Star formation in outer rings of S0 galaxies - I. NGC 6534 and MCG 11-22-015статья
Статья опубликована в высокорейтинговом журнале
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Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 16 января 2019 г.
Аннотация:Though S0 galaxies are usually thought to be `red and dead', they often demonstrate star formation organized in ring structures. We try to clarify the nature of this phenomenon and its difference from star formation in spiral galaxies. Two early-type galaxies with outer rings, NGC 6534 and MCG 11-22-015, are selected to be studied. After inspecting the gas excitation in the rings using Baldwin-Phillips-Terlevich method, we estimate the star formation rates (SFR) in the two outer rings of our galaxies by using several SFR indicators - narrow-band photometry in the H-alpha emission line and archival GALEX ultraviolet images of the galaxies. The ionized gas is excited by young stars in the ring of NGC 6534 and partly by shocks - in MCG 11-22-015. The oxygen abundances in the HII regions of the rings are solar. The derived SFRs allow to restore qualitatively star formation histories (SFH) in the rings: in NGC 6534 the SFH is flat during the last 100-200 Myr, in MCG 11-22-015 the star formation has started only a few Myr ago. We suggest that the rings in NGC 6534 and MCG 11-22-015 have different natures: the former is a resonant one, and the latter has been produced by a satellite. Recent outer gas accretion is needed in both cases.