Galaxies die earlier than expected

For a long time, scientists thought that in the primitive universe, galaxies with active star formation would only be observed. The James Webb space telescope now reveals that the galaxies have stopped forming stars earlier than expected.

A recent discovery of an international team, led by astronomers at the University of Geneva (UNIGE), deepens the tension between the theoretical models of cosmic evolution and real observations.

Among hundreds of spectra obtained with the programa RUBIES From the webb, the team found a record galaxy that had already stopped forming stars during a time when galaxies are usually growing very quickly.

This study was in the magazine The Astrophysical Journal.

In the early days of the universe, a typical galaxy Create gas surrounding intergalactic medium and transforms this gas into stars.

This process increases your massleading to even more efficient gas and accelerated stellar formation. However, galaxies do not grow indefinitely due to a process that astronomers designate “extinction“.

In the local universe, about half of the observed galaxies ceased to form stars – They extinguished and failed to grow.

Astronomers refer to them as quiescent galaxies, extinct or “red and dead.” They appear red because they no longer contain blue stars Youth and bright – only older and smaller red stars are left.

A particularly high fraction of quiescent galaxies is found among massive galaxieswhich are often observed as having morphologies elliptical.

Usually, the formation of these red and dead galaxies takes a long time, because have to accumulate a large number of stars before the star formation process is finally interrupted. What really causes extinction in the galaxies It is still a great puzzle.

“Finding the first examples of Quiescent Massive Galaxies (GMQs) in the primitive universe is fundamental, as it sheds light on their possible training mechanisms,” he says Pascal OeschProfessor at the Department of Astronomy, Faculty of Sciences of UNIGE and co -author of the scientific article.

The search for such systems has been an important goal of astronomers for years.

Observations in disagreement with theoretical expectations

With the advancement of technology, in particular the near infrared concea, astronomers confirmed the existence of quiescent massive galaxies (GMQS) in increasingly early cosmic times.

Its inferred abundance has been difficult to reconcile with theoretical models of galactic formation, which provide for such systems should take longer to form-to.

With the James Webb Space Telescope, this tension was taken to a red deviation of 5 (1.2 billion years after Big Bang), where several GMQs have been confirmed in recent years. The new study led by Unige reveals that these galaxies graduated even sooner and faster what was thought.

In JWST cycle 2, Rubies Survey (Red Unknowns: Bright Infrared Extragalactic Survey), one of the largest European extragagatic investigation programs that uses the NIRSPEC instrument, obtained spectroscopic observations of Several thousands of galaxiesincluding hundreds of newly discovered sources from JWST initial data.

A recordist “dead” galaxy

Among these new experts, scientists identified the farthest massive massive galaxy found to date, with a shift to the 7.29 concealed red, only ~ 700 million years after Big Bang.

NIRSPEC/PRISM spectrum reveals a star population surprisingly old in such a young universe.

The detailed modeling of spectrum and image data shows that the galaxy has formed a mass of more than 10 billion (10¹⁰) In the first 600 million years after the Big Bang, before rapidly ceasing to star formation, thus confirming its quiescent nature.

“The discovery of this galaxy, called Rubies-UDS-QG-Z7, implies that massive massive galaxies in the first billion years of the universe are more than 100 times more abundant than any model predicted to date,” he says Andrea WeibelDoctoral student of the Department of Astronomy of the Faculty of Sciences of UNIGE and first author of the scientific article.

This, in turn, suggests that Key factors in theoretical models (For example, the effects of stellar winds and the force of flows fed by the formation of mass stars and massive black holes) may have to be reviewed. The galaxies died much earlier than these models can predict.

Perspectives on the nuclei of the giant galaxies

Finally, the small physical dimension of Rubies-UDS-QG-Z7, measured in only ~ 650 light years, implies a high star mass density comparable to the largest central densities observed in galaxies quiescent to deviations to slightly inferior red (Z ~ 2-5).

These galaxies are likely to evolve into the galaxies older and most massive elliptics in the local universe.

“The discovery of Rubies-UDS-QG-Z7 provides the first strong evidence that the centers of some nearby massive elliptical galaxies may have existed since the early hundreds of millions of the universe,” he concludes Anna de Graaffmain researcher of the Rubies program and at the Max Planck Institute of Astronomy in Heidelberg, and the second author of the scientific article.