H+K SPECTROSCOPY OF LUMINOUS INFRARED GALAXIES

We present 1.428 to 2.5 mu m spectra of a sample of ten infrared lumin ous galaxies, obtained with the Fourier Transform Spectrograph at the CFH Telescope. This critical wavelength range lies on the boundary bet ween spectral regions dominated by emission from stars or from dust an d non-thermal sources. Because of the large spectral range covered, no n-stellar contributions can be identified through their effect on the continuum. Stellar energy distributions are characterised by their con tinua as well as by molecular features, essentially due to CO and H2O. Eight of the luminous IRAS galaxy spectra are consistent with essenti ally stellar but highly obscured emission, and two clearly show an add itional non-stellar contribution. The preliminary analysis of the star burst spectra is based on evolutionary population synthesis and on a l ibrary of near-IR stellar spectra obtained with the same instrument. L imits on the burst durations and the relative contributions of emissio n components, and estimates of the extinction are derived. The discuss ion accounts for the area over which the spectra are integrated and to some extent for the inhomogeneous space distribution of the component s. While strong CO absorption identifies powerful bursts aged similar to 9 Myr or more, a near-IR stellar energy distribution dominated by g iant stars can hide the blue emission from a very young burst, reveale d only by emission lines (NGC 253). Model predictions and the detailed analysis of individual starburst spectra will be presented more exten sively in a following paper.