arXiv subjects

Maurizio Paolillo

Publications and source records attributed to Maurizio Paolillo.

82 records · Page 5Linked to original sources

arXiv2012

A multi-wavelength study of the gravitational lens COSMOS J095930+023427

We present a multi-wavelength study of the gravitational lens COSMOS J095930+023427 (z=0.89), together with the associated galaxy group located at $z\sim0.7$ along the line of sight and the lensed background galaxy. The source redshift is currently unknown, but estimated to be at $z_s \sim 2$. The analysis is based on the available public HST, Subaru, Chandra imaging data, and VLT spectroscopy. The lensing system is an early-type galaxy showing a strong [OII] emission line, and produces 4 bright images of the distant background source. It has an Einstein radius of 0.79", about 4 times large than the effective radius. We perform a lensing analysis using both a Singular Isothermal Ellipsoid (SIE) and a Peudo-Isothermal Elliptical Mass Distribution (PIEMD) for the lensing galaxy, and find that the final results on the total mass, the dark matter (DM) fraction within the Einstein radius and the external shear due to a foreground galaxy group are robust with respect of the choice of the parametric model and the source redshift (yet unknown). We measure the luminous mass from the photometric data, and find the DM fraction within the Einstein radius $f_{\rm DM}$ to be between $0.71\pm 0.13$ and $0.79 \pm 0.15$, depending on the unknown source redshift. Meanwhile, the non-null external shear found in our lensing models supports the presence and structure of a galaxy group at $z\sim0.7$, and an independent measurement of the 0.5-2 keV X-ray luminosity within 20" around the X-ray centroid provides a group mass of $M=(3-10)\times 10^{13}$ M$_{\odot}$, in good agreement with the previous estimate derived through weak lensing analysis.

astro-ph.CO↗

arXiv2012

Characterising galaxy groups: spectroscopic observations of the Shakhbazyan sample

Groups of galaxies are the most common cosmic structures. However, due to the poor statistics, projection effects and the lack of accurate distances, our understanding of their dynamical and evolutionary status is still limited. This is particularly true for the so called Shakhbazyan groups (SHK) which are still largely unexplored due to the lack of systematic spectroscopic studies of both their member galaxies and the surrounding environment. In our previous paper, we investigated the statistical properties of a large sample of SHK groups using Sloan Digital Sky Survey data and photometric redshifts. Here we present the follow-up of 5 SHK groups (SHK 10, 71, 75, 80, 259) observed within our spectroscopic campaign with the Telescopio Nazionale Galileo, aimed at confirming their physical reality and strengthening our photometric results. For each of the selected groups we were able to identify between 6 and 13 spectroscopic members, thus confirming the robustness of the photometric redshift approach in identifying real galaxy over-densities. Consistently with the finding of our previous paper, the structures studied here have properties spanning from those of compact and isolated groups to those of loose groups. For what the global physical properties are concerned (total mass, mass-to-light ratios, etc.), we find systematic differences with those reported in the literature by previous studies. Our analysis suggests that previous results should be revisited; we show in fact that, if the literature data are re-analysed in a consistent and homogeneous way, the properties obtained are in agreement with those estimated for our sample.

astro-ph.CO↗

arXiv2012

Constraints on sterile neutrino dark matter from XMM--Newton observation of M33

Using archival XMM-Newton observations of the diffuse and unresolved components emission in the inner disc of M33 we exclude the possible contribution from narrow line emission in the energy range 0.5-5 keV more intense than 10^{-6}-10^{-5} erg/s. Under the hypothesis that sterile neutrinos constitute the majority of the dark matter in M33, we use this result in order to put constraints on their parameter space in the 1-10 keV mass range.

astro-ph.GA↗

arXiv2011

Extracting Knowledge From Massive Astronomical Data Sets

The exponential growth of astronomical data collected by both ground based and space borne instruments has fostered the growth of Astroinformatics: a new discipline laying at the intersection between astronomy, applied computer science, and information and computation (ICT) technologies. At the very heart of Astroinformatics is a complex set of methodologies usually called Data Mining (DM) or Knowledge Discovery in Data Bases (KDD). In the astronomical domain, DM/KDD are still in a very early usage stage, even though new methods and tools are being continuously deployed in order to cope with the Massive Data Sets (MDS) that can only grow in the future. In this paper, we briefly outline some general problems encountered when applying DM/KDD methods to astrophysical problems, and describe the DAME (DAta Mining & Exploration) web application. While specifically tailored to work on MDS, DAME can be effectively applied also to smaller data sets. As an illustration, we describe two application of DAME to two different problems: the identification of candidate globular clusters in external galaxies, and the classification of active galactic nuclei (AGN). We believe that tools and services of this nature will become increasingly necessary for the data-intensive astronomy (and indeed all sciences) in the 21st century.

astro-ph.IM↗

arXiv2011

Probing the GC-LMXB connection in NGC 1399: a wide-field study with HST and Chandra

We present a wide field study of the Globular Clusters/Low Mass X-ray Binary (LMXB) connection in the giant elliptical NGC1399. The large FOV of the ACS/WFC, combined with the HST and Chandra high resolution, allow us to constrain the LMXB formation scenarios in elliptical galaxies. We confirm that NGC1399 has the highest LMXB fraction in GCs of all nearby elliptical galaxies studied so far, even though the exact value depends on galactocentric distance due to the interplay of a differential GC vs galaxy light distribution and the GC color dependence. In fact LMXBs are preferentially hosted by bright, red GCs out to $>5 R_{eff}$ of the galaxy light. The finding that GC hosting LMXBs follow the radial distribution of their parent GC population, argues against the hypothesis that the external dynamical influence of the galaxy affects LMXB formation in GCs. On the other hand field LMXBs closely match the host galaxy light, thus indicating that they are originally formed in situ and not inside GCs. We measure GC structural parameters, finding that the LMXB formation likelihood is influenced independently by mass, metallicity and GCs structural parameters. In particular the GC central density plays a major role in predicting which GC host accreting binaries. Finally our analysis shows that LMXBs in GCs are marginally brighter than those in the field, and in particular the only color-confirmed GC with $L_X>10^{39}$ erg s$^{-1}$ shows no variability, which may indicate a superposition of multiple LMXBs in these systems.

