59 research outputs found
Extending the relation from clusters to groups-Impact of cool core nature, AGN feedback, and selection effects
We aim to investigate the bolometric relation for galaxy
groups, and study the impact of gas cooling, feedback from supermassive black
holes, and selection effects on it. With a sample of 26 galaxy groups we
obtained the best fit relation for five different cases
depending on the ICM core properties and central AGN radio emission, and
determined the slopes, normalisations, intrinsic and statistical scatters for
both temperature and luminosity. Simulations were undertaken to correct for
selection effects (e.g. Malmquist bias) and the bias corrected relations for
groups and clusters were compared. The slope of the bias corrected
relation is marginally steeper but consistent with clusters
(). Groups with a central cooling time less than 1 Gyr (SCC groups)
show indications of having the steepest slope and the highest normalisation.
For the groups, the bias corrected intrinsic scatter in is
larger than the observed scatter for most cases, which is reported here for the
first time. Lastly, we see indications that the groups with an extended central
radio source have a much steeper slope than those groups which have a CRS with
only core emission. Additionally, we also see indications that the more
powerful radio AGN are preferentially located in NSCC groups rather than SCC
groups.Comment: Accepted for publication in Astronomy and Astrophysic
ICM cooling, AGN feedback and BCG properties of galaxy groups-Five properties where groups differ from clusters
Using Chandra data for a sample of 26 galaxy groups, we constrained the
central cooling times (CCTs) of the ICM and classified the groups as strong
cool-core (SCC), weak cool-core (WCC) and non-cool-core (NCC) based on their
CCTs. The total radio luminosity of the brightest cluster galaxy (BCG) was
obtained using radio catalog data and literature, which was compared to the CCT
to understand the link between gas cooling and radio output. We determined
K-band luminosities of the BCG with 2MASS data, and used it to constrain the
masses of the SMBH, which were then compared to the radio output. We also
tested for correlations between the BCG luminosity and the overall X-ray
luminosity and mass of the group.
The observed cool-core/non-cool-core fractions for groups are comparable to
those of clusters. However, notable differences are seen. For clusters, all
SCCs have a central temperature drop, but for groups, this is not the case as
some SCCs have centrally rising temperature profiles. While for the cluster
sample, all SCC clusters have a central radio source as opposed to only 45% of
the NCCs, for the group sample, all NCC groups have a central radio source as
opposed to 77% of the SCC groups. For clusters, there are indications of an
anticorrelation trend between radio luminosity and CCT which is absent for the
groups. Indications of a trend of radio luminosity with black hole mass
observed in SCC clusters is absent for groups. The strong correlation observed
between the BCG luminosity and the cluster X-ray luminosity/cluster mass
weakens significantly for groups.
We conclude that there are important differences between clusters and groups
within the ICM cooling/AGN feedback paradigm.Comment: Accepted for publication in Astronomy and Astrophysic
Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
We demonstrate the usability of mm-wavelength imaging data obtained from the
APEX-SZ bolometer array to derive the radial temperature profile of the hot
intra-cluster gas out to radius r_500 and beyond. The goal is to study the
physical properties of the intra-cluster gas by using a non-parametric
de-projection method that is, aside from the assumption of spherical symmetry,
free from modeling bias. We use publicly available X-ray imaging data from the
XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data
from the APEX-SZ experiment at 150 GHz to de-project the density and
temperature profiles for the relaxed cluster Abell 2204. We derive the gas
density, temperature and entropy profiles assuming spherical symmetry, and
obtain the total mass profile under the assumption of hydrostatic equilibrium.
For comparison with X-ray spectroscopic temperature models, a re-analysis of
the recent Chandra observation is done with the latest calibration updates.
Using the non-parametric modeling we demonstrate a decrease of gas temperature
in the cluster outskirts, and also measure the gas entropy profile. These
results are obtained for the first time independently of X-ray spectroscopy,
using SZE and X-ray imaging data. The contribution of the SZE systematic
uncertainties in measuring T_e at large radii is shown to be small compared to
the Chandra systematic spectroscopic errors. The upper limit on M_200 derived
from the non-parametric method is consistent with the NFW model prediction from
weak lensing analysis.Comment: Replaced with the published version; A&A 519, A29 (2010
Testing the Low-Mass End of X-Ray Scaling Relations with a Sample of Chandra Galaxy Groups
Well-determined scaling relations between X-ray observables and cluster mass
are essential for using large cluster samples for cosmology. Cluster relations
such as the Lx-T, M-T, Lx-M relations, have been investigated extensively,
however the question remains whether these relations hold true also for groups.
