arXiv subjects

M. V. Alonso

Publications and source records attributed to M. V. Alonso.

At least 37 records · Page 2Linked to original sources

arXiv2012

Compact Groups of Galaxies selected by stellar mass: The 2MASS Compact Group Catalogue

We present a photometric catalogue of compact groups of galaxies (p2MCGs) automatically extracted from the 2MASS extended source catalogue. A total of 262 p2MCGs are identified, following the criteria of Hickson (1982), of which 230 survive visual inspection. Only 1/4 of these groups were previously known compact groups (CGs). Among the 144 p2MCGs that have all their galaxies with known redshifts, 85 have 4 or more accordant galaxies. This v2MCG sample of velocity-filtered p2MCGs constitutes the largest sample of CGs catalogued to date, with both well-defined selection criteria and velocity filtering, and is the first CG sample selected by stellar mass. We compared the properties of the 78 v2MCGs with > 3000 km/s with the properties of other CG samples, as well as those (mvCGs) extracted from the semi-analytical model of Guo et al. (2011) run on the high-resolution Millennium-II simulation. In this mvCG sample, 2/3 of the groups are physically dense. The space density of v2MCGs within 6000 km/s is 4 times that of the Hickson sample up to the same distance and with the same criteria used here, but still 40% less than that of mvCGs. The v2MCG constitutes the first group catalogue showing statistically significant signs of wide magnitude gaps (according to Tremaine-Richstone statistics) and centrally located 1st-ranked galaxies, both consistent with the predictions obtained from mvCGs. By virtue of its automatic selection with the popular Hickson criteria, its size, its selection on stellar mass, and its statistical signs of mergers and centrally located brightest galaxies, the v2MCG catalogue appears to be the laboratory of choice to study compact groups of 4 or more galaxies of comparable luminosity. [Abridged]

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arXiv2012

Galaxies behind the Galactic plane: First results and perspectives from the VVV Survey

Vista Variables in The Via Lactea (VVV) is an ESO variability survey that is performing observations in near infrared bands (ZYJHKs) towards the Galactic bulge and part of the disk with the completeness limits at least 3 mag deeper than 2MASS. In the present work, we searched in the VVV survey data for background galaxies near the Galactic plane using ZYJHKs photometry that covers 1.636 square degrees. We identified 204 new galaxy candidates by analyzing colors, sizes, and visual inspection of multi-band (ZYJHKs) images. The galaxy candidates colors were also compared with the predicted ones by star counts models considering a more realistic extinction model at the same completeness limits observed by VVV. A comparison of the galaxy candidates with the expected one by Milennium simulations is also presented. Our results increase the number density of known galaxies behind the Milky Way by more than one order of magnitude. A catalog with galaxy properties including ellipticity, Petrosian radii and ZYJHKs magnitudes is provided, as well as comparisons of the results with other surveys of galaxies towards Galactic plane.

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arXiv2011

VVV DR1: The First Data Release of the Milky Way Bulge and Southern Plane from the Near-Infrared ESO Public Survey VISTA Variables in the Via Lactea

The ESO Public Survey VISTA Variables in the Via Lactea (VVV) started in 2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane region and is expected to run for ~5 years. In this paper we describe the progress of the survey observations in the first observing season, the observing strategy and quality of the data obtained. The observations are carried out on the 4-m VISTA telescope in the ZYJHKs filters. In addition to the multi-band imaging the variability monitoring campaign in the Ks filter has started. Data reduction is carried out using the pipeline at the Cambridge Astronomical Survey Unit. The photometric and astrometric calibration is performed via the numerous 2MASS sources observed in each pointing. The first data release contains the aperture photometry and astrometric catalogues for 348 individual pointings in the ZYJHKs filters taken in the 2010 observing season. The typical image quality is ~0.9-1.0". The stringent photometric and image quality requirements of the survey are satisfied in 100% of the JHKs images in the disk area and 90% of the JHKs images in the bulge area. The completeness in the Z and Y images is 84% in the disk, and 40% in the bulge. The first season catalogues contain 1.28x10^8 stellar sources in the bulge and 1.68x10^8 in the disk area detected in at least one of the photometric bands. The combined, multi-band catalogues contain more than 1.63x10^8 stellar sources. About 10% of these are double detections due to overlapping adjacent pointings. These overlapping multiple detections are used to characterise the quality of the data. The images in the JHKs bands extend typically ~4 mag deeper than 2MASS. The magnitude limit and photometric quality depend strongly on crowding in the inner Galactic regions. The astrometry for Ks=15-18 mag has rms ~35-175 mas.

