X-ray Spectroscopic Observations Research Articles

Mass‐to‐Light Ratios of Groups and Clusters of Galaxies

We constrain the mass-to-light ratios, gas mass fractions, baryon mass fractions and the ratios of total to luminous mass for a sample of eight nearby relaxed galaxy groups and clusters: A262, A426, A478, A1795, A2052, A2063, A2199 and MKW4s. We useASCA spatially resolved spectroscopic X-ray observations and ROSAT PSPC images to constrain the total and gas masses of these clusters. To measure cluster luminosities we use galaxy catalogs resulting from the digitization and automated processing of the second generation Palomar Sky Survey plates calibrated with CCD images in the Gunn-Thuan g, r, and i bands. Under the assumption of hydrostatic equilibrium and spherical symmetry, we can measure the total masses of clusters from their intra-cluster gas temperature and dens ity profiles. Spatially resolved ASCA spectra show that the gas temperature decreases with increasing distance from the center. By comparison, the assumption that the gas is isothermal results in an underestimate of the total ma ss at small radii, and an overestimate at large cluster radii. We have obtained luminosity functions for all clusters in our sample. After correcting for background and foreground galaxies, we estimate the total cluster luminosity using Schechter function fits to the galaxy catalogs. In the three lowest redshift clusters where we can sample to fainter absolute magnitudes, we have detected a flattening of the luminosity function at intermediate magni tudes and a rise at the faint end. These clusters were fitted with a sum of two Schechter functions. The remaining cl usters were well fitted with a single Schechter function. Assuming H0 = 50 h50 km s -1 Mpc -1 , the measured mass-to-light ratios are ∼ 100 h50 M⊙/L⊙. This, along with a high baryonic fraction, is indicative of a low density universe with 0 ∼ 0.15 - 0.2. Subject headings: Cosmology — galaxies: clusters: individual — intergalactic medium — X-rays: galaxies

Anatomy of a Merger: A Numerical Model of A754

A754 is a well-observed cluster of galaxies (z = 0.054) that exhibits a variety of morphological peculiarities. These include a bar of X-ray emission that is offset significantly from the galaxy distribution, an elongated X-ray surface brightness distribution extending between two distinct peaks in the galaxy distribution, and an extremely nonisothermal and asymmetric intracluster medium temperature morphology. Using these observational constraints, we present a numerical hydro/N-body model of A754 in which two clusters (2.5:1 mass ratio) have merged nearly in the plane of the sky less than 0.5 Gyr ago with an impact parameter of ~120 kpc and an impact velocity of ~2500 km s-1 (roughly the escape velocity of the primary cluster). Our models allow us to identify the origin of A754's peculiar X-ray and temperature morphologies, the underlying hydrodynamical processes that shape them, and their future evolution. We make detailed predictions for future high-resolution X-ray spectroscopic observations (e.g., Astro-E). We discuss general properties of our models that will be characteristic of off-axis mergers. In particular, we find significant nonthermal pressure support within the central region that could bias cluster mass estimates. We find significant angular momentum imparted on the gas distribution in the cluster. We find that mixing of the subcluster gas components is an inefficient process, particularly at large radii. Finally, we find that subsequent dark matter core passages result in an extended relaxation timescale.

High-Resolution Measurement of the Kα Spectrum of Fexxv–xviii: New Spectral Diagnostics of Nonequilibrium Astrophysical Plasmas

We present laboratory measurements of high-resolution spectra of iron Kα emission under transient ionization conditions similar to those that are believed to exist in stellar flares and young supernova remnants. Taking advantage of our high spectral resolution (λ/Δλ ≥ 2000), we identify a number of transitions that can serve as diagnostics of ionizing plasmas. By varying the excitation energy in the experiments, we constrain the effects of the electron distribution on these diagnostic lines. Using our measured line ratios, we deduce values for the ionization time, η = Net, in the plasma, which agree with the actual values to ~20% accuracy. This result gives us confidence to our ability to derive similar constraints on astrophysical plasmas from remote X-ray spectroscopic observations.

