Fakultäten » Mathematisch-naturwissenschaftliche Fakultät » Physik-Institut » Prof. Dr. Philippe Jetzer » Jetzer

Completed research project

Title / Titel Colour and stellar population gradients in galaxies (2010)
PDF Abstract (PDF, 14 KB)
Summary / Zusammenfassung We analyze the color gradients (CGs) of  50 000 nearby Sloan Digital Sky Survey (SDSS) galaxies estimated by their photometrical parameters (Sersic index, total magnitude, and e ective radius). From synthetic spectral models based on a simpli ed star formation recipe, we derive the mean spectral properties, and explain the observed radial trends of the color as gradients of the stellar population age and metallicity. Color gradients have been correlated with color, luminosity, size, velocity dispersion, and stellar mass. Distinct behaviours are found for early- and late-type galaxies (ETGs and LTGs), pointing 3 to slightly di erent physical processes at work in di erent morphological types and at di erent mass scales. In particular, the most massive ETGs (M? >1011M ) have shallow (even at) CGs in correspondence of shallow (negative) metallicity gradients. In the stellar mass range 1010:3��10:5 < M? < 1011M , the metallicity gradients reach their minimum of  ��0:5 dex��1. At M?  1010:3��10:5M , color and metallicity gradient slopes suddenly change. They turn out to anti-correlate with the mass, becoming highly positive at the very low masses, the transition from negative to positive occurring at M?  109��9:5M . These correlations are mirrored by similar trends of CGs with the e ective radius and the velocity dispersion. We have also found that age gradients anti-correlate with metallicity gradients, as predicted by hierarchical cosmological simulations for ETGs. On the other side, LTGs have gradients which systematically decrease with mass (and are always more negative than in ETGs), consistently with the expectation from gas infall and supernovae feedback scenarios. Metallicity is found to be the main driver of the trend of color gradients, especially for LTGs, but age gradients are not negligible and seem to play a signi cant role too. Owing to the large dataset, we have been able to highlight that older galaxies have systematically shallower age and metallicity gradients than younger ones. The emerging picture is qualitatively consistent with the predictions from hydrodynamical and chemo-dynamical simulations. In particular, our results for high-mass galaxies are in perfect agreement with predictions based on the merging scenario, while the evolution of LTGs and younger and less massive ETGs seems to be mainly driven by infall and supernovae feedback. The paper is in press in MNRAS [
Project leadership and contacts /
Projektleitung und Kontakte
Prof Philippeq Jetzer (Project Leader)  
Dr Crescenzo Tortora  
Funding source(s) /
Unterstützt durch
Universität Zürich (position pursuing an academic career), SNF (Personen- und Projektförderung)
Duration of Project / Projektdauer Jan 2010 to Dec 2010