For studies of diffuse gases in the temperature range 105 – 106K, observations of O VI absorption in the spectra of background stars provide an important supplement to information from surveys of soft x-ray emission. We report here the first observations of O VI absorption recorded at a resolution of 3 km s−1 for the stars 15 Mon and HD 64760. Both stars are behind regions that are suspected to be old supernova remnants. The observations were made with the Interstellar Medium Absorption Profile Spectrograph (IMAPS) during its flight on the ORFEUS-SPAS II mission in late 1996.

The SAS 2 and COS B observations have established the existence of diffuse γ-rays in our Galaxy in various energy ranges. The diffuse radiation is attributed to the interaction of cosmic ray nuclei and electrons with the particles of interstellar atomic and molecular gas (via the decay of pions and bremsstrahlung, respectively). Inverse Compton scattering of interstellar photons by the high energy electrons of cosmic rays may also be contributing to this background. In addition some contribution may come from discrete sources of γ-rays.

When computing synthetic spectra we have to be aware of the strength of the lines. The determination of the required dipole strengths, oscillator strengths and transition probabilities is based on the evaluation of the dipole matrix elements. These quadratic functionals are defined by integrals over the whole space composed of the eigenfunctions P of the atomic system belonging to the eigenvalues Em and En, respectively:

If in the neighborhood of neutron stars exist clouds of hydrogen atoms, they are the natural astronomical object for realization of the model of hydrogen atom in a strong magnetic field ~ 108 T.

Theoretical arguments indicate that the ISM is inhomogeneous; Mathews estimated that the ~ 1M⊙ of metal ejected by each supernova event into the ISM is trapped locally within the hot bubbles. Since in elliptical galaxies, there is no overlapping of expanding supernova remnants after galactic wind period, it is expected that this inhomogeneity persists for a long time. The observations also suggests that the ISM of elliptical galaxies is inhomogeneous. Based on these arguments, we studied the evolution of the multiphase (inhomogeneous) ISM.

We have analyzed ASCA data of about 30 early type galaxies, and studied their X-ray emitting ISM (InterStellar Medium) properties. Our study has been motivated by the apparently very low metallicity of the ISM, which cannot easily be reconciled with theoretical predictions. By carefully examining the abundance ratios and uncertainties in the Fe-L complex, we have concluded that the ISM abundances in X-ray luminous galaxies are in fact about 1 solar. Therefore, the severe discrepancy between the ISM and stellar abundance has been relaxed. The ISM metallicity of X-ray fainter galaxies are uncertain, but at least SNe Ia contribution to the ISM abundance is smaller than in the X-ray luminous ones.

X-ray emission from spiral galaxies without activity is thought to consist of low-mass X-ray binaries (LMXBs), and the Einstein observations established the relation between X-ray (0.2-4 keV) and optical luminosities as log(LX/LB) ~ −4 (Fabbiano, 1992). This relation has been used when discussing the activity other than LMXBs (Iyomoto, 1996). However, spectral information of Einstein Observatory was rather poor above 3 keV, where LMXBs would emit significant energy flux. Therefore we performed ASCA observations of two normal spirals, NGC2903 and NGC628, in order to better calibrate the LX - LB relation.

We have performed spherically symmetric, time-dependent hydrodynamical calculations for the X-ray emitting gas around elliptical galaxies, NGC4472, for the purpose to reproduce profiles of temperature and density. Stellar mass loss rate and type Ia supernova rate are assumed to be constant. Thermal conduction is introduced to stabilize against thermal instability due to radiative cooling.

Winds from massive stars and supernovae in starburst galaxies drive global outflows of hot X-ray emitting plasma, as seen in M82 and NGC 253. These galactic winds are important for understanding galaxy evolution & formation, chemical enrichment of the IGM, and the starburst phenomenon itself.

X-ray observations provide the only direct probe of the hot gas in these winds. However, the limitations of current X-ray observatories and factors such as complex temperature structure, mass loading by ambient material and projection effects all make the link between the observed data and existing 1 & 2-D modeling and theory difficult to make.

We have therefore begun a program of numerical simulations of galactic winds, concentrating on predicting their observable X-ray properties. We present some initial results, comparing them to the archetypal starburst wind system M82.

The radio galaxy NGC 612 (z = 0.0290; Spinrad et al. 1985) exhibits bright (~ 11 Jy at 843 MHz) double lobes at a large scale of about 500 kpc x 130 kpc with a very faint core (Jones & McAdam 1992). We performed ASCA observations (AO-4; PI = Kaneda) of NGC 612 on July 12-14, 1996, in search for inverse-Compton (IC) X-rays from the radio lobes.

