Luc Binette

Stellar jets with intrinsically variable sources

Models for high Mach number, isothermal, pressure-matched jets ejected from sources with variable velocities are presented. It is found that the relaxation of the assumption of a time-independent source allows the complex position-velocity diagrams and multiple bow shock structures observed in some stellar jets to be explained in a straightforward way. Analytic and numerical models are presented for jets with variable velocity sources. A comparison with previously published observations of the HH 46/47 jet is performed which shows how the velocity variations observed along a jet can be used to reconstruct the past time variability of the source. This technique is promising for future studies of the mechanism by which stellar jets are produced. 41 refs.

Are the Narrow-Line Regions in Active Galaxies Dusty and Radiation Pressure Dominated?

The remarkable similarity between emission spectra of narrow-line regions (NLRs) in Seyfert galaxies has long presented a mystery. In photoionization models, this similarity implies that the ionization parameter is nearly always the same, about U ~ 0.01. Here we present dusty, radiation pressure-dominated photoionization models that can provide natural physical insight into this problem. In these models, dust and the radiation pressure acting upon it provide the controlling factor in moderating the density, excitation, and surface brightness of photoionized NLR structures. Additionally, photoelectric heating by the dust is important in determining the temperature structure of the models. These models can also explain the coexistence of the low-, intermediate-, and coronal ionization zones within a single self-consistent physical structure. The radiation pressure acting on dust may also be capable of driving the fast (~3000 km s-1) outflows such as are seen in the HST observations of NGC 1068.

Atomic T Tauri disk winds heated by ambipolar diffusion - I. Thermal structure

Motivated by recent subarcsecond resolution observations of jets from T Tauri stars, we extend the work of Saer (1993a,b) by computing the thermal and ionization structure of self-similar, magnetically-driven, atomic disk winds heated by ambipolar diusion. Improvements over his work include: (1) new magnetized cold jet solutions consistent with the underlying accretion disk (Ferreira 1997); (2) a more accurate treatment of ionization and ion-neutral momentum exchange rates; and (3) predictions for spatially resolved forbidden line emission (maps, long-slit spectra, and line ratios), presented in a companion paper, Garcia et al. (2001). As in Saer (1993a), we obtain jets with a temperature plateau around 10 4 K, but ionization fractions are revised downward by a factor of 10{100. This is due to previous omission of thermal speeds in ion-neutral momentum-exchange rates and to dierent jet solutions. The physical origin of the hot temperature plateau is outlined. In particular we present three analytical criteria for the presence of a hot plateau, applicable to any given MHD wind solution where ambipolar diusion and adiabatic expansion are the dominant heating and cooling terms. We nally show that, for solutions favored by observations, the jet thermal structure remains consistent with the usual approximations used for MHD jet calculations (thermalized, perfectly conducting, single hydromagnetic cold fluid calculations).

Atomic T Tauri disk winds heated by ambipolar diffusion - II. Observational tests

We summarize results on the thermal and ionization structure of self-similar, magnetically-driven, atomic disk winds heated by ambipolar diffusion. We improve upon earlier work by Safier by considering (1) new MHD solutions consistent with underlying cold keplerian disk equilibrium, (2) a more accurate treatment of the micro-physics, and (3) predictions for spatially resolved forbidden line emission (maps, long-slit spectra). The temperature plateau ≃ 10 4 K found earlier is recovered, but ionization fractions are revised downward by a factor of 10, due to previous omission of thermal speeds in ion-neutral momentum-exchange rates. The physical origin of the temperature plateau is outlined. Predictions are then compared with T Tauri star observations, with emphasis on the necessity of suitable beam convolution. Jet widths and variations in line profiles with distance and line tracer are well reproduced. However, predicted maximum velocities are too high, total densities too low, and the low-velocity [O i] component is too weak. Denser, slower MHD winds from warm disks might resolve these discrepancies.

