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1.
Starting with nearby galaxy clusters like Virgo and Coma, and continuing out to the furthest galaxy clusters for which ISO
results have yet been published (z = 0.56), we discuss the development of knowledge of the infrared and associated physical properties of galaxy clusters from
early IRAS observations, through the “ISO-era” to the present, in order to explore the status of ISO's contribution to this
field. Relevant IRAS and ISO programmes are reviewed, addressing both the cluster galaxies and the still-very-limited evidence
for an infrared-emitting intra-cluster medium.
ISO made important advances in knowledge of both nearby and distant galaxy clusters, such as the discovery of a major cold
dust component in Virgo and Coma cluster galaxies, the elaboration of the correlation between dust emission and Hubble-type,
and the detection of numerous Luminous Infrared Galaxies (LIRGs) in several distant clusters. These and consequent achievements
are underlined and described.
We recall that, due to observing time constraints, ISO's coverage of higher-redshift galaxy clusters to the depths required
to detect and study statistically significant samples of cluster galaxies over a range of morphological types could not be
comprehensive and systematic, and such systematic coverage of distant clusters will be an important achievement of the Spitzer
Observatory.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, the Netherlands, and the United Kingdom) and with the participation of ISAS and NASA. 相似文献
2.
K. L. Aplin 《Space Science Reviews》2008,137(1-4):213-224
Atmospheric charged clusters are formed in a series of rapid chemical reactions after ionisation, leaving a central ion X+ or X? clustered with n ligands (Y) n . In solar system tropospheres and stratospheres there are two distinct cluster regimes: the terrestrial planets contain largely hydrated clusters (i.e. Y=H2O), whereas the gas planets and their moons have organic or nitrogenated cluster species. These classifications are largely based on model predictions, since hardly any measurements are available. The few existing composition measurements are reviewed, including the recent detection of massive charged particles in Titan’s upper atmosphere. Technologies for both remote sensing and in situ measurements of atmospheric charged clusters are discussed. Preliminary measurements in the terrestrial atmosphere are presented indicating that ambient charged cluster species interact with downwelling infra-red radiation at 9.15 μm, even in the presence of cloud. This supports the possibility of future infrared detection of charged clusters. 相似文献
3.
A. C. Fabian 《Space Science Reviews》1985,40(3-4):653-660
The X-ray emission from the intracluster gas is a rich source of information on the metal abundance, evolution and mass profile of clusters. Methods for determining the mass of gas are reviewed; the total mass is uncertain. The best data so far available concentrate on the cluster core. Cooling flows are found within the cores of a significant fraction of rich and poor clusters, as well as in relatively isolated elliptical galaxies. 相似文献
4.
The response of the lower and middle atmosphere to variations in solar irradiance typical of those observed to take place over the 11-year activity cycle has been investigated. The effects on radiative heating rates of changing total solar irradiance, solar spectral irradiance and two different assumptions concerning stratospheric ozone have been studied with a radiative transfer code. The response in the stratosphere depends on the changes specified in the ozone distribution which is not well known. A general circulation model (GCM) of the atmosphere up to 0.1 mbar (about 65 km) has been used to study the impacts of these changes on the thermodynamical structure. The results in the troposphere are very similar to those reported by Haigh99 using a quite different GCM. In the middle atmosphere the model is able to reproduce quite well the observed seasonal evolution of temperature and wind anomalies. Calculations of radiative forcing due to solar variation are presented. These show that the thermal infrared component of the forcing, due to warming of the stratosphere, is important but suggest a near balance between the longwave and shortwave effects of the increased ozone so that ozone change may not be important for net radiative forcing. However, the structure of the ozone change does affect the detailed temperature response and the spectral composition of the radiation entering the troposphere. 相似文献
5.
Cloud formation in the atmosphere is related to the presence of water vapour, cloud condensation nuclei (CCN) and ice nuclei (IN). Ionisation in the atmosphere is caused by a variety of sources, but the contribution from cosmic rays is always present and is modulated by the solar cycle. Methods of investigating the variability in ionisation are described. The mechanisms proposed by which (1) ionisation could influence cloud formation, and (2) by which changes to the CCN and IN could occur are discussed. Direct formation of sulphate CN is conceivable in atmospheric air by radioactivity, and charging of molecular clusters leads to greater collisions rates than for neutral clusters. Modification of the ice nucleation efficiency of aerosol could also have atmospheric effects through latent heat release. However in both cases definitive atmospheric experimental work is lacking and therefore any link between solar variability and clouds remains unproven. 相似文献
6.
7.
