Powerful High-Velocity Dispersion Molecular Hydrogen Associated with an Intergalactic Shock Wave in Stephan's Quintet

• Published in: The Astrophysical journal 2006-03, Vol.639 (2), p.L51-L54
• Main Authors: Appleton, P. N, Xu, Kevin C, Reach, William, Dopita, Michael A, Gao, Y, Lu, N, Popescu, C. C, Sulentic, J. W, Tuffs, R. J, Yun, M. S
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 1538-4357; 0004-637X; 1538-4357
• DOI: 10.1086/502646

We present the discovery of strong mid-infrared emission lines of molecular hydrogen of apparently high-velocity dispersion (6870 km s super(-1)) originating from a group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope observations reveal emission lines of molecular hydrogen and little else. This is the first time an almost pure H sub(2) line spectrum has been seen in an extragalactic object. Along with the absence of PAH-dust features and very low excitation ionized gas tracers, the spectra resemble shocked gas seen in Galactic supernova remnants, but on a vast scale. The molecular emission extends over 24 kpc along the X-ray-emitting shock front, but it has 10 times the surface luminosity as the soft X-rays and about one-third the surface luminosity of the IR continuum. We suggest that the powerful H sub(2) emission is generated by the shock wave caused when a high-velocity intruder galaxy collides with filaments of gas in the galaxy group. Our observations suggest a close connection between galaxy-scale shock waves and strong broad H sub(2) emission lines, like those seen in the spectra of ultraluminous infrared galaxies where high-speed collisions between galaxy disks are common.