Hubble Space Telescope ultraviolet spectral energy distributions for threeultraluminous infrared galaxies

We present Hubble Space Telescope Faint Object Camera ultraviolet (lambda = 2300 Angstrom, 1400 Angstrom) images of three ultraluminous infrared galax ies (ULIGs: L-ir > 10(12) L.) selected from the IRAS Revised Bright Galaxy Sample. The purpose is to estimate spectral energy distributions (SEDs) to facilitate the identification of similar objects at high redshift in deep o ptical, infrared, and submillimeter surveys. till three galaxies, VII Zw 03 1 (=IRAS F05081+7936), IRAS F12112+0305, and IRAS F22491-1808, were well de tected with the F220W filter. Two of the three were marginally detected wit h the F140W filter. The fluxes, together with ground-based optical and infr ared photometry, are used to compute SEDs over a wide wavelength range. The measured SEDs drop from the optical to the ultraviolet, but the magnitude of the drop ranges from a factor of similar to 3 in IRAS F22491-1808 to a f actor of similar to 100 in VII Zw 031. This is most likely due to different internal extinctions. Such an interpretation is also suggested by extrapol ating to ultraviolet wavelengths the optical internal extinction measured i n VII Zw 031. K-corrections are calculated to determine the colors of the s ample galaxies as seen at high redshifts. Galaxies such as VII Zw 031 have very low observed rest-frame UV fluxes, which means that such galaxies at h igh redshift will be extremely red or even missing in optical surveys. On t he other hand, galaxies such as IRAS F12112+0305 and IRAS F22491-1808, if s een at high redshift, would be sufficiently blue that they would not easily be distinguished from normal held galaxies and therefore, identified as UL IGs. The implication is then that submillimeter surveys may be the only mea ns of properly identifying the majority of ULIGs at high redshift.