arXiv subjects

Cesare Chiosi

Publications and source records attributed to Cesare Chiosi.

At least 19 recordsLinked to original sources

arXiv2026

A simple yet effective model of galaxy mergers

In the context of the hierarchical formation of galaxies, we investigated the role played by mergers in shaping the scale relations of galaxies, that is the projections of their Fundamental Plane onto the \IeRe, \IeSig, \MRa\ and \Lsig\ planes. To this aim, we developed a simple model of multiple dry mergers among galaxies by suitably combing the formalism and properties of the so-called infall models of galaxy formation and evolution with the formalism of the scalar Virial Theorem. In this context, we mimicked the hierarchical formation of galaxies and generated simple models of galaxies undergoing a number mergers in the course of their evolution. The results are used to interpret the large scale simulations and the companion scale relations from observational and theoretical perspectives. The aim is to interpret the observational data of the MANGA and WINGS samples and the results of theoretical detailed numerical cosmo-hydro-dynamical simulations, such as Illustris-TNG100. In this context, we derived the above scale relations for our theoretical models and compared them with the observational counterparts from the MANGA and WINGS database, (and indirectly the large scale simulations of Illustris-TNG100). The multiple dry merging mechanism is able to explain all the main characteristics of the observed scale relations of galaxies, such as slopes, scatters, curvatures and zones of exclusion. The distribution of galaxies in these planes is continuously changing across time because of the merging activity and other physical processes, such as star formation, quenching, energy feedback, and so forth.} The precision of the present simple merger theory is comparable with that obtained by the modern cosmo-hydro-dynamical simulations, with the advantage of providing a rapid exploratory response on the consequences engendered by different physical effects.

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arXiv2026

The scaling relations of galaxies with different morphology: comparison among WINGS, MANGA and Illustris data samples

We present a panoramic view of several scaling relations (ScRs) of galaxies of different morphology. The ScRs are obtained from the data of two large surveys (WINGS and MANGA). We analyze the distribution (parameterized by the percent over the total) of galaxies in each region of the diagnostic planes that are set up by means of suitable physical quantities. In addition to this, we discuss the origin of the differences observed in the ScRs between the two samples. Finally, we compare the observational data with the theoretical ones taken from two subsets of the Illustris large scale simulations (TNG50 and TNG100) and we discuss how the comparison should be performed for a correct statistical answer.

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arXiv2025

The role of dry mergers in shaping the scaling relations of galaxies

In the context of the hierarchical formation of galaxies, we investigated the role played by mergers in shaping the scaling relations of galaxies, that is the projections of their Fundamental Plane onto the Ie-Re, Ie-Sigma, Ms-Re and L-Sigma planes. To this aim, based on the scalar Virial Theorem, we developed a simple theory of multiple dry mergers to read both the large scale simulations and the companion scaling relations. The aim was to compare the results of this approach with the observational data and with two of the most recent and detailed numerical cosmo-hydro-dynamical simulations, that is Illustris-TNG and EAGLE (Evolution and Assembly of GaLaxies and their Environments). We derived the above scaling relations for the galaxies of the MaNGA (Mapping Nearby Galaxies at APO) and WINGS (Wide-field Imaging of Nearby Galaxy-Clusters Survey) databases and compared them with the observational data, the numerical simulations, and the results of our simple theory of dry mergers. The multiple dry merging mechanism is able to explain all the main characteristics of the observed scaling relations of galaxies, such as slopes, scatters, curvatures and zones of exclusion. The distribution of galaxies in these planes is continuously changing across time because of the merging activity and other physical processes, such as star formation, quenching, energy feedback, and so forth. The simple merger theory presented here yields the correct distribution of galaxies in the main scaling relations at all cosmic epochs. The precision is comparable with that obtained by the modern cosmo-hydro-dynamical simulations, with the advantage of providing a rapid exploratory response on the consequences engendered by different physical effects.

