KISO H IMAGING OBSERVATIONS OF NEARBY GALAXIES

INTRODUCTION

For narrow-band H imaging observations of nearby galaxies, we have two advantages in using the 105 cm Schmidt telescope at the Kiso Observatory. First, the small f/3.1 focal ratio of this telescope yields efficient detection of extended diffuse light. Second, an installed CCD camera with 1024 square pixels (TI215) has a field of view of arcminutes which is wide enough to cover nearby galaxies with large angular size.

The goal of our narrow-band imaging observations is to investigate the factors which regulate the star formation efficiency (SFE). The SFE can be estimated as the fraction of the mass of on-going star formation measured from the H intensity over the molecular gas mass from the CO intensity. A number of nearby galaxies have been observed with CO emission at the Nobeyama Radio Observatory (NRO). However, very small numbers of such galaxies have been observed at H. Hence we have begun to obtain a homogeneous set of H images of these galaxies with the Kiso Schmidt telescope. Along with K'-band images, we investigate the effect on the SFE from factors such as gas density, galactic structures (arms and bars), morphology, and environment. The star formation rate has been studied case by case in the context of threshold gas surface density (Kennicutt, 1989; Kuno et al, 1995; Hunter & Plummer, 1996). We study not only the star formation efficiency (H / CO) but also the star formation rate (H), based on the forthcoming homogeneous set of H images.

We have selected more than 30 isolated face-on spiral and dwarf galaxies and have so far observed 10 of them, including NGC 628 (M74), NGC 6946, NGC 5236 (M83), and IC 10. We also observed Hickson's compact group HCG92 (e.g. Hickson, 1994) to assess environmental effects.

© Copyright Astronomical Society of Australia 1997