L. N. da Costa

Universidad de La Laguna, San Cristóbal de La Laguna, Canary Islands, Spain

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Publications (76)228.91 Total impact

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    ABSTRACT: We present the combination of optical data from the Science Verification phase of the Dark Energy Survey (DES) with near infrared data from the ESO VISTA Hemisphere Survey (VHS). The deep optical detections from DES are used to extract fluxes and associated errors from the shallower VHS data. Joint 7-band (grizYJK) photometric catalogues are produced in a single 3 sq-deg DECam field centred at 02h26m-04d36m where the availability of ancillary multi-wavelength photometry and spectroscopy allows us to test the data quality. Dual photometry increases the number of DES galaxies with measured VHS fluxes by a factor of ~4.5 relative to a simple catalogue level matching and results in a ~1.5 mag increase in the 80% completeness limit of the NIR data. Almost 70% of DES sources have useful NIR flux measurements in this initial data release. Photometric redshifts are estimated for a subset of galaxies with spectroscopic redshifts and initial results, although currently limited by small number statistics, indicate that the VHS data can help reduce the photometric redshift scatter at both z<0.5 and z>1. We present example DES+VHS colour selection criteria for high redshift Luminous Red Galaxies at z~0.7 as well as luminous quasars. Using spectroscopic observations in this field we show that the additional VHS fluxes are useful for the selection of both populations. The combined DES+VHS dataset, which will eventually cover almost 5000 sq-deg, will therefore enable a range of new science and be ideally suited for target selection for future wide-field spectroscopic surveys.
    07/2014;
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    ABSTRACT: We measure the weak-lensing masses and galaxy distributions of four massive galaxy clusters observed during the Science Verification phase of the Dark Energy Survey with the purpose of 1) validating the DECam imager for the task of measuring weak-lensing shapes, and 2) utilizing DECam's large field of view to map out the clusters and their environments over 90 arcmin. We conduct a series of rigorous tests on astrometry, photometry, image quality, PSF modeling, and shear measurement accuracy to single out flaws in the data and also to identify the optimal data processing steps and parameters. We find Science Verification data from DECam to be suitable for lensing analyses. The PSF is generally well-behaved, but the modeling is rendered difficult by a flux-dependent PSF width. We employ photometric redshifts to distinguish between foreground and background galaxies, and a red-sequence cluster finder to provide cluster richness estimates and cluster-galaxy distributions. By fitting NFW profiles to the clusters in this study, we determine weak-lensing masses that are in agreement with previous work. For Abell 3261, we provide the first estimates of redshift, weak-lensing mass, and richness. In addition, the cluster-galaxy distributions indicate the existence of filaments attached to 1E 0657-56 and RXC J2248.7-4431, stretching out as far as 1 degree (approximately 20 Mpc), showcasing the potential of DECam and DES for detailed studies of degree-scale features on the sky.
    05/2014;
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    ABSTRACT: We investigate the chemo-kinematic properties of the Milky Way disc by exploring the first year of data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), and compare our results to smaller optical high-resolution samples in the literature, as well as results from lower resolution surveys such as GCS, SEGUE and RAVE. We start by selecting a high-quality sample in terms of chemistry ($\sim$ 20.000 stars) and, after computing distances and orbital parameters for this sample, we employ a number of useful subsets to formulate constraints on Galactic chemical and chemodynamical evolution processes in the Solar neighbourhood and beyond (e.g., metallicity distributions -- MDFs, [$\alpha$/Fe] vs. [Fe/H] diagrams, and abundance gradients). Our red giant sample spans distances as large as 10 kpc from the Sun, increasing by at least a factor of eight the studied volume with respect to the most recent chemodynamical studies. We find remarkable agreement between the recently published local (d $<$ 100 pc) high-resolution high-S/N HARPS sample and our local HQ sample (d $<$ 1 kpc). The local MDF peaks slightly below solar metallicity, and exhibits an extended tail towards [Fe/H] $= -$1, whereas a sharper cutoff is seen at larger metallicities. The APOGEE data also confirm the existence of a gap in the abundance diagram. When expanding our sample to cover three different Galactocentric distance bins, we find the high-[$\alpha$/Fe] stars to be rare towards the outer zones, as previously suggested in the literature. For the gradients in [Fe/H] and [$\alpha$/Fe], measured over a range of 6 $ < $ R $ <$ 11 kpc in Galactocentric distance, we find a good agreement with the gradients traced by the GCS and RAVE dwarf samples. For stars with 1.5 $<$ z $<$ 3 kpc, we find a positive metallicity gradient and a negative gradient in [$\alpha$/Fe].
