Interacting Galaxy Pair CPG 108

This R-band image shows the galaxy pair CPG 108, from Karachentsev's catalog of galaxy pairs. The image was obtained with the 1.1-m Hall telescope of Lowell Observatory. This pair of 15th-magnitude galaxies lies in the direction of Camelopardalis, less than 10 degrees from Polaris, at a distance of about 200 million light-years. The image is displayed using a logarithmic intensity transformation, spanning an area about 7.3 by 7.2 arcminutes. North is up and east to the left.

CPG 108 has a useful combination of orbital direction and disk orientation to show the relative directions of the galaxies' spin and orbital vectors. The 150 km/s difference in their radial velocities indicates that the orbit is not seen too close to pole-on, so that the galaxies' rotation curves can tell which way they spin relative to the orbit. This combination figures in some theoretical work on the origin of galaxy pairs, as well as how galaxy encounters can touch off episodes of star formation. This figure comes from a paper analyzing direct and retrograde encounters, showing that both members of K108 are undergoing retrograde passages. The visible evidence of this is that the directions of the rotation curves (redshift versus location along each galaxy's major axis) tilt in the opposite sense from the redshift difference between the two galaxies. For both galaxies, the eastern (left) side is approaching us. The angle defined here was used, along with velocity differences, to select a subsample of Karachentsev pairs that would be seen less than 30 degrees from the prbital plane.

CPG 108 image and rotation curves

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