The Clustering Properties of Lyman Break Galaxies at Redshiftz ∼ 3

We present a new measure of the angular two-point correlation function ofLyman-break galaxies (LBGs) at z~3, obtained from the variance of galaxy countsin 2-dimensional cells. By avoiding binning of the angular separations, thismethod is significantly less affected by shot noise than traditional measures,and allows for a more accurate determination of the correlation function. Weused a sample of about 1,000 galaxies with R<=25.5 extracted from the survey bySteidel and collaborators, and found the following results. At scales in therange 30<~theta<~100 arcsec, the angular correlation function w(theta) can beaccurately described as a power law with slope beta=0.50 +0.25-0.50(1 sigmarandom)-0.10(systematic), shallower than the measure presented by Giavalisco etal. However, the spatial correlation length, derived by Limber deprojection, isin very good agreement with the previous measures, confirming the strongspatial clustering of these sources. We discuss in detail the effects of bothrandom and systematic errors, in particular of the so called ``integralconstraint'' bias, to which we set a lower limit using numerical simulations.This suggests that the current samples do not yet provide a ``fairrepresentation'' of the large-scale distribution of LBGs at z~3. An intriguingresult of our analysis is that at angular separations smaller than theta<~30arcsec the correlation function seems to depart from the power-law fitted atlarger scales and become smaller. This feature is detected at the ~90 per centconfidence level and, if real, it can provide information on the number densityand spatial distribution of LBGs within their host halos as well as the sizeand the mass of the halos.Comment: 67 pages, 16 figures, accepted for publication in the Astrophysical Journa