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| - Colours, luminosity functions and counts of galaxies
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| - Standard models for deep galaxy counts are based on luminosity functions (LFs) that have a relatively flat faint end (α ∼ − 1.0). Galaxy counts in the B band exceed the prediction of such models from a factor of 2 to more than a factor of 5, forcing the introduction of strong luminosity and/or density evolution. Recently Marzke, Huchra & Geller, using the CfA redshift survey sample, found that the number of galaxies in the range −16 < MZw< − 13 exceeds the extrapolation of a flat faint-end LF by a factor of 2. Here we show that this steep LF substantially contributes to justify the observed blue galaxy counts without invoking strong luminosity and/or density evolution. Furthermore we show that taking into account the variation of the B − K colour as a function of the morphological types and assuming a mean value 〈B − K〉 < 2.5 for dwarf galaxies, we reproduce well also the observed K-band deep galaxy counts. This assumption is supported by the strong correlation we found between B − K colour of galaxies and their infrared absolute magnitude: galaxies become bluer with decreasing luminosity.
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