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arXiv2009

VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way

We describe the public ESO near-IR variability survey (VVV) scanning the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. The survey will take 1929 hours of observations with the 4-metre VISTA telescope during five years (2010-2014), covering ~10^9 point sources across an area of 520 deg^2, including 33 known globular clusters and ~350 open clusters. The final product will be a deep near-IR atlas in five passbands (0.9-2.5 microns) and a catalogue of more than 10^6 variable point sources. Unlike single-epoch surveys that, in most cases, only produce 2-D maps, the VVV variable star survey will enable the construction of a 3-D map of the surveyed region using well-understood distance indicators such as RR Lyrae stars, and Cepheids. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi LAT, XMM-Newton, GAIA and ALMA for a complete understanding of the variable sources in the inner Milky Way. This public survey will provide data available to the whole community and therefore will enable further studies of the history of the Milky Way, its globular cluster evolution, and the population census of the Galactic Bulge and center, as well as the investigations of the star forming regions in the disk. The combined variable star catalogues will have important implications for theoretical investigations of pulsation properties of stars.

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arXiv2004

The Globular Cluster System of NGC 1399: III. VLT Spectroscopy and Database

Radial velocities of 468 globular clusters around NGC 1399, the central galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest sample of globular cluster velocities around any galaxy obtained so far. The mean velocity uncertainty is 50 km/sec. This data sample is accurate and large enough to be used in studies of the mass distribution of NGC 1399 and the properties of its globular cluster system. Here we describe the observations, the reduction procedure, and discuss the uncertainties of the resulting velocities. The complete sample of cluster velocities which is used in a dynamical study of NGC 1399 is tabulated. A subsample is compared with previously published values.

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arXiv2004

The Globular Cluster System of NGC 1399. II. Kinematics of a Large Sample of Globular Clusters

We study the kinematics and dynamics of the globular cluster system of NGC 1399, the central galaxy of the Fornax cluster. The observational data consists of medium resolution spectra, obtained at the Very Large Telescope. Our sample comprises 468 radial velocities in the magnitude range 20 < m_R < 23. This is the largest sample of globular cluster velocities around any galaxy obtained so far. The radial range is 2 arcmin < r < 9 arcmin, corresponding to 11 kpc to 50 kpc of galactocentric distance. There is the possibility that unbound clusters and/or objects in the foreground contaminate the NGC 1399 cluster sample. Under strong error selection, practically no objects are found with velocities lower than 800 km/s or higher than 2000 km/s. Since the extreme velocities influence the velocity dispersion considerably, uncertainty regarding the exact value of the dispersion remains. Within the above velocity limits, we derive a projected velocity dispersion for the total sample of 274+-9 km/s which within the uncertainties remains constant over the entire radial range. Without any velocity restriction, it increases to 325 km/s. Blue and red clusters show different dispersions corresponding to their different surface density profiles. Spherical models point to a circular velocity of 415+-30$ km/s, assuming isotropy for the red clusters. This value is constant out to 40 kpc. The inferred dark halo potential can be well represented by a logarithmic potential. Also a halo of the NFW type fits well to the observations. Some mass profiles derived from X-ray analyses do not agree with a constant circular velocity within our radial range, irrespective of its exact value.

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arXiv2003

Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data

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.

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arXiv2003

Redshift-Distance Survey of Early-Type Galaxies: Circular Aperture Photometry

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.

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arXiv2002

Redshift-distance Survey of Early-type Galaxies: The D_n-sigma Relation

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.

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arXiv2002

Redshift-distance Survey of Early-type Galaxies: the ENEARc Cluster Sample

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.

