arXiv subjects

Massimo Capaccioli

Publications and source records attributed to Massimo Capaccioli.

36 records · Page 2Linked to original sources

arXiv2017

VEGAS-SSS II: Comparing the globular cluster systems in NGC3115 and NGC1399 using VEGAS and FDS survey data

We analyze the globular cluster (GC) systems in two very different galaxies, N3115 and N1399. With the papers of this series, we aim at highlighting common and different properties in the GC systems in galaxies covering a wide range of parameter space. We compare the GCs in N3115 and N1399 as derived from the analysis of u, g, and i band images taken with the VST telescope as part of the VEGAS and FDS surveys. We selected GC candidates using as reference the morpho-photometric and color properties of confirmed GCs. The surface density of GCs in N3115 reveal a morphology similar to the profile of field stars; the same is true when blue and red GCs are taken separately. The GC maps for N1399 are richer in structure and confirm the existence of an intracluster GC component. We confirm the presence of a spatial offset in the N1399 GC centroid and find that the centroid of the GCs for N3115 coincides well with the galaxy center. Both GC systems show unambiguous color bimodality in g-i and u-i. The azimuthal average of the radial density profiles in both galaxies reveals a larger spatial extent for the total GCs population with respect to the galaxy surface brightness profile. As for the specific frequency of GCs, Sn, we find it is a factor of two higher in N1399 than for N3115. By inspecting the radial behavior of the specific frequency, Sn(<r), for the total, blue, and red GCs, we find notable similarities between the trends for red GCs in the two targets. In spite of extremely different host environments, the red GCs in both cases appear closely linked to the light distribution of field stars. Blue GCs extend to larger galactocentric scales than red GCs, marking a significant difference between the two galaxies: the blue/red GCs and field stellar components of N3115 appear well thermalized with each other and the blue GCs in N1399 appear to fade into an unrelaxed intracluster GC population.

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arXiv2017

A VST and VISTA study of globular clusters in NGC253

Aims. We analyze the properties of the sources in the NGC253 to define an up to date catalog of GC candidates in the galaxy. Methods. Our analysis is based on the science verification data of two ESO survey telescopes, VST and VISTA. Using ugri photometry from VST and JKs from VISTA, GC candidates were selected using the morpho-photometric and color properties of spectroscopically confirmed GCs available in the literature. The strength of the results was verified against available archival HST/ACS data from the GHOSTS survey. Results. The adopted GC selection leads to the definition of a sample of ~350 GC candidates. At visual inspection, we find that 82 objects match all the requirements for selecting GC candidates and 155 are flagged as uncertain GC candidate; 110 are unlikely GCs, most likely background galaxies. Furthermore, our analysis shows that four of the previously spectroscopically confirmed GCs, i.e., ~20% of the total spectroscopic sample, are more likely either background galaxies or high-velocity Milky Way stars. The radial density profile of the selected best candidates shows the typically observed r1/4-law radial profile. The analysis of the color distributions reveals only marginal evidence of the presence of color bimodality, which is normally observed in galaxies of similar luminosity. The GC luminosity function does not show the typical symmetry, mainly because of the lack of bright GCs. Part of the bright GCs missing might be at very large galactocentric distances or along the line of sight of the galaxy dusty disk. Conclusions. Using ugriJKs photometry we purged the list of GCs with spectroscopic membership and photometric GC candidates in NGC 253. Our results show that the use of either spectroscopic or photometric data only does not generally ensure a contaminant-free sample and a combination of both spectroscopy and photometry is preferred.

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arXiv2015

Unveiling a Rich System of Faint Dwarf Galaxies in the Next Generation Fornax Survey

We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded $u, g$ and $i$-band image obtained with the DECam wide-field camera mounted on the 4-meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the {\it Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii $0.1\!<\!r_e\!<\!2.8$ kpc and average effective surface brightness values $22.0\!<\!μ_i\!<\!28.0$ mag arcsec$^{-2}$. We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters.~We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of $M_i\!=\!-8.0$\,mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of $>\!75\%$ at luminosities brighter than $M_i\!\simeq\!-15.0$ mag to $0\%$ at luminosities fainter than $M_i\!\simeq\!-10.0$ mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below $\sim\!100$ kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.

