657 research outputs found
HI studies of the Sculptor group galaxies. VIII. The background galaxies: NGC 24 and NGC 45
In order to complete our HI survey of galaxies in the Sculptor group area,
VLA observations of NGC 24 and NGC 45 are presented. These two galaxies of
similar magnitude M_B ~ -17.4 lie in the background of the Sculptor group and
are low surface brightness galaxies, especially NGC 45. The HI distribution and
kinematics are regular for NGC 24 while NGC 45 exhibits a kinematical twist of
its major axis. A tilted-ring model shows that the position angle of the major
axis changes by ~25 degrees. A best-fit model of their mass distribution gives
mass-to-light ratios for the stellar disk of 2.5 and 5.2 for NGC 24 and NGC 45
respectively. These values are higher than the ones expected from stellar
population synthesis models. Despite the large dark matter contribution, the
galaxy mass is still dominated by the stellar component in their very inner
regions. These high mass-to-light ratios are typical of what is seen in low
surface brightness galaxies and may indicate that, in those galaxies, disks are
far from the maximum disk case. The halo parameters derived from the best-fit
models are thus lower limits.Comment: 23 pages, 10 figures, accepted for publication in The Astronomical
Journa
Extended HI Rotation Curve and Mass Distribution of M31
New HI observations of Messier 31 (M31) obtained with the Effelsberg and
Green Bank 100-m telescopes make it possible to measure the rotation curve of
that galaxy out to ~35 kpc. Between 20 and 35 kpc, the rotation curve is nearly
flat at a velocity of ~226 km/s. A model of the mass distribution shows that at
the last observed velocity point, the minimum dark-to-luminous mass ratio is
\~0.5 for a total mass of 3.4 10^11 Msol at R < 35 kpc. This can be compared to
the estimated MW mass of 4.9 10^11 Msol for R < 50 kpc.Comment: 4 pages, 2 figures, accepted for publication in ApJ Letter
The magnetic fields of large Virgo Cluster spirals
Because of its proximity the Virgo Cluster is an excellent target for
studying interactions of galaxies with the cluster environment. Both the
high-velocity tidal interactions and effects of ram pressure stripping by the
intracluster gas can be investigated. Optical and/or \ion{H}{i} observations do
not always show effects of weak interactions between galaxies and their
encounters with the cluster medium. For this reason we searched for possible
anomalies in the magnetic field structure in Virgo Cluster spirals which could
be attributed to perturbations in their gas distribution and kinematics. Five
angularly large Virgo Cluster spiral galaxies (NGC 4501, NGC 4438, NGC 4535,
NGC 4548 and NGC 4654) were the targets for a sensitive total power and
polarization study using the 100-m radio telescope in Effelsberg at 4.85 GHz.
For two objects polarization data at higher frequencies have been obtained
allowing Faraday rotation analysis. Distorted magnetic field structures were
identified in all galaxies. Interaction-induced magnetized outflows were found
in NGC 4438 (due to nuclear activity) and NGC 4654 (a combination of tidal
tails and ram pressure effects). Almost all objects (except the anaemic NGC
4548) exhibit distortions in polarized radio continuum attributable to
influence of the ambient gas. For some galaxies they agree with observations of
other species, but sometimes (NGC 4535) the magnetic field is the only tracer
of the interaction with the cluster environment. The cluster environment
clearly affects the evolution of the galaxies due to ram pressure and tidal
effects. Magnetic fields provide a very long-lasting memory of past
interactions. Therefore, they are a good tracer of weak interactions which are
difficult to detect by other observations.Comment: 13 pages, 12 figure
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
On the analyticity and Gevrey class regularity up to the boundary for the Euler Equations
We consider the Euler equations in a three-dimensional Gevrey-class bounded
domain. Using Lagrangian coordinates we obtain the Gevrey-class persistence of
the solution, up to the boundary, with an explicit estimate on the rate of
decay of the Gevrey-class regularity radius
H-alpha Kinematics of the SINGS Nearby Galaxies Survey. II
This is the second part of an H-alpha kinematics follow-up survey of the
Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this program
is to shed new light on the role of baryons and their kinematics and on the
dark/luminous matter relation in the star forming regions of galaxies, in
