Clustering of galaxies: evolution, segregation and baryon acoustic oscillations

In this thesis, we tackle several open problems in the study of large-scale structure through the clustering of galaxies. To this end, we analyse data from some of the latest surveys, and we also develop new statistical techniques needed for this analysis in specific cases. In the first part, we focus on small and intermediate scales, where the relation between galaxy properties and their clustering (known as segregation) is important. The work in this part is driven by the exploitation of data from the ongoing Advanced Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey, which is perfectly suited to study the evolution of segregation trough cosmic time. We developed a method for the recovery of the real-space clustering from photometric surveys with the characteristics of ALHAMBRA. This method is based on the use of the projected correlation function, and is adapted to data with typical photometric redshift errors Dz < 0.015 (1+z). We tested the method using N-body simulations, and then applied it to the calculation of the correlation function for several samples drawn from the ALHAMBRA survey. We divided our sample in three redshift bins, and selected several galaxy samples in each of them based on B-band luminosity. In the range of scales studied, the correlation function for all samples was well fitted by a power law. We observed as well the effects of evolution, and of luminosity segregation. We also reviewed the basic tools available in the framework of the statistics of marked point processes to study galaxy segregation. We illustrated their application using a galaxy sample drawn from the 2dFGRS, characterised by a spectral classification parameter. We introduced the mark connection function, showing that it gives valuable information when analysing different galaxy populations defined by some set of galaxy characteristics. In the second part, we focus on the study of a large scale feature of the galaxy distribution, the baryon acoustic oscillations (BAO). We measured the two-point correlation function for several samples drawn from the largest surveys to date, 2dFGRS and SDSS. We obtained a peak corresponding to BAO at the expected scale in all cases, which shows the reliability of the detection of this feature. Finally, we developed a new method for the analysis of the BAO phenomenon. This method makes use of the possibilities of wavelets methods to look for the actual structures in configuration space which are responsible for the BAO. It is also based on the use of two complementary mass tracers, and we illustrated it using a catalogue formed by `Main' and Luminous Red Galaxy samples from SDSS. In this way, we showed how we were able not only to detect BAO in the samples, but also to localise regions giving lower or higher BAO signal. This kind of information is completely lost when using the traditional two-point statistics methods

DarkMix: Mixture Models for the Detection and Characterization of Dark Matter Halos

Dark matter simulations require statistical techniques to properly identify and classify their halos and structures. Nonparametric solutions provide catalogs of these structures but lack the additional learning of a model-based algorithm and might misclassify particles in merging situations. With mixture models, we can simultaneously fit multiple density profiles to the halos that are found in a dark matter simulation. In this work, we use the Einasto profile (Einasto 1965, 1968, 1969) to model the halos found in a sample of the Bolshoi simulation (Klypin et al. 2011), and we obtain their location, size, shape and mass. Our code is implemented in the R statistical software environment and can be accessed on https://github.com/LluisHGil/darkmix.Comment: 25 pages, 22 figures, 5 table

The Near-Infrared Surface Brightness Distribution of NGC4696

We present H-band observations of the elliptical galaxy NGC4696, the brightest member of the Centaurus cluster of galaxies. We have measured its light profile, using a two-dimensional fitting algorithm, out to a radius of 180 arcsec (37 h^{-1}_{70} kpc). The profile is well described by a de Vaucouleurs law, with an effective radius of 35.3 +/- 1.0 h^{-1}_{70} kpc. There is no need for the extra free parameter allowed by a Sersic law. Allowing for a variation of 0.3% in the sky level, the profile obtained is compatible with data from 2MASS. The profile shows no sign of either a truncation or an extended halo.Comment: Accepted for publication in PASA. 5 pages, 3 figure

Uncertainty in 2-point correlation function estimators and BAO detection in SDSS DR7

We study the uncertainty in different two-point correlation function (2PCF) estimators in currently available galaxy surveys. This is motivated by the active subject of using the baryon acoustic oscillations (BAOs) feature in the correlation function as a tool to constrain cosmological parameters, which requires a fine analysis of the statistical significance. We discuss how estimators are affected by both the uncertainty in the mean density $\bar{n}$ and the integral constraint $\frac{1}{V^2}\int_{V^2} \hat{\xi} (r) d^3r =0$ which necessarily causes a bias. We quantify both effects for currently available galaxy samples using simulated mock catalogues of the Sloan Digital Sky Survey (SDSS) following a lognormal model, with a Lambda-Cold Dark Matter ($\Lambda\text{CDM}$) correlation function and similar properties as the samples (number density, mean redshift for the $\Lambda\text{CDM}$ correlation function, survey geometry, mass-luminosity bias). Because we need extensive simulations to quantify small statistical effects, we cannot use realistic N-body simulations and some physical effects are neglected. Our simulations still enable a comparison of the different estimators by looking at their biases and variances. We also test the reliability of the BAO detection in the SDSS samples and study the compatibility of the data results with our $\Lambda\text{CDM}$ simulations.Comment: 14 pages, 6 figures, 3 table