The Narrow-Line Region of Narrow-Line Seyfert 1 Galaxies*

This work studies the optical emission-line properties and physical conditions of the narrow-line region (NLR) of seven narrow-line Seyfert 1 galaxies (NLS1s) for which high signal-to-noise ratio spectroscopic observations were available. The resolution is 340 km s-1 (at Hα) over the wavelength interval 3700-9500 A, enabling us to separate the broad and narrow components of the permitted emission lines. Our results show that the flux carried out by the narrow component of Hβ is, on average, 50% of the total line flux. As a result, the [O III] λ5007/Hβ ratio emitted in the NLR varies from 1 to 5, instead of the universally adopted value of 10. This has strong implications for the required spectral energy distribution that ionizes the NLR gas. Photoionization models that consider a NLR composed of a combination of matter-bounded and ionization-bounded clouds are successful at explaining the low [O III] λ5007/Hβ ratio and the weakness of low-ionization lines of NLS1s. Variation of the relative proportion of these two type of clouds nicely reproduces the dispersion of narrow-line ratios found among the NLS1 sample. Assuming similar physical model parameters of both NLS1s and the normal Seyfert 1 galaxy NGC 5548, we show that the observed differences of emission-line ratios between these two groups of galaxies can be explained, to a first approximation, in terms of the shape of the input ionizing continuum. Narrow emission-line ratios of NLS1s are better reproduced by a steep power-law continuum in the EUV-soft X-ray region, with spectral index α ~ -2. Flatter spectral indices (α ~ -1.5) match the observed line ratios of NGC 5548 but are unable to provide a good match to the NLS1 ratios. This result is consistent with ROSAT observations of NLS1s, which show that these objects are characterized by steeper power-law indices than those of Seyfert 1 galaxies with strong broad optical lines.

Probing the absorbing haloes around two high-redshift radio galaxies with VLT-UVES

We present VLT-UVES echelle spectroscopy of the HI and C IV absorption in the spatially- extended Lyemission around two high-redshift radio galaxies 0200+015 (z=2.23) and 0943- 242 (z=2.92). The absorbers in 0943-242 exhibit little additional struct ure compared with previous low- resolution spectroscopy and the main absorber is still consistent with HI column density of ∼ 10 19 cm 2 . This is consistent with a picture in which the absorbing gas has low density and low metallicity and is distributed in a smooth absorbing shell located beyond the emission- line gas. However, the main absorbers in 0200+015 are very different. The previous single absorber fit of H I column density ≃ 10 19 cm 2 , now splits into two ∼ 4 × 10 14 cm 2 ab- sorbers which extend more than 15 kpc to obscure additional Lyemission coincident with a radio lobe in these high-resolution observations. Althoug h consistent with the shell-like dis- tribution for the absorption systems, 0200+015 requires a much higher metal enrichment than 0943-242. The metallicity, inferred from the C IV absorption, is considerably lower in 0943- 242 than in 0200+015. We explain these differences with an evolutionary scenario based on the size of the radio source. In both sources the HI absorption gas originates from either a gas-rich merger or pristine cluster gas which cools and collapses towards the centre of the dark matter halo. The higher metallicity in the larger radio source (0200+015) may be a result of a starburst driven superwind (concurrent with the triggering of the radio emission) which has engulfed the outer halo in this older source. We also find a significant blue asymmetry in the HeII �1640 emission line, suggesting that the line emitting gas is outflowing from the central regi ons. Dust obscuration toward the central engine, presumably due to the dusty torus invoked in Unified Scheme, prevents us from seeing outflow away from our line-of-sight.

HI in the protocluster environment at z > 2: absorbing haloes and the Lyα forest

We present VLT-UVES echelle spectra of the Lyemission and absorption in five radio galax- ies at redshifts z=2.55-4.1. Together with data from our pilot study, we have a sample of 7 such systems with radio source sizes ∼ 1 − 90 kpc with which to address the origin of the absorbing gas. Echelle resolution again reveals that some systems with NHI > 10 18 cm 2 in lower resolution data in fact consist of several weaker absorbers with NHI 2.

