Pour one out

Astronomers get a glimpse of a galaxy on the verge of death

ID2299 is bleeding out gas.

A single galaxy encompasses billions of stars and their solar systems, all held together by the sheer force of gravity.

But even galaxies die.

After all of its star-forming gas runs out, and all of its stars have burned out, a galaxy dies. It will one day happen to the Milky Way, too.

Until today, astronomers had never witnessed a distant galaxy on its death bed. However, recent observations by the Atacama Large Millimeter/submillimeter Array (ALMA) have given astronomers their first view of a large galactic being nearing its death.

The findings are detailed in a study published Monday in the journal Nature Astronomy, and help astronomers in their understanding of how galaxies evolve over time until they die.

The team of astronomers behind the new study stumbled upon this dying galaxy by mere accident. As they were observing a host of nearly 100 galaxies in distant locations, they noticed something odd about galaxy ID2299.

Although ALMA, the array of telescopes located in northern Chile, had only caught a glimpse of ID2299 for a few minutes, the researchers could see that the galaxy had a tail of gas that was being ejected from it. You can see the gas ejecting itself from the galaxy in the rendering below:

In this artist's impression of the dying galaxy in question, a tail of ejected gas can be seen stemming from the galaxy.ESO/M. Kornmesser

The gas is being ejected at a startling rate, the equivalent of 10,000 Suns a year. Additionally, it is removing 46 percent of the galaxy's total cold gas.

Annagrazia Puglisi, a researcher at Durham University in the UK, and the lead author behind the new study, confirmed the "death" in a statement released with the research:

“This is the first time we have observed a typical massive star-forming galaxy in the distant Universe about to 'die' because of a massive cold gas ejection,” Puglisi said.

The galaxy is located 9 billion light-years away from Earth, meaning that it existed at a time when the universe was merely 4.5 billion years old (scientists believe that the universe was formed 13.8 billion years ago).

During that time, star formation in galaxies was at a much higher rate than it is today.

Galaxy ID2299 is forming stars hundreds of times faster than our Milky Way, and therefore the gas that remained in the galaxy will quickly be consumed as more stars continue to be born.

As a result, the galaxy will meet its final demise in just a few tens of million years.

Why did the galaxy die?

Although they are not certain of the cause of death, the team of astronomers behind the study believes that the galaxy's untimely death was brought on by the collision between two galaxies, which merged to form ID2299.

The telltale sign that there had been a galactic collision was a "tidal tail." Tidal tails are an elongated stream of stars and gas that extend outwards from a merged galaxy after two galaxies have collided into each other to form one.

Although scientists had previously suggested that these tidal tails form from the star formation process and activity of the black holes at the center of the galaxy, the recent observations of ID2299 suggest that the tails of star-forming gas could also be the result of a galactic merger.

Therefore, the authors behind the new study suggest that previous observations of 'tidal tails' on other galaxies may have been caused by galaxies colliding rather than star formation.

"This might lead us to revise our understanding of how galaxies ‘die’."

“Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar,” Emanuele Daddi, a researcher at Saclay Nuclear Research Centre, and co-author of the new study, said in a statement. "This might lead us to revise our understanding of how galaxies ‘die’."

The researchers are planning on conducting future observations of galaxy ID2299 in order to get a better understanding of the mechanism behind the ejected tail of gas. By studying the relationship between the star-forming gas and the galaxy's eventual death, astronomers are hoping to understand how galaxies evolve over time until they stop giving birth to stars, and die.

Abstract: Feedback-driven winds from star formation/active galactic nuclei (AGN) might be a relevant channel for abruptly quenching star formation in massive galaxies. However, both observations and simulations support the idea of non-conflicting co-evolution and self-regulation of these processes. Furthermore, evidence of disruptive events capable of fast quenching is rare and constraints on their statistical prevalence are lacking. Here we present a massive starburst galaxy at z = 1.4 which is ejecting 46 ± 13% of its molecular gas mass at a startling rate of & 10, 000 Myr1. A broad component red-shifted from the galaxy emission is detected in four (low- and high-J) CO/[CI] transitions and in the ionized phase, ensuring a robust estimate of the expelled gas mass. The implied statistics suggest that similar events are potentially a major quenching channel. However, our observations provide compelling evidence that this is not a feedback-driven wind but rather material from a merger, likely tidally ejected. This finding challenges some literature studies where the role of feedback-driven winds might be overstated.
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