relation with studies at other wavelengths. The data for 37 galaxies are
presented. The observations were made using Fabry-Perot interferometry with the
photon-counting camera FaNTOmM on 4 different telescopes, namely the
Canada-France-Hawaii 3.6m, the ESO La Silla 3.6m, the William Herschel 4.2m,
and the Observatoire du mont Megantic 1.6m telescopes. The velocity fields are
computed using custom IDL routines designed for an optimal use of the data. The
kinematical parameters and rotation curves are derived using the GIPSY
software. It is shown that non-circular motions associated with galactic bars
affect the kinematical parameters fitting and the velocity gradient of the
rotation curves. This leads to incorrect determinations of the baryonic and
dark matter distributions in the mass models derived from those rotation
curves.Comment: 18 pages, 5 figures, 4 tables. Accepted for publication in MNRAS. All
high-res. figures are available at
http://www.astro.umontreal.ca/fantomm/singsII
The Milky Way: An Exceptionally Quiet Galaxy; Implications for the formation of spiral galaxies
[Abridged]We compare both the Milky Way and M31 galaxies to local external
disk galaxies within the same mass range, using their relative locations in the
planes formed by V_flat versus M_K, j_disk, and the average Fe abundance of
stars in the galaxy outskirts. We find, for all relationships, that the MW is
systematically offset by ~ 1 sigma, showing a significant deficiency in stellar
mass, in angular momentum, in disk radius and [Fe/H] in the stars in its
outskirts at a given V_flat. On the basis of their location in the M_K, V_flat,
and R_d volume, the fraction of spirals like the MW is 7+/-1%, while M31
appears to be a "typical'' spiral. Our Galaxy appears to have escaped any
significant merger over the last ~10 Gyrs which may explain why it is deficient
by a factor 2 to 3 in stellar mass, angular momentum and outskirts metallicity
and then, unrepresentative of the typical spiral. As with M31, most local
spirals show evidence for a history shaped mainly by relatively recent merging.
We conclude that the standard scenario of secular evolution is generally unable
to reproduce the properties of most (if not all) spiral galaxies. However, the
so-called "spiral rebuilding'' scenario proposed by Hammer et al. 2005 is
consistent with the properties of both distant galaxies and of their
descendants - the local spirals.Comment: 14 pages, 6 figures, to appear in Ap
The magnetic fields of large Virgo cluster spirals: Paper II
The Virgo cluster of galaxies provides excellent conditions for studying
interactions of galaxies with the cluster environment. Both the high-velocity
tidal interactions and effects of ram pressure stripping by the intracluster
gas can be investigated in detail. We extend our systematic search for possible
anomalies in the magnetic field structures of Virgo cluster spirals in order to
characterize a variety of effects and attribute them to different disturbing
agents. Six angularly large Virgo cluster spiral galaxies (NGC4192, NGC4302,
NGC4303, NGC4321, NGC4388, and NGC4535) were targets of a sensitive total power
and polarization study using the 100-m radio telescope in Effelsberg at 4.85GHz
and 8.35GHz (except for NGC4388 observed only at 4.85GHz, and NGC4535 observed
only at 8.35GHz). Magnetic field structures distorted to various extent are
found in all galaxies. Three galaxies (NGC4302, NGC4303, and NGC4321) show some
signs of possible tidal interactions, while NGC4388 and NGC4535 have very
likely experienced strong ram-pressure and shearing effects, respectively,
visible as distortions and asymmetries of polarized intensity distributions. As
in our previous study, even strongly perturbed galaxies closely follow the
radio-far-infrared correlation. In NGC4303 and NGC4321, we observe symmetric
spiral patterns of the magnetic field and in NGC4535 an asymmetric pattern.
Magnetic fields allow us to trace even weak interactions that are difficult to
detect with other observations. Our results show that the degree of distortions
of a galaxy is not a simple function of the distance to the cluster center but
reflects also the history of its interactions. The angle between the velocity
vector and the rotation vector of a galaxy may be a general parameter that
describes the level of distortions of galactic magnetic fields.Comment: 12 pages, 18 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
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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