1,749 research outputs found
Angular Power Spectrum of the Microwave Background Anisotropy seen by the COBE Differential Microwave Radiometer
The angular power spectrum estimator developed by Peebles (1973) and Hauser &
Peebles (1973) has been modified and applied to the 2 year maps produced by the
COBE DMR. The power spectrum of the real sky has been compared to the power
spectra of a large number of simulated random skies produced with noise equal
to the observed noise and primordial density fluctuation power spectra of power
law form, with . Within the limited range of spatial scales
covered by the COBE DMR, corresponding to spherical harmonic indices 3 \leq
\ell \lsim 30, the best fitting value of the spectral index is with the Harrison-Zeldovich value approximately
0.5 below the best fit. For 3 \leq \ell \lsim 19, the best fit is . Comparing the COBE DMR at small to
the at from degree scale anisotropy experiments
gives a smaller range of acceptable spectral indices which includes .Comment: 22 pages of LaTex using aaspp.sty and epsf.sty with appended
Postscript figures, COBE Preprint 94-0
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Southern Hemisphere Measurements of the Anisotropy in the Cosmic Microwave Background Radiation
The Dipole Observed in the COBE DMR Four-Year Data
The largest anisotropy in the cosmic microwave background (CMB) is the
mK dipole assumed to be due to our velocity with respect to the
CMB. Using the four year data set from all six channels of the COBE
Differential Microwave Radiometers (DMR), we obtain a best-fit dipole amplitude
mK in the direction , where the first
uncertainties are statistical and the second include calibration and combined
systematic uncertainties. This measurement is consistent with previous DMR and
FIRAS resultsComment: New and improved version; to be published in ApJ next mont
QSO 0130-4021: A third QSO showing a low Deuterium to Hydrogen Abundance Ratio
We have discovered a third quasar absorption system which is consistent with
a low deuterium to hydrogen abundance ratio, D/H = 3.4 times 10^-5. The z ~ 2.8
partial Lyman limit system towards QSO 0130-4021 provides the strongest
evidence to date against large D/H ratios because the H I absorption, which
consists of a single high column density component with unsaturated high order
Lyman series lines, is readily modeled -- a task which is more complex in other
D/H systems. We have obtained twenty-two hours of spectra from the HIRES
spectrograph on the W.M. Keck telescope, which allow a detailed description of
the Hydrogen. We see excess absorption on the blue wing of the H I Lyman alpha
line, near the expected position of Deuterium. However, we find that Deuterium
cannot explain all of the excess absorption, and hence there must be
contamination by additional absorption, probably H I. This extra H I can
account for most or all of the absorption at the D position, and hence D/H = 0
is allowed. We find an upper limit of D/H < 6.7 times 10^-5 in this system,
consistent with the value of D/H ~ 3.4 times 10^-5 deduced towards QSO
1009+2956 and QSO 1937-1009 by Burles and Tytler (1998a, 1998b). This
absorption system shows only weak metal line absorption, and we estimate [Si/H]
< -2.6 -- indicating that the D/H ratio of the system is likely primordial. All
four of the known high redshift absorption line systems simple enough to
provide useful limits on D are consistent with D/H = 3.4 +/- 0.25 times 10^-5.
Conversely, this QSO provides the third case which is inconsistent with much
larger values.Comment: 18 pages, 5 figures, submitted to Ap
The CFH Optical PDCS survey (COP) I: The Data
This paper presents and gives the COP (COP: CFHT Optical PDCS; CFHT:
Canada-France-Hawaii Telescope; PDCS: Palomar Distant Cluster Survey) survey
data. We describe our photometric and spectroscopic observations with the MOS
multi-slit spectrograph at the CFH telescope. A comparison of the photometry
from the PDCS (Postman et al. 1996) catalogs and from the new images we have
obtained at the CFH telescope shows that the different magnitude systems can be
cross-calibrated. After identification between the PDCS catalogues and our new
images, we built catalogues with redshift, coordinates and V, I and
Rmagnitudes. We have classified the galaxies along the lines of sight into
field and structure galaxies using a gap technique (Katgert et al. 1996). In
total we have observed 18 significant structures along the 10 lines of sight.Comment: 40 pages, 13 figures, accepted in A
A z=0.9 supercluster of X-ray luminous, optically-selected, massive galaxy clusters
We report the discovery of a compact supercluster structure at z=0.9. The
structure comprises three optically-selected clusters, all of which are
detected in X-rays and spectroscopically confirmed to lie at the same redshift.
The Chandra X-ray temperatures imply individual masses of ~5x10^14 Msun. The
X-ray masses are consistent with those inferred from optical--X-ray scaling
relations established at lower redshift. A strongly-lensed z~4 Lyman break
galaxy behind one of the clusters allows a strong-lensing mass to be estimated
for this cluster, which is in good agreement with the X-ray measurement.
Optical spectroscopy of this cluster gives a dynamical mass in good agreement
with the other independent mass estimates. The three components of the
RCS2319+00 supercluster are separated from their nearest neighbor by a mere <3
Mpc in the plane of the sky and likely <10 Mpc along the line-of-sight, and we
interpret this structure as the high-redshift antecedent of massive (~10^15
Msun) z~0.5 clusters such as MS0451.5-0305.Comment: ApJ Letters accepted. 5 pages in emulateapj, 3 figure
Search For Unresolved Sources In The COBE-DMR Two-Year Sky Maps
We have searched the temperature maps from the COBE Differential Microwave
Radiometers (DMR) first two years of data for evidence of unresolved sources.
The high-latitude sky (|b| > 30\deg) contains no sources brighter than 192 uK
thermodynamic temperature (322 Jy at 53 GHz). The cumulative count of sources
brighter than threshold T, N(> T), is consistent with a superposition of
instrument noise plus a scale-invariant spectrum of cosmic temperature
fluctuations normalized to Qrms-PS = 17 uK. We examine the temperature maps
toward nearby clusters and find no evidence for any Sunyaev-Zel'dovich effect,
\Delta y < 7.3 x 10^{-6} (95% CL) averaged over the DMR beam. We examine the
temperature maps near the brightest expected radio sources and detect no
evidence of significant emission. The lack of bright unresolved sources in the
DMR maps, taken with anisotropy measurements on smaller angular scales, places
a weak constraint on the integral number density of any unresolved
Planck-spectrum sources brighter than flux density S, n(> S) < 2 x 10^4 (S/1
Jy)^{-2} sr^{-1}.Comment: 16 pages including 2 figures, uuencoded PostScript, COBE preprint
94-0
Galois covers of the open p-adic disc
This paper investigates Galois branched covers of the open -adic disc and
their reductions to characteristic . Using the field of norms functor of
Fontaine and Wintenberger, we show that the special fiber of a Galois cover is
determined by arithmetic and geometric properties of the generic fiber and its
characteristic zero specializations. As applications, we derive a criterion for
good reduction in the abelian case, and give an arithmetic reformulation of the
local Oort Conjecture concerning the liftability of cyclic covers of germs of
curves.Comment: 19 pages; substantial organizational and expository changes; this is
the final version corresponding to the official publication in Manuscripta
Mathematica; abstract update
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