ASCA observation of the Galactic Center

X-ray imaging and spectroscopic observations near the Galactic Center in the 0.5–10 keV energy band were carried out with the X-ray satellite ASCA. Several X-ray sources were detected. Luminosities of the sources are estimated to be of order 10 35–10 36 erg s −1. The largely extended emission with K-shell transition lines from highly ionized atoms were confirmed. Moreover, an extended emission of the 6.4 keV line from the low ionized iron atom was discovered. The 6.4 keV line intensity is elongated to the north-east from the Galactic Center along the galactic plane and well correlates with the distribution of the dense molecular clouds observed in the radio bands. We interpret that the 6.4 keV line originates from the florescent from the molecular cloud irradiated by bright X-ray source.

Temperature and Metallicity of a Massive X-Ray Cluster at Redshift 0.5

view Abstract Citations (62) References (67) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Temperature and Metallicity of a Massive X-Ray Cluster at Redshift 0.5 Donahue, Megan Abstract We present spectroscopic X-ray observations, obtained with the Advanced Satellite for Cosmology and Astrophysics (ASCA), of MS 0451.6-0305, the most luminous cluster of galaxies and one of the most distant (z = 0.54) in the Extended Medium-Sensitivity Survey (EMSS). We find that the hot gas in this cluster has a temperature of 10.4 +/- 1.2 keV, which is very hot but commensurate with its X-ray luminosity (2-10 keV rest frame) of 2.2 x 10^45^ h_50_^-2^ ergs s^-1^, if the relationship between L_x_ and T_x_ is the same at redshift 0.5 as nearby. The iron abundance of this gas is 0.15_-0.12_^+0.11^ solar, somewhat lower than, but consistent with, the iron abundance of hot gas in nearby clusters. The temperature of this gas, when combined with the image parameters of the ROSAT Position Sensitive Proportional Counter (PSPC) X-ray map and with the assumption that the gas is isothermal and in nearly hydrostatic equilibrium with the cluster gravitational potential, implies a hot gas mass of 4.1 x 10^13^ h_50_^-5/2^ H_sun_ and a total mass (including the dark matter) of 10^15^ h_50_^-1^ H_sun) within a radius of 1 h_50_^-1^ Mpc. The total mass is consistent with the mass estimated from gravitational lensing observations. The ratio of hot gas mass to the total mass is thus only ~4%(+/- 2%, conservatively), lower than the ratio of the gas to total mass in Coma or other clusters within the same physical scale. These observations are consistent with a picture of cluster evolution in which an early starburst phase provides most of the intracluster iron and intracluster gas, and a substantial fraction of the baryonic matter is initially associated with galaxies. Publication: The Astrophysical Journal Pub Date: September 1996 DOI: 10.1086/177671 Bibcode: 1996ApJ...468...79D Keywords: GALAXIES: INTERGALACTIC MEDIUM; GALAXIES: CLUSTERS: INDIVIDUAL ALPHANUMERIC: MS 0016+16; GALAXIES: CLUSTERS: INDIVIDUAL ALPHANUMERIC: MS 0451.6-0305; X-RAYS: GALAXIES; COSMOLOGY: DARK MATTER full text sources ADS | data products SIMBAD (3) NED (2) HEASARC (1)

The electronic structure of a model bimetallic catalyst: symmetry-resolved density of states at Γ̅gG for Cu/Ru(111)

The ruthenium hcp(0001) surface covered by a copper monolayer has become an important model system for investigating central questions regarding the catalytic behavior of bimetallic materials. We argue that the dominant modifications of the clean Ru surface electronic structure are relatively insensitive to the stacking of the layers near the surface, and we therefore carry out surface Green's function TB-LMTO computations to determine the symmetry- and layer-resolved density of states at k‖ = 0 (Γ̅gG) for fcc Cu/Ru(111), fcc Cu(111) and fcc Ru(111). At Γ̅gG there are two irreducible representations, a non-degenerate one, Γ̅gG1, to which the s, pz, and d3z2−r2 states belong and a doubly degenerate one, Γ̅gG2, to which the px, py; dxy, dx22t-y2; and dxz, dyz states belong. While we obtain various new surface resonances and bound states, our principal finding is that the Cu overlayer suppresses the upper Γ̅gG2 subband of Ru at the surface. This finding suggests a simple theoretical interpretation of the X-ray spectroscopic observations and a possible basis for understanding the chemical behavior of this material.

