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P. Saracco

Publications and source records attributed to P. Saracco.

At least 37 records · Page 2Linked to original sources
arXiv2016

An interacting quark-diquark model. Strange and nonstrange baryon spectroscopy and other observables

We describe the relativistic interacting quark-diquark model formalism and its application to the calculation of strange and nonstrange baryon spectra. The results are compared to the existing experimental data. We also discuss the application of the model to the calculation of other baryon observables, like baryon magnetic moments, open-flavor strong decays and baryon masses with self-energy corrections.

hep-ph↗
arXiv2016

Ultramassive dense early-type galaxies: velocity dispersions and number density evolution since z=1.6

In this paper we investigate the mass assembly history of ultramassive (Mstar > 10^11Msun) dense (Sigma = Mstar/(2*pi*Re^2) > 2500 Msun/pc^2) early-type galaxies (ETGs) over the last 9 Gyr. We have traced the evolution of the number density rho of ultramassive dense ETGs and have compared their structural (effective radius Re and stellar mass Mstar) and dynamical (velocity dispersion sigma_e) parameters over the redshift range 0 < z < 1.6. We have derived the number density at 1.6 < z < 1 from the MUNICS and GOODS-South surveys, while we have used the COSMOS and SDSS spectroscopic surveys to probe the intermediate and local redshift range. For the comparison of the dynamical and structural parameters, we have collected the ultramassive dense ETGs at 1.2 < z < 1.6 for which velocity dispersion measurements are available (11 ETGs). For 4 of them we present unpublished estimates of sigma_e. We probe the intermediate redshift range, and the local universe using the samples of ETGs by Saglia et al. (2010), Zahid et al. (2015), and by Thomas et al. (2010). We find that the number density of ultramassive dense ETGs evolves as rho(z) = K*(1 + z)^(0.3\pm0.8) implying a decrease of ~ 25% of the population since z = 1.6. By comparing the values of Re, Mstar, and sigma_e of ultramassive dense ETGs over the range 0 < z < 1.6 we find that all the high-z ETGs have a counterpart in the local universe. This implies either that the majority (~70%) of ultramassive dense ETGs has already completed its assembly and its shaping at = 1.4, or that, if a significant fraction of them evolves in size, new ultramassive dense ETGs must form at z < 1.5 to maintain their number density almost constant. The difficulty into identify good progenitors for these new dense ETGs at z < 1.5, and the stellar populations properties of local ultramassive dense ETGs point toward the first hypothesis.

astro-ph.GA↗
arXiv2014

The population of early-type galaxies: how it evolves with time and how it differs from passive and late-type galaxies

The aim of our analysis is twofold. On the one hand we are interested in addressing whether a sample of ETGs morphologically selected differs from a sample of passive galaxies in terms of galaxy statistics. On the other hand we study how the relative abundance of galaxies, the number density and the stellar mass density for different morphological types change over the redshift range 0.6 =10^(11) M_sol) galaxies, with the fraction of massive ETGs rising up to 40% and the fraction of massive LTGs decreasing down to 60%. Moreover, we find that the number density and the stellar mass density of the whole population of massive galaxies increase almost by a factor of ~10 between 0.6 3-4x10^(11) M_sol) both ETGs and LTGs do not increase since z~2.5, contrary to the lower mass galaxies. This suggests that the population of the most massive galaxies formed at z>2.5-3 and that the assembly of such high-mass galaxies is not effective at lower redshift.

astro-ph.GA↗
arXiv2014

Lower mass normalization of the stellar initial mass function for dense massive early-type galaxies at z ~ 1.4

This paper aims at understanding if the normalization of the stellar initial mass function (IMF) of massive early-type galaxies (ETGs) varies with cosmic time and/or with mean stellar mass density Sigma (M*/2πRe^2). For this purpose we collected a sample of 18 dense (Sigma>2500 M_sun/pc^2) ETGs at 1.2 = 1.4 follow the same IMF-sigma_e trend of typical local ETGs, but with a lower mass-normalization. Nonetheless, once the IMF-sigma_e trend we have found for high-z dense ETGs is compared with that of local ETGs with similar Sigma and sigma_e, they turn out to be consistent. The similarity between the IMF-sigma_e trends of dense high-z and low-z ETGs over 9 Gyr of evolution and their lower mass-normalization with respect to the mean value of local ETGs suggest that, independently on formation redshift, the physical conditions characterizing the formation of a dense spheroid lead to a mass spectrum of new formed stars with an higher ratio of high- to low-mass stars with respect to the IMF of normal local ETGs.

