1,721,139 research outputs found
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
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
Photochemical evolution of elliptical galaxies - II. The impact of merging-induced starbursts
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