Nicola Rosario Napolitano | Sun Yat-Sen University (original) (raw)

Papers by Nicola Rosario Napolitano

Astronomy & Astrophysics

The multi-band photometry of the VOICE imaging data, overlapping with 4.9 deg2 of the Chandra Dee... more The multi-band photometry of the VOICE imaging data, overlapping with 4.9 deg2 of the Chandra Deep Field South (CDFS) area, enables both shape measurement and photometric redshift estimation to be the two essential quantities for weak lensing analysis. The depth of magAB is up to 26.1 (5σ limiting) in r-band. We estimate the excess surface density (ESD; ΔΣ) based on galaxy–galaxy measurements around galaxies at lower redshift (0.10 < zl < 0.35) while we select the background sources as those at higher redshift ranging from 0.3 to 1.5. The foreground galaxies are divided into two major categories according to their colour (blue and red), each of which has been further divided into high- and low-stellar-mass bins. The halo masses of the samples are then estimated by modelling the signals, and the posterior of the parameters are sampled using a Monte Carlo Markov chain process. We compare our results with the existing stellar-to-halo mass relation (SHMR) and find that the blue lo...

Monthly Notices of the Royal Astronomical Society

Next-generation surveys will provide photometric and spectroscopic data of millions to billions o... more Next-generation surveys will provide photometric and spectroscopic data of millions to billions of galaxies with unprecedented precision. This offers a unique chance to improve our understanding of the galaxy evolution and the unresolved nature of dark matter (DM). At galaxy scales, the density distribution of DM is strongly affected by feedback processes, which are difficult to fully account for in classical techniques to derive galaxy masses. We explore the capability of supervised machine learning (ML) algorithms to predict the DM content of galaxies from ‘luminous’ observational-like parameters, using the TNG100 simulation. In particular, we use photometric (magnitudes in different bands), structural (the stellar half-mass radius and three different baryonic masses), and kinematic (1D velocity dispersion and the maximum rotation velocity) parameters to predict the total DM mass, DM half-mass radius, and DM mass inside one and two stellar half-mass radii. We adopt the coefficient...

Monthly Notices of the Royal Astronomical Society

The star formation history (SFH) of galaxies is critical for understanding galaxy evolution. Hydr... more The star formation history (SFH) of galaxies is critical for understanding galaxy evolution. Hydrodynamical simulations enable us to precisely reconstruct the SFH of galaxies and establish a link to the underlying physical processes. In this work, we present a model to describe individual galaxies’ SFHs from three simulations: TheThreeHundred, Illustris-1, and TNG100-1. This model divides the galaxy SFH into two distinct components: the ‘main sequence’ and the ‘variation’. The ‘main sequence’ part is generated by tracing the history of the SFR − M* main sequence of galaxies across time. The ‘variation’ part consists of the scatter around the main sequence, which is reproduced by fractional Brownian motions. We find that: (1) the evolution of the main sequence varies between simulations; (2) fractional Brownian motions can reproduce many features of SFHs; however, discrepancies still exist; and (3) the variations and mass-loss rate are crucial for reconstructing the SFHs of the simul...

The Astrophysical Journal

Next-generation large sky surveys will observe up to billions of galaxies for which basic structu... more Next-generation large sky surveys will observe up to billions of galaxies for which basic structural parameters are needed to study their evolution. This is a challenging task that, for ground-based observations, is complicated by seeing-limited point-spread functions (PSFs). To perform a fast and accurate analysis of galaxy surface brightness, we have developed a family of supervised convolutional neural networks (CNNs) to derive Sérsic profile parameters of galaxies. This work presents the first two Galaxy Light profile CNNs (GaLNets) of this family. The first one is trained using galaxy images only (GaLNet-1), and the second is trained with both galaxy images and the local PSF (GaLNet-2). We have compared the results from GaLNets with structural parameters (total magnitude, effective radius, Sérsic index, etc.) derived from a set of galaxies from the Kilo-Degree Survey by 2DPHOT as a representative of the “standard” PSF-convolved Sérsic fitting tools. The comparison shows that Ga...