Some evidence supports a break at low masses, possibly caused by the influence
of non-gravitational physics on low-mass systems. The main goal of this work is
to test scaling relations for the low-mass range to check whether there is a
systematic difference between clusters and groups, and to extend this method of
reliable cluster mass determination for future samples down to the group
regime. We compiled a statistically complete sample of 112 X-ray galaxy groups,
26 with Chandra data. Temperature, metallicity, and surface brightness profiles
were created, and used to determine the main physical quantities and scaling
relations. We then compared the group properties to the HIFLUGCS clusters and
other samples. We present profiles and scaling relations of the whole sample. T
and Z profiles behave universally, except for the cores. The Lx-T, M-T, Lx-M,
Mg-M, M-Yx, and Lx-Yx relations are in good agreement with clusters. The Lx-T
relation steepens for T<3keV, which could point to a larger impact of heating
mechanisms on cooler systems. We found a strong drop in the gas mass fraction
below 1keV, which indicates the ICM is less dominant in groups and the galaxies
have a stronger influence on the system. In all relations the intrinsic scatter
for groups is larger, which appears not correlated with merger activity but
could be due to scatter caused by baryonic physics in the group cores. We also
demonstrate the importance of selection effects. We have found evidence for a
similarity break between groups and clusters. However this does not have a
strong effect on scaling relations.Comment: 31 pages, accepted to A&
Visuomotor Cerebellum in Human and Nonhuman Primates
In this paper, we will review the anatomical components of the visuomotor cerebellum in human and, where possible, in non-human primates and discuss their function in relation to those of extracerebellar visuomotor regions with which they are connected. The floccular lobe, the dorsal paraflocculus, the oculomotor vermis, the uvula–nodulus, and the ansiform lobule are more or less independent components of the visuomotor cerebellum that are involved in different corticocerebellar and/or brain stem olivocerebellar loops. The floccular lobe and the oculomotor vermis share different mossy fiber inputs from the brain stem; the dorsal paraflocculus and the ansiform lobule receive corticopontine mossy fibers from postrolandic visual areas and the frontal eye fields, respectively. Of the visuomotor functions of the cerebellum, the vestibulo-ocular reflex is controlled by the floccular lobe; saccadic eye movements are controlled by the oculomotor vermis and ansiform lobule, while control of smooth pursuit involves all these cerebellar visuomotor regions. Functional imaging studies in humans further emphasize cerebellar involvement in visual reflexive eye movements and are discussed
Hot atmospheres of galaxies, groups, and clusters of galaxies
Most of the ordinary matter in the local Universe has not been converted into
stars but resides in a largely unexplored diffuse, hot, X-ray emitting plasma.
It pervades the gravitational potentials of massive galaxies, groups and
clusters of galaxies, as well as the filaments of the cosmic web. The physics
of this hot medium, such as its dynamics, thermodynamics and chemical
composition can be studied using X-ray spectroscopy in great detail. Here, we
present an overview of the basic properties and discuss the self similarity of
the hot "atmospheres" permeating the gravitational halos from the scale of
galaxies, through groups, to massive clusters. Hot atmospheres are stabilised
by the activity of supermassive black holes and, in many ways, they are of key
importance for the evolution of their host galaxies. The hot plasma has been
significantly enriched in heavy elements by supernovae during the period of
maximum star formation activity, probably more than 10 billion years ago. High
resolution X-ray spectroscopy just started to be able to probe the dynamics of
atmospheric gas and future space observatories will determine the properties of
the currently unseen hot diffuse medium throughout the cosmic web.Comment: Accepted for publication in the book "Reviews in Frontiers of Modern
Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka;
publisher Springer Nature) funded by the European Union Erasmus+ Strategic
Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556
A Neural Network that Generates Attractive Vector Fields for Robot Control
: A method to teach a neural network the capability of creating attractive vector fields for robot path planning is presented and discussed. The property of attractive behaviour is embedded into the artificially generated training data and subsequently transfered to a MLP by learning. In the vicinity of the attractor in state space to which the system converges, a local vector field is unfolded, thus forcing the network to learn the major property of attractors. The neural network associates the vector of state-change \DeltaS with the actual state S of a dynamic system to establish a representation of the governing system dynamics. Part of this work has been published (Goerke and Eckmiller, 1994). Learned attractive vector fields, show to be powerfull for tasks where global capabilities are needed, such as stable control or trajectory generation with on-line obstacle avoidance. 1 Introduction For most systems the dynamic behaviour can be described as the change in state which is compl..
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