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"A fascinating mystery!" – Ghost galaxies: living fossils of the dawn of the universe

Posted on February 27, 2019

Hubble Deep Field Image

"One of the interesting possibilities is that some of these ghostly galaxies are living fossils from the dawn of the universe when stars and galaxies appeared in a very different environment than the one in the world. today, "said Aaron Romanowsky, an astronomer at UCO and an associate professor in the Department of Physics and Astronomy. at the University of San José State. "Their birth is truly a fascinating mystery that our team seeks to solve."

A team of astronomers led by the Observatories of the University of California (UCO) studied in detail a galaxy so weak and so virgin that it served as a control capsule, sealed soon after the Dawn of our universe, to be next opened by the The latest technology at the observatory WM Keck, the Keck Cosmic Web Imager (KCWI).

This transparent and ghostly galaxy, called DGSAT I, contradicts the current theory of GOD formation. All previously studied UDGs were in clusters of galaxies, which served as a foundation for the theory that they were once "normal" galaxies, but over time they became a mess because of events violent in the cluster.

"There seemed to be a relatively neat image of the origins of galaxies, from spirals to ellipticals and giants to dwarves," said lead author Ignacio Martín-Navarro, a postdoctoral researcher at UCO. "However, the recent discovery of GOD has raised new questions about the complexity of this table. All the UDGs that have been studied in detail so far have been in clusters of galaxies: dense regions of violent interactions where the characteristics of galaxies at birth have been blurred by a difficult adolescence. "

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Because BDSD I is a rare exception in a key distribution group found outside a cluster, it provides a better understanding of the past. There has not been much activity around him that can alter its composition and evolution. In order to find out what made this galaxy so insensitive to stars, the team used KCWI to map the composition of the galaxy.

"The chemical composition of a galaxy provides a record of environmental conditions at the time of its formation, as well as how trace minerals in the human body can reveal lifelong dietary habits and exposure to pollutants." , said co-author Romanowsky.

DGSAT I surprised the researchers with its chemical composition. Current galaxies usually contain more heavy elements, such as iron and magnesium, compared to ancient galaxies born just after the Big Bang. But KCWI revealed that DGSAT I appears to be anemic; the iron content of the galaxy is remarkably low, as if it were formed from an almost virgin gas cloud that was not polluted by the supernova death of previous stars. And yet, DGSAT I's magnesium levels are normal, which is what astronomers expect to find in modern galaxies. It's strange because these two elements are released during supernova events; you do not usually find one without the other.

Anemic early galaxies

DGSAT I (left), an ultra-diffuse galaxy (UDG), is shown next to a normal spiral galaxy (right) for comparison purposes. Both are similar in size, but UDGs like DGSAT have so few stars, you can see through them, galaxies in the background. (A. Romanowsky and D. Martinez-Delgado)

"We do not understand this combination of pollutants, but one of our ideas is that extreme supernova fire caused the galaxy to have a size size during its teenage years, so as to keep magnesium preferentially iron Said Romanowsky.

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UDGs are a relatively new class of galaxies that were discovered in 2015. They are as large as the Milky Way but have 100 to 1000 times fewer stars than our own galaxy, making them barely visible and difficult. to study.

KCWI is designed to overcome this obstacle with its extreme sensitivity and ability to capture high-resolution spectra from the farthest and farthest objects of our universe, such as UDGs.

"There is only one other instrument in the world with KCWI capabilities that allows us to measure the chemical composition of low light-intensity galaxies," said co-author Jean Brodie, professor of Astronomy and astrophysics at UCO. "But this one is in the southern hemisphere, where we do not have a good view of the SASB I, which is in the North."

KCWI performs a type of observation called full-field spectroscopy, which captures data in 3-D instead of 2-D. Traditionally, astronomers had two ways to study celestial objects, either by imaging or by spectroscopy. This instrument breaks the barrier between the two. In one observation, KCWI captures both the image and the spectrum of each pixel in the image, which reveals the physical properties of the object, such as composition, temperature, velocity, and so on.

"These are the kinds of observations for which we built KCWI; continue to push the boundaries to get the most information among the weakest objects, "said John O'Meara, Chief Scientist at Keck Observatory. "We are very excited to see how many objects like DGSAT I can study with Keck and continue to transform our understanding of how galaxies form and evolve over time."

The researchers plan to use the KCWI again, this time to make a closer observation of another GOD similar to DGSAT I; they plan to expand its composition in more detail in the hope of providing more data that could help astronomers identify the origin of the GMUs.

The new version of Hubble's deep image is displayed at the top of the page. In dark gray, you can see the new light that has been found around the galaxies in this field. This light corresponds to the brightness of more than a hundred billion suns. It took nearly three years for researchers at the Instituto de Astrofísica de Canarias to produce this deepest image of the Universe ever captured in space, recovering a large amount of "lost" light around the largest galaxies of the famous Hubble Ultra-Deep Field.

The Daily Galaxy via the W. M. Keck Observatory

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