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arXiv2024

Galaxies' properties in the Fundamental Plane across time

Context: Using the Illustris-1 and IllustrisTNG-100 simulations we investigate the properties of the Fundamental Plane (FP), that is the correlation between the effective radius Re, the effective surface intensity Ie and the central stellar velocity dispersion (sigma) of galaxies, at different cosmic epochs. Aims: Our aim is to study the properties of galaxies in the FP and its projections across time, adopting samples covering different intervals of mass. We would like to demonstrate that the position of a galaxy in the FP space strongly depends on its degree of evolution, that might be represented by the beta and L'_0 parameters entering the L-sigma^beta(t) law. Methods: Starting from the comparison of the basic relations among the structural parameters of artificial and real galaxies at low redshift, we obtain the fit of the FP and its coefficients at different cosmic epochs for samples of different mass limits. Then, we analyze the dependence of the galaxy position in the FP space as a function of the beta parameter and the star formation rate (SFR). Results: We find that: 1) the coefficients of the FP change with the mass range of the galaxy sample; 2) the low luminous and less massive galaxies do not share the same FP of the bright massive galaxies; 3) the scatter around the fitted FP is quite small at any epoch and increases when the mass interval increases; 4) the distribution of galaxies in the FP space strongly depends on the $β$ values (i.e. on the degree of virialization and the star formation rate). Conclusions: The FP is a complex surface that is well approximated by a plane only when galaxies share similar masses and condition of virialization.

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arXiv2023

The scaling relations of galaxies back in time: the road toward virialization

Context. The structural scaling relations (SSRs) of galaxies, i.e. the observed correlations between effective radius, effective surface intensity and velocity dispersion, are important tools for understanding how evolution proceeds. Aims. In this paper we aim to demonstrate that the evolution of the SSRs back in time is governed by the combination of the virial theorem (VT) and the relation $L=L'_0 σ^{β(t)}$, where the parameters $β$ and $L'_0$ vary with time and from galaxy to galaxy. Methods. Using the WINGS database for the galaxies at redshift $z=0$ and the Illustris-1 and Illustris-TNG databases of artificial galaxies, for the galaxies up to redshift $z=4$, we analyse the SSRs back in time and, by means of simple algebraic expressions for $L'_0$ and $β$ (functions of time and other physical quantities), we derive the expected paths followed by galaxies in the various SSRs toward the distributions observed at $z=0$. Results. The distribution of galaxies in the SSRs is ultimately related to the evolution in luminosity and velocity dispersion that are empirically mirrored by the $L=L'_0 σ^{β(t)}$ law. Furthermore, the $β$ parameter works as a thermometer of the virialization of a galaxy. This parameter can assume either positive or negative values, and its absolute value attains high values when the galaxy is close to the virial condition, while it tends to zero when the galaxy is far from it. Conclusions. As the SSRs change with time, the method we are proposing allows us to decipher the temporal evolution of galaxies.

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arXiv2023

A new framework for understanding the evolution of early-type galaxies

We have recently suggested that the combination of the scalar virial theorem ($M_s \sim R_e σ^2$) and the $L=L'_0 σ^β(t)$ law, with L'_0 and $β$ changing from galaxy to galaxy (and with time), can provide a new set of equations valid for investigating the evolution of early-type galaxies (ETGs) (Donofrio & Chiosi, 2022). These equations are able to account for the tilt of the Fundamental Plane (FP) and to explain the observed distributions of ETGs in all its projections. In this paper we analyze the advantages offered by those equations, derive the $β$ and $L'_0$ parameters for real and simulated galaxies, and demonstrate that, according to the value of $β$, galaxies can move only along some permitted directions in the FP projections. Then, we show that simple galaxy models that grow in mass by infall of gas and form stars with a star formation rate depending on the stellar velocity dispersion nicely reproduce the observed distributions of ETGs in the FP projections and yield $β$s that agree with the measured ones. We derive the mutual relationships among the stellar mass, effective radius, velocity dispersion, and luminosity of ETGs as a function of $β$ and calculate the coefficients of the FP. Then, using the simple infall models, we show that the star formation history of ETGs is compatible with the $σ$-dependent star formation rate, and that both positive and negative values of $β$ are possible in a standard theory of galaxy evolution. The parameter $β(t)$ offers a new view of the evolution of ETGs. In brief, i) it gives a coherent interpretation of the FP and of the motions of galaxies in its projections; ii) it is the fingerprint of their evolution; iii) it measures the degree of virialization of ETGs; iv) and finally it allows us to infer their evolution in the near past.

