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We present a technique to fit the stellar components of the Galaxy by comparing Hess Diagrams (HDs) generated from TRILEGAL models to real data. We apply this technique, which we call MWFITTING, to photometric data from the first 3 yr of the Dark Energy Survey (DES). After removing regions containing known resolved stellar systems such as globular clusters, dwarf galaxies, nearby galaxies, the Large Magellanic Cloud, and the Sagittarius Stream, our main sample spans a total area of ∼2300 deg2. We further explore a smaller subset (∼1300 deg2) that excludes all regions with known stellar streams and stellar overdensities. Validation tests on synthetic data possessing similar properties to the DES data show that the method is able to recover input parameters with a precision better than 3 per cent. We fit the DES data with an exponential thick disc model and an oblate double power-law halo model. We find that the best-fitting thick disc model has radial and vertical scale heights of 2.67 ± 0.09 kpc and 925 ± 40 pc, respectively. The stellar halo is fit with a broken power-law density profile with an oblateness of 0.75 ± 0.01, an inner index of 1.82 ± 0.08, an outer index of 4.14 ± 0.05, and a break at 18.52 ± 0.27 kpc from the Galactic centre. Several previously discovered stellar overdensities are recovered in the residual stellar density map, showing the reliability of MWFITTING in determining the Galactic components. Simulations made with the best-fitting parameters are a promising way to predict Milky Way star counts for surveys such as the LSST and Euclid.

We report the discovery of a new star cluster, DES 3, in the constellation of Indus, and deeper observations of the previously identified satellite DES J0222.7−5217 (Eridanus III). DES 3 was detected as a stellar overdensity in first-year Dark Energy Survey data, and confirmed with deeper photometry from the 4.1-m Southern Astrophysical Research (SOAR) telescope. The new system was detected with a relatively high significance and appears in the DES images as a compact concentration of faint blue point sources. We determine that DES 3 is located at a heliocentric distance of 76.2 kpc and it is dominated by an old ( 9.8Gyr) and metal-poor ([Fe/H] −1.84) population. While the age and metallicity values of DES 3 are comparable to typical globular clusters (objects with a high stellar density, stellar mass of ∼105 M and luminosity MV ∼ −7.3), its half-light radius (rh ∼ 6.87 pc) and luminosity (MV ∼ −1.7) are more indicative of faint star cluster. Based on the angular size, DES 3, with a value of rh ∼ 0. 31, is among the smallest faint star clusters known to date. Furthermore, using deeper imaging of DES J0222.7−5217 taken with the SOAR telescope, we update structural parameters and perform the first isochrone modelling. Our analysis yields the first age ( 12.6Gyr) and metallicity ([Fe/H] −2.01) estimates for this object. The half-light radius (rh 11.24 pc) and luminosity (MV −2.4) of DES J0222.7−5217 suggest that it is likely a faint star cluster. The discovery of DES 3 indicates that the census of stellar systems in the MilkyWay is still far from complete, and demonstrates the power of modern wide-field imaging surveys to improve our knowledge of the Galaxy’s satellite population.

