Stellar populations of galaxies

In the general case of unresolved stellar populations, we wish to constrain the star formation of galaxies using their integrated light spectra. For this we use multi-wavelength observations and models.

Such an analysis involves two clearly separate steps:

• The modelling of the spectral properties of the stellar populations. The team is involved in the development of the high resolution SSP models PEGASE-HR, and in developping an understanding of the IR evolution of SSPs.

  

  synthetic single stellar populations of various ages and solar metallicity obtained with PEGASE-HR. Normalisation is arbitrary, and the age increases from top to bottom.

• The interpretation of observed galaxy spectra through comparison to the above models. It is natural to assume that any galactic spectrum is the sum of several elementary populations born in subsequent bursts. The decomposition and age-dating of an observed population into its main components is a very delicate problem, subject to various sources or error. The team contributes to the development of panspectral analysis techniques and the understanding of systematic uncertainties in the reconstruction of the star formation history of galaxies by such means. See also the STECMAP page .

  

  Fit of the nuclear star cluster of NGC300 by a linear combination of PEGASE-HR SSPs. Black: data, red: fit, green: flux recalibration. The quality of data, models and the fit allows to constrain the age of this cluster to about 2 Gyr.