Pure Luminosity Evolution models for faint field galaxy samples

We have examined a set of pure luminosity evolution (PLE) models in order to explore up to what extent the rapidly increasing observational constraints from faint galaxy samples can be understood in this simple framework. We find that a PLE model, in which galaxies evolve mildly in time even in the rest frame UV, can reproduce most of the observed properties of faint galaxies assuming an open ($\Omega\sim0$) universe. In particular, such a model is able to fit reasonably well the number counts in the $U,~b_j,~r_f,~I$, and $K$ bands, as well as the colour and redshift distributions derived from most of the existing samples. The most significant discrepancy between the predictions of this model and the data is the $z$ distribution of faint $K$-selected galaxies. Significantly worse fits are obtained with PLE models for the theoretically attractive value of $\Omega = 1$, although a simple number luminosity evolution model with a significant amount of merger events fits the data also in this cosmology.Comment: 15 pages, plain tex (insert encapsulated postscript figures), plus an extra figure Fig3c.ps and the tex-macro mn.tex uuencoded, gzipp'ed tar file -- accepted by MNRA

The ultraviolet spectra of early type galaxies

The average spectral energy distribution for a sample of bright elliptical galaxies is presented in the range lambda lambda 2000 to 3200 A. Spectral synthesis indicates that elliptical galaxies are most likely older than 9 Gyrs. The ultraviolet flux is consistent with a population of red horizontal branch stars, as those present in metal rich globular clusters. Data for distant first ranked cluster galaxies show indications of spectral evolution

Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies

We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large-Magellanic-Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young ($\sim10$-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.Comment: 27 pages, 21 figures. Accepted for publication in MNRA

Physical properties of 6dF dwarf galaxies

Spectral synthesis is basically the decomposition of an observed spectrum in terms of the superposition of a base of simple stellar populations of various ages and metallicities, producing as output the star formation and chemical histories of a galaxy, its extinction and velocity dispersion. The STARLIGHT code provides one of the most powerful spectral synthesis tools presently available. We have applied this code to the entire Six-Degree-Field Survey (6dF) sample of nearby star-forming galaxies, selecting dwarf galaxy candidates with the goal of: (1) deriving the age and metallicity of their stellar populations and (2) creating a database with the physical properties of our sample galaxies together with the FITS files of pure emission line spectra (i.e. the observed spectra after subtraction of the best-fitting synthetic stellar spectrum). Our results yield a good qualitative and quantitative agreement with previous studies based on the Sloan Digital Sky Survey (SDSS). However, an advantage of 6dF spectra is that they are taken within a twice as large fiber aperture, much reducing aperture effects in studies of nearby dwarf galaxies.Comment: To appear in JENAM Symposium "Dwarf Galaxies: Keys to Galaxy Formation and Evolution", P. Papaderos, S. Recchi, G. Hensler (eds.). Lisbon, September 2010, Springer Verlag, in pres

Validation of stellar population and kinematical analysis of galaxies

3D spectroscopy produces hundreds of spectra from which maps of the characteristics of stellar populations (age-metallicity) and internal kinematics of galaxies can be derived. We carried on simulations to assess the reliability of inversion methods and to define the requirements for future observations. We quantify the biases and show that to minimize the errors on the kinematics, age and metallicity (in a given observing time) the size of the spatial elements and the spectral dispersion should be chosen to obtain an instrumental velocity dispersion comparable to the physical dispersion.Comment: 5 pages, 3 figures, extended version of a poster proceeding to appear in "Science Perspectives for 3D Spectroscopy", eds. M. Kissler-Patig, M. M. Roth and J. R. Walsh, ESO Astrophysics Symposia. (The two last pages with figures are not in the conference proceedings.