We present near-infrared images obtained with the HST NICMOS camera for a sample of 9 luminous ( LIGs : L _ { IR } ( 8 - 1000 \mu { m } ) \geq 10 ^ { 11 } L _ { \odot } ) and 15 ultra-luminous ( ULIGS : L _ { IR } \geq 10 ^ { 12 } L _ { \odot } ) infrared galaxies .
The sample includes representative systems classified as warm ( f _ { 25 \mu { m } } / f _ { 60 \mu { m } } > 0.2 ) and cold ( f _ { 25 \mu { m } } / f _ { 60 \mu { m } } \leq 0.2 ) based on the mid-infrared colors and systems with nuclear emission lines classified as HII ( i.e .
starburst ) , QSO , Seyfert and LINER .
The morphologies of the sample galaxies are diverse and provide further support for the idea that they are created by the collision or interactions of spiral galaxies .
Although no new nuclei are seen in the NICMOS images , the NICMOS images do reveal new spiral structures , bridges , and circumnuclear star clusters .
The colors and the luminosities of the observed clusters are consistent with them being young ( 10 ^ { 7 - 8 } yrs ) , formed as a result of galactic interactions and having masses much greater than those of Galactic globular .
In NGC 6090 and VV114 , they are preferentially situated along the area of overlap of the two galactic disks .

With the exception of IR 17208-0018 , all of the ULIGs have at least one compact ( 2.2 \mu m FWHM \leq 200 pc ) nucleus .
Analysis of the near-infrared colors ( i.e. , m _ { 1.1 - 1.6 } vs . m _ { 1.6 - 2.2 } ) derived from 1.1 \arcsec diameter apertures suggests that the warm galaxies have near-infrared colors consistent with QSO+hot dust emission and the cold galaxies , as a group , have near-infrared colors consistent with reddened starlight .
In addition , the cold ULIG UGC 5101 ( and possibly three others ) have near-infrared colors suggesting an additional AGN-like near-infrared component in the nucleus .
In a 2 kpc-diameter aperture measurement , the global colors of all of the cold galaxies except UGC 5101 are consistent with starlight with a few magnitudes of visual extinction .
The general dichotomy of the near-infrared properties of the warm and the cold galaxies are further supported by the light distributions - seven of the eight warm galaxies have unresolved nuclear emission that contributes significantly ( i.e. , \geq 30 - 40 % ) to the total near-infrared luminosity .
The smooth , more extended light observed in all of the galaxies is most likely comprised of giant and supergiant stars , but evidence at longer wavelengths suggests that these stars contribute little to the high 8–1000 \mu m luminosity of these galaxies .
Finally , light profiles of nine of the 24 systems were fit well by an r ^ { 1 / 4 } law ( and not so well by an exponential disk profile ) .
Whether these star systems eventually become massive central bulges or giant elliptical galaxies will depend on how efficiently the present ISM is converted into stars .