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Showing papers in "The Astrophysical Journal in 1992"


Journal ArticleDOI
TL;DR: In this article, it is argued that a convective dynamo can also generate a very strong dipole field after the merger of a neutron star binary, but only if the merged star survives for as long as about 10-100 ms.
Abstract: It is proposed that the main observational signature of magnetars, high-field neutron stars, is gamma-ray bursts powered by their vast reservoirs of magnetic energy. If they acquire large recoils, most magnetars are unbound from the Galaxy or reside in an extended, weakly bound Galactic corona. There is evidence that the soft gamma repeaters are young magnetars. It is argued that a convective dynamo can also generate a very strong dipole field after the merger of a neutron star binary, but only if the merged star survives for as long as about 10-100 ms. Several mechanisms which could impart a large recoil to these stars at birth, sufficient to escape from the Galactic disk, are discussed.

2,482 citations


Journal ArticleDOI
TL;DR: In this paper, the first year of data from the differential microwave radiometers on the Cosmic Background Explorer was presented, and the angular autocorrelation of the signal in each radiometer channel and cross-correlation between channels were consistent and gave a primordial fluctuation power-law spectrum with index of 1.1 +/- 0.5, and an rms-quadrupole-normalized amplitude of 16 +/- 4 micro-K.
Abstract: Results of the first year of data from the differential microwave radiometers on the Cosmic Background Explorer are presented. Statistically significant structure that is well described as scale-invariant fluctuations with a Gaussian distribution is shown. The rms sky variation, smoothed to a total 10-deg FWHM Gaussian, is 30 +/-5 micro-K for Galactic latitude greater than 20-deg data with the dipole anisotropy removed. The rms cosmic quadrupole amplitude is 13 +/-4 micro-K. The angular autocorrelation of the signal in each radiometer channel and cross-correlation between channels are consistent and give a primordial fluctuation power-law spectrum with index of 1.1 +/-0.5, and an rms-quadrupole-normalized amplitude of 16 +/-4 micro-K. These features are in accord with the Harrison-Zel'dovich spectrum predicted by models of inflationary cosmology.

2,195 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that gamma-ray bursts are created in the mergers of double neutron star binaries and black hole neutron star binary at cosmological distances, and the strongest bursts should be found close to, but not at the centers of, galaxies at redshifts of order 0.1, and should be accompanied by bursts of gravitational radiation from the spiraling-in binary which could be detected by LIGO.
Abstract: We propose that gamma-ray bursts are created in the mergers of double neutron star binaries and black hole neutron star binaries at cosmological distances. Two different processes provide the electromagnetic energy for the bursts: neutrino-antineutrino annihilation into electron-position pairs during the merger, and magnetic flares generated by the Parker instability in a postmerger differentially rotating disk. In both cases, an optically thick fireball of size less than or approximately equal to 100 km is initially created, which expands ultrarelativistically to large radii before radiating. The scenario is only qualitative at this time, but it eliminates many previous objections to the cosmological merger model. The strongest bursts should be found close to, but not at the centers of, galaxies at redshifts of order 0.1, and should be accompanied by bursts of gravitational radiation from the spiraling-in binary which could be detected by LIGO.

1,216 citations


Journal ArticleDOI
TL;DR: In this article, the authors extend the graphite-silicate grain model from the Milky Way to the Magellanic Clouds and find that the empirical extinction curves in the Large and Small Magellan Clouds can be reproduced by adjusting only the relative abundances of graphite and silicate grains, while leaving all other model properties fixed to those appropriate for the Galactic extinction curve.
Abstract: Interstellar dust in the Magellanic Clouds, with a weak or nearly absent 2175 A extinction feature, may be of interest in studies of galaxies in early stages of chemical evolution. To this inquiry, we extend the graphite-silicate grain model, introduced by Mathis, Rumpl, and Nordsieck and developed by Draine and Lee (1984) from the Milky Way to the Magellanic Clouds. We find that the empirical extinction curves in the Large and Small Magellanic Clouds can be reproduced by adjusting only the relative abundances of graphite and silicate grains, while leaving all other model properties fixed to those appropriate for the Galactic extinction curve. Using the graphite-silicate models, we calculate the absorption and scattering optical depths, the mass-density ratio of interstellar dust to neutral hydrogen, and the Kramers-Kronig relation for all three galaxies. We also present a fitting function for the three extinction curves, valid not only over the observed range of wavelengths but also over the full range as predicted by the models. All the quantities we derived here are independent of the dust-to-gas ratios in the Milky Way and the Magellanic Clouds, and can be applied to other galaxies if they contain Galactic or Magellanic-type dust.

