Segregation effects in DEEP2 galaxy groups

Raquel S. Nascimento; André L. B. Ribeiro; Paulo A. A. Lopes

doi:10.1093/mnras/stw2321

paper

Segregation effects in DEEP2 galaxy groups

arXiv:1609.04352 · doi:10.1093/mnras/stw2321

Abstract

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 8 members within a radius of 4Mpc. 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( $z \leq 0.6$ ) and high( $z > 0.6$ ) redshift groups. Assuming that the color 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 $R < R_{200}$ in the low-z sample than in the high-z sample. Our analysis indicates statistical evidence of kinematic segregation, at the 99%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%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%c.l. From the comparison of blue/red and bright/faint fractions, and considering the approximate lookback timescale between the two samples ( $\sim$ 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 $z \sim 0.8$ to $z \sim 0.4$ .

13 pages, 12 figures, Accepted for publications in MNRAS

Segregation effects in DEEP2 galaxy groups

Abstract

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