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S. Zaggia

Publications and source records attributed to S. Zaggia.

At least 163 records · Page 9Linked to original sources
arXiv2004

UVES observations of the Canis Major overdensity

We present the first detailed chemical abundances for three giant stars which are candidate members of the Canis Major overdensity, obtained by using FLAMES-UVES at VLT. The stars, in the background of the open cluster NGC 2477, have radial velocities compatible with a membership to this structure. However, due to Galactic disc contamination, radial velocity by itself is unable to firmly establish membership. The metallicities span the range -0.5 < [Fe/H] < +0.1. Assuming that at least one of the three stars is indeed a member of CMa implies that this structure has undergone a high level of chemical processing, comparable to that of the Galactic disc. The most metal-rich star of the sample, EIS 6631, displays several abundance ratios which are remarkably different from those of Galactic stars: [alpha/Fe] ~-0.2, [Cu/Fe] ~+0.25, [La/Fe]~+0.6, [Ce/Fe]~+0.8 and [Nd/Fe]~+0.6. These ratios make it likely that this star was formed in an external galaxy.

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arXiv2004

Probing the Canis Major stellar over-density as due to the Galactic warp

Proper-motion, star counts and photometric catalog simulations are used to explain the detected stellar over-density in the region of Canis Major (CMa), claimed to be the core of a disrupted dwarf galaxy (Martin et al. 2004, Bellazzini et al. 2003), as due to the Galactic warp and flare in the external disk. We compare the kinematics of CMa M-giant selected sample with surrounding Galactic disk stars in the UCAC2 catalog and find no peculiar proper motion signature: CMa stars mimic thick disk kinematics. Moreover, when taking into account the Galactic warp and flare of the disk, 2MASS star count profiles reproduce the CMa stellar over-density. This star count analysis is confirmed by direct comparison with synthetic color-magnitude diagrams simulated with the Besancon models (Robin et al. 2003) that include the warp and flare of the disk. The presented evidence casts doubt on the identification of the CMa over-density as the core of a disrupted Milky Way satellite. This however does not make clear the origin of over-densities responsible for the ring structure in the anticenter direction of the Galactic halo (Newberg et al. 2002; Yanny et al. 2003; Zaggia et al. 2004, in preparation).

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arXiv2003

Photometric redshifts with the Multilayer Perceptron Neural Network: application to the HDF-S and SDSS

We present a technique for the estimation of photometric redshifts based on feed-forward neural networks. The Multilayer Perceptron (MLP) Artificial Neural Network is used to predict photometric redshifts in the HDF-S from an ultra deep multicolor catalog. Various possible approaches for the training of the neural network are explored, including the deepest and most complete spectroscopic redshift catalog currently available (the Hubble Deep Field North dataset) and models of the spectral energy distribution of galaxies available in the literature. The MLP can be trained on observed data, theoretical data and mixed samples. The prediction of the method is tested on the spectroscopic sample in the HDF-S (44 galaxies). Over the entire redshift range, $0.1<z<3.5$, the agreement between the photometric and spectroscopic redshifts in the HDF-S is good: the training on mixed data produces sigma_z(test) ~ 0.11, showing that model libraries together with observed data provide a sufficiently complete description of the galaxy population. The neural system capability is also tested in a low redshift regime, 0<z<0.4, using the Sloan Digital Sky Survey Data Release One (DR1) spectroscopic sample. The resulting accuracy on 88108 galaxies is sigma_z(test) ~ 0.022. Inputs other than galaxy colors - such as morphology, angular size and surface brightness - may be easily incorporated in the neural network technique. An important feature, in view of the application of the technique to large databases, is the computational speed: in the evaluation phase, redshifts of 10^5 galaxies are estimated in few seconds.

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arXiv2003

Search for the Optical Counterpart of the Vela Pulsar X-ray Nebula

Observations of the Vela pulsar region with the Chandra X-ray observatory have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN), which showed an overall similarity with the Crab PWN. However, contrary to the Crab, no firm detection of the Vela PWN in optical has been reported yet. To search for the optical counterpart of the X-ray PWN, we analyzed deep optical observations performed with different telescopes. We compared the optical images with those obtained with the Chandra ACIS to search for extended emission patterns which could be identified as counterparts of the X-ray nebula elements. Although some features are seen in the optical images, we find no correlation with the X-ray structure. Thus, we conclude that the diffuse optical emission is more likely associated with filaments in the host Vela SNR. The derived upper limits on the optical flux from the PWN are compatibile, within the uncertainties, with the values expected on the basis of the extrapolations of the X-ray data.

