30 research outputs found
The survival of the Sgr dwarf galaxy and the flatness of the rotation curve of the Galaxy
How has the ``fluffy'' core of the Sgr dwarf galaxy survived multiple strong
shocks from the tidal force of the Galactic halo and disc since the formation
of the core a Hubble time ago? A scenario that Sgr was deflected to its current
orbit by the Magellanic Clouds after a rendezvous on the north Galactic pole
2-3 Gyrs ago is examined. It is shown that the conditions of the collision fix
both the sense of circulation of Sgr and the LMC around the Galaxy and the
slope of the Galactic rotation curve. The model argues that the two orthogonal
polar circles traced by a dozen or so Galactic halo dwarf galaxies and globular
clusters (LMC-SMC-Magellanic Stream-Draco-Ursa Minor along
and M54-Ter 7-Ter 8-Arp 2-NGC 2419-Pal 15 along ) are streams of
tidal relics from two ancient galaxies which was captured on two intersecting
polar rosette orbits by the Galaxy. Our results favor the interpretation of
microlensing towards the LMC being due to source or lens stars in tidal
features of the Magellanic Clouds. We discuss direct and indirect observations
to test the collision scenario.Comment: 11 pages including 3 ps figures and an added appendix for deriving
the strength and probability of the encounte
Detection of a Corrugated Velocity Pattern in the Spiral Galaxy NGC 5427
Here we report the detection, in Halpha emission, of a radial corrugation in
the velocity field of the spiral galaxy NGC 5427. The central velocity of the
Halpha line displays coherent, wavy-like variations in the vicinity of the
spiral arms. The spectra along three different arm segments show that the
maximum amplitude of the sinusoidal line variations are displaced some 500 pc
from the central part of the spiral arms. The peak blueshifted velocities
appear some 500 pc upstream the arm, whereas the peak redshifted velocities are
located some 500 pc downstream the arm. This kinematical behavior is similar to
the one expected in a galactic bore generated by the interaction of a spiral
density wave with a thick gaseous disk, as recently modeled by Martos & Cox
(1998).Comment: Accepted for publication in Ap
The Vertical Structure of the Outer Milky Way HI Disk
We examine the outer Galactic HI disk for deviations from the b=0 plane by
constructing maps of disk surface density, mean height, and thickness. We find
that the Galactic warp is well described by a vertical offset plus two Fourier
modes of frequency 1 and 2, all of which grow with Galactocentric radius.
Adding the m=2 mode accounts for the large asymmetry between the northern and
southern warps. We use a Morlet wavelet transform to investigate the spatial
and frequency localization of higher frequency modes; these modes are often
referred to as "scalloping." We find that the m=10 and 15 scalloping modes are
well above the noise, but localized; this suggests that the scalloping does not
pervade the whole disk, but only local regions.Comment: Accepted by ApJ. 17 pages, 18 figures. Color maps are available at
http://astron.berkeley.edu/~elevin
Peripheral neuropathy associated with eosinophilia-myalgia syndrome.
In 1989, the Centers for Disease Control recognized the existence of an epidemic illness characterized by myalgia and eosinophilia in individuals taking preparations containing L-tryptophan. We evaluated 3 patients with eosinophilia-myalgia syndrome who presented with subacute progressive neuropathies. The neuropathies were predominantly motor and maximal in the lower extremities. Two patients were confined to a wheelchair and one was ventilator-dependent and bedridden. Sensory loss predominantly involved small fiber modalities. Electrophysiological studies showed multifocal marked conduction slowing and conduction block indicating segmental demyelination, with associated axonal degeneration that was accentuated distally. Examination of sural nerve biopsy specimens demonstrated axonal degeneration in all 3 patients and perivascular infiltrates in 2. Levels of quinolinic acid, a neurotoxic metabolite of L-tryptophan, were elevated in the cerebrospinal fluid in the 2 patients in whom it was measured. The cause of the neuropathy is unknown but may include immune mechanisms or toxicity of eosinophils, L-tryptophan, its metabolic products, or contaminants within L-tryptophan preparations
Peripheral neuropathy associated with eosinophilia-myalgia syndrome.
In 1989, the Centers for Disease Control recognized the existence of an epidemic illness characterized by myalgia and eosinophilia in individuals taking preparations containing L-tryptophan. We evaluated 3 patients with eosinophilia-myalgia syndrome who presented with subacute progressive neuropathies. The neuropathies were predominantly motor and maximal in the lower extremities. Two patients were confined to a wheelchair and one was ventilator-dependent and bedridden. Sensory loss predominantly involved small fiber modalities. Electrophysiological studies showed multifocal marked conduction slowing and conduction block indicating segmental demyelination, with associated axonal degeneration that was accentuated distally. Examination of sural nerve biopsy specimens demonstrated axonal degeneration in all 3 patients and perivascular infiltrates in 2. Levels of quinolinic acid, a neurotoxic metabolite of L-tryptophan, were elevated in the cerebrospinal fluid in the 2 patients in whom it was measured. The cause of the neuropathy is unknown but may include immune mechanisms or toxicity of eosinophils, L-tryptophan, its metabolic products, or contaminants within L-tryptophan preparations