Research in Astronomy and Astrophysics

With the advent of new spectroscopic surveys from ground and space, observing up to hundreds of m... more With the advent of new spectroscopic surveys from ground and space, observing up to hundreds of millions of galaxies, spectra classification will become overwhelming for standard analysis techniques. To prepare for this challenge, we introduce a family of deep learning tools to classify features in one-dimensional spectra. As the first application of these Galaxy Spectra neural Networks (GaSNets), we focus on tools specialized in identifying emission lines from strongly lensed star-forming galaxies in the eBOSS spectra. We first discuss the training and testing of these networks and define a threshold probability, P L , of 95% for the high-quality event detection. Then, using a previous set of spectroscopically selected strong lenses from eBOSS, confirmed with the Hubble Space Telescope (HST), we estimate a completeness of ∼80% as the fraction of lenses recovered above the adopted P L . We finally apply the GaSNets to ∼1.3M eBOSS spectra to collect the first list of ∼430 new high-qu...

arXiv (Cornell University), Dec 1, 2007

N-body + hydrodynamical simulations of formation and evolution of galaxy groups in a ΛCDM cosmolo... more N-body + hydrodynamical simulations of formation and evolution of galaxy groups in a ΛCDM cosmology have been performed. The properties of the galaxy populations in 12 groups are here discussed, with focus on the colour-magnitude relation in both normal and fossil groups.

The Astrophysical Journal, 2021

We present 97 new high-quality strong lensing candidates found in the final ∼350 deg2 that comple... more We present 97 new high-quality strong lensing candidates found in the final ∼350 deg2 that complete the full ∼1350 deg2 area of the Kilo-Degree Survey (KiDS). Together with our previous findings, the final list of high-quality candidates from KiDS sums up to 268 systems. The new sample is assembled using a new convolutional neural network (CNN) classifier applied to r-band (best-seeing) and g, r, and i color-composited images separately. This optimizes the complementarity of the morphology and color information on the identification of strong lensing candidates. We apply the new classifiers to a sample of luminous red galaxies (LRGs) and a sample of bright galaxies (BGs) and select candidates that received a high probability to be a lens from the CNN (P CNN). In particular, setting P CNN > 0.8 for the LRGs, the one-band CNN predicts 1213 candidates, while the three-band classifier yields 1299 candidates, with only ∼30% overlap. For the BGs, in order to minimize the false positive...

The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with... more The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will scan 1,500 deg2 in four optical filters (u, g, r, i). Designed to be a weak lensing survey, it is ideal for galaxy evolution studies, thanks to the high spatial resolution of VST, the excellent seeing and the photometric depth. The surface photometry has provided with structural parameters (e.g. size and Sersic index), aperture and total magnitudes have been used to obtain photometric redshifts from Machine Learning methods and stellar masses/luminositites from stellar population synthesis. Our project aimed at investigating the evolution of the colour and structural properties of galaxies with mass and environment up to redshift \(z \sim 0.5\) and more, to put constraints on galaxy evolution processes, as galaxy mergers.

The Astrophysical Journal, 2020

We report new high-quality galaxy scale strong lens candidates found in the Kilo Degree Survey da... more We report new high-quality galaxy scale strong lens candidates found in the Kilo Degree Survey data release 4 using Machine Learning. We have developed a new Convolutional Neural Network (CNN) classifier to search for gravitational arcs, following the prescription by Petrillo et al. (2019a) and using only r−band images. We have applied the CNN to two "predictive samples": a Luminous red galaxy (LRG) and a "bright galaxy" (BG) sample (r < 21). We have found 286 new high probability candidates, 133 from the LRG sample and 153 from the BG sample. We have then ranked these candidates based on a value that combines the CNN likelihood to be a lens and the human score resulting from visual inspection (P-value) and we present here the highest 82 ranked candidates with P-values ≥ 0.5. All these high-quality candidates have obvious arc or point-like features around the central red defector. Moreover, we define the best 26 objects, all with scores P-values ≥ 0.7 as a "golden sample" of candidates. This sample is expected to contain very few false positives and thus it is suitable for follow-up observations. The new lens candidates come partially from the the more extended footprint adopted here with respect to the previous analyses, partially from a larger predictive sample (also including the BG sample). These results show that machine learning tools are very promising to find strong lenses in large surveys and more candidates that can be found by enlarging the predictive samples beyond the standard assumption of LRGs. In the future, we plan to apply our CNN to the data from next-generation surveys such as the Large Synoptic Survey Telescope, Euclid, and the Chinese Space Station Optical Survey.

Symposium - International Astronomical Union, 2003

Planetary nebulae observed in our Milky Way galaxy and in the galaxies of the Local Group do impr... more Planetary nebulae observed in our Milky Way galaxy and in the galaxies of the Local Group do impress us for their morphologies and complexities. But when we look at planetary nebulae outside the Local Group, all this must be forgotten, as they become unresolved and merely points of green light. This paper will review how these green spots of light can be used as probes of the mass distribution and dynamics of elliptical galaxies and nearby clusters.

Symposium - International Astronomical Union, 2004

We have found a correlation between the M / L global gradients and the structural parameters of t... more We have found a correlation between the M / L global gradients and the structural parameters of the luminous components of a sample of 19 early-type galaxies. Such a correlation supports the hypothesis that there is a connection between the dark matter content and the evolution of the baryonic component in such systems.

