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تسجيل مستخدم جديدShocks and Star Formation in Stephans Quintet. I. Gemini Spectroscopy of H{alpha}-bright knots
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تأليف
I. S. Konstantopoulos
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We present a Gemini-GMOS spectroscopic study of HST-selected H{alpha}-emitting regions in Stephans 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 $approx$40 sources are distributed across the system, but most densely concentrated in the $sim$kpc-long shock region. Their spectra neatly divide them into narrow- and 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 H{alpha}-emitters confirm their nature as H II regions (90% of the sample) or molecular gas heated by a shock-front propagating at $lesssim$300 km/s. 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 pile-up regions in models of interacting galaxies. The H{alpha} 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 Stephans 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.
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