Michele Cappellari

Abstract:

The SAURON integral-field survey reveals that small (∼0.1,Re) kinematically decoupled cores (KDCs) in early-type galaxies are increasingly young toward the center and are typically found in fast-rotating galaxies, while large KDCs (∼0.5 Re) have homogeneously old stars and are present in non-rotating galaxies (McDermid et al. 2006). GALEX UV imaging further allows the direct identification of regions of recent star formation (0.5 Gyr). In NGC 2974 for example, young stars are identified in the center and an outer ring Jeong et al. 2006). Nuclear and inner ionised-gas rings (Sarzi et al. 2006) then suggest that current star formation is bar-driven. The CO detection rate of SAURON early-type galaxies is 40% (Combes et al. in prep.). Synthesis imaging reveals that it is generally contained in a well-ordered central disk, both in galaxies with a (young) central stellar disk (e.g. NGC 4459, NGC 4526) or a (young) KDC (e.g. NGC 3032, NGC 4150) (Young et al. in prep.). CO also traces well the young stellar populations and ionised gas distribution and kinematics, but in KDCs not always the stellar kinematics Emsellem et al. 2004; Sarzi et al. 2006; Kuntschner et al. 2006). © 2007 International Astronomical Union.

Abstract:

In this poster contribution, we present results from high spatial resolution integral-field spectroscopy of elliptical (E) and lenticular (S0) galaxies from the SAURON representative survey, obtained with the OASIS and GMOS spectrographs. These seeing-limited observations explore the central 10'10 (typically one kiloparsec diameter) regions of these galaxies using a spatial sampling four times higher than SAURON (027 vs. 094 spatial elements), resulting in almost a factor of two improvement in the median PSF. These data allow accurate study of the central regions to complement the large-scale view provided by SAURON. We derive the stellar and gas kinematics, stellar absorption-line strengths and nebular emission-line strengths for our sample, and derive maps of the luminosity-weighted stellar age, metallicity and abundance ratio via stellar population models. From these data we find a wealth of structures either not seen or poorly resolved in the SAURON data, including a number of kinematically-decoupled cores (KDCs) in the centres of some galaxies. We compare the intrinsic size and luminosity-weighted stellar age of all the visible KDCs in the full SAURON sample, and find two types of components: kiloparsec-scale KDCs, which are older than 8 Gyr, and are found in galaxies with little net rotation; and compact KDCs, which have intrinsic diameters of less than a few hundred parsec, show a range of stellar ages from 0.5 - 15 Gyr (with 5/6 younger than 5 Gyr), are found exclusively in fast-rotating galaxies, and are close to counter-rotating around the same axis as their host. Of the 7 galaxies in the SAURON sample with integrated luminosity-weighted ages less than 5 Gyr, 5 show such compact KDCs, suggesting a link between counter-rotation and recent star-formation. We show that this may be partly due to a combination of small sample size at young ages, and an observational bias, since young KDCs are easier to detect than their older and/or co-rot ating counterparts.

Abstract:

We investigate the well-known correlations between the dynamical rnass-to-light ratio M/L and other global observables of elliptical (E) arid lenticular (S0) galaxies. We construct two-integral Jeans and three-integral Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field stellar kinematics to about one effective (half-light) radius Re. The comparison of the dynamical M/L with the (M/L)pop inferred from the analysis of the stellar population, indicates that dark matter in early-type galaxies contributes ∼30% of the total mass inside one Re, in agreement with previous studies, with significant variations from galaxy to galaxy. Our results suggest a variation in M/L at constant (M/L)pop, which seems to be linked to the galaxy dynamics. We speculate that fast rotating galaxies have lower dark matter fractions than the slow rotating and generally more massive ones. © EAS, EDP Sciences 2006.