2,654 research outputs found
Cosmological formation and chemical evolution of an elliptical galaxy
No full textAims: We aim to study the effect of a cosmologically motivated gas infall law for the formation of a massive elliptical galaxy in order to understand its impact on the formation of spheroids.
Methods: We replace the empirical infall law of the model by Pipino & Matteucci with a cosmologically derived infall law for the formation of an elliptical galaxy. We compare our predictions with observations. We also compare the obtained results with those of Pipino & Matteucci.
Results: We computed models with and without galactic winds; we found that models without wind predict a too large current SNIa rate. In particular, the cosmological model produces a current SNIa value which is about ten times higher than the observed values. Moreover models without wind predict a high current SNII rate, too large even if compared with the recent GALEX data. The predicted SNII rate for the model with wind, on the other hand, is too low if compared with the star formation histories given by GALEX. The mean value for the [Mg/Fe] ratio in the dominant stellar population of the simulated galaxy, as predicted by the cosmological model, is too low if compared to observations. This is a very important result indicating that the cosmological infall law is in contradiction to the chemical evolution.
Conclusions: A cosmologically derived infall law for an elliptical galaxy cannot reproduce all the chemical constraints given by observations. The problem resides in the fact that the cosmologically derived infall law implies a slow gas accretion with a consequent star formation rate active for a long period. In this situation low [Mg/Fe] ratios are produced for the dominant stellar population in a typical elliptical, at variance with observations
Fusione nucleare: l’energia delle stelle
No full textIntervengono
Leonida Antonio Gizzi, Istituto Nazionale di Ottica del CNR, sede di Pisa, associato INFN
Francesca Matteucci, docente di Astrofisica, Università di Trieste, accademico dei Lincei
Modera
Stefano Sandrelli, divulgatore e astrofisico, INAF-Osservatorio Astronomico di Brera
E = mc2, diceva Einstein. Ovvero: la materia si può trasformare in energia e viceversa. Ma se per produrre energia bastasse solo un po’ di materia, non avremmo risolto ogni possibile crisi energetica? In che modo si realizza questa trasformazione in Natura? E a che punto è arrivata la ricerca per riprodurre questo fenomeno in laboratorio? Cercheremo di capirne di più, dialogando con Francesca Matteucci, docente di astrofisica presso l’Università di Trieste e Leonida Gizzi, Direttore del Laboratorio Laser Intensi dell’Istituto Nazionale di Ottica del CNR di Pisa. E scopriremo che le risposte a queste domande non solo ci illuminano sul nostro futuro prossimo, ma anche sul nostro passato remoto e sulla nostra origine cosmica
Chemical evolution of galaxies
No full textThe term “chemical evolution of galaxies” refers to the evolution of abundances of chemical species in galaxies, which is due to nuclear processes occurring in stars and to gas flows into and out of galaxies. This book deals with the chemical evolution of galaxies of all morphological types (ellipticals, spirals and irregulars) and stresses the importance of the star formation histories in determining the properties of stellar populations in different galaxies. The topic is approached in a didactical and logical manner via galaxy evolution models which are compared with observational results obtained in the last two decades: The reader is given an introduction to the concept of chemical abundances and learns about the main stellar populations in our Galaxy as well as about the classification of galaxy types and their main observables. In the core of the book, the construction and solution of chemical evolution models are discussed in detail, followed by descriptions and interpretations of observations of the chemical evolution of the Milky Way, spheroidal galaxies, irregular galaxies and of cosmic chemical evolution. The aim of this book is to provide an introduction to students as well as to amend our present ideas in research; the book also summarizes the efforts made by authors in the past several years in order to further future research in the field
Chemical evolution of dwarf irregular and blue compact galaxies
No full textAims: Dwarf irregular and blue compact galaxies are very interesting objects since they are relatively simple and unevolved. We aim at deriving the formation and chemical evolution history of late-type dwarf galaxies and at comparing it with DLA systems.
Methods: We present new models for the chemical evolution of these galaxies by assuming different regimes of star formation (bursting and continuous) and different kinds of galactic winds (normal and metal-enhanced). The dark-to-baryonic mass ratio is assumed to be ten in these models. The chemical evolution model follows the evolution of He, C, N, O, S, Si, and Fe in detail. We have collected the most recent data on these galaxies and compared them with our model's results. We also collected data for damped-Lyman α-systems.
Results: Our results show that in order to reproduce all the properties of these galaxies, including the spread in the chemical abundances, the star formation should have proceeded in bursts and the number of bursts should be not more than ten in each galaxy, and that metal-enhanced galactic winds are required. The presence of metal-enhanced galactic winds can by itself reproduce the observed mass-metallicity relation, although an increasing efficiency of star formation and/or number and/or duration of bursts can also reproduce such a relation equally well.
