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Field near Spiral Galaxy NGC 4945

This image is an enlargement at full resolution of a smaller region (about 1/67 by area) of a sky field around the spiral galaxy NGC 4945 . It is assembled from five 15-minute R(ed)-narrowband (shown in red), four 5-minute B(lue)-band (shown in green), and five 1000-second U(ltraviolet)-band (shown in blue) exposures, obtained in January 1999 during the Science Verification phase with the Wide-Field-Imager (WFI) at the MPG/ESO 2.2-m telescope at La Silla. At the recession velocity of NGC 4945, the red filter, centred at 665 nm with an FWHM (full width at half maximum) of only 1.2 nm, does not include the H-alpha emission line of interstellar hydrogen in this galaxy. The original resolution of about 1 arcsec corresponds to roughly 62 light-years at the distance of NGC 4945 (13 million light-years). In addition to NGC 4945 itself, some much more distant galaxies can be recognized as faint, slightly red light patches in the field. The vast majority of the point-like sources are stars in the Milky Way. However, a fair number of those near NGC 4945 are globular clusters belonging to this galaxy.

Each frame records 8184 x 8196 = 67,076,064 pixels, and thus the total number of data points (pixels) of the 14 CCD frames used to make this photo is almost 10 9. Their collective information content corresponds to more than 70 x 10 9 photons (not counting those from the Earth's upper atmosphere that were recorded simultaneously). It covers 1001 x 1002 pixels and measures about 4 x 4 arcmin 2 in the sky. The structure of the faint and distant spiral galaxy at the centre is well visible in this reproduction.


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