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 $2^{\prime \prime }\le \theta \le 6^{\prime \prime }$ over what would be expected from an extrapolation of \wt measured at larger $\theta$. The significance of this excess is $\approx 5\sigma$. At larger scales, $6^{\prime \prime }<\theta \le 24^{\prime \prime }$, 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 ($6^{\prime \prime }<\theta \le 24^{\prime \prime }$) the data is best described by a model where clustering evolution in $\xi (r,z)$ has taken place. Strong luminosity evolution cannot be ruled out with the present data. At smaller scales, $2^{\prime \prime }\le \theta \le 6^{\prime \prime }$, our data are formally fit by models where $\epsilon =-2.4(\Omega =0.2,r_o=5.1h^{-1}$Mpc) or $r_o=7.3h^{-1}$Mpc $(\Omega =0.2,\epsilon =0)$. 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., $\epsilon \le 0$. 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

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