    11/2013;
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    ABSTRACT: The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The survey's broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEE's primary sample consists of ~100,000 red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases.
    Proceedings of the International Astronomical Union 08/2013; 5.
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    ABSTRACT: We address the problem of separating stars from galaxies in future large photometric surveys. We focus our analysis on simulations of the Dark Energy Survey (DES). In the first part of the paper, we derive the science requirements on star/galaxy separation, for measurement of the cosmological parameters with the Gravitational Weak Lensing and Large Scale Structure probes. These requirements are dictated by the need to control both the statistical and systematic errors on the cosmological parameters, and by Point Spread Function calibration. We formulate the requirements in terms of the completeness and purity provided by a given star/galaxy classifier. In order to achieve these requirements at faint magnitudes, we propose a new method for star/galaxy separation in the second part of the paper. We first use Principal Component Analysis to outline the correlations between the objects parameters and extract from it the most relevant information. We then use the reduced set of parameters as input to an Artificial Neural Network. This multi-parameter approach improves upon purely morphometric classifiers (such as the classifier implemented in SExtractor), especially at faint magnitudes: it increases the purity by up to 20% for stars and by up to 12% for galaxies, at i-magnitude fainter than 23.
    06/2013;
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    ABSTRACT: The Dark Energy Survey (DES) will be unprecedented in its ability to probe exceptionally large cosmic volumes to relatively faint optical limits. Primarily designed for the study of comparatively low redshift (z<2) galaxies with the aim of constraining dark energy, an intriguing byproduct of the survey will be the identification of massive (>10^(12.0) M_sun) galaxies at z>~4. This will greatly improve our understanding of how galaxies form and evolve. By both passively evolving the low redshift mass function and extrapolating the observed high redshift mass function, we find that such galaxies should be rare but nonetheless present at early times, with predicted number densities of ~0.02 deg^-2. The unique combination of depth and coverage that DES provides will allow the identification of such galaxies should they exist - potentially identifying hundreds of such sources. We then model possible high redshift galaxies and determine their detectability using the DES filter sets and depths. We model sources with a broad range stellar properties and find that for these galaxies to be detected they must be either sufficiently young, high mass and/or relatively dust free (E(B-V)<0.45) - with these parameters jointly affecting each galaxy's detectability. We also propose colour-colour selection criteria for the identification of both pristine and dusty sources and find that, although contamination fractions will be high, the most reliable candidate massive high redshift galaxies are likely to be identifiable in the DES data through prioritisation of colour-selected sources.
    Monthly Notices of the Royal Astronomical Society 06/2013; · 5.52 Impact Factor
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    ABSTRACT: In this work we present the science portal that is being developed to be used for the Dark Energy Survey (DES). It is a web-based tool that integrates several tools to access data and advanced science products, monitor the progress of the survey and data reduction, a broad range of science algorithms in a user-friendly interface. Here we focus on the capabilities of the Science Portal to host tools that generate and analyze simulations of the stellar population in the Milky Way (MW). This tool (AddStar) was employed in the recent paper by Rossetto et al. (2011) where the expected resolved stellar sample of DES was simulated. This simulation led to forecasts on how DES will be able to explore the MW structure and composition. In this work we also discuss the possible application to other large area surveys to make similar predictions. AddStar in conjunction with other scientific tools in the Science Portal can add artificial objects such as a spheroidal galaxy with a complex SFH or a globular cluster with an associated tidal tail. This set of tools creates a simulated sky with realistic conditions enabling the user to make accurate predictions for satellite galaxies discovery efficiency.
