557 research outputs found
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
Impulsive Gas Fueling to Galactic Center in a Barred Galaxy Due to Falls of Gas Clouds
We have studied the evolution of the central hundred pc region of barred
galaxies by performing numerical simulations realizing multi-phase nature of
gas. Our simulations have shown that a stellar bar produces an oval gas ring
namely the -2 ring within as the bar grows. The ring is
self-gravitationally unstable enough to trigger formations of gas clouds.
Although the gas clouds initially rotate in the -2 ring, cloud-cloud
collisions and/or energy injections into the gas ring by Type II supernovae
deviate some of the clouds from the ring orbit. After the deviation, the
deviated clouds repeat collisions with the other clouds, which rotate in the
-2 ring, during several rotations. These processes effectively reduce the
angular momentum of the deviated gas cloud. As a result, the gas cloud finally
falls into the galactic center, and episodic gas supply to the galactic center
takes place.Comment: 10 pages, 9 figures, accepted for publication in PAS
Mass Supply to Galactic Center due to Nested Bars in the Galaxy
We investigate rapid mass supply process by nested bars in the Galaxy by
numerical simulation. We simulate gas flow in the whole galaxy disk with nested
bars, which are the outer bar and the inner bar, especially with highly spatial
resolution in the galactic central region. We assume two cases of inner bar
size which are a smaller one and a larger one than the radius of the 200 pc gas
ring which is corresponds to the Central Molecular Zone. From our numerical
results, in the large size bar cases, the inner bars with large elongation
induce sufficient mass inflow and destroy the 200 pc gas ring. On the other
hand, in the small size bar cases, the inner bars with large elongation induce
large mass inflow and do not destroy the 200 pc gas ring. This mass inflow is
caused by straight shocks excited by the inner bar. In this case, nuclear gas
disks of ~ 15 pc radius are formed. The nuclear gas disks are
self-gravitationally unstable and we expect formation of compact star clusters
under strong tidal force in the nuclear gas disks. We discuss evolution of the
nuclear gas disk.Comment: 36 pages, 11 figures. Submitted to Ap
Massive core/star formation triggered by cloud-cloud collision: Effect of magnetic field
We study effect of magnetic field on massive dense core formation in
colliding unequal molecular clouds by performing magnetohydrodynamic
simulations with sub-parsec resolution (0.015 pc) that can resolve the
molecular cores. Initial clouds with the typical gas density of the molecular
clouds are immersed in various uniform magnetic fields. The turbulent magnetic
fields in the clouds consistent with the observation by Crutcher et al. (2010)
are generated by the internal turbulent gas motion before the collision, if the
uniform magnetic field strength is 4.0 G. The collision speed of 10 km
s is adopted, which is much larger than the sound speeds and the
Alfv\'{e}n speeds of the clouds. We identify gas clumps with gas densities
greater than 5 10 g cm as the dense cores and trace
them throughout the simulations to investigate their mass evolution and
gravitational boundness. We show that a greater number of massive,
gravitationally bound cores are formed in the strong magnetic field (4.0
G) models than the weak magnetic field (0.1 G) models. This is partly
because the strong magnetic field suppresses the spatial shifts of the shocked
layer that should be caused by the nonlinear thin shell instability. The
spatial shifts promote formation of low-mass dense cores in the weak magnetic
field models. The strong magnetic fields also support low-mass dense cores
against gravitational collapse. We show that the numbers of massive,
gravitationally bound cores formed in the strong magnetic field models are much
larger than the isolated, non-colliding cloud models, which are simulated for
comparison. We discuss the implications of our numerical results on massive
star formation.Comment: Published in PASJ (for special issue on cloud-cloud collision). This
arXiv version is similar to the published paper (
https://academic.oup.com/pasj/article/doi/10.1093/pasj/psaa059/5867032
Tidal disruption of dark matter halos around proto-globular clusters
Tidal disruption of dark matter halos around proto-globular clusters in a
halo of a small galaxy is studied in the context of the hierarchical clustering
scenario by using semi-cosmological N-body/SPH simulations assuming the
standard cold dark matter model (). Our analysis on formation and
evolution of the galaxy and its substructures archives until . In such
a high-redshift universe, the Einstein-de Sitter universe is still a good
approximation for a recently favored -dominated universe, and then our
results does not depend on the choice of cosmology. In order to resolve small
gravitationally-bound clumps around galaxies and consider radiative cooling
below , we adopt a fine mass resolution (m_{\rm SPH} = 1.12 \times
10^3 \Msun). Because of the cooling, each clump immediately forms a
`core-halo' structure which consists of a baryonic core and a dark matter halo.