Nossa amostra de trabalho consistiu das cercanias das Nuvens de Magalhães dentro da area amostrada pelo Dark Energy Survey. Nos concentramos na amostra de aglomerados da Grande Nuvem de Magalhães e na descoberta de uma sobredensidade estelar associada a Pequena Nuvem de Magalhães, sobre as quais faremos aqui uma breve descrição, baseada nos resumos já publicados. A Grande Nuvem de Magalhães possui um sistema rico e diversificado de aglomerados estelares, cujas idades, abundâncias químicas e posições oferecem informação a respeito do histórico de formação estelar desta galáxia. Nós usamos as imagens dos dados de verificação científica do Dark Energy Survey para aumentar o censo de aglomerados conhecidos na região externa da Grande Nuvem de Magalhães e para determinar os parâmetros físicos de uma grande número destes objetos usando uma amostra homogênea, tanto fotom elétrica quanto espacialmente. Nossa amostra contém 255 aglomerados identificados visualmente, dos quais 109 não estão listados em nenhum catálogo prévio. Nós quantificamos o efeito de adensamento estelar para a amostra produzida pela equipe de gerenciamento dos dados do Dark Energy Survey e concluímos que a completeza da amostra estelar e < 10% no centro de aglomerados típicos da Grande Nuvem de Magalhães. Desenvolvemos então um arranjo de tarefas para amostrar e medir as magnitudes e posições das estrelas nos candidatos a aglomerados da Grande Nuvem de Magalhães utilizando o conjunto de pacotes daophot. Tamb em implementamos um método de máxima probabilidade para ajustar perfis de densidade individuais, bem como diagramas cor-magnitude. Para 117 aglomerados (de um total de 255) dos candidatos, sendo 28 aglomerados até então não catalogados, obtivemos idades, metalicidades, m odulo de distância e parâmetros estruturais confiáveis, confirmando sua natureza de sistemas físicos. The distribution of cluster metallicities shows a radial dependence, with no clusters more metal-rich than [Fe/H] ' 0:7 beyond 8 kpc from the center of that galaxy. The age distribution has two peaks at ' 1.2 Gyr and ' 2.7 Gyr. The age-metallicity relation shows that even with an external sample, there is a global agreement with other studies that sampled more central regions of the Large Magellanic Cloud. In addition, this age-metallicity relation is well described as bounded by the analytical model from Pagel & Tautvaisiene (1998) and the empirical model from Harris & Zaritsky (2009). But neither of them describes accurately the clusters set. We also report here the discovery of a stellar over-density 8 north of the center of the Small Magellanic Cloud, baptized as SMCNOD (Small Magellanic Cloud Northern Over-Density), using data from the rst two years of the Dark Energy Survey (DES) and the rst year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarly composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity = 0:6 and a size of 6x2 deg. It has an absolute magnitude of MV = 7:7, rh = 2:1 kpc, and V (r < rh) = 31.2 mag arcsec2. We estimate a stellar mass of 105 M , following a Kroupa mass function. The SMCNOD was probably removed from the SMC disk by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent LMC-SMC encounters. This scenario is supported by the lack of signi cant HI gas. Other potential scenarios for the SMCNOD origin are a transient over-density within the Small Magellanic Cloud tidal radius or a primordial SMC satellite in advanced stage of disruption. Estimamos uma massa estelar de 105 massas solares, seguindo uma função de massa inicial de Kroupa. A SMCNOD foi provavelmente removida do disco da Pequena Nuvem de Magalhães via tidal stripping, pois e localizada próximo da extremidade da Corrente de Magalhães (Magellanic Stream) e, segundo a literatura, houve recentes encontros entre a LMC e a SMC. Este cenário e apoiado pela significante falta de Hidrogênio neutro. Outros cenários potenciais para a origem da SMCNOD são: uma sobredensidade transitória dentro do raio de mar e ou uma satélite primordial em estado avançado de ruptura. Our working sample comprised the outskirts of the Magellanic Clouds encompassed by the Dark Energy Survey. We focused in the star cluster system of the Large Magellanic Cloud and on the discovery of a stellar over-density associated to the Small Magellanic Cloud, which we will brie y describe here, based on already published abstracts. The Large Magellanic Cloud harbors a rich and diverse system of star clusters, whose ages, chemical abundances, and positions provide information about the Large Magellanic Cloud history of star formation. We use Science Veri cation imaging data from the Dark Energy Survey to increase the census of known star clusters in the outer Large Magellanic Cloud and to derive physical parameters for a large sample of such objects using a spatially and photometrically homogeneous data set. Our sample contains 255 visually identi ed cluster candidates, of which 109 were not listed in any previous catalog. We quantify the crowding e ect for the stellar sample produced by the Dark Energy Survey Data Management pipeline and conclude that the stellar completeness is < 10% inside typical Large Magellanic cluster cores. We therefore develop a pipeline to sample and measure stellar magnitudes and positions around the cluster candidates using daophot. We also implement a maximumlikelihood method to t individual density pro les and colour-magnitude diagrams. For 117 (from a total of 255) of the cluster candidates (28 uncatalogued clusters), we obtain reliable ages, metallicities, distance moduli and structural parameters, con rming their nature as physical systems.