Observations of energy conversion in the solar flare plasma

Soft x-ray spectroscopic observations give evidence for magnetic energy conversion in the solar atmosphere during flares. Non-thermal broadenings and blue-shifted components, observed in hot emission lines during the impulsive phase of flares, can be interpreted as a manifestation of magnetic energy conversion and of energy transport from the primary energy release site to the chromosphere, respectively. Large non-thermal broadenings in soft x-ray lines emitted from the coronal plasma are observed in the period immediately preceding the onset of solar flares and during the flare impulsive phase, suggesting a relation to the initiation of the primary process of energy release and particle acceleration. Non-thermal broadenings can be interpreted as turbulent mass motions in the regions where magnetic reconnection occurs. Blue wings in soft x-ray lines appear at the onset of flares, as evidence for chromospheric evaporation, in coincidence with the onset of the impulsive phase of energy release. The dynamics of the evaporating plasma depends on the mechanism of chromospheric heating, and, in turn, on the form of energy which is predominant in the coronal loops as a result of the primary energy release. The observed evaporation velocities suggest that particle beams play a dominant role in transferring energy along the loop, at least in large flares.

Measurements of the separation between the ablation surface and the absorption region from x-ray spectroscopic observations in laser-heated plasmas.

The separation between the ablation surface and the absorption region (called the ``stand-off distance'') in laser-heated planar target experiments is determined from x-ray spectroscopic measurements of the K\ensuremath{\alpha} emission and the resonance lines of highly charged ions. In the intensity range 2\ifmmode\times\else\texttimes\fi{}${10}^{12}$--${10}^{13}$ W/${\mathrm{cm}}^{2}$ of a Nd:glass laser (${\ensuremath{\lambda}}_{L}$=1.06 \ensuremath{\mu}m) the K\ensuremath{\alpha} emission is shown to be produced almost entirely by reabsorption of the x-ray line emission from the hot plasma. By relating the experimentally measured spatial width of the K\ensuremath{\alpha} emission region to that of the resonance line emission region through modeling different x-ray source intensity distributions, a stand-off distance of \ensuremath{\sim}150 \ensuremath{\mu}m is determined which is consistent with theoretical estimates.

LABORATORY ASTROPHYSICS EXPERIMENTS IN X-RAY TRANSFER PHYSICS RELEVANT TO COSMIC ACCRETION-POWERED SOURCES

The interpretation of upcoming cosmic soft X-ray spectroscopic observations may require a vast improvement in the state of our knowledge of basic atomic physics and radiation transfer processes, particularly for the important class of accretion-powered systems such as cataclysmic variables, X-ray binaries, and active galactic nuclei. For these sources, short wavelength spectral features are formed in the transfer of X-radiation from a powerful central source outward through a cooler, surrounding medium. The line emitting gas is photoionized and the level populations are determined largely by recombination cascades and photoexcitation as opposed to collisional effects. These processes can be rather complex and many uncertainties remain. We are developing a new approach to this problem using time-resolved studies of laser produced plasmas. Experiments which are currently underway include the measurements of : (a) inner and outer shell photoabsorption cross-sections of intermediate ions of abundant elements, and (b) fluorescent excitation processes due to wavelength coincidences of resonant transitions from different ions. In connection with this program, we have developed a novel reflection grating spectrometer coupled to a streak camera which provides high resolution spectra at soft X-ray and EUV wavelengths at the sub-nanosecond level .We describe our laboratory facility and some of our preliminary experimental results.

X-ray spectroscopy of high temperature plasma in solar flares

X-ray spectroscopic observations with high wavelength resolution provide information on plasma density, temperature and emission measure together with bulk and turbulent velocity data for the hot plasma. Observations carried out during the 1980 solar maximum with spectrometers on the SMM, P78-1 and Hinotori spacecraft will be reviewed with emphasis on the advances made possible by these missions. During the next solar maximum, flare studies with particular emphasis on the impulsive phase will be undertaken by the Japanese Solar-A mission. Those instruments designed to study the hot plasma will be described and their proposed role in clarifying the nature of the impulsive phase discussed.

