Strong Clustering of Faint Galaxies at Small Angular Scales

Abstract

The 2-point angular correlation function of galaxies, \wt, has been computed on equatorial fields observed with the CTIO 4m prime focus, within a total area of 2.31 deg$^2$. In the magnitude range $19\le m_R \le 21.5$, corresponding to $<z>\approx 0.35$, we find an excess of power in \wt at scales $2''\leθ\le6''$ over what would be expected from an extrapolation of \wt measured at larger $θ$. The significance of this excess is $\approx 5σ$. At larger scales, $6''< θ\le 24''$, the amplitude of \wt is 1.6 times smaller than the standard no evolutionary model. At these scales there is remarkable agreement between the present data and Infante \& Pritchet (1995). At large angular scales ($6''< θ\le 24''$) the data is best described by a model where clustering evolution in $ξ(r,z)$ has taken place. Strong luminosity evolution cannot be ruled out with the present data. At smaller scales, $2''\le θ\le 6''$, our data are formally fit by models where $ε=-2.4 (Ω=0.2, r_o=5.1h^{-1}$Mpc) or $r_o = 7.3h^{-1}$Mpc $(Ω=0.2, ε=0)$. If the mean redshift of our sample is 0.35 then our data show a clear detection of the scale ($\approx 19h^{-1}kpc$) where the clustering evolution approaches a highly non linear regime, i.e., $ε\le 0$. The rate at which galaxies merge has been computed. If this rate is proportional to $(1+z)^m$, then $m=2.2 \pm 0.5$.

10 pages, LaTeX text, 2 Postscript figures, To appear in ApJ Lett