EAS Publications Series, 2006

We use the mass-to-light gradients in early-type galaxies to infer the global dark matter fractio... more We use the mass-to-light gradients in early-type galaxies to infer the global dark matter fraction, f d =M d /M * , for these systems. We discuss implications about the total star formation efficiency in dark-matter halos and show that the trend of f d with mass produces virial mass-to-light ratios which are consistent with semianalitical models. Preliminary kurtosis analysis of the quasi-constant M/L galaxies in Romanowsky et al. seems at odd with Dekel et al. simulations.

Monthly Notices of the Royal Astronomical Society, 2015

We have estimated photometric redshifts (z phot) for more than 1.1 million galaxies of the public... more We have estimated photometric redshifts (z phot) for more than 1.1 million galaxies of the public European Southern Observatory (ESO) Kilo-Degree Survey (KiDS) data release 2. KiDS is an optical wide-field imaging survey carried out with the Very Large Telescope (VLT) Survey Telescope (VST) and the OmegaCAM camera, which aims to tackle 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 that was obtained by merging spectroscopic data sets from the Galaxy and Mass Assembly (GAMA) data release 2 and the Sloan Digital Sky Survey III (SDSS-III) data release 9. The overall 1σ uncertainty on z = (z spec − z phot)/(1 + z spec) is ∼0.03, with a very small average bias of ∼0.001, a normalized median absolute deviation of ∼0.02 and a fraction of catastrophic outliers (| z| > 0.15) of ∼0.4 per cent.

Astronomy & Astrophysics, 2015

We present the first deep photometry of what may be a good candidate for a forming polar-ring gal... more We present the first deep photometry of what may be a good candidate for a forming polar-ring galaxy at redshift z 0.05. The object FCSS J033710.0-354727 is a background galaxy in the VST Deep Field of the Fornax cluster. The deep exposures combined with the high angular resolution of the OmegaCam at VST allowed us to carry out the first detailed photometric analysis for this system in the g and i bands to derive the galaxy structure and colors. Results show that the central object resembles a disk galaxy, surrounded by a ring-like structure that is twice as extended as the central disk. The warped geometry and bright knots observed along the polar direction, as well as some debris detected on the NW side with colors similar to those of the galaxy, suggest that the polar structure is still forming. We argue that the wide polar ring or disk is the result of the ongoing disruption of a companion galaxy in the potential well of the central object, which is two to three times more massive than the accreting galaxy.

Monthly Notices of the Royal Astronomical Society, 2014

STEP (the SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy) is a Guarante... more STEP (the SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy) is a Guaranteed Time Observation survey being performed at the VST (the ESO VLT Survey Telescope). STEP will image an area of 74 deg 2 covering the main body of the Small Magellanic Cloud (32 deg 2), the Bridge that connects it to the Large Magellanic Cloud (30 deg 2) and a small part of the Magellanic Stream (2 deg 2). Our g, r, i, Hα photometry is able to resolve individual stars down to magnitudes well below the main-sequence turn-off of the oldest populations. In this first paper, we describe the observing strategy, the photometric techniques and the upcoming data products of the survey. We also present preliminary results for the first two fields for which data acquisition is completed, including some detailed analysis of the two stellar clusters IC 1624 and NGC 419.

ESO ASTROPHYSICS SYMPOSIA European Southern Observatory

Using the Planetary Nebula Spectrograph, we have observed and measured the velocities for 2764 PN... more Using the Planetary Nebula Spectrograph, we have observed and measured the velocities for 2764 PNe in the disk and halo of the Andromeda galaxy. Preliminary analysis using a basic ring model shows a rotation curve in good agreement with that obtained from Hi data out to ∼ 20 kpc. Some substructure has also been detected within the velocity field, which can be modeled as the continuation of the tidal-remnant known as the Southern Stream, as it passes through Andromeda's disk.

