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Astron. Astrophys. Suppl. Ser. 133, 387-399

Results of the digital co-addition of thirteen Schmidt films of the Virgo cluster of galaxies

A.C. Katsiyannis1 - S.N. Kemp2 - D.S. Berry1 - J. Meaburn1

1 - Department of Physics and Astronomy, University of Manchester, Oxford Rd., Manchester M13 9PL, UK
2 - Instituto de Astrofísica de Canarias, C/ Via Lactea, E-38200 La Laguna, Tenerife, Spain

Received February 23; accepted April 24, 1998


We have digitally co-added APM scans of 13 Kodak TechPan films of the SE region of the Virgo cluster of galaxies. The $\approx\!
 6.2\hbox{$^\circ$}\times 6.2\hbox{$^\circ$}$ field of the R-band films combined with the resolution of $\approx\!2$ arcsec pixel-1 results in data file sizes of about 222 MBytes. The 13 scanned films have been aligned, co-added, corrected for vignetting effects and cleaned of stellar features. To illustrate the astrophysical uses of this technique, we present high contrast images of a sample of Virgo cluster and background galaxies. Several very faint, but very clearly seen features, such as the interaction between IC 3481, IC 3481A and IC 3483 and filaments outside of the common envelope of NGC 4438 & NGC 4435, can be seen for the first time. We present an image of the halo of M 87 showing its great extent, and an image of the central regions of the cluster which shows no real evidence for interactions between the galaxies in this region. We also present high-quality images of the previously-identified "jet" and shell features around M 89. We also present an image of the whole field which appears to show large variations in brightness of the intra-cluster medium across the region, with the brightest regions in the northern part in the central regions of the cluster, though we caution against this interpretation until we have investigated the large variation in emulsion sensitivity across individual films more thoroughly.

Key words: techniques: image processing -- galaxies: structure -- galaxies: haloes -- galaxies: interactions -- galaxies: clusters: Virgo cluster

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