First results from the ISO-IRAS Faint Galaxy Survey

We present the first results from the ISO-IRAS Faint Galaxy Survey (IIFGS), a program designed to obtain ISO observations of the most distant and lumi nous galaxies in the IRAS Faint Source Survey by filling short gaps in the ISO observing schedule with pairs of 12 mu m ISOCAM and 90 mu m ISOPHOT obs ervations. As of 1997 October, over 500 sources have been observed, with an ISOCAM detection rate over 80%, covering over 1.25 deg(2) of sky to an 11. 5 mu m point-source completeness limit of approximately 1.0 mJy (correspond ing to a similar to 10 sigma detection sensitivity). Observations are prese nted for nine sources detected by ISOPHOT and ISOCAM early in the survey fo r which we have ground-based G- and I-band images and optical spectroscopy. The ground-based data confirm that the IIFGS strategy efficiently detects moderate-redshift (z = 0.11-0.38 for this small sample) strong emission lin e galaxies with L-60 mu m greater than or similar to 10(11) L.; one of our sample has L-60 mu m > 10(12) L. (H-0 = 75 km s(-1) Mpc(-1), Omega = 1). Th e infrared-optical spectral energy distributions are comparable to those of nearby luminous infrared galaxies, which span the range from pure starburs t (e.g., Arp 220) to infrared QSO (Mrk 231). Two of the systems show signs of strong interaction, and four show active galactic nucleus (AGN)-like exc itation; one of the AGNs, F15390+6038, which shows a high excitation Seyfer t 2 spectrum, has an unusually warm far- to mid-infrared color and may be a n obscured QSO. The IIFGS sample is one of the largest and deepest samples of infrared-luminous galaxies available, promising to be a rich sample for studying infrared-luminous galaxies up to,z similar to 1 and for understand ing the evolution of infrared galaxies and the star formation rate in the u niverse.