263 research outputs found
Photometric Redshift Calibration with Self Organising Maps
Accurate photometric redshift calibration is central to the robustness of all
cosmology constraints from cosmic shear surveys. Analyses of the KiDS
re-weighted training samples from all overlapping spectroscopic surveys to
provide a direct redshift calibration. Using self-organising maps (SOMs) we
demonstrate that this spectroscopic compilation is sufficiently complete for
KiDS, representing of the effective 2D cosmic shear sample. We use the
SOM to define a represented `gold' cosmic shear sample, per tomographic
bin. Using mock simulations of KiDS and the spectroscopic training set, we
estimate the uncertainty on the SOM redshift calibration, and find that
photometric noise, sample variance, and spectroscopic selection effects
(including redshift and magnitude incompleteness) induce a combined maximal
scatter on the bias of the redshift distribution reconstruction () of
in all tomographic bins. We show
that the SOM calibration is unbiased in the cases of noiseless photometry and
perfectly representative spectroscopic datasets, as expected from theory. The
inclusion of both photometric noise and spectroscopic selection effects in our
mock data introduces a maximal bias of , or at
confidence, once quality flags have been applied to the SOM. The method
presented here represents a significant improvement over the previously adopted
direct redshift calibration implementation for KiDS, owing to its diagnostic
and quality assurance capabilities. The implementation of this method in future
cosmic shear studies will allow better diagnosis, examination, and mitigation
of systematic biases in photometric redshift calibration.Comment: 22 pages, 10 figures, 4 appendices, accepted for publication in A&
Luminous red galaxies in the Kilo Degree Survey: selection with broad-band photometry and weak lensing measurements
We use the overlap between multiband photometry of the Kilo-Degree Survey
(KiDS) and spectroscopic data based on the Sloan Digital Sky Survey (SDSS) and
Galaxy And Mass Assembly (GAMA) to infer the colour-magnitude relation of
red-sequence galaxies. We then use this inferred relation to select luminous
red galaxies (LRGs) in the redshift range of over the entire KiDS
Data Release 3 footprint. We construct two samples of galaxies with different
constant comoving densities and different luminosity thresholds. The selected
red galaxies have photometric redshifts with typical photo-z errors of
that are nearly uniform with respect to
observational systematics. This makes them an ideal set of galaxies for lensing
and clustering studies. As an example, we use the KiDS-450 cosmic shear
catalogue to measure the mean tangential shear signal around the selected LRGs.
We detect a significant weak lensing signal for lenses out to
KiDS+VIKING+GAMA: Halo occupation distributions and correlations of satellite numbers with a new halo model of the galaxy-matter bispectrum for galaxy-galaxy-galaxy lensing
Halo models and halo occupation distributions (HODs) are important tools to
model the galaxy and matter distribution. We present and assess a new method
for constraining the parameters of HODs using the gravitational lensing shear
around galaxy pairs, galaxy-galaxy-galaxy-lensing (G3L). In contrast to
galaxy-galaxy-lensing, G3L is sensitive to correlations between the per-halo
numbers of galaxies from different populations. We use G3L to probe these
correlations and test the default hypothesis that they are negligible. We
derive a halo model for G3L and validate it with realistic mock data from the
Millennium Simulation and a semi-analytic galaxy model. Then, we analyse public
data from the Kilo-Degree Survey (KiDS), the VISTA Infrared Kilo-Degree Galaxy
Survey (VIKING) and data from the Galaxy And Mass Assembly Survey (GAMA) to
infer the HODs of galaxies at in five different stellar mass bins
between and and two colours
(red and blue), as well as correlations between satellite numbers. The analysis
recovers the true HODs in the simulated data within the credibility
range. The inferred HODs vary significantly with colour and stellar mass. There
is also strong evidence () for correlations, increasing with halo
mass, between the numbers of red and blue satellites and galaxies with stellar
masses below $10^{10} \Msun. Possible causes of these correlations are the
selection of similar galaxies in different samples, the survey flux limit, or
physical mechanisms like a fixed ratio between the satellite numbers of
distinct populations. The decorrelation for halos with smaller masses is
probably an effect of shot noise by low-occupancy halos. The inferred HODs can
be used to complement galaxy-galaxy-lensing or galaxy clustering HOD studies or
as input to cosmological analyses and improved mock galaxy catalogues.Comment: 20 pages + Appendix, 14 Figures. Submitted to Astronomy &
Astrophysics. Abstract is abridge
