UK-led robotic sky scanner reveals its first galactic fingerprint

A major telescope upgrade has peered through to the distant Universe to map out the spectra of a pair of galaxies 280 million light years away from Earth.

The spectra provide a first glimpse of the sky from the WHT Enhanced Area Velocity Explorer (WEAVE) – a unique upgrade to the William Herschel Telescope (WHT) in La Palma on the Canary Islands. After its integration into the WHT last year, WEAVE has now begun its on-sky commissioning phase, ready to reveal more than 12 million spectra of stars and galaxies over the next five years with researchers from the University of Edinburgh playing a leading role in the planned surveys.  

Understanding the Universe through spectra

Spectroscopy is an essential element in an astronomer’s toolbox, splitting the light into its different wavelength components. Analysing this light reveals useful scientific information e.g. the speed of the object observed, the atoms it is made of and its temperature. If an image tells us what an astronomical object looks like, its spectrum tells us what it is.

First galactic spectra with WEAVE

A galaxy spectrum is the combination of spectra from the millions of stars in an observed galaxy. Studying the features of a galaxy spectrum allows astronomers to understand what types of stars the galaxy contains, and the relative abundances of each type of star. This tells us about how the galaxy formed and changed over time.

First-light observations with WEAVE were carried out with the large integral-field unit (LIFU) fibre bundle, one of WEAVE's three fibre systems. The team observed the heart of the galaxy group Stephan’s Quintet, a group of five interacting galaxies 280 million light-years from Earth, in the constellation Pegasus. The instrument was aimed at NGC 7318a and NGC 7318b, a pair of galaxies at the centre of the group, undergoing a major galaxy collision.

The WEAVE LIFU measures separate spectra for 547 different regions in and around the two galaxies, recording the colours of their light from the ultraviolet to the near-infrared. These spectra reveal the motions of stars and gas, the chemical composition of the stars, the temperatures and densities of the gas clouds, and more. These data will help astronomers learn how galaxy collisions transform the galaxies in the group.

Eight surveys using WEAVE

In the coming five years, the ING will assign 70% of the time available on the WHT to eight major surveys with WEAVE, selected out of those proposed by the astronomical communities of the partner countries. All these surveys require spectra of up to millions of individual stars and galaxies, a goal now obtainable thanks to WEAVE's ability to observe almost 1000 objects at a time.

Over 500 astronomers from across Europe, including a number of University of Edinburgh researchers, have organized these eight surveys, covering studies of stellar evolution, Milky Way science, galaxy evolution and cosmology. WEAVE will study galaxies near and far to learn the history of their growth, and will obtain millions of spectra of stars in the Milky Way.

Dr Kenneth Duncan at the School’s Institute for Astronomy is Deputy Science Team Lead of the WEAVE-LOFAR survey, a cornerstone of the WEAVE science:

These observations represent a huge milestone and really show off the unique capabilities of the WEAVE instrument. The amazing detail they reveal hints at the extraordinary scientific potential of the millions of spectra the WEAVE surveys will obtain in the next few years.

 The WEAVE-LOFAR (LOw Frequency ARray) survey has a broad selection of science goals, including measuring the physical processes that have shaped galaxies over the last 10 billion years of cosmic history. The team will use WEAVE in its most efficient MOS (multi-object spectroscopy) mode to obtain more than a million spectra of sources chosen on the basis of their radio emission detected by the LOFAR radio telescope (including programmes led by Prof. Philip Best at the School’s Institute for Astronomy ). This radio selection means that WEAVE-LOFAR will be very efficient, since the sample is rich with star-forming galaxies and sources dominated by black-hole accretion. 

Other Edinburgh researchers will use WEAVE data to unravel the detailed formation history of the Milky Way and its nearest galactic siblings.  Through measuring the speeds and heavy element contents of several million stars, WEAVE will provide the sharpest picture to date of how our home galaxy came to be.