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arXiv2015

The first and second data releases of the Kilo-Degree Survey

The Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will image 1500 square degrees in four filters (ugri), and together with its near-infrared counterpart VIKING will produce deep photometry in nine bands. Designed for weak lensing shape and photometric redshift measurements, the core science driver of the survey is mapping the large-scale matter distribution in the Universe back to a redshift of ~0.5. Secondary science cases are manifold, covering topics such as galaxy evolution, Milky Way structure, and the detection of high-redshift clusters and quasars. KiDS is an ESO Public Survey and dedicated to serving the astronomical community with high-quality data products derived from the survey data, as well as with calibration data. Public data releases will be made on a yearly basis, the first two of which are presented here. For a total of 148 survey tiles (~160 sq.deg.) astrometrically and photometrically calibrated, coadded ugri images have been released, accompanied by weight maps, masks, source lists, and a multi-band source catalog. A dedicated pipeline and data management system based on the Astro-WISE software system, combined with newly developed masking and source classification software, is used for the data production of the data products described here. The achieved data quality and early science projects based on the data products in the first two data releases are reviewed in order to validate the survey data. Early scientific results include the detection of nine high-z QSOs, fifteen candidate strong gravitational lenses, high-quality photometric redshifts and galaxy structural parameters for hundreds of thousands of galaxies. (Abridged)

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arXiv2015

Machine Learning based photometric redshifts for the KiDS ESO DR2 galaxies

We estimated photometric redshifts (zphot) for more than 1.1 million galaxies of the ESO Public Kilo-Degree Survey (KiDS) Data Release 2. KiDS is an optical wide-field imaging survey carried out with the VLT Survey Telescope (VST) and the OmegaCAM camera, which aims at tackling open questions in cosmology and galaxy evolution, such as the origin of dark energy and the channel of galaxy mass growth. We present a catalogue of photometric redshifts obtained using the Multi Layer Perceptron with Quasi Newton Algorithm (MLPQNA) model, provided within the framework of the DAta Mining and Exploration Web Application REsource (DAMEWARE). These photometric redshifts are based on a spectroscopic knowledge base which was obtained by merging spectroscopic datasets from GAMA (Galaxy And Mass Assembly) data release 2 and SDSS-III data release 9. The overall 1 sigma uncertainty on Delta z = (zspec - zphot) / (1+ zspec) is ~ 0.03, with a very small average bias of ~ 0.001, a NMAD of ~ 0.02 and a fraction of catastrophic outliers (| Delta z | > 0.15) of ~0.4%.

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arXiv2015

VEGAS: A VST Early-type GAlaxy Survey. I. Presentation, wide-field surface photometry, and substructures in NGC 4472

We present the VST Early-type GAlaxy Survey (VEGAS), which is designed to obtain deep multiband photometry in g, r, i, of about one hundred nearby galaxies down to 27.3, 26.8, and 26 mag/arcsec^2 respectively, using the ESO facility VST/OmegaCAM. The goals of the survey are 1) to map the light distribution up to ten effective radii, r_e, 2) to trace color gradients and surface brightness fluctuation gradients out to a few r_e for stellar population characterization, and 3) to obtain a full census of the satellite systems (globular clusters and dwarf galaxies) out to 20% of the galaxy virial radius. The external regions of galaxies retain signatures of the formation and evolution mechanisms that shaped them, and the study of nearby objects enables a detailed analysis of their morphology and interaction features. To clarify the complex variety of formation mechanisms of early-type galaxies (ETGs), wide and deep photometry is the primary observational step, which at the moment has been pursued with only a few dedicated programs. The VEGAS survey has been designated to provide these data for a volume-limited sample with exceptional image quality. In this commissioning photometric paper we illustrate the capabilities of the survey using g- and i-band VST/OmegaCAM images of the nearby galaxy NGC 4472 and of smaller ETGs in the surrounding field. Our surface brightness profiles reach rather faint levels and agree excellently well with previous literature. Genuine new results concern the detection of an intracluster light tail in NGC 4472 and of various substructures at increasing scales. We have also produced extended (g-i) color profiles. The VST/OmegaCAM data that we acquire in the context of the VEGAS survey provide a detailed view of substructures in the optical emission from extended galaxies, which can be as faint as a hundred times below the sky level.

