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"If we look at these plates of the sky to the naked eye, they seem rather dull because they are literally empty, devoid of light sources nearby, and we are eager to see what Euclid will reveal once. he will fix those eyes. dark on our cosmic past, "said Rene Laureijs, project manager Euclid at ESA, about the many discoveries to come.
Scientists from the Euclid Consortium have selected three extremely dark areas of the sky that will be the subject of the deepest observations of the mission, with the aim of exploring rare and rare objects of the Universe. The three fields contain a minimal amount of bright stars from the Milky Way – which "overshadow" weak sources such as distant galaxies; dust particles from the interstellar medium of the Milky Way – obscuring light from distant and weak sources; and so-called zodiacal light – the diffuse glow of dust in the solar system, which affects the sensitivity of observations.
The position of the Euclid Deep Fields – one in the northern sky and two in the southern sky – was announced last week at the consortium's annual meeting in Helsinki, Finland. With its planned launch in 2022, ESA's Euclid mission is making great progress both materially and scientifically. Once in space, Euclid will examine a significant portion of the sky and represent billions of galaxies across the Universe to investigate the ten billion years of our cosmic history.
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Most of the mission's observations will be devoted to the Euclid-wide investigation, covering about 15,000 square degrees – more than a third of the total sky – with an unprecedented combination of sharpness and sensitivity.
The deep fields of Euclid. Credit: ESA / Gaia / DPAC; Euclid Consortium. Acknowledgment: Euclid Consortium Survey Group
The observations will allow scientists to study two cosmological phenomena: the evolution of how galaxies have agglomerated over the last 10 billion years and the distortion of images of galaxies due to the presence of ordinary and dark matter interposing between them and us, an effect called gravitational. lens. These two phenomena respond to the key scientific objective of the mission: to dive into the history of the expansion of the Universe and characterize the acceleration of this expansion over the last billion years, which would be caused by the mysterious black energy.
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In addition, about 10% of Euclid's observation time will be devoted to an in-depth investigation, observing only three areas of the sky several times: Euclid's deep fields. The remaining time will be devoted to dedicated calibrations of Euclid's two complex and extremely sensitive instruments – the Visible Imager, VIS, and the Near Infrared Spectrophotometer, NISP.
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With a cumulative surface area of 40 square degrees, which corresponds to just over 200 times the footprint of the full moon in the sky, Euclid's deep fields cover a portion of the celestial sphere which, though much smaller that the vast investigation of the mission, remains remarkable for a thorough investigation.
The selection of domains was presented on June 4th at the Euclid Consortium's annual meeting, led by Yannick Mellier of the Institute of Astrophysics in Paris, France, and composed of 1,500 scientists from across Europe. United States and Canada.
One of the three fields, the Euclid Deep Field North, with an area of 10 square degrees, is located very close to the ecliptic north pole, in the constellation Draco, the dragon. The proximity of the ecliptic pole ensures maximum coverage throughout the year; the exact position was chosen to achieve maximum overlap with one of the deep fields studied by NASA's infrared workhorse, the Spitzer Space Telescope.
The other two fields are located in the southern sky. The challenge was to choose a region as close as possible to the southern ecliptic pole, which would provide the best possible coverage while avoiding light sources in this area, which is home to the Great Magellanic Cloud, one of the galactic neighbors of our Milky Way.
Euclid Fornax's deep field, also covering 10 square degrees, is located in the southern constellation of Fornax, the furnace. It encompasses the much smaller Chandra Deep Field South, a 0.11 degree square region of the sky that has been extensively studied over the last two decades with NASA's Chandra X-ray observatories and XMM-Newton's ESA, as well as the NASA / ESA Hubble. Space telescope and large ground telescopes.
The third and largest of these fields is the Euclid Deep Field South, which covers 20 square degrees in the southern constellation of Horologium, the pendulum clock. It was the most complex of the three to choose for a variety of technical reasons, also taking into account the capabilities of future ground-based wide-field telescopes, such as the large synoptic telescope. To date, no deep sky study has covered this area, which offers tremendous potential for exciting new discoveries.
"We are confident that Euclid 's deep fields will become a prime target in the coming years for multi – wavelength observations made by many ground – based and space – based telescopes. that they will be as useful and renowned as other deep fields studied in the past, "adds Scaramella.
Expected view of Euclid's deep field Fornax. Credit: Euclid Consortium (image); NASA / ESA, Hubble, CANDELS, Koekemoer et al. 2011, Grogin et al. 2011 (data)
In contrast to the approximately 30,000 single-visit observations required to cover the Euclid-wide survey, each targeting a slightly different field from the other and with little overlap, the satellite will make numerous visits to Euclid Deep Fields. Each field of deep field is observed at least 40 times to discover sources half as bright as in the wide survey.
Euclid's in-depth investigation has a twofold function: firstly, it provides a set of precise data to validate the main cosmological analysis based on the broad study, on the other hand, it is also essential to return to the same parts of the sky several times. stability monitoring and calibration throughout the mission.
The three deep fields provide a window for examining large quantities of galaxies, referring to the time of formation of the first stars and galaxies, which occurred during the first billion years of history of the universe. Due to the cosmic expansion, the light emitted by these galaxies is deflected towards the infrared. They are better detected in infrared wavelengths, which are difficult to access from the ground because of the Earth's atmosphere. Obtaining comparable data from Euclid's in-depth field survey would require several decades of continuous observation time from the best near-infrared facilities.
Together, the relatively large cumulative surface area of 40 degrees squared, the depth of the survey, and Euclid's imaging and spectroscopic capabilities in the infrared maximizes the likelihood of deep survey discovery. The survey will detect several hundred thousand galaxies per square degree; in the case of the farthest sources (with a red shift greater than six, corresponding to cosmic epochs when the Universe was less than a billion years old), estimates of the detection rate vary between a few dozen and at most a few hundred sources per square degree of uncertainty, due to poor statistics derived from existing observational data. This will change with Euclid, who can study an area of this size much faster than Hubble or even the future NASA / ESA / CSA James Webb space telescope would require.
Detections from Euclid's in-depth survey are attractive targets for follow-up observations with future installations such as the James Webb Space Telescope, scheduled for launch in 2021, the very large telescope of the European Southern Observatory (ESO) ) Integrated Chile and next-generation radio telescopes, such as the Square Kilometer Array (SKA), will be installed in South Africa and Australia in the 2020s. Repeated observation of Euclid's deep fields will also reveal analyze sources whose brightness and properties vary over time.
Programs are currently underway to observe parts of Euclid Deep Fields with Spitzer and several ground-based telescopes: Keck, Subaru, Gran Telescopio Canarias (GTC) and ESO's very large telescope (VLT). Euclid's extensive investigation will lead to a multitude of exciting and unexpected investigations, particularly when combined with independent field surveys will be conducted using other state-of-the-art observatories that will be available in the near future. . These include the eROSITA X-ray telescope, to be launched later this month, and the large Synoptic Survey telescope, currently under construction in Chile, USA, as well as the upcoming space observatory in the near future. NASA infrared, SPHEREx.
The Daily Galaxy via ESA
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