1,156 citations


Journal ArticleDOI
TL;DR: The physical conditions in the gamma-ray-emitting blazar 3C 279 are discussed in this article, where it is proposed that the gamma rays are produced in a relativistic jet via the synchrotron self-Compton mechanism.
Abstract: The physical conditions in the gamma-ray-emitting blazar 3C 279 are discussed. The requirement of transparency for gamma-rays, together with the observation of rapid variability, imply that the high-energy radiation is anisotropic. It is proposed that the gamma-rays are produced in a relativistic jet via the synchrotron self-Compton mechanism. The gamma-ray spectrum is the high-energy extension of the inverse Compton radiation responsible for the X-ray emission. It is softer than the X-ray spectrum, owing to upper cutoffs in the electron energy spectra along the jet. The same electrons are responsible for the low-frequency emission via synchrotron radiation. The expected correlation of variability at different frequencies is discussed. 38 refs.

946 citations


Journal ArticleDOI
Abstract: Polynomial fit coefficients have been obtained for the energy dependences of the photoelectric absorption cross sections of 17 astrophysically important elements. These results allow the calculation of X-ray absorption in the energy range 0.03-10 keV in material with noncosmic abundances.

909 citations


Journal ArticleDOI
TL;DR: In this article, the deformation of a magnetically active star is explained by variations in the distribution of angular momentum as the star goes through its activity cycle, typically requiring that the active star be variable at the ΔL/L⇒0.1 level, and be differentially rotating at the δΩ/Ω ⇒ 0.01 level.
Abstract: Some eclipsing variables are observed to undergo orbital period modulations of amplitude ΔP/P∼10 −5 over time scales of decades or longer. These modulations can be explained by the gravitational coupling of the orbit to variations in the shape of a magnetically active star in the system. The variable deformation of the active star is produced by variations in the distribution of angular momentum as the star goes through its activity cycle. This mechanism typically requires that the active star be variable at the ΔL/L⇒0.1 level, and be differentially rotating at the ΔΩ/Ω⇒0.01 level

904 citations


Journal ArticleDOI
TL;DR: In this paper, the Jeans mass and magnetic critical mass for the clumps in these clouds were determined, and it was shown that these clumps are magnetically supercritical, i.e., they are not supported by magnetic fields alone.
Abstract: A substantial fraction of the mass of a giant molecular cloud (GMC) in the Galaxy is confined to clumps which occupy a small fraction of the volume of the cloud. A majority of the clumps in several well-studied GMCs (Ophiuchus, Orion G, Rosette, Cepheus OB3) are not in gravitational virial equilibrium, but instead are confined by the pressure of the surrounding medium. These clumps thus violate one of 'Larson's (1981) laws'. Generalizing the standard virial analysis for spherical clouds to spheroidal clouds, we determine the Jeans mass and the magnetic critical mass for the clumps in these clouds. The Alfven Mach number, which is proportional to the internal velocity dispersion of the clumps divided by the Alfven velocity, is estimated to be of order unity for all the clumps. The more massive clumps, which are in gravitational virial equilibrium, are too massive to be supported by magnetic fields alone (i.e., they are magnetically supercritical). Internally generated turbulence must play a key role in supporting these clumps.

884 citations


Journal ArticleDOI
TL;DR: In this paper, the structural properties of hot galaxies were analyzed using a 3-space (k) model, in which the axes are parameters that are physically meaningful, such as central velocity dispersion, effective surface brightness, and effective radius.
Abstract: Results are reported from an analysis of the structural properties of dynamically hot galaxies which combines central velocity dispersion, effective surface brightness, and effective radius into a new 3-space (k), in which the axes are parameters that are physically meaningful. Hot galaxies are found to divide into groups in k-space that closely parallel conventional morphological classifications, namely, luminous ellipticals, compacts, bulges, bright dwarfs, and dwarf spheroidals. A major sequence is defined by luminous ellipticals, bulges, and most compacts, which together constitute a smooth continuum in k-space. Several properties vary smoothly with mass along this continuum, including bulge-to-disk ratio, radio properties, rotation, degree of velocity anisotropy, and 'unrelaxed'. A second major sequence is comprised of dwarf ellipticals and dwarf spheroidals. It is suggested that mass loss is a major factor in hot dwarf galaxies, but the dwarf sequence cannot be simply a mass-loss sequence, as it has the wrong direction in k-space.

