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1.
The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas collapsing in large-scale filaments and probably harbours
a substantial fraction of the baryons in the local Universe. Absorption-line measurements in the ultraviolet (UV) and in the
X-ray band currently represent the best method to study the WHIM at low redshifts. We here describe the physical properties
of the WHIM and the concepts behind WHIM absorption line measurements of H i and high ions such as O vi, O vii, and O viii in the far-ultraviolet and X-ray band. We review results of recent WHIM absorption line studies carried out with UV and X-ray
satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss their implications for our knowledge of the WHIM. 相似文献
2.
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
3.
Alain Abergel Laurent Verstraete Christine Joblin René Laureijs Marc-Antoine Miville-Deschênes 《Space Science Reviews》2005,119(1-4):247-271
Infrared spectroscopy and photometry with ISO covering most of the emission range of the interstellar medium has led to important
progress in the understanding of the physics and chemistry of the gas, the nature and evolution of the dust grains and also
the coupling between the gas and the grains. We review here the ISO results on the cool and low-excitation regions of the
interstellar medium, where T
gas≲ 500 K, n
H∼ 100–105 cm−3 and the electron density is a few 10−4.
JEL codes: D24, L60, 047
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
4.
Scott D. Barthelmy Louis M. Barbier Jay R. Cummings Ed E. Fenimore Neil Gehrels Derek Hullinger Hans A. Krimm Craig B. Markwardt David M. Palmer Ann Parsons Goro Sato Masaya Suzuki Tadayuki Takahashi Makota Tashiro Jack Tueller 《Space Science Reviews》2005,120(3-4):143-164
he burst alert telescope (BAT) is one of three instruments on the
Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and localizes the burst direction to an
accuracy of 1–4 arcmin within 20 s after the start of the event. The GRB trigger initiates an autonomous spacecraft slew to
point the two narrow field-of-view (FOV) instruments at the burst location within 20–70 s so to make follow-up X-ray and optical
observations. The BAT is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed
of 32,768 pieces of CdZnTe (4×4×2 mm), and the coded-aperture mask is composed of ∼52,000 pieces of lead (5×5×1 mm) with a
1-m separation between mask and detector plane. The BAT operates over the 15–150 keV energy range with ∼7 keV resolution,
a sensitivity of ∼10−8 erg s−1 cm−2, and a 1.4 sr (half-coded) FOV. We expect to detect > 100 GRBs/year for a 2-year mission. The BAT also performs an all-sky
hard X-ray survey with a sensitivity of ∼2 m Crab (systematic limit) and it serves as a hard X-ray transient monitor. 相似文献
5.
We are making precise determinations of the abundance of the light isotope of helium, 3He. The 3He abundance in Milky Way sources impacts stellar evolution, chemical evolution, and cosmology. The abundance of 3He is derived from measurements of the hyperfine transition of 3He+ which has a rest wavelength of 3.46 cm (8.665 GHz). As with all the light elements, the present interstellar 3He abundance results from a combination of Big Bang Nucleosynthesis (BBNS) and stellar nucleosynthesis. We are measuring the
3He abundance in Milky Way H ii regions and planetary nebulae (PNe). The source sample is currently comprised of 60 H ii regions and 12 PNe. H ii regions are examples of zero-age objects that are young relative to the age of the Galaxy. Therefore their abundances chronicle
the results of billions of years of Galactic chemical evolution. PNe probe material that has been ejected from low-mass (M≤ 2M
⊙) to intermediate-mass (M∼2–5M
⊙) stars to be further processed by future stellar generations. Because the Milky Way ISM is optically thin at centimeter wavelengths,
our source sample probes a larger volume of the Galactic disk than does any other light element tracer of Galactic chemical
evolution. The sources in our sample possess a wide range of physical properties (including object type, size, temperature,
excitation, etc.). The 3He abundances we derive have led to what has been called “The 3He Problem”. 相似文献
6.
