Gas In Active Galactic Nuclei Research Articles

EUV and Soft X-ray Evidence for Partially Ionized Gas in Active Galactic Nuclei

We present a synoptic study of active galactic nuclei (AGN) detected by EUVE. We also present complementary ROSAT PSPC spectra for these sources and for other AGN in directions of low galactic absorption. It is found that the best-fit power-law photon indices of the X-ray spectra at 0.1–2.4 keV are anti-correlated with their galactic hydrogen columns. The indices for the 0.9–2.4 keV range do not show such a correlation, and are considerably smaller (i.e. flatter). We discuss a number of possible interpretations of this correlation but only one of these, the presence of a partially ionized absorbing gas in the AGN, explains the observations satisfactorily. The ubiquity of this effect suggests that this component be may very common in AGN.

Anisotropic induced Compton scattering - Constraints on models of active galactic nuclei

Induced Compton scattering can cause strong spectral distortion when the Thomson scattering optical depth τT exceeds 5 × 109 K/T, where T is the brightness temperature. Observations of intraday variability in several compact radio sources and direct brightness temperature measurements of ~ 1–4 × 1012 K from orbiting VLBI prompt a re-examination of this process. We seek observable signatures of induced scattering, using a model for non-linear radiative transfer on a lattice. Induced Compton scattering can significantly increase the brightness temperature at low frequencies and may lead to the formation of steep gradients in the spectrum, and angular discontinuities in the observed intensity. An ultracompact high-brightness core surrounded by a tenuous electron-scattering shell should thus show a faint halo whose spectrum peaks at a lower frequency than the core. Thicker shells can be strongly limb-brightened; frequency-dependent superluminal expansion is also possible. The strongest signatures of induced Compton scattering are strong spectral variation in the source structure and large, frequency-dependent, linear polarization. Under some conditions, stimulated Raman scattering off collective plasma waves, which has similar observational characteristics, may dominate over induced Compton scattering off individual electrons and screened ions. As yet, there is no compelling evidence that induced Compton scattering has been observed in compact radio sources. This implies a (model-dependent) upper limit on the Thomson optical depth of plasma in the vicinity of the source. Future VLBI observations, with greater dynamic range, may provide valuable tracers of dense ionized gas in active galactic nuclei. Infrared observations of blazars should be scrutinized for evidence of induced scattering.

Inner shell of optically thin gas in active galactic nuclei

The Lyα and Balmer line profiles in more than 50 Seyfert 1 galaxies and QSOs are studied. Approximately 60% of the objects show similar profiles, 25% show smaller FWHM of Hβ or Hα. In five objects the Lyα profiles have stronger wings than the Balmer lines. The Lyα/Balmer ratio increases along both wings, suggesting an inner envelope of a very broad-line region. This region accounts for up to 10% of the total Balmer line emission and 50% of the Lyα emission. The far wings are often fitted with a power-law curve better than logarithmic

The emission-line gas in quasars and active nuclei Implications for the nature of core-dominant radio sources

view Abstract Citations (20) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The emission-line gas in quasars and active nuclei Implications for the nature of core-dominant radio sources Heckman, T. M. Abstract The properties of the optical emission-line gas in active galactic nuclei and quasars are shown to be inconsistent with models in which "core-dominant" radio sources are simply classical double ("lobe-dominant") radio sources viewed down the axis of a relativistic jet. Publication: The Astrophysical Journal Pub Date: August 1983 DOI: 10.1086/184081 Bibcode: 1983ApJ...271L...5H Keywords: Galactic Nuclei; Quasars; Radio Galaxies; Line Spectra; Plasma Jets; Radio Emission; Astrophysics full text sources ADS |

Cosmic-ray driving of gas in active nuclei

The effect of subrelativistic cosmic rays as the source of energy and ionization for the gas in active galactic nuclei is investigated using fluid-dynamic calculations. The thermal state of the gas is determined by the balance of heating from the cosmic rays and radiative cooling. Nuclear models were calculated with cosmic-ray luminosities of 10/sup 43//sup .//sup 6/ to 10/sup 47//sup .//sup 6/ ergs s/sup -1/ and gas number densities of 10/sup 4//sup .//sup 9/ to 10/sup 7//sup .//sup 8/ cm/sup -3/. These result in the formation of a dense shell which reaches outward velocities of 10/sup 3/--10/sup 4/ km s/sup -1/ and maintains temperatures within 10/sup 4/--10/sup 5/ K. This dense phase may produce the broad Balmer wings observed in some objects. A hot cavity forms between the shell and the source and reaches 10/sup 8/ K. This gas will be seen as an X-ray source. Rayleigh-Taylor instabilities in the shell can provide a source for the observed cloud structure. The high mass loss rate may be replenished by stellar loss processes if a dense star cluster exists in the nucleus.

Cosmic Ray Acceleration of Gas in Active Galactic Nuclei.

Cosmic Ray Acceleration of Gas in Active Galactic Nuclei.