76 research outputs found
The Organization of the Primate Insular Cortex
Long perceived as a primitive and poorly differentiated brain structure, the primate insular cortex recently emerged as a highly evolved, organized and richly connected cortical hub interfacing bodily states with sensorimotor, environmental, and limbic activities. This insular interface likely substantiates emotional embodiment and has the potential to have a key role in the interoceptive shaping of cognitive processes, including perceptual awareness. In this review, we present a novel working model of the insular cortex, based on an accumulation of neuroanatomical and functional evidence obtained essentially in the macaque monkey. This model proposes that interoceptive afferents that represent the ongoing physiological status of all the organs of the body are first being received in the granular dorsal fundus of the insula or âprimary interoceptive cortex,â then processed through a series of dysgranular poly-modal âinsular stripes,â and finally integrated in anterior agranular areas that serve as an additional sensory platform for visceral functions and as an output stage for efferent autonomic regulation. One of the agranular areas hosts the specialized von Economo and Fork neurons, which could provide a decisive evolutionary advantage for the role of the anterior insula in the autonomic and emotional binding inherent to subjective awareness
Constraining q_0 with Cluster Gas Mass Fractions: A Feasibility Study
As the largest gravitationally bound objects in the universe, clusters of
galaxies may contain a fair sample of the baryonic mass fraction of the
universe. Since the gas mass fraction from the hot ICM is believed to be
constant in time, the value of the cosmological deceleration parameter
can be determined by comparing the calculated gas mass fraction in nearby and
distant clusters (Pen 1997). To test the potential of this method, we compare
the gas fractions derived for a sample of luminous (erg
s), nearby clusters with those calculated for eight luminous, distant
() clusters using ASCA and ROSAT observations. For consistency,
we evaluate the gas mass fraction at a fixed physical radius of 1
Mpc (assuming ). We find a best fit value of with -0.47 <
q_0 < 0.67 at 95% confidence. We also determine the gas fraction using the
method of Evrard, Metzler, & Navarro (1997) to find the total mass within
, the radius where the mean overdensity of matter is 500 times the
critical density. In simulations, this method reduces the scatter in the
determination of gravitational mass without biasing the mean. We find that it
also reduces the scatter in actual observations for nearby clusters, but not as
much as simulations suggest. Using this method, the best fit value is with -0.50 < q_0 < 0.64. The excellent agreement between these two
methods suggests that this may be a useful technique for determining . The
constraints on should improve as more distant clusters are studied and
precise temperature profiles are measured to large radii.Comment: 8 pages, 4 figures, uses emulateapj.sty, onecolfloat.st
HIFLUGCS: Galaxy cluster scaling relations between X-ray luminosity, gas mass, cluster radius, and velocity dispersion
We present relations between X-ray luminosity and velocity dispersion
(L-sigma), X-ray luminosity and gas mass (L-Mgas), and cluster radius and
velocity dispersion (r500-sigma) for 62 galaxy clusters in the HIFLUGCS, an
X-ray flux-limited sample minimizing bias toward any cluster morphology. Our
analysis in total is based on ~1.3Ms of clean X-ray XMM-Newton data and 13439
cluster member galaxies with redshifts. Cool cores are among the major
contributors to the scatter in the L-sigma relation. When the
cool-core-corrected X-ray luminosity is used the intrinsic scatter decreases to
0.27 dex. Even after the X-ray luminosity is corrected for the cool core, the
scatter caused by the presence of cool cores dominates for the low-mass
systems. The scatter caused by the non-cool-core clusters does not strongly
depend on the mass range, and becomes dominant in the high-mass regime. The
observed L-sigma relation agrees with the self-similar prediction, matches that
of a simulated sample with AGN feedback disregarding six clusters with <45
cluster members with spectroscopic redshifts, and shows a common trend of
increasing scatter toward the low-mass end, i.e., systems with sigma<500km/s. A
comparison of observations with simulations indicates an AGN-feedback-driven
impact in the low-mass regime. The best fits to the relations
for the disturbed clusters and undisturbed clusters in the observational sample
closely match those of the simulated samples with and without AGN feedback,
respectively. This suggests that one main cause of the scatter is AGN activity
providing feedback in different phases, e.g., during a feedback cycle. The
slope and scatter in the observed r500-sigma relation is similar to that of the
simulated sample with AGN feedback except for a small offset but still within
the scatter.Comment: 45 pages, 28 figures, A&A proof-version, high-resolution figures in