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arXiv2021

The Fundamental Plane in the hierarchical context

Context. The Fundamental Plane (FP) relation and the distribution of early-type galaxies (ETGs) in the FP projections, cannot be easily explained in the hierarchical framework, where galaxies grow up by merging and star formation episodes. Aims. We want to show here that both the FP and its projections arise naturally from the combination of the Virial Theorem (VT) and a new time-dependent relation, describing how luminosity and stellar velocity dispersion change during galaxy evolution. This relation has the form of the Faber-Jackson (FJ) relation but a different physical meaning: the new relation is $L = L'_0(t) σ^{β(t)}$, where its coefficients $L'_0$ and $β$ are time-dependent and can vary considerably from object to object, at variance with those obtained from the fit of the $L - σ$ plane. Methods. We derive the equations of the FP and its projections as a function of $β$ and $L'_0$, by combining the VT and the $L = L'_0(t) σ^{β(t)}$ law. Then, from their combination we derive the expression of the FP as a function of $β$ and the solutions for $β$ and $L'_0$. Results. We demonstrate that the observed properties of ETGs in the FP and its projections can be understood in terms of variations of $β$ and $L'_0$. These two parameters encrypt the history of galaxy evolution across the cosmic epochs and determine the future aspect of the FP and its projections. Using the solutions found for $β$ and $L'_0$ for each galaxy at the present epoch, we derive the coefficients of the FP (and FJ relation) and show that, the values of the coefficients coming form the fit, obtained in the literature, originate from the average of the single FP coefficients derived for each galaxy. In addition, we show that the variations of beta naturally explain the curvature observed in the FP projections and the correct position of the Zone of Exclusion.

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arXiv2021

Past, present and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei

We review the properties of the established Scaling Relations (SRs) of galaxies and active galactic nuclei (AGN), focusing on their origin and expected evolution back in time, providing a short history of the most important progresses obtained up to now and discussing the possible future studies. We also try to connect the observed SRs with the physical mechanisms behind them, examining to what extent current models reproduce the observational data. The emerging picture clarifies the complexity intrinsic to the galaxy formation and evolution process as well as the basic uncertainties still affecting our knowledge of the AGN phenomenon. At the same time, however, it suggests that the detailed analysis of the SRs can profitably contribute to our understanding of galaxies and AGN.

astro-ph.GA↗

arXiv2020

A tomography of the $\log(\langle I\rangle_e)-\log(R_e)$ plane

Context. We present a reanalysis of the distribution of galaxies in the $\log(\langle I\rangle_e)-\log(R_e)$ plane under a new theoretical perspective. Aims. Using the data of the WINGS database and those of the Illustris simulation we will demonstrate that the origin of the observed distribution in this parameter space can be understood only by accepting a new interpretation of the $\log(L)$-$\log(σ)$ relation Methods. We simulate the distribution of galaxies in the $\log(\langle I\rangle_e)-\log(R_e)$ plane starting from the new $L=L_0'σ^β$ relation proposed by D'Onofrio et al. (2020) and we discuss the physical mechanisms that are hidden in this empirical law. Results. The artificial distribution obtained assuming that beta spans either positive and negative values and that $L'_0$ changes with $β$, is perfectly superposed to the observational data, once it is postulated that the Zone of Exclusion (ZoE) is the limit of virialized and quenched objects. Conclusions. We have demonstrated that the distribution of galaxies in the $\log(\langle I\rangle_e)-\log(R_e)$ plane is not linked to the peculiar light profiles of the galaxies of different luminosity, but originate from the mass assembly history of galaxies, made of merging, star formation events, star evolution and quenching of the stellar population.

