'Missing' galactic mergers come to light with new technique

January 8, 2019, University of Colorado at Boulder
A computer simulation of a galaxy (left); the same galaxy adjusted to appear as it might in an observation by the Sloan Digital Sky Survey (middle); a computer simulation of a merging pair of galaxies (right). Credit: Nevin et al., 2019

Galaxy mergers—in which two galaxies join together over billions of years in sometimes-dramatic bursts of light—aren't always easy for astronomers to spot. Now, scientists from the University of Colorado Boulder have developed a new technique for finding these cosmic couplings in surveys of the night sky.

In new research, a team led by Rebecca Nevin designed a computer program that scans through surveys of galaxies to look for a wide range of signs that a merger might be happening. That includes the shape of the resulting galaxies and how the stars inside are moving.

That's important, Nevin said, because such mergers may be an important step in the building of huge, spiral galaxies like the Milky Way and in kicking off the formation of new stars.

She will present her group's findings Jan. 8 at a press briefing at the 233rd Meeting of the American Astronomical Society in Seattle.

"The goal is to build a bigger sample of merging galaxies than ever before," said Nevin, a graduate student in the Department of Astrophysical and Planetary Science (APS).

Nevin's work builds on observations from the Sloan Digital Sky Survey (SDSS), a long-running census of the night sky undertaken by a research partnership that includes CU Boulder. Scientists on that survey have snapped about 500 million images of space since 1998, many of them showing galaxies far away from Earth.

But to date, no one technique has been able to look through such surveys and find all types of galaxy mergers at all stages in their development, Nevin said.

"People have been looking at pictures of galaxies and saying, 'that's a merger" or 'that's not a ,'" she said. "But people are also really bad at doing that, and they miss a lot of galaxies."

To locate those missing mergers, Nevin and her colleagues designed a series of simulations that seek to capture a wide range of different ways that two galaxies might bump into each other.

"These simulated allow us to follow billions of years of evolution directly, whereas observations of real galaxies are limited to single moments in time," said Laura Blecha, an assistant professor at the University of Florida who led the simulation work.

The researchers used those simulations to train a computer program to recognize the telltale fingerprints of these unions. The team, which included Julia Comerford of CU Boulder and Jenny Greene of Princeton University, then employed the same program to scan real-life images of galaxies collected by the SDSS.

And it worked: depending on the types of galaxies involved the team's technique could correctly identify fusing 80 percent of the time or more. Nevin and her colleagues will publish their findings shortly in The Astrophysical Journal.

The group didn't stop there. She and her colleagues are also working to incorporate measurements of the way that stars in a galaxy move, or their "kinematics," into the hide-and-seek tool.

"This is a novel approach because it's bringing imaging techniques and the kinematics together," Nevin said.

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3 comments

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valeriy_polulyakh
1 / 5 (2) Jan 08, 2019
There are some very complicated issues of galaxy formation. Unfortunately, here is the same problem as with the stars. The origin of galaxies remains unclear, in spite of huge activity in the field. What the "formation" means? It means that we have the material that is assembling into galaxies.
https://www.acade...ome_From
https://www.acade...rvations
Da Schneib
3.3 / 5 (7) Jan 08, 2019
One thing that didn't get said is that this new algorithm detected *all* the galaxy mergers that were previously known. Also, by how much this increased the number of known mergers. Since there is no paper yet published (not surprising, this will be a real coup at the AAS meeting, and it's traditional to make such a presentation before publishing), I don't have a link to an arXiv paper. Perhaps this article can be updated with the paper's DOI when the publication occurs. Or another article released that has that information.
rrwillsj
not rated yet Jan 09, 2019
please correct me if I am wrong valerie. Are you asking for a coherent.regulated, & orderly system to precisely explain the beginnings & subsequent evolution of Stars & Galaxies?

Evolution, whether biological or stellar, is a chaotic process. Every organism will develop unique survival traits. Every star or galaxy will develop unique characteristics.
We are finding examples of distinctive materials & history the asteroids & moons of our own Solar System.

For all these, the similarities are trivial. It is the differences, the unique features that fascinate me. In the Classical meaning of the word "fascinate".

A good example would be choral music. Consider a Robert Shaw chorus.
How he trained them to first sing in small groups. Then brought all those groups together in a mighty crescendo of Human vocal power!

Yet that "Wall of Sound" consists of ordinary people. Who together create an extraordinary, temporary harmony. Then go back to their separate lives.

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