Quasar Broad Line Regions Research Articles

Correlations between the broad line cloud temperature of 3C 273, the Lyman-Alpha intensity and the UV spectral index

He used IUE uv monitoring data of 3C 273 to measure the Lyα line intensity F( Lyα), estimated the “Cerenkov redshift”, and determined the particle population in the second energy level, R 2. Together with the observed line intensity ratios Hα/Hβ and Lyα/Hβ, we then found the temperature of the HI zone in the broad line cloudlets to be T = 12000, 9100, 8600 K at three different epochs. These T values are clearly correlated with the values of the uv spectral index α uv and the latter vary monotonicaliy with f( Lyα), in agreement with expectations from the Cerenkov line emission model of the broad line region of quasars.

Quasar Emission Line Profile Modelling

We present fits of models for the C IV λ 1549, N V λ1240 and Lα lines to observed profile data. Since these lines depend sensitively on the cloud ionization parameter (defined as the ratio of the illuminating flux to the cloud pressure; c.f. Krolik, McKee, and Tarter, 1981) and pressure, their relative strengths constrain the distribution of clouds in quasar broad line regions. We make the following assumptions: That the distribution of clouds around the continuum source is spherical and that the cloud motion relative to the continuum source is radial; that the clouds are in pressure equilibrium with hot intercloud medium (ICM) whose mass flux is conserved; and that the line fluxes emitted by the clouds as a consequence of the continuum illumination is given by “standard” (e.g. Kwan and Krolik, 1981) photoionization models. The cloud mass flux is not assumed to be constant, but is allowed to vary with velocity in order to fit the data. For the purposes of illustration, we have chosen a specific dynamical model: isothermal freefall with TICM = 108K. The cloud column density is assumed to be fixed at 1023cm−2.

The influence of a thermal plasma on synchrotron radiation

The synchrotron emission from relativistic electrons in a thermal plasma with large-scale random magnetic fields is considered. In this case, the spectral synchrotron power of a single electron can be given in closed form allowing exact analytical expressions for the synchrotron emissivity, absorption coefficient, intensity and total energy loss of particles to be derived. The influence of various physical parameters such as gas density, magnetic field strength, particle's Lorentz factor on the resulting emissivities, intensities and energy loss is discussed in detail. Below the Razin– Tsytovich frequency vR = 20 Hz (ne/l cm−3) (B/l Gauss)−1, the spectral appearance of synchrotron radiation both in the optically thin and thick case is quite different than the vacuum behaviour. Since in the quasar broad line regions, vR is of the order 1011 Hz the suppression of synchrotron radiation may explain why most quasars are radio quiet. Likewise, the necessary physical conditions for the occurrence of synchrotron masering in the optically thick case are given. We obtain optical depth |τ|>1 for compact nonthermal sources. The total energy loss of a single particle is shown to be exponentially reduced at Lorentz factors less than γR = 2·1. 10−3 (ne/1 cm−3)½ (B/1 Gauss)−1.

A NEW MODEL OF THE BROAD EMISSION-LINE REGIONS OF QUASARS

In the broad-line regions of quasars, there exist three different line-emission mechanisms, i. e. the line from recombination, the line from collisional excitation, and the line by the Cerenkov effect. However, the Cerenkov-line photon can avoid the resonance absorption because of the Cerenkov redshift, and can escape easily from the deep inner part of the gas, i. e. the gas appears more transparent for the Cerenkov line than for the conventional spontaneous transition line. For an optically thick dense gas, only if there are sufficient relativistic electrons, the intensity of the Cerenkov line will be dominating. Taking the quasar 3C 273 as an example, it is shown that only if N e =104—10 6 cm -3 , the calculated Cerenkov L α luminosity is in agreement with observations.

New considerations on the broad-line regions of quasars

In the broad-line regions of quasars, there exist three different line emission mechanisms, i.e., the Cerenkov line and conventional line by recombination and collisional excitation. However, the Cerenkov line photon can avoid the resonance absorption because of the Cerenkov redshift and can escape easily from the deep inner part of the gas, i.e., gas appears more transparent for the Cerenkov line than for a conventional line. For an optically thick dense gas, if there are sufficient relativistic electrons, the intensity of the Cerenkov line will be dominating. Taking the quasar 3C 273 as an example, it is shown that only if N(e) is roughly 10 to the 4th to -10 to the 6th/cu cm, the calculated Cerenkov Ly-alpha luminosity is in agreement with observation. 13 references.