KiDS+VIKING-450:Improved cosmological parameter constraints from redshift calibration with self-organising maps
We present updated cosmological constraints for the KiDS+VIKING-450 cosmic
shear data set (KV450), estimated using redshift distributions and photometric
samples defined using self-organising maps (SOMs). Our fiducial analysis finds
marginal posterior constraints of ; smaller than, but otherwise consistent with,
previous work using this data set (). We analyse
additional samples and redshift distributions constructed in three ways:
excluding certain spectroscopic surveys during redshift calibration, excluding
lower-confidence spectroscopic redshifts in redshift calibration, and
considering only photometric sources which are jointly calibrated by at least
three spectroscopic surveys. In all cases, the method utilised here proves
robust: we find a maximal deviation from our fiducial analysis of for all samples defined and analysed using our SOM. To demonstrate
the reduction in systematic biases found within our analysis, we highlight our
results when performing redshift calibration without the DEEP2 spectroscopic
data set. In this case we find marginal posterior constraints of
; a difference with respect to the fiducial that
is both significantly smaller than, and in the opposite direction to, the
equivalent shift from previous work. These results suggest that our improved
cosmological parameter estimates are insensitive to pathological
misrepresentation of photometric sources by the spectroscopy used for direct
redshift calibration, and therefore that this systematic effect cannot be
responsible for the observed difference between estimates made with KV450
and Planck CMB probes.Comment: 10 pages, 3 figures, 4 appendices, accepted for publication in A&A
Letter
Cosmic star formation history with tomographic CIB-galaxy cross-correlation
In this work, we probe the star formation history of the Universe using
tomographic cross-correlation between the cosmic infrared background (CIB) and
galaxy samples. The galaxy samples are from the Kilo-Degree Survey (KiDS),
while the CIB maps are made from \planck\, sky maps. We measure the
cross-correlation in harmonic space with a significance of 43. We model
the cross-correlation with a halo model, which links CIB anisotropies to star
formation rates (SFR) and galaxy abundance. We assume that SFR has a lognormal
dependence on halo mass, while galaxy abundance follows the halo occupation
distribution (HOD) model. The cross-correlations give a best-fit maximum star
formation efficiency of at a halo
mass . The derived
star formation rate density (SFRD) is well constrained up to . The
constraining power at high redshift is mainly limited by the KiDS survey depth.
A combination with external SFRD measurements from previous studies gives
. This tightens
the SFRD constraint up to , yielding a peak SFRD of
at
, corresponding to a lookback time of
Gyr. Both constraints are consistent, and the derived
SFRD agrees with previous studies and simulations. Additionally, we estimate
the galaxy bias of KiDS galaxies from the constrained HOD parameters and
yield an increasing bias from at to
at . Finally, we provide a forecast for future
galaxy surveys and conclude that, due to their considerable depth, future
surveys will yield a much tighter constraint on the evolution of the SFRD.Comment: 22 pages, 14 figures, 3 tables, the abstract is abridge
G10/COSMOS : 38 band (far-UV to far-IR) panchromatic photometry using LAMBDAR
We present a consistent total flux catalogue for a ∼1 deg2 subset of the Cosmic Evolution Survey (COSMOS) region (RA ∈ [149∘.55, 150∘.65], Dec. ∈ [1∘.80, 2∘.73]) with near-complete coverage in 38 bands from the far-ultraviolet to the far-infrared. We produce aperture matched photometry for 128 304 objects with i < 24.5 in a manner that is equivalent to the Wright et al. catalogue from the low-redshift (z < 0.4) Galaxy and Mass Assembly (GAMA) survey. This catalogue is based on publicly available imaging from GALEX, Canada–France–Hawaii Telescope, Subaru, Visible and Infrared Survey Telescope for Astronomy, Spitzer and Herschel, contains a robust total flux measurement or upper limit for every object in every waveband and complements our re-reduction of publicly available spectra in the same region. We perform a number of consistency checks, demonstrating that our catalogue is comparable to existing data sets, including the recent COSMOS2015 catalogue. We also release an updated Davies et al. spectroscopic catalogue that folds in new spectroscopic and photometric redshift data sets. The catalogues are available for download at http://cutout.icrar.org/G10/dataRelease.php. Our analysis is optimised for both panchromatic analysis over the full wavelength range and for direct comparison to GAMA, thus permitting measurements of galaxy evolution for 0 < z < 1 while minimizing the systematic error resulting from disparate data reduction methods.Publisher PDFPeer reviewe
Local-Oscillator Noise Coupling in Balanced Homodyne Readout for Advanced Gravitational Wave Detectors