808 citations


Journal ArticleDOI
TL;DR: In this article, the two-point statistics of the gravitationally induced ellipticities of distant images were analyzed to provide a direct probe of the mass fluctuation spectrum P(k).
Abstract: We analyze the two-point statistics of the gravitationally induced ellipticities of distant images whick provide a direct probe of the mass fluctuation spectrum P(k). The analysis extends previous work in the following respects : (1) We explore the relation between the ellipticity pattern of the background galaxies and the projected density of foreground matter. (2) We calculate angular power spectra, using the analogue of Limber's equation in the Fourier domain, as well as angular correlation functions. (3) The analysis is valid for arbitrary evolution of P(k) and for an arbitrary distance distribution for the galaxies

768 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined surveys of M dwarfs within 20 pc to determine the incidence of stellar companions within a specific range of separation, the farthest being ∼10 4 AU.
Abstract: We examine surveys of M dwarfs within 20 pc to determine the incidence of stellar companions. Observational data are drawn from high-quality surveys, including IR-array imaging, precise velocities, IR speckle interferometry, and visual imaging, and their respective incompleteness is determined. Each technique permits detection of companions down to the H-burning limit, and each is nearly complete (owing to the proximity of M dwarfs) within a specific range of separation, the farthest being ∼10 4 AU

Journal ArticleDOI
TL;DR: In this paper, an inversion code of Stokes line profiles is presented, which allows the recovery of the stratification of the temperature, the magnetic field vector, and the line of sight velocity through the atmosphere.
Abstract: An inversion code of Stokes line profiles is presented. It allows the recovery of the stratification of the temperature, the magnetic field vector, and the line of sight velocity through the atmosphere, and the micro- and macro-turbulence velocities, which are assumed to be constant with depth. It is based on the response functions, which enter a Marquardt nonlinear least-squares algorithm in a natural way. Response functions are calculated at the same time as the full radiative transfer equation for polarized light is integrated

Journal ArticleDOI
TL;DR: In this paper, a Henyey-type stellar evolution code was modified to allow its application to binary stellar evolution calculations, making it possible to trace the effects of mass and angular momentum loss from the binary, as well as mass transfer within the binary system.
Abstract: The way in which binary interaction affects the presupernova evolution of massive close binaries and the resulting supernova explosions is investigated systematically by means of a Henyey-type stellar evolution code that was modified to allow its application to binary stellar evolution calculations. The code makes it possible to trace the effects of mass and angular momentum loss from the binary, as well as mass transfer within the binary system. It is found that a large number of binary scenarios can be distinguished, depending on the type of binary interaction and the evolutionary stage of the supernova progenitor at the time of the interaction. Monte Carlo simulations are performed to estimate the frequencies of the occurrence of various scenarios. It is found that, because of a previous binary interaction, 15-30 percent of all massive stars (with initial masses greater than about 8 solar masses) become helium stars, and another 5 percent of all massive stars end their lives as blue supergiants rather than as red supergiants.

Journal ArticleDOI
TL;DR: In this paper, the authors explored the proposition that Herbig Ae/Be stars are young intermediate mass stars surrounded by optically thick accretion disks from a study of 47 such objects.
Abstract: The proposition that Herbig Ae/Be stars are young intermediate mass stars surrounded by optically thick accretion disks is explored. From a study of 47 such objects, a subset of 30 stars is identified whose spectral energy distributions can be interpreted convincingly in terms of pre-main sequence stars surrounded by massive optically thick circumstellar accretion disks. Constraints on the physical properties of the disks, such as size, mass, accretion rate, lifetime, and radial structure are derived from the photometric data.

Journal ArticleDOI
TL;DR: In this paper, the authors extend the canonical exponential potential scalar field inflation modified hot big bang model by adding an inflation epoch coupling, between the scalar fields responsible for inflation and an Abelian gauge field.
Abstract: We extend the canonical exponential potential scalar field inflation modified hot big bang model by adding an inflation epoch coupling, between the scalar field Φ responsible for inflation and an Abelian gauge field A μ , ∞e αΦ F μν F μν (where F μν =∂ μ A ν −∂ ν A μ and α is a parameter)

