2017MNRAS.464..183N

We investigate segregation phenomena in galaxy groups in the range of 0.2 < z < 1. We study a sample of groups selected from the 4th Data Release of the DEEP2 galaxy redshift survey. We used only groups with at least eight members within a radius of 4 Mpc. Outliers were removed with the shifting gapper techinque and, then, the virial properties were estimated for each group. The sample was divided into two stacked systems: low(z <= 0.6) and high (z > 0.6) redshift groups. Assuming that the colour index (U - B)₀ can be used as a proxy for the galaxy type, we found that the fraction of blue (star-forming) objects is higher in the high-z sample, with blue objects being dominant at M_B > -19.5 for both samples, and red objects being dominant at M_B < -19.5 only for the low-z sample. Also, the radial variation of the red fraction indicates that there are more red objects with R < R₂₀₀ in the low-z sample than in the high-z sample. Our analysis indicates statistical evidence of kinematic segregation, at the 99 per cent c.l., for the low-z sample: redder and brighter galaxies present lower velocity dispersions than bluer and fainter ones. We also find a weaker evidence for spatial segregation between red and blue objects, at the 70 per cent c.l. The analysis of the high-z sample reveals a different result: red and blue galaxies have velocity dispersion distributions not statistically distinct, although redder objects are more concentrated than the bluer ones at the 95 per cent c.l. From the comparison of blue/red and bright/faint fractions, and considering the approximate lookback time-scale between the two samples (∼3 Gyr), our results are consistent with a scenario where bright red galaxies had time to reach energy equipartition, while faint blue/red galaxies in the outskirts infall to the inner parts of the groups, thus reducing spatial segregation from z ∼ 0.8 to z ∼ 0.4.