Near-infrared imaging of nearby galaxies

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Wide field imaging in near-infrared bands, which is important for studies of nearby galaxies and star forming regions in our Galaxy, has not been performed yet, since neither plates nor large format arrays sensitive at wavelength longer than ^<1 \mu m> were available. We have tested a unique combination of an infrared camera with a large format array and a fast f-ratio telescope. The detector used PtSi array. The array size is 512x512 pixels, and the pixel size is 26 micron x 20 micron. The field of view is 14' x 11' and the pixel resolution is 1.6" x1.3" when attached to the prime focus of the 105cm Schmidt telescope at Kiso observatory. Though the quantum efficiency of the array is low, the excellent uniformity, stability and low read-out noise of the camera combined with the fast f-ratio of the telescope resulted in a calibration accuracy of 0.1% of the sky background in a image obtained through 70 minute exposure in the H-band.A camera with PtSi 1040x1040 chip is now under development, using a chip with an improved quantum efficiency and filling factor. The field of view will be 18.4' x 18.4' at prime focus of the Kiso Schmidt telescope. It will be a powerful tool for imaging objects of large apparent size and for surveys. We are planning to obtain multi-color photometry at optical and infrared wavelengths of nearby galaxies.