We examine the faint-end slope of the rest-frame V-band luminosity function ( LF ) , with respect to galaxy spectral type , of field galaxies with redshift z < 0.5 , using a sample of 80,820 galaxies with photometric redshifts in the Cosmic Evolution Survey ( COSMOS ) field .
For all galaxy spectral types combined , the LF slope ranges from -1.24 to -1.12 , from the lowest redshift bin to the highest .
In the lowest redshift bin ( 0.02 < z < 0.1 ) , where the magnitude limit is M _ { V } \lesssim - 13 , the slope ranges from \alpha \sim - 1.1 for galaxies with early-type spectral energy distributions ( SEDs ) , to \alpha \sim - 1.9 for galaxies with low-extinction starburst SEDs .
In each galaxy SED category ( Ell , Sbc , Scd/Irr , and starburst ) , the faint-end slopes grow shallower with increasing redshift ; in the highest redshift bin ( 0.4 < z < 0.5 ) , \alpha \sim - 0.5 and -1.3 for early-types and starbursts respectively .
The steepness of \alpha at lower redshift could be qualitatively explained by large numbers of faint dwarf galaxies , perhaps of low surface brightness , which are not detected at higher redshifts .