New integral field optical fiber spectroscopy obtained with the INTEGRAL system , together with archival HST WFPC2 and NICMOS images , have been used to investigate the ultraluminous infrared galaxy IRAS 17208 - 0014 , one of the coldest and most luminous objects in the IRAS 1 Jy sample .

We have found that the optical nucleus is not coincident with the true ( near-IR and dynamical ) nucleus , but it is displaced by 1.3 kpc ( 1.5 ^ { \prime \prime } ) from it .
As a consequence , the previous optical spectral classifications for the nucleus of this galaxy have to be revised and changed from HII to LINER .
The ionized gas emission is concentrated around the optical nucleus , where a young ( 5-6 Myr ) , massive ( 3 \pm 1 \times 10 ^ { 8 } \thinspace \hbox { $ \hbox { M } _ { \odot } $ } ) , and luminous ( 6 \pm 2 \times 10 ^ { 10 } \thinspace \hbox { $ \hbox { L } _ { \odot } $ } ) starburst is detected .
Contrary to what is found in dynamically young ULIRGs , no strong line emission tracing star-forming regions , or tidal-dwarf galaxies , is detected in the inner parts of the tidal tails .

The 2D gas velocity field identifies the optically faint K-band nucleus as the dynamical nucleus of the galaxy , and shows that the 3 kpc , tilted ( i \sim 35 degree ) disk is rotating at \Delta Vsin i = 250 km s ^ { -1 } .
Radial motions of gas are found along the minor kinematic axis which , according to the geometry of the system , are well interpreted as inflow perpendicular to the inner disk .
The existence of such inflows supports the idea that , as a consequence of the merging process , gas is channeling from the external regions , several kpc away , into the nuclear regions where the massive starburst reported above is taking place .

The kinematical , morphological , and photometric evidence presented here supports the idea that in IRAS 17208-0014 we are witnessing a luminous , cool ULIRG which is at the final coalescence phase of a system composed of two spirals with m \leq m ^ { * } , a mass ratio of \sim 2:1 , each consisting of a disk+bulge internal structure , that have been involved in a prograde encounter .
This system will most likely evolve into an intermediate-mass ( \sim L ^ { * } ) elliptical .
The multifrequency empirical evidence gathered so far shows no trace of a luminous QSO , and indicates that starbursts dominate the energy output in this galaxy .
Therefore IRAS 17208 - 0014 does not follow the behavior expected in the ’ ULIRG to QSO ’ evolutionary scenario proposed by Sanders et al. , but support the one recently proposed by Colina et al , where two low mass disk galaxies would produce luminous cool ULIRGs that would not evolve into a QSO phase .

The present study illustrates some caveats to bear in mind when studying high-z galaxies lacking 2D spectral information of adequate linear resolution , and shows that near and mid-IR integral field spectroscopy is needed to derive the relevant astrophysical quantities .