Hot Gas Emission Research Articles

Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas

There is a general agreement that the conspicuous extranuclear X-ray, optical-line, and radio-contiuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyze the interaction of the wind with a two-component disk-halo ambient interstellar medium and argue that this two-component representation is crucial for adequate modeling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the X-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex 'filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions r elated to the origin and development of the 'filaments'. The filament parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A 'mild' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk and halo gas without strongly affecting the gaseous disk, thus creating conditions for virtually free vertical escape of the hot gas at the later, much more violent supernova-dominated phases of the starburst. We calculate the luminosity, mass, and effective temperature of the X-ray emitting gas in the 'soft' (0.1 to 0.7 keV, 0.7 to 2.2 keV, and 0.1 to 2.2 keV) and 'hard' (1.6 to 8.3 keV) energy bands and estimate the contribution of different gaseous components to the X-ray flux in these bands. Analysis of these parameters enables us to make conclusions regarding the nature of the X-ray-emitting material. We have inferred that the bulk of the soft thermal X-ray emission from starbursts arises in the wind-shocked material of the disk and halo gas rather than in the wind material itself. This enables us to predict that the integrated soft X-ray spectra of starbursts need not show an overabundance of heavy elements which are believed to be produced copiously in the centers of starbursts. Unlike soft X-ray emission, the hard component of thermal X-ray emission is found to originate in the wind material ejected from the starburst region. However, the derived ratio of hard-to-soft X-ray luminosities is too small compared to that observed in starbursts. We conclude therefore that the observed hard X-ray emission of starbursts is probably not associated with the thermal emission of hot wind or ambient shocked gas. Typical temperatures of the bulk of the soft X-ray-emitting material in our very different models have been found to agree well with the ones estimated on the basis of the ROSAT data for the soft component of X-ray emission of nearby starbursts. We predict that temperatures of the extranuclear soft X-ray-emitting gas in starburst galaxies with heavy element abundances near solar should be close to T(sub Xs = 2 to 5 x 10(exp 6)K.

Application of laser holographic interferometry to temperature measurements in buoyant air jets

HE present work is concerned with the temperature measurements on a heated, round, air jet-like or plumelike flow using a real-time holographic interferometry. Buoyant jets arid plumes occur in many environmental problems, from the discharge of thermal effluents into lakes or oceans, to the emission of hot gas in the atmosphere through chimneys. The study of jet- and plume-like flows has been a subject of investigation for almost a half-decade. In most previous investigations of buoyant air jets and plumes, temperatures were measured using intrusive apparatus, for instance, thermocouples1 and the two-wire probes.2 However, temperature distributions typically encountered in these kinds of flows are spatially and temporally variant and require measurements with high spatial and temporal resolution. Recognition of this need has resulted in a considerable effort toward development of a wide range of diagnostic techniques. Owing to current significant progress in the laser optical diagnostics, nonintrusive temperature measurements can be made by many techniques such as holographic interferometry, MachZehnder interferometry, light-scattering thermometry,3-5 and so forth. Among these nonintrusive techniques available for the experimental study of air jets and plumes, holographic interfefometry has the capability for less expensive, in situ, planewise temperature measurements with high spatial and temporal resolution. It is this technique that is employed in the present work.

Studying the internal kinematics of galaxies using the calcium infrared triplet

view Abstract Citations (122) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Studying the internal kinematics of galaxies using the calcium infrared triplet. Dressler, A. Abstract The Ca II IR triplet lines 8498, 8542, and 8662 Å are strong in a wide variety of stellar types, making this an ideal spectral region for studying the internal kinematics of neighboring galaxies. With the calcium triplet it is possible to measure systemic velocity, velocity dispersion, and line strength even in galaxies whose light is dominated by young stars, hot gas, or nonthermal emission. Results are given for some sample galaxies, including radial profiles of v, σ, and γ for M31, M32, and NGC 1068. Both M31 and M32 show a cusplike rise in velocity dispersion of 30% - 50% in the central few parsecs. These data suggest a rising M/L in each nucleus perhaps due to a black hole of order 106-7 solar masses. Publication: The Astrophysical Journal Pub Date: November 1984 DOI: 10.1086/162579 Bibcode: 1984ApJ...286...97D Keywords: Atomic Energy Levels; Calcium; Galactic Rotation; Infrared Spectra; Line Spectra; Stellar Motions; Andromeda Galaxy; Astronomical Spectroscopy; Black Holes (Astronomy); Data Acquisition; Data Reduction; Galactic Nuclei; Nonthermal Radiation; Seyfert Galaxies; Stellar Evolution; Velocity Distribution; Astrophysics full text sources ADS | data products NED (6) SIMBAD (2)

Measurement of the burning surface temperatures of propellant compositions by infra-red emission

The temperatures of extremely thin surface layers of burning solid propellant compositions have been determined by measurement of their infra-red radiation. Specific wavelengths, at which the flame gas emission is low, have been selected for the measurements. The path length of the radiating gaseous flame through which the surface is viewed has been reduced using a specially designed burner so that adequate correction for gas emission can be made. The surface temperatures of ammonium perchlorate compositions have been examined in some detail and the effect of the magnitude of the absorption coefficient of the material on the observed temperature has been demonstrated with this system. For example, at wavelengths at which the absorption coefficient is low, the surface temperatures of very weak fuel ammonium perchlorate powder mixtures appear to fall somewhat as the burning rate increases but in spectral regions of suitably high absorption coefficient the surface temperatures remain virtually constant, irrespective of the burning rate. The surface temperature for such mixtures burning at atmospheric pressure is 495° ± 15°C. Practical propellant compositions, based on ammonium perchlorate and containing rather more than stoichiometric proportions of fuel, give the same temperature provided that the hot gas emission can be successfully eliminated, but observed temperatures are in some instances raised (to a maximum of about 560°C) by gas interference. It is concluded that the process taking place at the burning ammonium perchlorate surface is an equilibrium sublimation process and that the rate of consumption of the solid is controlled by subsequent gas phase reactions among the dissociation products. The average surface temperature of double-base propellants increases with increase of burning rate, although it is likely that the liquid nitric ester component vaporizes at constant temperature. The retention of carbonaceous products near the burning surface of some compositions makes measurements of surface temperature inaccurate and has so far prevented the determination of the precise temperature dependence of the nitrocellulose decomposition. Double-base compositions have surface temperatures ranging from 300° to 400°C at atmospheric pressure. Binder-fuels currently used in composite propellants have surface temperatures close to 500°C when burning in a diffusion flame with oxygen.