M. I. Desai G. M. Mason R. E. Gold S. M. Krimigis C. M. S. Cohen R. A. Mewaldt J. E. Mazur J. R. Dwyer 《Space Science Reviews》2007,130(1-4):243-253
Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged
∼0.1–60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results
show the following: (1) The Fe/O ratio decreases with increasing energy up to ∼10 MeV/nuc in ∼92% of the events and up to
∼60 MeV/nuc in ∼64% of the events. (2) The rare isotope 3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (3) The heavy ion abundances are not
systematically organized by the ion’s M/Q ratio when compared with the solar wind values. (4) Heavy ion abundances from C–Fe exhibit systematic M/Q-dependent enhancements that are remarkably similar to those seen in 3He-rich SEP events and CME-driven interplanetary (IP) shock events. Taken together, these results confirm the role of shocks
in energizing particles up to ∼60 MeV/nuc in the majority of large SEP events of cycle 23, but also show that the seed population
is not dominated by ions originating from the ambient corona or the thermal solar wind, as previously believed. Rather, it
appears that the source material for CME-associated large SEP events originates predominantly from a suprathermal population
with a heavy ion enrichment pattern that is organized according to the ion’s mass-per-charge ratio. These new results indicate
that current LSEP models must include the routine production of this dynamic suprathermal seed population as a critical pre-cursor
to the CME shock acceleration process. 相似文献
7.
R. A. Leske R. A. Mewaldt C. M. S. Cohen A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):335-340
Measurements below several MeV/nucleon from Wind/LEMT and ACE/ULEIS show that elements heavier than Zn (Z=30) can be enhanced by factors of ∼100 to 1000, depending on species, in 3He-rich solar energetic particle (SEP) events. Using the Solar Isotope Spectrometer (SIS) on ACE we find that even large SEP
(LSEP) shock-accelerated events at energies from ∼10 to >100 MeV/nucleon are often very iron rich and might contain admixtures
of flare seed material. Studies of ultra-heavy (UH) SEPs (with Z>30) above 10 MeV/nucleon can be used to test models of acceleration and abundance enhancements in both LSEP and 3He-rich events. We find that the long-term average composition for elements from Z=30 to 40 is similar to standard solar system values, but there is considerable event-to-event variability. Although most
of the UH fluence arrives during LSEP events, UH abundances are relatively more enhanced in 3He-rich events, with the (34<Z<40)/O ratio on average more than 50 times higher in 3He-rich events than in LSEP events. At energies >10 MeV/nucleon, the most extreme event in terms of UH composition detected
so far took place on 23 July 2004 and had a (34<Z<40)/O enhancement of ∼250–300 times the standard solar value. 相似文献
8.
The baryon density of the universe B is well measured indirectly from Big-Bang nucleo-synthesis, in particular by recent measurements of the D/H ratio in high-redshift QSO absorption systems. In addition, very recent measurements of the second maximum of the power-spectrum of the CMB fine scale anisotropy allow to constrain B at z1000. Both results agree and yield B=0.02h
–2. Direct measurements of the diffuse baryonic component (intergalactic gas) at redshifts z=3 and 1.5 and in the local universe are reviewed and shown to be much more difficult. Available observations are consistent with the hypothesis that at z=3 and possibly still at z=1.5 nearly all baryons are located in the highly ionized L forest component, while at later epochs the contribution of a low-density, shock-heated component (105–107 K), the so called warm-hot intergalactic medium (WHIM), occupies with decreasing redshift an increasing fraction of all baryons. Methods to detect this component and the difficulty to make quantitative estimates are described. In the local universe
of all baryons may be hidden in the WHIM. Yet at z=1.5, this component contains at least a factor of 5 less material. 相似文献
9.
