arXiv subjects

L. Piovan

Publications and source records attributed to L. Piovan.

14 recordsLinked to original sources

arXiv2018

GalMod: a Galactic synthesis population model

We present a new Galaxy population synthesis Model (GalMod). GalMod is a star-count model featuring an asymmetric bar/bulge as well as spiral arms and related extinction. The model, initially introduced in Pasetto et al. (2016b), has been here completed with a central bar, a new bulge description, new disk vertical profiles and several new bolometric corrections. The model can generate synthetic mock catalogs of visible portions of the Milky Way (MW), external galaxies like M31, or N-body simulation initial conditions. At any given time, e.g., a chosen age of the Galaxy, the model contains a sum of discrete stellar populations, namely bulge/bar, disk, halo. These populations are in turn the sum of different components: the disk is the sum of spiral arms, thin disks, a thick disk, and various gas components, while the halo is the sum of a stellar component, a hot coronal gas, and a dark matter component. The Galactic potential is computed from these population density profiles and used to generate detailed kinematics by considering up to the first four moments of the collisionless Boltzmann equation. The same density profiles are then used to define the observed color-magnitude diagrams in a user-defined field of view from an arbitrary solar location. Several photometric systems have been included and made available on-line and no limits on the size of the field of view are imposed thus allowing full sky simulations, too. Finally, we model the extinction adopting a dust model with advanced ray-tracing solutions. The model's web page (and tutorial) can be accessed at www.GalMod.org.

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arXiv2015

Exploring an Alternative Channel of Evolution Towards SNa Ia Explosion

In this paper we explore the possibility that isolated CO-WDs with mass smaller than the Chandrasekhar limit may undergo nuclear runaway and SNa explosion, triggered by the energy produced by under-barrier pycno-nuclear reactions between carbon and light elements. Such reactions would be due to left over impurities of the light elements, which would remain inactive until the WDs transit from the liquid to the solid state. We devise a simple formulation for the coulombian potential and the local density in a ionic lattice affected by impurities and introduce it in the known rates of pycno-nuclear reactions for multi-component plasmas. Our semi-analytical results indicate that the energy generated by these pycno-nuclear reactions exceeds the WD luminosity and provides enough energy to elementary cells of matter to balance the energy cost for C-ignition at much younger ages than the age of the Universe, even for WDs with masses as low as $\simeq 0.85\, M_\odot$. A thermonuclear runaway may thus be triggered in isolated WDs. The explosion would occur from few hundred thousand to a few million years after the WD formation in the mass interval $0.85 - 1.2\, M_\odot$.

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arXiv2014

Detailed AGB evolutionary models and near infrared colours of intermediate-age stellar populations: Tests on star clusters

We investigate the influence of Asymptotic Giant Branch stars on integrated colours of star clusters of ages between ~100 Myr and a few gigayears, and composition typical for the Magellanic Clouds. We use state-of-the-art stellar evolution models that cover the full thermal pulse phase, and take into account the influence of dusty envelopes on the emerging spectra. We present an alternative approach to the usual isochrone method, and compute integrated fluxes and colours using a Monte Carlo technique that enables us to take into account statistical fluctuations due to the typical small number of cluster stars. We demonstrate how the statistical variations in the number of Asymptotic Giant Branch stars and the temperature and luminosity variations during thermal pulses fundamentally limit the accuracy of the comparison (and calibration, for population synthesis models that require a calibration of the Asymptotic Giant Branch contribution to the total luminosity) with star cluster integrated photometries. When compared to observed integrated colours of individual and stacked clusters in the Magellanic Clouds, our predictions match well most of the observations, when statistical fluctuations are taken into account, although there are discrepancies in narrow age ranges with some (but not all) set of observations.

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arXiv2013

The Role of Dust in Models of Population Synthesis

We have employed state-of-the-art evolutionary models of low and intermediate-mass AGB stars, and included the effect of circumstellar dust shells on the spectral energy distribution (SED) of AGB stars, to revise the Padua library of isochrones (Bertelli et al. 1994). The major revision involves the thermally pulsing AGB phase, that is now taken from fully evolutionary calculations by Weiss & Ferguson (2009). Two libraries of about 600 AGB dust-enshrouded SEDs each have also been calculated, one for oxygen-rich M-stars and one for carbon-rich C-stars. Each library accounts for different values of input parameters like the optical depth {\tau}, dust composition, and temperature of the inner boundary of the dust shell. These libraries of dusty AGB spectra have been implemented into a large composite library of theoretical stellar spectra, to cover all regions of the Hertzsprung-Russell Diagram (HRD) crossed by the isochrones. With the aid of the above isochrones and libraries of stellar SEDs, we have calculated the spectro-photometric properties (SEDs, magnitudes, and colours) of single-generation stellar populations (SSPs) for six metallicities, more than fifty ages (from 3 Myr to 15 Gyr), and nine choices of the Initial Mass Function. The new isochrones and SSPs have been compared to the colour-magnitude diagrams (CMDs) of field populations in the LMC and SMC, with particular emphasis on AGB stars, and the integrated colours of star clusters in the same galaxies, using data from the SAGE (Surveying the Agents of Galaxy Evolution) catalogues. We have also examined the integrated colours of a small sample of star clusters located in the outskirts of M31. The agreement between theory and observations is generally good. In particular, the new SSPs reproduce the red tails of the AGB star distribution in the CMDs of field stars in the Magellanic Clouds.