Journal ArticleDOI
TL;DR: In this paper, chemical and structural evolutionary models for the Magellanic Clouds assuming bimodal star formation and gas infall are presented, in relation to the observed chemical abundances of the clouds and are compared with our own Galaxy.
Abstract: Chemical and structural evolutionary models for the Magellanic Clouds assuming bimodal star formation and gas infall are presented. The models are discussed in relation to the observed chemical abundances of the Clouds and are compared with our own Galaxy. The detailed abundances derived from previous work are investigated for any obvious trends with metallicity or differences compared with the Galaxy. Considering all the data, conclusions are drawn on the possible star formation histories of the Magellanic Clouds and the implications for our own Galaxy

Journal ArticleDOI
TL;DR: In this paper, the first results from a survey of the integrated spectra of 90 nearby galaxies are presented, which is used as a comparison sample for spectroscopic survey of more distant galaxies.
Abstract: This paper presents the first results from a survey of the integrated spectra of 90 nearby galaxies. Intermediate- and low-resolution spectrophotometry over the 3650-7000 A range has been used to compile a spectral atlas of galaxies (published in a companion paper) and to investigate the systematic behavior of the emission-line spectra in normal and peculiar galaxies. The data are especially useful as a comparison sample for spectroscopic survey of more distant galaxies.

Journal ArticleDOI
TL;DR: In this article, a critical review of the existing data on ionization and dielectronic recombination and present new computations of radiative recombination rate coefficients of Fe(+14) through Fe(−25) using the photoionization cross sections of Clark et al.
Abstract: In the past few years important progress has been made on the knowledge of ionization and recombination rates of iron, an astrophysically abundant heavy element and a major impurity in laboratory fusion devices. We make a critical review of the existing data on ionization and dielectronic recombination and present new computations of radiative recombination rate coefficients of Fe(+14) through Fe(+25) using the photoionization cross sections of Clark et al. (1986). We provide analytical fits to the recommended data (direct ionization and excitation-autoionization cross sections; radiative and dielectronic recombination rate coefficients). Finally we determine the iron ionic fractions at ionization equilibrium and compare them with previous computations as well as with observational data.

Journal ArticleDOI
TL;DR: In this paper, it was shown that if all protospirals contain subgalactic clouds with a similar mass spectrum, the specific frequency of globular clusters around spirals will be constant.
Abstract: We suggest that at least some globular clusters are formed during the interaction or merger of galaxies. Such events could explain the disk population of clusters in the Galaxy, the young globulars in the Magellanic Clouds, the excess of clusters around ellipticals relative to spirals of the same luminosity and the anomalously large globular cluster systems around some galaxies in the center of galaxy clusters. We show that if all protospirals contain subgalactic clouds with a similar mass spectrum, the specific frequency of globular clusters around spirals will be constant

Journal ArticleDOI
TL;DR: In this article, a 2D hydrodynamics code was proposed to model the dynamics of the wind and shock structure formed by the collision in early-type binary systems, which self-consistently accounts for radiative cooling and represents a significant improvement over previous attempts to model these systems.
Abstract: The dynamics of the wind and shock structure formed by the wind collision in early-type binary systems is examined by means of a 2D hydrodynamics code, which self-consistently accounts for radiative cooling, and represents a significant improvement over previous attempts to model these systems. The X-ray luminosity and spectra of the shock-heated region, accounting for wind attenuation and the influence of different abundances on the resultant level and spectra of X-ray emission are calculated. A variety of dynamical instabilities that are found to dominate the intershock region is examined. These instabilities are found to be particularly important when postshock material is able to cool. These instabilities disrupt the postshock flow and add a time variability of order 10 percent to the X-ray luminosity. The X-ray spectrum of these systems is found to vary with the nuclear abundances of winds. These theoretical models are used to study several massive binary systems, in particular V444 Cyg and HD 193793.

Journal ArticleDOI
TL;DR: In this article, numerical simulations of hierarchical galaxy formation, including gasdynamics, star formation, and supernova feedback, are presented, where the authors model the collapse of isolated constant-density perturbations, initially in solid-body rotation and in Hubble flow.
Abstract: Numerical simulations of hierarchical galaxy formation, including gasdynamics, star formation, and supernova feedback, are presented. The simulations model the collapse of isolated constant-density perturbations, initially in solid-body rotation and in Hubble flow. The perturbations are made of dark and baryonic matter in a 10:1 ratio. Small-scale power is added using the Zel'dovich approximation, assuming a power-law slope of -2.5. We are successful in making a three-component system that resembles a spiral galaxy: a thin disk made of stars and gas, a spheroidal component made of stars, and a dark matter halo