D. Breitschwerdt R. Egger M. J. Freyberg P. C. Frisch J. V. Vallerga 《Space Science Reviews》1996,78(1-2):173-182
Recently, observations with the rosat PSPC instrument and the spectrometers onboard the euve satellite have given new detailed information on the structure and physical conditions of the Local Bubble. From the early rocket experiments, and in particular from the WISCONSIN Survey, the existence of a diffuse hot gas in the vicinity of the solar system, extending out to about 100 pc, has been inferred in order to explain the emission below 0.3 keV. The higher angular resolution and sensitivity of rosat made it possible to use diffuse neutral clouds as targets for shadowing the soft X-ray background. Thus, in some directions, more than half of the flux in the 0.25 keV band appears to come from outside the Local Bubble. Further, measurements of the diffuse EUV in the LISM, show surprisingly few emission lines. These findings are in conflict with the standard LHB model, which assumes a local hot (T 106
K) plasma in CIE. Model calculations, based on the non-equilibrium cooling of an expanding plasma, show a promising way of reconciling all available observations. Thus the present temperature within the LB may be as low as 4 × 104
K and its number density as large as 2 × 10–2
cm
–3, giving a total pressure that is roughly in agreement with the Local Cloud.Abbreviations CIE
collisional ionization equilibrium
- ISM
Interstellar Medium
- LHB
Local Hot Bubble
- LB
Local Bubble
- LISM
Local ISM
- SB
superbubble
- SXR
soft X-ray
- SXRB
SXR Background
- VLISM
Very Local ISM
Heisenberg Fellow 相似文献
10.
Priscilla C. Frisch 《Space Science Reviews》1995,72(3-4):499-592
There is a warm tenuous partially ionized cloud (T104 K,n(HI)0.1 cm–3,n(Hii 0.22–0.44 cm–3) surrounding the solar system which regulates the environment of the solar system, determines the structure of the heliopause region, and feeds neutral interstellar gas into the inner solar system. The velocity (V–20 km s–1 froml335°,b0° in the local standard of rest) and enhanced Caii and Feii abundances of this cloud suggest an origin as evaporated gas from cloud surfaces in the Scorpius-Centaurus Association. Although the soft X-ray emission attributed to the Local Bubble is enigmatic, optical and ultraviolet data are consistent with bubble formation caused by star formation epochs in the Scorpius-Centaurus Association as regulated by the nearby spiral arm configuration. The cloud surrounding the solar system (the local fluff) appears to be the leading region of an expanding interstellar structure (the squall line) which contains a magnetic field causing polarization of the light of nearby stars, and also absorption features in nearby upwind stars. The velocity vectors of the solar system and local fluff are perpendicular in the local standard of rest. Combining this information with the low column densities seen towards Sirius in the anti-apex direction, and the assumption that the cloud velocity vector is parallel to the surface normal, suggests that the Sun entered the local fluff within the historical past (less than 10 000 years ago) and is skimming the surface of the cloud. Comparison of magnesium absorption lines towards Sirius and anomalous cosmic-ray data suggest the local fluff is in ionization equilibrium.Reason has moons, but moons not hers, Lie mirror'd on her sea, Confounding her astronomers, But, O! delighting me.Ralph Hodgson 相似文献
11.
Marie-Helene Ulrich 《Space Science Reviews》1981,28(1):89-104
3C 273 is the most extensively studied quasar both from the ground and from space. Recent satellite observations have given important information on the overall electromagnetic spectrum of 3C 273 in the -ray, X-ray, and UV ranges. The most salient results are: (i) the energy per decade of frequency emitted by 3C 273 is nearly constant between 6000 Å and 500 MeV and is 20 × 1046 erg s-1 for H = 50 km s-1 Mpc-1; (ii) there is no absorption in the soft X-ray range in contrast to the X-ray spectrum of Seyfert nuclei; (iii) the optical and UV spectra cannot be fitted by power-law spectra only, and the energy distribution in this range suggests that a substantial fraction of the energy in the UV is emitted as back-body radiation at 20 000 K. If the peculiar shape of the UV spectrum is indeed caused by black-body radiation, then an estimate of the energy emitted under this form is 2.5 × 1046erg s-1, corresponding to an optically thick disk of 1016 cm in diameter.The UV spectrum of 3C 273 shows absorption lines at zero redshift caused by interstellar matter in the disk and halo of our Galaxy. The strength of C iv 1550 in absorption indicates the presence of a hot outer region in the halo. Extragalactic objects with mostly continuous UV spectra, such as 3C 273, are very promising UV sources which allow us to observe the absorbing material over the entire line of sight throughout the galactic halo. 相似文献
12.
