The lack of star formation gradients in galaxy groups up to z~1.6
  In the local Universe, galaxy properties show a strong dependence on
environment. In cluster cores, early type galaxies dominate, whereas
star-forming galaxies are more and more common in the outskirts. At higher
redshifts and in somewhat less dense environments (e.g. galaxy groups), the
situation is less clear. One open issue is that of whether and how the star
formation rate (SFR) of galaxies in groups depends on the distance from the
centre of mass. To shed light on this topic, we have built a sample of X-ray
selected galaxy groups at 0<z<1.6 in various blank fields (ECDFS, COSMOS,
GOODS). We use a sample of spectroscopically confirmed group members with
stellar mass M >10^10.3 M_sun in order to have a high spectroscopic
completeness. As we use only spectroscopic redshifts, our results are not
affected by uncertainties due to projection effects. We use several SFR
indicators to link the star formation (SF) activity to the galaxy environment.
Taking advantage of the extremely deep mid-infrared Spitzer MIPS and
far-infrared Herschel PACS observations, we have an accurate, broad-band
measure of the SFR for the bulk of the star-forming galaxies. We use
multi-wavelength SED fitting techniques to estimate the stellar masses of all
objects and the SFR of the MIPS and PACS undetected galaxies. We analyse the
dependence of the SF activity, stellar mass and specific SFR on the
group-centric distance, up to z~1.6, for the first time. We do not find any
correlation between the mean SFR and group-centric distance at any redshift. We
do not observe any strong mass segregation either, in agreement with
predictions from simulations. Our results suggest that either groups have a
much smaller spread in accretion times with respect to the clusters and that
the relaxation time is longer than the group crossing time.