Appendix F can be found in the electronic version on the A&A we
RXJ1716.6+6708: a young cluster at z=0.81
Clusters of galaxies at redshifts nearing one are of special importance since
they may be caught at the epoch of formation. At these high redshifts there are
very few known clusters. We present follow-up ASCA, ROSAT HRI and Keck LRIS
observations of the cluster RXJ1716.6+6708 which was discovered during the
optical identification of X-ray sources in the North Ecliptic Pole region of
the ROSAT All-Sky Survey. At z=0.809, RXJ1716.6+6708 is the second most distant
X-ray selected cluster so far published and the only one with a large number of
spectroscopically determined cluster member velocities. The optical morphology
of RXJ1716.6+6708 resembles an inverted S-shape filament with the X-rays coming
from the midpoint of the filament. The X-ray contours have an elongated shape
that roughly coincide with the weak lensing contours. The cluster has a low
temperature, kT=5.66{+1.37 -0.58} keV, and a very high velocity dispersion
sigma_{los}=1522{+215 -150} km s^{-1}. While the temperature is commensurate
with its X-ray luminosity of (8.19 +/- 0.43)x10^{44} h_{50}^{-2} erg s^{-1}
(2-10 keV rest frame), its velocity dispersion is much higher than expected
from the sigma-T_X relationship of present-day clusters with comparable X-ray
luminosity. RXJ1716.6+6708 could be an example of a protocluster, where matter
is flowing along filaments and the X-ray flux is maximum at the impact point of
the colliding streams of matter.Comment: Latex file, 18 pages, 4 figures, accepted for publication in the
Astronomical Journa
The REFLEX Galaxy Cluster Survey VII: Omega_m and sigma_8 from cluster abundance and large-scale clustering
For the first time the large-scale clustering and the mean abundance of
galaxy clusters are analysed simultaneously to get precise constraints on the
normalized cosmic matter density and the linear theory RMS
fluctuations in mass . A self-consistent likelihood analysis is
described which combines, in a natural and optimal manner, a battery of
sensitive cosmological tests where observational data are represented by the
(Karhunen-Lo\'{e}ve) eigenvectors of the sample correlation matrix. This method
breaks the degeneracy between and . The cosmological tests
are performed with the ROSAT ESO Flux-Limited X-ray (REFLEX) cluster sample.
The computations assume cosmologically flat geometries and a non-evolving
cluster population mainly over the redshift range . The REFLEX sample
gives the cosmological constraints and their random errors of
and . Possible systematic errors are evaluated by estimating the
effects of uncertainties in the value of the Hubble constant, the baryon
density, the spectral slope of the initial scalar fluctuations, the mass/X-ray
luminosity relation and its intrinsic scatter, the biasing scheme, and the
cluster mass density profile. All these contributions sum up to total
systematic errors of and
.Comment: 10 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Weak lensing mass reconstructions of the ESO Distant Cluster Survey
We present weak lensing mass reconstructions for the 20 high-redshift
clusters i n the ESO Distant Cluster Survey. The weak lensing analysis was
performed on deep, 3-color optical images taken with VLT/FORS2, using a
composite galaxy catalog with separate shape estimators measured in each
passband. We find that the EDisCS sample is composed primarily of clusters that
are less massive than t hose in current X-ray selected samples at similar
redshifts, but that all of the fields are likely to contain massive clusters
rather than superpositions of low mass groups. We find that 7 of the 20 fields
have additional massive structures which are not associated with the clusters
and which can affect the weak lensing mass determination. We compare the mass
measurements of the remaining 13 clusters with luminosity measurements from
cluster galaxies selected using photometric redshifts and find evidence of a
dependence of the cluster mass-to-light ratio with redshift. Finally we
determine the noise level in the shear measurements for the fields as a
function of exposure time and seeing and demonstrate that future ground-based
surveys which plan to perform deep optical imaging for use in weak lensing
measurements must achieve point-spread functions smaller than a median of 0.6"
FWHM.Comment: 35 pages, 24 figures, accepted to A&A, a version with better figure
resolution can be found at http://www.mpa-garching.mpg.de/ediscs/papers.htm
The XMMâNEWTON ⊠Project: I. The X-ray luminosity â temperature relation at z>0.4
