THE AGES OF DISTURBED FIELD ELLIPTIC GALAXIES - I - GLOBAL PROPERTIES

Near-infrared images of elliptical galaxies with morphological signatu res of recent merger activity have been obtained. If this merger activ ity stimulated significant and distributed star formation within the r egion defined by R < 1.5R(e), then JHK photometry in this region shoul d detect the presence of an intermediate-age stellar population associ ated with this event. Our observations, however, show that these galax ies occupy the same locus of points in the J-H versus H-K plane as ell iptical galaxies with no signs of recent merger activity. This strongl y constrains the global fractional amount of intermediate-age (1-3 Gyr ) stellar mass to be no more than 10%-15%, and in most cases the data are consistent with all the stellar mass being old (T > 10 Gyr) and me tal-rich ([Fe/H] greater than or equal to -0.3). We argue that any rec ent merger activity was, therefore, not accompanied by a significant e pisode of distributed star formation within the region defined by R < 1.5R(e) and that the bluer UBV colors often observed in this region fo r some of these galaxies are due to the accretion of lower mass compan ions or relative abundance differences. The possibility of a strongly centralized starburst resulting from the merger, instead of a more dis tributed star-forming episode, is fully discussed in Paper II of this series, in which similar tight constraints on this activity will be di scussed.