Research and Work Activities
December 2009
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From 3 Sept. 2007 up to 31 Aug. 2009, I worked as Senior Engineer at the Institute of
Theoretical Astrophysics of the University of Oslo (UiO), under the supervision of Prof. V.
Hansteen. Here, I am dealt with the management and improvement of the Quick Look and
Data Analysis (QL/DA) software for the data of the EIS telescope on-board Hinode. Hinode is a satellite devoted to the study of the Sun, which carries three telescopes able to take simultaneous observations in three different bands. Among them, EIS (EUV Imaging
Spectrometer) performs spectral-imaging in the extreme ultra-violet band. The preprocessed
EIS data are stored in the Science Data Center archive at the UiO and hence made available to everybody worldwide. The QL/DA software is the first instrument to easily manage and extract scientific information from these data. It is written in object-oriented IDL and it is part of the solar-software IDL package, routinely used in solar astrophysics. In this context, my work consisted in maintaining and updating the QL/DA software, as well as adding new features related to the calibration, visualization and analysis of the data.
Previously, my research work focused on extragalactic astronomy and cosmology, with particular attention to clusters of galaxies and to the large scale structure of the universe. The main areas of activity and expertise concerned the production of realistic numerical simulations and simulated observations. Related jobs consisted of the development and improvement of simulation codes and tools of analysis.
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As post-doc at the University of Illinois at Urbana-Champaign, in collaboration with Prof.
Ricker, I studied the effect of the central active galactic nuclei (AGN) on the intra-cluster medium (ICM), in relationship to the cooling-flow problem in galaxy clusters. I simulated the later stages of the life of the AGN ejecta, modelling them as bubbles filled by radio plasma and in pressure equilibrium with the environment. Buoyancy, development of instabilities, and mixing will then drive the evolution of the radio-sources, in turn affecting the ICM properties. The study was performed through a set of simulations realized by the code FLASH, which solves the equations of gas-dynamics on an adaptive Eulerian grid via the piecewise-parabolic method (PPM). Cooling and eventual thermal conduction were accounted for in the simulations.
The main result of this study, as published in Gardini (2007), consists in showing that the buoyant rise of radio-sources induces gas motions which drive material in to the cooling cluster core from warmer external regions. Thus the cooling rate in the cluster centre is at least partially reduced by the exchange and mixing of the central gas with hotter external material. This effect mitigates the discrepancy between the expected cool temperatures in cluster centres and the relatively warm observed ones.
While the magnetic field is also expected to affect the dynamics of the radio sources, it is usually neglected or unrealistically modelled in simulations due to its high computational cost. After obtaining computational resources from the NCSA to extend this work via the inclusion of a realistic three-dimensional magnetic field, new preliminary MHD simulations were produced.
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In collaboration with A. Sanderson (University of Birmingham), I also analysed simulated
X-ray images generated by X-MAS (see below) of these clusters,.
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X-MAS (X-ray MAp Simulator, Gardini et. al, 2004) is a software package that generates simulated observations of the intra-cluster medium by the Chandra X-ray orbiting telescope, starting from hydro-dynamical simulations. I developed it at the University of Padua, in collaboration with L. Moscardini, G. Tormen and E. Rasia (University of Padua), S. De
Grandi (Observatory of Brera), and P. Mazzotta (University of Roma 2).
Briefly, X-MAS works as follows. A spectrum of emissivity is assigned to each gas particle or fluid element in the simulation, according to a chosen emission model (e.g. APEC or
MeKaL). Then spatial images of the cluster differential flux are constructed by integrating over the volumes of all of the particles along the line of sight. These images are used, pixel by pixel, as input models to XSPEC, which creates photon spectra for the different pixels of the Chandra CCD detectors. Thus information on direction and energy is preserved. The photon events are then stored in one file, together with background events.
The format of the synthetic data is identical to real observations, and henceforth they can be processed and analysed using the same tools (CIAO). X-MAS takes into account most of the physical characteristics of Chandra: ARF and RMF are fully reproduced, while an average
PSF can be introduced into the simulation process.
