WEAVE spectrograph begins study of galaxy formation and evolution
More than 500 astronomy professionals from all over Europe, including members of the IEEC, have designed and planned a total of five years of operations for this instrument recently at the Canary Islands Observatory
A versatile instrument that, combined with Gaia's measurements, can address a wide range of stellar and galactic science, from the origin of the Milky Way to the chemistry of the most distant galaxies
The Isaac Newton Group of Telescopes (ING) and the WEAVE instrument team present observations of the first light (the first use) with the WEAVE spectrograph. This is a powerful new generation multifibre spectrograph in the William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory (La Palma, Canary Islands) which has recently been launched and is already generating high-quality data.
Astronomers from all over Europe, including members of the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) have planned eight surveys for observation with WEAVE, including studies of stellar evolution, the Milky Way, the galaxy evolution and cosmology. In line with the European Space Agency's Gaia satellite, WEAVE will be used to obtain spectra of several million stars in the disc and halo of our galaxy, enabling the archaeology of the Milky Way. Nearby and distant galaxies will be studied to know the history of their growth. And quasars will be used as indications to map the spatial distribution and interaction of gas and galaxies when the universe was only about 20% of today's age.
First light observations: Stephan's Quintet galaxies
WEAVE targeted two galaxies at the centre of Stephan's Quintet (a group of interacting galaxies) named NGC 7318a and NGC 7318b. This group had already been observed with the Hubble, Spitzer and Chandra telescopes, among others, and more recently also with the James Webb Space Telescope (JWST). Its galaxies, four of which are 280 million light-years from Earth, are colliding with each other, providing an excellent "close-up" laboratory for studying the consequences of galaxy collisions and subsequent evolution.
The William Herschel telescope with the WEAVE instrument. The WEAVE fibre positioner is located in the 1.8-metre black box on the upper ring. Optical fibres run through the telescope structure to the platform on the left, which houses the spectrograph. Credit: Sebastian Kramer.
The observations of the first light were carried out with the so-called ‘Large Integral Field Unit’ (LIFU) fibre array, one of WEAVE’s three fibre systems. When using the LIFU, 547 very compact optical fibres transmit the light from a hexagonal area of the sky to the spectrograph, where it is analysed and recorded.
WEAVE’s LIFU has measured a large number of individual spectra of the galaxies NGC 7318a and NGC 7318b and their surroundings, and has examined the intensity of the colours of their light, from the ultraviolet to the near-infrared. These spectra reveal, among other information, details essential for studying the collision processes, such as the motion and distribution of stars and gas, and their chemical composition. From these data, we can learn how galaxy collisions transform the other galaxies in the group.
The study demonstrates that the LIFU part of WEAVE not only works, but produces high-quality data. The ING telescopes will continue to deliver results of high scientific impact in the coming years.
In this image, the blue, green and red colours in the central part indicate speeds derived from the WEAVE spectra and are superimposed on an image of Stephan's Quintet composed of starlight (from the CFHT telescope) and X-ray emission from hot gas (bluish vertical diffuse band, from the Chandra X-ray Observatory). The speeds obtained by WEAVE indicate that the left-centred galaxy (NGC 7318b, painted blue) is entering the group from behind at about almost 3 000 000 km/h. This high-speed collision wreaks havoc on NGC 7318b. Clouds of hydrogen gas —the fuel needed for the formation of new stars — are receding from the galaxy. This is likely to slow down the rate of new star formation in this galaxy. The WEAVE spectra will help to find out the fate of the expelled gas as it moves out into the space between the galaxies in the group. Credits: X-ray (blue): NASA/CXC/CfA/E. O'Sullivan, optics (brown): Canada-France-Hawaii-Telescope/Coelum, WEAVE LIFU: Marc Balcells.
The Catalan contribution to the WEAVE spectrograph
This project involves scientists from the Institute of Cosmos Sciences of the Universitat de Barcelona (ICCUB) and the Universitat Politècnica de Catalunya · Barcelona Tech (UPC). The IEEC is taking part with researchers from the ICCUB and UPC units. The Catalan institutions have worked, from the beginning of the project, on the definition of the scientific objectives and the selection of the objects to be observed —from stars in various evolutionary phases to star clusters— as well as in the sampling of quasars, extremely bright and very distant active nuclei galaxies. Specifically, researchers Maria Monguió and Mercè Romero-Gómez (ICCUB-IEEC), and Roberto Raddi (UPC), are members of the international working groups on young stars, galactic archaeology and white dwarfs that make up the team of scientists responsible for planning the observations. Teresa Antoja and Ignasi Pérez-Ràfols, also members of the IEEC at the ICCUB, co-lead the research teams responsible for galactic disc dynamics and quasars, respectively.
Dr Monguió says: "After years of preparation, we hope to soon be able to obtain the first spectra of stars in the disc of our galaxy. The quantity and quality of the millions of spectra we expect to observe will allow us, among other things, to analyse regions of recent star formation and to measure how stars move. These data, together with those provided by the Gaia mission, will allow us to address fundamental questions about the formation and evolution of the Milky Way”.
WEAVE, a new generation spectrograph
The WEAVE spectrograph uses optical fibres to collect light from celestial objects and transmits it to a spectrograph that separates the light according to its different wavelengths. It can work at two different spectral resolutions, which are used to measure the speeds of objects in the line of sight (using the Doppler effect) and to determine their chemical composition.
The versatility of WEAVE is one of its main strengths. While the LIFU mode contains hundreds of fibres in a compact distribution, essential for imaging extended areas of the sky, in the MOS (multi-object spectroscopy) mode about a thousand individual fibres can be placed (by two robots) to simultaneously collect light from stars, galaxies or quasars.
During the first five years of operation, spectra of millions of individual stars and galaxies are expected, a goal that can be achieved thanks to the WEAVE spectrograph's ability to observe so many bodies at once.
Press release prepared in collaboration with the Communication offices of the Institute of Cosmos Sciences (ICCUB), the Universitat de Barcelona (UB) and the Universitat Politècnica de Catalunya · Barcelona Tech (UPC).
Main Image
Caption: Image of the James Webb Space Telescope (JWST) from Stephan's quintet, with the outline of the WEAVE LIFU pointing for the first-light observation. Each circle indicates an optical fibre 2.6 arcseconds in diameter. The observation provides physical information on the different regions of each of the galaxies, as well as their immediate surroundings, spanning 120 000 light-years from one end to the other.
Credits: NASA, ESA, CSA, STScI (background image); Aladin (fibre overlay).
Links
– IEEC
– ICCUB
– UPC
– WEAVE
– ING
More information
This research is presented in a paper entitled “The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation”, by Shoko Jin, Scott C. Trager et al., accepted for publication by Monthly Notices of the Royal Astronomical Society. You can also check ING’s press release.
The Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of 25 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centers, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.
IEEC is a private non-profit foundation, governed by a Board of Trustees composed of Generalitat de Catalunya and four other institutions that each have a research unit, which together constitute the core of IEEC R&D activity: the Universitat de Barcelona (UB) with the research unit ICCUB — Institute of Cosmos Sciences; the Universitat Autònoma de Barcelona (UAB) with the research unit CERES — Center of Space Studies and Research; the Universitat Politècnica de Catalunya · BarcelonaTech (UPC) with the research unit CTE — Research Group in Space Sciences and Technologies; the Spanish Research Council (CSIC) with the research unit ICE — Institute of Space Sciences. The IEEC is a CERCA (Centres de Recerca de Catalunya) centre.
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