Radiation Hydrodynamics of the Broad Line Region in Seyfert Galaxies and Quasars

The broad line region in quasars and in the nuclei of active galaxies is the site of remarkable hydrodynamic activity unprecedented elsewhere in the universe. Considerable theoretical effort has been directed to determine how this intense radiation is related to high velocity gas motions in these small regions, which, because of their great distances, cannot be resolved by direct observation. A better theoretical understanding of the nature of the broad line-emitting gas involves many novel aspects of radiation hydrodynamics and may eventually provide insights into the nature of the mysterious quasar phenomenon itself.Continuum and emission line properties of active galaxies and quasars are sufficiently similar that there is little doubt that both can be accounted for by a similar or closely related physical model. The main difference is one of luminosity; typical quasars are considerably brighter than Seyfert galaxies.In the discussion below the relevant observations of quasars and active galaxies are briefly reviewed with an emphasis on the physical properties of the line-emitting gas and its immediate environment. Arguments that support the importance of radiation forces in producing the observed gas velocities are summarized. Finally, the nature of the acceleration process is described with particular attention paid to the various instabilities that may be present and which are generally characteristic of situations in which plasma velocities result directly from the deposition of radiative momentum. In fact, these troublesome instabilities suggest that radiative forces, although very strong, may provide only a partial explanation of the gasdynamical activity observed.

Cerenkov line emission: The L?/H?, H?/H?, P?/H? intensity ratios of quasars

We use the Cerenkov line emission mechanism to give a new explanation of the observed intensity ratios, particularly the Lα/Hβ ratio, of the emission lines of quasars. We give equations that restrict the choice of the parameter values. The parameters are the characteristic energy of the relativistic electrons, the number density of neutral hydrogen and its relative level populations. With reasonable choice of the parmaeters, we can obtain calculated Lα/Hβ, Hα/Hβ, Pα/Hα ratios in agreement with observed values. Our estimate for the gas density in the broad line region of quasars is ∼1015 cm−3, very different from previous estimates. Unlike previous theories, such a high density causes no difficulties with the Cerenkov line emission.

Observational tests of X-ray heating in the broad-line region of quasars and Seyfert galaxies

view Abstract Citations (17) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observational tests of X-ray heating in the broad-line region of quasars and Seyfert galaxies. Kriss, G. A. Abstract Baldwin (1977) has inferred that the Ly-alpha/H-alpha line ratio in quasars was a factor of 10 lower than predicted by case B recombination theory, and direct observations of the Ly-alpha line in low-redshift quasars and Seyfert galaxies and of the Balmer lines in high-redshift quasars have confirmed this discrepancy. The present investigation is concerned with the Ly-alpha/H-alpha and Fe II/H-beta line ratios of a larger sample of quasars and Seyfert galaxies, taking into account the possibility of X-ray heating. Attention is given to details regarding the data set and to tests of X-ray heating in the broad-line region. The significance of the tests for the predictions of a model considered by Kwan and Krolik (1981) is evaluated. Publication: The Astrophysical Journal Pub Date: February 1984 DOI: 10.1086/161719 Bibcode: 1984ApJ...277..495K Keywords: Quasars; Seyfert Galaxies; Spectral Line Width; X Ray Sources; Balmer Series; H Lines; Lyman Alpha Radiation; Photoionization; Astrophysics full text sources ADS | data products SIMBAD (46) NED (41)

The heating of dust in the broad-line regions of active galaxies and quasars

The present investigation is concerned with the relevant energy sources which heat (and, in many cases, destroy) the dust grains in the emission-line clouds (ELCs) that give rise to the broad-line emission seen in active extragalactic objects. The heating rates from the external radiation field, trapped line radiation, and the diffuse bound-free continua are compared. The relevant grain parameters are considered, taking into account the composition, size, and emission and absorption cross sections. Three distinct regions of an ELC are identified, including the cloud face, the extended ionized zone, and the neutral zone. The thermal emission of the dust in each of these regions is shown to be different. An upper limit to the heating is provided by an LTE model which is discussed.