of no evolution in the dual quasar fraction when broadly matching the quasar selection. These results may indicate a scenario in which the frequency of the simultaneous triggering of luminous quasars is not as sensitive as expected to the cosmic evolution of the merger rate or gas content of galaxies.
Abstract
We conduct a search for galaxy-scale strong gravitational lens systems in Data Release 4 of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP), consisting of data taken up to the S21A ...semester. We select 103191 luminous red galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) sample that have deep multiband imaging from the HSC SSP and use the YattaLens algorithm to identify lens candidates with blue arc-like features automatically. The candidates are visually inspected and graded based on their likelihood of being a lens. We find eight definite lenses, 28 probable lenses, and 138 possible lenses. The new lens candidates generally have lens redshifts in the range 0.3 ≲ zL ≲ 0.9, a key intermediate redshift range to study the evolution of galaxy structure. Follow-up spectroscopy will confirm these new lenses and measure source redshifts to enable detailed lens modeling.
ABSTRACT
We present spectroscopic confirmation of three new two-image gravitationally lensed quasars, compiled from existing strong lens and X-ray catalogues. Images of HSC J091843.27–022007.5 show a ...red galaxy with two blue point sources at either side, separated by 2.26 arcsec. This system has a source and a lens redshifts zs = 0.804 and zℓ = 0.459, respectively, as obtained by our follow-up spectroscopic data. CXCO J100201.50+020330.0 shows two point sources separated by 0.85 arcsec on either side of an early-type galaxy. The follow-up spectroscopic data confirm the fainter quasar has the same redshift with the brighter quasar from the Sloan Digital Sky Survey (SDSS) fiber spectrum at zs = 2.016. The deflecting foreground galaxy is a typical early-type galaxy at a redshift of zℓ = 0.439. SDSS J135944.21+012809.8 has two point sources with quasar spectra at the same redshift zs = 1.096, separated by 1.05 arcsec, and fits to the HSC images confirm the presence of a galaxy between these. These discoveries demonstrate the power of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP)’s deep imaging and wide sky coverage. Combined with existing X-ray source catalogues and follow-up spectroscopy, the HSC-SSP provides us unique opportunities to find multiple-image quasars lensed by a foreground galaxy.
We report the discovery of four doubly imaged quasar lenses. All the four systems are selected as lensed quasar candidates from the Sloan Digital Sky Survey data. We confirm their lensing hypothesis ...with additional imaging and spectroscopic follow-up observations. The discovered lenses are SDSS J0743+2457 with the source redshift zs = 2.165, the lens redshift zl = 0.381, and the image separation θ = 1.″034, SDSS J1128+2402 with zs = 1.608 and θ = 0.″844, SDSS J1405+0959 with zs = 1.810, zl ≈ 0.66, and θ = 1.″978, and SDSS J1515+1511 with zs = 2.054, zl = 0.742, and θ = 1.″989. It is difficult to estimate the lens redshift of SDSS J1128+2402 from the current data. Two of the four systems (SDSS J1405+0959 and SDSS J1515+1511) are included in our final statistical lens sample to derive constraints on dark energy and the evolution of massive galaxies.
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