Low-density environments E galaxies in Mid IR Spectral synthesis of stellar populations ULIRG UV studies GRASIL

The history of galaxy evolution cannot be separated from the environment in which galaxies live. A large number of research programs developed at OAPd study Local galaxies. These programs are performed using various instrumentations (VLT, HST, Spitzer, Galex) and exploring different wavelength regions in order to obtain the fundamental photometric, structural and kinematic properties of the galaxies in different environments and at different epochs of evolution.

Observational and phenomenological work focuses on properties of nearby Early-Type galaxies (ETG). Elliptical galaxies are considered the fossil evidence of the galaxy evolution. At OAPd we attempt to understand the evolution of early-type galaxies studying their spectral energy distribution from the Far UV with GALEX, to the Optical and to Mid Infrared with Spitzer. We found that the downsizing effect is clearly evident from the differential average age (with ETGs in denser environments being slightly older). The chemical pattern is suggestive of feedback processes that render the star formation more prolonged and less efficient in the lower potential halos, independently from the environment. There may also be an effect of dry merging in the larger systems.

The X-ray properties of poor groups dominated by an E galaxy have been also studied looking for an evolutionary link between poor groups and "fossil" groups. Our studies suggest that X-ray luminous poor systems are probably already evolved groups. Typically they posses a large fraction of associated faint galaxies. In X-ray faint systems, the ETG may show fine structures (see e.g. Arp 227 system). We analysed shells galaxies as prototypical example of ETGs showing fine structures. We show that a recent accretion episode may explain the behaviour of their GALEX (FUV-NUV) color vs. optical-line strength indices. We suggest that X-ray faint groups, dominated by these ETGs, are probably still evolving groups where, among drivers of the secular evolution, accretion of faint companions plays a role.

At OAPD we are also studying the properties of interacting galaxies, of Ultra luminous galaxies (ULIRG) and of the cold (molecular) gas component in galaxies and in nearby poor groups. For ULIRG we derive ages, SFR timescale, evolutionary status optical depth and mass of dense molecular gas. The latter compare well with the masses obtained with HCN line luminosities and allow us to make predictions of other molecular lines that can be observed by next generation of millimetric telescopes in high redshift galaxies.

We have also developed the GRASIL model to compute the spectral evolution from radio to far UV of stellar systems, especially taking into account the effects of dust reprocessing.

Past studies