WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan's Quintet

TL;DR

This study uses multi-wavelength observations and advanced spectroscopy to analyze the origin, properties, and impact of a large-scale shock front in Stephan's Quintet, revealing its effects on different gas phases and dust survival.

Contribution

It provides the first detailed, high-precision localization and characterization of the shock front in Stephan's Quintet using the WEAVE integral field spectrograph and multi-wavelength data.

Findings

Shock is hypersonic in cold gas, matching emission line ratios.

Shock is relatively weak in hot plasma, with Mach number 2-4.

Adiabatic compression explains increased radio emission.

Abstract

We present a detailed study of the large-scale shock front in Stephan's Quintet, a byproduct of past and ongoing interactions. Using integral-field spectroscopy from the new William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE), recent 144 MHz observations from the LOFAR Two-metre Sky Survey (LoTSS), and archival data from the Very Large Array and James Webb Space Telescope (JWST), we obtain new measurements of key shock properties and determine its impact on the system. Harnessing the WEAVE large integral field unit's (LIFU) field of view (90 $\times$ 78 arcsec$^{2}$), spectral resolution ($R\sim2500$) and continuous wavelength coverage across the optical band, we perform robust emission line modeling and dynamically locate the shock within the multi-phase intergalactic medium (IGM) with higher precision than previously possible. The shocking of the cold gas phase is hypersonic, and comparisons with shock models show that it can readily account for the observed emission line ratios. In contrast, we demonstrate that the shock is relatively weak in the hot plasma visible in X-rays (with Mach number of $\mathcal{M} \sim 2 - 4$), making it inefficient at producing the relativistic particles needed to explain the observed synchrotron emission. Instead, we propose that it has led to an adiabatic compression of the medium, which has increased the radio luminosity ten-fold. Comparison of the Balmer line-derived extinction map with the molecular gas and hot dust observed with JWST suggests that pre-existing dust may have survived the collision, allowing the condensation of H$_{2}$ - a key channel for dissipating the shock energy.