582 research outputs found
X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters I: Number Counts and Spatial Distribution
We present an analysis of the X-ray bright point source population in 43
massive clusters of galaxies observed with the Chandra X-ray Observatory. We
have constructed a catalog of 4210 rigorously selected X-ray point sources in
these fields, which span a survey area of 4.2 square degrees. This catalog
reveals a clear excess of sources when compared to deep blank-field surveys,
which amounts to roughly 1 additional source per cluster, likely Active
Galactic Nuclei (AGN) associated with the clusters. The excess sources are
concentrated within the virial radii of the clusters, with the largest excess
observed near the cluster centers. The average radial profile of the excess
X-ray sources of the cluster are well described by a power law (N(r) ~ r^\beta)
with an index of \beta ~ -0.5. An initial analysis using literature results on
the mean profile of member galaxies in massive X-ray selected clusters
indicates that the fraction of galaxies hosting X-ray AGN rises with increasing
clustercentric radius, being approximately 5 to 10 times higher near the virial
radius than in the central regions. This trend is qualitatively similar to that
observed for star formation in cluster member galaxies.Comment: 18 Pages, 10 Figures, Submitted to MNRAS. Please contact Steven
Ehlert ([email protected]) for higher resolution figures. Updated to
reflect small changes requested by referee. This version has been accepted
into MNRA
Shallow Dark Matter Cusps in Galaxy Clusters
We study the evolution of the stellar and dark matter components in a galaxy
cluster of from to the present epoch using
the high-resolution collisionless simulations of Ruszkowski & Springel (2009).
At the dominant progenitor halos were populated with spherical model
galaxies with and without accounting for adiabatic contraction. We apply a
weighting scheme which allows us to change the relative amount of dark and
stellar material assigned to each simulation particle in order to produce
luminous properties which agree better with abundance matching arguments and
observed bulge sizes at . This permits the study of the effect of initial
compactness on the evolution of the mass-size relation. We find that for more
compact initial stellar distributions the size of the final Brightest Cluster
Galaxy grows with mass according to , whereas for more extended
initial distributions, . Our results show that collisionless
mergers in a cosmological context can reduce the strength of inner dark matter
cusps with changes in logarithmic slope of 0.3 to 0.5 at fixed radius. Shallow
cusps such as those found recently in several strong lensing clusters thus do
not necessarily conflict with CDM, but may rather reflect on the initial
structure of the progenitor galaxies, which was shaped at high redshift by
their formation process.Comment: 8 pages, 4 figures, submitted to MNRA
Содовые подземные воды юга-востока Западной Сибири: определение и распространение
Дается определение понятия "содовые воды", приводятся условия локализации подземных содовых вод на юго-востоке Западной Сибири и некоторые их химические особенности. Definition of the term "soda water", the conditions of localization of underground soda waters on the South-East of Western Siberia and some of their chemical features are given
Resurrecting the Red from the Dead: Optical Properties of BCGs in X-ray Luminous Clusters
We present measurements of surface brightness and colour profiles for the
brightest cluster galaxies (BCGs) in a sample of 48 X-ray luminous galaxy
clusters. These data were obtained as part of the Canadian Cluster Comparison
Project (CCCP). The Kormendy relation of our BCGs is steeper than that of the
local ellipticals, suggesting differences in the assembly history of these
types of systems. We also find that while most BCGs show monotonic colour
gradients consistent with a decrease in metallicity with radius, 25% of the
BCGs show colour profiles that turn bluer towards the centre (blue-cores). We
interpret this bluing trend as evidence for recent star formation. The excess
blue light leads to a typical offset from the red sequence of 0.5 to 1.0 mag in
(g'-r'), thus affecting optical cluster studies that may reject the BCG based
on colour. All of the blue-core BCGs are located within ~10 kpc of the peak in
the cluster X-ray emission. Furthermore, virtually all of the BCGs with recent
star formation are in clusters that lie above the Lx-Tx relation. Based on
photometry alone, these findings suggest that central star formation is a
ubiquitous feature of BCGs in dynamically relaxed cool-core clusters. This
implies that while AGNs and other heating mechanisms are effective at tempering
cooling, they do not full compensate for the energy lost via radiation.Comment: 20 pages, 11 figures, 3 tables. Accepted to MNRAS Updated text in
Introduction and Conclusion Section
Photometric Properties and Scaling Relations of Early Type Brightest Cluster Galaxies
We investigate the photometric properties of the early type Brightest Cluster
Galaxies (BCGs) using a carefully selected sample of 85 BCGs from the C4
cluster catalogue with redshift less than 0.1. We perform accurate background
subtractions, and surface photometry for these BCGs to 25 \magsec in the
Sloan -band. By quantitatively analysing the gradient of the Petrosian
profiles of BCGs, we find that a large fraction of BCGs have extended stellar
envelopes in their outskirts; more luminous BCGs tend to have more extended
stellar halos that are likely connected with mergers. A comparison sample of
elliptical galaxies was chosen with similar apparent magnitude and redshift
ranges, for which the same photometric analysis procedure is applied. We find
that BCGs have steeper size-luminosity () and Faber-Jackson
() relations than the bulk of early type galaxies.
