Constraints on the Ω M − Ω Λ - plane from Elliptical Galaxy Counts ?

Here we present a pilot study into whether elliptical galaxy counts alone, can place a useful constraint on the Ω M − Ω Λ-plane. The elliptical galaxy counts are drawn from three surveys: The Millennium Galaxy Catalogue (16 > B KP N O > 20), the B-band Parallel Survey (20 > B AB > 24) and the Hubble Deep Fields (23 > B AB > 28). The elliptical luminosity function used in the modeling was derived from a combination of the Millennium Galaxy Catalogue, the two-degree field galaxy redshift survey and the Sloan Digital Sky Survey (M E/S0 * = −19.90, φ E/S0 * = 0.0019 Mpc −3 and α E/S0 = −0.75 for H o = 75km/s/Mpc). We adopt a benchmark model and tweak the various input parameters by their uncertainties to determine the impact upon the counts. We find that if the faint-end slope of the elliptical galaxy luminosity function is known to ∆α < 0.1, then over the magnitude range 16 < B < 23 the counts depend most critically upon the cosmology, and can be used to place a weak constraint on the Ω M − Ω Λ-plane.