Medium & High Resolution Spectral Synthesis of Stellar Populations
Left: Radial variation. The two lines in each plot refer to index values corrected to re/4 (solid line) and re/2 (dashed line). Right: Effect of environment. The solid line represents the entire sample, red diamonds only those objects in low density environments (1/r5 < 0.5) and green triangles only those in high density environments (1/r5 > 1.5). Values are differences with respect to those of the entire sample at σ= 200 kms-1
Medium-High resolution spectral synthesis of stellar populations has proven to be the most powerful tool for the analysis of the optical integrated light of galaxies. Narrow band absorption-lineindices are widely used since almost two decades (Brodie & Hanes 1986, Worthey et al. 1994, Bressan et al 1996, Annibali et al. 2007) to disentangle age and metallicity effects, given their negligible sensitivity to attenuation and accurate flux calibration. A particular point of concern in the study of integrated light of early type galaxies (ETGs) is that models based on synthetic atmospheres, that can account for arbitrary chemical composition, do not reproduce well the red giant stars that likely dominate these systems, while observed spectra of late giants do not cover the chemical pattern needed to fit observations. To cope with this difficulty, we are currently developing mixed models, i.e. based on both empirical and theoretical stellar libraries (Annibali et al. 2007). Results: We have modelled new narrow band indices (Lick system) of simple stellar population (SSP) models, accounting for the presence of α/Fe-enhancement (Annibali et al. 2007). The SSPs cover a wide range of ages (0.1-16 Gyr), metallicity (0.0004≤Z≤0.05), and [α/Fe] ratios (0-0.8). With these models we have analysed a limited sample of 70 field ETGs with high S/N spectra (Rampazzo et al. 2005, Annibali et al. 2006, 2007) and much larger volume-limited (0.005<z
We are also currently performing high resolution (2Å) spectral models of SSPs by combining the MILES empirical spectral library (Sanchez-Blazquez et al 2006) with theoretical atmosphere models (Bertone et al 2007 and NEXTGEN). The main purpose is to obtain an adequate reproduction of observed spectral features in the optical (see lower figure), which is out of reach with current theoretical atmosphere models and, at the same time, to cover a wide wavelength range, from the far UV to the FIR. The latter requirement is mandatory for panchromatic studies of stellar populations in galaxies allowed by recent ground and space facilities.
People: F. Annibali, A. Bressan, M. Clemens, R. Rampazzo
Collaboration: M. Chavez, E. Bertone (INAOE, Mex), W. W. Zeilinger (IAU, Wien), L. Danese (SISSA)
Recent Publications: Clemens et al. (2009), MNRAS 392,35; Annibali et al. (2007), A&A 463,455