Context.
Weak lensing and clustering statistics beyond two-point functions can capture non-Gaussian information about the matter density field, thereby improving the constraints on cosmological ...parameters relative to the mainstream methods based on correlation functions and power spectra.
Aims.
This paper presents a cosmological analysis of the fourth data release of the Kilo Degree Survey based on the density split statistics, which measures the mean shear profiles around regions classified according to foreground densities. The latter is constructed from a bright galaxy sample, which we further split into red and blue samples, allowing us to probe their respective connection to the underlying dark matter density.
Methods.
We used the state-of-the-art model of the density splitting statistics and validated its robustness against mock data infused with known systematic effects such as intrinsic galaxy alignment and baryonic feedback.
Results.
After marginalising over the photometric redshift uncertainty and the residual shear calibration bias, we measured for the full KiDS-bright sample a structure growth parameter of $ S_8\equiv \sigma_8 \sqrt{\Omega_{\mathrm{m}}/0.3}=0.73^{+0.03}_{-0.02} $ that is competitive and consistent with two-point cosmic shear results, a matter density of Ω
m
= 0.27 ± 0.02, and a constant galaxy bias of
b
= 1.37 ± 0.10.
We present a new method for the mitigation of observational systematic effects in angular galaxy clustering through the use of corrective random galaxy catalogues. Real and synthetic galaxy data from ...the Kilo Degree Survey’s (KiDS) 4th Data Release (KiDS-1000) and the Full-sky Lognormal Astro-fields Simulation Kit package, respectively, are used to train self-organising maps to learn the multivariate relationships between observed galaxy number density and up to six systematic-tracer variables, including seeing, Galactic dust extinction, and Galactic stellar density. We then create ‘organised’ randoms; random galaxy catalogues with spatially variable number densities, mimicking the learnt systematic density modes in the data. Using realistically biased mock data, we show that these organised randoms consistently subtract spurious density modes from the two-point angular correlation function
w
(
ϑ
), correcting biases of up to 12
σ
in the mean clustering amplitude to as low as 0.1
σ
, over an angular range of 7 − 100 arcmin with high signal-to-noise ratio. Their performance is also validated for angular clustering cross-correlations in a bright, flux-limited subset of KiDS-1000, comparing against an analogous sample constructed from highly complete spectroscopic redshift data. Each organised random catalogue object is a clone carrying the properties of a real galaxy, and is distributed throughout the survey footprint according to the position of the parent galaxy in systematics space. Thus, sub-sample randoms are readily derived from a single master random catalogue through the same selection as applied to the real galaxies. Our method is expected to improve in performance with increased survey area, galaxy number density, and systematic contamination, making organised randoms extremely promising for current and future clustering analyses of faint samples.
One probe for systematic effects in gravitational lensing surveys is the presence of so-called
B
modes in the cosmic shear two-point correlation functions,
ξ
±
(
ϑ
), since lensing is expected to ...produce only
E
-mode shear. Furthermore, there exist ambiguous modes that cannot uniquely be assigned to either
E
- or
B
-mode shear. In this paper we derive explicit equations for the pure-mode shear correlation functions,
ξ
±
E
/
B
(
ϑ
), and their ambiguous components,
ξ
±
amb
(
ϑ
), that can be derived from the measured
ξ
±
(
ϑ
) on a finite angular interval,
ϑ
min
≤
ϑ
≤
ϑ
max
, such that
ξ
±
(
ϑ
) can be decomposed uniquely into pure-mode functions as
ξ
+
=
ξ
+
E
+
ξ
+
B
+
ξ
+
amb
and
ξ
−
=
ξ
−
E
−
ξ
−
B
+
ξ
−
amb
. The derivation is obtained by defining a new set of Complete Orthogonal Sets of
E
and
B
mode-separating Integrals (COSEBIs), for which explicit relations are obtained and which yields a smaller covariance between COSEBI modes. We derive the relation between
ξ
±
E
/
B
/amb
and the underlying
E
- and
B
-mode power spectra. The pure-mode correlation functions can provide a diagnostic of systematics in configuration space. We then apply our results to Scinet LIght Cone Simulations (SLICS) and the Kilo-Degree Survey (KiDS-1000) cosmic shear data, calculate the new COSEBIs and the pure-mode correlation functions, as well as the corresponding covariances, and show that the new statistics fit equally well to the best fitting cosmological model as the previous KiDS-1000 analysis and recover the same level of (insignificant)
B
modes. We also consider in some detail the ambiguous modes at the first- and second-order level, finding some surprising results. For example, the shear field of a point mass, when cut along a line through the center, cannot be ascribed uniquely to an
E
-mode shear and is thus ambiguous; additionally, the shear correlation functions resulting from a random ensemble of point masses, when measured over a finite angular range, correspond to an ambiguous mode.
ABSTRACT
In this study, we present a new experimental design using clustering-based redshift inference to measure the evolving galaxy luminosity function (GLF) spanning 5.5 decades from L ∼ 1011.5 to ...106 L⊙. We use data from the Galaxy And Mass Assembly (GAMA) survey and the Kilo-Degree Survey (KiDS). We derive redshift distributions in bins of apparent magnitude to the limits of the GAMA-KiDS photometric catalogue: mr ≲ 23; more than a decade in luminosity beyond the limits of the GAMA spectroscopic redshift sample via clustering-based redshift inference. This technique uses spatial cross-correlation statistics for a reference set with known redshifts (in our case, the main GAMA sample) to derive the redshift distribution for the target ensemble. For the calibration of the redshift distribution, we use a simple parametrization with an adaptive normalization factor over the interval 0.005 < z < 0.48 to derive the clustering redshift results. We find that the GLF has a relatively constant power-law slope α ≈ −1.2 for −17 ≲ Mr ≲ −13, and then appears to steepen sharply for −13 ≲ Mr ≲ −10. This upturn appears to be where globular clusters (GCs) take over to dominate the source counts as a function of luminosity. Thus, we have mapped the GLF across the full range of the z ∼ 0 field galaxy population from the most luminous galaxies down to the GC scale.
