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Title: Shocks and star formation in Stephan's Quintet. I. Gemini spectroscopy of Hα-bright knots

We present a Gemini-GMOS spectroscopic study of Hubble Space Telescope (HST)-selected Hα-emitting regions in Stephan's Quintet (HCG 92), a nearby compact galaxy group, with the aim of disentangling the processes of shock-induced heating and star formation in its intra-group medium. The ≈40 sources are distributed across the system, but most densely concentrated in the ∼kiloparsec-long shock region. Their spectra neatly divide them into narrow- and broad-line emitters, and we decompose the latter into three or more emission peaks corresponding to spatial elements discernible in HST imaging. The emission-line ratios of the two populations of Hα-emitters confirm their nature as H II regions (90% of the sample) or molecular gas heated by a shock front propagating at ≲300 km s{sup –1}. Their redshift distribution reveals interesting three-dimensional structure with respect to gas-phase baryons, with no H II regions associated with shocked gas, no shocked regions in the intruder galaxy NGC 7318B, and a sharp boundary between shocks and star formation. We conclude that star formation is inhibited substantially, if not entirely, in the shock region. Attributing those H II regions projected against the shock to the intruder, we find a lopsided distribution of star formation in this galaxy, reminiscent of pileupmore » regions in models of interacting galaxies. The Hα luminosities imply mass outputs, star formation rates, and efficiencies similar to nearby star-forming regions. Two large knots are an exception to this, being comparable in stellar output to the prolific 30 Doradus region. We also examine Stephan's Quintet in the context of compact galaxy group evolution, as a paradigm for intermittent star formation histories in the presence of a rich, X-ray-emitting intra-group medium. All spectra are provided as supplemental materials.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ; ;  [7] ;  [8] ;  [9]
  1. Australian Astronomical Observatory, P.O. Box 915, North Ryde NSW 1670 (Australia)
  2. NASA Herschel Science Center (NHSC), California Institute of Technology, Pasadena, CA 91125 (United States)
  3. Institut d'Astrophysique Spatiale, Université Paris-Sud XI, F-91405 Orsay, Cedex (France)
  4. Giant Magellan Telescope Organisation, Pasadena, CA 91101 (United States)
  5. Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF (United Kingdom)
  6. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
  7. Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada)
  8. Space Telescope Science Institute and European Space Agency, Baltimore, MD 21218 (United States)
  9. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States)
Publication Date:
OSTI Identifier:
22351536
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 784; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; DISTRIBUTION; EFFICIENCY; EMISSION; EVOLUTION; EXCEPTIONS; GALAXIES; INTERACTIONS; LUMINOSITY; MASS; RED SHIFT; SHOCK WAVES; SPACE; SPECTRA; SPECTROSCOPY; STARS; TELESCOPES; THREE-DIMENSIONAL CALCULATIONS; X RADIATION