Abstract
I discuss my latest observational data and ideas about decoupled gaseous subsystems in nearby lenticular galaxies. As an extreme case of inclined gaseous disks, I demonstrate a sample of inner polar disks, derive their incidence, about 10% among the volume-limited nearby S0 galaxies, and discuss their origin. However, large-scale decoupled gaseous disks at intermediate inclinations are also a rather common phenomenon among the field S0 galaxies. I suggest that the geometry of outer gas accretion and the final morphology of the galaxy may be tightly related: inclined gas infall may prevent star formation in the accreted disk and force the disk galaxy to be a lenticular.
Highlights
Minor merging, or gas accretion from outside, is thought to be the main driver of evolution of disk galaxies [1]
Though we have found a few cases of the inner polar disks which warp in the galaxy outer parts into counterrotating large-scale gaseous disks
The observational result obtained by Butcher and Oemler and summarized in their final paper [39] concerned the difference in content of galaxy clusters between z = 0 and z = 0.4: in nearby rich clusters, like Coma, most galaxies were red, being morphologically ellipticals and lenticulars, while in distant clusters the fraction of blue galaxies rised significantly, up to 25%
Summary
Gas accretion from outside, is thought to be the main driver of evolution of disk galaxies [1]. The gas in S0s often reveals itself as regularly rotating ionized-gas disk (51% of all ETG [7]), though it is mostly ionized not by young massive stars [8] All this gas seems to be accreted in recent events from outside. It is implied by frequent misalignments between the rotation axes of the stellar and gaseous components in S0s. When we have studied the sample of strictly isolated nearby S0s, we have found that half of all ionized-gas disks in the isolated S0s counterrotates the stars when observing with the long-slit spectrographs along the disk isophote major axes [11].
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