Galaxy clusters are ideal tracers of the large-scale structure and evolution of the universe. They are thus good probes for the matter content of the universe, the existence of dark matter, and for the statistics of the large-scale structure of the matter distribution. X-ray observations provide a very effective tool to characterize individual galaxy clusters as well as the cluster population. With the detailed analysis of X-ray observations of galaxy clusters the matter composition of clusters is obtained which can be taken as representative of the matter composition of the universe. Based on galaxy cluster surveys in X-rays a census of the galaxy cluster population and statistical measures of the spatial distribution of clusters is obtained. Comparison of the results with predictions from cosmological models yields interesting cosmological model constraints and in particular favours a low density universe. 相似文献
8.
The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun, and determines the boundary
conditions of the heliosphere. Both the Sun and interstellar clouds move through space, so these boundary conditions change
with time. Data and theoretical models now support densities in the cloud surrounding the solar system of n(H0)=0.22±0.06
cm−3, and n(e−)∼0.1 cm−3, with larger values allowed for n(H0) by radiative transfer considerations. Ulysses and Extreme Ultraviolet
Explorer satellite He0 data yield a cloud temperature of 6400 K. Nearby interstellar gas appears to be structured and inhomogeneous.
The interstellar gas in the Local Fluff cloud complex exhibits elemental abundance patterns in which refractory elements are
enhanced over the depleted abundances found in cold disk gas. Within a few parsecs of the Sun, inconclusive evidence for factors
of 2–5 variation in Mg+ and Fe+ gas phase abundances is found, providing evidence for variable grain destruction. In principle,
photoionization calculations for the surrounding cloud can be compared with elemental abundances found in the pickup ion and
anomalous cosmic-ray populations to model cloud properties, including ionization, reference abundances, and radiation field.
Observations of the hydrogen pile up at the nose of the heliosphere are consistent with a barely subsonic motion of the heliosphere
with respect to the surrounding interstellar cloud. Uncertainties on the velocity vector of the cloud that surrounds the solar
system indicate that it is uncertain as to whether the Sun and α Cen are or are not immersed in the same interstellar cloud.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
Priscilla C. Frisch 《Space Science Reviews》2009,143(1-4):191-204
Interstellar material around the Sun is typical for our neighborhood of the Galaxy. The physical properties and kinematics of the partially ionized interstellar material (ISM) near the Sun are typical of warm diffuse clouds in the solar vicinity. The direction of the interstellar magnetic field at the heliosphere, the polarization of light from nearby stars, and the kinematics of nearby clouds are naturally explained in terms of the S1 superbubble shell. The interstellar radiation field at the Sun appears to be harder than the field ionizing ambient diffuse gas, which may be a consequence of the low opacity of the tiny cloud surrounding the heliosphere. 相似文献
10.
11.
A. Grimberg D. S. Burnett P. Bochsler H. Baur R. Wieler 《Space Science Reviews》2007,130(1-4):293-300
We discuss data of light noble gases from the solar wind implanted into a metallic glass target flown on the Genesis mission.
Helium and neon isotopic compositions of the bulk solar wind trapped in this target during 887 days of exposure to the solar
wind do not deviate significantly from the values in foils of the Apollo Solar Wind Composition experiments, which have been
exposed for hours to days. In general, the depth profile of the Ne isotopic composition is similar to those often found in
lunar soils, and essentially very well reproduced by ion-implantation modelling, adopting the measured velocity distribution
of solar particles during the Genesis exposure and assuming a uniform isotopic composition of solar wind neon. The results
confirm that contributions from high-energy particles to the solar wind fluence are negligible, which is consistent with in-situ
observations. This makes the enigmatic “SEP-Ne” component, apparently present in lunar grains at relatively large depth, obsolete.
20Ne/ 22Ne ratios in gas trapped very near the metallic glass surface are up to 10% higher than predicted by ion implantation simulations.
We attribute this superficially trapped gas to very low-speed, current-sheet-related solar wind, which has been fractionated
in the corona due to inefficient Coulomb drag. 相似文献
12.
13.
Janssen L.H. Van Der Spek G.A. 《IEEE transactions on aerospace and electronic systems》1985,(2):208-219
From October 1982 through May 1983 an extensive weather clutter registration program was executed near the Dutch coast. Coherent echo series of 2 s were obtained from a cluster of adjacent antenna pencil beams every 10 or 15 min., mainly between 16:00 and 08:30 h and on the weekends. The beam cluster was pointed toward the intensity maximum of the clutter volume. The radar operated at 5650 MHz. Spectra with 10 Hz Doppler resolution have been computed by averaging over 19 discrete Fourier transforms of overlapping and tapered subseries of 200 echo vectors. To quantify the deviation from a Gaussian shape a spectral variability is defined which is computed for every estimated spectrum. It is found that the deviation from Gaussian is considerable in about one-fourth of the spectra. A selection of "typical worst case" spectra is presented. 相似文献
14.
