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21.
Clusters of galaxies are self-gravitating systems of mass ∼1014–1015
h
−1 M⊙ and size ∼1–3h
−1 Mpc. Their mass budget consists of dark matter (∼80%, on average), hot diffuse intracluster plasma (≲20%) and a small fraction
of stars, dust, and cold gas, mostly locked in galaxies. In most clusters, scaling relations between their properties, like
mass, galaxy velocity dispersion, X-ray luminosity and temperature, testify that the cluster components are in approximate
dynamical equilibrium within the cluster gravitational potential well. However, spatially inhomogeneous thermal and non-thermal
emission of the intracluster medium (ICM), observed in some clusters in the X-ray and radio bands, and the kinematic and morphological
segregation of galaxies are a signature of non-gravitational processes, ongoing cluster merging and interactions. Both the
fraction of clusters with these features, and the correlation between the dynamical and morphological properties of irregular
clusters and the surrounding large-scale structure increase with redshift.
In the current bottom-up scenario for the formation of cosmic structure, where tiny fluctuations of the otherwise homogeneous
primordial density field are amplified by gravity, clusters are the most massive nodes of the filamentary large-scale structure
of the cosmic web and form by anisotropic and episodic accretion of mass, in agreement with most of the observational evidence.
In this model of the universe dominated by cold dark matter, at the present time most baryons are expected to be in a diffuse
component rather than in stars and galaxies; moreover, ∼50% of this diffuse component has temperature ∼0.01–1 keV and permeates
the filamentary distribution of the dark matter. The temperature of this Warm-Hot Intergalactic Medium (WHIM) increases with
the local density and its search in the outer regions of clusters and lower density regions has been the quest of much recent
observational effort.
Over the last thirty years, an impressive coherent picture of the formation and evolution of cosmic structures has emerged
from the intense interplay between observations, theory and numerical experiments. Future efforts will continue to test whether
this picture keeps being valid, needs corrections or suffers dramatic failures in its predictive power. 相似文献
22.
L. Bassani A.J. Dean G. Di Cocco 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
The relative contribution to the γ-ray background of different types of sources, namely Seyfert Galaxies, Quasars, BL Lac objects, radio galaxies and field galaxies is estimated under the hypothesis that the cosmic diffuse flux is the result of a superposition of many unresolved galaxies. The γ-ray data indicate that the Seyfert volume emissivity matches that of the diffuse background at few hundred keV and exceeds it at higher energies by as much as a factor of about 4. Whilst normal galaxies contribute less than 0.1%, BL Lac objects, Quasars and Radio Galaxies may contribute as much as 5–10% each, even without significant evolution. In this paper we explore different ways of reconciling the observational data on active galaxies with the measured diffuse background level. 相似文献
23.
24.
P. Jovanović V. Borka Jovanović D. Borka T. Bogdanović 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We used a model of a relativistic accretion disk around a supermassive black hole (SMBH), based on ray-tracing method in the Kerr metric, to study the variations of the composite Fe Kα line emitted from two accretion disks around SMBHs in a binary system. We assumed that the orbit of such a binary is approximately Keplerian, and simulated the composite line shapes for different orbital elements, accretion disk parameters and mass ratios of the components. The obtained results show that, if observed in the spectra of some SMBH binaries during their different orbital phases, such composite Fe Kα line profiles could be used to constrain the orbits and several properties of such SMBH binaries. 相似文献
25.
L. Solovyeva S. AnokhinJ.-L. Sauvageot 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We present the results of analysis XMM-Newton data of galaxy cluster CL0016+16, which enables us to trace X-ray emission and temperature profile up to the virial radius. We obtained similar results using three different backgrounds. We checked the possibility of detection of cluster emission up to the virial radius with XMM-Newton data with hydrodynamical cosmology simulation from the Adaptive Mesh Refinement technique, code RAMSES by Teyssier [Teyssier, R. Cosmological hydrodynamics with adaptive mesh refinement. A new high resolution code called RAMSES. A&A 385, 337, 2002], convolution with XMM-Newton and the data base of the spectra by Sauvageot et al. [Sauvageot, J.-L., Belsole, E., Pratt, G.W. The late merging phase of a galaxy cluster: XMM EPIC observations of A 3266. A&A, 444, 673, 2005]. For the first time we were able to compute the mass of CL0016 up to R200, we found, assuming hydrostatic equilibrium framework, M200 = (1.15 ± 0.11) × 1015M⊙. 相似文献
26.
