Star formation in outer rings of S0 galaxies. IV. NGC 254: a double-ringed S0 with gas counter-rotationстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 8 апреля 2022 г.
Аннотация:Though S0 galaxies are usually considered ``red and dead'', they often demonstrate star formation organized into ring structures. We try to clarify the nature of this phenomenon and its difference from star formation in spiral galaxies. Here we investigate the nearby moderate luminosity S0 galaxy NGC 254 using long-slit spectroscopy taken with the South African Large Telescope and publicly available imaging data. Applying a full spectral fitting, we analyzed gaseous and stellar kinematics as well as ionized gas excitation and metallicity and stellar population properties resolved by radius. An advanced approach of simultaneous fitting spectra and photometric data allowed us quantify the fraction of hidden counter-rotating stars in this galaxy. We found that the ionized gas is counterrotating with respect to the stars throughout NGC 254 disk, indicating an external origin of the gas. The star formation fed by this counterrotating gas occurs within two rings, an outer ring at R=55'' - 70'' and an inner ring at R=18'', which is closer to the center than the inner stellar ring. The star formation rate is weak, 0.02 solar mass per year in total, the gas metallicity is slightly subsolar. Regarding the nature of the starforming ring, we argue a recent, less than 1 Gyr ago, cold gas accretion as a result of a minor merger from a retrograde orbit, which has already formed 1% of counterrotating stars.