astro-ph.GA↗

arXiv2020

The parallelism between galaxy clusters and early-type galaxies: II. Clues on the origin of the scaling relations

Context. This is the second work dedicated to the observed parallelism between galaxy clusters and early-type galaxies. The focus is on the distribution of these systems in the scaling relations (SRs) observed when effective radii, effective surface brightness, total luminosities and velocity dispersions are mutually correlated. Aims. Using the data of the Illustris simulation we try to speculate on the origin of the observed SRs. Methods. We compare the observational SRs extracted from the database of the WIde-field Nearby Galaxy-cluster Survey (WINGS) with the relevant parameters coming from the Illustris simulations. Then we use the simulated data at different redshift to infer the evolution of the SRs. Results. The comparison demonstrate that galaxy clusters (GCs) at z~0 follow the same log(L)-log(sigma) relation of early-type galaxies (ETGs) and that both in the log(Ie)-log(Re) and log(Re)-log(M*) planes the distribution of GCs is along the sequence defined by the brightest and massive early-type galaxies (BCGs). The Illustris simulation reproduces the tails of the massive galaxies visible both in the log(Ie)-log(Re) and log(Re)-log(M*) planes, but fail to give the correct estimate of the effective radii of the dwarf galaxies that appear too large and those of GCs that are too small. The evolution of the SRs up to z=4 permits to reveal the complex evolutionary paths of galaxies in the SRs and indicate that the line marking the Zone of Exclusion (ZoE), visible both in the log(Ie)-log(Re) and log(Re)-log(M*) planes, is the trend followed by virialized and passively evolving systems. Conclusions. We speculate that the observed SRs originate from the intersection of the virial theorem and a relation L=L_0 x sigma^beta where the luminosities depend on the star formation history.

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arXiv2020

The parallelism between galaxy clusters and early-type galaxies: III. The Mass-Radius Relationship

Context. This is the third study of a series dedicated to the observed parallelism of properties between Galaxy Clusters and Groups(GCGs) and early-type galaxies (ETGs). Aims. Here we investigate the physical origin of the Mass-Radius Relation (MRR). Methods. Having collected literature data on masses and radii for objects going from Globular Clusters (GCs) to ETGs and GCGs, we set up the MR-plane and compare the observed distribution with the MRR predicted by theoretical models both for the monolithic and hierarchical scenarios. Results. We argue that the distributions of stellar systems in the MR-plane is due to complementary mechanisms: (i) on one hand, as shown in paper II, the relation of the virial equilibrium does intersect with a relation that provides the total luminosity as a function of the star formation history; (ii) on the other hand, the locus predicted for the collapse of systems should be convolved with the statistical expectation for the maximum mass of the halos at each comsic epoch. This second aspect provides a natural boundary limit explaining either the curved distribution observed in the MR-plane and the existence of a zone of avoidance. Conclusions. The distribution of stellar systems in the MR-plane is the result of two combined evolution, that of the stellar component and that of the halo component.

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arXiv2019

On the pressure equilibrium and timescales in the scale free convection theory

Convection is one of the fundamental energy transport processes in physics and astrophysics, and its description is central to allstellar models. In the context of stellar astrophysics, the mixing length theory is the most successful approximation to handle theconvection zones inside the stars because of its simplicity and rapidity. The price to pay is the mixing length parameter that isintroduced to derive the velocity of convective elements, the temperature gradients in the convective regions and finally the energy flux carried by convection. The mixing length is a free parameter that needs to be calibrated on observational data. Pasetto et al. (2014) have proposed a new theory that determines all the properties of convective regions and the convective transport of energy with no need for a free parameter. In this study, we aim to discuss the merits of this new approach and the limits of its applicability in comparison with the mixing length theory. We present an analytical and numerical investigation of the main physical assumptions made by Pasetto et al. (2014) and compare them with the counterparts of the mixing length theory. We also present here the homogeneous isotropic limit of the Pasetto et al. (2014) theory and discuss some numerical examples to address and clarify misconceptions often associated with the new formalism.

