Gas stripping by radiation drag from an interstellar cloud

We perform two-dimensional hydrodynamic simulation on the gas stripping by radiation drag from an interstellar cloud moving in uniform radiation fields. To properly include relativistic radiation drag, the radiation hydrodynamic equation is solved with taking into account the dilution of radiation fields by optical depth of the cloud. As a result, it is found that the optically-thin surface layers are effectively stripped by radiation drag from an optically-thick gas cloud, and simultaneously stripped gas loses momentum. The momentum loss time-scale is found to be on the order of $10^{8}$ years under intensive radiation fields which are expected in the early phase of galaxy evolution. The present results show that the radiation drag is an effective mechanism to extract angular momentum from interstellar medium and allows it to accrete onto the galactic center. The mass accretion driven by radiation drag may lead to the formation of a central supermassive black hole.Comment: 8 pages, 8 figures. Accepted for MNRA

Transformation Properties of External Radiation Fields, Energy-Loss Rates and Scattered Spectra, and a Model for Blazar Variability

We treat transformation properties of external radiation fields in the proper frame of a plasma moving with constant speed. The specific spectral energy densities of external isotropic and accretion-disk radiation fields are derived in the comoving frame of relativistic outflows, such as those thought to be found near black-hole jet and gamma-ray burst sources. Nonthermal electrons and positrons Compton-scatter this radiation field, and high-energy protons and ions interact with this field through photomeson and photopair production. We revisit the problem of the Compton-scattered spectrum associated with an external accretion-disk radiation field, and clarify a past treatment by the authors. Simple expressions for energy-loss rates and Thomson-scattered spectra are given for ambient soft photon fields consisting either of a surrounding external isotropic monochromatic radiation field, or of an azimuthally symmetric, geometrically thin accretion-disk radiation field. A model for blazar emission is presented that displays a characteristic spectral and variability behavior due to the presence of a direct accretion-disk component. The disk component and distinct flaring behavior can be bright enough to be detected from flat spectrum radio quasars with {\it GLAST}. Spectral states of blazars are characterized by the relative importance of the accretion-disk and scattered radiation fields and, in the extended jet, by the accretion disk, inner jet, and cosmic microwave background radiation fields.Comment: 43 pages, 12 figures, ApJ, in press; includes improvements in response to referee report, added references, section of detectability with GLAS

Effects of External Radiation Fields on Line Emission - Application to Star-forming Regions

A variety of astronomical environments contain clouds irradiated by a combination of isotropic and beamed radiation fields. For example, molecular clouds may be irradiated by the isotropic cosmic microwave background (CMB), as well as by a nearby active galactic nucleus (AGN). These radiation fields excite atoms and molecules and produce emission in different ways. We revisit the escape probability theorem and derive a novel expression that accounts for the presence of external radiation fields. We show that when the field is isotropic the escape probability is reduced relative to that in the absence of external radiation. This is in agreement with previous results obtained under ad hoc assumptions or with the two-level system, but can be applied to complex many-level models of atoms or molecules. This treatment is in the development version of the spectral synthesis code Cloudy. We examine the spectrum of a Spitzer cloud embedded in the local interstellar radiation field, and show that about 60 percent of its emission lines are sensitive to background subtraction. We argue that this geometric approach could provide an additional tool toward understanding the complex radiation fields of starburst galaxies.Comment: 12 pages, 7 figures, accepted for publication to Ap

Radiation Reaction fields for an accelerated dipole for scalar and electromagnetic radiation

The radiation reaction fields are calculated for an accelerated changing dipole in scalar and electromagnetic radiation fields. The acceleration reaction is shown to alter the damping of a time varying dipole in the EM case, but not the scalar case. In the EM case, the dipole radiation reaction field can exert a force on an accelerated monopole charge associated with the accelerated dipole. The radiation reaction of an accelerated charge does not exert a torque on an accelerated magnetic dipole, but an accelerated dipole does exert a force on the charge. The technique used is that originally developed by Penrose for non-singular fields and extended by the author for an accelerated monopole charge.Comment: 11 page

Electromagnetic and gravitational radiation from the coherent oscillation of electron-positron pairs and fields

Integrating equations of particle-number and energy-momentum conservation and Maxwell field equations, we study the oscillation and drift of electron and positron pairs coherently with fields after these pairs are produced in external electromagnetic fields. From the electric current of oscillating pairs, we obtain the energy spectrum of electromagnetic dipole radiation. This narrow spectrum is so peculiar that the detection of such radiation can identify pair production and oscillation in strong laser fields. We also obtain the energy spectrum of gravitational quadrapole radiation from the energy-momentum tensor of oscillating pairs and fields. Thus, we discuss the generation of gravitational waves on the basis of rapid development of strong laser fields.Comment: 6 pages, 4 figure