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Observed characteristics of globular clusters in the ultra-diffuse dwarf galaxy IKN
As a result of observations at BTA in a long-slit mode with the SCORPIO-1 instrument
(Afanasyev and Moiseev 2005), the spectra were obtained and radial velocities, age,
metallicity, and abundances of chemical elements Mg, Ca, and C were determined for the
first time for 4 globular clusters in the closest representative of the rarest class
galaxies - the ultra-diffuse dwarf galaxy (UDG) IKN - located at a distance of 3.75 Mpc.
UDGs have diameters of the order of several kiloparsecs and very low surface brightness.
They consist of old stars. Globular clusters in IKN turned out to be old and low-metal,
similar in chemical abundance to NGC6341 in the Milky Way. The results of this work are
important for understanding the properties of stellar populations of IKN and verifying
the presence of the dark matter in the UDG.
Authors:
Sharina M.E. (SAO RAS), Shimansky V.V. (KFU)
Published:
1. Sharina M.E., Shimansky V.V. «Globular cluster spectroscopy in the spheroid
dwarf galaxy IKN», 2019, Astronomical Journal, Volume 96, No. 8, p. 674-686
Chemical composition of gas in polar-ring galaxies
In galaxies with polar rings, outer rings of stars, gas, and dust are observed
rotating almost perpendicular to the disk of the central galaxy. This peculiar
morphology is the result of gravitational interaction with the matter of a
different direction of the rotation momentum. This can be a merger with an
orthogonally oriented companion, capture of the dwarf companion matter, or gas
accretion from extended cosmological filaments. The last scenario is gaining
more and more popularity, but accurate measurements of the chemical composition
of gas are necessary to verify it, since the theory predicts a relatively low
abundance of heavier elements in it. As a result of spectroscopic studies carried
out at the 6-m SAO RAS telescope, the number of galaxies with polar rings with
measured oxygen abundance was three times increased. Moreover, all galaxies
follow the standard "luminosity-metallicity" ratio, which rejects for them
the scenario of the formation of polar structures by accretion from filaments.
It is also shown that a significant role in gas ionization is played by shock
waves arising from the collision of gaseous clouds of the ring and the stellar
disk of the galaxy. This effect has long been predicted but was previously
observed only in a single galaxy.
Authors:
O.V. Egorov, A.V. Moiseev (SAO RAS, SAI MSU)
Published:
1. O.V. Egorov, A.V. Moiseev, Metallicity and ionization state of the gas in
polar-ring galaxies, 2018, MNRAS, v. 486, p. 4186
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