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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of The Korean Astronomical Society
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The Korean Astronomical Society
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Volume & Issues
Volume 37, Issue 5 - Dec 2004
Volume 37, Issue 4 - Dec 2004
Volume 37, Issue 3 - Sep 2004
Volume 37, Issue 2 - Jun 2004
Volume 37, Issue 1 - Mar 2004
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EUV AND SOFT X-RAY EMISSION IN CLUSTERS OF GALAXIES
BOWYER STUART ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 295~297
DOI : 10.5303/JKAS.2004.37.5.295
Observations with EUVE, ROSAT, and BeepoSAX have shown that some clusters of galaxies produce intense EUV emission. These findings have produced considerable interest; over 100 papers have been published on this topic in the refereed literature. A notable suggestion as to the source of this radiation is that it is a 'warm' (106 K) intracluster medium which, if present, would constitute the major baryonic component of the universe. A more recent variation of this theme is that this material is 'warm-hot' intergalactic material condensing onto clusters. Alternatively, inverse Compton scattering of low energy cosmic rays against cosmic microwave background photons has been proposed as the source of this emission. Various origins of these particles have been posited, including an old (
Giga year) population of cluster cosmic rays; particles associated with relativistic jets in the cluster; and cascading particles produced by shocks from sub-cluster merging. The observational situation has been quite uncertain with many reports of detections which have been subsequently contradicted by analyses carried out by other groups. Evidence supporting a thermal and a non-thermal origin has been reported. The existing EUV, FUV, and optical data will be briefly reviewed and clarified. Direct observational evidence from a number of different satellites now rules out a thermal origin for this radiation. A new examination of subtle details of the EUV data suggests a new source mechanism: inverse Compton scattered emission from secondary electrons in the cluster. This suggestion will be discussed in the context of the data.
IMAGING NON-THERMAL X-RAY EMISSION FROM GALAXY CLUSTERS: RESULTS AND IMPLICATIONS
HENRIKSEN MARK ; HUDSON DANNY ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 299~305
DOI : 10.5303/JKAS.2004.37.5.299
We find evidence of a hard X-ray excess above the thermal emission in two cool clusters (Abell 1750 and IC 1262) and a soft excess in two hot clusters (Abell 754 and Abell 2163). Our modeling shows that the excess components in Abell 1750, IC 1262, and Abell 2163 are best fit by a steep power law indicative of a significant non-thermal component. In the case of Abell 754, the excess emission is thermal, 1 ke V emission. We analyze the dynamical state of each cluster and find evidence of an ongoing or recent merger in all four clusters. In the case of Abell 2163, the detected, steep spectrum, non-thermal X-ray emission is shown to be associated with the weak merger shock seen in the temperature map. However, this shock is not able to produce the flatter spectrum radio halo which we attribute to post-shock turbulence. In Abell 1750 and IC 1262, the shocked gas appears to be spatially correlated with non-thermal emission suggesting cosmic-ray acceleration at the shock front.
GALAXY CLUSTERS IN GAMMA-RAYS: AN ASSESSMENT FROM OBSERVATIONS
REIMER OLAF ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 307~313
DOI : 10.5303/JKAS.2004.37.5.307
Clusters of galaxies are believed to constitute a population of astrophysical objects potentially able to emit electromagnetic radiation up to gamma-ray energies. Evidence of the existence of non-thermal radiation processes in galaxy clusters is indicated from observations of diffuse radio halos, hard X-ray and EUV excess emission. The presence of cosmic ray acceleration processes and its confinement on cosmological timescales nearly inevitably yields in predicting energetic gamma-ray emission, either directly deduceably from a cluster's multifreqency emission characteristics or indirectly during large-scale cosmological structure formation processes. This theoretical reasoning suggests several scenarios to actually detect galaxy clusters at gamma-ray wavelengths: Either resolved as individual sources of point-like or extended gamma-ray emission, by investigating spatial-statistical correlations with unidentified gamma-ray sources or, if unresolved, through their contribution to the extragalactic diffuse gamma-ray background. In the following I review the situation concerning the proposed relation between galaxy clusters and high-energy gamma-ray observations from an observational point-of-view.
PROPERTIES AND SPECTRAL BEHAVIOUR OF CLUSTER RADIO HALOS
FERETTI L. ; BRUNETTI G. ; GIOVANNINI G. ; KASSIM N. ; ORRU E. ; SETTI G. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 315~322
DOI : 10.5303/JKAS.2004.37.5.315
Several arguments have been presented in the literature to support the connection between radio halos and cluster mergers. The spectral index distributions of the halos in A665 and A2163 provide a new strong confirmation of this connection, i.e. of the fact that the cluster merger plays an important role in the energy supply to the radio halos. Features of the spectral index (flattening and patches) are indication of a complex shape of the radiating electron spectrum, and are therefore in support of electron reacceleration models. Regions of flatter spectrum are found to be related to the recent merger. In the undisturbed cluster regions, instead, the spectrum steepens with the distance from the cluster center. The plot of the integrated spectral index of a sample of halos versus the cluster temperature indicates that clusters at higher temperature tend to host halos with flatter spectra. This correlation provides further evidence of the connection between radio emission and cluster mergers.
RADIO RELICS IN CLUSTERS OF GALAXIES
GIOVANNINI GABRIELE ; FERETTI LUIGINA ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 323~328
DOI : 10.5303/JKAS.2004.37.5.323
In this paper we review the observational results on Relic radio sources in clusters of galaxies. We discuss their observational properties, structures and radio spectra. We will show that Relics can be divided according to their size, morphology, and location in the galaxy cluster. These differences could be related to physical properties of Relic sources. The comparison with cluster conditions suggests that Relics could be related to shock waves originated by cluster mergers.
OBSERVING MAGNETIC FIELDS ON LARGE SCALES
RUDNICK LAWRENCE ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 329~335
DOI : 10.5303/JKAS.2004.37.5.329
Observations of magnetic fields on scales up to several Mpc are important for understanding cluster and large-scale structure evolution. Our current census of such structures is heavily biased - towards fields of several
G, towards fields in deep potential wells, and towards high inferred field strengths m cooling flow and other clusters from improper analysis of rotation measure data. After reviewing these biases, I show some recent results on two relics that are powered in very different ways. I describe new investigations that are now uncovering weak diffuse fields in the outskirts of clusters and other low density environments, and the good prospects for further progress.
