Dr. Silva et Gd. Bothun, THE AGES OF DISTURBED FIELD ELLIPTIC GALAXIES - I - GLOBAL PROPERTIES, The Astronomical journal (New York), 116(1), 1998, pp. 85-101
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.