NGC 17, the remnant of a galaxy merger in Cetus

NGC 34

NGC 17 (also designated NGC 34) is the remnant of a galaxy merger that lies some 242 million light-years away in the constellation Cetus, the Whale. It is moving away from us at 5881 kilometers per second.

This galaxy features a single nucleus, containing a blue central disk with delicate fine structure in the outer parts, and tidal tails indicative of a merger of two former disk galaxies of unequal mass. At present these galaxies appear to have completed their merger.

The remnant shows clear signs that the recent merger was gas-rich and accompanied by a starburst:
it has a rich system of young star clusters; the blue central disk appears to be young, has a smooth structure and its optical light is dominated by a poststarburst population of approximately 400 million years old; and the center of NGC 17 drives a strong outflow of cool, neutral gas.

NGC 17 seems to have first experienced a galaxy-wide starburst that then shrank to its current central and obscured state. The strong gaseous outflow came last. The galaxy is still gas-rich and can sustain its strong central starburst and present mild central activity for some time to come.

This image was taken by the Hubble Space Telescope.
Image Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)