167 research outputs found
Low-frequency connectivity is associated with mild traumatic brain injury
AbstractMild traumatic brain injury (mTBI) occurs from a closed-head impact. Often referred to as concussion, about 20% of cases complain of secondary psychological sequelae, such as disorders of attention and memory. Known as post-concussive symptoms (PCS), these problems can severely disrupt the patient's quality of life. Changes in local spectral power, particularly low-frequency amplitude increases and/or peak alpha slowing have been reported in mTBI, but large-scale connectivity metrics based on inter-regional amplitude correlations relevant for integration and segregation in functional brain networks, and their association with disorders in cognition and behaviour, remain relatively unexplored. Here, we used non-invasive neuroimaging with magnetoencephalography to examine functional connectivity in a resting-state protocol in a group with mTBI (n = 20), and a control group (n = 21). We observed a trend for atypical slow-wave power changes in subcortical, temporal and parietal regions in mTBI, as well as significant long-range increases in amplitude envelope correlations among deep-source, temporal, and frontal regions in the delta, theta, and alpha bands. Subsequently, we conducted an exploratory analysis of patterns of connectivity most associated with variability in secondary symptoms of mTBI, including inattention, anxiety, and depression. Differential patterns of altered resting state neurophysiological network connectivity were found across frequency bands. This indicated that multiple network and frequency specific alterations in large scale brain connectivity may contribute to overlapping cognitive sequelae in mTBI. In conclusion, we show that local spectral power content can be supplemented with measures of correlations in amplitude to define general networks that are atypical in mTBI, and suggest that certain cognitive difficulties are mediated by disturbances in a variety of alterations in network interactions which are differentially expressed across canonical neurophysiological frequency ranges
The thermal SZ tomography
The thermal Sunyaev-Zel'dovich (tSZ) effect directly measures the thermal
pressure of free electrons integrated along the line of sight and thus contains
valuable information on the thermal history of the universe. However, the
redshift information is entangled in the projection along the line of sight.
This projection effect severely degrades the power of the tSZ effect to
reconstruct the thermal history. We investigate the tSZ tomography technique to
recover this otherwise lost redshift information by cross correlating the tSZ
effect with galaxies of known redshifts, or alternatively with matter
distribution reconstructed from weak lensing tomography. We investigate in
detail the 3D distribution of the gas thermal pressure and its relation with
the matter distribution, through our adiabatic hydrodynamic simulation and the
one with additional gastrophysics including radiative cooling, star formation
and supernova feedback. (1) We find a strong correlation between the gas
pressure and matter distribution, with a typical cross correlation coefficient
r ~ 0.7 at k . 3h/Mpc and z < 2. This tight correlation will enable robust
cross correlation measurement between SZ surveys such as Planck, ACT and SPT
and lensing surveys such as DES and LSST, at ~20-100{\sigma} level. (2) We
propose a tomography technique to convert the measured cross correlation into
the contribution from gas in each redshift bin to the tSZ power spectrum.
Uncertainties in gastrophysics may affect the reconstruction at ~ 2% level, due
to the ~ 1% impact of gastrophysics on r, found in our simulations. However, we
find that the same gastrophysics affects the tSZ power spectrum at ~ 40% level,
so it is robust to infer the gastrophysics from the reconstructed redshift
resolved contribution.Comment: 10 pages, 7 figures, 2 appendices, accepted by Ap
Cosmic Flows on 100 Mpc/h Scales: Standardized Minimum Variance Bulk Flow, Shear and Octupole Moments
The low order moments, such as the bulk flow and shear, of the large scale
peculiar velocity field are sensitive probes of the matter density fluctuations
on very large scales. In practice, however, peculiar velocity surveys are
usually sparse and noisy, which can lead to the aliasing of small scale power
into what is meant to be a probe of the largest scales. Previously, we
developed an optimal ``minimum variance'' (MV) weighting scheme, designed to
overcome this problem by minimizing the difference between the measured bulk
flow (BF) and that which would be measured by an ideal survey. Here we extend
this MV analysis to include the shear and octupole moments, which are designed
to have almost no correlations between them so that they are virtually
orthogonal. We apply this MV analysis to a compilation of all major peculiar
velocity surveys, consisting of 4536 measurements. Our estimate of the BF on
scales of ~ 100 Mpc/h has a magnitude of |v|= 416 +/- 78 km/s towards Galactic
l = 282 degree +/- 11 degree and b = 6 degree +/- 6 degree. This result is in
disagreement with LCDM with WMAP5 cosmological parameters at a high confidence
level, but is in good agreement with our previous MV result without an
orthogonality constraint, showing that the shear and octupole moments did not
contaminate the previous BF measurement. The shear and octupole moments are
consistent with WMAP5 power spectrum, although the measurement noise is larger
for these moments than for the BF. The relatively low shear moments suggest
that the sources responsible for the BF are at large distances.Comment: 13 Pages, 7 figures, 4 tables. Some changes to reflect the published
versio
The luminosity of supernovae of type Ia from TRGB distances and the value of H_0
Distances from the tip of the red-giant branch (TRGB) in the halo Population
of galaxies - calibrated through RR Lyr stars as well as tied to Hipparcos
parallaxes and further supported by stellar models - are used to determine the
luminosity of six nearby type Ia supernovae (SN 2011fe, 2007sr, 1998bu, 1989B,
1972E, and 1937C). The result is M_V^corr = -19.41 +/- 0.05. If this value is
applied to 62 SNe Ia with 3000< v < 20,000 km/s a large-scale value of the
Hubble constant follows of H_0 = 64.0 +/- 1.6 +/- 2.0. The SN HST Project gave
H_0 = 62.3 +/- 1.3 +/- 5.0 from ten Cepheid-calibrated SNe Ia (Sandage et al.