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arXiv2001

Pre-FLAMES Survey: Observations of Selected Stellar Fields

This paper presents the first set of fully calibrated images and associated stellar catalogs of the Pre-FLAMES survey being carried out by the ESO Imaging Survey (EIS) project. The primary goal of this survey is to provide the ESO community with data sets from which suitable target lists can be extracted for follow-up observations with the new VLT facility FLAMES. For this purpose 160 stellar fields have been selected for observations in B, V and I using the 8kx8k Wide Field Imager (WFI) at the MPG/ESO 2.2 m telescope at La Silla. These data have been used to assess the observing strategy adopted and to define suitable reduction techniques and procedures for the preparation of input catalogs for FLAMES. The images and catalogs presented here are publicly available and can be requested from the URL address ``http://www.eso.org/eis''.

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arXiv1999

ESO Imaging Survey: Past Activities and Future Prospects

The ESO Imaging Survey (EIS) is an ongoing project to carry out public imaging surveys to support programs on the ESO Very Large Telescope (VLT). The first phase of the project started in July 1997 and consisted of a moderately deep, large-area survey (EIS-WIDE) and a deep optical/infrared survey (EIS-DEEP) using the ESO New Technology Telescope (NTT). EIS has recently reached another milestone with the completion of a Pilot Survey using the Wide-Field Image (WFI), an 8k by 8k mosaic CCD camera mounted on the MPG/ESO 2.2m telescope at La Silla. This paper briefly reviews the results of the original EIS and gives an update of the results obtained from the observations carried out as part of the Pilot Survey. Work in progress on the development of an advanced pipeline for handling data from large CCD mosaics and facilities to make the access to data products easier for external users are also discussed.

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arXiv1998

ESO Imaging Survey. AXAF Field: Deep Optical-Infrared Observations, Data Reduction and Photometry

This paper presents ground-based data obtained from deep optical and infrared observations carried out at the ESO 3.5 New Technology Telescope (NTT) of a field selected for its low HI content for deep observations with AXAF. These data were taken as part of the ESO Imaging Survey (EIS) program, a public survey conducted in preparation for the first year of operation of the VLT. Deep CCD images are available for five optical passbands, reaching 2 sigma limiting magnitudes of U_AB~27.0, B_AB~27, V_AB~26.5, R_AB~26.5 and I_AB~26. An area of ~56 square arcmin is covered by UBVR observations, and ~30 square arcmin also in I. The infrared observations cover a total area of ~83 square arcmin, reaching J_AB~24.5 and K_AB~23.5. This paper describes the observations and data reduction. It also presents images of the surveyed region and lists the optical and infrared photometric parameters of the objects detected on the co-added images of each passband, as well as multicolor optical and infrared catalogs. These catalogs together with the astrometrically and photometrically calibrated co-added images are public and can be retrieved from the URL http://www.eso.org/eis/ . This data set completes the ESO Imaging Survey program sixteen months after it began in July 1997.

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arXiv1998

ESO Imaging Survey. Hubble Deep Field South: Optical-Infrared Observations, Data Reduction and Photometry

This paper presents ground-based data obtained from deep optical and infrared observations of the HST Hubble Deep Field South (HDF-S) field carried out at the ESO 3.5 New Technology Telescope (NTT). These data were taken as part of the ESO Imaging Survey (EIS) program, a public survey coordinated by ESO and member states, in preparation for the first year of operation of the VLT. Deep CCD images are available for five optical passbands, reaching 2 sigma limiting magnitudes of U_AB~27.0, B_AB~26.5, V_AB~26, R_AB~26, I_AB~25, covering a region of ~25 square arcmin, which includes the HST WPFC2 field. The infrared observations cover a total area of ~42 square arcmin and include both the HST WFPC2 and STIS fields. The observations of the WFPC2 region were conducted in JHKs passbands, reaching J_AB~25, and H_AB and K_AB~24.0. Due to time constraints, the adjacent field, covering the STIS field, has been observed only in R, I and JHKs, while no observations were conducted covering the NIC3 field. This paper describes the observations and data reduction. It also presents images of the surveyed region and lists the optical and infrared photometric parameters of the objects detected on the co-added images of each passband, as well as multicolor optical and infrared catalogs. These catalogs together with the astrometrically and photometrically calibrated co-added images are being made public world-wide and can be retrieved from the world-wide web (http://www.eso.org/eis).

