Dl. Clements et al., OPTICAL IMAGING OF ULTRALUMINOUS IRAS GALAXIES - HOW MANY ARE MERGERS, Monthly Notices of the Royal Astronomical Society, 279(2), 1996, pp. 477-497
We present the results of R-band imaging observations of a sample of 6
0 ultraluminous IRAS galaxies (ULIRGs). All the objects are taken from
our ULIRG survey. The bulk of these objects are in a magnitude-limite
d subsample of this survey with B-J < 19.5, consisting of 56 objects.
We find that 51 of the 56 main-sample objects (91 per cent) are mergin
g and/or disturbed systems, whilst four of the remaining five have clo
se, usually disturbed, companions. Only one of the main sample of obje
cts is isolated and quiescent. The result that almost all of these ULI
RGs are disturbed systems contradicts some of the earlier observations
. We consider possible origins for this discrepancy, and conclude that
deeper images of isolated and quiescent ULIRGs may well reveal previo
usly undetected signs of disturbance.