arXiv subjects

W. Steffen

Publications and source records attributed to W. Steffen.

43 records · Page 3Linked to original sources

arXiv1996

Evidence for an outflow from the Seyfert galaxy NGC 4051

New observations using narrow band imaging, long-slit spectroscopy and MERLIN observations of the nuclear region of the Seyfert galaxy NGC~4051 have been made. An edge brightened, triangular region of ionized gas extending 420 pc from the centre of the galaxy has been detected. Long-slit spectra of this ionised gas, taken at 1.5\arcsec\ from the core, show the \oiii\ emission line to consist of two velocity components, both blue-shifted from the systemic radial velocity, with velocity widths of 140\kms\ and separated by 120\kms. This region is co-spatial with weak extended radio emission and is suggestive of a centrally driven outflow. The \oiii\ line spectrum and image of this region have been modelled as an outflowing conical structure at 50\degr\ to the line of sight with a half opening angle of 23\degr . In addition to the extended structure, high resolution MERLIN observations of the 18-cm nuclear radio emission reveal a compact (1\arcsec) radio triple source in PA 73$^{\circ}$. This source is coincident with the HST-imaged emission line structure. These high resolution observations are consistent with a more compact origin of activity (i.e. a Seyfert nucleus) than a starburst region.

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arXiv1996

Highly supersonic motions within the outer features of the Eta Carinae nebulosity

Spatially resolved H$α$ and [N{\sc ii}] line profiles have been obtained over striking features in the outer regions of the Eta Carinae nebula. The highly irregular outer `shell' of low ionization, [N{\sc ii}] bright, knots has been shown to exhibit radial velocities between -1200 and +300 km/s with respect to the systemic radial velocity, over its perimeter. Furthermore, several knots have been found which appear to emit only in the H$α$ line with radial velocities up to -1450 km/s. However, the most intriguing features are a narrow `spike' that projects through this outer shell and a faint `arc' of emission that extends well beyond it. The `spike', which exhibits a change of radial velocity along its length, could be a narrow collimated jet with an outflow velocity of > 1000 km/s. In one interpretation the `arc' is modelled by a conical outflow and mechanisms for generating [N{\sc ii}] emission from highly supersonic gas are also discussed.

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arXiv1996

IRAS04210+0400: Modeling the optical spectra from flaring large scale jets

The emission-lines in the active galaxy IRAS\,0421+0400 show a dramatic ($\sim$\,900\kms) increase in the velocity spread at the position of radio hot-spots which are located at the beginning of extended radio lobes. We study a simple geometric model of an opening outflow which reproduces the structure found in the long-slit emission-line spectrum of the hot-spot regions. The predicted bifurcations in the optical image structure of these regions is confirmed by deep \oiii\,line-imaging. We propose that this phenomenon is the result of a jet emerging from the galaxy through the boundary between the interstellar and intergalactic medium. A similar model has previously been suggested as an explanation for wide angle tail radio sources (WAT's). If our model proves to be correct in more detailed future observations, then IRAS\,0421+0400 provides a unique possibility to study the flaring jet phenomenon at optical wavelengths.

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arXiv1996

Jets and the emission-line spiral structure in IRAS 04210+0400

We examine models in which jets are responsible for the formation of the emission-line spiral structure in IRAS 04210+0400. The kiloparsec-scale radio lobes in this active galaxy appear to be related to its extended emission-line spiral structure. The radio structure consists mainly of extended symmetrically bent, FR\,I-type lobes, which follow the emission-line spiral structure at their inner edge. In the central region of the galaxy a double radio source is observed with a separation of approximately 1\,arcsec between its components, which are extremely well aligned with the hotspot from which the southern lobe expands outwards. Hill et al (1988) suggested a model for the emission-line spiral structure invoking compressed interstellar matter, which is dragged away from the original jet path by the rotating ambient medium. From consideration of the propagation speed of the jets and the transverse ram pressure exerted by the rotating environment, we exclude this scenario as a possible origin of the spiral structure. We favour a model in which the jets themselves are bent by the rotating interstellar medium and possibly follows the emission-line spiral arms. We present fits of the model to the observed optical spiral structure. High sensitivity radio observations will be required to decide on the nature of the peculiar spiral structure in IRAS 04210+0400.

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arXiv1995

IRAS 0421+0400: jets crossing an ISM/IGM interface?

The emission lines in the active galaxy IRAS 0421+0400 show a dramatic (~ 900 km/s) increase in the velocity spread at the position of radio hotspots which are located at the beginning of extended radio lobes. We study a model which explains this phenomenon as the result of a jet emerging through the boundary between the interstellar and intergalactic media. A similar scenario has previously been suggested as an explanation for wide angle tail radio sources (WATs). Based on our model, we simulate the longslit spectra of these regions and compare the results with the observations and find that it can explain most of the details in the observed longslit spectra.

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arXiv1995

Kinematics of ionized gas associated with the radio nucleus and lobes in the active galaxy IRAS 04210+0400

We have used high resolution longslit spectroscopy to investigate the ionized gas in the active galaxy IRAS 04210+0400 and its association with the radio structure. We suggest that two of the ionized components are associated with the central double radio source and observe that the relative positions of these components vary for different emission lines. Both results are consistent with the radio components representing the working surfaces of a pair of jets emerging from the centre of the galaxy. In this scenario, the optical emission in the centre arises behind the bowshocks produced by the jets in the interstellar medium. The emission lines are detected and show a dramatic (~ 900 km/s) spread in velocity at the position of the radio lobe hotspots. We suggest a model which explains this phenomenon as the result of a jet head emerging through the boundary between the interstellar and intergalactic medium. A similar scenario has previously been suggested as a model to explain wide angle tail radio sources (WAT's). Based on this model, we simulate the longslit spectra of these regions and compare the results with the observations.

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arXiv1995

A Helical Model for the Compact Jet in 3C345

We present a simple model for the apparent superluminal motion along curved trajectories of features observed in the compact radio jet of the quasar 3C345. The model is inspired by the magneto-hydrodynamic approach of Camenzind (1986), and assumes a conical geometry of the jet within about three milliarcseconds of the radio core. Simultaneous conservation of three out of four physical parameters is used to derive analytic solutions for the equation of motion of the idealized jet features. These are the jet's kinetic energy, angular momentum, and momentum along the jet axis. Conservation of angular momentum is required to fit the observed trajectories at distances larger than 3 milliarcsec, in agreement with the kinematic predictions of Camenzind's model. The best-fit model variant preserves angular momentum, kinetic energy, and opening angle, with an inclination of the jet axis to the line of sight 6.8 degrees, an opening angle 0.95 degrees, and Lorentz factors 5.8 and 4.6 for components C4 and C5, respectively (H_o=100 km/(s Mpc)). The model ignores turbulent small-scale motion of the jet components, and it does not take into account the overall bending of the jet beyond about 4 milliarcseconds, restricting it's applicability to the inner few milliarcseconds from the core.

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