Scientific project

The evolution of galaxies is a complex process which depends on the history of stellar populations, gas, dust, and on the interactions between galaxies and their environment. Understanding the formation of stars and galaxies implies detailed studies of their chemistry and dynamics. High performance observing tools used by astronomers are:

• spectroscopy at high and intermediate resolutions (chemistry and history of stellar populations),

• 3D spectroscopy (dynamics),

• high quality imagery (morphology)

• multi-wavelength photometry (radiative processes, dust and star formation).

Comparison of local galaxies properties with those of the more distant Universe (up to z ~ 1.5) allows to explore the period during which the major part of stars have been formed. Fundamental questions still remain unanswered:

• How did spiral galaxies form ?

• What is the origin of the Hubble's diagram which describes the morphology of local galaxies ?

To answer these questions, we will investigate the evolution of the star formation rate (SFR), from distant galaxies (z ~ 1.5) to the Local Universe and will try to constrain the processes of dynamical evolution which lead to the morphology and internal kinematics of the nearby galaxies. During the last years, several galaxy evolution studies pointed out that understanding the properties of distant galaxies requires reference samples of the Local Universe built with the same selection criteria.

This is why our project aims at associating two multi-parametric and multi-wavelength databases : the first one HyperLeda, is already operational and public, the second one in development, will deal with the data produced by the guaranteed time observations obtained at the fiber-fed multi-object GIRAFFE spectrograph.

The GIRAFFE database will first gather the whole of the 30,000 spectra of stars and galaxies obtained during 35 nights of the GIRAFFE guaranteed time observation, and install the 3D spectroscopy analysis tools. A "Large program" has been proposed for the VLT to determine the 3D velocity fields of 400 massive galaxies with z between 0.25 and 0.9, establish the evolution of the mass to luminosity ratio, and check the galaxy coalescence hypothesis. Several elements are required for the development of the MIGALE database:

• multi-parametric measurements of nearby galaxy samples
• similar measurements at larger distances
• specific tools allowing comparison of measurements taken at various distances; they should allow to separate physical evolution effects from spatial resolution, bandwidth shifts and selection bias effects.
• diagnostic tools for tests of different evolution scenarii.

We will elaborate these tools taking care of inter-operability and re-usability for other projects.This approach will allow us to propose and build future instruments for the Virtual Observatory. They will be available for processing on the flight of data archives from various centres (CDS, ESO...).

Last update 1/22/2004