93 research outputs found
Dark matter in galaxies
Dark matter in galaxies, its abundance, and its distribution remain a subject
of long-standing discussion, especially in view of the fact that neither dark
matter particles nor dark matter bodies have yet been found. Experts' opinions
range from a very large number of completely dark galaxies exist to nonbaryonic
dark matter does not exist at all in any significant amounts. We discuss
astronomical evidence for the existence of dark matter and its connection with
visible matter and examine attempts to estimate its mass and distribution in
galaxies from photometry, dynamics, gravitational lensing, and other
observations (the cosmological aspects of the existence of dark matter are not
considered in this review). In our view, the presence of dark matter in and
around galaxies is a well-established fact. We conclude with an overview of
mechanisms by which a dark halo can influence intragalactic processes.Comment: 82 pages, 35 figure
WSRT observations and surface photometry of two unusual spiral galaxies
We discuss the results of a mass decomposition of two spiral galaxies, NGC
6824 and UGC 11919. In a previous analysis of the Hyperleda catalog, the
galaxies were identified as having a peculiar dynamical . The aim of this
study is to confirm or disprove the preliminary findings, indicating a
non-standard stellar initial mass function (IMF) for the galaxies. The surface
photometry in B, V, and R bands was carried out with the Apache Point 0.5-m
telescope and the \ion{H}{I} data cubes were obtained with the Westerbork
Synthesis Radio Telescope (WSRT). Photometric profiles were decomposed into
bulge and exponential disk components. Using the obtained \ion{H}{I} data
cubes, rotation curves of both galaxies were constructed. Employing the
photometric profiles, the mass distribution of the galaxies was decomposed into
mass components: bulge, stellar disk, gas, and pseudo-isothermal dark halo. We
conclude that NGC 6824 possesses a stellar disk with mass-to-light ratio
, in agreement with its color . On the
contrary, UGC 11919 appears to have a very lightweight disk. Its dynamically
estimated mass corresponds to a low stellar disk mass-to-light ratio
. Under standard assumptions, this ratio does
not agree with the relatively red color of the disk, while a bottom light
stellar initial mass function is needed to explain the observations.Comment: 14 pages, 14 figures, accepted for publication in Astronomy and
Astrophysic
Do low surface brightness galaxies have dense disks?
The disk masses of four low surface brightness galaxies (LSB) were estimated
using marginal gravitational stability criterion and the stellar velocity
dispersion data which were taken from Pizzella et al., 2008 [1]. The
constructed mass models appear to be close to the models of maximal disk. The
results show that the disks of LSB galaxies may be significantly more massive
than it is usually accepted from their brightnesses. In this case their surface
densities and masses appear to be rather typical for normal spirals. Otherwise,
unlike the disks of many spiral galaxies, the LSB disks are dynamically
overheated.Comment: 14 pages, 10 figures, submitted to Astronomy Report
- …