LBT-LUCIFER spectroscopy: kinematics of a compact early type galaxy at z\simeq1.4

Abstract: We present a high signal to noise (S/N$>$10) medium resolution (R=2000) LBT-LUCIFER spectrum of the early-type galaxy (ETG) S2F1-142 at $z\simeq1.4$. By means of the CaT line at $8662$ \AA, we measured its redshift $z=1.386\pm 0.001$ and we estimated its velocity dispersion $\sigma_{v}=340 ^{-60}_{+120}$ km/s. Its corresponding virial mass is 3.9$\times10^{11}$ M$\odot$, compatible with the stellar mass estimates obtained assuming Initial Mass Functions (IMFs) less dwarf rich than the Salpeter one. S2F1-142 is a compact galaxy with $R{e}$=3.1$\pm$0.2 kpc, i.e., an effective radius more than three times smaller than the average $R_{e}$ of early-type galaxies with the same mass in the local universe. At the same time, we found local and high redshift galaxies with a similar mass content and similar effective radius confirming that it is fully consistent with the already available measures of $R_{e}$ and $\sigma_{v}$ both in the local and in the distant universe. Considering the distribution of $R_{e}$ and $\sigma_{v}$ as a function of the stellar mass content of ETGs, both in the local and in the distant universe, we noticed that the measured velocity dispersions of the more compact galaxies are on average slightly lower than expected on the basis of their compactness and the virial theorem, suggesting that {\it i)} their dark matter content is lower than in the more diffuse galaxies and/or {\it ii)} their luminosity profiles are steeper than in the more diffuse galaxies and/or {\it iii)} their larger compactness is an apparent effect caused by the overestimate of their stellar mass content (due to bottom lighter IMF and/or systematic affecting the stellar mass estimates).