Star Formation in Galaxies

Executive Summary

For an comprehensive view of the star formation the study of the interstellar medium is needed. In our group it is carried out including its different phases, from the distribution of cold gas, both molecular and atomic, the warm component of the HII regions, till the very hot gas responsible for the X-ray emission. For the warm ionized component, members of this group are international experts in the physical properties and chemical composition of the HII regions from different points of view: for individual regions, detailed studies of the internal structure can be carried out using mainly spectroscopy in the optical and ultraviolet ranges. Emission line fluxes can be measured and electron temperatures, density and chemical composition are derived. In addition, useful properties of the ionizing population can be inferred from these studies, incorporating theoretical photo-ionization modeling of the regions using photo-ionization codes. The study of the diffuse component of the ISM can be carried out using spectroscopy of emission and absorption lines (mainly in the ultraviolet), whereas for the study of the less dense and very hot component of the IGM we make use of measurements of X ray emission. Both measurements are provided by satellites.



Detailed Research

The formation and evolution of massive stars in external galaxies is one of the earlier and continued lines of research in our group. This research is carried out from different and complementary points of views, ranging from the detailed study of particular giant star forming regions (in their full luminosity range, including the most luminous galactic violent stellar bursts), and including statistical studies of the large scale distribution of star formation in whole individual galaxies and in clusters (see below). These studies of single star forming regions are carried out both from observations (using spectroscopic and narrow and broad band photometric techniques) and from models (by developing stellar population synthesis codes). The main star formation parameters are related to the mode of star formation (burst or continuous), the evolutionary phase of the stellar population (its age or age distribution), and the stellar mass distribution (the shape and limits of the mass function). The studies of the large scale distribution of the star forming regions include the spatial distribution in the parent galaxy (and its dependence on the galaxy structural parameters), and their use as tracers of the structure of the galaxy (i.e. the distribution of the stellar populations and of the overall kinematics of the galaxy). Furthermore, we study the star formation from the viewpoint of the radiative, mechanical and chemical feedback of the massive stars with their surrounding interstellar medium, both at the local scale of single star forming regions and at the overall galaxy wide scale of violent nuclear starbursts. These studies encompass a wide range of spatial resolutions, from the resolution of single stars in local group galaxies, to the study of the integrated radiation from the most distant galaxies (see below). One of the approaches that we follow is to study the systematic statistical effects introduced in the study of the integrated radiation from stellar populations as a function of the statistical sampling.

The main goal is to determine the parameters that characterize the processes of intense star formation in different environments. We intend to improve our knowledge of the mechanisms that trigger these starbursts, their impact on the environment, and to determine their feedback cycle. We will focus on two different but complementary approaches: one based on the study of star forming galaxies, selected by their Halpha luminosities. We have compiled already a large sample of Halpha emitting galaxies. We plan to use the large catalogues to obtain information about the influence of the environment on the spatial distribution and the intensity of the recent star formation in cluster galaxies. In addition, we will study the chemical abundances of star forming region, to investigate how environmental processes act on cluster galaxies compared to field galaxies. We will complement this study with the application of multiwavelength spectral energy distribution fitting techniques and synthetic models of galaxy evolution. This, together with IR data provided by new technological facilities (VLT, Spitzer, Herschel, JWST), will shed light on the star formation histories of cluster galaxies of different masses. This will increase our knowledge of the formation and evolution of galaxies in clusters.

For both approaches we will focus also on the study of the metallicity and photo-chemical evolution of galaxies, to investigate how environmental processes influence the evolution of galaxies located in groups and clusters with respect to field galaxies.

Scientific objectives

  1. To carry out an extensive analysis of the new populations of star-forming galaxies in clusters discovered in our previous work. The statistical analysis of the sample will be performed together with the derivation of the local variance of their star formation properties, their total luminosity functions and the impact of environment on the possible triggering mechanisms of star formation.
  2. To perform a multifrequency characterization of star forming galaxies in clusters with data covering a broad spectral range from the UV to the FIR. To fit synthetic SED models, taking into account the effects of dust, to investigate the star formation histories of these galaxies.
  3. To study the influence of the environment on the chemical evolution of star forming galaxies. The observed properties (from spatially resolved optical spectra) compared to theoretical models will shed light on the mechanisms that alter the metallicity of cluster galaxies.