    09/2012;
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    ABSTRACT: We examine the impact of using photometric redshifts for studying the evolution of both the global galaxy luminosity function (LF) and that for different galaxy types. To this end we compare LFs obtained using photometric redshifts from the CFHT Legacy Survey (CFHTLS) D1 field with those from the spectroscopic survey VIMOS VLT Deep Survey (VVDS) comprising ~4800 galaxies. We find that for z<2, in the interval of magnitudes considered by this survey, the LFs obtained using photometric and spectroscopic redshifts show a remarkable agreement. This good agreement led us to use all four Deep fields of CFHTLS comprising ~386000 galaxies to compute the LF of the combined fields and estimate directly the error in the parameters based on field-to-field variation. We find that the characteristic absolute magnitude M* of Schechter fits fades by ~0.7mag from z~1.8 to z~0.3, while the characteristic density phi* increases by a factor of ~4 in the same redshift bin. We use the galaxy classification provided by the template fitting program used to compute photometric redshifts and split the sample into galaxy types. We find that these Schechter parameters evolve differently for each galaxy type, an indication that their evolution is a combination of several effects: galaxy merging, star formation quenching and mass assembly. All these results are compatible with those obtained by different spectroscopic surveys such as VVDS, DEEP2 and zCosmos, which reinforces the fact that photometric redshifts can be used to study galaxy evolution, at least for the redshift bins adopted so far. This is of great interest since future very large imaging surveys containing hundreds of millions of galaxies will allow to obtain important precise measurements to constrain the evolution of the LF and to explore the dependence of this evolution on morphology and/or color helping constrain the mechanisms of galaxy evolution.
    The Astronomical Journal 05/2011; 142(2). · 4.97 Impact Factor
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    ABSTRACT: Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2x10^8 stars will be sampled in DES grizY filters. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy. DES will probe low-mass stellar and sub-stellar objects at depths from 3 to 8 times larger than SDSS. The faint end of the main-sequence will be densely sampled beyond 10 kpc. The slope of the low mass end of the stellar IMF will be constrained to within a few hundredth dex, even in the thick disk and halo. In the sub-stellar mass regime, the IMF slope will be potentially constrained to within dlog \phi(m) / dlog m ~ 0.1$. About 3x10^4 brown dwarf and at least 7.6x10^5 white dwarf candidates will be selected, the latter embedded into the thick disk and halo. The stellar halo flattening will also be constrained to within a few percent. DES will probe the main sequence of new Milky Way satellites and halo clusters for distances out to ~ 120 kpc, therefore yielding stellar surface density contrasts 1.6-1.7 times larger than those attainable with SDSS. It will also allow detection of these objects in the far reaches of the stellar halo, substantially increasing the number and quality of probes to the Galactic potential. Combined with northern samples, such as the SDSS, the DES stellar sample will yield constraints on the structure and stellar populations of Galactic components in unprecedented detail. In particular, the combined sample from both hemispheres will allow detailed studies of halo and thick disk asymmetries and triaxiality.
    The Astronomical Journal 04/2011; 141(6). · 4.97 Impact Factor
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    ABSTRACT: Compact elliptical galaxies are extremely rare objects that populate a puzzling gap in the range of structural parameters of spheroidal galaxies. It is unclear whether they share a common origin with their giant-elliptical cousins or represent a separate population with a physically different formation history. As part of an ongoing search for compact elliptical galaxies, we analyzed ugiz imaging of the regions around ten bright elliptical galaxies to search for compact companions. The images were taken at SOAR using the SOAR Optical Imager. These observations represent the first stage of the SOAR Ultracompact Dwarf Survey (SUDS), which uses optical and infrared colors to distinguish nearby compact ellipticals from foreground stars and background galaxies. Our analysis of the SOAR photometry has identified a candidate compact elliptical galaxy located approximately 36 kpc in projection from the bright elliptical galaxy NGC1653. Further SOAR data will constrain the redshift, velocity dispersion, chemical composition, and dark matter content of this rare relic of early galaxy formation.
    01/2011;
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    ABSTRACT: Presentamos gradientes radiales del índice de Lick Mg2 para 40 galaxias tempranas. En gráficas de 4Mg2 vs. indicadores de masa, tales como log o, el borde inferior de la distribución de puntos puede estar poblada por galaxias formadas predominantemente por colapso monolítico. Las galaxias que muestran gradientes más planos a mayor masa pueden representar objetos que han sufrido importantes episodios de fusión. Por tanto, nuestros resultados apoyan un escenario de formación híbrida. Para eliminar posibles efectos de edad, calculamos los gradientes de metalicidad (4[Z=H]) usando los índices Mg2 y H para un modelo de poblacion estelar de [ =Fe] = 0:3. Las conclusiones permanecen igual.
