1. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba The Spatial Clustering of Ultra Steep Spectrum radio sources and galaxies. Carlos G. Bornancini¹, Nelson D. Padilla², Diego García Lambas¹ ³ and Carlos De Breuck 4. ¹ Grupo de Investigaciones en Astronomía Teórica y Experimental, IATE, Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba. ² Department of Astronomy, Pontificia Universidad Católica, Santiago, Chile. ³ Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina. 4 European Southern Observatory, Garching, Germany.

2. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba Overview. Radio loud galaxies trace the upper envelope of the K luminosity in this K-z diagram (from De Breuck et al. 2002).

3. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba Finding high-z radio galaxies: USS Search Technique. k-correction effects on radio wavelenghts. Ultra Steep Spectrum criterion:,where

4. HzRGs: Brightest Cluster Galaxies Intrinsic clues HzRGs are amongst the most massive and presumably oldest ellipticals (Jarvis et al. 2001, De Breuck et al. 2002)HzRGs are amongst the most massive and presumably oldest ellipticals (Jarvis et al. 2001, De Breuck et al. 2002) Epoch of CDM galaxy assembly coincides with peak of QSO and RG activity (West 1994)Epoch of CDM galaxy assembly coincides with peak of QSO and RG activity (West 1994) HST observations of HzRGs show extreme clumpiness as expected for hierarchical formation of BCGs from LBGs (Pentericci et al. 1998, 1999)HST observations of HzRGs show extreme clumpiness as expected for hierarchical formation of BCGs from LBGs (Pentericci et al. 1998, 1999) Environmental clues RGs at 0 < z < 1 lie in moderately rich clusters (Hill & Lilly 1991, Best 2000, Best et al. 2003, Bornancini et al. 2003)RGs at 0 < z < 1 lie in moderately rich clusters (Hill & Lilly 1991, Best 2000, Best et al. 2003, Bornancini et al. 2003) Excess of companion galaxies ( emitters ) at very high redshifts (z= 2, 3, 4 and 5) (Kurk et al. 2000, Venemans et al. 2002, Miley et al. 2004)Excess of companion galaxies ( emitters ) at very high redshifts (z= 2, 3, 4 and 5) (Kurk et al. 2000, Venemans et al. 2002, Miley et al. 2004) Extreme radio rotation measures (Carilli et al. 1997, Pentericci et al. 2000)Extreme radio rotation measures (Carilli et al. 1997, Pentericci et al. 2000) Extended X-rays around 3CR sources up to z = 1.8 (Crawford et al. 1999, Fabian et al. 2001)Extended X-rays around 3CR sources up to z = 1.8 (Crawford et al. 1999, Fabian et al. 2001) Giant Lyá emitting gas halos around HzRGs (Pentericci et al. 1998, 1999)Giant Lyá emitting gas halos around HzRGs (Pentericci et al. 1998, 1999)

5. USS Sample (De Breuck et al. 2004). k-corrections taken from Mannucci et al. (2001) Correlations between SUMSS and NVSS radio catalogues. ( ) ( ) 27 USS fields with 0.5<z<1.7 obtained with IRIS2 (AAT), limiting magnitude =20. Cosmology: Absolute magnitudes

6. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba Spatial Clustering USS-galaxy Limber´s equation.

7. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba Modelling redshift distribution K20 Survey (Cimatti et al. 2002) (480 galaxies). ( ) ( )

8. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba Projected cross-correlation function 12 USS targets with spectroscopic redshift in the range 0.6<z<1.7. The error bars correspond to the 1 sigma uncertainty estimated using the Jackknife resampling technique (Efron 1982).

9. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba Dependence of galaxy clustering on luminosity of USSs. Extende USS sample with spectroscopic or expected redshift in the range 0.5<z<1.7. and For and For

10. Comparison with N-Body Simulations. Log(M)=12.35, 12.68, 13.2, 13.85 y 14.57 Simulation characteristics: GALFORM semi-analytic galaxies (Cole et al. 2000). Outputs at z=0,1 and 3. Cosmology: (, ) particles. Mass resolution Number of Dark matter haloes with masses greater than ranges from 400,000 at z=3 to 2,200,000 at z =0. The number of GALFORM galaxies ranges from 20,000,000 to 120,000,000 galaxies at z=3 and z=0 respectively.

11. Carlos Guillermo Bornancini IATE Group, Observatorio Astronómico Córdoba Conclusions. We have analyzed clustering properties of galaxies in the field of 0.5<z<1.7 Ultra Steep Spectrum (USS radio galaxies) selected from SUMSS and NVSS radio surveys We estimated the spatial clustering correlation lenght for galaxies in these fields, through the Limber equation. A comoving correlation lenght is derived and, for the USS sample with spectroscopic redshifts 0.6<z<1.7. We examine also how the correlation lenght depends on USS luminosity. The best fits correlation parameters increases from for to for. From our comparison with numerical simulations, we find that clusters of galaxies with masses have a cluster galaxy correlation amplitude comparable to those found between USS hosts and galaxies. Our results suggests that distant radio galaxies are excellent tracers of galaxy overdensities and may pinpoint the progenitors of present day rich clusters of galaxies.