AKARI far-infrared source counts in the Lockman Hole

We report initial results of far-infrared observations of the Lockman Hole with Far-Infrared Surveyor onboard the AKARI infrared satellite. On the basis of slow-scan observations of a 0.degrees 6 x 1.degrees 2 contiguous area, we obtained source number counts at 65, 90, and 140 mu m down to 77, 26, and 194 mJy (3 sigma), respectively. The counts at 65 and 140 mu m show good agreement with the Spitzer results. However, our 90 mu m counts are clearly lower than the predicted counts by recent evolutionary models that fit the Spitzer counts in all the MIPS bands. Our 90 mu m counts above 26 mJy account for about 7% of the cosmic background. These results provide strong constraints on the evolutionary scenario, and suggest that the current models may require modifications.