Shock-enhanced C+ Emission and the Detection of H2O from the Stephan's Quintet Group-wide Shock Using Herschel

November 2013 • 2013ApJ...777...66A

Authors • Appleton, P. N. • Guillard, P. • Boulanger, F. • Cluver, M. E. • Ogle, P. • Falgarone, E. • Pineau des Forêts, G. • O'Sullivan, E. • Duc, P. -A. • Gallagher, S. • Gao, Y. • Jarrett, T. • Konstantopoulos, I. • Lisenfeld, U. • Lord, S. • Lu, N. • Peterson, B. W. • Struck, C. • Sturm, E. • Tuffs, R. • Valchanov, I. • van der Werf, P. • Xu, K. C.

Abstract • We present the first Herschel spectroscopic detections of the [O I] 63 μm and [C II] 158 μm fine-structure transitions, and a single para-H2O line from the 35 × 15 kpc2 shocked intergalactic filament in Stephan's Quintet. The filament is believed to have been formed when a high-speed intruder to the group collided with a clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (>1000 km s-1) luminous [C II] line profiles, as well as fainter [O I] 63 μm emission. SPIRE FTS observations reveal water emission from the p-H2O (111-000) transition at several positions in the filament, but no other molecular lines. The H2O line is narrow and may be associated with denser intermediate-velocity gas experiencing the strongest shock-heating. The [C II]/PAHtot and [C II]/FIR ratios are too large to be explained by normal photo-electric heating in photodissociation regions. H II region excitation or X-ray/cosmic-ray heating can also be ruled out. The observations lead to the conclusion that a large fraction the molecular gas is diffuse and warm. We propose that the [C II], [O I], and warm H2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the intergalactic medium is dissipated to small scales and low velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [C II]/[O I] ratio, and the relatively high [C II]/H2 ratios observed. The discovery that [C II] emission can be enhanced, in large-scale turbulent regions in collisional environments, has implications for the interpretation of [C II] emission in high-z galaxies.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.


IPAC Authors


Phil Appleton

Senior Scientist