2006). The agreement of young Population I (Cepheids) and old, metal-poor
Population II (TRGB) distance indicators is satisfactory. The combined weighted
result is H_0 = 63.7 +/- 2.3 (i.e. +/-3.6%). The result can also be reconciled
with WMAP5 data (Reid et al. 2010).Comment: 9 pages, 3 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
Consistently Large Cosmic Flows on Scales of 100 Mpc/h: a Challenge for the Standard LCDM Cosmology
Peculiar velocity surveys have non-uniform spatial distributions of tracers,
so that the bulk flow estimated from them does not correspond to that of a
simple volume such as a sphere. Thus bulk flow estimates are generally not
strictly comparable between surveys, even those whose effective depths are
similar. In addition, the sparseness of typical surveys can lead to aliasing of
small scale power into what is meant to be a probe of the largest scales. Here
we introduce a new method of calculating bulk flow moments where velocities are
weighted to give an optimal estimate of the bulk flow of an idealized survey,
with the variance of the difference between the estimate and the actual flow
being minimized. These "minimum variance" estimates can be designed to estimate
the bulk flow on a particular scale with minimal sensitivity to small scale
power, and are comparable between surveys. We compile all major peculiar
velocity surveys and apply this new method to them. We find that most surveys
we studied are highly consistent with each other. Taken together the data
suggest that the bulk flow within a Gaussian window of radius 50 Mpc/h is 407
km/s toward l=287 and b=8. The large-scale bulk motion is consistent with
predictions from the local density field. This indicates that there are
significant density fluctuations on very large scales. A flow of this amplitude
on such a large scale is not expected in the WMAP5-normalized LCDM cosmology,
for which the predicted one-dimensional r.m.s. velocity is ~110 km/s. The large
amplitude of the observed bulk flow favors the upper values of the WMAP5
error-ellipse, but even the point at the top of the WMAP5 95% confidence
ellipse predicts a bulk flow which is too low compared to that observed at >98%
confidence level.Comment: 19 Pages, 7 Figures, MNRAS in Press. Added some references and text
to reflect post proofs manuscrip
Sharpening the Precision of the Sunyaev-Zel'dovich Power Spectrum
Using both halo model calculations and a large sample of simulated SZ maps,
we demonstrate that high-mass clusters add significant non-Gaussian variance to
measurements of the SZ power spectrum amplitude. The difficulty in correctly
accounting theoretically for the contribution of these objects to the
uncertainty in C_l leads to a reduced sensitivity to \sigma_8. We show that a
simple solution is to mask out the brightest clusters in the map before
measuring the power spectrum. We demonstrate that fairly conservative masking
can reduce the variance and Gaussianize the statistics significantly, thus
increasing the sensitivity to cosmological parameters. Choosing which objects
to mask is non-trivial; we found that using a fixed sky density produced a
well-defined and well-behaved estimate that can easily be applied to real maps.
For example, masking the 10 (90) brightest clusters in a 100 deg^2 SZ map will
improve the sensitivity to C_l by a factor of two at l = 1000 (2000) and 1.5 at
l = 2000 (4000). We show that even in the presence of astrophysical foregrounds
(primary CMB and point sources) and instrument noise, one can increase the
precision on measurements of \sigma_8 by masking up to 0.9 clusters/deg^2.Comment: 11 pages, 8 figures, submitted to Ap
A Simple Empirically Motivated Template for the Unresolved Thermal Sunyaev-Zeldovich Effect
We develop a model for the power spectrum of unresolved clusters of galaxies
arising from the thermal Sunyaev-Zeldovich (tSZ) effect. The model is based on
a'universal' gas pressure profile constrained by X-ray observations and
includes a parameter to describe departures from self-similar evolution. The
model is consistent with recent Planck observations of the tSZ effect for X-ray
clusters with redshifts z<1 and reproduces the low amplitude for the tSZ
inferred from recent ground based observations. By adjusting two free
parameters, we are able to reproduce the tSZ power spectra from recent
numerical simulations to an accuracy that is well within theoretical
uncertainties. Our model provides a simple, empirically motivated tSZ template
that may be useful for the analysis of new experiments such as Planck.Comment: 6 pages 4 figure
First simultaneous optical/near-infrared imaging of an X-ray selected, high-redshift cluster of galaxies with GROND: the galaxy population of XMMU J0338.7+0030 at z=1.1
The XMM-Newton Distant Cluster Project is a serendipitous survey for clusters
of galaxies at redshifts z>=0.8 based on deep archival XMM-Newton observations.
