Large-scale structure in the ELAIS S1 survey

We present an analysis of the two-point angular correlation function of The European Large-Area Infrared Space Observatory (ELAIS) S1 survey. The survey covers 4 deg(2) and contains 462 sources detected at 15 mum to a 5 flux limit of 0.45 mJy. Using the 329 extragalactic sources not repeated in different observations, we detect a significant clustering signal; the resulting angular correlation function can be fitted by a power law w (theta)=Atheta(1-gamma) with A=0.014+/-0.005 and gamma=2.04+/-0.18. Using the observed redshift distribution of the objects (from spectroscopic and photometric redshifts), we invert Limber's equation and deduce a spatial correlation length r(0)=4.3(-0.7)(+0.4) h(-1) Mpc. This is smaller than that obtained from optical surveys but it is in agreement with results from IRAS. This extends to higher redshift the observational evidence that infrared selected surveys show smaller correlation lengths (i.e. reduced clustering amplitudes) than optical surveys.