Galaxies hold only 10 percent of the visible matter in the universe. The rest is spread through intergalactic and circumgalactic space, the latter being the region surrounding galaxies. For the first time, astronomers have spotted how this area becomes enriched by new matter.
Theories have suggested that circumgalactic space receives gas and dust from galactic winds pushing material out of galaxies. Unfortunately, observations couldn’t fully explain it. Astronomers had seen events creating winds stretching over 30,000 light-years, but circumgalactic space can extend 10 times as far.
As reported in Nature, an American-British team has directly observed an outflow stretching over 320,000 light-years and spanning 260,000 light-years across. The winds were emitted from the massive but compact galaxy SDSS J211824.06+001729.4, which has been nicknamed Makani, meaning "wind" in Hawaiian.
“Makani is not a typical galaxy,” co-author Professor Alison Coil, from the University of California, San Diego, said in a statement. “It’s what’s known as a late-stage major merger – two recently combined similarly massive galaxies, which came together because of the gravitational pull each felt from the other as they drew nearer. Galaxy mergers often lead to starburst events, when a substantial amount of gas present in the merging galaxies is compressed, resulting in a burst of new star births. Those new stars, in the case of Makani, likely caused the huge outflows – either in stellar winds or at the end of their lives when they exploded as supernovae.”
While events such as this might happen several times in a galaxy's lifetime, they are quite short. So catching a galaxy in the act is not easy. The team combined observations from one of the newest instruments on the Keck Observatory, the Keck Cosmic Web Imager, with Hubble and ALMA observations.
Thanks to this incredible tech they were able to identify the extended outflow, which is believed to have been thrown out a few hundred million years ago as well as a more recent one that was launched only a few million years ago. The properties of the two outflows match expectations from theoretical models.
“The earlier outflow has flowed to large distances from the galaxy, while the fast, recent outflow has not had time to do so,” explained lead author David Rupke, associate professor of physics at Rhodes College.
Rupke and the team stress the importance of these observations. We finally have a complete picture of how a massive galaxy is enriching the circumgalactic medium.