Search

We present the results of the first observations of the emission line galaxies (ELG) of the extended Baryon Oscillation Spectroscopic Survey. From the total 9000 targets, 4600 have been selected from the Dark Energy Survey (DES). In this subsample, the total success rate for redshifts between 0.6 and 1.2 is 71 and 68 per cent for a bright and a faint samples, respectively, including redshifts measured from a single strong emission line. The mean redshift is 0.80 for the bright and 0.87 for the faint sample, while the percentage of unknown redshifts is 15 and 13 per cent, respectively. In both cases, the star contamination is lower than 2 per cent. We evaluate how well the ELG redshifts are measured using the target selection photometry and validating with the spectroscopic redshifts measured by eBOSS. We explore different techniques to reduce the photometric redshift outliers fraction with a comparison between the template fitting, the neural networks and the random forest methods. Finally, we study the clustering properties of the DES SVA1 ELG samples. We select only the most secure spectroscopic redshift in the redshift range 0.6 < z < 1.2, leading to a mean redshift for the bright and faint sample of 0.85 and 0.90, respectively. We measure the projected angular correlation function and obtain a galaxy bias averaging on scales from 1 to 10 Mpc h−1 of 1.58 ± 0.10 for the bright sample and 1.65 ± 0.12 for the faint sample. These values are representative of a galaxy population with MB − log(h) < −20.5, in agreement with what we measure by fitting galaxy templates to the photometric data.

We present a study of quasar selection using the supernova fields of the Dark Energy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/ probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) mid- IR W1 - W2 color, a mixture of WISE and DES colors (g − i and i - W1), and a mixture of Vista Hemisphere Survey and DES colors (g − i and i − K ). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band χ2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg2 of the DES supernova fields. The catalog includes quasars with redshifts up to z4 and brighter than i = 22 mag, although the catalog is not complete up to this magnitude limit.

We study the galaxy populations in 74 Sunyaev–Zeldovich effect selected clusters from the South Pole Telescope survey, which have been imaged in the science verification phase of the Dark Energy Survey. The sample extends up to z ∼ 1.1 with 4 × 1014M ≤ M200 ≤ 3 × 1015M . Using the band containing the 4000 Å break and its redward neighbour, we study the colour–magnitude distributions of cluster galaxies to ∼m∗ + 2, finding that: (1)The intrinsic rest frame g − r colour width of the red sequence (RS) population is ∼0.03 out to z ∼ 0.85 with a preference for an increase to ∼0.07 at z = 1, and (2) the prominence of the RS declines beyond z ∼ 0.6. The spatial distribution of cluster galaxies is well described by the NFW profile out to 4R200 with a concentration of cg = 3.59+0.20 −0.18, 5.37+0.27 −0.24 and 1.38+0.21 −0.19 for the full, the RS and the blue non-RS populations, respectively, but with ∼40 per cent to 55 per cent cluster to cluster variation and no statistically significant redshift or mass trends. The number of galaxies within the virial region N200 exhibits a mass trend indicating that the number of galaxies per unit total mass is lower in the most massive clusters, and shows no significant redshift trend. The RS fraction within R200 is (68 ± 3) per cent at z = 0.46, varies from ∼55 per cent at z = 1 to ∼80 per cent at z = 0.1 and exhibits intrinsic variation among clusters of ∼14 per cent. We discuss a model that suggests that the observed redshift trend in RS fraction favours a transformation time-scale for infalling field galaxies to become RS galaxies of 2–3 Gyr.

Chemically peculiar stars in dwarf galaxies provide a window for exploring the birth environment of stars with varying chemical enrichment. We present a chemical abundance analysis of the brightest star in the newly discovered ultra-faint dwarf galaxy candidate Tucana III. Because it is particularly bright for a star in an ultra-faint Milky Way (MW) satellite, we are able to measure the abundance of 28 elements, including 13 neutron-capture species. This star, DES J235532.66−593114.9 (DES J235532), shows a mild enhancement in neutron-capture elements associated with the r-process and can be classified as an r-I star. DES J235532 is the first r-I star to be discovered in an ultra-faint satellite, and Tuc III is the second extremely low-luminosity system found to contain rprocess enriched material, after Reticulum II. Comparison of the abundance pattern of DES J235532 with r-I and r-II stars found in other dwarf galaxies and in the MW halo suggests a common astrophysical origin for the neutron-capture elements seen in all r-process enhanced stars. We explore both internal and external scenarios for the r-process enrichment of Tuc III and show that with abundance patterns for additional stars, it should be possible to distinguish between them.