Laboratory Astrophysics Experiments in X-Ray Transfer Physics Relevant to Cosmic Accretion-Powered Sources

AbstractThe interpretation of upcoming cosmic soft X-ray spectroscopic observations may require a vast improvement in the state of our knowledge of basic atomic physics and radiation transfer processes, particularly for the important class of accretion-powered systems such as cataclysmic variables, X-ray binaries, and active galactic nuclei. For these sources, short wavelength spectral features are formed in the transfer of X-radiation from a powerful central source outward through a cooler, surrounding medium. The line emitting gas is photoionized and the level populations are determined largely by recombination cascades and photoexcitation as opposed to collisional effects. These processes can be rather complex and many uncertainties remain. We are developing a new approach to this problem using time-resolved studies of laser produced plasmas. Experiments which are currently underway include the measurements of: (a) inner and outer shell photoabsorption cross-sections of intermediate ions of abundant elements, and (b) fluorescent excitation processes due to wavelength coincidences of resonant transitions from different ions. In connection with this program, we have developed a novel reflection grating spectrometer coupled to a streak camera which provides high resolution spectra at soft X-ray and EUV wavelengths at the sub-nanosecond level. We describe our laboratory facility and some of our preliminary experimental results.

X-ray emission lines from three Galactic bulge sources

X-ray spectroscopic observations obtained with the Einstein objective grating spectrometer (OGS) and monitor proportional counter (MPC) instruments of three Galactic bulge sources, the globular cluster burst source 1820-30, the burster Serpens X-1, and the GX 9+9 are presented. Joint spectral fits to the OGS and MPC data are consistent for all three sources with either a thermal bremsstrahlung model with temperature ranging from 6 to 10 keV or with a two-component blackbody model, where one component may be associated with the neutron star and one with the accretion disk. The spectra of Serpens X-1 and 1820-30 harden with increases in intensity. The implications of the results for recent models of low-mass X-ray binaries are discussed.

High-resolution X-ray spectroscopic evidence of nonequilibrium conditions in the Cygnus Loop

High-resolution spectroscopic X-ray observations of a portion of the Cygnus Loop made with the Focal Plane Crystal Spectrometer aboard the Einstein Observatory are reported. Emission lines for O VII, O VIII, and Ne IX are measured, and upper limits are set to other transitions in O VII and O VIII. The detected emission line fluxes are consistent with emission from an equilibrium plasma with an electron temperature of about 3 x 10 to the 6th K, a value similar to that obtained by numerous previous observers. The absence of any O VII forbidden line emission strongly suggests that the emitting plasma is not in collisional ionization equilibrium. This is shown to be the case using several line diagnostics formed from the observed emission lines and a simple model describing the X-ray emission from an ionizing nonequilibrium plasma.

The mass profile and gas content of M87

X-ray images and spectroscopic observations, in particular of the Fe L lines, are used to constrain the structure of the hot gas and gravitating matter around M87 with respect to allowable temperature gradient, and therefore gravitational potential, over the 1-10 arcmin radius range. Models in which the gravitating mass has a core radius of about 25 kpc are favored, suggesting that the material is associated with M87 rather than with the Virgo cluster as a whole. The gas temperature is noted to vary slowly beyond 5 arcmin, while the variation in the inner regions is not consistent with thermal conduction models for powering the central X-ray emission.

Infrared observations of RS CVn stars

The paper presents infrared photometry of the RS CVn binary stars AR Lac (1.2-10 microns) and MM Her (1.2-3.5 microns) as they egressed from their primary and secondary eclipses; of the eclipsing systems RS CVn and Z Her at maximum light (1.2-10 microns) and of the non-eclipsing systems UX Ari and HR 1099 (1.2-10 microns). An analysis of these and published V data based on flux ratio diagrams (linear analogues of color-color diagrams) shows that G and K stars supply the infrared light of these systems. In AR Lac, the combined light of a G5-K0 subgiant and either a late F dwarf or an early F subgiant can account for the observed visual and infrared light curves. None of these systems shows infrared emission from circumstellar matter. This result is simply understood: dust grains would not be expected to form in the physical conditions surrounding the subgiant, and the corona and chromosphere (whose properties have been deduced from spectroscopic X-ray observations) should not produce appreciable infrared emission.