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arXiv1998

The NTT Susi Deep Field

We present a deep BVrI multicolor catalog of galaxies in a 5.62 sq.arcmin field 80 arcsec south of the high redshift (z=4.7) quasar BR 1202-0725, derived from observations with the direct CCD camera SUSI at the ESO NTT. The formal 5$σ$ magnitude limits (in 2 x FWHM apertures) are 26.9, 26.5, 25.9 and 25.3 in B, V, r and I respectively. Counts, colors for the star and galaxy samples are discussed and a comparison with a deep HST image in the I band is presented. The percentage of merged or blended galaxies in the SUSI data to this magnitude limit is estimated to be not higher than 1%. At the same galactic latitude of the HDF but pointing toward the galactic center, the star density in this field is found to be ~3 times higher, with ~20% of the objects with V-I > 3.0. Reliable colors have been measured for galaxies selected down to r = 26. The choice of the optical filters has been optimized to define a robust multicolor selection of galaxies at 3.8 <= z <= 4.4. Within this interval the surface density of galaxy candidates with r < 26 in this field is 2.7 +/- 0.4 arcmin^-2 corresponding to a comoving density of Star Formation Rate at 3.8 <= z <= 4.4 of 10^{-2.00} - 10^{-1.82} h^3 Mo /yr/ Mpc^3.

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arXiv1998

Structure and kinematics of the peculiar galaxy NGC 128

This is a multiband photometric and spectroscopic study of the peculiar S0 galaxy NGC128. We present results from broad (B and R) and narrow band optical CCD photometry, near (NIR) and far (FIR) infrared observations, long slit spectroscopy, and Fabry-Perot interferometry (CIGALE). The peculiar peanut shape morphology of the galaxy is observed both at optical and near-infrared wavelengths. The stellar disk is thick and distorted (arc-bended), with a color asymmetry along the major axis due to the presence of a large amount of dust, estimated through NIR and FIR data of ~6x10^6 M_sun, in the region of interaction with the companion galaxy NGC127. The color maps are nearly uniform over the whole galaxy, but for the major axis asymmetry, and a small gradient toward the center indicating the presence of a redder disk-like component. The H_alpha image indeed reveals the existence of a tilted gaseous ``disk'' around the center, oriented with the major axis toward the companion galaxy NGC127. Long slit and CIGALE data confirm the presence of gas in a disk-like component counter-rotating and inclined approximately of 50 deg. to the line of sight. The mass of the gas disk in the inner region is ~2.7x10^4 M_sun. The stellar velocity field is cylindrical up to the last measured points of the derived rotation curves, while the velocity dispersion profiles are typical for an S0 galaxy, but for an extended constant behaviour along the minor axis.

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arXiv1998

ESO Imaging Survey VI. The last 12 square degrees

This paper presents the I-band data obtained by the ESO Imaging Survey (EIS) over two patches of the sky, 6 square degrees each, centered at $α\sim 5^h40^m$, $δ\sim -24^\circ50^m$, and $α\sim 9^h50^m$, $δ\sim -21^\circ 00^m$. The data are being made public in the form of object catalogs and, photometrically and astrometrically calibrated pixel maps. These products together with other useful information can be found at "http://www.eso.org/eis". The overall quality of the data in the two fields is significantly better than the other two patches released earlier and cover a much larger contiguous area. The total number of objects in the catalogs extracted from these frames is over 700,000 down to $I\sim23$, where the galaxy catalogs are 80% complete. The star counts are consistent with model predictions computed at the position of the patches considered. The galaxy counts and the angular two-point correlation functions are also consistent with those of the other patches showing that the EIS data set is homogeneous and that the galaxy catalogs are uniform.

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arXiv1998

ESO Imaging Survey VII. Distant Cluster Candidates over 12 square degrees

In this paper the list of candidate clusters identified from the I-band data of the ESO Imaging Survey (EIS) is completed using the images obtained over a total area of about 12 square degrees. Together with the data reported earlier the total I-band coverage of EIS is 17 square degrees, which has yielded a sample of 252 cluster candidates in the redshift range $0.2 \lsim z \lsim 1.3$. This is the largest optically-selected sample currently available in the Southern Hemisphere. It is also well distributed in the sky thus providing targets for a variety of VLT programs nearly year round.

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arXiv1998

ESO Imaging Survey IV. Exploring the EIS Multicolor Data

This paper presents preliminary lists of potentially interesting point-like sources extracted from multicolor data obtained for a 1.7 square degree region near the South Galactic Pole. The region has been covered by the ESO Imaging Survey (EIS) in B, V,I, and offers a unique combination of area and depth.These lists, containing a total of 330 objects nearly all brighter than I~21.5, over 1.27 square degrees (after removing some bad regions), are by-products of the process of verification and quality control of the object catalogs being produced. Among the color selected targets are candidate very low mass stars/brown dwarfs (54), white-dwarfs (32), and quasars (244). In addition, a probable fast moving asteroid was identified. The objects presented here are natural candidates for follow-up spectroscopic observations and illustrate the usefulness of the EIS data for a broad range of science and for providing possible samples for the first year of the VLT.