Monthly Notices of the Royal Astronomical Society, 2014

We present an overview of a multiwavelength survey of the Shapley Supercluster (SSC; z ∼ 0.05) co... more We present an overview of a multiwavelength survey of the Shapley Supercluster (SSC; z ∼ 0.05) covering a contiguous area of 260 h −2 70 Mpc 2 including the supercluster core. The project main aim is to quantify the influence of cluster-scale mass assembly on galaxy evolution in one of the most massive structures in the local Universe. The Shapley Supercluster Survey (ShaSS) includes nine Abell clusters (A3552, A3554, A3556, A3558, A3559, A3560, A3562, AS0724, AS0726) and two poor clusters (SC1327−312, SC1329−313) showing evidence of cluster-cluster interactions. Optical (ugri) and near-infrared (K) imaging acquired with VLT Survey Telescope and Visible and Infrared Survey Telescope for Astronomy allow us to study the galaxy population down to m + 6 at the supercluster redshift. A dedicated spectroscopic survey with AAOmega on the Anglo-Australian Telescope provides a magnitude-limited sample of supercluster members with 80 per cent completeness at ∼m + 3. We derive the galaxy density across the whole area, demonstrating that all structures within this area are embedded in a single network of clusters, groups and filaments. The stellar mass density in the core of the SSC is always higher than 9 × 10 9 M Mpc −3 , which is ∼40× the cosmic stellar mass density for galaxies in the local Universe. We find a new filamentary structure (∼7 Mpc long in projection) connecting the SSC core to the cluster A3559, as well as previously unidentified density peaks. We perform a weak-lensing analysis of the central 1 deg 2 field of the survey obtaining for the central cluster A3558 a mass of M 500 = 7.63 +3.88 −3.40 × 10 14 M , in agreement with X-ray based estimates.

Astronomy & Astrophysics, 2015

We present a study of globular clusters (GCs) and other small stellar systems (SSSs) in the field... more We present a study of globular clusters (GCs) and other small stellar systems (SSSs) in the field of NGC 3115, observed as part of the ongoing wide-field imaging survey VEGAS, carried out with the 2.6 m VST telescope. We used deep g and i observations of NGC 3115, a well-studied lenticular galaxy that is covered excellently well in the 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 allowed us to accurately study the distribution and properties of SSSs as a function of galactocentric distance, well beyond ∼20 galaxy effective radii, in a way that is rarely possible. Our analysis of colors, magnitudes, and sizes of SSS candidates confirms the results from existing studies, some of which were carried out with 8-10 m class telescopes, and further extends them to previously unreached galactocentric distances with similar accuracy. In particular, we find a color bimodality for the GC population and a de Vaucouleurs r 1/4 profile for the surface density of GCs similar to the galaxy light profile. The radial color gradient of blue and red GCs previously found, for instance, by the SLUGGS survey with Subaru and Keck data, is further extended out to the largest galactocentric radii inspected, ∼65 kpc. In addition, the surface density profiles of blue and red GCs taken separately are well approximated by a r 1/4 density profile, with the fraction of blue GCs being slightly larger at larger radii. We do not find hints of a trend for the red GC subpopulation 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 GC subpopulations. Finally, from inspecting SSS sizes and colors, we obtain a list of ultracompact dwarf galaxies and GC candidates suitable for future spectroscopic follow-up. In conclusion, our study shows i) the reliability of the methodologies developed to study SSSs in the field of bright early-type galaxies; and ii) the great potential of the VEGAS survey to produce original results on SSSs science, mainly thanks to the wide-field imaging adopted.

The Astrophysical Journal, 2013

We present results from SPH-cosmological simulations, including self-consistent modeling of super... more We present results from SPH-cosmological simulations, including self-consistent modeling of supernova feedback and chemical evolution, of galaxies belonging to two clusters and 12 groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming (SF) activity, as parameterized by their specific star formation rate (sSFR), across a redshift range up to z = 2. The overall ZM relation for the composite population evolves according to a redshift-dependent quadratic functional form that is consistent with other empirical estimates, provided that the highest mass bin of the brightest central galaxies is excluded. Its slope shows irrelevant evolution in the passive sample, being steeper in groups than in clusters. However, the subsample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. The scatter of the passive sample is dominated by low-mass galaxies at all redshifts and keeps constant over cosmic times. The mean metallicity is highest in cluster cores and lowest in normal groups, following the same environmental sequence as that previously found in the red sequence building. The ZM relation for the SF sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The SF galaxies make up a tight sequence in the SFR-M * plane at high redshift, whose scatter increases with time alongside the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the SF galaxies, while on the contrary more active galaxies in terms of simple SFR are also metal-richer. Finally, the [O/Fe] abundance ratio is presented too: we report a strong increasing evolution with redshift at given mass, especially at z 1. The expected increasing trend with mass is recovered when only considering the more massive galaxies. We discuss these results in terms of the mechanisms driving the evolution within the high-and low-mass regimes at different epochs: mergers, feedback-driven outflows, and the intrinsic variation of the star formation efficiency.

