1,773 research outputs found
HI properties of nearby galaxies from a volume-limited sample
We consider global HI and optical properties of about three hundred nearby
galaxies with V km/s. The majority of them have individual
photometric distance estimates. The galaxy sample parameters, e.g. their linear
diameters, their HI mass-to-luminosity ratio, their total mass-to-luminosity
ratio, their mean optical surface brightness show some known and some new
correlations implying a meaningful dynamic explanation. For the LV galaxies
their HI mass and angular momentum follow a nearly linear relation expected for
rotating gaseous disks being near the threashold of gravitational instability,
favourable for active star formation.Comment: 5 pages, 9 figures, uses laa.sty accepted by A&A Suppl. Serie
6-meter telescope observations of three dwarf spheroidal galaxies with very low surface brightness
Dwarf spheroidal galaxies (dSphs) are mostly investigated in the Local Group.
DSphs are difficult targets for observations because of their small size and
very low surface brightness. Here we measure spectroscopic and photometric
parameters of three candidates for isolated dSphs, KKH65=BTS23, KK180, and
KK227, outside the Local Group. The galaxies are found to be of low metallicity
and low velocity dispersion. They are among the lowest surface brightness
objects in the Local Universe. According to the measured radial velocities,
metallicities, and structural and photometric parameters, KKH65 and KK227 are
representatives of the ultra-diffuse quenched galaxies. KKH65 and KK227 belong
to the outer parts of the groups NGC3414 and NGC5371, respectively. KK180 is
located in the Virgo cluster infall region.Comment: 4 pages, 3 figures, 3 tables, 3 Appendices with 5 figures and 3
table
Giant acceleration in slow-fast space-periodic Hamiltonian systems
Motion of an ensemble of particles in a space-periodic potential well with a
weak wave-like perturbation imposed is considered. We found that slow
oscillations of wavenumber of the perturbation lead to occurrence of directed
particle current. This current is amplifying with time due to giant
acceleration of some particles. It is shown that giant acceleration is linked
with the existence of resonant channels in phase space
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