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.

Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with masses 20 GeV annihilating via the bb¯ or τ+τ− channels.

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.

The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey (DES). The SV footprint covers a large portion of the outer LargeMagellanic Cloud (LMC), providing photometry 1.5 mag fainter than the main sequence turn-off of the oldest LMC stellar population.We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = −38. ◦ 14 ± 0. ◦ 08 (near side in the north) and a position angle for the line of nodes of θ0 = 129. ◦ 51 ± 0. ◦ 17. We find that stars younger than ∼4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R>4 Gyr = 1.41 ± 0.01 kpc, while the younger population has R

In this study, we present a detailed study of mass segregation in the globular cluster NGC 6397. First, we carry out a photometric analysis of projected European SouthernObservatory (ESO)– Very Large Telescope (VLT) data (between 1 and 10 arcmin from the cluster centre), presenting the luminosity function corrected by completeness. The luminosity function shows a higher density of bright stars near the central region of the data with respect to the outer region. We calculate a deprojected model (covering the whole cluster), estimating a total number of 193 000 ± 19 000 stars. The shapes of the surface brightness and density-number profiles versus the radial coordinate r (instead of the projected coordinate R) lead to a decreasing luminosity and thus mass for an average star, up to 1 arcmin, quantifying the mass segregation. The deprojected model does not show evidence of mass segregation outside this region.

Neste trabalho eu desenvolvo um método para a determinação dos quatro principais parâmetros de um aglomerado globular (idade, metalicidade, avermelhamento e modulo de distancia) através de diagramas cor-magnitude, por comparação com modelos teóricos (isócronas). Usando diagramas cor-magnitude sintéticos determino a precisão e a incerteza do método por comparação com o banco de isócronas de Dartmouth e de Padova (PARSEC). Como exemplo, determino a os parâmetros do aglomerado globular NGC 6397, o segundo aglomerado globular mais próximo do sistema solar, utilizando múltiplas observações e múltiplas cores. Os parâmetros são comparados com a idade do Universo e dados espectroscópicos de estrelas do aglomerado e chegam a uma boa concordância. Os parâmetros ajustados são 12 ± 0, 5 Ganos, metalicidade [Fe/H] = −1, 8±0, 25, avermelhamento [E(B-V)] = 0, 12±0.01 e módulo de distância (m-M) = 12,04. Discuto a diferença entre os valores finais dos parâmetros para um conjunto de muitos dados em relação com os parâmetros para apenas um diagrama cor-magnitude e a diferença entre o ajuste para cores do ultravioleta até o infravermelho. In this work I develop a method to determine the four main parameters of a galactic globular cluster (age, metallicity, reddening and distance modulus) by comparing color-magnitude diagrams to theoretical models (isochrones). Using synthetic colormagnitude diagrams I determine the accuracy and uncertainties of the method by comparison with the isochrone databases from Dartmouth and Padova (PARSEC). As an example, I determine the parameters for the globular cluster NGC 6397, the second nearest to the Sun, using multiple observations and multiple colors. The parameters are compared with the age of the Universe and spectroscopic data of cluster stars and yields a good agreement. The parameters fitted are 12 ± 0.5 Gyr, metallicity [Fe/H] = −1.8, reddening [E(B-V)] = 0.12 ± 0.01 and distance modulus (m-M) = 12.04. I discussed the difference between the final parameters values for many data sets with parameter values in a single color-magnitude diagram and the difference between the fit to colors from the ultraviolet to the infrared.