Dust inhibits shock wave in iconic group of galaxies

November 27th, 2024

Footprint of the WEAVE GA surveys on the sky in Galactic coordinates (ℓ, b) in an Aitoff projection overlaid on the Gaia DR3 (Gaia Collaboration 2023a) density contours of stars with parallax measures, G < 16, and −10 deg < δ < 80 deg (in stars deg⁻²). HR chemo-dynamical survey: black dots; Open Clusters survey: red stars; disc-dynamics LR survey: dark green dots; high-latitude LR survey (shared with the WL and WQ surveys): thick yellow outline, where the region hashed using thinner yellow lines shows the provisional area to be surveyed at ∼100 per cent coverage factor, while the remaining area for this survey will be surveyed with an ∼30 per cent coverage factor. Known stellar streams and dwarf spheroidal galaxies covered within the pointed part of the high-latitude LR survey: light green stars. The available declination range arises from the impact of differential atmospheric refraction on targets near the edge of the field on the typical 1-hour WEAVE-Survey OB. Near-polar targets like NGC 188 require short exposures outside of the normal WEAVE-Survey OBs. Credit: Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad557

The shock wave triggered by one of the five galaxies making up the iconic Stephan's Quintet appears to be less disruptive than previously thought, with the shock likely being cushioned by dust particles in the surrounding gas. This is according to the analysis of the first scientific observations of WEAVE, a state-of-the-art instrument co-developed by Leiden astronomers for a telescope on the Spanish island of La Palma.

This finding is presented by a team of more than 60 astronomers, led by Marina Arnaudova (University of Hertfordshire, UK), who present their findings in the Monthly Notices of the Royal Astronomical Society. From Leiden, scientists involved in the development of the instrument include Remko Stuik, Reinout van Weeren, Huub Röttgering and Elena Rossi.

The researchers analyzed the characteristics of the moving gas in Stephan's Quintet, a group of five galaxies 300 million light years away that was discovered in 1877 by Edouard Stephan. One of the five galaxies, NGC 7318b, is speeding through the region at 3 million kilometers per hour, causing a shock wave that in turn leads to chaotic movements in the gas.

The researchers discovered that the shock wave has a dual nature. When the shock rips through pockets of cold gas at hypersonic speeds, electrons are torn away from atoms, leaving a glowing trail of charged gas, as seen with WEAVE. The shock weakens, however, when it passes through hot gas instead of cold gas. The researchers suspect that the hot gas contains dust particles that absorb the shock wave.

"We came up with the concept of WEAVE 15 years ago. An excellent team of engineers and scientists made this instrument a reality, and Martina's exciting results show how powerful WEAVE will be," says Scott Trager (Kapteyn Astronomical Institute, University of Groningen), lead scientist of WEAVE.

WEAVE stands for William Herschel Telescope Enhanced Area Velocity Explorer. The instrument allows astronomers to measure the velocities of thousands of stars and galaxies simultaneously, along with other possible measurements. The core of WEAVE consists of nearly a thousand movable glass fibers that makes it somewhat like a weaving loom.

WEAVE was developed and built by the Netherlands, Spain and the UK, with contributions from France and Italy. The scientific results published today are based on the first science observations that were taken using WEAVE's Large Integral Field Unit, a system developed and built by the Netherlands Research School for Astronomy (NOVA) and its Optical & Infrared Instrumentation Group.

More information:
M I Arnaudova et al, WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan's Quintet, Monthly Notices of the Royal Astronomical Society (2024). DOI: 10.1093/mnras/stae2235

Shoko Jin et al, The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation, Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad557

Provided by Leiden University