Application of photometric redshifts on the correlation properties of galaxies and matter

In the past years cosmology, the science of the universe as a whole, has seen tremendous progress. The Lambda-Cold-Dark-Matter scenario is widely accepted as the standard model of cosmology describing the evolution of the universe and its main constituents. Most cosmological parameters are known to a few percent accuracy now. This concordance cosmological model together with the basic theory of cosmological physics is presented in Chap. 1. Albeit, the main contributors to the energy density of the universe, Dark Matter (DM) and Dark Energy (DE), have not been observed so far in the laboratory. We can now predict the expansion history, the age, the energy density, etc. of the universe but we do not know the physical origin of the majority of the ingredients driving this cosmic evolution. There is hope that dark matter particles will be detected in the laboratory soon, either via passive detectors that measure the properties of these hypothetically weakly interacting massive particles (WIMPs) penetrating through the Earth, or actively via events created in the next generation of particle accelerators like the Large Hadron Collider. For DE, however, the situation is different. No concept was presented yet to detect this component, which is responsible for the accelerated expansion of the universe, in the laboratory. With its physical origin being completely unknown the only way to learn more about its properties, like e.g. its equation of state describing the time-evolution, will be from observational cosmology. Different methods are proposed to shed light on the nature of DE. One of them is the measurement of coherent distortions in the shape of galaxies due to the gravitational deflection of light by the large-scale structure of the universe, called cosmic shear. Another one is the detection of baryonic acoustic oscillations in the two-point correlation function of galaxies. The accuracy of both of these promising methods for constraining DE properties depends heavily on the measurement of redshifts, hence distances, of many million galaxies. This cannot be done in the traditional way by taking spectra for these large samples. Rather, approximate redshifts, called photometric redshifts, must be estimated from the colours of the galaxies. While the determination of cosmological parameters like the equation of state of DE is not the subject of this thesis, the photometric redshift technique is introduced and analysed in great detail in Chaps. 4 & 5. Understanding the efficacy of this tool and its shortcomings is essential for many large future survey projects tackling the questions above. Besides these purely cosmological questions which are hoped to be answered by the measurements of galaxy properties, it is the galaxy population itself we are interested in. In particular, we still have no precise picture about how galaxies form and how they evolve. The behaviour of the DM component which is the dominant driver of cosmological structure formation seems to be well understood through large N-body simulations, although we do not know about the nature of the DM particles. In contrast to this, the formation and evolution of galaxies involve mainly well-known baryonic physics. But the processes involved like star-formation, hydrodynamics, radiative feedback, etc. are so complicated that we are still far from a coherent description of galaxy formation and evolution. This ignorance is partly caused by the fact that we cannot observe a galaxy form and evolve directly because of the very long timescales for these processes. Due to the finite speed of light, looking at increasingly distant/redshifted galaxies means looking at younger objects. One main task to understand the physics of galaxy evolution is to identify which objects at an early cosmic epoch evolve into which type of galaxies observed today. Again, photometric redshift and similar techniques like the Lyman-break technique can be applied to select galaxies at different epochs. The properties of these samples, e.g. their clustering, can be studied and compared to numerical simulations. By doing so one gets insight into the relationship between the properties of luminous matter in form of galaxies and the underlying structure in form of DM halos. If this is done for several cosmic epochs, the evolution of galaxies can be understood in more detail because the evolution of the halo population is well-known from simulations. We contribute to the field of galaxy formation and evolution in this thesis by analysing the clustering properties of an unprecedented large sample of galaxies at redshift z~3. The selection of these Lyman-break galaxies (LBGs), the simulation of their properties, and the measurement of their two-point correlation function is described in Chap. 6. As a result we obtain estimates for the masses of the halos that host these galaxies, and these masses are compared to estimates at different redshifts from other studies to detect evolutionary trends in the galaxy-DM relationship. Neither the photometric redshift analyses nor the study of z~3 Lyman-break galaxies would be possible without high-quality imaging data from a modern multi-chip CCD camera. The general concepts of the complex processing of the raw data to reach scientifically exploitable images, also called data reduction, is presented in Chap. 2. These techniques are applied to a specific dataset, the optical data of the ESO Deep Public Survey (DPS), which forms the basis of most analyses presented in this thesis

On the complementarity of galaxy clustering with cosmic shear and flux magnification

In this paper, we motivate the use of galaxy clustering measurements using photometric redshift information, including a contribution from flux magnification, as a probe of cosmology. We present cosmological forecasts when clustering data alone is used, and when clustering is combined with a cosmic shear analysis. We consider two types of clustering analysis: firstly, clustering with only redshift auto-correlations in tomographic redshift bins; secondly, using all available redshift bin correlations. Finally, we consider how inferred cosmological parameters may be biased using each analysis when flux magnification is neglected. Results are presented for a Stage III ground-based survey, and a Stage IV space-based survey modelled with photometric redshift errors, and values for the slope of the luminosity function inferred from CFHTLenS catalogues. We find that combining clustering information with shear can improve constraints on cosmological parameters, giving an improvement to a Dark Energy Task Force-like figure of merit by a factor of 1.33 when only auto-correlations in redshift are used for the clustering analysis, rising to 1.52 when cross-correlations in redshift are also included. The addition of galaxy-galaxy lensing gives further improvement, with increases in figure of merit by a factor of 2.82 and 3.7 for each type of clustering analysis respectively. The presence of flux magnification in a clustering analysis does not significantly affect the precision of cosmological constraints when combined with cosmic shear and galaxy-galaxy lensing. However if magnification is neglected, inferred cosmological parameter values are biased, with biases in some cosmological parameters larger than statistical errors. (Abridged)Comment: Accepted by MNRAS, 18 pages, 12 Figures, 3 Table