FARADAY ROTATION OBSERVATIONS OF MAGNETIC FIELDS IN GALAXY CLUSTERS
CLARKE TRACY E. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 337~342
DOI : 10.5303/JKAS.2004.37.5.337
The presence of magnetic fields in the intracluster medium in clusters of galaxies has been revealed through several different observational techniques. These fields may be dynamically important in clusters as they will provide additional pressure support to the intracluster medium as well as inhibit transport mechanisms such as thermal conduction. Here, we review the current observational state of Faraday rotation measure studies of the cluster fields. The fields are generally found to be a few to 10
G in non-cooling core clusters and ordered on scales of 10 - 20 kpc. Studies of sources at large impact parameters show that the magnetic fields extend from cluster cores to radii of at least 500 kpc. In central regions of cooling core systems the field strengths are often somewhat higher (10 - 40
G) and appear to be ordered on smaller scales of a few to 10 kpc. We also review some of the recent work on interpreting Faraday rotation measure observations through theory and numerical simulations. These techniques allow us to build up a much more detailed view of the strength and topology of the fields.
NEW PROBES OF INTERGALACTIC MAGNETIC FIELDS BY RADIOMETRY AND FARADAY ROTATION
KRONBERG PHILIPP P. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 343~347
DOI : 10.5303/JKAS.2004.37.5.343
The energy injection of galactic black holes (BH) into the intergalactic medium via extragalactic radio source jets and lobes is sufficient to magnetize the IGM in the filaments and walls of Large Scale Structure at < [B] >
or more. It appears that this process of galaxy-IGM feedback is the primary source of IGM cosmic rays(CR) and magnetic field energy. Large scale gravitational infall energy serves to re-heat the intergalactic magnetoplasma in localities of space and time, maintaining or amplifying the IGM magnetic field, but this can be thought of as a secondary process. I briefly review observations that confirm IGM fields around this level, describe further Faraday rotation measurements in progress, and also the observational evidence that magnetic fields in galaxy systems around z=2 were approximately as strong then,
10 Gyr ago, as now.
A BAYESIAN VIEW ON FARADAY ROTATION MAPS - SEEING THE MAGNETIC POWER SPECTRUM IN CLUSTERS OF GALAXIES
VOGT CORINA ; ENBLIN TORSTEN A. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 349~353
DOI : 10.5303/JKAS.2004.37.5.349
Magnetic fields are an important ingredient of galaxy clusters and are indirectly observed on cluster scales as radio haloes and radio relics. One promising method to shed light on the properties of cluster wide magnetic fields is the analysis of Faraday rotation maps of extended extragalactic radio sources. We developed a Fourier analysis for such Faraday rotation maps in order to determine the magnetic power spectra of cluster fields. In an advanced step, here we apply a Bayesian maximum likelihood method to the RM map of the north lobe of Hydra A on the basis of our Fourier analysis and derive the power spectrum of the cluster magnetic field. For Hydra A, we measure a spectral index of -5/3 over at least one order of magnitude implying Kolmogorov type turbulence. We find a dominant scale of about 3 kpc on which the magnetic power is concentrated, since the magnetic autocorrelation length is
. Furthermore, we investigate the influences of the assumption about the sampling volume (described by a window function) on the magnetic power spectrum. The central magnetic field strength was determined to be
for the most likely geometries.
LARGE SCALE MAGNETIC FIELDS IN LENS GALAXIES
NARASIMHA D. ; CHITRE S. M. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 355~359
DOI : 10.5303/JKAS.2004.37.5.355
Differential Faraday Rotation measurements between the images of same background source, of multiply-imaged gravitational lens systems can be effectively used to provide a valuable probe to establish the existence of large-scale ordered magnetic fields in lensing galaxies as well as galaxy clusters. Estimates of the magnetic field in lens galaxies, based on the radio polarization measurements do not appear to show any clear evidence for evolution with redhsift of the coherent large scale magnetic field between redshift of 0.9 and the present epoch. However, our method clearly establishes the presence of coherent large scale magnetic field in giant ellitpical galaxies.
X-RAY STUDIES OF THE INTRACLUSTER MEDIUM IN CLUSTERS OF GALAXIES - CHARACTERIZING GALAXY CLUSTERS AS GIANT LABORATORIES
BOHRINGER HANS ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 361~369
DOI : 10.5303/JKAS.2004.37.5.361
Galaxy clusters as the densest and most prominent regions within the large-scale structure can be used as well characterizable laboratories to study astrophysical processes on the largest scales. X-ray observations provide currently the best way to determine the physical properties of galaxy clusters and the environmental parameters that describe them as laboratories. We illustrate this use of galaxy clusters and the precision of our understanding of them as laboratory environments with several examples. Their application to determine the matter composition of the Universe shows good agreement with results from other methods and is therefore a good test of our understanding. We test the reliability of mass measurements and illustrate the use of X-ray diagnostics to study the dynamical state of clusters. We discuss further studies on turbulence in the cluster ICM, the interaction of central AGN with the radiatively cooling plasma in cluster cooling cores and the lessons learned from the ICM enrichment by heavy elements.
X-RAYING LARGE-SCALE STRUCTURE
HENRY J. PATRICK ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 371~374
DOI : 10.5303/JKAS.2004.37.5.371
We review the observational evidence for the existence of a warm-hot intergalactic medium (WHIM). We expect that the morphology of this material is similar to that of cosmic rays and magnetic fields in large-scale structure, i.e., filaments connecting clusters of galaxies. Direct evidence for the WHIM, either in emission or absorption, is weak.
X-RAY EMISSION FROM THE WARM-HOT INTERGALACTIC MEDIUM
KAASTRA JELLE S. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 375~379
DOI : 10.5303/JKAS.2004.37.5.375
In this paper I give an overview of the detection of emission from the warm-hot intergalactic medium (WHIM) in the outer parts of clusters of galaxies. The evidence for the presence of soft excess X-ray emission in 7 out of 21 clusters is summarized, and it is demonstrated that several of these clusters show the signatures of thermal emission in the outer parts. A strong signature is the presence of redshifted O VII emission at 0.57 keV. In the central parts, several clusters show also a soft excess, but m this case the observations cannot well discriminate between a thermal or non-thermal origin of the soft X-ray excess.
