Correlations between the size and the stellar population properties of quiescent galaxies

We aim to state new constraints on the mechanisms that can drive the growth in size of massive galaxies through the stellar population properties of quiescent galaxies within the stellar mass-size plane. Our sample is composed of ∼830 quiescent galaxies down to I ≤ 23 from the ALHAMBRA survey with reliable size measurements up to redshift z∼1. The stellar content (age, metallicity, and extinction) of galaxies is retrieved via SED-fitting and composite stellar population models using the multi-band photometry of ALHAMBRA and the code MUFFIT. At fixed stellar mass, our results point out that more compact quiescent galaxies are older, more rich in metals, and slightly less reddened by dust than their more extended counterparts since z∼1. We state that the regions of constant stellar population parameters in the stellar mass-size plane are well reproduced by lines of the form M_\star ∝ r_c^{0.5-0.6}, which are also compatible with constant values of velocity dispersion using spectroscopic quiescent galaxies from SDSS. This result points out that the driver of stellar populations would be partly related to dynamical properties of galaxies, as well as to stellar mass. Scenarios including mergers or the ``progenitor'' bias also agree with these results to explain the growth in size of quiescent galaxies.