IDENTIFYING DYNAMICALLY YOUNG GALAXY GROUPS VIA WIDE-ANGLE TAIL GALAXIES: A CASE STUDY IN THE COSMOS FIELD AT z = 0.53

We present an analysis of a wide-angle tail (WAT) radio galaxy located in a galaxy group in the COSMOS field at a redshift of z = 0.53 (hereafter CWAT-02). We find that the host galaxy of CWAT-02 is the brightest galaxy in the group although it does not coincide with the center of mass of the system. Estimating (1) the velocity of CWAT-02, relative to the intra-cluster medium, and (2) the line-of-sight peculiar velocity of CWAT-02's host galaxy, relative to the average velocity of the group, we find that both values are higher than those expected for a dominant galaxy in a relaxed system. This suggests that CWAT-02's host group is dynamically young and likely in the process of an ongoing group merger. Our results are consistent with previous findings showing that the presence of a WAT galaxy in a galaxy group or cluster can be used as an indicator of dynamically young non-relaxed systems. Taking the unrelaxed state of CWAT-02's host group into account, we discuss the impact of radio-active galactic nucleus (AGN) heating from CWAT-02 onto its environment, in the context of the missing baryon problem in galaxy groups. Our analysis strengthens recent results suggesting that radio-AGN heating may be powerful enough to expel baryons from galaxy groups.