Recovering the real-space correlation function from photometric redshift surveys

Measurements of clustering in large-scale imaging surveys that make use of photometric redshifts depend on the uncertainties in the redshift determination. We have used light-cone simulations to show how the deprojection method successfully recovers the real space correlation function when applied to mock photometric redshift surveys. We study how the errors in the redshift determination affect the quality of the recovered two-point correlation function. Considering the expected errors associated to the planned photometric redshift surveys, we conclude that this method provides information on the clustering of matter useful for the estimation of cosmological parameters that depend on the large scale distribution of galaxies.Comment: 11 pages, 8 figures. Accepted for publication in MNRA

Galaxy clusters and groups in the ALHAMBRA Survey

We present a catalogue of 348 galaxy clusters and groups with $0.2<z<1.2$ selected in the 2.78 $deg^2$ ALHAMBRA Survey. The high precision of our photometric redshifts, close to $1\%$, and the wide spread of the seven ALHAMBRA pointings ensure that this catalogue has better mass sensitivity and is less affected by cosmic variance than comparable samples. The detection has been carried out with the Bayesian Cluster Finder (BCF), whose performance has been checked in ALHAMBRA-like light-cone mock catalogues. Great care has been taken to ensure that the observable properties of the mocks photometry accurately correspond to those of real catalogues. From our simulations, we expect to detect galaxy clusters and groups with both $70\%$ completeness and purity down to dark matter halo masses of $M_h\sim3\times10^{13}\rm M_{\odot}$ for $z<0.85$. Cluster redshifts are expected to be recovered with $\sim0.6\%$ precision for $z<1$. We also expect to measure cluster masses with $\sigma_{M_h|M^*_{CL}}\sim0.25-0.35\, dex$ precision down to $\sim3\times10^{13}\rm M_{\odot}$, masses which are $50\%$ smaller than those reached by similar work. We have compared these detections with previous optical, spectroscopic and X-rays work, finding an excellent agreement with the rates reported from the simulations. We have also explored the overall properties of these detections such as the presence of a colour-magnitude relation, the evolution of the photometric blue fraction and the clustering of these sources in the different ALHAMBRA fields. Despite the small numbers, we observe tentative evidence that, for a fixed stellar mass, the environment is playing a crucial role at lower redshifts (z$<$0.5).Comment: Accepted for publication in MNRAS. Catalogues and figures available online and under the following link: http://bascaso.net46.net/ALHAMBRA_clusters.htm

The miniJPAS & J-NEP surveys: Identification and characterization of the Lyα\alpha Emitter population and the Lyα\alpha Luminosity Function

We present the Lyman-$a$ (Lya) Luminosity Function (LF) at $2.05<z<3.75$, estimated from a sample of 67 Lya-emitter (LAE) candidates in the J-PAS Pathfinder surveys: miniJPAS and J-NEP. These two surveys cover a total effective area of $\sim 1.14$ deg$^2$ with 54 Narrow Band (NB) filters across the optical range, with typical limiting magnitudes of $\sim 23$. This set of NBs allows to probe Lya emission in a wide and continuous range of redshifts. We develop a method for detecting Lya emission for the estimation of the Lya LF using the whole J-PAS filter set. We test this method by applying it to the miniJPAS and J-NEP data. In order to compute the corrections needed to estimate the Lya LF and to test the performance of the candidates selection method, we build mock catalogs. These include representative populations of Lya Emitters at $1.9<z<4.5$ as well as their expected contaminants, namely low-$z$ galaxies and $z<2$ QSOs. We show that our method is able to provide the Lya LF at the intermediate-bright range of luminosity ($\rm 10^{43.5} erg\,s^{-1} \lesssim L_{Lya} \lesssim 10^{44.5} erg\,s^{-1}$). The photometric information provided by these surveys suggests that our samples are dominated by bright, Lya-emitting Active Galactic Nuclei. At $L_{{\rm Ly}a}<10^{44.5}$ erg\,s$^{-1}$, we fit our Lya LF to a power-law with slope $A=0.70\pm0.25$. We also fit a Schechter function to our data, obtaining: Log(\Phi^* / \text{Mpc^{-3}})=-6.30^{+0.48}_{-0.70}, Log$(L^*/ \rm erg\,s^{-1})=44.85^{+0.50}_{-0.32}$, $a=-1.65^{+0.29}_{-0.27}$. Overall, our results confirm the presence of an AGN component at the bright-end of the Lya LF. In particular, we find no significant contribution of star-forming LAEs to the Lya LF at Log$(L_{\rm Lya}$ / erg\,s$^{-1}$)>43.5. This work serves as a proof-of-concept for the results that can be obtained with the upcoming data releases of the J-PAS survey.Comment: 25 pages, 15 figures, submitted to A&