928 research outputs found
Milky Way rotation curve from proper motions of red clump giants
We derive the stellar rotation curve of the Galaxy in the range of
Galactocentric radii of R=4-16 kpc at different vertical heights from the
Galactic plane of z between -2 and +2 kpc. We used the PPMXL survey, which
contains the USNO-B1 proper motions catalog cross-correlated with the
astrometry and near-infrared photometry of the 2MASS Point Source Catalog. To
improve the accuracy of the proper motions, we calculated the average proper
motions of quasars to know their systematic shift from zero in this PPMXL
survey, and we applied the corresponding correction to the proper motions of
the whole survey, which reduces the systematic error. We selected from the CM
diagram K vs. (J-K) the red clump giants and used the information of their
proper motions to build a map of the rotation speed of our Galaxy.
We obtain an almost flat rotation curve with a slight decrease for higher
values of R or |z|. The most puzzling result is obtained for the farthest
removed and most off-plane regions, where a significant deviation from a null
average proper motion (~4 mas/yr) in the Galactic longitude direction for the
anticenter regions can be directly translated into a rotation speed much lower
than in the solar Galactocentric radius: an average speed of
82+/-5(stat.)+/-58(syst.) km/s. A scenario with a rotation speed lower than 150
km/s in these regions of our explored zone is intriguing, and invites one to
reconsider different possibilities for the dark matter distribution. However,
given the high systematic errors, we cannot conclude about this. Hence, more
measurements of the proper motions at high R and |z| are necessary to validate
the exotic scenario that would arise if this low speed were confirmed.Comment: 10 pages, accepted for publication in A&A. v2: an erratum is
correcte
Peaks in the CMBR power spectrum. I. Mathematical analysis of the associated real space features
The purpose of our study is to understand the mathematical origin in real
space of modulated and damped sinusoidal peaks observed in cosmic microwave
background radiation anisotropies. We use the theory of the Fourier transform
to connect localized features of the two-point correlation function in real
space to oscillations in the power spectrum. We also illustrate analytically
and by means of Monte Carlo simulations the angular correlation function for
distributions of filled disks with fixed or variable radii capable of
generating oscillations in the power spectrum. While the power spectrum shows
repeated information in the form of multiple peaks and oscillations, the
angular correlation function offers a more compact presentation that condenses
all the information of the multiple peaks into a localized real space feature.
We have seen that oscillations in the power spectrum arise when there is a
discontinuity in a given derivative of the angular correlation function at a
given angular distance. These kinds of discontinuities do not need to be abrupt
in an infinitesimal range of angular distances but may also be smooth, and can
be generated by simply distributing excesses of antenna temperature in filled
disks of fixed or variable radii on the sky, provided that there is a non-null
minimum radius and/or the maximum radius is constrained.Comment: accepted to be published in Physica
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