Furthermore, the power-law indices ( and ) in these relations
increase as the isophotal limits become deeper. For isophotal limits from 22 to
25 \magsec, BCGs are usually larger than the bulk of early type galaxies, and
a large fraction () of BCGs have disky isophotal shapes. The
differences in the scaling relations are consistent with a scenario where the
dynamical structure and formation route of BCGs may be different from the bulk
of early type galaxies, in particular dry (dissipationless) mergers may play a
more important role in their formation; we highlight several possible dry
merger candidates in our sample.Comment: 15 pages, 15 figures, and 2 tables; in press in MNRAS. Accepted 2007
November 23, Received 2007 November 23; in original form of 2007 August
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Beyond the Global Brain Differences:Intraindividual Variability Differences in 1q21.1 Distal and 15q11.2 BP1-BP2 Deletion Carriers
BACKGROUND: Carriers of the 1q21.1 distal and 15q11.2 BP1-BP2 copy number variants exhibit regional and globalbrain differences compared with noncarriers. However, interpreting regional differences is challenging if a globaldifference drives the regional brain differences. Intraindividual variability measures can be used to test for regionaldifferences beyond global differences in brain structure.METHODS: Magnetic resonance imaging data were used to obtain regional brain values for 1q21.1 distal deletion (n =30) and duplication (n = 27) and 15q11.2 BP1-BP2 deletion (n = 170) and duplication (n = 243) carriers and matchednoncarriers (n = 2350). Regional intra-deviation scores, i.e., the standardized difference between an individual’sregional difference and global difference, were used to test for regional differences that diverge from the globaldifference.RESULTS: For the 1q21.1 distal deletion carriers, cortical surface area for regions in the medial visual cortex, posterior cingulate, and temporal pole differed less and regions in the prefrontal and superior temporal cortex differedmore than the global difference in cortical surface area. For the 15q11.2 BP1-BP2 deletion carriers, cortical thicknessin regions in the medial visual cortex, auditory cortex, and temporal pole differed less and the prefrontal andsomatosensory cortex differed more than the global difference in cortical thickness.CONCLUSIONS: We find evidence for regional effects beyond differences in global brain measures in 1q21.1 distaland 15q11.2 BP1-BP2 copy number variants. The results provide new insight into brain profiling of the 1q21.1 distaland 15q11.2 BP1-BP2 copy number variants, with the potential to increase understanding of the mechanismsinvolved in altered neurodevelopment
All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe
The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class
mission concept that will provide essential contributions to multimessenger
astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in
the 200 keV to 10 GeV energy range with a wide field of view, good spectral
resolution, and polarization sensitivity. Therefore, AMEGO is key in the study
of multimessenger astrophysical objects that have unique signatures in the
gamma-ray regime, such as neutron star mergers, supernovae, and flaring active
galactic nuclei. The order-of-magnitude improvement compared to previous MeV
missions also enables discoveries of a wide range of phenomena whose energy
output peaks in the relatively unexplored medium-energy gamma-ray band
Galaxy bulges and their massive black holes: a review
With references to both key and oft-forgotten pioneering works, this article
starts by presenting a review into how we came to believe in the existence of
massive black holes at the centres of galaxies. It then presents the historical
development of the near-linear (black hole)-(host spheroid) mass relation,
before explaining why this has recently been dramatically revised. Past
disagreement over the slope of the (black hole)-(velocity dispersion) relation
is also explained, and the discovery of sub-structure within the (black
hole)-(velocity dispersion) diagram is discussed. As the search for the
fundamental connection between massive black holes and their host galaxies
continues, the competing array of additional black hole mass scaling relations
for samples of predominantly inactive galaxies are presented.Comment: Invited (15 Feb. 2014) review article (submitted 16 Nov. 2014). 590
references, 9 figures, 25 pages in emulateApJ format. To appear in "Galactic
Bulges", E. Laurikainen, R.F. Peletier, and D.A. Gadotti (eds.), Springer
Publishin
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