Optical Spectra of Four Normal Galaxies
Large aperture spectra of four nearby normal galaxies spanning the Hubble Sequence: E4, Sa, Sc, Sm/Im. Notice the gradual change in overall stellar populations, and increase in emission line strength from early to late Hubble types.
Note: most ground-based optical spectra use 2-4 arcsec apertures which, for nearby galaxies, only includes the nuclear light. However, in this project Kennicutt used a 60 arcsec aperture to include nucleus, bulge, and disk light. One of his aims was to provide low-redshift templates to compare with the spectra of high-redshift galaxies, for which small apertures include the whole galaxy.
Source: Kennicutt 1998, ARAA, 38 189; Fig 1.
For more of Kennicutt's spectra, with DSS images for each galaxy, visit the U Washington site: [o-link]