We present a
Hubble
Space Telescope (HST) weak gravitational lensing study of nine distant and massive galaxy clusters with redshifts 1.0 ≲
z
≲ 1.7 (
z
median
= 1.4) and Sunyaev Zel’dovich (SZ) ...detection significance
ξ
> 6.0 from the South Pole Telescope Sunyaev Zel’dovich (SPT-SZ) survey. We measured weak lensing galaxy shapes in HST/ACS
F
606
W
and
F
814
W
images and used additional observations from HST/WFC3 in
F
110
W
and VLT/FORS2 in
U
HIGH
to preferentially select background galaxies at
z
≳ 1.8, achieving a high purity. We combined recent redshift estimates from the CANDELS/3D-HST and HUDF fields to infer an improved estimate of the source redshift distribution. We measured weak lensing masses by fitting the tangential reduced shear profiles with spherical Navarro-Frenk-White (NFW) models. We obtained the largest lensing mass in our sample for the cluster SPT-CL J2040−4451, thereby confirming earlier results that suggest a high lensing mass of this cluster compared to X-ray and SZ mass measurements. Combining our weak lensing mass constraints with results obtained by previous studies for lower redshift clusters, we extended the calibration of the scaling relation between the unbiased SZ detection significance
ζ
and the cluster mass for the SPT-SZ survey out to higher redshifts. We found that the mass scale inferred from our highest redshift bin (1.2 <
z
< 1.7) is consistent with an extrapolation of constraints derived from lower redshifts, albeit with large statistical uncertainties. Thus, our results show a similar tendency as found in previous studies, where the cluster mass scale derived from the weak lensing data is lower than the mass scale expected in a
Planckν
ΛCDM (i.e.
ν
Λ cold dark matter) cosmology given the SPT-SZ cluster number counts.
We present a map of the total intrinsic reddening across ≃ 90 deg2 of the Large Magellanic Cloud (LMC) derived using optical (ugriz) and near-infrared (IR; YJKs) spectral energy distributions (SEDs) ...of background galaxies. The reddening map is created from a sample of 222 752 early-type galaxies based on the lephareχ2 minimization SED-fitting routine. We find excellent agreement between the regions of enhanced intrinsic reddening across the central (4 × 4 deg2) region of the LMC and the morphology of the low-level pervasive dust emission as traced by far-IR emission. In addition, we are able to distinguish smaller, isolated enhancements that are coincident with known star-forming regions and the clustering of young stars observed in morphology maps. The level of reddening associated with the molecular ridge south of 30 Doradus is, however, smaller than in the literature reddening maps. The reduced number of galaxies detected in this region, due to high extinction and crowding, may bias our results towards lower reddening values. Our map is consistent with maps derived from red clump stars and from the analysis of the star formation history across the LMC. This study represents one of the first large-scale categorizations of extragalactic sources behind the LMC and as such we provide the lephare outputs for our full sample of ~2.5 million sources.
We present the final data release of the Kilo-Degree Survey (KiDS-DR5), a public European Southern Observatory (ESO) wide-field imaging survey optimised for weak gravitational lensing studies. We ...combined matched-depth multi-wavelength observations from the VLT Survey Telescope and the VISTA Kilo-degree INfrared Galaxy (VIKING) survey to create a nine-band optical-to-near-infrared survey spanning 1347 deg 2 . The median r -band 5 σ limiting magnitude is 24.8 with median seeing 0.7″. The main survey footprint includes 4 deg 2 of overlap with existing deep spectroscopic surveys. We complemented these data in DR5 with a targeted campaign to secure an additional 23 deg 2 of KiDS- and VIKING-like imaging over a range of additional deep spectroscopic survey fields. From these fields, we extracted a catalogue of 126 085 sources with both spectroscopic and photometric redshift information, which enables the robust calibration of photometric redshifts across the full survey footprint. In comparison to previous releases, DR5 represents a 34% areal extension and includes an i -band re-observation of the full footprint, thereby increasing the effective i -band depth by 0.4 magnitudes and enabling multi-epoch science. Our processed nine-band imaging, single- and multi-band catalogues with masks, and homogenised photometry and photometric redshifts can be accessed through the ESO Archive Science Portal.
Discrepancies between cosmological parameter estimates from cosmic shear surveys and from recent Planck cosmic microwave background measurements challenge the ability of the highly successful ...\(\Lambda\)CDM model to describe the nature of the Universe. To rule out systematic biases in cosmic shear survey analyses, accurate redshift calibration within tomographic bins is key. In this paper, we improve photo-\(z\) calibration via Bayesian hierarchical modeling of full galaxy photo-\(z\) conditional densities, by employing \(\textit{StratLearn}\), a recently developed statistical methodology, which accounts for systematic differences in the distribution of the spectroscopic training/source set and the photometric target set. Using realistic simulations that were designed to resemble the KiDS+VIKING-450 dataset, we show that \(\textit{StratLearn}\)-estimated conditional densities improve the galaxy tomographic bin assignment, and that our \(\textit{StratLearn}\)-Bayesian framework leads to nearly unbiased estimates of the target population means. This leads to a factor of \(\sim 2\) improvement upon the previously best photo-\(z\) calibration method. Our approach delivers a maximum bias per tomographic bin of \(\Delta \langle z \rangle = 0.0095 \pm 0.0089\), with an average absolute bias of \(0.0052 \pm 0.0067\) across the five tomographic bins.
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