Galactic Cannibalization Sparks Powerful Radio Galaxies

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Those who have taken an astronomy class at some point have probably been exposed to the standard “Hubble tuning fork” classification galaxies. You have your “spirals” and your “ellipticals” and, oh yeah, there are a few “irregulars” that don’t quite fit.

Now, imagine a time in the universe where those irregular galaxies were all around, and they fed the most powerful radio-emitting black holes. That is what a group of astronomers, led by Cristina Ramos Almeida, have imaged with one of the largest telescopes on Earth.

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This study looked at powerful radio galaxies (PRGs) between 600 million and 6 billion light years away. So, these aren’t our nearest neighbors, and some are seen as they were when the universe was about half of its present age. These galaxies are PRGs because the supermassive black hole at the center is gobbling up nearby material. But what is making these black holes so active when many more galaxies, such as our own, have a “quiet” black hole?

It turns out, that when carefully imaged by the 8.1-meter Gemini telescope in Chile, most of these galaxies show weird shapes such as shells, tidal tails, multiple central nuclei, and other evidence of being the product of merging galaxies. These are the first observations to show such a strong correlation, confirming the emerging picture that galaxy mergers triggered many active galaxies in our universe’s history.

Look at that picture again (above). It’s not the most aesthetically pleasing, as these galaxies are very distant even for our biggest telescopes. However, these data provide a wealth of scientific information and another piece of the great galaxy evolution puzzle.

Image: The QSO is the light from the active central black hole of one galaxy, and PRG the center of the other.. T1, T2, and T3 indicate tidal tails, or stars being pulled away from the galaxies by their interactions. Credit: Almeida et. al/Gemini.

This work is accepted for publication in the Monthly Notices of the Royal Astronomical Society, and the preprint is available on astro-ph. 

Thanks also to Ned Wright’s Cosmology Calculator!