99 research outputs found
Boosted Tidal Disruption by Massive Black Hole Binaries During Galaxy Mergers FROM The View of N-Body Simulation
Supermassive black hole binaries (SMBHBs) are productions of the hierarchical
galaxy formation model. There are many close connections between central SMBH
and its host galaxy because the former plays very important roles on the
formation and evolution of a galaxy. For this reason, the evolution of SMBHBs
in merging galaxies is an essential problem. Since there are many discussions
about SMBHB evolution in gas rich environment, we focus on the quiescent
galaxy, using tidal disruption as a diagnostic tool. Our study is based on a
series of numerical large particle number direct N-body simulations for dry
major mergers. According to the simulation results, the evolution can be
divided into three phases. In phase I, the tidal disruption rate for two well
separated SMBHs in merging system has similar level to single SMBH in isolate
galaxy. After two SMBHs getting close enough to form a bound binary in phase
II, the disruption rate can be enhanced for ~ 2 order of magnitudes within a
short time. This "boosted" disruption stage finishes after the SMBHB evolving
to compact binary system in phase III, corresponding to a drop back of
disruption rate to a level of a few times higher than that in Phase I. How to
correctly extrapolate our N-body simulation results to reality, and
implications of our results to observations, are discussed too.Comment: 16 pages, Accepted for publication in Ap
Orbital evolution of the Carina dwarf galaxy and self-consistent star formation history determination
We present a new study of the evolution of the Carina dwarf galaxy that
includes a simultaneous derivation of its orbit and star formation history. The
structure of the galaxy is constrained through orbital parameters derived from
the observed distance, proper motions, radial velocity and star formation
history. The different orbits admitted by the large proper motion errors are
investigated in relation to the tidal force exerted by an external potential
representing the Milky Way (MW). Our analysis is performed with the aid of
fully consistent N-body simulations that are able to follow the dynamics and
the stellar evolution of the dwarf system in order to determine
self-consistently the star formation history of Carina. We find a star
formation history characterized by several bursts, partially matching the
observational expectation. We find also compatible results between dynamical
projected quantities and the observational constraints. The possibility of a
past interaction between Carina and the Magellanic Clouds is also separately
considered and deemed unlikely.Comment: Accepted in A&
On the Influence of Minor Mergers on the Radial Abundance Gradient in Disks of Milky Way-like Galaxies
We investigate the influence of stellar migration caused by minor mergers
(mass ratio from 1:70 to 1:8) on the radial distribution of chemical abundances
in the disks of Milky Way-like galaxies during the last four Gyr. A GPU-based
pure N-body tree-code model without hydrodynamics and star formation was used.
We computed a large set of mergers with different initial satellite masses,
positions, and orbital velocities. We find that there is no significant
metallicity change at any radius of the primary galaxy in the case of accretion
of a low-mass satellite of 10 M (mass ratio 1:70) except for the
special case of prograde satellite motion in the disk plane of the host galaxy.
The accretion of a satellite of a mass M (mass
ratio 1:23) results in an appreciable increase of the chemical abundances at
galactocentric distances larger than kpc. The radial abundance
gradient flattens in the range of galactocentric distances from 5 to 15 kpc in
the case of a merger with a satellite with a mass
M. There is no significant change in the abundance gradient slope in
the outer disk (from kpc up to 25 kpc) in any merger while the scatter
in metallicities at a given radius significantly increases for most of the
satellite's initial masses/positions compared to the case of an isolated
galaxy. This argues against attributing the break (flattening) of the abundance
gradient near the optical radius observed in the extended disks of Milky
Way-like galaxies only to merger-induced stellar migration.Comment: 17 pages, 15 figures, accepted for publication in Ap
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Exercise addiction – the emergence of a new disorder
An optimal level of regular physical activity plays an important role in the maintenance of physical and mental health. However, excessive exercise in a minority of individuals can have adverse effects on health and lead to exercise addiction. Exercise addiction can be conceptualised as a behavioural addiction. The aim of this paper is to outline the current knowledge on the concept, epidemiology, aetiology, comorbidity, and possible interventions of exercise addiction
Galactic Halo Stars in Phase Space :A Hint of Satellite Accretion?
The present day chemical and dynamical properties of the Milky Way bear the
imprint of the Galaxy's formation and evolutionary history. One of the most
enduring and critical debates surrounding Galactic evolution is that regarding
the competition between ``satellite accretion'' and ``monolithic collapse'';
the apparent strong correlation between orbital eccentricity and metallicity of
halo stars was originally used as supporting evidence for the latter. While
modern-day unbiased samples no longer support the claims for a significant
correlation, recent evidence has been presented by Chiba & Beers
(2000,AJ,119,2843) for the existence of a minor population of high-eccentricity
metal-deficient halo stars. It has been suggested that these stars represent
the signature of a rapid (if minor) collapse phase in the Galaxy's history.
