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C. Another Remarkable Filamentary Structure

The interconnected double nebula shown on the Plate IV was discovered by Dr. A. G. WILSON during the sky survey and had also been spotted previously by the author during his systematic search for dwarf galaxies and for intergalactic matter with the 18-inch Schmidt.


Plate IV. Photograph obtained with the 200-inch telescope on Eastman 103a-0 emulsion, exposure time 30 minutes. Coordinates for the center of the system are approximately R.A. 23h 39m 16s and Decl. -3° 49' (Epoch, 1950). Scale indicates one minute of arc.

The taffy like filament which connects the two galaxies and which on closer inspection of the original appears as the continuation of one of the spiral arms of the southern spiral galaxy is perhaps the most striking example among the intergalactic structures of this type. The "countertide" protruding to the southwest from the southern galaxy seems to be the continuation of its second spiral arm. Lying to the north and west of our system IC 1505 lies at the upper edge of our plate. On original photographs with the 200-inch reflector and with the 48-inch Schmidt it has sometime appeared to the author as if the north following spiral were connected by a wide veil like structure with IC 1505. This observation, however, is so far a mere conjecture.

Dr. HUMASON kindly observed the spectra of the two spirals of our double galaxy with the prime focus spectrograph of the 200-inch telescope (dispersion 370 Å/mm). The results which he obtained are as follows.

Northern Nebula. Vs = 7016 km/sec. Rather unexpectedly this galaxy shows pronounced emission lines in its spectrum including Halpha, Hbeta, Hgamma and strong lambda3727.

Southern Nebula. Vs = 6777 km/sec. and surprisingly enough, a very washed out spectrum with no trace of any emission lines.

On the old scale the distance of our double galaxy is about 45 million light years and the length of the whole formation projected unto a plane normal to the line of sight is 125000 light years.

A most interesting structural feature is to be found in the geometry of the obscuring regions which, like the bands on some snakes, encircle the southern nebulae crosswise. These bands running at right angles to the axis of the whole formation are suggestive of dust clouds that are being whirled around the nebula in a fashion analogous to the peripheral columnar vortices which are generated in a gas between two rotating cylinders (30).

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