Where are Compact Groups in the local Universe?

DIAZ GIMENEZ, EUGENIA; ZANDIVAREZ, ARIEL

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2015 vol. 578

0004-6361

Aims. The purpose of this work is to perform an statistical analysis on the location of compact groups in the universe from observational and semianalytical points of view. Methods. We used the velocity filtered compact group sample extracted from the Two Micron All Sky Survey for our analysis. We also used a new sample of galaxy groups identified in the 2M++ galaxy redshift catalogue as tracers of the large scale structure. We defined a procedure to search in redshift space for those compact groups that can be considered embedded in other overdense systems and applied this criterion for several possible combinations of dierent compact and galaxy group subsamples. We also performed similar analyses for simulated compact and galaxy groups identified in a 2M++ mock galaxy catalogue constructed from the Millennium Run Simulation I plus a semianalytical model of galaxy formation. Results. We observed that only 27% of the compact groups can be considered embedded in larger overdense systems,i.e, most of the compact groups are more likely to be isolated systems. The embedded compact groups show statistically smaller sizes and brighter surface brightnesses than non-embedded systems. No evidence was found that embedded compact groups are more likely to inhabit galaxy groups with a given virial mass or with a particular dynamical state. We found very similar results when the analysis is performed using mock compact and galaxy groups. From the semianalytical studies, we predicted that 70% of the embedded compact groups are likely to be 3D physically dense systems. Finally, real space information allowed us to reveal the bimodal behaviour of the distribution of 3D minimum distances between compact and galaxy groups. Conclusions. The location of compact groups should be carefully taken into account when comparing properties of galaxies in a priori dierent environments.