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Abstract: We use a sample of about 48,000 SDSS early-type galaxies to show that oldergalaxies have smaller half-light radii re and larger velocity dispersions sigmathan younger ones of the same stellar mass Mstar. We use the age-correctedluminosity Lcorr as a proxy for Mstar to minimize biases: below Lcorr~1e11Lsun, galaxies with age ~11 Gyrs have re smaller by 40% and sigma larger by25%, compared to galaxies that are ~4 Gyrs younger. The sizes and velocitydispersions of more luminous galaxies vary by less than 15%, whatever theirage, a challenge for current galaxy formation models. A closer check revealsthat the lowering in the dispersion is caused by older galaxies that show asignificant departure from the re-Lcorr and sigma-Lcorr relations at highLcorr. Such features might find an explanation in models where more massivegalaxies undergo more minor mergers than less massive galaxies at late times,thus causing a break in the homology. In terms of the Fundamental Plane ofearly-type galaxies, the data indicate that all galaxies show a significant andsimilar increase in the dynamical-to-stellar mass ratio with increasing mass,independent of their age. However, older galaxies have smaller Mdyn-Mstarratios than objects which formed more recently. These findings may suggest thatlower mass galaxies and, at fixed stellar mass, higher redshift galaxies,formed from gas-richer progenitors, thus underwent more dissipation andcontraction.



Author: Francesco Shankar 1, Mariangela Bernardi 2 1-MPA, 2-UPENN

Source: https://arxiv.org/







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