Huynh Anh Nguyen Le Soojong Pak Myungshin Im Minjin Kim Chae Kyung Sim Luis C. Ho 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We present medium resolution near-infrared host galaxy spectra of low redshift quasars, PG 0844+349 (z = 0.064), PG 1226+023 (z = 0.158), and PG 1426+015 (z = 0.086). The observations were done by using the Infrared Camera and Spectrograph (IRCS) at the Subaru 8.2 m telescope. The full width at half maximum of the point spread function was about 0.3 arcsec by operations of an adaptive optics system, which can effectively resolve the quasar spectra from the host galaxy spectra. We spent up to several hours per target and developed data reduction methods to reduce the systematic noises of the telluric emissions and absorptions. From the obtained spectra, we identified absorption features of Mg I (1.503 μm), Si I (1.589 μm) and CO (6-3) (1.619 μm), and measured the velocity dispersions of PG 0844+349 to be 132 ± 110 km s−1 and PG 1426+015 to be 264 ± 215 km s−1. By using an MBH–σ relation of elliptical galaxies, we derived the black hole (BH) mass of PG 0844+349, log(MBH/M⊙)=7.7±5.5 and PG 1426+015,log(MBH/M⊙)=9.0±7.5. These values are consistent with the BH mass values from broad emission lines with an assumption of a virial factor of 5.5. 相似文献
27.
C. Alenka Negrete Deborah Dultzin Paola Marziani Jack W. Sulentic 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We describe an alternate way to estimate Broad Line Region (BLR) radii for type-1 AGN based on determination of physical conditions in the BLR under the assumption that the line emitting gas is photoionized by a central continuum source. We derive “diagnostic” intensity ratios involving UV lines Aliiiλ1860, Siiii]λ1892 and Civλ1549 which enable us to compute the ionizing photon flux, and hence BLR radius from the ionization parameter definition. We compare our estimates of BLR radii with values independently obtained from reverberation monitoring of Hβ and, in a few cases, of C ivλ1549. We analyze the interpretation of the photoionization estimates in the 4D eigenvector 1 context, and discuss in some detail the case of 3C 390.3. For this object we are able to provide not only the ionizing photon flux, but also an estimate of density and ionization parameter from the measured diagnostic ratios. We also compare black hole masses obtained from this method with values derived from widely-applied correlations between mass, line broadening and luminosity. Good agreement is found for both radius and black hole mass comparisons. 相似文献
28.
K.K. Singh H. Bhatt S. Bhattacharyya N. Bhatt A.K. Tickoo R.C. Rannot 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):766-778
In this work, we study the short term flaring activity from the high synchrotron peaked blazar Mrk 501 detected by the FACT and H.E.S.S. telescopes in the energy range 2–20 TeV during June 23–24, 2014 (MJD 56831.86–56831.94). We revisit this major TeV flare of the source in the context of near simultaneous multi-wavelength observations of –rays in MeV-GeV regime with Fermi-LAT, soft X-rays in 0.3–10 keV range with Swift-XRT, hard X-rays in 10–20 keV and 15–50 keV bands with MAXI and Swift-BAT respectively, UV-Optical with Swift-UVOT and 15 GHz radio with OVRO telescope. We have performed a detailed temporal and spectral analysis of the data from Fermi-LAT, Swift-XRT and Swift-UVOT during the period June 15–30, 2014 (MJD 56823–56838). Near simultaneous archival data available from Swift-BAT, MAXI and OVRO telescope along with the V-band optical polarization measurements from SPOL observatory are also used in the study of giant TeV flare of Mrk 501 detected by the FACT and H.E.S.S. telescopes. No significant change in the multi-wavelength emission from radio to high energy –rays during the TeV flaring activity of Mrk 501 is observed except variation in soft X-rays. The varying soft X-ray emission is found to be correlated with the –ray emission at TeV energies during the flaring activity of the source. The soft X-ray photon spectral index is observed to be anti-correlated with the integral flux showing harder-when-brighter behavior. An average value of 4.5 for V-band optical polarization is obtained during the above period whereas the corresponding electric vector position angle changes significantly. We have used the minimum variability timescale from the H.E.S.S. observations to estimate the Doppler factor of the emission region which is found to be consistent with the previous studies of the source. 相似文献
29.
There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this
way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment.
Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their
time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a
single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and
environmental properties. 相似文献
30.
The Warm-Hot Intergalactic Medium (WHIM) is thought to contribute about 40–50% to the baryonic budget at the present evolution
stage of the universe. The observed large scale structure is likely to be due to gravitational growth of density fluctuations
in the post-inflation era. The evolving cosmic web is governed by non-linear gravitational growth of the initially weak density
fluctuations in the dark energy dominated cosmology. Non-linear structure formation, accretion and merging processes, star
forming and AGN activity produce gas shocks in the WHIM. Shock waves are converting a fraction of the gravitation power to
thermal and non-thermal emission of baryonic/leptonic matter. They provide the most likely way to power the luminous matter
in the WHIM. The plasma shocks in the WHIM are expected to be collisionless. Collisionless shocks produce a highly non-equilibrium
state with anisotropic temperatures and a large differences in ion and electron temperatures. We discuss the ion and electron
heating by the collisionless shocks and then review the plasma processes responsible for the Coulomb equilibration and collisional
ionisation equilibrium of oxygen ions in the WHIM. MHD-turbulence produced by the strong collisionless shocks could provide
a sizeable non-thermal contribution to the observed Doppler parameter of the UV line spectra of the WHIM. 相似文献