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arXiv2001

Mg_2-sigma in Early-Type Galaxies and Spiral Bulges

We analyze new measurements of the Mg_2 central line strength index and velocity dispersion (sigma) for the galaxies of the ENEAR survey. The observations are now complete (da Costa et al. 2000) and the sample contains 1223 early-type galaxies. We also analyze the line strength indices for a sample of 95 spiral bulges (from Sa to Sbc). For the early-type galaxies we find: i) that the Mg_2-sigma relation for Es and S0s are nearly the same, with both populations showing comparable scatter, and ii) a marginal difference in the slope of the Mg_2-sigma relation for cluster and field early-type galaxies. However, we suggest that before interpreting such a difference in the framework of a mass-metallicity relation, it is important to take into account the effects of rotation in the Mg_2-sigma relation. Our preliminary results indicate that once the rotation effects are minimized by choosing a sample containing only slow rotators, the Mg_2-sigma relation is similar both for isolated and clustered galaxies. More data on rotational velocities of early-type galaxies are needed to confirm this result. For spiral bulges, we find that their locus in the Mg_2-sigma plane lies always below the one occupied by early-type galaxies.

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arXiv2000

Redshift-Distance Survey of Early-Type Galaxies. IV. Dipoles of the Velocity Field

We use the recently completed redshift-distance survey of nearby early-type galaxies (ENEAR) to measure the dipole component of the peculiar velocity field to a depth of cz ~ 6000 km/s. The sample consists of 1145 galaxies brighter than m_B=14.5 and cz < 7000 km/s, uniformly distributed over the whole sky, and 129 fainter cluster galaxies within the same volume. Most of the Dn-sigma distances were obtained from new spectroscopic and photometric observations conducted by this project, ensuring the homogeneity of the data over the whole sky. These 1274 galaxies are objectively assigned to 696 objects -- 282 groups/clusters and 414 isolated galaxies. We find that within a volume of radius ~ 6000 km/s, the best-fitting bulk flow has an amplitude of |vbulk| =220 +/- 42 km/s in the CMB restframe, pointing towards l=304 +/- 16 degrees, b=25 +/- 11 degrees. The error in the amplitude includes statistical, sampling and possible systematic errors. This solution is in excellent agreement with that obtained by the SFI Tully-Fisher survey. Our results suggest that most of the motion of the Local Group is due to fluctuations within 6000 km/s, in contrast to recent claims of large amplitude bulk motions on larger scales.

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arXiv2000

Comparison of the ENEAR Peculiar Velocities with the PSCz Gravity Field

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky $D_n-σ$ catalog and that derived from the galaxy distribution of the IRAS PSCz redshift survey. The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500km/s at 3000km/s. The general flow patterns in the filtered ENEAR and PSCz velocity fields agree well within 6000km/s, assuming a linear biasing relation between the mass and the PSCz galaxies. The comparison allows us to determine the parameter $β=Ω^{0.6}/b$, where $Ω$ is the cosmological density parameter and $b$ is the linear biasing factor. A likelihood analysis of the ENEAR and PSCz modes yields $β=0.5 +- 0.1$, in good agreement with values obtained from Tully-Fisher surveys.

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arXiv2000

ENEAR Redshift-Distance Survey: Cosmological Constraints

We present an analysis of the ENEAR sample of peculiar velocities of elliptical galaxies, obtained with D_n-σdistances. We use the velocity correlation function to analyze the statistics of the field-object's velocities, while the analysis of the cluster data is based on the estimate of their rms peculiar velocity, Vrms. The statistics of the model velocity field is parameterized by the amplitude, η_8=σ_8 Ω_m^{0.6}, and by the shape parameter, Γ. From the velocity correlation statistics we obtain η_8=0.51{-0.09}{+0.24} for Γ=0.25 at the 2σlevel. Even though less constraining, a consistent result is obtained by comparing the measured Vrms of clusters to linear theory predictions. For Γ=0.25 we find η_8=0.63{-0.19}{+0.22}$ at 1σ. Overall, our results point toward a statistical concordance of the cosmic flows traced by spirals and early-type galaxies, with galaxy distances estimated using TF and D_n-σdistance indicators, respectively.