The Astrophysical Journal, 2003

We use a high resolution collisionless simulation of a Virgo-like cluster in a ΛCDM cosmology to ... more We use a high resolution collisionless simulation of a Virgo-like cluster in a ΛCDM cosmology to determine the velocity and clustering properties of the diffuse stellar component in the intracluster region at the present epoch. The simulated cluster builds up hierarchically and tidal interactions between member galaxies and the cluster potential produce a diffuse stellar component free-flying

Astronomy & Astrophysics

The multi-band photometry of the VOICE imaging data, overlapping with 4.9 deg2 of the Chandra Dee... more The multi-band photometry of the VOICE imaging data, overlapping with 4.9 deg2 of the Chandra Deep Field South (CDFS) area, enables both shape measurement and photometric redshift estimation to be the two essential quantities for weak lensing analysis. The depth of magAB is up to 26.1 (5σ limiting) in r-band. We estimate the excess surface density (ESD; ΔΣ) based on galaxy–galaxy measurements around galaxies at lower redshift (0.10 < zl < 0.35) while we select the background sources as those at higher redshift ranging from 0.3 to 1.5. The foreground galaxies are divided into two major categories according to their colour (blue and red), each of which has been further divided into high- and low-stellar-mass bins. The halo masses of the samples are then estimated by modelling the signals, and the posterior of the parameters are sampled using a Monte Carlo Markov chain process. We compare our results with the existing stellar-to-halo mass relation (SHMR) and find that the blue lo...

Monthly Notices of the Royal Astronomical Society

Next-generation surveys will provide photometric and spectroscopic data of millions to billions o... more Next-generation surveys will provide photometric and spectroscopic data of millions to billions of galaxies with unprecedented precision. This offers a unique chance to improve our understanding of the galaxy evolution and the unresolved nature of dark matter (DM). At galaxy scales, the density distribution of DM is strongly affected by feedback processes, which are difficult to fully account for in classical techniques to derive galaxy masses. We explore the capability of supervised machine learning (ML) algorithms to predict the DM content of galaxies from ‘luminous’ observational-like parameters, using the TNG100 simulation. In particular, we use photometric (magnitudes in different bands), structural (the stellar half-mass radius and three different baryonic masses), and kinematic (1D velocity dispersion and the maximum rotation velocity) parameters to predict the total DM mass, DM half-mass radius, and DM mass inside one and two stellar half-mass radii. We adopt the coefficient...

Monthly Notices of the Royal Astronomical Society

The star formation history (SFH) of galaxies is critical for understanding galaxy evolution. Hydr... more The star formation history (SFH) of galaxies is critical for understanding galaxy evolution. Hydrodynamical simulations enable us to precisely reconstruct the SFH of galaxies and establish a link to the underlying physical processes. In this work, we present a model to describe individual galaxies’ SFHs from three simulations: TheThreeHundred, Illustris-1, and TNG100-1. This model divides the galaxy SFH into two distinct components: the ‘main sequence’ and the ‘variation’. The ‘main sequence’ part is generated by tracing the history of the SFR − M* main sequence of galaxies across time. The ‘variation’ part consists of the scatter around the main sequence, which is reproduced by fractional Brownian motions. We find that: (1) the evolution of the main sequence varies between simulations; (2) fractional Brownian motions can reproduce many features of SFHs; however, discrepancies still exist; and (3) the variations and mass-loss rate are crucial for reconstructing the SFHs of the simul...

The Astrophysical Journal

Next-generation large sky surveys will observe up to billions of galaxies for which basic structu... more Next-generation large sky surveys will observe up to billions of galaxies for which basic structural parameters are needed to study their evolution. This is a challenging task that, for ground-based observations, is complicated by seeing-limited point-spread functions (PSFs). To perform a fast and accurate analysis of galaxy surface brightness, we have developed a family of supervised convolutional neural networks (CNNs) to derive Sérsic profile parameters of galaxies. This work presents the first two Galaxy Light profile CNNs (GaLNets) of this family. The first one is trained using galaxy images only (GaLNet-1), and the second is trained with both galaxy images and the local PSF (GaLNet-2). We have compared the results from GaLNets with structural parameters (total magnitude, effective radius, Sérsic index, etc.) derived from a set of galaxies from the Kilo-Degree Survey by 2DPHOT as a representative of the “standard” PSF-convolved Sérsic fitting tools. The comparison shows that Ga...

