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]/PAH_tot 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.

Links

• PREPRINT http://arxiv.org/abs/1309.1525
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2013ApJ...777...66A
• ELECTR https://doi.org/10.1088%2F0004-637X%2F777%2F1%2F66
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2013ApJ...777...66A
• PDF https://iopscience.iop.org/article/10.1088/0004-637X/777/1/66/pdf
• PDF https://stacks.iop.org/0004-637X/777/66/pdf
• DATA http://archives.esac.esa.int/hsa/whsa/?ACTION=PUBLICATION&ID=2013ApJ...777...66A
• DATA https://cda.harvard.edu/chaser?obsid=789
• DATA https://irsa.ipac.caltech.edu/bibdata/2013/A/2013ApJ...777...66A.html