2,306 research outputs found
Near term measurements with 21 cm intensity mapping: neutral hydrogen fraction and BAO at z<2
It is shown that 21 cm intensity mapping could be used in the near term to
make cosmologically useful measurements. Large scale structure could be
detected using existing radio telescopes, or using prototypes for dedicated
redshift survey telescopes. This would provide a measure of the mean neutral
hydrogen density, using redshift space distortions to break the degeneracy with
the linear bias. We find that with only 200 hours of observing time on the
Green Bank Telescope, the neutral hydrogen density could be measured to 25%
precision at redshift 0.54<z<1.09. This compares favourably to current
measurements, uses independent techniques, and would settle the controversy
over an important parameter which impacts galaxy formation studies. In
addition, a 4000 hour survey would allow for the detection of baryon acoustic
oscillations, giving a cosmological distance measure at 3.5% precision. These
observation time requirements could be greatly reduced with the construction of
multiple pixel receivers. Similar results are possible using prototypes for
dedicated cylindrical telescopes on month time scales, or SKA pathfinder
aperture arrays on day time scales. Such measurements promise to improve our
understanding of these quantities while beating a path for future generations
of hydrogen surveys.Comment: 6 pages, 5 figures. Submitted to Phys. Rev. D. Addressed reviewer
comments. Changed figure format, added more detailed technical discussion,
and added forecasts for aperture arrays. Added references
Lack of clustering in low-redshift 21-cm intensity maps cross-correlated with 2dF galaxy densities
We report results from 21-cm intensity maps acquired from the Parkes radio
telescope and cross-correlated with galaxy maps from the 2dF galaxy survey. The
data span the redshift range and cover approximately 1,300
square degrees over two long fields. Cross correlation is detected at a
significance of . The amplitude of the cross-power spectrum is low
relative to the expected dark matter power spectrum, assuming a neutral
hydrogen (HI) bias and mass density equal to measurements from the ALFALFA
survey. The decrement is pronounced and statistically significant at small
scales. At , the cross power spectrum is more
than a factor of 6 lower than expected, with a significance of .
This decrement indicates either a lack of clustering of neutral hydrogen (HI),
a small correlation coefficient between optical galaxies and HI, or some
combination of the two. Separating 2dF into red and blue galaxies, we find that
red galaxies are much more weakly correlated with HI on scales, suggesting that HI is more associated with blue
star-forming galaxies and tends to avoid red galaxies.Comment: 12 pages, 3 figures; fixed typo in meta-data title and paper author
Superconducting electronic state in optimally doped YBa2Cu3O7-d observed with laser-excited angle-resolved photoemission spectroscopy
Low energy electronic structure of optimally doped YBa2Cu3O7-d is
investigated using laser-excited angle-resolved photoemission spectroscopy. The
surface state and the CuO chain band that usually overlap the CuO2 plane
derived bands are not detected, thus enabling a clear observation of the bulk
superconducting state. The observed bilayer splitting of the Fermi surface is
~0.08 angstrom^{-1} along the (0,0)-(pi,pi) direction, significantly larger
than Bi2Sr2CaCu2O8+d. The kink structure of the band dispersion reflecting the
renormalization effect at ~60 meV shows up similarly as in other hole-doped
cuprates. The momentum-dependence of the superconducting gap shows
d_{x^2-y^2}-wave like amplitude, but exhibits a nonzero minimum of ~12 meV
along the (0,0)-(pi,pi) direction. Possible origins of such an unexpected
"nodeless" gap behavior are discussed.Comment: 9 pages, 10 figures; revised version accepted for publication in
Phys. Rev.
