New galaxy images reveal a troubled start to the Universe


October 21, 2021

(Nanowerk News) New images have revealed detailed clues to how the first stars and structures formed in the Universe, and suggest the formation of the Galaxy got off to a turbulent start.

An international team of astronomers from the University of Nottingham and the Centro de Astrobiología (CAB, CSIC-INTA) used data from the Hubble Space Telescope (HST) and the Gran Telescopio Canarias (GTC), the so-called Frontier Fields , to locate and study some of the smallest, weaker galaxies in the neighboring universe. This revealed that the formation of the galaxy was likely to be unstable.

The first results have just been published in the journal Monthly notices from the Royal Astronomical Society (“Emission Line Galaxies in the SHADS Frontier Fields I: Candidate Selection and the Discovery of Bursty Ha Emitters”).

Image from the SHADS study.

One of the most interesting questions that astronomers have been trying to answer for decades is how and when the first galaxies formed. Regarding the how, one possibility is that the formation of the first stars within galaxies has started at a steady rate, slowly building an increasingly massive system. Another possibility is that the formation was more violent and discontinuous, with intense but short-lived gusts of star formation triggered by events such as mergers and increased gas accretion.

“The formation of a galaxy can be compared to a car,” explains Pablo G. Pérez-González, one of the co-authors of the article, affiliated with the Centro de Astrobiología (CAB / CSIC-INTA) in Spain, and principal investigator of the international collaboration behind this study. “The early galaxies could have had a ‘diesel’ star-forming engine, slowly but continuously adding new stars, without much acceleration, and slowly turning gas into relatively small stars for long periods of time. Or the formation could have been choppy, with star-forming bursts producing impossibly large stars disrupting the galaxy and causing it to go out of business for a while, if not forever. Each scenario is linked to different processes, such as galaxy mergers or the influence of supermassive black holes, and they affect when and how the carbon or oxygen, essential to our lives, is formed. .

Using the gravitational lens power of some of the most massive galaxy clusters in the Universe with the exceptional GTC data from a project called Survey for high-z Red and Dead Sources (SHARDS), astronomers searched for analogues close to the very first galaxies formed in the Universe, in order to be able to study them in much more detail.

Dr Alex Griffiths of the University of Nottingham was one of the UK’s principal investigators in the study, he explains: “Until we have the new James Webb Space Telescope, we cannot observe first galaxies ever formed, they are just too weak. So we looked for similar beasts in the nearby universe and we dissected them with the most powerful telescopes we have today.

Researchers have combined the power of the most advanced telescopes, such as the HST and GTC, using “natural telescopes”. Professor Chris Conselice, University of Manchester is a co-author of the study, he said: “Some galaxies live in large groups, which we call clusters, which contain enormous amounts of mass. in the form of stars, but also gas and dark matter. Their mass is so great that they bend space-time and act like natural telescopes. We call them gravitational lenses and they allow us to see faint and distant galaxies with improved brightness and higher spatial resolution ”.

Observations of some of these massive clusters acting as gravitational telescopes form the basis of the Frontier Field investigation. The study showed that the formation of the galaxy was likely to be interrupted with bursts of activity followed by lulls. Dr Griffiths of the University of Nottingham said: ‘Our main result is that the onset of galaxy formation is irregular, like a jerky car engine, with periods of enhanced star formation followed by sleepy intervals. It is unlikely that galaxy mergers played a substantial role in triggering these star-forming bursts and it is more likely due to alternate causes that enhance gas accretion, we must seek these alternatives.

“We were able to find these objects using high-quality SHARDS data coupled with imaging data from the Hubble Space Telescope to detect hot gas heated by newly formed stars in very small galaxies. This hot gas emits in certain wavelengths, what are called emission lines, just like neon light. Analysis of these emission lines can provide insight into the formation and evolution of a galaxy.

“The SHARDS Frontier Fields observations made with GTC provided the deepest data ever collected to discover dwarf galaxies through their emission lines, allowing us to identify systems with recently triggered star formation,” Pérez adds. -González, one of the co-authors of the article and principal investigator of the GTC SHARDS Frontier Fields project.


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