Stellar X-Ray Emission as an Indicator of Stellar Magnetic Activity

An overview of recent Einstein Observatory observations and theoretical modeling of stellar x-ray emission is presented, with particular emphasis upon the role such studies can play furthering our understanding of stellar magnetic activity. We argue that solar observations can be used to show that coronal emission is morphologically related to surface magnetic field activity; to establish a quantitative link between the observed soft x-ray flux and the mean surface (photospheric) magnetic flux; and, in sum, to demonstrate that soft x-ray emission is a sensitive diagnostic for the presence of surface magnetic fields, uncomplicated by radiative transfer effects and the resulting coupling to the underlying atmosphere (which may introduce unwanted correlations with spectral type and luminosity class). Recent analyses of stellar x-ray observations from the Einstein Observatory have focused on the interpretation of stellar coronal emission and possibly-related surface magnetic activity within the framework of our understanding of solar activity; including “loop” models of stellar coronae, observations of coronal emission variability on a wide range of time scales (which provide information on the morphology of the emitting plasma), and observations and modeling of low-resolution spectroscopic x-ray observations (which test the applicability of solar modeling). These recent results, which I review, all reenforce the argument that stellar coronal emission constitutes an excellent probe for studying stellar magnetic activity over a wide dynamic range, one which may prove to be uniquely suited to studying such activity in distant (and hence faint) sources.

Highly stripped ions in everyday astrophysics

The quality and quantity of X-ray spectroscopic observations of celestial objects have improved immensely in the last few years with solar observations by the Solar Maximum Mission and P78-1 satellites and observations of other objects by the Einstein satellite. Here we review some recent work on density and temperature diagnostic line ratios with the implications for the ionization state of solar flare plasma and the elemental abundances in supernova remnants.

A Morphological Classification of Clusters of Galaxies from Einstein Images

The earliest Uhuru observations showed that cluster X-ray sources were not associated with single individual galaxies but were extended sources (Gursky et al. 1971, Kellogg et al. 1972, and Forman et al. 1972). The detection of iron line emission from X-ray spectroscopic observations (Mitchell et al. 1976 and Serlemitsos et al. 1977) showed both that the dominant X-ray emission process was thermal bremsstrahlung and that the gas had been processed through stellar systems before being injected into the intracluster medium.

The contribution of young galaxies to the X-ray background

The contribution of young galaxies to the diffuse X-ray background is estimated and two mechanisms by which young galaxies may emit hard X-rays are considered. The first mechanism is direct thermal bremsstrahlung emission from a hot galactic wind powered by supernovae. Estimating mass-loss rates from galaxies by arguments based on metallicity and on the X-ray spectroscopic observations of rich clusters, it is shown that galactic winds may contribute substantially to the background. The second mechanism relies on the decreased metallicity of young galaxies to increase the number of supergiant stars and hence the numbers of hard X-ray binaries. This effect quantitatively explains the relatively large X-ray luminosity of the Magellanic clouds and also indicates that binaries in young galaxies may contribute a significant fraction of the diffuse X-ray background. Both mechanisms require that the epoch of galaxy formation be recent (redshift less than 2-3) in order to account for the observed spectral temperature (45 keV) of the hard X-ray background.

X-Ray Spectra of Clusters of Galaxies

Now that the predominantly thermal nature of the X-ray emission from clusters of galaxies is well established (see e.g. Mushotzky et al. 1978, Smith et al. 1979), it is appropriate to ask what further information can be gleaned from X-ray spectroscopic observations. While the above publications made use of data from the OSO-8 satellite, two newer experiments have been flown by our group on the HEAO-1 and HEAO-2 (Einstein) satellites. The first of these, the A-2 experiment, was comprised of gas proportional counters like our OSO-8 detectors, while the second, the Solid State Spectrometer (SSS), is a cooled Si detector with narrow field of view and heightened energy resolution.