828 research outputs found
A massive high density effective theory
We derive an effective theory for dense, cold and massive quark matter. To
this end, we employ a general effective action formalism where antiquarks and
quarks far from the Fermi surface, as well as hard gluons, are integrated out
explicitly. We show that the resulting effective action depends crucially on
the projectors used to separate quarks from antiquarks. If one neglects the
quark masses in these projectors, the Feynman rules of the effective theory
involve quark mass insertions which connect quark with antiquark propagators.
Including the quark masses into these projectors, mass insertions do not appear
and the Feynman rules are identical to those found in the zero-mass limit.Comment: 7 pages, 6 figure
The Maximum Optical Depth Towards Bulge Stars From Axisymmetric Models of the Milky Way
It has been known that recent microlensing results towards the bulge imply
mass densities that are surprisingly high given dynamical constraints on the
Milky Way mass distribution. We derive the maximum optical depth towards the
bulge that may be generated by axisymmetric structures in the Milky Way, and
show that observations are close to surpassing these limits. This result argues
in favor of a bar as a source of significantly enhanced microlensing. Several
of the bar models in the literature are discussed.Comment: Latex, 6 pages, 4 figures, uses aas2pp4 and epsf style files.
Accepted for publication in ApJ Letter
The shape of the velocity ellipsoid in NGC 488
Theories of stellar orbit diffusion in disk galaxies predict different rates
of increase of the velocity dispersions parallel and perpendicular to the disk
plane, and it is therefore of interest to measure the different velocity
dispersion components in galactic disks of different types. We show that it is
possible to extract the three components of the velocity ellipsoid in an
intermediate-inclination disk galaxy from measured line-of-sight velocity
dispersions on the major and minor axes. On applying the method to observations
of the Sb galaxy NGC 488, we find evidence for a higher ratio of vertical to
radial dispersion in NGC 488 than in the solar neighbourhood of the Milky Way
(the only other place where this quantity has ever been measured). The
difference is qualitatively consistent with the notion that spiral structure
has been relatively less important in the dynamical evolution of the disk of
NGC 488 than molecular clouds.Comment: 5 pages LaTex, including 2 figures, mn.sty, submitted to MNRA
Disc heating in NGC 2985
Various processes have been proposed to explain how galaxy discs acquire
their thickness. A simple diagnostic for ascertaining this ``heating''
mechanism is provided by the ratio of the vertical to radial velocity
dispersion components. In a previous paper we have developed a technique for
measuring this ratio, and demonstrated its viability on the Sb system NGC 488.
Here we present follow-up observations of the morphologically similar Sab
galaxy NGC 2985, still only the second galaxy for which this ratio has been
determined outside of the solar neighbourhood. The result is consistent with
simple disc heating models which predict ratios of less
than oneComment: 5 pages, 4 figures. Accepted for publication in MNRA
Kinematic detection of the double nucleus in M31
Using a spectrum obtained under moderate (of order 1 arcsecond) seeing, we
show that the double nucleus in M31 produces a strong kinematic signature even
though the individual components are not spatially resolved. The signature
consists of a significant asymmetric wing in the stellar velocity distribution
close to the center of the system. The properties of the second nucleus derived
from this analysis agree closely with those measured from high-spatial
resolution Hubble Space Telescope images. Even Space Telescope only has
sufficient resolution to study the structure of very nearby galactic nuclei
photometrically; this spectroscopic approach offers a tool for detecting
structure such as multiple nuclei in a wider sample of galaxy cores.Comment: 4 pages of uuencoded compressed postscript, figures included.
Accepted for publication in MNRA
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