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
13.
J. S. Kaastra A. M. Bykov S. Schindler J. A. M. Bleeker S. Borgani A. Diaferio K. Dolag F. Durret J. Nevalainen T. Ohashi F. B. S. Paerels V. Petrosian Y. Rephaeli P. Richter J. Schaye N. Werner 《Space Science Reviews》2008,134(1-4):1-6
We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together
to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of
galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the
“missing baryon” problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic
medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and
clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and
discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists
wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations. 相似文献
14.
The invention of the neutron monitor pile for the study of cosmic-ray intensity-time and energy changes began with the discovery
in 1948 that the nucleonic component cascade in the atmosphere had a huge geomagnetic latitude dependence. For example, between
0° and 60° this dependence was a ∼ 200–400% effect – depending on altitude – thus opening the opportunity to measure the intensity
changes in the arriving cosmic-ray nuclei down to ∼1–2 GeV nucl−1 for the first time. In these measurements the fast (high energy) neutron intensity was shown to be a surrogate for the nuclear
cascade intensity in the atmosphere.
The development of the neutron monitor in 1948–1951 and the first geomagnetic latitude network will be discussed. Among its
early applications were:
(1) to prove that there exists interplanetary solar modulation of galactic cosmic-rays (1952), and;
(2) to provide the evidence for a dynamical heliosphere (1956).
With the world-wide distribution of neutron monitor stations that are presently operating (∼ 50) many novel investigations
are still to be carried out, especially in collaborations with spacecraft experiments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
W. R. Binns M. E. Wiedenbeck M. Arnould A. C. Cummings G. A. de Nolfo S. Goriely M. H. Israel R. A. Leske R. A. Mewaldt G. Meynet L. M. Scott E. C. Stone T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):439-449
We have measured the isotopic abundances of neon and a number of other species in the galactic cosmic rays (GCRs) using the
Cosmic Ray Isotope Spectrometer (CRIS) aboard the ACE spacecraft. Our data are compared to recent results from two-component
(Wolf–Rayet material plus solar-like mixtures) Wolf–Rayet (WR) models. The three largest deviations of galactic cosmic ray
isotope ratios from solar-system ratios predicted by these models, 12C/16O, 22Ne/20Ne, and 58Fe/56Fe, are very close to those observed. All of the isotopic ratios that we have measured are consistent with a GCR source consisting
of ∼20% of WR material mixed with ∼80% material with solar-system composition. Since WR stars are evolutionary products of
OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of our data with WR models
suggests that OB associations within superbubbles are the likely source of at least a substantial fraction of GCRs. In previous
work it has been shown that the primary 59Ni (which decays only by electron-capture) in GCRs has decayed, indicating a time interval between nucleosynthesis and acceleration
of >105 y. It has been suggested that in the OB association environment, ejecta from supernovae might be accelerated by the high
velocity WR winds on a time scale that is short compared to the half-life of 59Ni. Thus the 59Ni might not have time to decay and this would cast doubt upon the OB association origin of cosmic rays. In this paper we
suggest a scenario that should allow much of the 59Ni to decay in the OB association environment and conclude that the hypothesis of the OB association origin of cosmic rays
appears to be viable. 相似文献
16.
J. S. Kaastra F. B. S. Paerels F. Durret S. Schindler P. Richter 《Space Science Reviews》2008,134(1-4):155-190
We discuss the different physical processes that are important to understand the thermal X-ray emission and absorption spectra
of the diffuse gas in clusters of galaxies and the warm-hot intergalactic medium. The ionisation balance, line and continuum
emission and absorption properties are reviewed and several practical examples are given that illustrate the most important
diagnostic features in the X-ray spectra. 相似文献
17.
