ABSTRACT

We used HST Planetary Camera images of M83 in the Hα, U, V, and I filters to study the ionizing clusters in the nuclear starburst region. Our high resolution images revealed detailed structure, previously not visible in ground-based observations.

INTRODUCTION

M83 is a well-studied barred spiral galaxy due to its proximity and its near face-on orientation (i=24°). The estimated distance to M83 ranges from 3.75 Mpc (de Vaucouleurs 1976) to 7.5 Mpc (Lord 1991). The nuclear region is well resolved in ground-based observations (e.g. Gallais et al. 1991), but with the HST Planetary Camera it is possible to probe the region in much greater detail. Our HST images actually allowed us to resolve individual clusters within the starburst regions.

OBSERVATIONS

We obtained high-resolution images of the nuclear regions with the Planetary Camera (pixel size= 0.″ 0436) on the Hubble Space Telescope (HST) on 14 December 1992. We chose U, V, and I filters which would reveal the ionizing star clusters in the bands. We were also able to obtain Ha images of M83 because its readshift (vhel = 504 km s-1 RC3) places Hα in the [NII] filter, F658N, near its peak sensitivity. Since the images were taken 126 days after the most recent WFPC decontamination, it was necessary to correct for contamination especially in the U-band image.

REDUCTION

The primary processing of the data was done at the Space Telescope Institute, which inclused flat-fielding, bias removal, and “dark” image subtraction. The nuclear region of M83 was on PC6. Processing at Goddard Space Flight Center included absolute flux calibration and the removal of cosmic rays.