Research in Astronomy and Astrophysics

With the advent of new spectroscopic surveys from ground and space, observing up to hundreds of m... more With the advent of new spectroscopic surveys from ground and space, observing up to hundreds of millions of galaxies, spectra classification will become overwhelming for standard analysis techniques. To prepare for this challenge, we introduce a family of deep learning tools to classify features in one-dimensional spectra. As the first application of these Galaxy Spectra neural Networks (GaSNets), we focus on tools specialized in identifying emission lines from strongly lensed star-forming galaxies in the eBOSS spectra. We first discuss the training and testing of these networks and define a threshold probability, P L , of 95% for the high-quality event detection. Then, using a previous set of spectroscopically selected strong lenses from eBOSS, confirmed with the Hubble Space Telescope (HST), we estimate a completeness of ∼80% as the fraction of lenses recovered above the adopted P L . We finally apply the GaSNets to ∼1.3M eBOSS spectra to collect the first list of ∼430 new high-qu...

arXiv (Cornell University), Dec 1, 2007

N-body + hydrodynamical simulations of formation and evolution of galaxy groups in a ΛCDM cosmolo... more N-body + hydrodynamical simulations of formation and evolution of galaxy groups in a ΛCDM cosmology have been performed. The properties of the galaxy populations in 12 groups are here discussed, with focus on the colour-magnitude relation in both normal and fossil groups.

The Astrophysical Journal, 2021

We present 97 new high-quality strong lensing candidates found in the final ∼350 deg2 that comple... more We present 97 new high-quality strong lensing candidates found in the final ∼350 deg2 that complete the full ∼1350 deg2 area of the Kilo-Degree Survey (KiDS). Together with our previous findings, the final list of high-quality candidates from KiDS sums up to 268 systems. The new sample is assembled using a new convolutional neural network (CNN) classifier applied to r-band (best-seeing) and g, r, and i color-composited images separately. This optimizes the complementarity of the morphology and color information on the identification of strong lensing candidates. We apply the new classifiers to a sample of luminous red galaxies (LRGs) and a sample of bright galaxies (BGs) and select candidates that received a high probability to be a lens from the CNN (P CNN). In particular, setting P CNN > 0.8 for the LRGs, the one-band CNN predicts 1213 candidates, while the three-band classifier yields 1299 candidates, with only ∼30% overlap. For the BGs, in order to minimize the false positive...

The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with... more The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will scan 1,500 deg2 in four optical filters (u, g, r, i). Designed to be a weak lensing survey, it is ideal for galaxy evolution studies, thanks to the high spatial resolution of VST, the excellent seeing and the photometric depth. The surface photometry has provided with structural parameters (e.g. size and Sersic index), aperture and total magnitudes have been used to obtain photometric redshifts from Machine Learning methods and stellar masses/luminositites from stellar population synthesis. Our project aimed at investigating the evolution of the colour and structural properties of galaxies with mass and environment up to redshift \(z \sim 0.5\) and more, to put constraints on galaxy evolution processes, as galaxy mergers.

The Astrophysical Journal, 2020

We report new high-quality galaxy scale strong lens candidates found in the Kilo Degree Survey da... more We report new high-quality galaxy scale strong lens candidates found in the Kilo Degree Survey data release 4 using Machine Learning. We have developed a new Convolutional Neural Network (CNN) classifier to search for gravitational arcs, following the prescription by Petrillo et al. (2019a) and using only r−band images. We have applied the CNN to two "predictive samples": a Luminous red galaxy (LRG) and a "bright galaxy" (BG) sample (r < 21). We have found 286 new high probability candidates, 133 from the LRG sample and 153 from the BG sample. We have then ranked these candidates based on a value that combines the CNN likelihood to be a lens and the human score resulting from visual inspection (P-value) and we present here the highest 82 ranked candidates with P-values ≥ 0.5. All these high-quality candidates have obvious arc or point-like features around the central red defector. Moreover, we define the best 26 objects, all with scores P-values ≥ 0.7 as a "golden sample" of candidates. This sample is expected to contain very few false positives and thus it is suitable for follow-up observations. The new lens candidates come partially from the the more extended footprint adopted here with respect to the previous analyses, partially from a larger predictive sample (also including the BG sample). These results show that machine learning tools are very promising to find strong lenses in large surveys and more candidates that can be found by enlarging the predictive samples beyond the standard assumption of LRGs. In the future, we plan to apply our CNN to the data from next-generation surveys such as the Large Synoptic Survey Telescope, Euclid, and the Chinese Space Station Optical Survey.

Symposium - International Astronomical Union, 2003

Planetary nebulae observed in our Milky Way galaxy and in the galaxies of the Local Group do impr... more Planetary nebulae observed in our Milky Way galaxy and in the galaxies of the Local Group do impress us for their morphologies and complexities. But when we look at planetary nebulae outside the Local Group, all this must be forgotten, as they become unresolved and merely points of green light. This paper will review how these green spots of light can be used as probes of the mass distribution and dynamics of elliptical galaxies and nearby clusters.

Symposium - International Astronomical Union, 2004

We have found a correlation between the M / L global gradients and the structural parameters of t... more We have found a correlation between the M / L global gradients and the structural parameters of the luminous components of a sample of 19 early-type galaxies. Such a correlation supports the hypothesis that there is a connection between the dark matter content and the evolution of the baryonic component in such systems.

