1,059 research outputs found
The Impact of Nonlinear Structure Formation on the Power Spectrum of Transverse Momentum Fluctuations and the Kinetic Sunyaev-Zel'dovich Effect
Cosmological transverse momentum fields, whose directions are perpendicular
to Fourier wave vectors, induce temperature anisotropies in the cosmic
microwave background via the kinetic Sunyaev-Zeldovich (kSZ) effect. The
transverse momentum power spectrum contains the four-point function of density
and velocity fields, . In the post-reionization
epoch, nonlinear effects dominate in the power spectrum. We use perturbation
theory and cosmological -body simulations to calculate this nonlinearity. We
derive the next-to-leading order expression for the power spectrum with a
particular emphasis on the connected term that has been ignored in the
literature. While the contribution from the connected term on small scales
() is subdominant relative to the unconnected term, we
find that its contribution to the kSZ power spectrum at at
can be as large as ten percent of the unconnected term, which would reduce the
allowed contribution from the reionization epoch () by twenty percent. The
power spectrum of transverse momentum on large scales is expected to scale as
as a consequence of momentum conservation. We show that both the leading
and the next-to-leading order terms satisfy this scaling. In particular, we
find that both of the unconnected and connected terms are necessary to
reproduce .Comment: 13 pages, 5 figures, Accepted to Ap
Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation
Magnetism of ruthernium pyrochlore oxides A2Ru2O7 (A = Hg, Cd, Ca), whose
electronic properties within a localized ion picture are characterized by
non-degenerate t2g orbitals (Ru5+, 4d3) and thereby subject to geometrical
frustration, has been investigated by muon spin rotation/relaxation (muSR)
technique. The A cation (mostly divalent) was varied to examine the effect of
covalency (Hg > Cd > Ca) on their electronic property. In a sample with A = Hg
that exhibits a clear metal-insulator (MI) transition below >> 100 K (which is
associated with a weak structural transition), a nearly commensurate magnetic
order is observed to develop in accordance with the MI transition. Meanwhile,
in the case of A = Cd where the MI transition is suppressed to the level of
small anomaly in the resistivity, the local field distribution probed by muon
indicates emergence of a certain magnetic inhomogeneity below {\guillemotright}
30 K. Moreover, in Ca2Ru2O7 that remains metallic, we find a highly
inhomogeneous local magnetism below >>25 K that comes from randomly oriented Ru
moments and thus described as a "frozen spin liquid" state. The systematic
trend of increasing randomness and itinerant character with decreasing
covalency suggests close relationship between these two characters. As a
reference for the effect of orbital degeneracy and associated Jahn-Teller
instability, we examine a tetravalent ruthernium pyrochlore, Tl2Ru2O7 (Ru4+,
4d4), where the result of muSR indicates a non-magnetic ground state that is
consistent with the formation of the Haldane chains suggested by neutron
diffraction experiment.Comment: 12 pages, 13 figure
Will Nonlinear Peculiar Velocity and Inhomogeneous Reionization Spoil 21cm Cosmology from the Epoch of Reionization?
The 21cm background from the epoch of reionization is a promising
cosmological probe: line-of-sight velocity fluctuations distort redshift, so
brightness fluctuations in Fourier space depend upon angle, which linear theory
shows can separate cosmological from astrophysical information. Nonlinear
fluctuations in ionization, density and velocity change this, however. The
validity and accuracy of the separation scheme are tested here for the first
time, by detailed reionization simulations. The scheme works reasonably well
early in reionization ( 80% ionized).Comment: 2 figures, matches published PRL versio
A Water Maser and Ammonia Survey of GLIMPSE Extended Green Objects (EGOs)
We present the results of a Nobeyama 45-m water maser and ammonia survey of
all 94 northern GLIMPSE Extended Green Objects (EGOs), a sample of massive
young stellar objects (MYSOs) identified based on their extended 4.5 micron
emission. We observed the ammonia (1,1), (2,2), and (3,3) inversion lines, and
detect emission towards 97%, 63%, and 46% of our sample, respectively (median
rms ~50 mK). The water maser detection rate is 68% (median rms ~0.11 Jy). The
derived water maser and clump-scale gas properties are consistent with the
identification of EGOs as young MYSOs. To explore the degree of variation among
EGOs, we analyze subsamples defined based on MIR properties or maser
associations. Water masers and warm dense gas, as indicated by emission in the
higher-excitation ammonia transitions, are most frequently detected towards
EGOs also associated with both Class I and II methanol masers. 95% (81%) of
such EGOs are detected in water (ammonia(3,3)), compared to only 33% (7%) of
EGOs without either methanol maser type. As populations, EGOs associated with
Class I and/or II methanol masers have significantly higher ammonia linewidths,
column densities, and kinetic temperatures than EGOs undetected in methanol
maser surveys. However, we find no evidence for statistically significant
differences in water maser properties (such as maser luminosity) among any EGO
subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane
Survey, we find no correlation between isotropic water maser luminosity and
clump number density. Water maser luminosity is weakly correlated with clump
(gas) temperature and clump mass.Comment: Astrophysical Journal, accepted. Emulateapj, 24 pages including 24
figures, plus 9 tables (including full content of online-only tables
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