astro-ph.GA↗
arXiv2014

Spectral detection of multiple stellar populations in z~1 early-type galaxies

We present a spectroscopic analysis based on measurements of two mainly age-dependent spectrophotometric indices in the 4000A rest frame region, i.e. H+K(CaII) and Delta4000, for a sample of 15 early-type galaxies (ETGs) at 0.7 < z_{spec} < 1.1, morphologically selected in the GOODS-South field. Ages derived from the two different indices by means of the comparison with stellar population synthesis models, are not consistent with each other for at least nine galaxies (60 per cent of the sample), while for the remaining six galaxies, the ages derived from their global spectral energy distribution (SED) fitting are not consistent with those derived from the two indices. We then hypothesized that the stellar content of many galaxies is made of two stellar components with different ages. The double-component analysis, performed by taking into account both the index values and the observed SED, fully explains the observational data and improves the results of the standard one-component SED fitting in 9 out of the 15 objects, i.e. those for which the two indices point towards two different ages. In all of them, the bulk of the mass belongs to rather evolved stars, while a small mass fraction is many Gyr younger. In some cases, thanks to the sensitivity of the H+K(CaII) index, we find that the minor younger component reveals signs of recent star formation. The distribution of the ages of the younger stellar components appears uniformly in time and this suggests that small amounts of star formation could be common during the evolution of high-z ETGs. We argue the possibility that these new star formation episodes could be frequently triggered by internal causes due to the presence of small gas reservoir.

astro-ph.GA↗
arXiv2014

Scaling relations of cluster elliptical galaxies at z~1.3. Distinguishing luminosity and structural evolution

[Abridged] We studied the size-surface brightness and the size-mass relations of a sample of 16 cluster elliptical galaxies in the mass range 10^{10}-2x10^{11} M_sun which were morphologically selected in the cluster RDCS J0848+4453 at z=1.27. Our aim is to assess whether they have completed their mass growth at their redshift or significant mass and/or size growth can or must take place until z=0 in order to understand whether elliptical galaxies of clusters follow the observed size evolution of passive galaxies. To compare our data with the local universe we considered the Kormendy relation derived from the early-type galaxies of a local Coma Cluster reference sample and the WINGS survey sample. The comparison with the local Kormendy relation shows that the luminosity evolution due to the aging of the stellar content already assembled at z=1.27 brings them on the local relation. Moreover, this stellar content places them on the size-mass relation of the local cluster ellipticals. These results imply that for a given mass, the stellar mass at z~1.3 is distributed within these ellipticals according to the same stellar mass profile of local ellipticals. We find that a pure size evolution, even mild, is ruled out for our galaxies since it would lead them away from both the Kormendy and the size-mass relation. If an evolution of the effective radius takes place, this must be compensated by an increase in the luminosity, hence of the stellar mass of the galaxies, to keep them on the local relations. We show that to follow the Kormendy relation, the stellar mass must increase as the effective radius. However, this mass growth is not sufficient to keep the galaxies on the size-mass relation for the same variation in effective radius. Thus, if we want to preserve the Kormendy relation, we fail to satisfy the size-mass relation and vice versa.

astro-ph.GA↗
arXiv2012

Algorithms and parameters for improved accuracy in physics data libraries

Recent efforts for the improvement of the accuracy of physics data libraries used in particle transport are summarized. Results are reported about a large scale validation analysis of atomic parameters used by major Monte Carlo systems (Geant4, EGS, MCNP, Penelope etc.); their contribution to the accuracy of simulation observables is documented. The results of this study motivated the development of a new atomic data management software package, which optimizes the provision of state-of-the-art atomic parameters to physics models. The effect of atomic parameters on the simulation of radioactive decay is illustrated. Ideas and methods to deal with physics models applicable to different energy ranges in the production of data libraries, rather than at runtime, are discussed.

physics.comp-ph↗
arXiv2012

Spatially Resolved Colors and Stellar Population Properties in Early-Type Galaxies at z ~ 1.5

We present F850LP-F160W color gradients for 11 early-type galaxies (ETGs) at 1.0 R_e we have found that the fraction of high-z ETGs with negative F850LP-F160W color gradients rises up to 100%. For each galaxy, we investigate the origin of the radial color variation with a technique based on the matching of both the spatially resolved color and the global spectral energy distribution (SED) to predictions of composite stellar population models. In fact, we find that the age of the stellar populations is the only parameter whose radial variation alone can fully account for the observed color gradients and global SEDs for half of the galaxies in our sample (6 ETGs), without the need of radial variation of any other stellar population property. For four out of these six ETGs, a pure metallicity variation can also reproduce the detected color gradients. Nonetheless, a minor contribution to the observed color gradients from radial variation of star-formation time scale, abundance of low-to-high mass stars and dust cannot be completely ruled out. For the remaining half of the sample, our analysis suggests a more complex scenario whereby more properties of the stellar populations need to simultaneously vary to generate the observed color gradients and global SED. Our results show that, despite the young mean age of our galaxies (<3-4 Gyr), they already exhibit significant differences among their stellar content. We have discussed our results within the framework of the widest accepted scenarios of galaxy formation and conclude that none of them can satisfactorily account for the observed distribution of color gradients and for the spatially resolved content of high-z ETGs.

astro-ph.CO↗
arXiv2012

On the central stellar mass density and the inside-out growth of early-type galaxies

