2015MNRAS.453..214D

We present a multiwavelength study of a newly discovered compact group (CG), SDSS J0959+1259, based data from XMM-Newton, Sloan Digital Sky Survey (SDSS) and the Calar Alto optical imager BUSCA. With a maximum velocity offset of 500 km/s, a mean redshift of 0.035, and a mean spatial extension of 480 kpc, this CG is exceptional in having the highest concentration of nuclear activity in the local Universe, established with a sensitivity limit LX > 4x10⁴⁰ erg/s in 2-10 keV band and R-band magnitude MR < -19. The group is composed of two type-2 Seyferts, one type-1 Seyfert, two LINERs and three star-forming galaxies. Given the high X-ray luminosity of LINERs which reaches ∼ 10⁴¹ erg/s, it is likely that they are also accretion driven, bringing the number of active nuclei in this group to five out of eight (AGN fraction of 60 per cent). The distorted shape of one member of the CG suggests that strong interactions are taking place among its galaxies through tidal forces. Therefore, this system represents a case study for physical mechanisms that trigger nuclear activity and star formation in CGs.