Interpreting The Unresolved Intensity Of Cosmologically Redshifted Line Radiation
Intensity mapping experiments survey the spectrum of diffuse line radiation rather than detect individual objects at high signal-to-noise ratio. Spectral maps of unresolved atomic and molecular line radiation contain three-dimensional information about the density and environments of emitting gas and efficiently probe cosmological volumes out to high redshift. Intensity mapping survey volumes also contain all other sources of radiation at the frequencies of interest. Continuum foregrounds are typically approximately 10(sup 2)-10(Sup 3) times brighter than the cosmological signal. The instrumental response to bright foregrounds will produce new spectral degrees of freedom that are not known in advance, nor necessarily spectrally smooth. The intrinsic spectra of fore-grounds may also not be well known in advance. We describe a general class of quadratic estimators to analyze data from single-dish intensity mapping experiments and determine contaminated spectral modes from the data themselves. The key attribute of foregrounds is not that they are spectrally smooth, but instead that they have fewer bright spectral degrees of freedom than the cosmological signal. Spurious correlations between the signal and foregrounds produce additional bias. Compensation for signal attenuation must estimate and correct this bias. A successful intensity mapping experiment will control instrumental systematics that spread variance into new modes, and it must observe a large enough volume that contaminant modes can be determined independently from the signal on scales of interest
An Isotopic Fingerprint of Electron-Phonon Coupling in High-Tc Cuprates
Angle-resolved photoemission spectroscopy with low-energy tunable photons
along the nodal direction of oxygen isotope substituted Bi2Sr2CaCu2O8+delta
reveals a distinct oxygen isotope shift near the electron-boson coupling "kink"
in the electronic dispersion. The magnitude (a few meV) and direction of the
kink shift are as expected due to the measured isotopic shift of phonon
frequency, which are also in agreement with theoretical expectations. This
demonstrates the participation of the phonons as dominant players, as well as
pinpointing the most relevant of the phonon branches.Comment: 5 pages, 3 figure
Erasing the Milky Way: new cleaning technique applied to GBT intensity mapping data
We present the first application of a new foreground removal pipeline to the current leading
H I intensity mapping data set, obtained by the Green Bank Telescope (GBT). We study
the 15- and 1-h-field data of the GBT observations previously presented in Mausui et al.
and Switzer et al., covering about 41 deg2 at 0.6 < z < 1.0, for which cross-correlations
may be measured with the galaxy distribution of the WiggleZ Dark Energy Survey. In the
presented pipeline, we subtract the Galactic foreground continuum and the point-source contamination
using an independent component analysis technique (FASTICA), and develop a
Fourier-based optimal estimator to compute the temperature power spectrum of the intensity
maps and cross-correlation with the galaxy survey data. We show that FASTICA is a reliable
tool to subtract diffuse and point-source emission through the non-Gaussian nature of their
probability distributions. The temperature power spectra of the intensity maps are dominated
by instrumental noise on small scales which FASTICA, as a conservative subtraction technique
of non-Gaussian signals, cannot mitigate. However, we determine similar GBT-WiggleZ
cross-correlation measurements to those obtained by the singular value decomposition (SVD)
method, and confirm that foreground subtraction with FASTICA is robust against 21 cm signal
loss, as seen by the converged amplitude of these cross-correlation measurements. We conclude
that SVD and FASTICA are complementary methods to investigate the foregrounds and
noise systematics present in intensity mapping data sets
Superconducting Volume Fraction in Overdoped Regime of La_2-x_Sr_x_CuO_4_: Implication for Phase Separation from Magnetic-Susceptibility Measurement
We have grown a single crystal of La_2-x_Sr_x_CuO_4_ in which the Sr
concentration, x, continuously changes from 0.24 to 0.29 in the overdoped
regime and obtained many pieces of single crystals with different x values by
slicing the single crystal. From detailed measurements of the magnetic
susceptibility, chi, of each piece, it has been found that the absolute value
of chi at the measured lowest temperature 2 K, |chi_2K_|, on field cooling
rapidly decreases with increasing x as well as the superconducting (SC)
transition temperature. As the value of |chi_2K_| is regarded as corresponding
to the SC volume fraction in a sample, it has been concluded that a phase
separation into SC and normal-state regions occurs in a sample of
La_2-x_Sr_x_CuO_4_ in the overdoped regime.Comment: 4 pages, 3 figures, ver. 2 has been accepted in J. Phys. Soc. Jp
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