Conclusions: Metal-enhanced winds, together with an increasing amount of star formation with galactic mass, are required to explain most of the properties of these galaxies. Normal galactic winds, where all the gas is lost at the same rate, do not reproduce the features of these galaxies. On the other hand, a global increase in the amount of star formation (increasing efficiency, number of bursts, or burst duration) with galactic mass is able by itself to reproduce the mass-metallicity relation even without winds, but without metal-enhanced winds is not able to explain many other constraints. We suggest that these galaxies should have suffered a different number of bursts varying from two to ten and that the efficiency of metal-enhanced winds should not have been too high (λmw ~ 1). We predict for these galaxies present-time type Ia SN rates from 0.00084 and 0.0023 per century. Finally, by comparing the abundance patterns of damped Lyman-α objects with our models, we conclude that they are very likely the progenitors of the current dwarf irregulars
A simple and general method for solving detailed chemical evolution with delayed production of iron and other chemical elements
No full textWe present a theoretical method for solving the chemical evolution of galaxies by assuming an instantaneous recycling approximation for chemical elements restored by massive stars and the delay time distribution formalism for delayed chemical enrichment by Type Ia Supernovae. The galaxy gas mass assembly history, together with the assumed stellar yields and initial mass function, represents the starting point of this method. We derive a simple and general equation, which closely relates the Laplace transforms of the galaxy gas accretion history and star formation history, which can be used to simplify the problem of retrieving these quantities in the galaxy evolution models assuming a linear Schmidt–Kennicutt law. We find that – once the galaxy star formation history has been reconstructed from our assumptions – the differential equation for the evolution of the chemical element X can be suitably solved with classical methods. We apply our model to reproduce the [O/Fe] and [Si/Fe] versus [Fe/H] chemical abundance patterns as observed at the solar neighbourhood by assuming a decaying exponential infall rate of gas and different delay time distributions for Type Ia Supernovae; we also explore the effect of assuming a non-linear Schmidt–Kennicutt law, with the index of the power law being k = 1.4. Although approximate, we conclude that our model with the single-degenerate scenario for Type Ia Supernovae provides the best agreement with the observed set of data. Our method can be used by other complementary galaxy stellar population synthesis models to predict also the chemical evolution of galaxies
The effects of Population III stars on the cemical and photometrical evolution of ellipticals
No full textThe predicted metallicity distribution of stars in dwarf spheroidal galaxies
No full textWe predict the metallicity distribution of stars and the ageÐmetallicity relation for six dwarfspheroidal (dSph) galaxies of the Local Group by means of a chemical evolution model thatis able to reproduce several observed abundance ratios, and the present-day total mass andgas content of these galaxies. The model adopts up-to-date nucleosynthesis and takes into
account the role played by supernovae of different types (II, Ia) allowing us to follow indetail the evolution of several chemical elements (H, D, He, C, N, O, Mg, Si, S, Ca and
Fe). Each galaxy model is specified by the prescriptions of the star formation rate and by
the galactic wind effciency chosen to reproduce the main features of these galaxies. These
quantities are constrained by the star formation histories of the galaxies as inferred by the
observed colourÐmagnitude diagrams (CMD). The main conclusions are: (i) Þve of the six
dSph galaxies are characterized by very low star formation efÞciencies ( 0.005Ð0.5 Gyr1)
with only Sagittarius having a higher one ( 1.0 Ð5.0 Gyr1); (ii) the wind rate is proportional
to the star formation rate and the wind efÞciency is high for all galaxies, in the range i
6Ð15; (iii) a high wind efÞciency is required in order to reproduce the abundance ratios and
the present-day gas mass of the galaxies; (iv) the predicted ageÐmetallicity relation implies
that the stars of the dSphs reach solar metallicities in a time-scale of the order of 2Ð6 Gyr,
depending on the particular galaxy; (v) the metallicity distributions of stars in dSphs exhibit
a peak around [Fe/H] 1.8 to 1.5 dex, with the exception of Sagittarius, which shows a
peak around [Fe/H] 0.8 dex; (iv) the predicted metallicity distributions of stars suggest
that the majority of stars in dSphs are formed in a range of metallicity in agreement with the
one of the observed stars
Galactic chemical evolution - Abundance gradients of individual elements
No full textModels for chemical evolution of the Galaxy are presented, where the most recent ideas on stellar nucleosynthesis and supernova (SN) progenitors are taken into account. It is assumed that the disk forms by accretion of primordial material coming from outside with a time-scale which is a function of the galactocentric distance. The possibility of forming the disk out of enriched halo gas is also studied in a simple way. The evolution of the abundances of several single elements is predicted as well as that of gas mass, SN rates and star formation rate, both in the solar neighborhood and in the whole disk, under different assumptions for the star formation rate. Abundance gradients along the galactic disk are well reproduced and a possible interpretation for the differences among gradients of different elements is given in terms of nucleosynthesis and stellar lifetimes. This interpretation can represent a key for understanding gradients also in external galaxies. In particular, a natural explanation is suggested for the positive gradient of S/O, found in M101 and M33
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