astro-ph.SR↗

arXiv2019

The parallelism between galaxy clusters and early-type galaxies: I. The light and mass profiles

We have analyzed the parallelism between the properties of galaxy clusters and early-type galaxies (ETGs) by looking at the similarity between their light profiles. We find that the equivalent luminosity profiles of all these systems in the \vfilt\ band, once normalized to the effective radius \re\ and shifted in surface brightness, can be fitted by the Sérsic's law \Sers\ and superposed with a small scatter ($\le0.3$ mag). By grouping objects in different classes of luminosity, the average profile of each class slightly deviates from the other only in the inner and outer regions (outside $0.1\leq r/R_e\leq 3$), but the range of values of $n$ remains ample for the members of each class, indicating that objects with similar luminosity have quite different shapes. The "Illustris" simulation reproduces quite well the luminosity profiles of ETGs, with the exception of in the inner and outer regions where feedback from supernovae and active galactic nuclei, wet and dry mergers, are at work. The total mass and luminosity of galaxy clusters as well as their light profiles are not well reproduced. By exploiting simulations we have followed the variation of the effective half-light and half-mass radius of ETGs up to $z=0.8$, noting that progenitors are not necessarily smaller in size than current objects. We have also analyzed the projected dark+baryonic and dark-only mass profiles discovering that after a normalization to the half-mass radius, they can be well superposed and fitted by the Sérsic's law.

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arXiv2018

Cosmological interpretation of the color-magnitude diagrams of galaxy clusters

We investigate the color-magnitude diagram (CMD) of cluster galaxies in the hierarchical $Λ$-CDM cosmological scenario using both single stellar populations and simple galaxy models. First, we analyze the effect of bursts and mergers and companion chemical pollution and rejuvenation of the stellar content on the integrated light emitted by galaxies. The dispersion of the galaxy magnitudes and colors on the $M_V-(B-V)$ plane is mainly due to mixing of ages and metallicities of the stellar populations, with mergers weighting more than bursts of similar mass fractions. The analysis is made using the Monte-Carlo technique applied to ideal model galaxies reduced to single stellar populations with galaxy-size mass to evaluate mass, age and metallicity of each object. We show that separately determining the contributions by bursts and mergers leads to a better understanding of observed properties of CMD of cluster galaxies. Then we repeat the analysis using suitable chemo-photometric models of galaxies whose mass is derived from the cosmological predictions of the galaxy content of typical clusters. Using the halo mass function and the Monte-Carlo technique, we derive the formation redshift of each galaxy and its photometric history. These are used to simulate the CMD of the cluster galaxies. The main conclusion is that most massive galaxies have acquired the red color they show today in very early epochs and remained the same ever since. The simulations nicely reproduce the Red Sequence, the Green Valley and the Blue Cloud, the three main regions of the CMD in which galaxies crowd.

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arXiv2017

Cosmic Star Formation: a simple model of the SFRD(z)

We investigate the evolution of the cosmic star formation rate density (SFRD) from redshift z=20 to z=0 and compare it with the observational one by Madau and Dickinson derived from recent compilations of UV and IR data. The theoretical SFRD(z) and its evolution are obtained using a simple model which folds together the star formation histories of prototype galaxies designed to represent real objects of different morphological type along the Hubble sequence and the hierarchical growing of structures under the action of gravity from small perturbations to large scale objects in Λ-CDM cosmogony, i.e. the number density of dark matter halos N(M,z). Although the overall model is very simple and easy to set up, it provides results that well mimic those obtained from large scale N-body simulations of great complexity. The simplicity of our approach allows us to test different assumptions for the star formation law in galaxies, the effects of energy feedback from stars to interstellar gas and the efficiency of galactic winds, and also the effect of N(M,z). The result of our analysis is that in the framework of the hierarchical assembly of galaxies the so-called time-delayed star formation under plain assumptions mainly for the energy feedback and galactic winds can reproduce the observational SFRD(z).

