NGC 5216/18: The Keenan System

Click on image for larger version.

In most pictures galaxies seem to be rather organized and substantial if not "solid-like" objects. However, no process better shows the ethereal and delicate nature of galaxies than when they collide. Unlike dancers on a dance floor, a galactic tango will strip stars and gas in a mutual promenade. The space in between the galaxies fills with these stars in new and perturbed orbits. The masses of the galaxies, their intrinsic internal structures, and their relative velocities (timescales) ultimately determine the resulting structure of the interaction.

In this example NGC 5216 (top) and NGC 5218 (below) have luminous debris connecting them across a distance that is no less than 22,000 lightyears. P. C. Keenan noted this double galaxy enigma in 1935 and noted the peculiar structure in his paper. It was later "rediscovered" by observers at Lick and Palomar observatories. Note that NGC 5218 has a countertide; a tidal tail that is in the opposite direction of the center of mass of the system. This is a typical structure of interacting double galaxy systems. These galaxies are estimated to be more than 100 million light years away.

Equipment

20in RC Optical Systems telescope Operating at f/8.4
Paramount ME Robotic Telescope Mount
SBIG ST10XME CCD camera with color filter wheel

L R G B color production was used to create this image.

Luminance = 120 minutes binned 1x1
Red = 20 minutes binned 2x2
Green = 20 minutes binned 2x2
Blue = 20 minutes binned 2x2

The image was brightened aggressively to show the tidal tails.

One iteration of L-R deconvolution (sharpening) algorithm using CCDsharp was applied to the luminance image.

Digital Development (DDP) via Maxim/DL was also used in order to display the the very dim and very bright details of the image simultaneously.

Minimum credit line: Sid Leach and Wil Milan/Adam Block/NOAO/AURA/NSF

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Updated: 03/27/2004