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arXiv1998

ESO Imaging Survey III. Multicolor Data near the South Galactic Pole

This paper presents multicolor data obtained for a 1.7 square degree region near the South Galactic Pole (patch B) as part of the ESO Imaging Survey (EIS). So far the observations have been conducted in B,V and I but are expected to be complemented by observations in the U band later in 1998. Object catalogs extracted from single exposure images are 80% complete down to B~24, V~23.5 and I ~22.5 and once coadded should reach about 0.5 mag deeper. The data are being made public in the form of catalogs, pixel maps, target lists and image "postage stamps" which can be retrieved from the Web. Counts of stars and galaxies and the angular two-point correlation function of galaxies are computed and compared to other available data to evaluate the depth and uniformity of the extrtacted object catalogs. In addition, color distributions of stellar objects are presented and compared to model predictions to examine the reliability of the colors. The results suggest that the overall quality of the catalogs extracted from the images is good and suitable for the science goals of the survey.

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arXiv1998

ESO Imaging Survey V. Cluster Search using Color Data

This paper presents 19 additional candidate clusters detected using the galaxy catalog extracted from the I-band images taken for the ESO Imaging Survey (EIS). The candidates are found over a region of 1.1 square degrees, located near the South Galactic Pole. Combined with the sample reported earlier, the number of candidates in the Southern Galactic Cap is now 54 over a total area of 3.6 square degrees. Images in V band are also available over 2.7 square degrees, and galaxy catalogs extracted from them over a uniform area of 2 square degrees have been used to further explore the reality of the I cluster candidates. Nearly all the I candidates with estimated redshifts <~ 0.5 are also identified in V. At higher redshifts, only rich candidates are detected in both bands.

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arXiv1998

The Galactic globular cluster NGC 1851: its dynamical and evolutionary properties

We have completely mapped the globular cluster NGC 1851 with VI CCD photometry, obtaining a CMD for ca. 20500 stars. From the apparent luminosity of the HB we derive a distance modulus (m-M)o=15.44+/-0.20. The presence of 7 "supra-HB" stars is confirmed. Six of them are identified as evolved descendants from HB progenitors. Synthetic HR diagrams demonstrate that the problem of the HB morphology could be solved by assuming a bimodal efficiency of the mass loss along the RGB. We find evidence that the radial distribution of the blue HB stars is different from that of the red HB and SGB stars. The first measurement of the mean absolute I magnitude for 22 known RR Lyr variables ( =0.12+/-0.20 at [Fe/H]=-1.28), is given. We found 7 new RR Lyr candidates (6 ab type and 1 c type), lowering the ratio N(c)/N(ab) to 0.38. From a sample of 25 globular clusters (including NGC 1851) a new calibration for DV(bump,HB) as a function of metallicity is derived, and we find some evidence for an age-metallicity relation among GCs. We identify 13 blue straggler stars, which do not show any sign of variability. The blue stragglers are less concentrated than the SGB stars with similar magnitudes for r>80". Finally, a radial dependence of the LF, a sign of mass segregation, is found. Transforming the LF into a mass function and correcting for mass segregation by means of multi-mass King-Michie models, we find a global MF exponent x(0)=0.2+/-0.3.

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arXiv1997

The Stellar Distribution of the Globular Cluster M55

We have used extensive V, I photometry (down to V=20.9) of 33615 stars in the direction of the globular cluster M55 to study the dynamical interaction of this cluster with the tidal fields of the Galaxy. An entire quadrant of the cluster has been covered, out to ~2.0 times the tidal radius. A CMD down to about 4 magnitudes below the turn-off is presented and analysed. A large population of BS has been identified. The BS are significantly more concentrated in the inner 300 arcsec, while they become less concentrated in the cluster envelope. We have obtained luminosity functions at various radial intervals from the center and their corresponding mass functions. Both clearly show the presence of mass segregation inside the cluster. A dynamical analysis shows that the observed mass segregation is compatible with what is predicted by multi-mass King-Michie models. The global mass function is very flat with a power-law slope of x=-1.0+/-0.4. This suggest that M55 might have suffered selective losses of stars, caused by tidal interactions with the Galactic disk and bulge. The radial density profile of M55 out to ~2.0 r_t suggests the presence of extra-tidal stars whose nature could be connected with the cluster.

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