HEATED INTRACLUSTER GAS AND RADIO CONNECTIONS: THE SINGULAR CASE OF MKW 3S
MAZZOTTA PASQUALE ; BRUNETTI GIANFRANCO ; GIACINTUCCI SIMONA ; VENTURI TIZIANA ; BARDELLI SANDRO ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 381~385
DOI : 10.5303/JKAS.2004.37.5.381
Similarly to other cluster of galaxies previously classified as cooling flow systems, the Chandra observation of MKW 3s reveals that this object has a complex X-ray structure hosting both a X-ray cavity and a X-ray filament. Unlike the other clusters, however, the temperature map of the core of MKW 3s shows the presence of extended regions of gas heated above the radially averaged gas temperature at any radius. As the cluster does not show evidences for ongoing major mergers Mazzotta et al. suggest a connection between the heated gas and the activity of the central AGN. Nevertheless, due to the lack of high quality radio maps, this interpretation was controversial. In this paper we present the results of two new radio observations of MKW 3s at 1.28 GHz and 604 MHz obtained at the GMRT. Together with the Chandra observation and a separate VLA observation at 327 MHz from Young, we show unequivocal evidences for a close connection between the heated gas region and the AGN activity and we briefly summarize possible implications.
TRACING BRIGHT AND DARK SIDES OF THE UNIVERSE WITH X-RAY OBSERVATIONS
SUTO YASUSHI ; YOSHIKAWA KOHJI ; DOLAG KLAUS ; SASAKI SHIN ; YAMASAKI NORIKO Y. ; OHASHI TAKAYA ; MITSUDA KAZUHISA ; TAWARA YUZURU ; FUJIMOTO RYUICHI ; FURUSHO TAE ; FURUZAWA AKIHIRO ; ISHIDA MANABU ; ISHISAKI YOSHITAKA ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 387~392
DOI : 10.5303/JKAS.2004.37.5.387
X-ray observations of galaxy clusters have played an important role in cosmology, especially in determining the cosmological density parameter and the fluctuation amplitude. While they represent the bright side of the universe together with the other probes including the cosmic microwave background and the Type Ia supernovae, the resulting information clearly indicates that the universe is dominated by dark components. Even most of cosmic baryons turns out to be dark. In order to elucidate the nature of dark baryons, we propose a dedicated soft-X-ray mission, DIOS (Diffuse Intergalactic Oxygen Surveyor). Recent numerical simulations suggest that approximately 30 to 50 percent of total baryons at z = 0 take the form of the warm-hot intergalactic medium (WHIM) with $10^5K < T < 10^7K $which has evaded the direct detection so far. The unprecedented energy resolution (
) of the XSA (X-ray Spectrometer Array) on-board DIGS enables us to identify WHIM with gas temperature
100 located at z < 0.3 through emission lines of OVII and OVIII. In addition, WHIMs surrounding nearby clusters are detectable with a typical exposure time of a day, and thus constitute realistic and promising targets for DIOS.
CURRENT STATUS OF SHOCK ACCELERATION THEORY
DRURY LUKE O'C ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 393~398
DOI : 10.5303/JKAS.2004.37.5.393
This paper describes some recent developments in our understanding of particle acceleration by shocks. It is pointed out that while good agreement now exists as to steady nonlinear modifications to the shock structure, there is. also growing evidence that the mesoscopic scales may not in fact be steady and that siginficant instabilties associated with magnetic field amplification may be a feature of strong collisionless plasma shocks.
THE ACCELERATION AND TRANSPORT OF COSMIC RAYS WITH HELIOSPHERIC EXAMPLES
JOKIPII J. R. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 399~404
DOI : 10.5303/JKAS.2004.37.5.399
Cosmic rays are ubiquitous in space, and are apparently present wherever the matter density is small enough that they are not removed by collisions with ambient particles. The essential similarity of their energy spectra in many different regions places significant general constraints on the mechanisms for their acceleration and confinement. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in Kolmogorov turbulence, can account for the universal specta. In comparison to shock acceleration, statistical acceleration, invoked in many situations, has significant disadvantages. The basic physics of acceleration and transport are discussed, and examples shown where it apparently works very well. However, there are now well-established situations where diffusive shock acceleration cannot be the accelerator. This problem will be discussed and possible acceleration mechanism evaluated. Statistical acceleration in these places is possible. In addition, a new mechanism, called diffusive compression acceleration, will be discussed and shown to be an attractive candidate. It has similarities with both statistical acceleration and shock acceleration.
COSMIC RAY ACCELERATION AT COSMOLOGICAL SHOCKS
KANG HYESUNG ; JONES T. W. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 405~412
DOI : 10.5303/JKAS.2004.37.5.405
Cosmological shocks form as an inevitable consequence of gravitational collapse during the large scale structure formation and cosmic-rays (CRs) are known to be accelerated at collisionless shocks via diffusive shock acceleration (DSA). We have calculated the evolution of CR modified shocks for a wide range of shock Mach numbers and shock speeds through numerical simulations of DSA in 1D quasi-parallel plane shocks. The simulations include thermal leakage injection of seed CRs, as well as pre-existing, upstream CR populations. Bohm-like diffusion is assumed. We show that CR modified shocks evolve to time-asymptotic states by the time injected particles are accelerated to moderately relativistic energies (p/mc
1), and that two shocks with the same Mach number, but with different shock speeds, evolve qualitatively similarly when the results are presented in terms of a characteristic diffusion length and diffusion time. We find that
of the particles passed through the shock are accelerated to form the CR population, and the injection rate is higher for shocks with higher Mach number. The CR acceleration efficiency increases with shock Mach number, but it asymptotes to
in high Mach number shocks, regardless of the injection rate and upstream CR pressure. On the other hand, in moderate strength shocks (
), the pre-existing CRs increase the overall CR energy. We conclude that the CR acceleration at cosmological shocks is efficient enough to lead to significant nonlinear modifications to the shock structures.
ULTRA HIGH ENERGY COSMIC RAYS AND THE MAGNETIZED UNIVERSE
OLINTO ANGELA V. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 413~420
DOI : 10.5303/JKAS.2004.37.5.413
The current state and future prospects of ultra high energy cosmic ray physics are reviewed. These cosmic rays with energies well above
eV are messengers of an unknown extremely high-energy universe.