Philipp P. Kronberg 《Space Science Reviews》1996,75(1-2):387-399
An overview is presented of the methods of probing for the geometry, and strength of intergalactic magnetic fields. Recent results are briefly surveyed for galaxy halos, galaxy clusters, and the intergalactic medium on various scales, and some rele vant physical processes and radiation processes are mentioned, as well as the coupling between intergalactic magnetic fields and cosmic rays.The general trend of recent results indicates that, wherever we detect intergalactic hot gas and galaxies, we also find magnetic fields at levels of 10–7 G, or higher. The hitherto undetected, weaker fields in the ratified i.g.m. and in large intergalactic voids could be probed by both Faraday rotation, and possibly using very energetic CR nuclei (> 1020eV), and/or transient extragalactic ray bursts. 相似文献
18.
David N. Burrows J. E. Hill J. A. Nousek J. A. Kennea A. Wells J. P. Osborne A. F. Abbey A. Beardmore K. Mukerjee A. D. T. Short G. Chincarini S. Campana O. Citterio A. Moretti C. Pagani G. Tagliaferri P. Giommi M. Capalbi F. Tamburelli L. Angelini G. Cusumano H. W. Bräuninger W. Burkert G. D. Hartner 《Space Science Reviews》2005,120(3-4):165-195
he Swift Gamma-Ray Explorer is designed to make prompt multiwavelength observations of gamma-ray bursts (GRBs) and GRB afterglows.
The X-ray telescope (XRT) enables Swift to determine GRB positions with a few arcseconds accuracy within 100 s of the burst onset.
The XRT utilizes a mirror set built for JET-X and an XMM-Newton/EPIC MOS CCD detector to provide a sensitive broad-band (0.2–10 keV) X-ray imager with effective area of > 120 cm2 at 1.5 keV, field of view of 23.6 × 23.6 arcminutes, and angular resolution of 18 arcseconds (HPD). The detection sensitivity
is 2×10−14 erg cm−2 s−1 in 104 s. The instrument is designed to provide automated source detection and position reporting within 5 s of target acquisition.
It can also measure the redshifts of GRBs with Fe line emission or other spectral features. The XRT operates in an auto-exposure
mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source intensity fades.
The XRT will measure spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and will follow
each burst for days or weeks.
Dedicated to David J. Watson, in memory of his valuable contributions to this instrument. 相似文献
19.
The three-dimensional structure of the solar maximum modulation of cosmic rays in the heliosphere can be studied for the first
time by comparing observations from Ulysses at high solar latitudes to those from in-ecliptic spacecraft, such as IMP-8. Observations through mid-2000 show that changes
in modulation remain well correlated at Earth and Ulysses up to latitudes of ∼60° south. The observed changes seem to be best correlated with changes in the inclination of the heliospheric
current sheet. The spectral index of the proton spectra at energies <100 MeV in the ecliptic and at high latitudes remain
roughly consistent with the T
+1 spectrum expected from modulation models, while the spectral index of the helium spectrum at both locations has changed smoothly
from the flat or even negative index spectra characteristic of anomalous component fluxes toward the T
+1 galactic spectrum with increasing modulation. Intensities near the equator and at high latitude remain nearly equal, and
latitudinal gradients for nucleonic cosmic rays thus remain small (<1% deg−1) at solar maximum. In the most recent data fluxes of protons and helium with energies less than ∼100 MeV nucl−1 measured by Ulysses are smaller than those measured at IMP-8, suggesting that the gradients may have switched to become negative toward the poles
even before a clear reversal of polarity for the solar magnetic dipole has been completed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
The imaging capabilities of the Exosat and Einstein satellites at soft X-ray wavelengths have begun to show that suitable Galactic X-ray sources have extended ( 10 arcmin) haloes due to scattering of soft X-rays by interstellar dust. A simple argument suggests that similar haloes, due to scattering by intergalactic dust, should exist around distant (z 1) quasars and detailed analysis confirms this conclusion. A search for such haloes around suitable X-ray quasars could provide valuable, model-independent, constraints on the amount and origin of intergalactic dust. 相似文献