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arXiv · 1309.1525

Shock-Enhanced C+ Emission and the Detection of H2O from Stephan's Quintet's Group-Wide Shock using Herschel

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

We present the first Herschel spectroscopic detections of the [OI]63 and [CII]158 micron fine-structure transitions, and a single para-H2O line from the 35 x 15 kpc^2 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 clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (> 1000 km s^-1) luminous [CII] line profiles, as well as fainter [OI]63micron 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 [CII]/PAH{tot) and [CII]/FIR ratios are too large to be explained by normal photo-electric heating in PDRs. HII 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 [CII], [OI] and warm H2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the IGM is dissipated to small scales and low-velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [CII]/[OI] ratio, and the relatively high [CII]/H2 ratios observed. The discovery that [CII] emission can be enhanced, in large-scale turbulent regions in collisional environments has implications for the interpretation of [CII] emission in high-z galaxies.

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P. N. Appleton, P. Guillard, F. Boulanger, M. E. Cluver, P. Ogle, E. Falgarone, G. Pineau Des Forets, E. O'Sullivan, P. -A. Duc, S. Gallagher, Y. Gao, T. Jarrett, I. Konstantopoulos, U. Lisenfeld, S. Lord, N. Lu, B. W. Peterson, C. Struck, E. Sturm, R. Tuffs, I. Valchanov, P. van der Werf, K. C. Xu. 2013-09-06. Shock-Enhanced C+ Emission and the Detection of H2O from Stephan's Quintet's Group-Wide Shock using Herschel. https://doi.org/10.1088/0004-637x%2F777%2F1%2F66

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