The nature of extremely red galaxies in the local universe
  We investigate the nature of extremely red galaxies (ERGs), objects whose
colours are redder than those found in the red sequence present in
colour-magnitude diagrams of galaxies. We selected from the Sloan Digital Sky
Survey Data Release 7 a volume-limited sample of such galaxies in the redshift
interval 0.010 < z < 0.030, brighter than M_r = -17.8 (magnitudes dereddened,
corrected for the Milky Way extinction) and with (g-r) colours larger than
those of galaxies in the red sequence. This sample contains 416 ERGs, which
were classified visually. Our classification was cross-checked with other
classifications available in the literature. We found from our visual
classification that the majority of objects in our sample are edge-on spirals
(73%). Other spirals correspond to 13%, whereas elliptical galaxies comprise
only 11% of the objects. After comparing the morphological mix and the
distributions of H\alpha/H\beta and axial ratios of ERGs and objects in the red
sequence, we suggest that dust, more than stellar population effects, is the
driver of the red colours found in these extremely red galaxies.
