105 research outputs found
Galaxy merging in MOND
We present the results of N-body simulations of dissipationless galaxy
merging in Modified Newtonian Dynamics (MOND). For comparison, we also studied
Newtonian merging between galaxies embedded in dark matter halos, with internal
dynamics equivalent to the MOND systems. We found that the merging timescales
are significantly longer in MOND than in Newtonian gravity with dark matter,
suggesting that observational evidence of rapid merging could be difficult to
explain in MOND. However, when two galaxies eventually merge, the MOND merging
end-product is hardly distinguishable from the final stellar distribution of an
equivalent Newtonian merger with dark matter.Comment: 5 pages, 2 color figures. To appear in MNRAS Letters. Added
references and discussion, conclusions unchange
Radially anisotropic systems with forces. II: radial-orbit instability
We continue to investigate the dynamics of collisionless systems of particles
interacting via additive interparticle forces. Here we focus on
the dependence of the radial-orbit instability on the force exponent .
By means of direct -body simulations we study the stability of equilibrium
radially anisotropic Osipkov-Merritt spherical models with Hernquist density
profile and with . We determine, as a function of , the
minimum value for stability of the anisotropy radius and of the
maximum value of the associated stability indicator . We find that, for
decreasing , decreases and increases, i.e.
longer-range forces are more robust against radial-orbit instability. The
isotropic systems are found to be stable for all the explored values of
. The end products of unstable systems are all markedly triaxial with
minor-to-major axial ratio , so they are never flatter than an E7 system.Comment: 12 pages, 6 figure
Vertical dynamics of disk galaxies in MOND
We investigate the possibility of discriminating between Modified Newtonian
Dynamics (MOND) and Newtonian gravity with dark matter, by studying the
vertical dynamics of disk galaxies. We consider models with the same circular
velocity in the equatorial plane (purely baryonic disks in MOND and the same
disks in Newtonian gravity embedded in spherical dark matter haloes), and we
construct their intrinsic and projected kinematical fields by solving the Jeans
equations under the assumption of a two-integral distribution function. We
found that the vertical velocity dispersion of deep-MOND disks can be much
larger than in the equivalent spherical Newtonian models. However, in the more
realistic case of high-surface density disks this effect is significantly
reduced, casting doubts on the possibility of discriminating between MOND and
Newtonian gravity with dark matter by using current observations.Comment: 8 pages, 7 figures. Accepted for publication in MNRAS. Added
referenc
The imprint of dark matter haloes on the size and velocity dispersion evolution of early-type galaxies
Early-type galaxies (ETGs) are observed to be more compact, on average, at than at , at fixed stellar mass. Recent observational
works suggest that such size evolution could reflect the similar evolution of
the host dark matter halo density as a function of the time of galaxy
quenching. We explore this hypothesis by studying the distribution of halo
central velocity dispersion () and half-mass radius () as
functions of halo mass and redshift , in a cosmological -CDM
-body simulation. In the range , we find
and , close to
the values expected for homologous virialized systems. At fixed in the
range we find
and . We show that
such evolution of the halo scaling laws is driven by individual haloes growing
in mass following the evolutionary tracks and , consistent with simple dissipationless merging models in
which the encounter orbital energy is accounted for. We compare the -body
data with ETGs observed at by populating the haloes with
a stellar component under simple but justified assumptions: the resulting
galaxies evolve consistently with the observed ETGs up to , but the
model has difficulty reproducing the fast evolution observed at .
We conclude that a substantial fraction of the size evolution of ETGs can be
ascribed to a systematic dependence on redshift of the dark matter haloes
structural properties.Comment: 15 pages, 14 figures, 1 table. Matches the Accepted version from
MNRA
Radial-orbit instability in modified Newtonian dynamics
The stability of radially anisotropic spherical stellar systems in modified
Newtonian dynamics (MOND) is explored by means of numerical simulations
performed with the N-body code N-MODY. We find that Osipkov-Merritt MOND models
require for stability larger minimum anisotropy radius than equivalent
Newtonian systems (ENSs) with dark matter, and also than purely baryonic
Newtonian models with the same density profile. The maximum value for stability
of the Fridman-Polyachenko-Shukhman parameter in MOND models is lower than in
ENSs, but higher than in Newtonian models with no dark matter. We conclude that
MOND systems are substantially more prone to radial-orbit instability than ENSs
with dark matter, while they are able to support a larger amount of kinetic
energy stored in radial orbits than purely baryonic Newtonian systems. An
explanation of these results is attempted, and their relevance to the MOND
interpretation of the observed kinematics of globular clusters, dwarf
spheroidal and elliptical galaxies is briefly discussed.Comment: 9 pages, 4 figures, accepted for publication in MNRA
Radial orbital anisotropy and the Fundamental Plane of elliptical galaxies
The existence of the Fundamental Plane (FP) imposes strong constraints on the
structure and dynamics of elliptical galaxies, and thus contains important
information on the processes of their formation and evolution. Here we focus on
the relations between the FP thinness and tilt and the amount of radial orbital
anisotropy. By using N-body simulations of galaxy models characterized by
observationally motivated density profiles, and also allowing for the presence
of live, massive dark matter halos, we explore the impact of radial orbital
anisotropy and instability on the FP properties. The numerical results confirm
a previous semi--analytical finding: the requirement of stability matches
almost exactly the thinness of the FP. In other words, galaxy models that are
radially anisotropic enough to be found outside the observed FP (with their
isotropic parent models lying on the FP) are unstable, and their end--products
fall back on the FP itself. We also find that a systematic increase of radial
orbit anisotropy with galaxy luminosity cannot explain by itself the whole tilt
of the FP, becoming the galaxy models unstable at moderately high luminosities:
at variance with the previous case their end--products are found well outside
the FP itself (abridged).Comment: 30 pages, 6 figures, MNRAS (accepted
Recovery of smell sense loss by mepolizumab in a patient allergic to dermatophagoides and affected by chronic rhinosinusitis with nasal polyps
Background: Chronic rhinosinusitis with nasal polyps (CRSwNP) frequently presents with dysfunction or loss of the
sense of smell, resulting in a signifcant impairment in quality of life. The medical treatments currently available may
improve the olfactory function in patients with CRSwNP, but such an outcome is generally only transitory. We report
the case of a patient with CRSwNP who completely recovered from smell sense loss by treatment with mepolizumab.
Case presentation: The patient was a 62-year-old female who has severe asthma induced by allergy to Dermatophagoides and concomitant CRSwNP. Any treatment for the latter, including oral and injective corticosteroids, was unsuccessful in the loss of smell. Due to the satisfaction of admission criteria to mepolizumab treatment for severe asthma,
treatment was initiated on March 2018, resulting in good clinical control of both asthma and CRSwNP, and particularly
in complete recovery of the smell loss after 4 months of treatment and still persisting.
Conclusion: In this case report, the treatment with mepolizumab in a patient allergic to Dermatophagoides and
afected by CRSwNP was associated with an improvement of anosmia. That fnding may be explained by a reduction
of the nasal obstruction by nasal polyp
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