636 research outputs found
The galaxy halo formation in the absence of violent relaxation and a universal density profile of the halo center
While N-body simulations testify for a cuspy profile of the central region of
the dark matter haloes, observations favor a shallow, cored density profile of
the central region of, at least, some spiral galaxies and dwarf spheroidals. We
show that a central profile, very close to the observed one, inevitably forms
in the center of dark matter haloes if we make a supposition about a moderate
energy relaxation of the system during the halo formation. If we assume the
energy exchange between dark matter particles during the halo collapse to be
not too intensive, the profile is universal: it depends almost not at all on
the properties of the initial perturbation and is very akin, but not identical,
to the Einasto profile with small Einasto index . We estimate the
size of the 'central core' of the distribution, i.e., the extent of the very
central region with a respectively gentle profile, and show that the cusp
formation is unlikely, even if the dark matter is cold. The obtained profile is
in a good agreement with observational data for, at least, some types of
galaxies, but clearly disagrees with N-body simulations.Comment: 8 pages, 4 figure
On the global well-posedness of a class of Boussinesq- Navier-Stokes systems
In this paper we consider the following 2D Boussinesq-Navier-Stokes systems
\partial_{t}u+u\cdot\nabla u+\nabla p+ |D|^{\alpha}u &= \theta e_{2}
\partial_{t}\theta+u\cdot\nabla \theta+ |D|^{\beta}\theta &=0 \quad with
and . When , , where is an explicit function
as a technical bound, we prove global well-posedness results for rough initial
data.Comment: 23page
Geometric optics and instability for semi-classical Schrodinger equations
We prove some instability phenomena for semi-classical (linear or) nonlinear
Schrodinger equations. For some perturbations of the data, we show that for
very small times, we can neglect the Laplacian, and the mechanism is the same
as for the corresponding ordinary differential equation. Our approach allows
smaller perturbations of the data, where the instability occurs for times such
that the problem cannot be reduced to the study of an o.d.e.Comment: 22 pages. Corollary 1.7 adde
WKB analysis for nonlinear Schr\"{o}dinger equations with potential
We justify the WKB analysis for the semiclassical nonlinear Schr\"{o}dinger
equation with a subquadratic potential. This concerns subcritical, critical,
and supercritical cases as far as the geometrical optics method is concerned.
In the supercritical case, this extends a previous result by E. Grenier; we
also have to restrict to nonlinearities which are defocusing and cubic at the
origin, but besides subquadratic potentials, we consider initial phases which
may be unbounded. For this, we construct solutions for some compressible Euler
equations with unbounded source term and unbounded initial velocity.Comment: 25 pages, 11pt, a4. Appendix withdrawn, due to some inconsistencie
Well-posedness of the Ericksen-Leslie system
In this paper, we prove the local well-posedness of the Ericksen-Leslie
system, and the global well-posednss for small initial data under the physical
constrain condition on the Leslie coefficients, which ensures that the energy
of the system is dissipated. Instead of the Ginzburg-Landau approximation, we
construct an approximate system with the dissipated energy based on a new
formulation of the system.Comment: 16 page
Physical conditions in the ISM of intensely star-forming galaxies at redshift~2
We analyze the physical conditions in the interstellar gas of 11 actively
star-forming galaxies at z~2, based on integral-field spectroscopy from the
ESO-VLT and HST/NICMOS imaging. We concentrate on the high H-alpha surface
brightnesses, large line widths, line ratios and the clumpy nature of these
galaxies. We show that photoionization calculations and emission line
diagnostics imply gas pressures and densities that are similar to the most
intense nearby star-forming regions at z=0 but over much larger scales (10-20
kpc). A relationship between surface brightness and velocity dispersion can be
explained through simple energy injection arguments and a scaling set by nearby
galaxies with no free parameters. The high velocity dispersions are a natural
consequence of intense star formation thus regions of high velocity dispersion
are not evidence for mass concentrations such as bulges or rings. External
mechanisms like cosmological gas accretion generally do not have enough energy
to sustain the high velocity dispersions. In some cases, the high pressures and
low gas metallicites may make it difficult to robustly distinguish between AGN
ionization cones and star formation, as we show for BzK-15504 at z=2.38. We
construct a picture where the early stages of galaxy evolution are driven by
self-gravity which powers strong turbulence until the velocity dispersion is
high. Then massive, dense, gas-rich clumps collapse, triggering star formation
with high efficiencies and intensities as observed. At this stage, the intense
star formation is likely self-regulated by the mechanical energy output of
massive stars.Comment: ApJ accepted main journal, 21 pages, 12 figure
Note on Global Regularity for 2D Oldroyd-B Fluids with Diffusive Stress
We prove global regularity of solutions of Oldroyd-B equations in 2 spatial
dimensions with spatial diffusion of the polymeric stresses
The Triangulum Extended (TREX) Survey: The Stellar Disk Dynamics of M33 as a Function of Stellar Age
Triangulum, M33, is a low mass, relatively undisturbed spiral galaxy that
offers a new regime in which to test models of dynamical heating. In spite of
its proximity, the dynamical heating history of M33 has not yet been well
constrained. In this work, we present the TREX Survey, the largest stellar
spectroscopic survey across the disk of M33. We present the stellar disk
kinematics as a function of age to study the past and ongoing dynamical heating
of M33. We measure line of sight velocities for ~4,500 disk stars. Using a
subset, we divide the stars into broad age bins using Hubble Space Telescope
and Canada-France-Hawaii-Telescope photometric catalogs: massive main sequence
stars and helium burning stars (~80 Myr), intermediate mass asymptotic branch
stars (~1 Gyr), and low mass red giant branch stars (~4 Gyr). We compare the
stellar disk dynamics to that of the gas using existing HI, CO, and Halpha
kinematics. We find that the disk of M33 has relatively low velocity dispersion
(~16 km/s), and unlike in the Milky Way and Andromeda galaxies, there is no
strong trend in velocity dispersion as a function of stellar age. The youngest
disk stars are as dynamically hot as the oldest disk stars and are dynamically
hotter than predicted by most M33 like low mass simulated analogs in Illustris.
The velocity dispersion of the young stars is highly structured, with the large
velocity dispersion fairly localized. The cause of this high velocity
dispersion is not evident from the observations and simulated analogs presented
here.Comment: 27 pages, 15 figures, 6 table
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