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February 3, 2023



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From Mexico, Roser Pelló presents the most distant object yet seen in the Universe


Over 160 scientists gathered at the Castillo de Chapultepec in Mexico City for the second "International Workshop on Science with the GTC" from 16th to 18th February to hear about science projects that have been proposed for the GTC. Roser Pelló, from the Observatoire de Midi Pyrénées Astrophysics Laboratory in France, produced one of the conference's biggest surprises when she unveiled a new discovery: the most distant object that has yet been seen in the Universe.

Workshops such as this one determine how observation time will be used once operations commence at the GTC. The first was held in Granada in 2002 and this one, in Mexico, looked at the work that the GTC’s first light instruments (OSIRIS and CanariCam) and the Gran Telescopio Milimétrico (GTM, a telescope currently under construction in Puebla, Mexico) will be doing.


What projects would you like to see happening at the GTC?

I would love to be able to look at the redshift fields of the farthest galaxies we can see - in other words, the locations where star formation first began in the primordial Universe. I am particularly interested in using spectroscopy and ultradeep photometry on this type of object, which would open up galaxies for us and allow us to look at the way they were formed and how they have evolved from their very first stages.

In your speech to the "International Workshop on Science with the GTC" surprised the delegates with the results of the research that you have been doing.

What I presented today was the first confirmation that, spectroscopically, one of our candidates for a source with redshift at between 7 and 10 has turned out to be a galaxy at a redshift of 10. In other words, it was formed when the Universe was starting to reionize. The Universe was originally neutral because its protons and electrons had combined to form hydrogen, in order to fuel the brightly shining massive stars (the first generation of stars) that had recently formed. The Universe began to ionize as the electrons (negatively charged) separated from the protons (positively charged) and stars started to form.

By using a number of lenses simultaneously to amplify the signals emitted by distant galaxies, we had been able to identify a number of possible candidate galaxies. It was at the VLT (Very Large Telescope) at the European Southern Observatory (ESO) that we obtained the first confirmation, using an emission line, that one of the galaxies we had identified at redshift between 9 and 11 was in fact at a redshift of 10, which was precisely what we were hoping to find.

The properties exhibited by this object appear to be broadly in line with current models of galaxy formation in the early Universe. It is like a large star cluster visible at a redshift of 10 - like other objects from the early stages of the Universe - and it contains very pronounced features of star formation: it is very blue and is likely to contain hot massive stars in its interior. We were also able to measure the extent to which the appearance of the emission line we were attempting to detect (Lyman , for those who are familiar with the subject) is weakened both by geometric effects and by the intergalactic matter between it and ourselves, which we are currently observing.

The main point is that we have located the most distant object that has ever been seen.

Which instruments at the GTC are best suited to your work?

EMIR (Espectrógrafo Multiobjeto Infrarrojo or Multi-object Infrared Spectrograph) is far and away the best-suited, given its multi-object capability and its ability to capture an entire spectral field in one go. The ISAAC instrument at the VLT, for example, would need six separate exposures to deal with just a small part of the spectral field that we need to work with. EMIR will allow us to work with the whole field at once. The benefits it will bring relative to the work we are currently doing with telescopes and the instruments currently available are immense. It will easily increase efficiency by a factor of 60 to 100.

So it is not just the fact that this telescope will have a light-collecting surface of over 10 metres that will make it special, but also its groundbreaking instruments?

Instruments are an integral part of a telescope these days - they are as important as eyes are to a human being. They really are an extremely important component, without which a telescope could neither make discoveries nor contribute its results to the international science community.

Fortunately the instruments being developed for the GTC will be cutting edge; and they will be installed on a telescope that will be the world’s largest, at a time when no instrument can rival them and no telescope will have greater potential. In the search for galaxies at very high redshift, whose principal characteristics are in the near infrared, EMIR and the GTC will be a winning combination for a number of years to come.

· More information about the discovery (in English and French):

Natalia R. Zelman

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