November 14, 2003
The goal of this investigation is to reconstruct the cosmic star formation rate density history from local observations and in doing so to gain insight into how galaxies might have formed and evolved. A new chemical evolution model is described which accounts for the formation of globular clusters as well as the accompanying field stars. When this model is used in conjunction with the observed age metallicity relations for the clusters and with input which allows for the form...
January 25, 2011
The integrated galactic initial mass function (IGIMF) is computed from the combination of the stellar initial mass function (IMF) and the embedded cluster mass function, described by a power law with index beta. The result of the combination is a time-varying IMF which depends on the star formation rate. We applied the IGIMF formalism to a chemical evolution model for the solar neighbourhood and compared the results obtained by assuming three possible values for beta with the...
June 12, 1998
Recently, there has been great progress toward observationally determining the mean star formation history of the universe. When accurately known, the cosmic star formation rate could provide much information about Galactic evolution, if the Milky Way's star formation rate is representative of the average cosmic star formation history. A simple hypothesis is that our local star formation rate is proportional to the cosmic mean. In addition, to specify a star formation history...
July 24, 2007
We study the evolution of 82302 star-forming (SF) galaxies from the SDSS. Our main goals are to explore new ways of handling star formation histories (SFH) obtained with our publicly available spectral synthesis code STARLIGHT, and apply them to investigate how SFHs vary as a function of nebular metallicity (Zneb). Our main results are: (1) A conventional correlation analysis shows how global properties such as luminosity, mass, dust content, mean stellar metallicity and mean...
August 30, 1999
The abundance gradients and the radial gas profile of the Galactic disc are analysed by means of a model for the chemical evolution of galaxies. As one of the major uncertainties in models for galaxy evolution is the star formation (SF) process, various SF laws are considered,to assess the response of model predictions to the different assumptions. Only some SF laws are successful in reproducing the metallicity gradient, and only if combined with a suitable infall timescale i...
February 23, 2018
In this thesis, the field star Initial Mass Function (IMF) and chemical evolution parameters for the Milky Way (MW) are derived using a forward modelling technique in combination with Bayesian statistics. Starting from a local MM disc model, observations of stellar samples in the Solar Neighbourhood are synthesised and compared to the corresponding volume-complete observational samples of Hipparcos stars. The resulting IMF, derived from observations in the range from 0.5 to 8...
May 11, 2004
We present a large and updated stellar evolution database for low-, intermediate- and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite stellar populations using population synthesis techniques. The stellar mass range is between \sim0.5Mo and 10Mo with a fine mass spacing. The metallicity [Fe/H] comprises 10 values ranging from -2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction r...
April 14, 2003
In this review I will describe a number of recent advances in extragalactic astronomy. First of all I will describe our current best estimates of the star formation history of the Universe. Then I will describe measurements of local galaxies and their stellar populations, concentrating on measurements of the luminosity functions and stellar population compositions of the different kinds of galaxies. Finally, I will investigate the relationship between these two sets of result...
February 2, 1999
We present results on the analysis of background field stars found in HST WFPC2 observations of six of the old globular clusters of the Large Magellanic Cloud. Treated as contaminants by the globular cluster analysts, we produce V-I,V color-magnitude diagrams of the field stars and use them to explore the LMC's star formation history. The photometry approaches V~26, well below the turnoff of an ancient ~14 Gyr LMC population of stars. We use a maximum-likelihood technique to ...
October 5, 1999
The large sample of main sequence stars with Hipparcos parallaxes and estimates of the radial velocity has been used to study the relations among kinematics, age and heavy element content for the solar neighbourhood. The samples with V> -30 km $\rm s^{-1}$, although including stars as old as 10^10 yr, have a very young component (age $\simgt$ 10^7 yr), and have a metallicity close to the solar one. Most of the stars with space velocity component V < -40 km $\rm s^{-1}$ have a...