EAS Publications Series, 2006

We use the mass-to-light gradients in early-type galaxies to infer the global dark matter fractio... more We use the mass-to-light gradients in early-type galaxies to infer the global dark matter fraction, f d =M d /M * , for these systems. We discuss implications about the total star formation efficiency in dark-matter halos and show that the trend of f d with mass produces virial mass-to-light ratios which are consistent with semianalitical models. Preliminary kurtosis analysis of the quasi-constant M/L galaxies in Romanowsky et al. seems at odd with Dekel et al. simulations.

Monthly Notices of the Royal Astronomical Society, 2015

We have estimated photometric redshifts (z phot) for more than 1.1 million galaxies of the public... more We have estimated photometric redshifts (z phot) for more than 1.1 million galaxies of the public European Southern Observatory (ESO) Kilo-Degree Survey (KiDS) data release 2. KiDS is an optical wide-field imaging survey carried out with the Very Large Telescope (VLT) Survey Telescope (VST) and the OmegaCAM camera, which aims to tackle 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 that was obtained by merging spectroscopic data sets from the Galaxy and Mass Assembly (GAMA) data release 2 and the Sloan Digital Sky Survey III (SDSS-III) data release 9. The overall 1σ uncertainty on z = (z spec − z phot)/(1 + z spec) is ∼0.03, with a very small average bias of ∼0.001, a normalized median absolute deviation of ∼0.02 and a fraction of catastrophic outliers (| z| > 0.15) of ∼0.4 per cent.

Astronomy & Astrophysics, 2015

We present the first deep photometry of what may be a good candidate for a forming polar-ring gal... more We present the first deep photometry of what may be a good candidate for a forming polar-ring galaxy at redshift z 0.05. The object FCSS J033710.0-354727 is a background galaxy in the VST Deep Field of the Fornax cluster. The deep exposures combined with the high angular resolution of the OmegaCam at VST allowed us to carry out the first detailed photometric analysis for this system in the g and i bands to derive the galaxy structure and colors. Results show that the central object resembles a disk galaxy, surrounded by a ring-like structure that is twice as extended as the central disk. The warped geometry and bright knots observed along the polar direction, as well as some debris detected on the NW side with colors similar to those of the galaxy, suggest that the polar structure is still forming. We argue that the wide polar ring or disk is the result of the ongoing disruption of a companion galaxy in the potential well of the central object, which is two to three times more massive than the accreting galaxy.

Monthly Notices of the Royal Astronomical Society, 2014

STEP (the SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy) is a Guarante... more STEP (the SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy) is a Guaranteed Time Observation survey being performed at the VST (the ESO VLT Survey Telescope). STEP will image an area of 74 deg 2 covering the main body of the Small Magellanic Cloud (32 deg 2), the Bridge that connects it to the Large Magellanic Cloud (30 deg 2) and a small part of the Magellanic Stream (2 deg 2). Our g, r, i, Hα photometry is able to resolve individual stars down to magnitudes well below the main-sequence turn-off of the oldest populations. In this first paper, we describe the observing strategy, the photometric techniques and the upcoming data products of the survey. We also present preliminary results for the first two fields for which data acquisition is completed, including some detailed analysis of the two stellar clusters IC 1624 and NGC 419.

ESO ASTROPHYSICS SYMPOSIA European Southern Observatory

Using the Planetary Nebula Spectrograph, we have observed and measured the velocities for 2764 PN... more Using the Planetary Nebula Spectrograph, we have observed and measured the velocities for 2764 PNe in the disk and halo of the Andromeda galaxy. Preliminary analysis using a basic ring model shows a rotation curve in good agreement with that obtained from Hi data out to ∼ 20 kpc. Some substructure has also been detected within the velocity field, which can be modeled as the continuation of the tidal-remnant known as the Southern Stream, as it passes through Andromeda's disk.