M32 is the nearest dwarf elliptical galaxy. Its center is known to have a mass concentration of 3 × 106 M⊙, which is usually interpreted as an evidence of a super massive black hole. We observed M32 with ASCA two times in July and August of 1996. An X-ray source was detected at the center of M32 and its first broad-band X-ray spectra were obtained. ASCA observations of M32 limit the activity of the central black hole to be less than 10−6 times of the Eddington limit. We also found two other bright sources within 12 arcmin from the M32 center. One is the newly appeared X-ray source and the other is G144. In this paper, we summarize the results on the new source and G144. For M32, please refer to the publication (Loewenstein et al. 1997).

A circulation hypothesis of spiral galaxies is proposed here to explain their spiral structure: the spiral arm material is going to the galactic center along a spiral orbit and then ejects from the galactic center in the form of two-way jets in opposite directions and finally, the ejected jets return to the galaxy in the form of spiral arms again, thereby forming a closed circulatory system.

Much attempts of statistical approach have been made to study the origin of heavy elements, distribution of dark matter and evolution of clusters of galaxies. Henry et al.(1991) reported a power-law relation; LX ∝ kTγ, γ ~ 2.7. Edge and Stwert(1991) found significant scatter in the correlation using 45 clusters. David at al.(1993) reported γ ~ 3.4 using 104 clusters.

Observations in X-ray and optical suggest that mergers of sub-clusters with galaxy clusters are quite common (for Coma see e.g., White et al. 1993; Colless & Dunn 1996; Ishizaka & Mineshige 1996). A merger leads to violent relaxation of the dissipationless dark matter resulting in a time-dependent gravitational potential. This in turn generates large-scale flows and shocks in the collisional baryonic intracluster gas (Takizawa & Mineshige 1997). Both the large scale flows and the shocks will excite turbulence in the gas. We focus here on turbulence generated by shocks, which is less dependent on the specifics of the merger. This paper is based on a more detailed work (Goldman 1997).

Cold and hot dark matter (CHDM) model is one of viable models which can reproduce the large scale structure of the universe. HDM may affect structure of clusters of galaxies in CHDM universe. Bryan et al. (1994) gave numerical results of CHDM model that explain some statistical features of X-ray clusters of galaxies, e.g. X-ray luminosiry-temperature realtion, L ∝~ T3.5, without considering radiative processes. However their numerical resolution is insufficient to resolve the cores of X-ray clusters. So, we simulate the formation of clusters in CHDM universe more carefully.

We observed five clusters of galaxies in Shapley supercluster with ASCA; A3562, SC13290-313, SC1327-312, A3558 and A3556, which are candidates for interacting clusters since their separation and relative velocities are only 1Mpc and 700-1000km/s (e.g. Raychaudhury et al. '91, Breen et al. '94, Scaramella et al. '89). Main purpose of mapping observations is to make clear the formation and evolution process of the clusters of galaxies in a supercluster. ASCA gives essential informations of ICM like the temperature distribution related to the dynamics; the interactions due to the infalling and merging events. They are important tests for observational cosmology (e.g. Hanami '93).

The hypothetical object called “failed cluster” of galaxies is described by Tucker et al. (1995, ApJ, 444, 532) as a large cloud of X-ray emitting hot gas without any visible galaxies. They made extensive survey of this type of objects using Einstein IPC database and found only one candidate, 0806+20.

The metal in the intracluster medium (ICM) has been ejected or stripped from galaxies. Thus measurements of the metal distribution and the relative abundance of elements, in particular Si/Fe, are important to study the evolution of galaxies, as well as to study the chemical evolution of the ICM. We present the results from ASCA observations of Abell 496 cluster of galaxies. A496 is a nearby rich cluster with a central cD galaxy. At the redshift z=0.0327 of A496, 1 arcmin is 53kpc, where we assumed H0 = 50kms−1Mpc−1, q0 = 0.5. A496 is known as a cooling flow cluster. Edge and Stewart (1991) obtained the mass flow rate of and the cooling radius of 177 ± 52kpc.

Intra-cluster spaces are filled with intra-cluster medium (ICM), whose typical temperature and density are TICM ~ 107.5 K and nICM ~ 10−3 cm−3, respectively (e.g., Sarazin 1988). Recent Faraday rotation measurements have revealed the existence of magnetic fields in ICM with few − 10 μG (e.g., Ge & Owen 1993). In ICM, the plasma β (the ratio of gas pressure to magnetic pressure) is almost “equipartition” value as follows:

The Coma cluster has been recognized as an archetype of rich and relaxed clusters, until recent ROSAT observations reveal that the intracluster medium (ICM) has a complex distribution (Briel et al. 1992; White et al. 1993). The X-ray surface brightness distribution shows a secondary peak around the galaxy NGC 4839, at 40' SW from the cluster center.