Discrepancies between the [O iii] and [S iii] temperatures in H ii regions

Context. Analysis of published [O iii ]a nd [Siii] temperatures measurements of emission line objects consisting of Hii galaxies, giant extragalactic Hii regions, Galactic Hii regions, and Hii regions from the Magellanic Clouds reveal that the [O iii] temperatures are higher than the corresponding values from [S iii] in most objects with gas metallicities in excess of 0.2 solar. For the coolest nebulae (the highest metallicities), the [O iii] temperature excess can reach ∼3000 K. Aims. We look for an explanation for these temperature differences and explore the parameter space of models with the aim of reproducing the observed trend of TO iii > TS iii in Hii regions with temperatures below 14 000 K. Methods. Using standard photoionization models, we varied the ionization parameter, the hardness of the ionizing continuum, and the gas metallicities in order to characterize how models behave with respect to the observations. We introduced temperature inhomogeneities and varied their mean squared amplitude t 2 . We explored the possibility of inhomogeneities in abundances by combining two models of widely different metallicity. We calculated models that consider the possibility of a non-Maxwell-Boltzmann energy distribution (a κ-distribution) for the electron energies. We also considered shock heating within the photoionized nebula. Results. Simple photoionization calculations yield nearly equal [O iii ]a nd [Siii] temperatures in the domain of interest. Hence these models fail to reproduce the [O iii] temperature excess. Models that consider temperature inhomogeneities, as measured by the mean squared amplitude t 2 ,a lso fail in the regime whereTO iii TO iii.

THE TRANSITION FROM “NORMAL” TO “BROAD ABSORPTION LINE QUASAR” OF TON 34

We report the emergence of a high-velocity, broad absorption line outflow in the luminous quasar Ton 34, at zq = 1.928. The outflow is detected through an ultraviolet C IV broad absorption line, in a spectrum obtained in 2006 January by the Sloan Digital Sky Survey. No absorption trough was present in two different spectra acquired in 1981 at Las Campanas and Palomar observatories, indicating the emergence of the outflow in less than ~8 yr (rest frame). The absorption line spans a velocity range from ~5000 to 25,000 km s–1, and resembles typical troughs found in broad absorption line quasars (BALQSOs). We measure a balnicity index 600 (though this value might be an underestimation due to a conservative placing of the continuum). The absorption trough is likely saturated, with the absorbing gas covering ~25% of the emitting region. We explore different scenarios for the emergence of this outflow, and find an existing wind moving across our line of sight to the source as the most likely explanation. This indicates that high-velocity outflows (producing broad absorption troughs in BALQSOs) might be ubiquitous in quasars, yet only become observable when the wind accidentally crosses our line of vision to the central source.

The triggering mechanism and properties of ionized outflows in the nearest obscured quasars

We have identified ionized outflows in the narrow line region of all but one SDSS type 2 quasars (QSO2) at z 1000 cm-3) and covers a region the size of a few kpc. This implies ionized outflow masses M~(0.3-2.4)x1e6 Msun and mass outflow rates M(dot)<few Msun yr-1. The triggering mechanism of the outflows is related to the nuclear activity. The QSO2 can be classified in two groups according to the behavior and properties of the outflowing gas. QSO2 in Group 1 (5/20 objects) show the most extreme turbulence, they have on average higher radio luminosities and higher excess of radio emission. QSO2 in Group 2 (15/20 objects) show less extreme turbulence, they have lower radio luminosities and, on average, lower or no radio excess. We propose that two competing outflow mechanisms are at work: radio jets and accretion disk winds. Radio jet induced outflows are dominant in Group 1, while disk winds dominate in Group 2. We find that the radio jet mode is capable of producing more extreme outflows. To test this interpretation we predict that: 1) high resolution VLBA imaging will reveal the presence of jets in Group 1 QSO2; 2) the morphology of their extended ionized nebulae must be more highly collimated and kinematically perturbed.