Employing velocity- and integrals of motion-phase space projections of these
stars, coupled with a series of N-body/Smoothed Particle Hydrodynamic (SPH)
chemodynamical simulations, we suggest an alternative mechanism for creating
such stars may be the recent accretion of a polar orbit dwarf galaxy.Comment: 12 pages(incl. figures). Accepted for publication in ApJ letters
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On the isolated dwarf galaxies: from cuspy to flat dark matter density profiles and metallicity gradients
The chemodynamical evolution of spherical multi-component self-gravitating
models for isolated dwarf galaxies is studied. We compare their evolution with
and without feedback effects from star formation processes. We find that
initially cuspy dark matter profiles flatten with time as a result of star
formation, without any special tuning conditions. Thus the seemingly flattened
profiles found in many dwarfs do not contradict the cuspy profiles predicted by
cosmological models. We also calculate the chemical evolution of stars and gas,
to permit comparisons with observational data.Comment: Accepted the 28/01/1
Dissipative N - body code for galaxy evolution
The evolving galaxy is considered as a system of baryonic fragments embedded
into the static dark nonbaryonic (DH) and baryonic (BH) halo and subjected to
gravitational and viscous interactions. Although the chemical evolution of each
separate fragment is treated in the frame of one -- zone close box model with
instantaneous recycling, its star formation (SF) activity is a function of mean
local gas density and, therefore, is strongly influenced by other interacting
fragments. In spite of its simplicity this model provides a realistic
description of the process of galaxy formation and evolution over the Hubble
timescale.Comment: 11 pages, LaTeX, 7 figures, using the article.sty, expected in
A&ApTr, 18, 83
Validity of abundances derived from spaxel spectra of the MaNGA survey
We measured the emission lines in the spaxel spectra of MaNGA galaxies in
order to determine the abundance distributions therein. It has been suggested
that the strength of the low-ionization lines, R_2, N_2, and S_2 may be
increased (relative to Balmer lines) in (some) spaxel spectra of the MaNGA
survey due to a contribution of the radiation of the diffuse ionized gas.
Consequently, the abundances derived from the spaxel spectra through
strong-line methods may suffer from large errors. We examined this expectation
by comparing the behaviour of the line intensities and the abundances estimated
through different calibrations for slit spectra of HII regions in nearby
galaxies, for fibre spectra from the SDSS, and for spaxel spectra of the MaNGA
survey. We found that the S_2 strength is increased significantly in the fibre
and spaxel spectra. The mean enhancement changes with metallicity and can be as
large as a factor of 2. The mean distortion of R_2 and N_2 is less than a
factor of 1.3. This suggests that Kaufmann et al.'s demarcation line between
AGNs and HII regions in the BPT diagram is a useful criterion to reject spectra
with significantly distorted strengths of the N_2 and R_2 lines. We find that
the three-dimensional R calibration, which uses the N_2 and R_2 lines, produces
reliable abundances in the MaNGA galaxies. The one-dimensional N2 calibration
produces either reliable or wrong abundances depending on whether excitation
and N/O abundance ratio in the target region (spaxel) are close to or differ
from those parameters in the calibrating points located close to the
calibration relation. We then determined abundance distributions within the
optical radii in the discs of 47 MaNGA galaxies. The optical radii of the
galaxies were estimated from the surface brightness profiles constructed based
on the MaNGA observations.Comment: 19 pages, 15 figures, accepted for publication in A&
Interaction of Recoiling Supermassive Black Holes with Stars in Galactic Nuclei
Supermassive black hole binaries (SMBHBs) are the products of frequent galaxy
mergers. The coalescence of the SMBHBs is a distinct source of gravitational
wave (GW) radiation. The detections of the strong GW radiation and their
possible electromagnetic counterparts are essential. Numerical relativity
suggests that the post-merger supermassive black hole (SMBH) gets a kick
velocity up to 4000 km/s due to the anisotropic GW radiations. Here we
investigate the dynamical co-evolution and interaction of the recoiling SMBHs
and their galactic stellar environments with one million direct N-body
simulations including the stellar tidal disruption by the recoiling SMBHs. Our
results show that the accretion of disrupted stars does not significantly
affect the SMBH dynamical evolution. We investigate the stellar tidal
disruption rates as a function of the dynamical evolution of oscillating SMBHs
in the galactic nuclei. Our simulations show that most of stellar tidal
disruptions are contributed by the unbound stars and occur when the oscillating
SMBHs pass through the galactic center. The averaged disruption rate is
~10^{-6} M_\odot yr^{-1}, which is about an order of magnitude lower than that
by a stationary SMBH at similar galactic nuclei. Our results also show that a
bound star cluster is around the oscillating SMBH of about ~ 0.7% the black
hole mass. In addition, we discover a massive cloud of unbound stars following
the oscillating SMBH. We also investigate the dependence of the results on the
SMBH masses and density slopes of the galactic nuclei.Comment: 38 pages, 10 figues; accepted for publication in Ap
Tracing the Evolution of SMBHs and Stellar Objects in Galaxy Mergers: An Multi-mass Direct N-body Model
By using direct N-body numerical simulations, we model the dynamical
co-evolution of two supermassive black holes (SMBHs) and the surrounding stars
in merging galaxies. In order to investigate how different stellar components
evolve during the merger, we generate evolved stellar distributions with an
initial mass function. Special schemes have also been developed to deal with
some rare but interesting events, such as tidal disruption of main sequence
stars, the plunge of low mass stars, white dwarfs, neutron stars and stellar
mass black holes, and the partial tidal disruption of red giants or asymptotic
giant branch stars. Our results indicate that the formation of a bound
supermassive black hole binary (SMBHB) will enhance the capture rates of
stellar objects by the SMBHs. Compared to the equal stellar mass model, the
multi-mass model tends to result in a higher average mass of disrupted stars.
Instead of being tidally disrupted by the SMBH, roughly half of the captured
main sequence stars will directly plunge into the SMBH because of their small
stellar radius. Giant stars, on the other hand, can be stripped of their
envelopes if they are close enough to the SMBH. Though most remnants of the
giant stars can survive after the disruption, a small fraction still could
plunge into the SMBH quickly or after many orbital periods. Our results also
indicate significant mass segregation of compact stars at the beginning of the
merger, and then this effect is destroyed as the two SMBHs form a bound binary.Comment: 36 pages, 11 figures, and 1 table. Accepted for publication in Ap
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