Bird's-eye View of Molecular Gas across Stephan's Quintet Galaxy Group and Intragroup Medium

Abstract We present the large-scale distribution and kinematics of cold molecular gas across the compact galaxy group Stephan’s Quintet, based on CO(2–1) observations performed with the Atacama Compact Array (ACA) and CO(1–0) data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We find coherent structures of molecular gas associated with the galaxies and intragroup medium, which follow the distribution of warm H 2 previously seen with the James Webb Space Telescope (JWST). CO is associated with a ridge of shocked gas that crosses the galaxy group, and with a spiral arm of the intruding galaxy NGC 7318b, which interacts with the intragroup medium along the ridge. Although the ridge contains widespread shocks, turbulent gas, and warm H 2 , the CO lines are narrower than elsewhere in Stephan’s Quintet (FWHM ∼ 25–65 km s −1 ), indicative of settled cold gas. At a distinctly different velocity, CO is found in the active galaxy NGC 7319 and northern star-forming region SQ-A. A bridge of turbulent molecular gas connects NGC 7319 with the ridge, covering a gap of ∼700 km s −1 between these structures. The gas excitation ranges from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mfenced close=")" open="" separators=""> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">CO</mml:mi> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>2</mml:mn> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mo>′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> / <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mfenced close=")" open="" separators=""> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">CO</mml:mi> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mo>′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> ∼ 0.3 in the bridge and SQ-A, to ∼0.5 along the ridge, to near unity in the center of NGC 7319. We also detect either a molecular outflow or turbulent molecular gas associated with the radio source in NGC 7319. These ACA data are part of a program with the Atacama Large Millimeter/submillimeter Array and JWST to study the physics of molecular gas from the largest to the smallest scales across the intragroup medium of Stephan’s Quintet.