ULTRA HIGH ENERGY COSMIC RAYS AND CLUSTERS
JONES T. W. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 421~426
DOI : 10.5303/JKAS.2004.37.5.421
I briefly review the current theoretical status of the origins of ultrahigh energy cosmic rays with special emphasis on models associated with galaxy clusters. Some basic constraints on models are laid out, including those that apply both to so-called 'top-down' and 'bottom-up' models. The origins of these UHECRs remain an enigma; no model stands out as a clear favorite. Large scale structure formation shocks, while very attractive conceptually in this context, are unlikely to be able to accelerate particles to energies much above
. Terminal shocks in relativistic AGN jets seem to be more viable candidates physically, but suffer from their rarity in the local universe. Several other, representative, models are outlined for comparison.
MAGNETIC FIELD IN THE LOCAL UNIVERSE AND THE PROPAGATION OF UHECRS
DOLAG KLAUS ; GRASSO DARIO ; SPRINGEL VOLKER ; TKACHEV IGOR ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 427~431
DOI : 10.5303/JKAS.2004.37.5.427
We use simulations of large-scale structure formation to study the build-up of magnetic fields (MFs) in the intergalactic medium. Our basic assumption is that cosmological MFs grow in a magnetohy-drodynamical (MHD) amplification process driven by structure formation out of a magnetic seed field present at high redshift. This approach is motivated by previous simulations of the MFs in galaxy clusters which, under the same hypothesis that we adopt here, succeeded in reproducing Faraday rotation measurements (RMs) in clusters of galaxies. Our ACDM initial conditions for the dark matter density fluctuations have been statistically constrained by the observed large-scale density field within a sphere of 110 Mpc around the Milky Way, based on the IRAS 1.2-Jy all-sky redshift survey. As a result, the positions and masses of prominent galaxy clusters in our simulation coincide closely with their real counterparts in the Local Universe. We find excellent agreement between RMs of our simulated galaxy clusters and observational data. The improved numerical resolution of our simulations compared to previous work also allows us to study the MF in large-scale filaments, sheets and voids. By tracing the propagation of ultra high energy (UHE) protons in the simulated MF we construct full-sky maps of expected deflection angles of protons with arrival energies
, respectively. Accounting only for the structures within 110 Mpc, we find that strong deflections are only produced if UHE protons cross galaxy clusters. The total area on the sky covered by these structures is however very small. Over still larger distances, multiple crossings of sheets and filaments may give rise to noticeable deflections over a significant fraction of the sky; the exact amount and angular distribution depends on the model adopted for the magnetic seed field. Based on our results we argue that over a large fraction of the sky the deflections are likely to remain smaller than the present experimental angular sensitivity. Therefore, we conclude that forthcoming air shower experiments should be able to locate sources of UHE protons and shed more light on the nature of cosmological MFs.
MERGERS, COSMIC RAYS, AND NONTHERMAL PROCESSES IN CLUSTERS OF GALAXIES
SARAZIN CRAIG L. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 433~438
DOI : 10.5303/JKAS.2004.37.5.433
Clusters of galaxies generally form by the gravitational merger of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. The basic properties of cluster mergers and their effects are discussed. Mergers drive shocks into the intracluster gas, and these shocks heat the intracluster gas. As a result of the impulsive heating and compression associated with mergers, there is a large transient increase in the X-ray luminosities and temperatures of merging clusters. These merger boost can affect X-ray surveys of clusters and their cosmological interpretation. Similar boosts occur in the strong lensing cross-sections and Sunyaev-Zeldovich effect in merging clusters. Merger shock and turbulence associated with mergers should also (re)accelerate nonthermal relativistic particles. As a result of particle acceleration in shocks and turbulent acceleration following mergers, clusters of galaxies should contain very large populations of relativistic electrons and ions. Observations and models for the radio, extreme ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles accelerated in these shocks will also be described. Gamma-ray observations with GLAST seem particularly promising.
EXTRAGALACTIC COSMIC RAYS AND MAGNETIC FIELDS: FACTS AND FICTION
ENBLIN TORSTEN ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 439~446
DOI : 10.5303/JKAS.2004.37.5.439
A critical discussion of our knowledge about extragalactic cosmic rays and magnetic fields is at-tempted. What do we know for sure? What are our prejudices? How do we confront our models with the observations? How can we assess the uncertainties in our modeling and in our observations? Unfortunately, perfect answers to these questions can not be given. Instead, I describe efforts I am involved in to gain reliable information about relativistic particles and magnetic fields in extragalactic space.
COSMIC RAYS AND GAMMA-RAYS IN LARGE-SCALE STRUCTURE
INOUE SUSUMU ; NAGASHIMA MASAHIRO ; SUZUKI TAKERU K. ; AOKI WAKO ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 447~454
DOI : 10.5303/JKAS.2004.37.5.447
During the hierarchical formation of large scale structure in the universe, the progressive collapse and merging of dark matter should inevitably drive shocks into the gas, with nonthermal particle acceleration as a natural consequence. Two topics in this regard are discussed, emphasizing what important things nonthermal phenomena may tell us about the structure formation (SF) process itself. 1. Inverse Compton gamma-rays from large scale SF shocks and non-gravitational effects, and the implications for probing the warm-hot intergalactic medium. We utilize a semi-analytic approach based on Monte Carlo merger trees that treats both merger and accretion shocks self-consistently. 2. Production of
by cosmic rays from SF shocks in the early Galaxy, and the implications for probing Galaxy formation and uncertain physics on sub-Galactic scales. Our new observations of metal-poor halo stars with the Subaru High Dispersion Spectrograph are highlighted.
THE QUEST FOR COSMIC RAY PROTONS IN GALAXY CLUSTERS
PFROMMER C. ; ENSSLIN T. A. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 455~460
DOI : 10.5303/JKAS.2004.37.5.455
There have been many speculations about the presence of cosmic ray protons (CRps) in galaxy clusters over the past two decades. However, no direct evidence such as the characteristic
-ray signature of decaying pions has been found so far. These pions would be a direct tracer of hadronic CRp interactions with the ambient thermal gas also yielding observable synchrotron and inverse Compton emission by additionally produced secondary electrons. The obvious question concerns the type of galaxy clusters most likely to yield a signal: Particularly suited sites should be cluster cooling cores due to their high gas and magnetic energy densities. We studied a nearby sample of clusters evincing cooling cores in order to place stringent limits on the cluster CRp population by using non-detections of EGRET. In this context, we examined the possibility of a hadronic origin of Coma-sized radio halos as well as radio mini-halos. Especially for mini-halos, strong clues are provided by the very plausible small amount of required CRp energy density and a matching radio profile. Introducing the hadronic minimum energy criterion, we show that the energetically favored CRp energy density is constrained to
of the thermal energy density in Perseus. We also studied the CRp population within the cooling core region of Virgo using the TeV
-ray detection of M 87 by HEGRA. Both the expected radial
-ray profile and the required amount of CRp support this hadronic scenario.