We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite EridanusII (Eri II). We identify 28 member stars in EriII, from which we measure a systemic radial velocity of vhel = 75.6 1.3 (stat.) 2.0 (sys.) km s-1 and a velocity dispersion of - 6.9+0.9 1.2 km s-1. Assuming that EriII is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of - ´ 1.2+ 10 0.3 0.4 7 M, indicating a mass-tolight ratio of - 420+140 210 M/L and confirming that it is a dark matter-dominated dwarf galaxy. From the equivalent width measurements of the Ca triplet lines of 16 red giant member stars, we derive a mean metallicity of [Fe/ H]=−2.38±0.13 and a metallicity dispersion of s[ / ] = - 0.47+ Fe H 0.09 0.12. The velocity of EriII in the Galactic standard of rest frame is vGSR=−66.6 km s-1, indicating that either EriII is falling into the Milky Way potential for the first time or that it has passed the apocenter of its orbit on a subsequent passage. At a Galactocentric distance of 370 kpc, Eri II is one of the Milky Way’s most distant satellites known. Additionally, we show that the bright blue stars previously suggested to be a young stellar population are not associated with EriII. The lack of gas and recent star formation in EriII is surprising given its mass and distance from the Milky Way, and may place constraints on models of quenching in dwarf galaxies and on the distribution of hot gas in the Milky Way halo. Furthermore, the large velocity dispersion of Eri II can be combined with the existence of a central star cluster to constrain massive compact halo object dark matter with mass 10 M.

We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite TucanaIII (Tuc III). We identify 26 member stars in TucIII from which we measure a mean radial velocity of vhel=−102.3±0.4 (stat.)±2.0(sys.) km s-1, a velocity dispersion of - 0.1+0.1 0.7 km s-1, and a mean metallicity of = - - [Fe/H] 2.42+0.08 0.07. The upper limit on the velocity dispersion is σ

We report the discovery of the eighth and ninth known Trojans in stable orbits around Neptune’s leading Lagrange point, L4. The objects 2014QO441 and 2014QP441 were detected in data obtained during the 2013–14 and 2014–15 observing seasons by the Dark Energy Survey, using the Dark Energy Camera (DECam) on the 4-m Blanco telescope at Cerro Tololo Inter-American Observatory. Both are in high-inclination orbits (18°.8 and 19°.4, respectively). With an eccentricity of 0.104, 2014QO441 has the most eccentric orbit of the 11 known stable Neptune Trojans. Here we describe the search procedure and investigate the objects’ long-term dynamical stability and physical properties.

We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model-or machine learning-based photometric redshift methods-ANNZ2, BPZ calibrated against BCC-Ufig simulations, SKYNET, and TPZ-are analyzed. For training, calibration, and testing of these methods, we construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evaluated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-z's. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 +/- 0.01 over the range 0.3 < z < 1.3, we construct three tomographic bins with means of z = {0.45;0.67;1.00}. These bins each have systematic uncertainties delta z

We report the discovery of a stellar stream in the Dark Energy Survey Year 1 (Y1A1) data. The discovery was made through simple color–magnitude filters and visual inspection of the Y1A1 data. We refer to this new object as the Phoenix stream, after its resident constellation. After subtraction of the background stellar population we detect a clear signal of a simple stellar population. By fitting the ridge line of the stream in color–magnitude space, we find that a stellar population with age τ=11.5±0.5 Gyr and [Fe/H]

We use the first-year Dark Energy Survey (DES) data down to previously unprobed photometric depths to search for stellar systems in the Galactic halo, therefore complementing the previous analysis of the same data carried out by our group earlier this year. Our search is based on a matched filter algorithm that produces stellar density maps consistent with stellar population models of various ages, metallicities, and distances over the survey area. The most conspicuous density peaks in these maps have been identified automatically and ranked according to their significance and recurrence for different input models. We report the discovery of one additional stellar system besides those previously found by several authors using the same first-year DES data. The object is compact, and consistent with being dominated by an old and metal-poor population. DES 1 is found at high significance and appears in the DES images as a compact concentration of faint blue point sources. Assuming different spatial profile parameterizations, the best-fitting heliocentric distance and total absolute magnitude in the range of 77.6–87.1 kpc and −3.00 MV −2.21, respectively. The half-light radius of this object, rh ∼ 10 pc and total luminosity are consistent with it being a low-mass halo cluster. It is also found to have a very elongated shape ( ∼ 0.57). In addition, our deeper probe of DES first-year data confirms the recently reported satellite galaxy candidate Horologium II as a significant stellar overdensity. We also infer its structural properties and compare them to those reported in the literature.

