566 research outputs found
On the Interpretation of the l-v Features in the Milky Way Galaxy
We model the gas dynamics of barred galaxies using a three-dimensional,
high-resolution, -body+hydrodynamical simulation and apply it to the Milky
Way in an attempt to reproduce both the large-scale structure and the clumpy
morphology observed in Galactic H\emissiontype{I} and CO diagrams. Owing
to including the multi-phase interstellar medium, self-gravity, star-formation
and supernovae feedback, the clumpy morphology, as well as the large-scale
features, in observed diagrams are naturally reproduced. We identify in
our diagrams with a number of not only large-scale peculiar features such
as the '3-kpc arm', '135-km s arm' and 'Connecting arm' but also clumpy
features such as `Bania clumps', and then link these features in a face-on view
of our model. We give suggestions on the real structure of the Milky Way and on
the fate of gas clumps in the central region.Comment: accepted to PAS
Growth of Intermediate Massive Black Holes in the Hierarchical Formation of Small Spiral Galaxies in the High-z Universe
Combining a theoretical model of mass accretion onto a galactic center with a
high-resolution -body/SPH simulation, we investigate the formation of an
intermediate massive black hole (IMBH) during the hierarchical formation of a
small spiral galaxy (with a total mass of ) in the high-
universe. We found that the rate of average mass accretion to the nucleus due
to the radiation drag exerted by newly formed stars in the forming galaxy is
yr. As a result of this accretion, an IMBH
with can be formed in the center of the spiral galaxy
at . We found that a central BH coevolves with the dark matter halo
from to . The mass ratio of the BH to the dark matter halo
is nearly constant from to .
This is because that change in the dark matter potential enhances star
formation in the central part of the galaxy, and as a result the BH evolves due
to mass accretion via the radiation drag. Therefore, our model naturally
predicts a correlation between massive BHs and dark matter halos. Moreover, it
is found that the final BH-to-bulge mass ratio () in a
small spiral galaxy at high- is much smaller than that in the large galaxies
(). Our results also suggest that the scatter in the observed
scaling relations between the bulge mass and black hole mass are caused by a
time lag between BH growth and growth of bulge. We also predict that the X-ray
luminosity of AGN is positively correlated with the CO luminosity in the
central region. By comparing our results with the properties of Lyman break
galaxies (LBGs), it is predicted that some LBGs have massive BHs of .Comment: 8pages, 7figures, accepted for publication in ApJ (Volume 628, 20
July 2005 issue
Nuclear Star-Forming Ring of the Milky Way: Simulations
We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star Formation, and supernova feedback. A ring of dense gas clouds forms as a result of X-1-X-2 orbit transfer, and our potential model results in a ring radius of similar to 200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star Formation rate (SFR) in the CMZ, similar to 2 x 10(7) M-circle dot and similar to 0.1 M-circle dot yr(-1). Star Formation in our simulations takes place mostly in the outermost X-2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star Formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.Korea Research Foundation KRF-2008-013-C00037MEST of Korea R31-1001NASA NNG 05-GC37G, NNX 10-AF84GNYSTAR Faculty Development ProgramAstronom
Effects of a Supermassive Black Hole Binary on a Nuclear Gas Disk
We study influence of a galactic central supermassive black hole (SMBH)
binary on gas dynamics and star formation activity in a nuclear gas disk by
making three-dimensional Tree+SPH simulations. Due to orbital motions of SMBHs,
there are various resonances between gas motion and the SMBH binary motion. We
have shown that these resonances create some characteristic structures of gas
in the nuclear gas disk, for examples, gas elongated or filament structures,
formation of gaseous spiral arms, and small gas disks around SMBHs. In these
gaseous dense regions, active star formations are induced. As the result, many
star burst regions are formed in the nuclear region.Comment: 19 pages, 11 figures, accepted for publication in Ap
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