astro-ph.HE↗

arXiv2010

DAME: A Web Oriented Infrastructure for Scientific Data Mining & Exploration

Nowadays, many scientific areas share the same need of being able to deal with massive and distributed datasets and to perform on them complex knowledge extraction tasks. This simple consideration is behind the international efforts to build virtual organizations such as, for instance, the Virtual Observatory (VObs). DAME (DAta Mining & Exploration) is an innovative, general purpose, Web-based, VObs compliant, distributed data mining infrastructure specialized in Massive Data Sets exploration with machine learning methods. Initially fine tuned to deal with astronomical data only, DAME has evolved in a general purpose platform which has found applications also in other domains of human endeavor. We present the products and a short outline of a science case, together with a detailed description of main features available in the beta release of the web application now released.

astro-ph.IM↗

arXiv2010

Proceedings of the "Wide Field X-ray Telescope" workshop

We list here the contents of the Proceedings of the "Wide Field X-ray Telescope" conference held in Bologna, Italy on 25-26 Nov 2009. The conference highlighted the scientific potential and discovery space provided by an X-ray mission concept characterized by a wide field-of-view (1 sq.deg.), large effective area (1 sq.mt.) and approximately constant PSF (~5 arcsec HEW) across the whole FOV. The index is in html form with clickable links to the individual contributions.

astro-ph.IM↗

arXiv2010

X-ray variability with WFXT: AGNs, transients and more

The Wide Field X-ray Telescope (WFXT) is a proposed mission with a high survey speed, due to the combination of large field of view (FOV) and effective area, i.e. grasp, and sharp PSF across the whole FOV. These characteristics make it suitable to detect a large number of variable and transient X-ray sources during its operating lifetime. Here we present estimates of the WFXT capabilities in the time domain, allowing to study the variability of thousand of AGNs with significant detail, as well as to constrain the rates and properties of hundreds of distant, faint and/or rare objects such as X-ray Flashes/faint GRBs, Tidal Disruption Events, ULXs, Type-I bursts etc. The planned WFXT extragalactic surveys will thus allow to trace variable and transient X-ray populations over large cosmological volumes.

astro-ph.IM↗

arXiv2009

Searching for Dark Matter in Messier 33

Among various approaches for indirect detection of dark matter, synchrotron emission due to secondary electrons/positrons produced in galactic WIMPs annihilation is raising an increasing interest. In this paper we propose a new method to derive bounds in the mchi - plane by using radio continuum observations of Messier 33, paying particular attention to a low emitting Radio Cavity. The comparison of the expected radio emission due to the galactic dark matter distribution with the observed one provides bounds which are comparable to those obtained from a similar analysis of the Milky Way. Remarkably, the present results are simply based on archival data and thus largely improvable by means of specifically tailored observations. The potentiality of the method compared with more standard searches is discussed by considering the optimistic situation of a vanishing flux (within the experimental sensitivity) measured inside the cavity by a high resolution radio telescope like ALMA. Under the best conditions our technique is able to produce bounds which are comparable to the ones expected after five years of Fermi LAT data taking for an hadronic annihilation channel. Furthermore, it allows to test the hypothesis that space telescopes like Pamela and Fermi LAT are actually observing electrons and positrons due to galactic dark matter annihilation into leptons.

astro-ph.HE↗

arXiv2004

High-Redshift Extremely Red Objects in the HST Ultra Deep Field Revealed by the GOODS IRAC Observations

Using early data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope, taken for the Great Observatories Origins Deep Survey (GOODS), we identify and study objects that are well-detected at 3.6um, but are very faint (and in some cases, invisible) in the Hubble Ultra Deep Field (HUDF) ACS and NICMOS images and in very deep VLT Ks-band imaging. We select a sample of 17 objects with f_nu(3.6um)/f_nu(z_{850})>20. The analysis of their spectral energy-distributions (SEDs) from 0.4 to 8.0um shows that the majority of these objects cannot be satisfactorily explained without a well-evolved stellar population. We find that most of them can be well fitted by a simple two-component model, where the primary component represents a massive, old population that dominates the strong IR emission, while the secondary component represents a low amplitude, on-going star-formation process that accounts for the weak optical fluxes. Their estimated photometric redshifts (z_p) range from 1.6 to 2.9, with the median at z_p=2.4. For the simple star formation histories considered here, their corresponding stellar masses range from 0.1 to 1.6e11 M_sun for a Chabrier Initial Mass Function (IMF). Their median rest-frame Ks-band absolute magnitude is -22.9 mag in AB system, or 1.5xL*(K) for present--day elliptical galaxies. In the scenario of pure luminosity evolution, such objects may be direct progenitors for at least 14 to 51% of the local population of early--type galaxies. Due to the small cosmic volume of the HUDF, however, this simple estimate could be affected by other effects such as cosmic variance and the strong clustering of massive galaxies. A full analysis of the entire GOODS area is now underway to assess such effects.

astro-ph↗