SECONDARY ELECTRONS IN CLUSTERS OF GALAXIES AND GALAXIES
HWANG CHORNG- YUAN ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 461~463
DOI : 10.5303/JKAS.2004.37.5.461
We investigate the role of secondary electrons in galaxy clusters and in ultra-luminous infrared galaxies (ULIGs). The radio emission in galaxy clusters and ULIGs is believed to be produced by the synchrotron radiation of relativistic electrons. Nonetheless, the sources of these relativistic electrons are still unclear. Relativistic secondary electrons can be produced from the hadronic interactions of cosmic-ray nuclei with the intra-cluster media (ICM) of galaxy clusters and the dense molecular clouds of ULIGs. We estimate the contribution of the secondary electrons in galaxy clusters and ULIGs by comparing observational results with theoretical calculations for the radio emission in these sources. We find that the radio halos of galaxy clusters can not be produced from the secondary electrons; on the other hand, at least for some ULIGs, the radio emission can be dominated by the synchrotron emission of the secondary electrons.
NONTHERMAL COMPONENTS IN THE LARGE SCALE STRUCTURE
MINIATI FRANCESCO ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 465~470
DOI : 10.5303/JKAS.2004.37.5.465
I address the issue of nonthermal processes in the large scale structure of the universe. After reviewing the properties of cosmic shocks and their role as particle accelerators, I discuss the main observational results, from radio to
-ray and describe the processes that are thought be responsible for the observed nonthermal emissions. Finally, I emphasize the important role of
-ray astronomy for the progress in the field. Non detections at these photon energies have already allowed us important conclusions. Future observations will tell us more about the physics of the intracluster medium, shocks dissipation and CR acceleration.
POSSIBLE MERGER SIGNATURE IN SZ MAPS
KOCH PATRICK ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 471~476
DOI : 10.5303/JKAS.2004.37.5.471
We propose an analytical model to estimate the influence of a merger on the thermal SZ effect. Following observations we distinguish between subsonic and transonic mergers. Using analytical velocity fields and the Bernoulli equation we calculate the excess pressure around a moving subcluster for an incompressible subsonic gas. Positive excess around the stagnation point and negative excess on the side of the subcluster lead to characteristic signatures in the SZ map, of the order of
compared to the unperturbed signal. For a transonic merger we calculate the change in the thermal spectral SZ function, resulting from bow shock accelerated electrons. The merger shock compression factor determines the power law tail of the new non-thermal electron population and is directly related to a shift in the crossover frequency. This shift is typically a few percent towards higher frequencies.
COSMIC RAYS ACCELERATED AT SHOCK WAVES IN LARGE SCALE STRUCTURE
RYU DONGSU ; KANG HYESUNG ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 477~482
DOI : 10.5303/JKAS.2004.37.5.477
Shock waves form in the intergalactic space as an ubiquitous consequence of cosmic structure formation. Using N-body/hydrodynamic simulation data of a ACDM universe, we examined the properties of cosmological shock waves including their morphological distribution. Adopting a diffusive shock acceleration model, we then calculated the amount of cosmic ray energy as well as that of gas thermal energy dissipated at the shocks. Finally, the dynamical consequence of those cosmic rays on cluster properties is discussed.
COSMIC RAY ACCELERATION DURING LARGE SCALE STRUCTURE FORMATION
BLASI PASQUALE ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 483~491
DOI : 10.5303/JKAS.2004.37.5.483
Clusters of galaxies are storage rooms of cosmic rays. They confine the hadronic component of cosmic rays over cosmological time scales due to diffusion, and the electron component due to energy losses. Hadronic cosmic rays can be accelerated during the process of structure formation, because of the supersonic motion of gas in the potential wells created by dark matter. At the shock waves that result from this motion, charged particles can be energized through the first order Fermi process. After discussing the most important evidences for non-thermal phenomena in large scale structures, we describe in some detail the main issues related to the acceleration of particles at these shock waves, emphasizing the possible role of the dynamical backreaction of the accelerated particles on the plasmas involved.
PARTICLE ACCELERATION AND NON-THERMAL EMISSION FROM GALAXY CLUSTERS
BRUNETTI GIANFRANCO ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 493~500
DOI : 10.5303/JKAS.2004.37.5.493
The existence and extent of non-thermal phenomena in galaxy clusters is now well established. A key question in our understanding of these phenomena is the origin of the relativistic electrons which may be constrained by the modelling of the fine radio properties of radio halos and of their statistics. In this paper we argue that present data favour a scenario in which the emitting electrons in the intracluster medium (ICM) are reaccelerated in situ on their way out. An overview of turbulent-particle acceleration models is given focussing on recent time-dependent calculations which include a full coupling between particles and MHD waves.
BLACK HOLE-IGM FEEDBACK, AND LINKS TO IGM FIELDS AND CR'S
KRONBER PHILIPP P. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 501~507
DOI : 10.5303/JKAS.2004.37.5.501
The uniquely large dimensions of Giant radio galaxies (GRGs) make it possible to probe for stringent limits on total energy content, Faraday rotation, Alfven speeds, particle transport and radiation loss times. All of these quantities are more stringently limited or specified for GRG's than in more 'normal' FRII radio sources. I discuss how both global and detailed analyses of GRG's lead to constraints on the CR electron acceleration mechanisms in GRG's and by extension in all FRII radio sources. The properties of GRG's appear to rule out large scale Fermi-type shock acceleration. The plasma parameters in these systems set up conditions that are favorable for magnetic reconnection, or some other very efficient process of conversion of magnetic to particle energy. We conclude that whatever mechanism operates in GRG's is probably the primary extragalactic CR acceleration mechanism in the Universe.