    Revista Mexicana de Astronomía y Astrofísica. 01/2006;
  • A. Cappi, C. Benoist, L. N. da Costa, S. Maurogordato
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    ABSTRACT: Three VLGs were selected from our catalogue of VLGs (see Table 1 of Paper I, Cappi et al., 1998A&A...335..779C), while a fourth galaxy satisfying the VLG definition was selected from the CfA catalogue (see Geller & Huchra, 1989Sci...246..897G); the 4 VLG fields were observed at OHP. Other 15 VLG fields were extracted from the 2dFGRS public catalogue (Cat. ), which has an overlap with the SSRS2 (Cat. ). While partially imposed by observational constraints (see below), our selection is random with respect to the VLG properties, and should be representative of the whole sample. In fact, one third of the selected VLGs are early-type galaxies, a fraction consistent with that of the total sample published in Paper I, Cappi et al. (1998A&A...335..779C). (3 data files).
    VizieR Online Data Catalog. 11/2003;
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    ABSTRACT: We present central velocity dispersions and Mg$_2$ line indices for an all-sky sample of $\sim$ 1178 elliptical and S0 galaxies, of which 984 had no previous measures. This sample contains the largest set of homogeneous spectroscopic data for a uniform sample of elliptical galaxies in the nearby universe. These galaxies were observed as part of the ENEAR project, designed to study the peculiar motions and internal properties of the local early-type galaxies. Using 523 repeated observations of 317 galaxies obtained during different runs, the data are brought to a common zero-point. These multiple observations, taken during the many runs and different instrumental setups employed for this project, are used to derive statistical corrections to the data and are found to be relatively small, typically $\lsim$ 5% of the velocity dispersion and 0.01 mag in the \mg line-strength. Typical errors are about 8% in velocity dispersion and 0.01 mag in \mg, in good agreement with values published elsewhere. Comment: 179 pages, 8 figures, 5 tables. Full tables 4 and 5 start on page 41
    The Astronomical Journal 08/2003; · 4.97 Impact Factor
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    ABSTRACT: We present R-band CCD photometry for 1332 early-type galaxies, observed as part of the ENEAR survey of peculiar motions using early-type galaxies in the nearby Universe. Circular apertures are used to trace the surface brightness profiles, which are then fit by a two-component bulge-disk model. From the fits we obtain the structural parameters required to estimate galaxy distances using the D_n-sigma and Fundamental Plane relations. We find that about 12% of the galaxies are well represented by a pure r^{1/4} law while 87% are best fit by a two component model. There are 356 repeated observations of 257 galaxies obtained during different runs that are used to derive statistical corrections and bring the data to a common system. We also use these repeated observations to estimate our internal errors. The accuracy of our measurements are tested by the comparison of 354 galaxies in common with other authors. Typical errors in our measurements are 0.011 dex for log{D_n}, 0.064 dex for log{r_e}, 0.086 mag arcsec^{-2} for <{mu_e}> and 0.09 for m_{R_C}, comparable to those estimated by other authors. The photometric data reported here represent one of the largest high-quality and uniform all-sky samples currently available for early-type galaxies in the nearby universe, especially suitable for peculiar motion studies. Comment: 51 pages, 12 figures, 6 tables, including full table6 (in http://webast.ast.obs-mip.fr/people/vicky/tables/) Accepted by AJ (scheduled for May 2003)
    The Astronomical Journal 02/2003; · 4.97 Impact Factor
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    ABSTRACT: This paper presents data on the ENEARc subsample of the larger ENEAR survey of the nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a D_n-sigma template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg_2, and the angular diameter d_n) as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies and new photometry is presented for 348 objects. Repeat and overlap observations with external data sets are used to construct a final merged catalog consisting of 640 early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to assign galaxies to clusters. In a companion paper these data are used to construct the template D_n-sigma distance relation for early-type galaxies which has been used to estimate galaxy distances and derive peculiar velocities for the ENEAR all-sky sample. Comment: 41 pages, 7 figures, and 8 tables. Accepted for publication in AJ
    The Astronomical Journal 03/2002; · 4.97 Impact Factor
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    ABSTRACT: R-band photometric and velocity dispersion measurements for a sample of 452 elliptical and S0 galaxies in 28 clusters are used to construct a template Dn-sigma relation. This template relation is constructed by combining the data from the 28 clusters, under the assumption that galaxies in different clusters have similar properties. The photometric and spectroscopic data used consist of new as well as published measurements, converted to a common system, as presented in an accompanying paper. The resulting direct relation, corrected for incompleteness bias, is logDn=1.203logsigma+1.406 the zero point has been defined by requiring distant clusters to be at rest relative to the cosmic microwave background. This zero point is consistent with the value obtained by using the distance to Virgo as determined by the Cepheid period-luminosity relation. This new Dn-sigma relation leads to a peculiar velocity of -72+/-189 km s-1 for the Coma Cluster. The scatter in the distance relation corresponds to a distance error of about 20%, comparable to the values obtained for the fundamental plane relation. Correlations between the scatter and residuals of the Dn-sigma relation with other parameters that characterize the cluster and/or the galaxy stellar population are also analyzed. The direct and inverse relations presented here have been used in recent studies of the peculiar velocity field mapped by the ENEAR all-sky sample. Based on observations at Complejo Astronomico El Leoncito (CASLEO), operated under agreement between the Consejo Nacional de Investigaciones Científicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan; Cerro Tololo Inter-American Observatory (CTIO), operated by the National Optical Astronomical Observatories, under AURA, Inc.; European Southern Observatory (ESO), partially under the ESO-ON agreement; Fred Lawrence Whipple Observatory (FLWO); Observatório do Pico dos Dias, operated by the Laboratório Nacional de Astrofísica (LNA); and the MDM Observatory on Kitt Peak.