The second generation of interferometric gravitational wave detectors are
quickly approaching their design sensitivity. For the first time these
detectors will become limited by quantum back-action noise. Several back-action
evasion techniques have been proposed to further increase the detector
sensitivity. Since most proposals rely on a flexible readout of the full
amplitude- and phase-quadrature space of the output light field, balanced
homodyne detection is generally expected to replace the currently used DC
readout. Up to now, little investigation has been undertaken into how balanced
homodyne detection can be successfully transferred from its ubiquitous
application in table-top quantum optics experiments to large-scale
interferometers with suspended optics. Here we derive implementation
requirements with respect to local oscillator noise couplings and highlight
potential issues with the example of the Glasgow Sagnac Speed Meter experiment,
as well as for a future upgrade to the Advanced LIGO detectors.Comment: 7 pages, 5 figure
Effects of static and dynamic higher-order optical modes in balanced homodyne readout for future gravitational waves detectors
With the recent detection of Gravitational waves (GW), marking the start of the new field of GW astronomy, the push for building more sensitive laser-interferometric gravitational wave detectors (GWD) has never been stronger. Balanced homodyne detection (BHD) allows for a quantum noise (QN) limited readout of arbitrary light field quadratures, and has therefore been suggested as a vital building block for upgrades to Advanced LIGO and third generation observatories. In terms of the practical implementation of BHD, we develop a full framework for analyzing the static optical high order modes (HOMs) occurring in the BHD paths related to the misalignment or mode matching at the input and output ports of the laser interferometer. We find the effects of HOMs on the quantum noise limited sensitivity is independent of the actual interferometer configuration, e.g. Michelson and Sagnac interferometers are effected in the same way. We show that misalignment of the output ports of the interferometer (output misalignment) only effects the high frequency part of the quantum noise limited sensitivity (detection noise). However, at low frequencies, HOMs reduce the interferometer response and the radiation pressure noise (back action noise) by the same amount and hence the quantum noise limited sensitivity is not negatively effected in that frequency range. We show that the misalignment of laser into the interferometer (input misalignment) produces the same effect as output misalignment and additionally decreases the power inside the interferometer. We also analyze dynamic HOM effects, such as beam jitter created by the suspended mirrors of the BHD. Our analyses can be directly applied to any BHD implementation in a future GWD. Moreover, we apply our analytical techniques to the example of the speed meter proof of concept experiment under construction in Glasgow. We find that for our experimental parameters, the performance of our seismic isolation system in the BHD paths is compatible with the design sensitivity of the experiment
Pure-mode correlation functions for cosmic shear and application to KiDS-1000
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
Magnification bias in galaxy surveys with complex sample selection functions
Gravitational lensing magnification modifies the observed spatial
distribution of galaxies and can severely bias cosmological probes of
large-scale structure if not accurately modelled. Standard approaches to
modelling this magnification bias may not be applicable in practice as many
galaxy samples have complex, often implicit, selection functions. We propose
and test a procedure to quantify the magnification bias induced in clustering
and galaxy-galaxy lensing (GGL) signals in galaxy samples subject to a
selection function beyond a simple flux limit. The method employs realistic
mock data to calibrate an effective luminosity function slope,
, from observed galaxy counts, which can then be used with
the standard formalism. We demonstrate this method for two galaxy samples
derived from the Baryon Oscillation Spectroscopic Survey (BOSS) in the redshift
ranges and , complemented by mock data
built from the MICE2 simulation. We obtain
and for the two BOSS samples. For BOSS-like
lenses, we forecast a contribution of the magnification bias to the GGL signal
between the angular scales of and with a cumulative
signal-to-noise ratio between and for sources from the Kilo-Degree
Survey (KiDS), between and for sources from the Hyper Suprime-Cam
survey (HSC), and between and for ESA Euclid-like source samples.
These contributions are significant enough to require explicit modelling in
future analyses of these and similar surveys.Comment: 15 pages, 13 figure
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