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arXiv2000

Deep HST+STIS Color-Magnitude Diagrams of the Dwarf Irregular Galaxy WLM: Detection of the Horizontal Branch

We have obtained V and I-band photometry for 1886 stars down to I=27 and V=28 in the field of the dwarf irregular galaxy WLM, using deep STIS CL and LP-band images taken in the parallel mode with the Hubble Space Telescope. The photometry is used to study the horizontal branch identified in WLM. The horizontal branch, extending blueward from the red giant clump, is an unambiguous signature of an old population. We demonstrate that it is possible to reach the horizontal branch of an old population at a distance of ~1 Mpc using STIS, with relatively short exposure times. From the VI color-magnitude diagram we obtain an accurate distance modulus (m-M)_0 = 24.95 \pm 0.13 for WLM by using the V-magnitude of the horizontal branch, and by adopting E(V-I)=0.03. The implications are: 1) WLM formed stars at high redshift, and 2) the old population of WLM can be representative of a protogalactic fragment, related to those accreted to form the Milky Way halo.

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arXiv1999

Redshift-Distance Survey of Early-type Galaxies. I. Sample Selection, Properties and Completeness

This is the first in a series of papers describing the recently completed all-sky redshift-distance survey of nearby early-type galaxies (ENEAR) carried out for peculiar velocity analysis. The sample is divided into two parts and consists of 1607 elliptical and lenticular galaxies with cz < 7000 km/s and with blue magnitudes brighter than m_B=14.5 (ENEARm), and of galaxies in clusters (ENEARc). Galaxy distances based on the Dn-sigma and Fundamental Plane (FP) relations are now available for 1359 and 1107 ENEARm galaxies, respectively, with roughly 80% based on new data gathered by our group. The Dn-sigma and FP template distance relations are derived by combining 569 and 431 galaxies in 28 clusters, respectively, of which about 60% are based on our new measurements. The ENEARm redshift-distance survey extends the earlier work of the 7S and the recent Tully-Fisher surveys sampling a comparable volume. In subsequent papers of this series we intend to use the ENEAR sample by itself or in combination with the SFI Tully-Fisher survey to analyze the properties of the local peculiar velocity field and to test how sensitive the results are to different sampling and to the distance indicators. We also anticipate that the homogeneous database assembled will be used for a variety of other applications and serve as a benchmark for similar studies at high-redshift.

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arXiv1999

The Nearby Early-type Galaxies Survey (ENEAR): Project description and Some Preliminary Results

The ENEAR project is an all-sky survey of nearby early-type galaxies. About 2200 new spectra and R-band images of over 1500 galaxies together with published data were assembled into a large catalog containing over 2000 objects with cz, sigma, photometric data, and line strengths on a uniform system. From this extensive database a magnitude-limited sample has been drawn comprising ~ 1400 galaxies brighter than m_B = 14.5, cz < 7000 km/s, and type T -2 or less with measured distances (ENEARf) and about 500 early-type galaxies in 28 clusters/groups (ENEARc) to derive an internally consistent D_n-sigma relation to estimate galaxy distances. In this contribution we discuss some general properties of ENEAR and briefly describe some preliminary results.

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arXiv1999

Two Galaxy Clusters: A3565 and A3560

We report 102 new redshifts and magnitudes for a sample of galaxies to RF ~ 15.5 mag in a 2.17 deg x 2.17 deg region centered on the galaxy IC 4296, the most luminous member of the A3565 cluster. Up to the limiting magnitude we find 29 cluster members, and measure a velocity dispersion of 228 km/s. The estimated total mass for this system is ~ 3.0 x h**-1 10**13 Msun (where h = H0/100 km/s/Mpc), and its dynamical properties are quite typical of poor clusters presenting X-ray emission. We also find that galaxies with absorption lines are more concentrated towards the center of the cluster, while systems with emission lines are mainly located in the outer parts. The small velocity dispersion of the cluster, coupled to the known presence of an interacting pair of galaxies, and the large extent of the brightest cluster galaxy, could indicate that galaxy formation through mergers may still be underway in this system. The surveyed region also contains galaxies belonging to the Shapley Concentration cluster A3560. Within 30 arc min of the cluster center, we detect 32 galaxies, for which we measure a velocity dispersion of 588 km/s and a mass of ~2 x h**-1 10**14 Msun. However, because our sample is restricted to galaxies brighter than M*, these values should be considered only as rough estimates.

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