We introduce redMaGiC, an automated algorithm for selecting luminous red galaxies (LRGs). The algorithm was specifically developed to minimize photometric redshift uncertainties in photometric large-scale structure studies. redMaGiC achieves this by self-training the colour cuts necessary to produce a luminosity-thresholded LRG sample of constant comoving density. We demonstrate that redMaGiC photo-zs are very nearly as accurate as the best machine learning-based methods, yet they require minimal spectroscopic training, do not suffer from extrapolation biases, and are very nearly Gaussian. We apply our algorithm to Dark Energy Survey (DES) Science Verification (SV) data to produce a redMaGiC catalogue sampling the redshift range z ∈ [0.2, 0.8]. Our fiducial sample has a comoving space density of 10−3 (h−1 Mpc)−3, and a median photo-z bias (zspec − zphoto) and scatter (σz/(1 + z)) of 0.005 and 0.017, respectively. The corresponding 5σ outlier fraction is 1.4 per cent.We also test our algorithm with Sloan Digital Sky Survey Data Release 8 and Stripe 82 data, and discuss how spectroscopic training can be used to control photo-z biases at the 0.1 per cent level.

We report the discovery of eight new ultra-faint dwarf galaxy candidates in the second year of optical imaging data from the Dark Energy Survey (DES). Six of these candidates are detected at high confidence, while two lowerconfidence candidates are identified in regions of non-uniform survey coverage. The new stellar systems are found by three independent automated search techniques and are identified as overdensities of stars, consistent with the isochrone and luminosity function of an old and metal-poor simple stellar population. The new systems are faint (MV > −4.7mag) and span a range of physical sizes (17 pc < r1/2 < 181 pc) and heliocentric distances (25 kpc < De < 214 kpc). All of the new systems have central surface brightnesses consistent with known ultrafaint dwarf galaxies (μ  27.5mag arcsec−2). Roughly half of the DES candidates are more distant, less luminous, and/or have lower surface brightnesses than previously known Milky Way satellite galaxies. Most of the candidates are found in the southern part of the DES footprint close to the Magellanic Clouds. We find that the DES data alone exclude (p < 10−3) a spatially isotropic distribution of Milky Way satellites and that the observed distribution can be well, though not uniquely, described by an association between several of the DES satellites and the Magellanic system. Our model predicts that the full sky may hold ∼100 ultra-faint galaxies with physical properties comparable to the DES satellites and that 20%–30% of these would be spatially associated with the Magellanic Clouds.

We present spectroscopic confirmation of two new gravitationally lensed quasars, discovered in the Dark Energy Survey (DES) and Wide-field Infrared Survey Explorer (WISE) based on their multiband photometry and extended morphology in DES images. Images of DES J0115−5244 show a red galaxy with two blue point sources at either side, which are images of the same quasar at zs = 1.64 as obtained by our long-slit spectroscopic data. The Einstein radius estimated from the DES images is 0.51 arcsec. DES J2146−0047 is in the area of overlap between DES and the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fibre spectrum shows a quasar component at zs = 2.38 and absorption by Mg II and Fe II at zl = 0.799, which we tentatively associate with the foreground lens galaxy. Our long-slit spectra show that the blue components are resolved images of the same quasar. The Einstein radius is 0.68 arcsec, corresponding to an enclosed mass of 1.6 × 1011M . Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data mining and model-based selection that is being applied to the entire DES data set.

