UCR: Best Measure of Star-Forming Material in Galaxy Clusters

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UCR: Best Measure of Star-Forming Material in Galaxy Clusters

Post by bystander » Fri Jul 21, 2017 12:00 am

Scientists Get Best Measure of Star-Forming Material in Galaxy Clusters in Early Universe
University of California, Riverside | W.M. Keck Observatory | 2017 Jul 20

The international SpARCS collaboration based at UC Riverside has made the best measurement yet of the amount of fuel available to form stars in clusters of galaxies located in the early universe.
[c][attachment=0]Tadpole-Galaxy[1].jpg[/attachment][/c][hr][/hr]
The international Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) collaboration based at the University of California, Riverside, has combined observations from several of the world’s most powerful telescopes to carry out one of the largest studies yet of molecular gas -- the raw material which fuels star formation throughout the universe -- in three of the most distant clusters of galaxies ever found, detected as they appeared when the universe was only four billion years old. ...

Clusters are rare regions of the universe consisting of tight groups of hundreds of galaxies containing trillions of stars, as well as hot gas and mysterious dark matter. First, the research team used spectroscopic observations from the W. M. Keck Observatory on Mauna Kea, Hawai’i, and the Very Large Telescope in Chile that confirmed 11 galaxies were star-forming members of the three massive clusters. Next, the researchers took images through multiple filters from NASA’s Hubble Space Telescope, which revealed a surprising diversity in the galaxies’ appearance, with some galaxies having already formed large disks with spiral arms.

One of the telescopes the SpARCS scientists used is the extremely sensitive Atacama Large Millimeter Array (ALMA) telescope capable of directly detecting radio waves emitted from the molecular gas found in galaxies in the early universe. ALMA observations allowed the scientists to determine the amount of molecular gas in each galaxy, and provided the best measurement yet of how much fuel was available to form stars. ...

ALMA Observations of Gas-Rich Galaxies in z ~ 1.6 Galaxy Clusters:
Evidence for Higher Gas Fractions in High-Density Environments
- A.G. Noble et al
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The Tadpole Galaxy is a disrupted spiral galaxy showing streams of gas <br />stripped by gravitational interaction with another galaxy. Molecular gas is <br />the required ingredient to form stars in galaxies in the early universe. <br />Credit: Hubble Legacy Archive, ESA, NASA and Bill Snyder.
The Tadpole Galaxy is a disrupted spiral galaxy showing streams of gas
stripped by gravitational interaction with another galaxy. Molecular gas is
the required ingredient to form stars in galaxies in the early universe.
Credit: Hubble Legacy Archive, ESA, NASA and Bill Snyder.
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Ann
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Re: UCR: Best Measure of Star-Forming Material in Galaxy Clusters

Post by Ann » Fri Jul 21, 2017 5:15 am

UCR wrote:

The researchers compared the properties of galaxies in these clusters with the properties of “field galaxies” (galaxies found in more typical environments with fewer close neighbors). To their surprise, they discovered that cluster galaxies had higher amounts of molecular gas relative to the amount of stars in the galaxy, compared to field galaxies. The finding puzzled the team because it has long been known that when a galaxy falls into a cluster, interactions with other cluster galaxies and hot gas accelerate the shut off of its star formation relative to that of a similar field galaxy (the process is known as environmental quenching).
“This is definitely an intriguing result,” said Gillian Wilson, a professor of physics and astronomy at UC Riverside and the leader of the SpARCS collaboration. “If cluster galaxies have more fuel available to them, you might expect them to be forming more stars than field galaxies, and yet they are not.”
Noble, a SpARCS collaborator and the study’s leader, suggests several possible explanations: It is possible that something about being in the hot, harsh cluster environment surrounded by many neighboring galaxies perturbs the molecular gas in cluster galaxies such that a smaller fraction of that gas actively forms stars. Alternatively, it is possible that an environmental process, such as increased merging activity in cluster galaxies, results in the observed differences between the cluster and field galaxy populations...
Galaxy cluster Abell 1689. There is a lot of gas here, but few new stars.
Credit: NASA; ESA; L. Bradley (Johns Hopkins University); R. Bouwens
(University of California, Santa Cruz); H. Ford (Johns Hopkins University);
and G. Illingworth (University of California, Santa Cruz)
This is so interesting. I remember checking Wikipedia to confirm my suspicion that elliptical galaxies generally lack gas. Instead, Wikipedia wrote that elliptical galaxies often contain a lot of gas. They just don't turn it into stars.

It's fascinating to think that the presence of many other nearby galactic neighbors would have such drastic effects on individual galaxies.

Are there any other major differences between cluster galaxies and field galaxies, and between cluster galaxies and members of small groups, like the Milky Way?

If the Milky Way had been smack in the middle of the Virgo Cluster, or, perhaps more interesting, in the central parts of the Coma Cluster, would we still have been here on the third planet from Sol to ponder our place in the Universe?

Ann
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