    The Astronomical Journal 01/2002; 123:2159-2182. · 4.97 Impact Factor
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    ABSTRACT: In this paper R-band photometric and velocity dispersion measurements for a sample of 452 elliptical and S0 galaxies in 28 clusters are used to construct a template D_n-sigma relation. This template relation is constructed by combining the data from the 28 clusters, under the assumption that galaxies in different clusters have similar properties. The photometric and spectroscopic data used consist of new as well as published measurements, converted to a common system, as presented in a accompanying paper. The resulting direct relation, corrected for incompleteness bias, is log{D_n} =1.203 log{sigma} + 1.406; the zero-point has been defined by requiring distant clusters to be at rest relative to the CMB. This zero-point is consistent with the value obtained by using the distance to Virgo as determined by the Cepheid period-luminosity relation. This new D_n-sigma relation leads to a peculiar velocity of -72 (\pm 189) km/s for the Coma cluster. The scatter in the distance relation corresponds to a distance error of about 20%, comparable to the values obtained for the Fundamental Plane relation. Correlations between the scatter and residuals of the D_n-sigma relation with other parameters that characterize the cluster and/or the galaxy stellar population are also analyzed. The direct and inverse relations presented here have been used in recent studies of the peculiar velocity field mapped by the ENEAR all-sky sample. Comment: 46 pages, 20 figures, and 7 tables. To appear in AJ, vol. 123, no. 5, May 2002
    Astronomical Journal - ASTRON J. 01/2002; 123(5):2159-2182.
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    ABSTRACT: We compare the peculiar velocities derived from the I-band Tully-Fisher (TF) relation for 989 field spiral galaxies in the SFI catalogue with the predicted velocity field derived from the IRAS PSCz galaxy redshift survey. We assume linear gravitational instability theory and apply the maximum likelihood technique, VELMOD, to SFI galaxies within cz<6000 km/s. The resulting calibration of the TF relation is consistent with a previous, independent calibration for a similar sample of spirals residing in clusters. Our analysis provides an accurate estimate of the quantity beta. Using the forward TF relation and smoothing the predicted velocity field with a Gaussian filter of radius 300 km/s, we obtain beta = 0.42 +/- 0.04 (1 sigma uncertainty). This value, as well as other parameters in the fit, are robust to varying the smoothing radius to 500 km/s and splitting the sample into spherical shells in redshift space. The one exception is the small-scale velocity dispersion, sigma_v, which varies from 200 km/s within cz= 4000 km/s 500 km/s at larger distance. For beta = 0.42, the residuals between the TF data and the PSCz gravity field are uncorrelated, indicating that the model provides a good fit to the data. More generally, a chi^2 statistic indicates that the PSCz model velocity field provides an acceptable (3 sigma) fit to the data for 0.3 < beta < 0.5. Comment: 23 pages including 11 Figures. Accepted by MNRAS
    Monthly Notices of the Royal Astronomical Society 04/2001; · 5.52 Impact Factor
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    ABSTRACT: We estimate the mass density fluctuations power spectrum (PS) on large scales by applying a maximum likelihood technique to the peculiar velocity data of the recently completed redshift-distance survey of early-type galaxies (hereafter ENEAR). Parametric cold dark matter (CDM)-like models for the PS are assumed, and the best-fitting parameters are determined by maximizing the probability of the model given the measured peculiar velocities of the galaxies, their distances and estimated errors. The method has been applied to CDM models with and without COBE normalization. The general results are in agreement with the high-amplitude power spectra found from similar analyses of other independent all-sky catalogue of peculiar velocity data such as MARK III and SFI, in spite of the differences in the way these samples were selected, the fact that they probe different regions of space and galaxy distances are computed