The tidal force from the host galaxy mainly strips the dark matter halo from
clumps and, as a result, theses clumps get dominated by baryons. Once a clump
is captured by the host halo, its mass drastically decreases each pericenter
passage. At , more than half of the clumps become baryon dominated
systems (baryon mass/total mass ). Our results support the tidal
evolution scenario of the formation of globular clusters and baryon dominated
dwarf galaxies in the context of the cold dark matter universe.Comment: 9page, 13 figures. Accepted for publication in ApJ. A high-resolution
PDF of the paper can be obtained from http://th.nao.ac.jp/~takayuki/ApJ05
How do different spiral arm models impact the ISM and GMC population?
The nature of galactic spiral arms in disc galaxies remains elusive.
Regardless of the spiral model, arms are expected to play a role in sculpting
the star-forming interstellar medium. As such, different arm models may result
in differences in the structure of the interstellar medium and molecular cloud
properties. In this study we present simulations of galactic discs subject to
spiral arm perturbations of different natures. We find very little difference
in how the cloud population or gas kinematics vary between the different
grand-design spirals, indicting that the interstellar medium on cloud scales
cares little about where spiral arms come from. We do, however, see a
difference in the interarm/arm mass spectra, {and minor differences in tails of
the distributions of cloud properties} (as well as radial variations in the
stellar/gaseous velocity dispersions). These features can be attributed to
differences in the radial dependence of the pattern speeds between the
different spiral models, and could act as a metric of the nature of spiral
structure in observational studies.Comment: 18 pages, 17 figures. Accepted for publication in MNRA
Whole-genome sequencing of Theileria parva strains provides insight into parasite migration and diversification in the african continent
The disease caused by the apicomplexan protozoan parasite Theileria parva, known as East Coast fever or Corridor disease, is one of the most serious cattle diseases in Eastern, Central, and Southern Africa. We performed whole-genome sequencing of nine T. parva strains, including one of the vaccine strains (Kiambu 5), field isolates from Zambia, Uganda, Tanzania, or Rwanda, and two buffalo-derived strains. Comparison with the reference Muguga genome sequence revealed 34 814–121 545 single nucleotide polymorphisms (SNPs) that were more abundant in buffalo-derived strains. High-resolution phylogenetic trees were constructed with selected informative SNPs that allowed the investigation of possible complex recombination events among ancestors of the extant strains. We further analysed the dN/dS ratio (non-synonymous substitutions per non-synonymous site divided by synonymous substitutions per synonymous site) for 4011 coding genes to estimate potential selective pressure. Genes under possible positive selection were identified that may, in turn, assist in the identification of immunogenic proteins or vaccine candidates. This study elucidated the phylogeny of T. parva strains based on genome-wide SNPs analysis with prediction of possible past recombination events, providing insight into the migration, diversification, and evolution of this parasite species in the African continent
Genome sequence of an Australian kangaroo, Macropus eugenii, provides insight into the evolution of mammalian reproduction and development.
BACKGROUND: We present the genome sequence of the tammar wallaby, Macropus eugenii, which is a member of the kangaroo family and the first representative of the iconic hopping mammals that symbolize Australia to be sequenced. The tammar has many unusual biological characteristics, including the longest period of embryonic diapause of any mammal, extremely synchronized seasonal breeding and prolonged and sophisticated lactation within a well-defined pouch. Like other marsupials, it gives birth to highly altricial young, and has a small number of very large chromosomes, making it a valuable model for genomics, reproduction and development. RESULTS: The genome has been sequenced to 2 × coverage using Sanger sequencing, enhanced with additional next generation sequencing and the integration of extensive physical and linkage maps to build the genome assembly. We also sequenced the tammar transcriptome across many tissues and developmental time points. Our analyses of these data shed light on mammalian reproduction, development and genome evolution: there is innovation in reproductive and lactational genes, rapid evolution of germ cell genes, and incomplete, locus-specific X inactivation. We also observe novel retrotransposons and a highly rearranged major histocompatibility complex, with many class I genes located outside the complex. Novel microRNAs in the tammar HOX clusters uncover new potential mammalian HOX regulatory elements. CONCLUSIONS: Analyses of these resources enhance our understanding of marsupial gene evolution, identify marsupial-specific conserved non-coding elements and critical genes across a range of biological systems, including reproduction, development and immunity, and provide new insight into marsupial and mammalian biology and genome evolution
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