Optical Imaging of Very Luminous Infrared Galaxy Systems: Photometric Properties and Late Evolution

A sample of 19 low redshift (0.03$<$z$<$0.07) very luminous infrared galaxy(VLIRG: $10^{11}L_\odot< $ L[8-1000 $\mu$m] $ < 10^{12} L_\odot$) systems (30galaxies) has been imaged in $B$, $V$, and $I$. These objects cover aluminosity range that is key to linking the most luminous infrared galaxieswith the population of galaxies at large. We have obtained photometry for allof these VLIRG systems, the individual galaxies (when detached), and theirnuclei, and the relative behavior of these classes has been studied in opticalcolor-magnitude diagrams. The photometric properties of the sample are alsocompared with previously studied samples of ULIRGs. The mean observedphotometric properties of VLIRG and ULIRG samples, considered as a whole, areindistinguishable at optical wavelengths. This suggests that not only ULIRG,but also the more numerous population of VLIRGs, have similar rest-frameoptical photometric properties as the submillimeter galaxies (SMG), reinforcingthe connection between low-{\it z} LIRGs -- high-{\it z} SMGs. When the nucleiof the {\it young} and {\it old} interacting systems are considered separately,some differences between the VLIRG and the ULIRG samples are found. Inparticular, the old VLIRGs are less luminous and redder than old ULIRG systems.If confirmed with larger samples, this behavior suggests that the late-stageevolution is different for VLIRGs and ULIRGs. Specifically, as suggested fromspectroscopic data, the present photometric observations support the idea thatthe activity during the late phases of VLIRG evolution is dominated bystarbursts, while a higher proportion of ULIRGs could evolve into a QSO type ofobject.Comment: 27 pages, 5 figures (degraded to reduce space). Figures 1 and 2 are multiple page figures (i.e. Fig 1a,b and Fig2a-g