ABSORPTION-LINE GRADIENTS IN THE BLUE AND NEAR-ULTRAVIOLET SPECTRA OF BRIGHT ELLIPTIC GALAXIES, AND IMPLICATIONS FOR STUDIES OF INTERMEDIATE REDSHIFT OBJECTS

Long-slit spectroscopic observations covering the wavelength interval 3000-4500 angstrom are used to investigate the radial behavior of atomic and molecular absorption features in the elliptical galaxies NGC 2693, NGC 3348, NGC 3379, NGC 4278, NGC 4486, and NGC 5044. There is a general tendency for metallic absorption features to weaken and continuum indices to flatten with increasing radius, in qualitative agreement with what is seen at visible wavelengths. All six galaxies contain significant (i.e., at the 3sigma level) gradients in the 4000 angstrom break. The rate of change of the 4000 angstrom break with radius, DELTA4000/DELTA log(r), is correlated with DELTAMg2/DELTA log(r), and the galaxy-to-galaxy scatter in DELTA4000/DELTA log(r) is larger than expected from experimental uncertainties alone. We compare the spectral indices of the various galaxies at the radius where Mg2 = 0.28, which corresponds roughly to [Fe/H] = 0, and find small galaxy-to-galaxy scatter. NGC 4486 is peculiar in that it has a very steep 4000 angstrom break gradient and relatively weak absorption features at Mg2 = 0.28, suggesting that the evolution of this galaxy has been very different from that of most other ellipticals. The data are also used to investigate aperture effects in spectroscopic observations of intermediate redshift galaxies. It is demonstrated that the failure to compensate for aperture effects in galaxies out to z = 0. 2 can introduce an apparent redshift dependence in the strength of the 4000 angstrom break which closely follows trends previously attributed to evolution.