El propósito de la tesis es presentar un método con el que construir catálogos de galaxias virtuales poblando simulaciones de N-cuerpos usando recetas basadas en el modelo ``Halo Occupation Distribution (HOD)''. Los catálogos generados cumplen una serie de propiedades observadas de las galaxias, tales como la función de luminosidad, el diagrama color-magnitud y la distribución espacial en función de la luminosidad y del color. Los datos observados provienen del ``Sloan Digital Sky Survey (SDSS)''. Se describe el marco teórico en el que se basa la producción de los catálogos, tanto el ``Halo model'' como el modelo HOD. Nuestros catálogos se construyen poblando con galaxias los catálogos de halos generados a partir de las simulaciones de N-cuerpos de materia oscura ``Marenostrum Institut de Ciències de l'Espai (MICE)''. Caracterizamos el catálogo de halos usado como input calculando la función de masa, la función de correlación a dos puntos y el bias lineal a gran escala de los halos. El modelo HOD proporciona recetas para poblar los halos con galaxias. Este modelo puede ser parametrizado de diversas maneras. En nuestro caso comenzamos generando catálogos de galaxias usando las recetas del modelo HOD propuestas por Skibba & Sheth en 2009. Debido a que el catálogo generado no se ajusta correctamente a las observaciones, investigamos de manera analítica el cálculo de dos parámetros del modelo HOD, Mmin y M1 (asumimos α=1), usando únicamente dos condiciones: la densidad media en número de galaxias y su bias. Luego calculamos los parámetros del modelo HOD que mejor ajustan la distribución espacial de las galaxias en función de la luminosidad mediante la construcción de un grid de catálogos que comprenden un amplio rango de tres parámetros del modelo HOD, Mmin, M1 y α. Para poder ajustar las observaciones es necesaria la introducción de nuevos ingredientes al modelo: la técnica ``SubHalo Abundance Matching (SHAM)'' y un perfil NFW modificado. Se crea un único catálogo que cumple al mismo tiempo la distribución espacial de galaxias para todas las luminosidades y todos los colores usando como input el catálogo de halos calculado del ``snapshot'' a redshift z=0 de la simulación ``MICE Grand Challenge''. El catálogo se construye siguiendo un nuevo algoritmo en el que se introducen algunas modificaciones: ``scatter'' en la relación entre la luminosidad de la galaxia central y la masa del halo, Mh, el parámetro M1 del modelo HOD se modela en función de Mh, y se incluye una tercera componente Gaussiana (en lugar de dos), para describir el diagrama color-magnitud. Se calcula la función de luminosidad y el bias de las galaxias lineal del catálogo generado. También se muestra el efecto que producen las velocidades peculiares de las galaxias en la distribución espacial de las galaxias, y la función de correlación angular en la escala de las oscilaciones acústicas de los bariones. Finalmente y brevemente se describen algunas de las actuales aplicaciones de los catálogos usados en los proyectos PAU y DES, en los que se incluyen características específicas para cada una de las galaxias como son las propiedades morfológicas, la magnitud en 42 filtros estrechos y la deformación provocada por el ``shear'' gravitacional., This thesis presents a method to build mock galaxy catalogues by populating N-body simulations using prescriptions based upon the halo occupation distribution model (HOD). The catalogues are constructed to follow some global local properties of the galaxy population already observed, such as the luminosity function, the colourmagnitude diagram and the clustering as a function of luminosity and colour. The observed data constraints come from the Sloan Digital Sky Survey (SDSS). The theoretical framework in which the production of the catalogues is based on, the halo model and the HOD, are described. Our mock catalogues are built from halo catalogues extracted from the Marenostrum Institut de Ci`encies de l’Espai Nbody dark matter simulations (MICE). We characterize our input halo catalogues by computing their halo mass function, two-point correlation function and linear large scale halo bias. The HOD provides prescriptions of how galaxies populate haloes. The HOD can be parameterized in several ways. We start by following the HOD recipes given by Skibba & Sheth 2009 to generate galaxy catalogues. Since the luminosity function of the catalogue does not fit observations, we investigate an analytical derivation of two HOD parameters, Mmin and M1 (α is assumed to be 1), by only using two observed constraints: the galaxy number density and bias. Then, a grid of 600 mock galaxy catalogues that covers a wide range of values of the three HOD parameters, Mmin, M1 and α, is generated to obtain the best-fit HOD parameters that match the observed clustering of galaxy luminosity threshold samples. As we cannot match observations we introduce additional ingredients: the SubHalo Abundance Matching (SHAM) and a modified NFW density profile. A unique mock galaxy catalogue that follows at the same time the clustering at all luminosities and colours is produced using the halo catalogue extracted from the snapshot at z=0 of the MICE Grand Challenge run. The catalogue is built by following a new algorithm in which several modifications are introduced: scatter in the halo mass - central luminosity relation, the HOD parameter M1 is set as a function of Mh, and three Gaussian components (instead of only two) are included to describe the colour-magnitude distribution. A derivation of the luminosity function and the linear galaxy bias of the mock catalogue is shown. How galaxy velocity affects the galaxy clustering and an estimation of the angular correlation function at the BAO scale are presented too. Finally, different versions of the catalogue currently used in PAU and DES projects, which include specific characteristics such as shear information or 42 different magnitudes in narrow band filters and also morphological properties for each galaxy, are briefly described.