First HST Images of a Compact Group: Seyfert's Sextet (Poster paper)

Summary

ABSTRACT

We present details of galaxy morphology in the compact group Seyfert's Sextet obtained with the HST-WFC.

INTRODUCTION

Seyfert's Sextet (SS, HCG 79) exhibits one of the highest galaxy surface density enhancements (> 10³, Sulentic 1987) outside the core of a rich galaxy cluster. There are convincing signs of interaction between the component galaxies, including: 1) optical evidence of bridges, tails and a common low light level envelope (Sulentic and Lorre 1983), and 2) a distorted distribution of neutral hydrogen (Williams et al. 1991).

HST OBSERVATION AND DECONVOLUTION

SS was observed with the WFC on 12 May 1992. Nine 15-minute exposures were taken with the F439W (B) filter and processed with the standard STScI pipeline. The frames were accurately registered (to within 1 pixel), allowing us to combine them into a single averaged picture. Cosmic rays were removed by ignoring pixels which were significantly (3σ) deviant from the corresponding pixels on other frames.

Deconvolution was performed using both the Richardson-Lucy package bundled in IRAF/STSDAS (refer to the STSDAS User Guide), and the σ-CLEAN algorithm (Keel 1991), optimized to change the point-spread function (PSF) according to position on the chip. PSFs were computed using the Tiny Tim (refer to The Tiny Tim User's Manual) package. A 50 iteration deconvolution was carried out with the Lucy package. After 80,000 iterations with CLEAN the model brightness distribution showed little change. Each of these algorithms presents strong and weak points. Lucy handled very well large structures (low spatial frequencies), such as the halo connecting the galaxies. However, the final brightness distribution seemed to be dependent on the number of iterations used.