Monthly Notices of the Royal Astronomical Society, 2014

We present an overview of a multiwavelength survey of the Shapley Supercluster (SSC; z ∼ 0.05) co... more We present an overview of a multiwavelength survey of the Shapley Supercluster (SSC; z ∼ 0.05) covering a contiguous area of 260 h −2 70 Mpc 2 including the supercluster core. The project main aim is to quantify the influence of cluster-scale mass assembly on galaxy evolution in one of the most massive structures in the local Universe. The Shapley Supercluster Survey (ShaSS) includes nine Abell clusters (A3552, A3554, A3556, A3558, A3559, A3560, A3562, AS0724, AS0726) and two poor clusters (SC1327−312, SC1329−313) showing evidence of cluster-cluster interactions. Optical (ugri) and near-infrared (K) imaging acquired with VLT Survey Telescope and Visible and Infrared Survey Telescope for Astronomy allow us to study the galaxy population down to m + 6 at the supercluster redshift. A dedicated spectroscopic survey with AAOmega on the Anglo-Australian Telescope provides a magnitude-limited sample of supercluster members with 80 per cent completeness at ∼m + 3. We derive the galaxy density across the whole area, demonstrating that all structures within this area are embedded in a single network of clusters, groups and filaments. The stellar mass density in the core of the SSC is always higher than 9 × 10 9 M Mpc −3 , which is ∼40× the cosmic stellar mass density for galaxies in the local Universe. We find a new filamentary structure (∼7 Mpc long in projection) connecting the SSC core to the cluster A3559, as well as previously unidentified density peaks. We perform a weak-lensing analysis of the central 1 deg 2 field of the survey obtaining for the central cluster A3558 a mass of M 500 = 7.63 +3.88 −3.40 × 10 14 M , in agreement with X-ray based estimates.

Astronomy & Astrophysics, 2015

We present a study of globular clusters (GCs) and other small stellar systems (SSSs) in the field... more We present a study of globular clusters (GCs) and other small stellar systems (SSSs) in the field of NGC 3115, observed as part of the ongoing wide-field imaging survey VEGAS, carried out with the 2.6 m VST telescope. We used deep g and i observations of NGC 3115, a well-studied lenticular galaxy that is covered excellently well in the 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 allowed us to accurately study the distribution and properties of SSSs as a function of galactocentric distance, well beyond ∼20 galaxy effective radii, in a way that is rarely possible. Our analysis of colors, magnitudes, and sizes of SSS candidates confirms the results from existing studies, some of which were carried out with 8-10 m class telescopes, and further extends them to previously unreached galactocentric distances with similar accuracy. In particular, we find a color bimodality for the GC population and a de Vaucouleurs r 1/4 profile for the surface density of GCs similar to the galaxy light profile. The radial color gradient of blue and red GCs previously found, for instance, by the SLUGGS survey with Subaru and Keck data, is further extended out to the largest galactocentric radii inspected, ∼65 kpc. In addition, the surface density profiles of blue and red GCs taken separately are well approximated by a r 1/4 density profile, with the fraction of blue GCs being slightly larger at larger radii. We do not find hints of a trend for the red GC subpopulation 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 GC subpopulations. Finally, from inspecting SSS sizes and colors, we obtain a list of ultracompact dwarf galaxies and GC candidates suitable for future spectroscopic follow-up. In conclusion, our study shows i) the reliability of the methodologies developed to study SSSs in the field of bright early-type galaxies; and ii) the great potential of the VEGAS survey to produce original results on SSSs science, mainly thanks to the wide-field imaging adopted.

The Astrophysical Journal, 2013

We present results from SPH-cosmological simulations, including self-consistent modeling of super... more We present results from SPH-cosmological simulations, including self-consistent modeling of supernova feedback and chemical evolution, of galaxies belonging to two clusters and 12 groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming (SF) activity, as parameterized by their specific star formation rate (sSFR), across a redshift range up to z = 2. The overall ZM relation for the composite population evolves according to a redshift-dependent quadratic functional form that is consistent with other empirical estimates, provided that the highest mass bin of the brightest central galaxies is excluded. Its slope shows irrelevant evolution in the passive sample, being steeper in groups than in clusters. However, the subsample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. The scatter of the passive sample is dominated by low-mass galaxies at all redshifts and keeps constant over cosmic times. The mean metallicity is highest in cluster cores and lowest in normal groups, following the same environmental sequence as that previously found in the red sequence building. The ZM relation for the SF sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The SF galaxies make up a tight sequence in the SFR-M * plane at high redshift, whose scatter increases with time alongside the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the SF galaxies, while on the contrary more active galaxies in terms of simple SFR are also metal-richer. Finally, the [O/Fe] abundance ratio is presented too: we report a strong increasing evolution with redshift at given mass, especially at z 1. The expected increasing trend with mass is recovered when only considering the more massive galaxies. We discuss these results in terms of the mechanisms driving the evolution within the high-and low-mass regimes at different epochs: mergers, feedback-driven outflows, and the intrinsic variation of the star formation efficiency.

The Astrophysical Journal, 2003

We use a high resolution collisionless simulation of a Virgo-like cluster in a ΛCDM cosmology to ... more We use a high resolution collisionless simulation of a Virgo-like cluster in a ΛCDM cosmology to determine the velocity and clustering properties of the diffuse stellar component in the intracluster region at the present epoch. The simulated cluster builds up hierarchically and tidal interactions between member galaxies and the cluster potential produce a diffuse stellar component free-flying