Journal ArticleDOI
TL;DR: In this paper, a mass distribution for a sample of 129 DA white dwarfs is presented, based on fitting hydrogen line profiles to the predictions of stellar atmosphere models, and the atmospheric parameters determined from spectroscopy are shown to be of improved accuracy over those obtained with other techniques.
Abstract: A mass distribution for a sample of 129 DA white dwarfs is presented, based on fitting hydrogen line profiles to the predictions of stellar atmosphere models. The atmospheric parameters determined from spectroscopy are shown to be of improved accuracy over those obtained with other techniques. The spectroscopic masses are in good agreement with those inferred from gravitational redshift measurements

Journal ArticleDOI
TL;DR: In this article, the authors detected a high probability correlation between Jupiter's orbital radius and the solar Einstein radius at the Galactic bulge by observing the light curve of a gravitationally lensed star in ∼20% of microlensing events.
Abstract: Planetary systems of Galactic disk stars can be detected as microlenses of stars in the Galactic bulge. Planets in a solar-like system positioned half-way to the Galactic center should leave a noticeable signature (magnification larger that 5%) on the light curve of a gravitationally lensed bulge star in ∼20% of the microlensing events. This high probability results from a coincidence between Jupiter's orbital radius and the solar Einstein radius at this distance. Typical planetary signals last for about 1 day, a small fraction of the approximately 1 month duration of the entire microlensing event

Journal ArticleDOI
TL;DR: In this paper, Fe and Mg indices from two homogenous collections of nuclear elliptical galaxy spectra are compared with model indices. And the average giant elliptical, the [Mg/Fe] ratio exceeds that of the most metal-rich stars in the solar neighborhood by ∼ 0.2-0.3 dex.
Abstract: Fe and Mg indices from two homogenous collections of nuclear elliptical galaxy spectra are compared with model indices. In the average giant elliptical, the [Mg/Fe] ratio exceeds that of the most metal-rich stars in the solar neighborhood by ∼0.2-0.3 dex, with a large spread about this mean. This result implies a variable «enrichment effectiveness» of Type II supernovae (SNs) compared with Type Ia SNs in the evolution of ellipticals, caused perhaps by differences in star formation time scales, the initial mass function, or the amount of Fe versus Mg ejected in galactic winds

Journal ArticleDOI
TL;DR: In this article, the structure and kinematics of the largest relaxed halos in each of 10 separate simulations were analyzed using N-body simulations on highly parallel supercomputers to study the structure of Galactic dark matter halos.
Abstract: We use N-body simulations on highly parallel supercomputers to study the structure of Galactic dark matter halos. The systems form by gravitational collapse from scale-free and more general Gaussian initial density perturbations in an expanding 400 Mpc 3 spherical slice of an Einstein-deSitter universe. We use N∼10 6 and a force softening e=5 kpc in most of our models. We analyze the structure and kinematics of the ∼10 2 largest relaxed halos in each of 10 separate simulations

Journal ArticleDOI
TL;DR: In this article, the authors used a 2D radiative transfer algorithm to calculate the thermally reradiated infrared spectra of the compact dust tori which are thought to surround many AGN.
Abstract: Using a new 2D radiative transfer algorithm, we have calculated the thermally reradiated infrared spectra of the compact dust tori which are thought to surround many AGN. These tori radiate anisotropically. Face-on tori may be from one-half to a few orders of magnitude brighter than edge-on tori throughout the infrared. Their spectra at nearly all viewing angles are basically 'bumps' which are about 50 percent wider than blackbodies and peak in the mid-infrared at a wavelength determined mainly by the flux of nuclear radiation on the inner edge of the torus. The infrared color temperatures are hotter for face-on tori than edge-on tori by about 100 K. The 10 micron silicate feature often associated with dust can appear in absorption, emission, or not at all. There is a rough tendency for absorption features to be more prominent for edge-on tori than for face-on tori.

