Cosmic Shear and Biasing

The correlation between cosmic shear, as measured by the image distortion of high-redshift galaxies, and the number counts of foreground galaxies is calculated. For a given power spectrum of the cosmic density fluctuations, this correlation is proportional to the bias factor, which can thus be directly measured. Perhaps of more immediate interest, this correlation provides a first-order measure of cosmic shear and is therefore easier to observe than quadratic measures hitherto proposed. Analytic approximations show that the expected signal-to-noise ratio of the correlation is large, so that a significant detection is possible with a moderate amount of data; in particular, it is predicted that the ongoing ESO Imaging Survey (EIS) will be able to detect this correlation on scales of ~10' at a 3 σ level, and with higher significance on smaller angular scales.