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arXiv2011

Formation and Evolution of the Dust in Galaxies. I. The Condensation Efficiencies

The growing interest in the high-z universe, where strongly obscured objects are present, has determined an effort to improve the simulations of dust formation and evolution in galaxies. Three main basic ingredients enter the problem influencing the total dust budget and the mixture of the dust grains: the types and amounts of dust injected by AGB stars and SNae and the accretion/destruction processes of dust in the ISM. They govern the relative abundances of the gas and dust in the ISM. In this study, we focus on star-dust and present a database of condensation efficiencies for the refractory elements C, O, Mg, Si, S, Ca and Fe in AGB stars and SNae that can be easily applied to the gaseous ejecta, in order to determine the amount and kind of refractory elements locally embedded into dust and injected into the ISM. The best theoretical recipes available nowadays in literature to estimate the amount of dust produced by SNae and AGB stars have been discussed and for SNae compared to the observations to get clues on the problem. The condensation efficiencies have been analyzed in the context of a classical chemical model of dust formation and evolution in the Solar Neighbourhood and Galactic Disk. Tables of coefficients are presented for (i) AGB stars at varying the metallicity and (ii) SNae at varying the density n_H of the ISM where the SNa explosions took place. In particular, we show how the controversial CNT approximation widely adopted to form dust in SNae, still gives good results and agrees with some clues coming from the observations. A new generation of dust formation models in SNae is however required to solve some contradictions recently emerged. A simple database of condensation efficiencies is set up to be used in chemical models including the effect of dust and meant to simulate galaxies going from primordial proto-galaxies to those currently seen in the local universe.

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arXiv2011

Formation and Evolution of the Dust in Galaxies. II. The Solar Neighbourhood

Over the past decade a new generation of chemical models have included the dust in the treatment of the ISM. This major accomplishment has been spurred by the growing amounts of data on the highly obscured high-z Universe and the intriguing local properties of the Solar Neighbourhood (SoNE). We present here a new model able to simulate the formation and evolution of dust in the ISM. The model follows the evolution of 16 elemental species, with particular attention to those that are simultaneously present in form of gas and dust, e.g. C, N, O, Mg, Si, S, Ca and Fe. In this study we focus on the SoNe and the MW Disk as a whole which are considered as laboratories to test the physical ingredients governing the dust evolution. Infall of primordial gas, birth and death of stars, radial flows of matter between contiguous shells, presence of a central bar, star-dust emission by SNae and AGB stars, dust destruction and accretion are taken into account. The model reproduces the local depletion of the elements in the gas, and simultaneously satisfies other constraints obtained from the observations. The evolution of the element abundances in the gas and dust has been well reproduced for plausible choices of the parameters. The Mg/Si ratio, in particular, drives the formation of silicates. We show that for most of the evolution of the MW, the main process for dust enrichment is the accretion in the cold regions of the ISM. SNae dominate in the early phases of the evolution. We have examined the main factors controlling the temporal window in which SNae govern the dust budget both in low and high star forming environments. The role played by AGB stars is discussed. We find that IMFs with regular slope in the range of massive stars better reproduce the observed depletions. The results obtained for the SoNe lead us to safely extend the model.

