New images have revealed detailed clues about how the first stars and
structures were formed in the Universe and suggest the formation of the
Galaxy got off to a fitful start.
An international team of astronomers from the University of Nottingham and
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 faintest galaxies
in the nearby universe. This has revealed the formation of the galaxy was
likely to be fitful. The first results have just been published in the
journal Monthly Notices of the Royal Astronomical Society (MNRAS).
One of the most interesting questions that astronomers have been trying to
answer for decades is how and when the first galaxies formed. Concerning the
how, one possibility is that the formation of the first stars within
galaxies started at a steady pace, slowly building up a more and more
massive system. Another possibility is that the formation was more violent
and discontinuous, with intense, but short lived bursts of star formation
triggered by events such as mergers and enhanced gas accretion.
"Galaxy formation can be compared to a car", explains Pablo G.
Pérez-González, one of the co-authors of the paper, affiliated to the Centro
de Astrobiología (CAB/CSIC-INTA) in Spain, and principal investigator of the
international collaboration behind this study. "The first galaxies might
have had a 'diesel' star-forming engine, slowly but continuously adding up
new stars, without much acceleration and gently turning gas into relatively
small stars for long periods of time. Or the formation could have been
jerky, with bursts of star formation producing incredibly large stars that
disrupt the galaxy and make it cease its activity for a while or even
forever. Each scenario is linked to different processes, such as galaxy
mergers or the influence of supermassive black holes, and they have an
effect on when and how the carbon or oxygen, that are essential for our
life, formed."
Using the gravitational lensing power of some of the Universe's most massive
galaxy clusters with the exceptional GTC data coming from a project entitled
the Survey for high-z Red and Dead Sources (SHARDS) the astronomers searched
for nearby analogs of the very first galaxies formed in the Universe, so
that they could be studied in much more detail.
Dr. Alex Griffiths from the University Nottingham was one of the lead UK
researchers on the study, he explains: "Until we have the new James Webb
Space telescope, we cannot observe the first galaxies ever formed, they are
just too faint. So we looked for similar beasts in the nearby Universe and
we dissected them with the most powerful telescopes we currently have."
The researchers combined the power of the most advanced telescopes, such as
HST and GTC, with the aid of "natural telescopes". Professor Chris
Conselice, from the University of Manchester is a co-author on the study, he
said: "Some galaxies live in large groups, what we call clusters, which
contain huge amounts of mass in the form of stars, but also gas and dark
matter. Their mass is so large that they bend space-time, and act as natural
telescopes. We call them gravitational lenses and they allow us to see faint
and distant galaxies with enhanced brightness and at a higher spatial
resolution".
Observations of some of these massive clusters acting as gravitational
telescopes is the base of the Frontier Field survey. The study showed that
the formation of the galaxy was likely to be stop-start with bursts of
activity followed by lulls. Dr. Griffiths from the University of Nottingham
said: "Our main result is that the start of galaxy formation is fitful, like
a jerky car engine, with periods of enhanced star formation followed by
sleepy intervals. It is unlikely that galaxy mergers have played a
substantial role in the triggering of these bursts of star formation and it
is more likely due to alternative causes that enhance gas accretion, we need
to search for those alternatives.
"We were able to find these objects due to the 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 we call emission lines, just as a neon light.
Analysing these emission lines can provide an insight into the formation and
evolution of a galaxy.".
"The SHARDS Frontier Fields observations carried out with GTC have provided
the deepest data ever taken for discovering dwarf galaxies through their
emission lines, allowing us to identify systems with recently triggered star
formation", adds Pérez-González, one of the co-authors of the paper and
principal investigator of the GTC SHARDS Frontier Fields project.
Reference:
Emission Line Galaxies in the SHARDS Frontier Fields I: Candidate Selection
and the Discovery of Bursty Ha Emitters, Monthly Notices of the Royal
Astronomical Society (2021).
DOI: 10.1093/mnras/stab2566
Tags:
Space & Astrophysics