SIMULATING NONTHERMAL RADIATION FROM CLUSTER RADIO GALAXIES
TREGILLIS I. L. ; JONES T. W. ; RYU DONGSU ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 509~515
DOI : 10.5303/JKAS.2004.37.5.509
We present results from an extensive synthetic observation analysis of numerically-simulated radio galaxy (RG) jets. This analysis is based on the first three-dimensional simulations to treat cosmic ray acceleration and transport self-consistently within a magnetohydrodynamical calculation. We use standard observational techniques to calculate both minimum-energy and inverse-Compton field values for our simulated objects. The latter technique provides meaningful information about the field. Minimum-energy calculations retrieve reasonable field estimates in regions physically close to the minimum-energy partitioning, though the technique is highly susceptible to deviations from the underlying assumptions. We also study the reliability of published rotation measure analysis techniques. We find that gradient alignment statistics accurately reflect the physical situation, and can uncover otherwise hidden information about the source. Furthermore, correlations between rotation measure (RM) and position angle (PA) can be significant even when the RM is completely dominated by an external cluster medium.
LOW-LEVEL RADIO EMISSION FROM RADIO GALAXIES AND IMPLICATIONS FOR THE LARGE SCALE STRUCTURE
KRISHNA GOPAL ; WIITA PAUL J. ; BARAI PARAMITA ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 517~525
DOI : 10.5303/JKAS.2004.37.5.517
We present an update on our proposal that during the 'quasar era' (1.5
3), powerful radio galaxies could have played a major role in the enhanced global star-formation, and in the widespread magnetization and metal pollution of the universe. A key ingredient of this proposal is our estimate that the true cosmological evolution of the radio galaxy population is likely to be even steeper than what has been inferred from flux-limited samples of radio sources with redshift data, when an allowance is made for the inverse Compton losses on the cosmic microwave background which were much greater at higher redshifts. We thus estimate that a large fraction of the clumps of proto-galactic material within the cosmic web of filaments was probably impacted by the expanding lobes of radio galaxies during the quasar era. Some recently published observational evidence and simulations which provide support for this picture are pointed out. We also show that the inverse Compton x-ray emission from the population of radio galaxies during the quasar era, which we inferred to be largely missing from the derived radio luminosity function, is still only a small fraction of the observed soft x-ray background (XRB) and hence the limit imposed on this scenario by the XRB is not violated.
THE ORDERING OF MAGNETIC FIELDS IN THE COSMOS
BIERMANN PETER L. ; KRONBER PHILIPP P. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 527~531
DOI : 10.5303/JKAS.2004.37.5.527
It is argued that the key task in understanding magnetic fields in the cosmos is to comprehend the origin of their order or coherence over large length scales in galaxies. Obtaining magnetic fields can be done in stars, whose lifetime is usually
rotations, while galactic disks have approximately 20 to 50 rotations in their lifetime since the last major merger, which established the present day gaseous disk. Disorder in the galactic magnetic fields is injected on the disk time scale of about 30 million years, about a tenth of the rotation period, so after one half rotation already it should become completely disordered. Therefore whatever mechanism Nature is using, it must compete with such a short time scale, to keep order in its house. This is the focal quest.
GENERATION OF MAGNETIC FIELDS IN COSMOLOGICAL SHOCKS
MEDVEDEV MIKHAIL V. ; SILVA LUIS O. ; FIORE MASSIMILIANO ; FONSECA RICARDO A. ; MORI WARREN B. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 533~541
DOI : 10.5303/JKAS.2004.37.5.533
The origin of magnetic fields in the universe remains an outstanding problem in cosmology. We propose that these fields are produced by shocks during the large-scale structure formation. We discuss the mechanism of the field generation via the counter-streaming (Weibel) instability. We also show that these Weibel-generated fields are long-lived and weakly coupled to dissipation. Subsequent field amplification by the intra-cluster turbulence may also take place, thus maintaining the magnetic energy density close to equipartition.
A GRADIENT-T SZE
HATTORI MAKOTO ; OKABE NOBUHIRO ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 543~546
DOI : 10.5303/JKAS.2004.37.5.543
The inverse Compton scattering of the cosmic microwave background (CMB) radiation with electrons in the intracluster medium which has a temperature gradient, was examined by the third-order perturbation theory of the Compton scattering. A new type of the spectrum distortion of the CMB was found and named as gradient T Sunyaev-Zel'dovich effect (gradT SZE). The spectrum has an universal shape. There is a zero distortion point, the cross over frequency, at 326GHz. When the hotter region locates closer to an observer, the intensity becomes brighter than the CMB in the frequency region lower than the cross over frequency and fainter than the CMB in the frequency region higher than the cross over frequency. When the cooler region locates closer to an observer, the distorted part of the spectrum has an opposite sign to the above case. The amplitude of the spectrum distortion does not de-pend on the electron density and depends on the heat conductivity and the total temperature variation along a line of sight. Therefore, the gradT SZE provides an unique opportunity to measure thermally nonequilibrium electron momentum distribution function in the ICM and combined with the X-ray measurements of the electron temperature distribution provides an opportunity of direct measurement of the heat conductivity in the ICM.
GENERATION OF MAGNETIC FIELDS BY TEMPERATURE GRADIENTS
OKABE NOBUHIRO ; HATTORI MAKOTO ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 547~551
DOI : 10.5303/JKAS.2004.37.5.547
We showed that magnetic fields are generated in the plasma which have the temperature inhomogeneities. The mechanism is the same as the Weibel instability because the velocity distribution functions are at non-equilibrium and anisotropic under the temperature gradients. The growth timescale is much shorter than the dynamical time of structure formation. The coherence length of magnetic fields at the saturated time is much shorter than kpc scale and then, at nonlinear phase, become longer by inverse-cascade process. We report the application of our results to clusters of galaxies, not including hydrodynamic effects.