Journal ArticleDOI
TL;DR: In this article, the authors investigated three mechanisms that promote the loss of magnetic flux from an isolated neutron star, including buoyant rise and dragging by superfluid neutron vectors, and found that the drift speed is proportional to the second power of the magnetic field strength.
Abstract: We investigate three mechanisms that promote the loss of magnetic flux from an isolated neutron star. Ohmic decay produces a diffusion of the magnetic field with respect to the charged particles. It proceeds at a rate that is inversely proportional to the electric conductivity and independent of the magnetic field strength. Ohmic decay occurs in both the fluid core and solid crust of a neutron star, but it is too slow to directly affect magnetic fields of stellar scale. Ambipolar diffusion involves a drift of the magnetic field and charged particles relative to the neutrons. The drift speed is proportional to the second power of the magnetic field strength if the protons form a normal fluid. Variants of ambipolar diffusion include both the buoyant rise and the dragging by superfluid neutron vortices of magnetic flux tubes. Ambipolar diffusion operates in the outer part of the fluid core where the charged particle composition is homogeneous, protons and electrons being the only species. The charged particle flux associated with ambipolar diffusion decomposes into a solenoidal and an irrotational component. Both components are opposed by frictional drag. The irrotational component perturbs the chemical equilibrium between neutrons, protons, and electrons, thus generating pressure gradients that effectively choke it. The solenoidal component is capable of transporting magnetic flux from the outer core to the crust on a short time scale. Magnetic flux that threads the inner core, where the charged particle composition is inhomogeneous, would be permanently trapped unless particle interactions could rapidly smooth departures from chemical equilibrium. Magnetic fields undergo a Hall drift related to the Hall component of the electric field. The drift speed is proportional to the magnetic field strength. Hall drift occurs throughout a neutron star. Unlike ohmic decay and ambipolar diffusion which are dissipative, Hall drift conserves magnetic energy. Thus, it cannot by itself be responsible for magnetic field decay. However, it can enhance the rate of ohmic dissipation. In the solid crust, only the electrons are mobile and the tangent of the Hall angle is large. There, the evolution of the magnetic field resembles that of vorticity in an incompressible fluid at large Reynolds number. This leads us to speculate that the magnetic field undergoes a turbulent cascade terminated by ohmic dissipation at small scales. The small-scale components of the magnetic field are also transported by Hall drift waves from the inner crust where ohmic dissipation is slow to the outer crust where it is rapid. The diffusion of magnetic flux through the crust takes ~ 5 x 10^8/B_(12) yr, where B_(12) is the crustal magnetic field strength measured in units of 10^(12) G.

Journal ArticleDOI
TL;DR: In this article, it is argued that the observed photospheric field should first be corrected for line-of-sight projection and then matched to the radial component of the potential field.
Abstract: It is shown that the line-of-sight matching procedure involved in potential field models of the solar corona do not make good use of the available data because there is strong evidence that the magnetic field is nearly radial, and therefore nonpotential, at the photosphere. It is argued that the observed photospheric field should first be corrected for line-of-sight projection and then matched to the radial component of the potential field. It is shown that this procedure yields much stronger polar fields than the standard method and produces better agreement with high-latitude coronal holes and with white-light structures in the outer corona. The relationship of both methods to the observed inclination angles of polar plumes is also discussed.

Journal ArticleDOI
TL;DR: The gamma-ray spectrum of 3C 279 during 1991 June exhibited a near-perfect power law between 50 MeV and over 5 GeV with a differential spectral index of -(2.02 +/- 0.07).
Abstract: The gamma-ray spectrum of 3C 279 during 1991 June exhibited a near-perfect power law between 50 MeV and over 5 GeV with a differential spectral index of -(2.02 +/- 0.07). If extrapolated, the gamma-ray spectrum of 3C 279 should be easily detectable with first-generation air Cerenkov detectors operating above about 0.3 TeV provided there is no intergalactic absorption. However, by using model-dependent lower and upper limits for the extragalactic infrared background radiation field, a sharp cutoff of the 3C 279 spectrum is predicted at between about 0.1 and about 1 TeV. The sensitivity of present air Cerenkov detectors is good enough to measure such a cutoff, which would provide the first opportunity to obtain a measurement of the extragalactic background infrared radiation field.

Journal ArticleDOI
TL;DR: In this article, self-consistent numerical results for a small sample of merging encounters between equal-mass disk galaxies are presented, which illustrate how self-gravitating disks respond to tidal perturbations and suggest an improved point of view on orbital decay in multicomponent systems.
Abstract: This paper presents self-consistent numerical results for a small sample of merging encounters between equal-mass disk galaxies. These calculations illustrate how self-gravitating disks respond to tidal perturbations and suggest an improved point of view on orbital decay in multicomponent systems. Preexisting spheroidal components merge rather gently, but the incomplete violent relaxation of the disks themselves is accompanied by a large drop in coarse-grained phase-space density. A detailed analysis of the orbital structure of these merger remnants shows how their shapes and kinematic properties are related to the initial disk spin vectors