[Abridged] In this paper we derive the central stellar mass density within a fixed radius and the effective stellar mass density within the effective radius for a complete sample of 34 ETGs morphologically selected at 0.9 2. Also, we show that the small scatter of the central mass density of ETGs compared to the large scatter of the effective mass density is simply a peculiar feature of the Sersic profile hence, independent of redshift and of any assembly history experienced by galaxies. Thus, it has no connection with the possible inside-out growth of ETGs. Finally, we find a tight correlation between the central stellar mass density and the total stellar mass of ETGs in the sense that the central mass density increases with mass as M^{~0.6}. This implies that the fraction of the central stellar mass of ETGs decreases with the mass of the galaxy. These correlations are valid for the whole population of ETGs considered independently of their redshift suggesting that they originate in the early-phases of their formation.

astro-ph.CO↗
arXiv2011

Evolutionary properties of the low-luminosity galaxy population in the NGC5044 Group

With this third paper of a series we present Johnson-Gunn B,g,V,r,i,z multicolour photometry for 79 objects, including a significant fraction of the faintest galaxies around NGC5044, assessing group membership on the basis of apparent morphology and low-resolution optical spectroscopy to estimate redshift for 21 objects. Together, dE's and Im's provide the bulk of the galaxy luminosity function, around M(g)\sim-18.0, while the S0 and dSph components dominate, respectively, the bright and faint-end tails of the distribution. This special mix places the NGC 5044 group just "midway" between the high-density cosmic aggregation scale typical of galaxy clusters, and the low-density environment of looser galaxy clumps like our Local Group. The bright mass of the 136 member galaxies with available photometry and morphological classification, amounts to a total of 2.3x10^{12}M_sun while current SFR within the group turns to be about or higher than 23M_sun/yr. In this regard, a drift toward bluer integrated colours is found to be an issue for dE's pointing to a moderate but pervasive star-formation activity even among nominally "quiescent" stellar systems. Through Lick narrow-band index analysis, dwarf ellipticals are found to share a sub-solar metallicity (-1.0 < [Fe/H] <-0.5) with a clear decoupling between Iron and alpha elements, as already established also for high-mass systems. Both dE's and dS0's are consistent with an old age, about one Hubble time, although a possible bias, toward higher values of age, may be induced by the gas emission affecting the Hbeta strength.

astro-ph.CO↗
arXiv2011

Quantifying the unknown: issues in simulation validation and their experimental impact

The assessment of the reliability of Monte Carlo simulations is discussed, with emphasis on uncertainty quantification and the related impact on experimental results. Methods and techniques to account for epistemic uncertainties, i.e. for intrinsic knowledge gaps in physics modeling, are discussed with the support of applications to concrete experimental scenarios. Ongoing projects regarding the investigation of epistemic uncertainties in the Geant4 simulation toolkit are reported.

physics.comp-ph↗
arXiv2011

Constraining the star formation and the assembly histories of normal and compact early-type galaxies at 1<z<2

[Abridged]We present a study based on a sample of 62 early-type galaxies (ETGs) at 0.9 5. Earlier stars formed at z_form>5 are assembled in compact and more massive (M_*>10^11 M_sun) ETGs while stars later formed (z_form<3) or resulting from subsequent episodes of star formation are assembled both in compact and normal ETGs. Thus, the older the stellar population the higher the mass of the hosting galaxy but not vice versa. This suggests that the epoch of formation may play a role in the formation of massive ETGs rather than the mass itself. The possible general scheme in which normal ~1.5 ETGs are descendants of high-z compact spheroids enlarged through subsequent dry mergers is not compatible with the current models which predict a number of dry mergers two orders of magnitude lower than the one needed. Moreover, we do not find evidence supporting a dependence of the compactness of galaxies on their redshift of assembly. Finally, we propose a simple scheme of formation and assembly of the stellar mass of ETGs based on dissipative gas-rich merger which can qualitatively account for the co-existence of normal and compact ETGs observed at ~1.5 in spite of the same stellar mass, the lack of normal ETGs with high z_form and the absence of correlation between compactness, stellar mass and formation redshift.

astro-ph.CO↗
arXiv2010

Ionisation Models for Nano-Scale Simulation

Two theory-driven models of electron ionization cross sections, the Binary-Encounter-Bethe model and the Deutsch-Märk model, have been design and implemented; they are intended to extend the simulation capabilities of the Geant4 toolkit. The resulting values, along with the cross sections included in the EEDL data library, have been compared to an extensive set of experimental data, covering more than 50 elements over the whole periodic table.

physics.comp-ph↗
arXiv2010

Design, development and validation of electron ionisation models for nano-scale simulation

Two theory-driven models of electron ionization cross sections, the Binary-Encounter-Bethe model and the Deutsch-Märk model, have been design and implemented; they are intended to extend the simulation capabilities of the Geant4 toolkit. The resulting values, along with the cross sections included in the EEDL data library, have been compared to an extensive set of experimental data, covering more than 50 elements over the whole periodic table.

physics.comp-ph↗
arXiv2010

New Physics Data Libraries for Monte Carlo Transport

The role of data libraries as a collaborative tool across Monte Carlo codes is discussed. Some new contributions in this domain are presented; they concern a data library of proton and alpha ionization cross sections, the development in progress of a data library of electron ionization cross sections and proposed improvements to the EADL (Evaluated Atomic Data Library), the latter resulting from an extensive data validation process.

physics.comp-ph↗