12,299 research outputs found
The rotationally stabilized VPOS and predicted proper motions of the Milky Way satellite galaxies
The satellite galaxies of the Milky Way (MW) define a vast polar structure
(VPOS), a thin plane perpendicular to the MW disc. Proper motion (PM)
measurements are now available for all of the 11 brightest, `classical'
satellites and allow an updated analysis of the alignment of their orbital
poles with this spatial structure. The coherent orbital alignment of 7 to 9 out
of 11 satellites demonstrates that the VPOS is a rotationally stabilized
structure and not only a pressure-supported, flattened ellipsoid. This allows
us to empirically and model independently predict the PMs of almost all
satellite galaxies by assuming that the MW satellite galaxies orbit within the
VPOS. As a test of our method, the predictions are best met by satellites whose
PMs are already well constrained, as expected because more uncertain
measurements tend to deviate more from the true values. Improved and new PM
measurements will further test these predictions. A strong alignment of the
satellite galaxy orbital poles is not expected in dark matter based simulations
of galaxy formation. Coherent orbital directions of satellite galaxies are,
however, a natural consequence of tidal dwarf galaxies formed together in the
debris of a galaxy collision. The orbital poles of the MW satellite galaxies
therefore lend further support to tidal scenarios for the origin of the VPOS
and are a very significant challenge for the standard LCDM model of cosmology.
We also note that the dependence of the MW satellite speeds on Galactocentric
distance appear to map an effective potential with a constant velocity of
approximately 240 km/s to about 250 kpc. The individual satellite velocities
are only mildly radial.Comment: 17 pages, 8 figures, 4 tables, accepted for publication in MNRA
The new Milky Way satellites: alignment with the VPOS and predictions for proper motions and velocity dispersions
The evidence that stellar systems surrounding the Milky Way (MW) are
distributed in a Vast Polar Structure (VPOS) may be observationally biased by
satellites detected in surveys of the northern sky. The recent discoveries of
more than a dozen new systems in the southern hemisphere thus constitute a
critical test of the VPOS phenomenon. We report that the new objects are
located close to the original VPOS, with half of the sample having offsets less
than 20 kpc. The positions of the new satellite galaxy candidates are so well
aligned that the orientation of the revised best-fitting VPOS structure is
preserved to within 9 degrees and the VPOS flattening is almost unchanged (31
kpc height). Interestingly, the shortest distance of the VPOS plane from the MW
center is now only 2.5 kpc, indicating that the new discoveries balance out the
VPOS at the Galactic center. The vast majority of the MW satellites are thus
consistent with sharing a similar orbital plane as the Magellanic Clouds,
confirming a hypothesis proposed by Kunkel & Demers and Lynden-Bell almost 40
years ago. We predict the absolute proper motions of the new objects assuming
they orbit within the VPOS. Independent of the VPOS results we also predict the
velocity dispersions of the new systems under three distinct assumptions: that
they (i) are dark-matter-free star clusters obeying Newtonian dynamics, (ii)
are dwarf satellites lying on empirical scaling relations of galaxies in dark
matter halos, and (iii) obey MOND.Comment: 17 pages, 6 figures, 5 tables. Updated to match version accepted for
publication in MNRA
Wars and Markets: How Bond Values Reflect World War II
Historical events are reflected in asset prices. In this paper, we analyse government bond prices of Germany and Austria traded on the Swiss bourse during WWII. Some war events that are generally considered crucial are clearly reflected in government bond prices. This holds, in particular, for the official outbreak of the war and the loss and gain of national sovereignty. Other events to which historians attach great importance are not reflected in bond prices: The most prominent example is Germany's capitulation in 1945. The analysis of financial markets provides a fruitful method to evaluate the importance contemporaries attached to historical events.Financial markets, economic history, WWII, Europe, cliometrics
- …