Cluster Magnification & the Mass-Richness Relation in CFHTLenS

Gravitational lensing magnification is measured with a significance of 9.7 sigma on a large sample of galaxy clusters in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). This survey covers ~154 deg^2 and contains over 18,000 cluster candidates at redshifts 0.2 <= z <= 0.9, detected using the 3D-Matched Filter cluster-finder of Milkeraitis et al. (2010). We fit composite-NFW models to the ensemble, accounting for cluster miscentering, source-lens redshift overlap, as well as nearby structure (the 2-halo term), and recover mass estimates of the cluster dark matter halos in range of ~10^13 M_sun to 2*10^14 M_sun. Cluster richness is measured for the entire sample, and we bin the clusters according to both richness and redshift. A mass-richness relation M_200 = M_0 (N_200 / 20)^beta is fit to the measurements. For two different cluster miscentering models we find consistent results for the normalization and slope, M_0 = (2.3 +/- 0.2)*10^13 M_sun, beta = 1.4 +/- 0.1 and M_0 = (2.2 +/- 0.2)*10^13 M_sun, beta = 1.5 +/- 0.1. We find that accounting for the full redshift distribution of lenses and sources is important, since any overlap can have an impact on mass estimates inferred from flux magnification.Comment: 11 pages, 8 figures, Accepted to MNRA

The RedGOLD cluster detection algorithm and its cluster candidate catalogue for the CFHT-LS W1

We present RedGOLD (Red-sequence Galaxy Overdensity cLuster Detector), a new optical/NIR galaxy cluster detection algorithm, and apply it to the CFHT-LS W1 field. RedGOLD searches for red-sequence galaxy overdensities while minimizing contamination from dusty star-forming galaxies. It imposes an Navarro–Frenk–White profile and calculates cluster detection significance and richness. We optimize these latter two parameters using both simulations and X-ray-detected cluster catalogues, and obtain a catalogue ∼80 per cent pure up to z ∼ 1, and ∼100 per cent (∼70 per cent) complete at z ≤ 0.6 (z ≲ 1) for galaxy clusters with M ≳ 10^(14) M_⊙ at the CFHT-LS Wide depth. In the CFHT-LS W1, we detect 11 cluster candidates per deg^2 out to z ∼ 1.1. When we optimize both completeness and purity, RedGOLD obtains a cluster catalogue with higher completeness and purity than other public catalogues, obtained using CFHT-LS W1 observations, for M ≳ 10^(14) M_⊙. We use X-ray-detected cluster samples to extend the study of the X-ray temperature–optical richness relation to a lower mass threshold, and find a mass scatter at fixed richness of σ_(lnM|λ) = 0.39 ± 0.07 and σ_(lnM|λ) = 0.30 ± 0.13 for the Gozaliasl et al. and Mehrtens et al. samples. When considering similar mass ranges as previous work, we recover a smaller scatter in mass at fixed richness. We recover 93 per cent of the redMaPPer detections, and find that its richness estimates is on average ∼40–50 per cent larger than ours at z > 0.3. RedGOLD recovers X-ray cluster spectroscopic redshifts at better than 5 per cent up to z ∼ 1, and the centres within a few tens of arcseconds

Lensing Magnification: A novel method to weigh high-redshift clusters and its application to SpARCS

We introduce a novel method to measure the masses of galaxy clusters at high redshift selected from optical and IR Spitzer data via the red-sequence technique. Lyman-break galaxies are used as a well understood, high-redshift background sample allowing mass measurements of lenses at unprecedented high redshifts using weak lensing magnification. By stacking a significant number of clusters at different redshifts with average masses of ~1-3x10^14M_sun, as estimated from their richness, we can calibrate the normalisation of the mass-richness relation. With the current data set (area: 6 deg^2) we detect a magnification signal at the >3-sigma level. There is good agreement between the masses estimated from the richness of the clusters and the average masses estimated from magnification, albeit with large uncertainties. We perform tests that suggest the absence of strong systematic effects and support the robustness of the measurement. This method - when applied to larger data sets in the future - will yield an accurate calibration of the mass-observable relations at z>~1 which will represent an invaluable input for cosmological studies using the galaxy cluster mass function and astrophysical studies of cluster formation. Furthermore this method will probably be the least expensive way to measure masses of large numbers of z>1 clusters detected in future IR-imaging surveys.Comment: 5 pages, 1 figure, 1 table, accepted by ApJL, minor revision

AMICO galaxy clusters in KiDS-DR3: weak-lensing mass calibration

We present the mass calibration for galaxy clusters detected with the AMICO code in KiDS DR3 data. The cluster sample comprises $\sim$ 7000 objects and covers the redshift range 0.1 < $z$ < 0.6. We perform a weak lensing stacked analysis by binning the clusters according to redshift and two different mass proxies provided by AMICO, namely the amplitude $A$ (measure of galaxy abundance through an optimal filter) and the richness $\lambda^*$ (sum of membership probabilities in a consistent radial and magnitude range across redshift). For each bin, we model the data as a truncated NFW profile plus a 2-halo term, taking into account uncertainties related to concentration and miscentring. From the retrieved estimates of the mean halo masses, we construct the $A$-$M_{200}$ and the $\lambda^*$-$M_{200}$ relations. The relations extend over more than one order of magnitude in mass, down to $M_{200} \sim 2 (5) \times 10^{13} M_\odot/h$ at $z$ = 0.2 (0.5), with small evolution in redshift. The logarithmic slope is $\sim 2.0$ for the $A$-mass relation, and $\sim 1.7$ for the $\lambda^*$-mass relation, consistent with previous estimations on mock catalogues and coherent with the different nature of the two observables.Comment: 19 pages, 16 figures, accepted by MNRA