LARGE SCALE MAGNETOGENESIS THROUGH RADIATION PRESSURE
LANGER MATHIEU ; PUGET JEAN-LOUP ; AGHANIM NABILA ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 553~556
DOI : 10.5303/JKAS.2004.37.5.553
We present a new model for the generation of magnetic fields on large scales occurring at the end of cosmological reionisation. The inhomogeneous radiation provided by luminous sources and the fluctuations in the matter density field are the major ingredients of the model. More specifically, differential radiation pressure acting on ions and electrons gives rise to electric currents which induce magnetic fields on large scales. We show that on protogalactic scales, this process is highly efficient, leading to magnetic field amplitudes of the order of
Gauss. While remaining of negligible dynamical impact, those amplitudes are million times higher than those obtained in usual astrophysical magnetogenesis models. Finally, we derive the relation between the power spectrum of the generated field and the one of the matter density fluctuations. We show in particular that magnetic fields are preferably created on large (galactic or cluster) scales. Small scale magnetic fields are strongly disfavoured, which further makes the process we propose an ideal candidate to explain the origin of magnetic fields in large scale structures.
THERMAL CONDUCTION IN MAGNETIZED TURBULENT GAS
CHO JUNGYEON ; LAZARIAN A. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 557~562
DOI : 10.5303/JKAS.2004.37.5.557
We discuss diffusion of particles in turbulent flows. In hydrodynamic turbulence, it is well known that distance between two particles imbedded in a turbulent flow exhibits a random walk behavior. The corresponding diffusion coefficient is
is the amplitude of the turbulent velocity and
is the scale of the turbulent motions. It Is not clear whether or not we can use a similar expression for magnetohydrodynamic turbulence. However, numerical simulations show that mixing motions perpendicular to the local magnetic field are, up to high degree, hydrodynamical. This suggests that turbulent heat transport in magnetized turbulent fluid should be similar to that in non-magnetized one, which should have a diffusion coefficient
. We review numerical simulations that support this conclusion. The application of this idea to thermal conductivity in clusters of galaxies shows that this mechanism may dominate the diffusion of heat and may be efficient enough to prevent cooling flow formation when turbulence is vigorous.
TURBULENCE STATISTICS FROM SPECTRAL LINE OBSERVATIONS
LAZARIAN A. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 563~570
DOI : 10.5303/JKAS.2004.37.5.563
Turbulence is a crucial component of dynamics of astrophysical fluids dynamics, including those of ISM, clusters of galaxies and circumstellar regions. Doppler shifted spectral lines provide a unique source of information on turbulent velocities. We discuss Velocity-Channel Analysis (VCA) and its offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical description of the spectral line statistics. Those techniques are well suited for studies of supersonic turbulence. We stress that a great advantage of VCS is that it does not necessary require good spatial resolution. Addressing the studies of mildly supersonic and subsonic turbulence we discuss the criterion that allows to determine whether Velocity Centroids are dominated by density or velocity. We briefly discuss ways of going beyond power spectra by using of higher order correlations as well as genus analysis. We outline the relation between Spectral Correlation Functions and the statistics available through VCA and VCS.
TURBULENCE PRODUCED BY TSUNAMIS IN GALAXY CLUSTERS
FUJITA YUTAKA ; MATSUMOTO TOMOAKI ; WADA KEIICHI ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 571~574
DOI : 10.5303/JKAS.2004.37.5.571
Clusters of galaxies are filled with X-ray emitted hot gas with the temperature of T
2-10 keV. Recent X-ray observations have been revealing unexpectedly that many cluster cores have complicated, peculiar X-ray structures, which imply dynamical motion of the hot gas. Moreover, X-ray spectra indicate that radiative cooling of the cool gas is suppressed by unknown heating mechanisms (the 'cooling flow problem'). Here we propose a novel mechanism reproducing both the inhomogeneous structures and dynamics of the hot gas in the cluster cores, based on state-of-the-art hydrodynamic simulations. We showed that acoustic-gravity waves, which are naturally expected during the process of hierarchical structure formation of the universe, surge in the X-ray hot gas, causing a serous impact on the core. This reminds us of tsunamis on the ocean surging into an distant island. We found that the waves create fully-developed, stable turbulence, which reproduces the complicated structures in the core. Moreover, if the wave amplitude is large enough, they can suppress the cooling of the core. The turbulence could be detected in near-future space X-ray missions such as ASTRO-E2.
MHD SIMULATIONS OF A MOVING SUB CLUMP WITH HEAT CONDUCTION
ASAI NAOKI ; FUKUDA NAOYA ; MATSUMOTO RYOJI ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 575~578
DOI : 10.5303/JKAS.2004.37.5.575
High resolution observations of cluster of galaxies by Chandra have revealed the existence of an X-ray emitting comet-like galaxy C153 in the core of cluster of galaxies A2125. The galaxy C153 moving fast in the cluster core has a distinct X-ray tail on one side, obviously due to ram pressure stripping, since the galaxy C153 crossed the central region of A2125. The X-ray emitting plasma in the tail is substantially cooler than the ambient plasma. We present results of two-dimensional magnetohydrodynamic simulations of the time evolution of a sub clump like C153 moving in magnetized intergalactic matter. Anisotropic heat conduction is included. We found that the magnetic fields are essential for the existence of the cool X-ray tail, because in non-magnetized plasma the cooler sub clump tail is heated up by isotropic heat conduction from the hot ambient plasma and does not form such a comet-like tail.
DETECTION OF EMISSION FROM WARM-HOT GAS IN THE UNIVERSE WITH XMM?
BOWYER STUART ; VIKHLININ ALEXEY ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 579~581
DOI : 10.5303/JKAS.2004.37.5.579
Recently, claims have been made of the detection of 'warm-hot' gas in the intergalactic medium. Kaastra et al. (2003) claimed detection of
K material in the Coma Cluster but studies by Arnaud et al. (2001), and our analysis of the Chandra observations of Coma (Vikhlinin et al. 2001), find no evidence for a
K gas in the cluster. Finoguenov et al. (2003) claimed the detection of
gas slightly off-center from the Coma Cluster. However, our analysis of ROSAT data from this region shows no excess in this region. We propose an alternative explanation which resolves all these conflicting reports. A number of studies (e.g. Robertson et al., 2001) have shown that the local interstellar medium undergoes charge exchange with the solar wind. The resulting recombination spectrum shows lines of O VII and O VIII (Wargelin et al. 2004). Robertson & Cravens (2003) have .shown that as much as
of the Galactic polar flux is heliospheric recombination radiation and that this component is highly variable. Sporadic heliospheric emission could account for all the claims of detections of 'warm-hot' gas and explain the conflicts cited above.