using different distance relations. For example, at k=0.1hMpc-1 the power spectrum value is P(k)Omega1.2=(6.5+/-3)×103(h- 1Mpc)3 and eta8≡sigma8Omega0.6=1.1- 0.35+0.2 the quoted uncertainties refer to 3sigma error level. We also find that, for LambdaCDM and OCDM COBE-normalized models, the best-fitting parameters are confined by a contour approximately defined by Omegah1.3=0.377+/-0.08 and Omegah0.88=0.517+/-0.083 respectively. Gamma-shape models, free of COBE normalization, result in the weak constraint of Gamma>=0.17 and in the rather stringent constraint of eta8=1.0+/-0.25. All quoted uncertainties refer to 3sigma confidence level (c.l.). The calculated PS has been used as a prior for Wiener reconstruction of the density field at different resolutions and the three-dimensional velocity field within a volume of radius ~80h-1Mpc. All major structures in the nearby Universe are recovered and are well matched to those predicted from all-sky redshift surveys. The robustness of these features has been tested with constrained realizations (CR). Analysis of the reconstructed three-dimensional velocity field yields a small bulk-flow amplitude (~160+/-60kms-1 at 60h-1Mpc) and a very small rms value of the tidal field (~60kms-1). The results give further support to the picture that most of the motion of the Local Group arises from mass fluctuations within the volume considered.
    Monthly Notices of the Royal Astronomical Society 01/2001; 326(1):375-386. · 5.52 Impact Factor
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    ABSTRACT: We introduce two new pair statistics, which relate close galaxy pairs to the merger and accretion rates. We demonstrate the importance of correcting these (and other) pair statistics for selection effects related to sample depth and completeness. In particular, we highlight the severe bias that can result from the use of a flux-limited survey. The first statistic, denoted N_c, gives the number of companions per galaxy, within a specified range in absolute magnitude. N_c is directly related to the galaxy merger rate. The second statistic, called L_c, gives the total luminosity in companions, per galaxy. This quantity can be used to investigate the mass accretion rate. Both N_c and L_c are related to the galaxy correlation function and luminosity function in a straightforward manner. We outline techniques which account for various selection effects, and demonstrate the success of this approach using Monte Carlo simulations. If one assumes that clustering is independent of luminosity (which is appropriate for reasonable ranges in luminosity), then these statistics may be applied to flux-limited surveys. These techniques are applied to a sample of 5426 galaxies in the SSRS2 redshift survey. Using close dynamical pairs, we find N_c(-21<M_B<-18) = 0.0226+/-0.0052 and L_c(-21<M_B<-18) = 0.0216+/-0.0055 10^{10} h^2 L_sun at z=0.015. These are the first secure estimates of low-z close pair statistics. If N_c remains fixed with redshift, simple assumptions imply that ~ 6.6% of present day galaxies with -21<M_B<-18 have undergone mergers since z=1. When applied to redshift surveys of more distant galaxies, these techniques will yield the first robust estimates of evolution in the galaxy merger and accretion rates. [Abridged] Comment: 26 pages (including 10 postscript figures) plus 3 gif figures. Accepted for publication in ApJ. Paper (including full resolution images) also available at http://www.astro.utoronto.ca/~patton/ssrs2, along with associated pair classification experiment (clickable version of Figure 5)
    The Astrophysical Journal 01/2000; · 6.73 Impact Factor

Publication Stats

923 Citations
228.91 Total Impact Points

Institutions

  • 2013
    • Universidad de La Laguna
      • Department of Astrophysics
      San Cristóbal de La Laguna, Canary Islands, Spain
  • 2003
    • Carnegie Mellon University
      • Department of Physics
      Pittsburgh, Pennsylvania, United States
  • 1998–2002
    • European Southern Observatory
      Arching, Bavaria, Germany
  • 1988
    • Observatório Nacional
      Rio de Janeiro, Rio de Janeiro, Brazil
  • 1987
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 1984
    • Harvard-Smithsonian Center for Astrophysics
      Cambridge, Massachusetts, United States