Morphological Classification of the LocalI‐ andK‐Band Galaxy Sample

Abstract

In this paper, we report on the morphologically segregated I- and K-band number counts at bright magnitudes from a wide-field deep survey. This survey has been carried out with the first large mosaic CCD camera (8192 × 8192) on the University of Hawaii 88 inch (2.24 m) telescope and the Canada-France-Hawaii Telescope (CFHT). This instrument allows us to take deep wide-field galaxy images efficiently. We have been able to obtain I-band number counts in a wide range from I = 12.5 to I = 22.5, and to classify the morphologies of galaxies down to I = 18.5. Morphologically segregated number counts for ellipticals, spirals, and irregulars are obtained for the first time with magnitudes brighter than I = 18.5. The morphological classifications correlate well with the galaxy colors. By modeling these number counts, we confirm that a no-evolution model can fit both K- and I-band number counts of ellipticals and spirals reasonably well, but the irregular/peculiar galaxies show a substantial excess at faint magnitudes over the no-evolution model. With the number counts at bright magnitudes, we further demonstrate that the rise in this excess begins by I = 20. This rise is consistent with a rapidly increasing star formation rate in low-luminosity galaxies at about z = 0.35.