We describe XMM-Newton Guaranteed Time observations of a sample of eight high redshift (0.45 < z < rvirial) bolometric luminosities, performed ÎČ-model fits to the radial surface profiles and made spectral fits to a single temperature isothermal model. We describe data analysis techniques that pay particular attention to background mitigation. We have also estimated temperatures and luminosities for two known clusters (Abell 2246 and RXJ1325.0-3814), and one new high redshift cluste r candidate (XMMU J084701.8 +345117), that were detected o ff-axis. Characterizing the L x â Tx relation as L x = L 6 ( T 6keV ) α , we find L 6 = 15 . 9 + 7 . 6 â 5 . 2 Ă 1044erg s â 1 and α =2.7 ±0.4 for an ⊠Π= 0 . 0 , ⊠M = 1 .0, H0 = 50 km s â 1 Mpc â 1 cosmology at a typical redshift z ⌠0 .55. Comparing with the low redshift study by Markevitch, 1998, we find α to be in agreement, and assuming L x â Tx to evolve as (1 + z ) A , we find A =0.68 ±0.26 for the same cosmology and A = 1 .52 + 0 .26 â 0 .27 for an ⊠Π= 0 . 7 , ⊠M = 0 . 3 cosmology. Our A values are very similar to those found previously by Vikhlinin et al., 2002 using a compilation of Chandra observations of 0 .39 < z < 1 .26 clusters. We conclude that there is now evidence from both XMM-Newton and Chandra for an evolutionary trend in the L x â Tx relation. This evolution is significantly below the level expected from the predictions of the self-similar model for an ⊠Π= 0 . 0 , ⊠M = 1 .0, cosmology, but consistent with self-similar model in an ⊠Π= 0 . 7 , ⊠M = 0 . 3 cosmology. Our observations lend support to the robustness and completeness of the SHARC and 160SD surveys
Discovery of a cluster of galaxies behind the Milky Way: X-ray and optical observations
We report the discovery of Cl 2334+48, a rich cluster of galaxies in the Zone
of Avoidance, identified in public images from the XMM-Newton archive. We
present the main properties of this cluster using the XMM-Newton X-ray data,
along with new optical spectroscopic and photometric observations. Cl 2334+48
is located at z = 0.271 +/- 0.001, as derived from the optical spectrum of the
brightest member galaxy. Such redshift agrees with a determination from the
X-ray spectrum (z = 0.263 (+0.012/-0.010)), in which an intense emission line
is matched to the rest wavelength of the Fe Kalpha complex. Its intracluster
medium has a plasma temperature of 4.92 (+0.50/-0.48) keV, sub-solar abundance
(0.38 +/- 0.12 Zsun), and a bolometric luminosity of 3.2 x 10^44 erg/s. A
density contrast delta = 2500 is obtained in a radius of 0.5 Mpc/h70, and the
corresponding enclosed mass is 1.5 x 10^14 Msun. Optical images show an
enhancement of g'-i' > 2.5 galaxies around the central galaxy, as expected if
these were cluster members. The central object is a luminous E-type galaxy,
which is displaced ~ 40 kpc/h70 from the cluster X-ray center. In addition, it
has a neighbouring arc-like feature (~ 22" or 90 kpc/h70 from it), probably due
to strong gravitational lensing. The discovery of Cl 2334+48 emphasises the
remarkable capability of the XMM-Newton to reveal new clusters of galaxies in
the Zone of Avoidance.Comment: 9 pages, 11 figures, Accepted for publication in A&A (on July 12,
2006
Properties of the intracluster medium in an ensemble of nearby galaxy clusters
We present a systematic analysis of the intracluster medium (ICM) in an X-ray flux limited sample of 45 galaxy clusters. Using archival ROSAT Position-Sensitive Proportional Counter (PSPC) data and published ICM temperatures, we present best-fit double and single beta model profiles, and extract ICM central densities and radial distributions. We use the data and an ensemble of numerical cluster simulations to quantify sources of uncertainty for all reported parameters. We examine the ensemble properties within the context of models of structure formation and feedback from galactic winds. We present best-fit ICM mass-temperature M-ICM-[T-X] relations for M-ICM calculated within r(500) and 1 h(50)(-1) Mpc. These relations exhibit small scatter (17%), providing evidence of regularity in large, X-ray flux limited cluster ensembles. Interestingly, the slope of the M-ICM-[T-X] relation (at limiting radius r(500)) is steeper than the self-similar expectation by 4.3 sigma. We show that there is a mild dependence of ICM mass fraction f(ICM) on [T-X]; the clusters with ICM temperatures below 5 keV have a mean ICM mass fraction [f(ICM)] = 0.160 +/- 0.008, which is significantly lower than that of the hotter clusters [f(ICM)] = 0.212 +/- 0.006 (90% confidence intervals). In apparent contradiction with previously published analyses, our large, X-ray flux limited cluster sample provides no evidence for a more extended radial ICM distribution in low-[T-X] clusters down to the sample limit of 2.4 keV. By analyzing simulated clusters we find that density variations enhance the cluster X-ray emission and cause M-ICM and f(ICM) to be overestimated by similar to 12%. Additionally, we use the simulations to estimate an f(ICM) depletion factor at r(500). We use the bias corrected mean f(ICM) within the hotter cluster subsample as a lower limit on the cluster baryon fraction. In combination with nucleosynthesis constraints this measure provides a firm upper limit on the cosmological density parameter for clustered matter Omega(M) less than or equal to (0.36 +/- 0.01) h(50)(-1/2).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60582/1/Mohr1999Properties.pd
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