CLUSTER MERGERS AND NON-THERMAL PHENOMENA: A STATISTICAL MAGNETO-TURBULENT MODEL
CASSANO R. ; BRUNETTI G. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 583~587
DOI : 10.5303/JKAS.2004.37.5.583
With the aim to investigate the statistical properties and the connection between thermal and non-thermal properties of the ICM in galaxy clusters, we have developed a statistical magneto-turbulent model which describes, at the same time, the evolution of the thermal and non-thermal emission from galaxy clusters. In particular, starting from the cosmological evolution of clusters, we follow cluster. mergers, calculate the spectrum of the magnetosonic waves generated in the ICM during these mergers, the evolution of relativistic electrons and the resulting synchrotron and Inverse Compton spectra. We show that the broad band (radio and hard x-ray) non-thermal spectral properties of galaxy clusters can be well accounted for by our model for viable values of the parameters (here we adopt a EdS cosmology).
OCCURENCE AND LUMINOSITY FUNCTIONS OF GIANT RADIO HALOS FROM MAGNETO-TURBULENT MODEL
CASSANO R. ; BRUNETTI G. ; SETTI G. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 589~592
DOI : 10.5303/JKAS.2004.37.5.589
We calculate the probability to form giant radio halos (
1 Mpc size) as a function of the mass of the host clusters by using a Statistical Magneto-Turbulent Model (Cassano & Brunetti, these proceedings). We show that the expectations of this model are in good agreement with the observations for viable values of the parameters. In particular, the abrupt increase of the probability to find radio halos in the more massive galaxy clusters (
) can be well reproduced. We calculate the evolution with redshift of such a probability and find that giant radio halos can be powered by particle acceleration due to MHD turbulence up to z
0.5 in a ACDM cosmology. Finally, we calculate the expected Luminosity Functions of radio halos (RHLFs). At variance with previous studies, the shape of our RHLFs is characterized by the presence of a cut-off at low synchrotron powers which reflects the inefficiency of particle acceleration in the case of less massive galaxy clusters.
FINDING COSMIC SHOCKS: SYNTHETIC X-RAY ANALYSIS OF A COSMOLOGICAL SIMULATION
HALLMAN ERIC J. ; RYU DONGSU ; KANG HYESUNG ; JONES T. W. ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 593~596
DOI : 10.5303/JKAS.2004.37.5.593
We introduce a method of identifying evidence of shocks in the X-ray emitting gas in clusters of galaxies. Using information from synthetic observations of simulated clusters, we do a blind search of the synthetic image plane. The locations of likely shocks found using this method closely match those of shocks identified in the simulation hydrodynamic data. Though this method assumes nothing about the geometry of the shocks, the general distribution of shocks as a function of Mach number in the cluster hydrodynamic data can be extracted via this method. Characterization of the cluster shock distribution is critical to understanding production of cosmic rays in clusters and the use of shocks as dynamical tracers.
THE CONTRIBUTION TO THE EXTRAGALACTIC γ-RAY BACKGROUND BY HADRONIC INTERACTIONS OF COSMIC RAYS PRODUCING EUV EMISSION IN CLUSTERS OF GALAXIES
KUO PING-HUNG ; BOWYER STUART ; HWANG CHORNG- YUAN ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 597~600
DOI : 10.5303/JKAS.2004.37.5.597
A substantial number of processes have been suggested as possible contributors to the extragalactic
-ray background (EGRB). Yet another contribution to this background will be emission produced in hadronic interactions of cosmic-ray protons with the cluster thermal gas; this class of cosmic rays (CRs) has been shown to be responsible for the EUV emission in the Coma Cluster of galaxies. In this paper we assume the CRs in the Coma Cluster is prototypic of all clusters and derive the contribution to the EGRB from all clusters over time. We examine two different possibilities for the scaling of the CR flux with cluster size: the number density of the CRs scale with the number density of the thermal plasma, and alternatively, the energy density of the CRs scale with the energy density of the plasma. We find that in all scenarios the EGRB produced by this process is sufficiently low that it will not be observable in comparison with other mechanisms that are likely to produce an EGRB.
LINEAR ANALYSIS OF PARKER-JEANS INSTABILITY WITH COSMIC-RAY
KUWABARA TAKUHITO ; KO CHUNG-MING ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 601~603
DOI : 10.5303/JKAS.2004.37.5.601
We present the results of the linear analysis for the Parker-Jeans instability in the magnetized gas disks including the effect of cosmic-ray diffusion along the magnetic field lines. We adopted an uni-formly rotating two temperature layered disk with a horizontal magnetic fields and solved the perturbed equations numerically. Fragmentation of gases takes place and filamentary structures are formed by the growth of the instability. Nagai et al. (1998) showed that the direction of filaments being formed by the Parker-Jeans instability depends on the strength of pressure outside the unperturbed gas disk. We found that at some range of external pressures the direction of filaments is also governed by the value of the diffusion coefficient of CR along the magnetic field lines k.
3D SIMULATIONS OF RADIO GALAXY EVOLUTION IN CLUSTER MEDIA
O'NEILL SEAN M. ; SHEARER PAUL ; TREGILLIS IAN L. ; JONES THOMAS W. ; RYU DONGSU ;
Journal of The Korean Astronomical Society, volume 37, issue 5, 2004, Pages 605~609
DOI : 10.5303/JKAS.2004.37.5.605
We present a set of high-resolution 3D MHD simulations exploring the evolution of light, supersonic jets in cluster environments. We model sets of high- and low-Mach jets entering both uniform surroundings and King-type atmospheres and propagating distances more than 100 times the initial jet radius. Through complimentary analyses of synthetic observations and energy flow, we explore the detailed interactions between these jets and their environments. We find that jet cocoon morphology is strongly influenced by the structure of the ambient medium. Jets moving into uniform atmospheres have more pronounced backflow than their non-uniform counterparts, and this difference is clearly reflected by morphological differences in the synthetic observations. Additionally, synthetic observations illustrate differences in the appearances of terminal hotspots and the x-ray and radio correlations between the high- and low-Mach runs. Exploration of energy flow in these systems illustrates the general conversion of kinetic to thermal and magnetic energy in all of our simulations. Specifically, we examine conversion of energy type and the spatial transport of energy to the ambient medium. Determination of the evolution of the energy distribution in these objects will enhance our understanding of the role of AGN feedback in cluster environments.