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arXiv2014

VEGAS-SSS. A VST survey of elliptical galaxies in the southern hemisphere: analysis of small stellar systems. Testing the methodology on the globular cluster system in NGC3115

We present a study of globular clusters (GCs) and other small stellar systems (SSSs) in the field of NGC3115, observed as part of the VEGAS imaging survey, carried out with the VST telescope. We use deep g and i data of NGC3115, a well-studied lenticular galaxy with excellent scientific literature. This is fundamental to test the methodologies, verify the results, and probe the capabilities of the VEGAS-SSS. Leveraging the large field of view of the VST allow us to accurately study of the distribution and properties of SSSs as a function of galactocentric distance Rgc, well beyond ~20 galaxy effective radii, in a way not often possible. Our analysis of colors, magnitudes and sizes of SSS candidates confirms the results from existing studies, some of which carried out with 8-10m class telescopes, and further extends them to unreached Rgc distances, with similar accuracy. We find a color bimodality for the GC population and a r1/4 profile for the surface density of GCs as for the galaxy light profile. The radial color gradient of blue and red GCs previously found, for instance by the SLUGGS survey, is further extended out to the largest Rgc inspected, ~65 kpc. The surface density profiles of blue and red GCs taken separately are well approximated by a r1/4 density profile, with the fraction of blue GCs being slightly larger at larger Rgc. We do not find hints of a trend for the red GC and for the GC turnover magnitude to vary with radius, but we observe a ~0.2 mag difference in the turnover magnitude of the blue and red GCs subpopulations. Inspecting SSS sizes and colors we obtained a list of UCDs and GC candidates suitable for future spectroscopic follow-up. In conclusion, our study shows the reliability of the methodologies developed to study SSSs in the field of bright early-type galaxies, and the great potential of the VEGAS survey to produce original results on SSSs science.

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arXiv2007

Surface Brightness Fluctuations from archival ACS images: a stellar population and distance study

We derive Surface Brightness Fluctuations (SBF) and integrated magnitudes in the V- and I-bands using Advanced Camera for Surveys (ACS) archival data. The sample includes 14 galaxies covering a wide range of physical properties: morphology, total absolute magnitude, integrated color. We take advantage of the latter characteristic of the sample to check existing empirical calibrations of absolute SBF magnitudes both in the I- and V-passbands. Additionally, by comparing our SBF and color data with the Teramo-SPoT simple stellar population models, and other recent sets of population synthesis models, we discuss the feasibility of stellar population studies based on fluctuation magnitudes analysis. The main result of this study is that multiband optical SBF data and integrated colors can be used to significantly constrain the chemical composition of the dominant stellar system in the galaxy, but not the age in the case of systems older than 3 Gyr. SBF color gradients are also detected and analyzed. These SBF gradient data, together with other available data, point to the existence of mass dependent metallicity gradients in galaxies, with the more massive objects showing a non--negligible SBF versus color gradient. The comparison with models suggests that such gradients imply more metal rich stellar populations in the galaxies' inner regions with respect to the outer ones.

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arXiv2007

Detection of Surface Brightness Fluctuations in Elliptical Galaxies imaged with the Advanced Camera for Surveys. B- and I-band measurements

Taking advantage of the exceptional capabilities of ACS on board of HST, we derive Surface Brightness Fluctuation (SBF) measurements in the B and I bands from images of six elliptical galaxies with $1500 \leq cz \leq 3500$. Given the low S/N ratio of the SBF signal in the blue band images, the reliability of the measurements is verified both with numerical simulations and experimental data tests. This paper presents the first published B- and I-band SBF measurements for distant ($\geq$ 20 Mpc) galaxies, essential for the comparisons of the models to observations of normal ellipticals. By comparing I-band data with our new Simple Stellar Population (SSP) models we find an excellent agreement and we confirm that I-band SBF magnitudes are mainly sensitive to the metallicity of the dominant stellar component in the galaxy, and are not strongly affected by the contribution of possible secondary stellar components. As a consequence I-band fluctuations magnitudes are ideal for distance studies. On the other hand, we show that standard SSP models do not reproduce the B-band SBF magnitudes of red ($(B-I)_0 \gsim 2.1$) galaxies in our sample. We explore the capability of two non--canonical models in properly reproducing the high sensitivity of B SBF to the presence of even small fractions of bright, hot stars (metal poor stars, hot evolved stars, etc.). The disagreement is solved both by taking into account hot (Post--AGB) stars in SSP models and/or by adopting Composite Stellar Population models. Finally, we suggest a limit value of the S/N for the B-band SBF signal required to carry out a detailed study of stellar population properties based on this technique.