... Low-significance candidate high-z clusters are followed up with the
seven-channel imager GROND (Gamma-Ray Burst Optical and Near-Infrared Detector)
that is mounted at a 2m-class telescope. ... The test case is XMMU
J0338.7+0030, suggested to be at z~1.45+/-0.15 from the analysis of the z-H vs
H colour-magnitude diagram obtained from the follow-up imaging. Later VLT-FORS2
spectroscopy enabled us to identify four members, which set this cluster at
z=1.097+/-0.002. To reach a better knowledge of its galaxy population, we
observed XMMU J0338.7+0030 with GROND for about 6 hr. The publicly available
photo-z code le Phare was used. The Ks-band number counts of the non-stellar
sources out of the 832 detected down to z'~26 AB-mag in the 3.9x4.3 square
arcmin region of XMMU J0338.7+0030 imaged at all GROND bands clearly exceed
those computed in deep fields/survey areas at ~20.5 - 22.5 AB-mag. The
photo-z's of the three imaged spectroscopic members yield z=1.12+/-0.09. The
spatial distribution and the properties of the GROND sources with a photo-z in
the range 1.01 - 1.23 confirm the correspondence of the X-ray source with a
galaxy over-density at a significance of at least 4.3 sigma. Candidate members
that are spectro-photometrically classified as elliptical galaxies define a red
locus in the i'-z' vs z' colour-magnitude diagram that is consistent with the
red sequence of the cluster RDCS J0910+5422 at z=1.106. XMMU J0338.7+0030 hosts
also a population of bluer late-type spirals and irregulars. The starbursts
among the photometric members populate both loci, consistently with previous
results. The analysis of the available data set indicates that XMMU
J0338.7+0030 is a low-mass cluster (M_200 ~ 1E14 M_sun) at z=1.1. (Abridged)Comment: accepted for publication in Astronomy & Astrophysics Main Journal, 27
pages, 24 figures, 1 tabl
Tidal alignments as a contaminant of redshift space distortions
We investigate the effect of orientation-dependent selection effects on
galaxy clustering in redshift space. It is found that if galaxies are aligned
by large-scale tidal fields, then these selection effects give rise to a
dependence of the observed galaxy density on the local tidal field, in addition
to the well-known dependences on the matter density and radial velocity
gradient. This alters the galaxy power spectrum in a way that is different for
Fourier modes parallel to and perpendicular to the line of sight. These tidal
galaxy alignments can thus mimic redshift space distortions, and thus result in
a bias in the measurement of the velocity power spectrum. If galaxy
orientations are affected only by the local tidal field, then the tidal
alignment effect has exactly the same scale and angular dependence as the
redshift space distortions in the linear regime, so it cannot be projected out
or removed by masking small scales in the analysis. We consider several toy
models of tidal alignments and orientation-dependent selection, normalize their
free parameter (an amplitude) to recent observations, and find that they could
bias the velocity amplitude f(z)G(z) by 5--10 per cent in some models, although
most models give much smaller contamination. We conclude that tidal alignments
may be a significant systematic error in redshift space distortion measurements
that aim to test general relativity via the growth of large-scale structure. We
briefly discuss possible mitigation strategies.Comment: 16 pages, 3 figures, matches MNRAS accepted version; extended
explanations and added new appendi
The COS-Halos Survey: Keck LRIS and Magellan MagE Optical Spectroscopy
We present high signal-to-noise optical spectra for 67 low-redshift (0.1 < z
< 0.4) galaxies that lie within close projected distances (5 kpc < rho < 150
kpc) of 38 background UV-bright QSOs. The Keck LRIS and Magellan MagE data
presented here are part of a survey that aims to construct a statistically
sampled map of the physical state and metallicity of gaseous galaxy halos using
the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). We
provide a detailed description of the optical data reduction and subsequent
spectral analysis that allow us to derive the physical properties of this
uniquely data-rich sample of galaxies. The galaxy sample is divided into 38
pre-selected L ~ L*, z ~ 0.2 "target" galaxies and 29 "bonus" galaxies that lie
in close proximity to the QSO sightlines. We report galaxy spectroscopic
redshifts accurate to +/- 30 km s-1, impact parameters, rest-frame colors,
stellar masses, total star formation rates, and gas-phase interstellar medium
oxygen abundances. When we compare the distribution of these galaxy
characteristics to those of the general low-redshift population, we find good
agreement. The L ~ L* galaxies in this sample span a diverse range of color
(1.0 < u-r < 3.0), stellar mass (10^9.5 < M/M_sun < 10^11.5), and SFRs (0.01 -
20 M_sun yr-1). These optical data, along with the COS UV spectroscopy,
comprise the backbone of our efforts to understand how halo gas properties may
correlate with their host galaxy properties, and ultimately to uncover the
processes that drive gas outflow and/or are influenced by gas inflow.Comment: 20 pages, 12 Figures, Submitted to ApJ
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