ABSORPTION-LINE GRADIENTS IN THE BLUE AND NEAR-ULTRAVIOLET SPECTRA OFBRIGHT 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 atom ic and molecular absorption features in the elliptical galaxies NGC 26 93, NGC 3348, NGC 3379, NGC 4278, NGC 4486, and NGC 5044. There is a g eneral tendency for metallic absorption features to weaken and continu um indices to flatten with increasing radius, in qualitative agreement with what is seen at visible wavelengths. All six galaxies contain si gnificant (i.e., at the 3sigma level) gradients in the 4000 angstrom b reak. The rate of change of the 4000 angstrom break with radius, DELTA 4000/DELTA log(r), is correlated with DELTAMg2/DELTA log(r), and the g alaxy-to-galaxy scatter in DELTA4000/DELTA log(r) is larger than expec ted from experimental uncertainties alone. We compare the spectral ind ices of the various galaxies at the radius where Mg2 = 0.28, which cor responds roughly to [Fe/H] = 0, and find small galaxy-to-galaxy scatte r. NGC 4486 is peculiar in that it has a very steep 4000 angstrom brea k gradient and relatively weak absorption features at Mg2 = 0.28, sugg esting 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 redshif t galaxies. It is demonstrated that the failure to compensate for aper ture effects in galaxies out to z = 0. 2 can introduce an apparent red shift dependence in the strength of the 4000 angstrom break which clos ely follows trends previously attributed to evolution.