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arXiv2011

Formation and Evolution of the Dust in Galaxies. III. The Disk of the Milky Way

Models of chemical evolution of galaxies including the dust are nowadays required to decipher the high-z universe. In a series of three papers we have tackled the problem and set a modern chemical evolution model. In the first paper (Piovan et al., 2011a) we revised the condensation coefficients for the elements that typically are present in the dust. In the second paper (Piovan et al., 2011b) we have implemented the dust into the Padova chemical model and tested it against the observational data for the Solar Neighbourhood. In this paper we extend it to the whole Disk of the Milky Way (MW). The Disk is used as a laboratory to analyze the spatial and temporal behaviour of (i) several dust grain families with the aid of which we can describe the ISM, (ii) the abundances in the gas, dust, and total ISM of the elements present in the dust and (iii) the depletion of the same elements. The temporal evolution of the dust and gas across the Disk is calculated under the effect of radial flows and a central Bar. The gradients of the abundances of C, N, O, Mg, Si, S, Ca and Fe in gas and dust across the Disk are derived as a function of time. The theoretical gradients nicely reproduce those derived from Cepheids, OB stars, Red Giants and HII regions. This provides the backbone for the companion processes of dust formation and evolution across the Disk. We examine in detail the contributions to dust by AGB stars, SNae and grain accretion in the ISM at different galacto-centric distances. Furthermore, we examine the variation of the ratio silicates/carbonaceous grains with time and position in the Disk. Finally, some hints about the depletion of the elements in regions of high and low SFR (inner and outer Disk) are presented. The results obtained make it possible to extend the model to other astrophysical situations or different theoretical models like the chemo-dynamical N-Body simulations.

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arXiv2011

ROBO: a Model and a Code for the Study of the Interstellar Medium

We present ROBO, a model and its companion code for the study of the interstellar medium (ISM). The aim is to provide an accurate description of the physical evolution of the ISM and to set the ground for an ancillary tool to be inserted in NBody-Tree-SPH (NB-TSPH) simulations of large scale structures in cosmological context or of the formation and evolution of individual galaxies. The ISM model consists of gas and dust. The gas chemical composition is regulated by a network of reactions that includes a large number of species (hydrogen and deuterium based molecules, helium, and metals). New reaction rates for the charge transfer in $\mathrm H^+$ and $\mathrm H_2$ collisions are presented. The dust contains the standard mixture of carbonaceous grains (graphite grains and PAHs) and silicates of which the model follows the formation and destruction by several processes. The model takes into account an accurate treatment of the cooling process, based on several physical mechanisms, and cooling functions recently reported in the literature. The model is applied to a wide range of the input parameters and the results for important quantities describing the physical state of the gas and dust are presented. The results are organized in a database suited to the artificial neural networks (ANNs). Once trained, the ANNs yield the same results obtained by ROBO, with great accuracy. We plan to develop ANNs suitably tailored for applications to NB-TSPH simulations of cosmological structures and/or galaxies.

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arXiv2011

MaNN: Multiple Artificial Neural Networks for modelling the Interstellar Medium

Modelling the complex physics of the Interstellar Medium (ISM) in the context of large-scale numerical simulations is a challenging task. A number of methods have been proposed to embed a description of the ISM into different codes. We propose a new way to achieve this task: Artificial Neural Networks (ANNs). The ANN has been trained on a pre-compiled model database, and its predictions have been compared to the expected theoretical ones, finding good agreement both in static and in dynamical tests run using the Padova Tree-SPH code \textsc{EvoL}. A neural network can reproduce the details of the interstellar gas evolution, requiring limited computational resources. We suggest that such an algorithm can replace a real-time calculation of mass elements chemical evolution in hydrodynamical codes.

astro-ph.IM↗

arXiv2009

GALEX UV properties of the polar ring galaxy MCG-05-07-001 and the shell galaxies NGC 1210 and NGC 5329

Systems of shells and polar rings in early-type galaxies are considered "bona fide" tracers of mass accretion and/or mergers. Their high frequency in low density environments suggests that such episodes could drive the evolution of at least a fraction of the early-type galaxy population. Their UV emission is crucial to test whether these galaxies host ongoing/recent star formation. We used far and near ultraviolet, optical, near infrared images, HI maps, and line strength indices to investigate the nuclear and outer regions of the galaxies as well as the regions where fine structures are present. The GALEX Near (NUV) and Far UV (FUV) images of MCG-05-07-001 and NGC 1210 show complex tidal tails and debris structures. The UV morphology of both galaxies appears so different from the optical one that the early-type classification may not apply. In both GALEX bands the polar ring of MCG-05-07-001 is the dominant feature, whereas an extended tidal tail dominates the FUV bands of NGC 1210. In MCG-05-07-001 and NGC 1210 there is a strong correlation between structures detected in the FUV and NUV bands and in HI. NGC 5329 does not show evidence of shells in the UV. We try to constrain the age of the accretion episode or merger which gave rise to the shells and polar rings with the aid of composite stellar populations that take the presence of dust into account. The presence of HI in both MCG-05-07-001 and NGC 1210 argues in favour of wet mergers. Models suggest the presence of very young stellar populations in MCG-05-07-001: the observations could be explained in the framework of a conspicuous burst of star formation that occurred <=1 Gyr ago and involved a large fraction of the galaxy mass. Our models suggest that also the nuclei of NGC 1210 and NGC 5329 could have been rejuvenated by an accretion episode about 2-4 Gyr ago. (abridged)

astro-ph.CO↗

arXiv2006

Study of ISM tracers in galaxies

We collected data for two samples of normal and interacting galaxies for a total of 2953 galaxies having fluxes in one or more of the following wavebands: FIR, 21 cm line, CO(1-0) lines and soft X-ray. The large set of data obtained allowed us to revisit some of the already known relations between the different tracers of the interstellar medium (ISM), such as the link between the FIR flux and the CO line emission, the relation between X-ray emission and the blue or FIR luminosity. The relation lacking from observations for early-type galaxies has been discussed and explained in detail in the frame of a suitable theoretical model, obtained by coupling chemo-dynamical N-body simulations with a dusty spectrophotometric code of population synthesis.