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arXiv2007

Astro-WISE: Chaining to the Universe

The recent explosion of recorded digital data and its processed derivatives threatens to overwhelm researchers when analysing their experimental data or when looking up data items in archives and file systems. While current hardware developments allow to acquire, process and store 100s of terabytes of data at the cost of a modern sports car, the software systems to handle these data are lagging behind. This general problem is recognized and addressed by various scientific communities, e.g., DATAGRID/EGEE federates compute and storage power over the high-energy physical community, while the astronomical community is building an Internet geared Virtual Observatory, connecting archival data. These large projects either focus on a specific distribution aspect or aim to connect many sub-communities and have a relatively long trajectory for setting standards and a common layer. Here, we report "first light" of a very different solution to the problem initiated by a smaller astronomical IT community. It provides the abstract "scientific information layer" which integrates distributed scientific analysis with distributed processing and federated archiving and publishing. By designing new abstractions and mixing in old ones, a Science Information System with fully scalable cornerstones has been achieved, transforming data systems into knowledge systems. This break-through is facilitated by the full end-to-end linking of all dependent data items, which allows full backward chaining from the observer/researcher to the experiment. Key is the notion that information is intrinsic in nature and thus is the data acquired by a scientific experiment. The new abstraction is that software systems guide the user to that intrinsic information by forcing full backward and forward chaining in the data modelling.

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arXiv2005

Detection of Radial Surface Brightness Fluctuation and Color Gradients in elliptical galaxies with ACS

We study surface brightness fluctuations (SBF) in a sample of 8 elliptical galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when available -- are presented. Galaxy surface brightness profiles are determined as well. We present the first SBF--broadband color calibration for the ACS/WFC F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies. We detect and study in detail the SBF variations within individual galaxies as a probe of possible changes in the underlying stellar populations. Inspecting both the SBF and color gradients in comparison to model predictions, we argue that SBF, and SBF-gradients, can in principle be used for unraveling the different evolutionary paths taken by galaxies, though a more comprehensive study of this issue would be required. We confirm that the radial variation of galaxy stellar population properties should be mainly connected to the presence of radial chemical abundance gradients, with the outer galaxy regions being more metal poor than the inner ones.

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arXiv2003

Polar Ring Galaxies and the Tully-Fisher relation

We have investigated the Tully-Fisher relation for Polar Ring Galaxies (PRGs), based on near infrared, optical and HI data available for a sample of these peculiar objects. Many PRGs show larger HI line-widths than expected for the observed K band luminosity, and this result is confirmed by a larger sample of objects, based on B-band data. This observational evidence may be related to the dark halo shape and orientation in these systems: the larger rotation velocities observed in PRGs can be explained by a flattened polar halo, aligned with the polar ring.

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arXiv2003

A Dearth of Dark Matter in Ordinary Elliptical Galaxies

The kinematics of the outer parts of three intermediate-luminosity elliptical galaxies have been studied using the Planetary Nebula Spectrograph. The galaxies' velocity dispersion profiles are found to decline with radius; dynamical modeling of the data indicates the presence of little if any dark matter in these galaxies' halos. This surprising result conflicts with findings in other galaxy types, and poses a challenge to current galaxy formation theories.

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arXiv2003

Narrow band survey for intragroup light in the Leo HI cloud. Constraints on the galaxy background contamination in imaging surveys for intracluster planetary nebulae

We have observed emission line objects located in a 0.26 deg^2 field in the M96 (Leo) group, coincident with the intergalactic HI cloud. The emission line objects were selected using the same procedure as used for the search for intracluster planetary nebulae in the Virgo cluster, and their m_5007 luminosity function has a bright cut-off ~1.2 magnitude fainter than for the PNLF associated with the elliptical galaxies in the M96 group.Therefore the vast majority of these emission line objects are compatible with not being intragroup planetary nebulae at the Leo group distance of 10 Mpc. Spectroscopic follow-up of two emission line objects in this Leo field showed that indeed these do not have the [OIII] doublet expected for a real PN. The brighter source is identified as a starburst object at redshift z = 3.128, because of a second emission in the near infrared, identified as FeII (λ2220 AA). From these data we derive three main results: (i) from the absence of PN we can determine a more stringent upper limit to the surface brightness in any old stellar population associated with the Leo HI cloud. (ii) This translates to an upper limit of 1.6% for the fraction of luminosity in a diffuse intragroup component in the densest 3 x 2 deg area of the Leo group,relative to the light in galaxies. (iii) Using this Leo field as a blank field, we derive an average fraction of 13.6% background emission line objects that enter in surveys of Virgo intracluster PN. The small fraction confirms the validity of the selection criteria for intracluster PN candidates in Virgo.