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arXiv2016

On the origin of the Fundamental Plane and Faber-Jackson relations: consequences for the star formation problem

The aim of this work is to show that the origin of the Fundamental Plane (FP) relation for early-type galaxies (ETGs) can be traced back to the existence of a fine-tuning between the average star formation rate $ $ of galaxies and their structural and dynamical characteristics. To get such result it is necessary to imagine the existence of two distinct "virtual planes" for each galaxy in the $\log(R_e)-\log(I_e)-\log(σ)$ space. The first one (named Virial Plane VP) represents the total galaxy mass using the scalar Virial Theorem and the mass-to-light ratio $M/L$, while the second plane comes from an expression of the total galaxy luminosity as a function of the mean star formation rate $ $ and the velocity dispersion $σ$, through a relation $L=L'_0 σ^{-2}$ (named here pseudo-Faber-Jackson (PFJ)) which is a mathematical convenient way for expressing the independency of light from the virial equilibrium. Its validity can be connected to the mutual correlation $L\simσ\sqrt{ }$ observed for all ETGs. A posteriori it is possible to see that this approach permits to explain the observed properties of the FP (tilt and scatter) and the Zone of Exclusions (ZOE) visible in the FP projections. Furthermore, the link between the properties of the FP and the SFR of galaxies provides a new idea of the star formation, as a phenomenon driven by the initial conditions of proto-galaxies and regulated across the whole cosmic history by the variation of the main galaxy parameters (mass, luminosity, structural shape and velocity dispersion).

astro-ph.GA↗

arXiv2014

Modelling galaxy spectra in presence of interstellar dust-III. From nearby galaxies to the distant Universe

Improving upon the standard evolutionary population synthesis (EPS) technique, we present spectrophotometric models of galaxies whose morphology goes from spherical structures to discs, properly accounting for the effect of dust in the interstellar medium (ISM). These models enclose three main physical components: the diffuse ISM composed by gas and dust, the complexes of molecular clouds (MCs) where active star formation occurs and the stars of any age and chemical composition. These models are based on robust evolutionary chemical models that provide the total amount of gas and stars present at any age and that are adjusted in order to match the gross properties of galaxies of different morphological type. We have employed the results for the properties of the ISM presented in Piovan, Tantalo & Chiosi (2006a) and the single stellar populations calculated by Cassarà et al. (2013) to derive the spectral energy distributions (SEDs) of galaxies going from pure bulge to discs passing through a number of composite systems with different combinations of the two components. The first part of the paper is devoted to recall the technical details of the method and the basic relations driving the interaction between the physical components of the galaxy. Then, the main parameters are examined and their effects on the spectral energy distribution of three prototype galaxies are highlighted. We conclude analyzing the capability of our galaxy models in reproducing the SEDs of real galaxies in the Local Universe and as a function of redshift.

astro-ph.GA↗

arXiv2012

The Origin of the Mass-Radius Relation of Early-Type Galaxies

Early-type galaxies obey a narrow relation traced by their stellar content between the mass and size (Mass- Radius relation). The wealth of recently acquired observational data essentially confirms the classical relations found by Burstein, Bender, Faber, and Nolthenius, i.e. log(R_1/2) \propto log(Ms)\simeq 0.54 for high mass galaxies and log(R_1/2) \propto log(Ms) \simeq 0.3 for dwarf systems (shallower slope), where R_1/2 and Ms are the half-light radius and total mass in stars, respectively. Why do galaxies follow these characteristic trends? What can they tell us about the process of galaxy formation? We investigate the mechanisms which concur to shape the Mass-Radius relation, in order to cast light on the physical origin of its slope, its tightness, and its zero point. We perform a theoretical analysis, and couple it with the results of numerical hydrodynamical (NB-TSPH) simulations of galaxy formation, and with a simulation of the Mass-Radius plane itself. We propose a novel interpretation of the Mass-Radius relation, which we claim to be the result of two complementary mechanisms: on one hand, the result of local physical processes, which fixes the ratio between masses and radii of individual objects; on the other hand, the action of cosmological global, statistical principles, which shape the distribution of objects in the plane. We reproduce the Mass-Radius relation with a simple numerical technique based on this view.

astro-ph.CO↗