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arXiv2006

Relations between ISM tracers in galaxies

We study the relations existing between fluxes emitted at CO(1-0) line, 60 and 100 micron wavelengths, B and soft X-ray wavebands for galaxies of all morphological types. The large set of data that we created allows to revisit some of known relations existing between the different tracers of the Interstellar Medium (ISM): the link between the FIR flux and the CO line emission, the relation between X-ray emission in non active galaxies and the blue or FIR luminosity. Using catalogues of galaxies and works presented in the literature, we collected fluxes in FIR, 21 cm, CO(0-1) line and soft X-ray for two samples, consisting of normal and interacting galaxies respectively. Joining together these samples, we have data for a total of 2953 galaxies, not all observed in the four above wavebands. All the relations found are discussed in the frame of the star formation activity that is the link for most of them. We note that when an active star formation is present, it may link the galaxy fluxes at almost all wavelengths, from X to microwaves. On the contrary, in early-type galaxies where the current star formation rate has faded out the X-FIR fluxes link disappears. This result obtained for early-type galaxies is discussed and explained in detail in the frame of a suitable theoretical model, obtained coupling chemo-dynamical N-body simulations with a dusty spectrophotometric code of population synthesis.

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arXiv2006

New response functions for absorption-line indices from high-resolution spectra

Basing on the huge library of 1-A resolution spectra calculated by Munari et al. over a large range of logT, log g, [Fe/H] and both for solar and a-enhanced abundance ratios [a/Fe], we present theoretical absorption-line indices on the Lick system. First we derive the so-called response functions (RFs) of Tripicco & Bell for a wide range of logT, log g, [Fe/H] and [a/Fe]=+0.4 dex. The RFs are commonly used to correct indices with solar [a/Fe] ratios to indices with [a/Fe]>0. Not only the RFs vary with the type of star but also with the metallicity. Secondly, with the aid of this and the fitting functions (FFs) of Worthey et al., we derive the indices for single stellar populations and compare them with those obtained by previous authors, e.g. Tantalo & Chiosi. The new RFs not only supersede the old ones by Tripicco & Bell, but also show that Hb increases with the degree of enhancement in agreement with the results by Tantalo & Chiosi. The new indices for single stellar populations are used to derive with aid of the recursive Minimum Distance method the age, metallicity and degree of enhancement of a sample of Galactic Globular Clusters for which these key parameters have been independently derived from the Colour-Magnitude Diagram and/or spectroscopic studies. The agreement is remarkably good.

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arXiv2005

Modelling galaxy spectra in presence of interstellar dust. I. The model of ISM and the library of dusty SSPs

In this paper, the first of a series of two devoted to modelling the spectra of galaxies of different morphological type in presence of dust, we present our description of the dust both in the diffuse ISM and the molecular clouds. Our model for the dust takes into account three components, i.e. graphite, silicates and polycyclic aromatic hydrocarbons. We consider and adapt to our aims two prescriptions for the size distribution of the dust grains and two models for the emission of the dusty ISM. We cross-check the emission and extinction models of the ISM by calculating the extinction curves and the emission for the typical environments of the Milky Way and the Large and Small Magellanic Clouds and by comparing the results with the observational data. The final model we have adopted is an hybrid one which stems from combining the analysis of Guhathakurta et al (1989) for the emission of graphite and silicates and Puget et al. (1985) for the PAH emission, and using the distribution law of Weingartner et al. (2001a) and the ionization model for PAHs of Weingartner et al. (2001b). We apply the model to calculate the SED of SSPs of different age and chemical composition, which may be severely affected by dust in young, massive stars while they are still embedded in their parental MCs. We use the "Ray Tracing" method to solve the problem of radiative transfer and to calculate libraries of SSP SEDs. Particular care is paid to model the contribution from PAHs, introducing different abundances of C in the population of very small carbonaceous grains (VSGs) and different ionization states in PAHs. The SEDs of young SSPs are then compared with observational data of star forming regions of four local galaxies successfully reproducing their SEDs from the UV-optical regions to the mid and far infrared.

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