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arXiv2001

Planetary nebulae as mass tracers of their parent galaxies: biases in the estimate of the kinematical quantities

Multi-object and multi-fiber spectrographs on 4 and 8 meter telescopes make it possible to use extragalactic planetary nebulae (PNe) in the outer halos of early-type galaxies as kinematical tracers, where classical techniques based on integrated stellar light fail. Until now, published PNe radial velocity samples are small, with only a few tens of radial velocity measurements (except for a few cases like NGC 5128 or M31), causing uncertainties in the mass and angular momentum estimates based on these data. To quantify these uncertainties, we have made equilibrium models for spherical galaxies, with and without dark matter, and via Montecarlo simulations we produce radial velocity samples with different sizes. We then apply, to these discrete radial velocity fields, the same standard kinematical analysis as it is commonly done with small samples of observed PNe radial velocities. By comparison of the inferred quantities with those computed from the analytical model, we test for systematic biases and establish a robust procedure to infer the angular momentum distribution and radial velocity dispersion profiles from such samples.

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arXiv1997

On the Cepheid variables of nearby galaxies III. NGC 3109

We extended to the R and I bands the light curve coverage for 8 Cepheids already studied in B and V by Capaccioli et al [AJ, 103, 1151 (1992)]. Sixteen additional Cepheid candidates have been identified and preliminary periods are proposed. The new Cepheids allow the period-luminosity relation to be extended one magnitude fainter. Apparent B, V, R, and I distance moduli have been calculated. Combining the data at different wavelengths, and assuming a true distance modulus of 18.50 mag for the LMC, we obtain for NGC 3109 a true distance modulus $(m-M)_0=25.67\pm0.16$, corresponding to $1.36\pm0.10$ Mpc. Adopting $E(B-V)=0.08$ for the LMC, the interstellar reddening for the Cepheids in NGC 3109 is consistent with 0. A discussion on the possible implications of this result is presented. A comparison of the period-color, period-amplitude, and period-luminosity relations suggests similar properties for the Cepheids in the LMC, NGC 3109, Sextans A, Sextans B, and IC 1613, though the uncertainties in the main parameter determination are still unsatisfactorily high for a firm conclusion on the universality of the period-luminosity relation.

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arXiv1993

High resolution kinematics of galactic globular clusters. II. On the significance of velocity dispersion measurements

Small number statistics may heavily affect the structure of the broadening function in integrated spectra of galactic globular cluster centers. As a consequence, it is a priori unknown how closely line broadening measure- ments gauge the intrinsic velocity dispersions at the cores of these stel- lar systems. We have tackled this general problem by means of Monte Carlo simulations. An examination of the mode and the frequency distribution of the measured values of the simulations indicates that the low value measured for the velocity dispersion of M30 (Zaggia etal 1992) is likely a reliable estimate of the velocity dispersion at the center of this cluster. The same methodology applied to the case of M15 suggests that the steep inward rise of the velocity dispersion found by Peterson, Seitzer and Cudworth (1989) is real, although less pronounced. Large-aperture observa- tions are less sensitive to statistical fluctuations, but are unable to detect strong variations in the dispersion wich occur within the aperture itself.

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arXiv1992

The ($\log R_e$, $μ_e$) Plane of Hot Stellar Systems

Two families of hot stellar systems, named {\it `ordinary'\/} and {\it 'bright'\/}, are identified in the ($\log R_e, μ_e$) plane built with a luminosity--limited sample of ellipticals and bulges of S0s and spirals of the Virgo and Fornax clusters. This finding, based on {\it ad hoc\/} new observations, is confirmed by a much larger set of literature data for $\sim1500$ galaxies. The {\it `ordinary'\/} family is biparametric: $L_T\propto I_e\,R_e^2$; its members are fainter that $M_B\simeq-19.3$ and smaller than $\re\simeq3$ kpc (whatever $M_B$ is). The {\it 'bright'\/} family is uniparametric ($μ_e$ depends on $R_e$ alone) and hosts brightest cluster members and QSO parent galaxies. We show that the segregation in the ($\log R_e, μ_e$) plane has an important counterpart in the behavior of various physical parameters, which is markedly different for galaxies smaller ({\it `ordinary'\/} family) and larger ({\it 'bright'\/} family) than $R_e=3$ kpc.

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