35 research outputs found
Balancing mass and momentum in the Local Group
In the rest frame of the Local Group (LG), the total momentum of the Milky
Way (MW) and Andromeda (M31) should balance to zero. We use this fact to
constrain new solutions for the solar motion with respect to the LG
centre-of-mass, the total mass of the LG, and the individual masses of M31 and
the MW. Using the set of remote LG galaxies at kpc from the MW and M31,
we find that the solar motion has amplitude in a direction pointing toward galactic longitude
and galactic latitude
. The velocities of M31 and the MW in
this rest frame give a direct measurement of their mass ratio, for which we
find . We combine these
measurements with the virial theorem to estimate the total mass within the LG
as .
Our value for is consistent with the sum of literature values
for and . This suggests that the mass of the LG is
almost entirely located within the two largest galaxies rather than being
dispersed on larger scales or in a background medium. The outskirts of the LG
are seemingly rather empty. Combining our measurement for and the
mass ratio, we estimate the individual masses of the MW and M31 to be and , respectively. Our analysis favours M31
being more massive than the MW by a factor of 2.3, and the uncertainties
allow only a small probability (9.8%) that the MW is more massive. This is
consistent with other properties such as the maximum rotational velocities,
total stellar content, and numbers of globular clusters and dwarf satellites,
which all suggest that .Comment: 16 pages, 11 figures, 3 tables. Accepted for publication in MNRA
Ultrasoft x-ray spectroscopy using multilayer mirrors on TCV
The TCV tokamak is equipped with a four-channel ultrasoft x-ray monochromator allowing low resolution (lambda/Deltalambda similar to 30) measurements in the energy range 200-800eV. Its main purpose is to simultaneously monitor emission from four of the main Kalpha resonance lines of highly ionized light impurities such as boron, carbon, nitrogen and oxygen. Wavelength selectivity is achieved using synthetic multilayer mirrors having 30-40 alternate layers with layer periods in the range 3-7 nm, depending on the design wavelength range. Recently the instrument was modified for measuring the radial profiles of Kalpha and Lyman-alpha lines from He-like and H-like intrinsic carbon impurities to allow estimates of impurity diffusivities by comparisons with simulations using the impurity transport code STRAHL