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

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DOIResolve DOI: http://doi.org/10.1088/0004-637X/784/1/1
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TypeArticle
Journal titleThe Astrophysical Journal
ISSN0004-637X
Volume784
Issue1
Article number1
Pages115; # of pages: 15
Subjectgalaxies: groups: individual (HCG 92); galaxies: individual (NGC 7317, NGC 7318A, NGC 7318B, NGC 7319); galaxies: interactions; galaxies: star formation; intergalactic medium; shock waves
AbstractWe 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-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 pileup 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.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); National Science Infrastructure
Peer reviewedYes
NPARC number21273038
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Record identifier751cd29a-a249-42ba-ae59-20693719e162
Record created2014-12-09
Record modified2016-07-18
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