The usefulness of the X-MAS package is noteworthy. For example, comparing the characteristics of the ICM in simulations with the same quantities obtained at the end of the data reduction and analysis enables us to check the reconstructed properties of clusters, and to determine the quantity of information retained or lost during the observation process.
Earlier research activities concerned mainly the application of cosmological N-body simulations to the study of the large-scale structure of the universe. Besides treating numerical aspects, I devoted particular attention to the comparison of computer outputs to observational data. This research was performed in the years 1995-2000 at the University of Milan.
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In a first work, the velocity dispersion in clusters was used as a test of cosmological models.
A significant effort was devoted to applying to the simulation data the algorithms used to obtain the reference observational sample. The approach used and the detailed results are described in Borgani et al. (1997).
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Later, I constructed a parallel version of the AP3M code (Couchman 1991), and extended the code to the study of low density universes, with or without cosmological constant
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, and of universes where a hot component (usually massive neutrinos) is present besides cold dark matter (CDM). The last model required a special treatment of initial conditions and the implementation of suitable methods to avoid spurious numerical effects during the run. The code was implemented in parallel mode on the HP-SPP2000 shared-memory parallel computer of the CILEA consortium (Segrate, Milan). The simulations of a CDM, a

CDM, and two mixed models were performed using a large number of particles and high force resolution.
Galaxy cluster haloes were identified in the simulation box and the mass function and correlation properties of cluster haloes were analysed, as described in Gardini et al. (1999,
2000). Then the comparison with observational data indicated that some cosmological models with massive neutrinos and no cosmological constant were in agreement with observations.
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A successive analysis described in Macciò et al. (2001) showed how the morphology
(quadrupole moment) of the most massive clusters depends on the cosmological model and can thus be used as a cosmological test.
 A paper written in collaboration with S. Bonometto and A. Macciò (1999) dealt with the properties of the Limber equation when the correlation length of the related objects depends on luminosity.
From June 2002 to July 2003, as well as from Sept. 2006 to Feb. 2007, I was employed by Joint-
Technologies S.R.L. (http://www.joint-tech.it), a software firm specializing in the development and management of databases by using client-server architecture. In this context, my activities consisted of the design and development of databases, maintenance and updating of applications, reverseengineering, ergonomics and testing. There I also learned the basics of the OOP and the Java language.
During Mar. 2007, I worked briefly at the Astronomical Observatory of Brera (Milan) on the analysis of X-ray images of galaxy clusters taken by XMM/Newton, and on the comparison of the
X-ray properties of the clusters with analogous properties in the optical band.
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Referees of Alessandro Gardini
Prof. Viggo H. Hansteen
University of Oslo
Institute of Theoretical Astrophysics
Sem Sælands vei 13
P.O. Box 1029 Blindern,
0315 Oslo, Norway email: viggo.hansteen@astro.uio.no phone: +47 228 56120
Dr. Davide Anceschi
Joint-Technologies s.r.l. via Molineria S.Giovanni, 10
29100 Piacenza, Italy email: davide.anceschi@joint-tech.it phone: +39 0523 315371
Prof. Paul M. Ricker
University of Illinois
Dept. of Astronomy
1002 West Green St.
61801 Urbana, IL, USA email: pmricker@uiuc.edu phone: +1 217 244 1187
Prof. Pasquale Mazzotta
University of Roma “Tor Vergata”
Department of Physics
Via della Ricerca Scientifica, 1
00133 Roma, Italy email: pasquale.mazzotta@roma2.infn.it phone: +39 06 72594503
Prof. Silvio A. Bonometto
University of Milano-Bicocca
Department of Physics “G. Occhialini”
Edificio U2 - Piazza delle Scienze 3
20126 Milano, Italy email: Silvio.Bonometto@mib.infn.it phone: +39 02 6448 2356
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