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ABSTRACT The great power offered by photoionization models of active galactic nuclei emission line regions has long been mitigated by the fact that very little is known about the spectral energy distribution (SED) between the Lyman limit, where intervening absorption becomes a problem, and 0.3 keV, where soft X-ray observations become possible. The emission lines themselves can, to some degree, be used to probe the SED, but only in the broadest terms. This paper employs a new generation of theoretical SEDs that are internally self-consistent, energy conserving, and tested against observations, to infer properties of the emission-line regions. The SEDs are given as a function of the Eddington ratio, allowing emission-line correlations to be investigated on a fundamental basis. We apply the simplest possible tests, based on the foundations of photoionization theory, to investigate the implications for the geometry of the emission-line region. The SEDs become more far-ultraviolet bright as the Eddington ratio increases, so the equivalent widths of recombination lines should also become larger, an effect that we quantify. The observed lack of correlation between Eddington ratio and equivalent width shows that the cloud covering factor must decrease as Eddington ratio increases. This would be consistent with recent models proposing that the broad-line region is a failed dusty wind off the accretion disc.
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Radio Spectral Energy Distributions for Single Massive Star Winds with Free–Free and Synchrotron Emission
Abstract The mass-loss rates from single massive stars are high enough to form radio photospheres at large distances from the stellar surface, where the wind is optically thick to (thermal) free–free opacity. Here we calculate the far-infrared, millimeter, and radio band spectral energy distributions (SEDs) that can result from the combination of free–free processes and synchrotron emission, to explore the conditions for nonthermal SEDs. Simplifying assumptions are adopted in terms of scaling relations for the magnetic field strength and the spatial distribution of relativistic electrons. The wind is assumed to be spherically symmetric, and we consider the effect of Razin suppression on the synchrotron emission. Under these conditions, long-wavelength SEDs with synchrotron emission can be either more steep or more shallow than the canonical asymptotic power-law SED from a nonmagnetic wind. When nonthermal emission is present, the resultant SED shape is generally not a power law; however, the variation in the slope can change slowly with wavelength. Consequently, over a limited range of wavelengths, the SED can masquerade as approximately a power law. While most observed nonthermal long-wavelength spectra are associated with binarity, synchrotron emission can have only a mild influence on single-star SEDs, requiring finer levels of wavelength sampling for the detection of the effect.
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- Award ID(s):
- 2009412
- PAR ID:
- 10486138
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 932
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 12
- Size(s):
- Article No. 12
- Sponsoring Org:
- National Science Foundation
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