Imaging X-ray observations of the Fornax cluster of galaxies centered on NGC 1399 and NGC 1404 are presented. NGC 1399 and NGC 1404, which are separated by about 10 arc minutes, are found to have an unusually high ratio of x-ray to optical flux. We consider the possibility that the x-radiation is produced by hot gas in the cores of the galaxies. Weak X-ray emission is also detected from a point almost exactly mid-way between NGC 1399 and NGC 1404. The combined emission from the galaxies is insufficient by over an order of magnitude to account for the the low-energy X-ray emission detected from this region by the HEAO-l satellite. It is suggested that the bulk of the HEAO-1 source is diffuse gas associated with the cluster as a whole, rather than individual galaxies. 相似文献
15.
The consequences of the interaction between the solar wind and the local interstellar medium for the wind region enclosed by the heliospheric shock are reviewed. After identifying the principal mechanisms to influence the dynamics of the solar wind, an approach allowing the simultaneous incorporation of neutral atoms, pick-up ions, cosmic rays and energetic electrons into a multifluid model of the expanding wind plasma is outlined. The effects of these particle species are discussed in detail, with special emphasis on the electron component which behaves more like a quasi-static hot gas rather than an expanding fluid. This electron gas is effectively trapped within a three-dimensional trough of a circumsolar electric potential whose outer fringes are possibly determined by the density distribution of anomalous cosmic rays. The electrons are proven to be a globally structered component of great importance for the solar wind momentum flow contributing to a triggering of the solar wind dynamics by asymmetric interstellar boundary conditions. Finally, the consequences for the relative motion of the Sun and the local interstellar medium as well as for the solar system as a whole are described. 相似文献
16.
Alexander Ruzmaikin 《Space Science Reviews》2001,95(1-2):43-53
Sunspots, seen as cool regions on the surface of the Sun, are a thermal phenomenon. Sunspots are always associated with bipolar magnetic loops that break through the solar surface. Thus to explain the origin of sunspots we have to understand how the magnetic field originates inside the Sun and emerges at its surface. The field predicted by mean-field dynamo theories is too weak by itself to emerge at the surface of the Sun. However, because of the turbulent character of solar convection the fields generated by dynamo are intermittent – i.e., concentrated into ropes or sheets with large spaces in between. The intermittent fields are sufficiently strong to be able to emerge at the solar surface, in spite of the fact that their mean (average) value is weak. It is suggested here that magnetic fields emerge at the solar surface at those random times and places when the total magnetic field (mean field plus fluctuations) exceeds the threshold for buoyancy. The clustering of coherently emerged loops results in the formation of a sunspot. A non-axisymmetric enhancement of the underlying magnetic field causes in the clustering of sunspots forming sunspot groups, clusters of activity and active longitudes. The mean field, which is not directly observable, is also important, being responsible for the ensemble regularities of sunspots, such as Hale's law of sunspot polarities and the 11-year periodicity. 相似文献
17.
Scattering of the cosmic microwave background (CMB) radiation by hot gas in clusters of galaxies produces a unique spectral signature – the Sunyaev–Zeldovich (S–Z) effect – that constitutes an important cosmological probe. The effect has been sensitively measured in more than 40 clusters, mostly with ground-based interferometric arrays operating at low microwave frequencies. These measurements have already yielded important information on cluster masses, and the Hubble constant. The scientific yield will be greatly increased when spectral and high-resolution spatial measurements of the effect in a large sample of nearby clusters will be made with stratospheric telescopes equipped with bolometric arrays. I review the current status of observational and theoretical S–Z work, and describe the main goals and challenges of using the effect as a more precise probe of cluster properties and cosmological parameters. 相似文献
18.
19.
C. Ferrari F. Govoni S. Schindler A. M. Bykov Y. Rephaeli 《Space Science Reviews》2008,134(1-4):93-118
We review observations of extended regions of radio emission in clusters; these include diffuse emission in ‘relics’, and
the large central regions commonly referred to as ‘halos’. The spectral observations, as well as Faraday rotation measurements
of background and cluster radio sources, provide the main evidence for large-scale intracluster magnetic fields and significant
densities of relativistic electrons. Implications from these observations on acceleration mechanisms of these electrons are
reviewed, including turbulent and shock acceleration, and also the origin of some of the electrons in collisions of relativistic
protons by ambient protons in the (thermal) gas. Improved knowledge of non-thermal phenomena in clusters requires more extensive
and detailed radio measurements; we briefly review prospects for future observations. 相似文献
20.
A series of observations of the Virgo cluster of galaxies with the Medium Energy experiment on board EXOSAT are presented. These take the form of two orthogonal scans meeting at M87. The observed count rates have been compared with those obtained with the IPC on board the EINSTEIN observatory and are found to be consistent with the the IPC surface brightness distribution. This fact together with spectral data obtained with Exosat indicates that the region around M87 is more or less isothermal (T 2–3 keV) out to > 80 arc min from the centre. Although a slight hardening is seen near the optical centroid of the cluster the results do not support a model which involves a hot ( 8 keV) intra-cluster medium. A mass of 5 × 1013 solar masses is derived for the inner 90 arc minutes of M87. 相似文献