In this paper we explore the clustering properties and the environment of the Extremely Red Objects ( EROs ; I - K > 4 mag ) detected in a \approx 180 arcmin ^ { 2 } deep ( Ks \approx 20 mag ) Ks -band survey of a region within the Phoenix Deep Survey , an on-going multiwavelength program aiming to investigate the nature and the evolution of faint radio sources .
Using our complete sample of 289 EROs brighter than Ks = 20 mag we estimate a statistically significant ( \approx 3.7 \sigma ) angular correlation function signal with amplitude A _ { w } = 8.7 ^ { +2.1 } _ { -1.7 } \times 10 ^ { -3 } ( assuming w ( \theta ) = A _ { w } \theta ^ { -0.8 } , with \theta in deg ) , consistent with earlier work based on smaller samples .
This amplitude suggests a clustering length in the range r _ { o } = 12 - 17 h ^ { -1 } Mpc , implying that EROs trace regions of enhanced density .
Using a novel method we further explore the association of EROs with galaxy overdensities by smoothing the K -band galaxy distribution using the matched filter algorithm of Postman et al .
( 1996 ) and then cross-correlating the resulting density maps with the ERO positions .
Our analysis provides direct evidence that EROs are associated with overdensities at redshifts z \gtrsim 1 .
We also exploit the deep radio 1.4 GHz data ( limiting flux 60 \mu Jy ) available to explore the association of EROs and faint radio sources and whether the two populations trace similar large scale structures .
Cross-correlation of the two samples ( after excluding 17 EROs with radio counterparts ) gives a 2 \sigma signal only for the sub-sample of high- z radio sources ( z > 0.6 ) .
Although the statistics are poor this suggests that it is the high- z radio sub-sample that traces similar structures with EROs .