Microstructure of Domain/Twin Intersections in Single Crystal YBa2Cu3O7−d

The Astrophysical Journal

Gómez

Raga³

et al. 1997

We study the kinematical and brightness evolution of emission line clouds in the narrow line region (NLR) of Seyfert galaxies during the passage of a jet. We derive a critical density above which a cloud remains radiative after compression by the jet cocoon. The critical density depends mainly on the cocoon pressure. Super-critical clouds increase in emission line brightness, while sub-critical clouds generally are highly overheated reducing their luminosity below that of the intercloud medium.Due to the pressure stratification in the bow-shock of the jet, a cylindrical structure of nested shells develops around the jet. The most compact and brightest compressed clouds surround the cloud-free channel of the radio jet. To support our analytical model we present a numerical simulation of a supersonic jet propagating into a clumpy NLR. The position-velocity diagram of the simulated Hα emission shows total line widths of the order of 500 km s −1 with large-scale variations in the radial velocities of the clouds due to the stratified pressure in the bow-shock region of the jet. Most of the luminosity is concentrated in a few dense clouds surrounding the jet. These morphological and kinematic signatures are all found in the well observed NLR of NGC 1068 and other Seyfert galaxies.

Section: Critical Cloud Densitiesmentioning

confidence: 99%

Jet-Cloud Interactions and the Brightening of the Narrow-Line Region in Seyfert Galaxies

The Astrophysical Journal

Gómez

Raga³

et al. 1997

“…This assumption is justified by estimating the cooling distance δ behind a shock of speed vs = 150 km s −1 in typical environmental gas with a hydrogen density of n0 =1 cm −3 , using the adiabatic compression factor of 4. We then have (Taylor, Dyson and Axon 1992) δ =m vskT…”

Section: Non-magnetic Casementioning

confidence: 99%

“…However, later, after the same timestep, the full arc has cooled. Therefore, a cooling distance for the bowshock measured from the head of the jet, as discussed by Taylor et al (1989Taylor et al ( , 1992, can at best be only an average property.…”

Section: Structurementioning

confidence: 99%

See 1 more Smart Citation

Jet cocoons and the formation of narrow-line clouds in Seyfert galaxies

Monthly Notices of the Royal Astronomical Society

Gómez

Williams

et al. 1997

We present non-adiabatic hydrodynamic simulations of a supersonic light jet propagating into a fully ionized medium of uniform density on a scale representative of the narrow line region (NLR) in Seyfert galaxies with associated radio jets. In this regime the cooling distance of the swept up gas in the bowshock of the jet is of the same order as the transverse extent of the jet bowshock, as opposed to the more extreme regimes found for more powerful adiabatic large scale jets or the slow galactic jets which have been simulated previously. We calculate the emissivity for the Hα line and radio synchrotron emission. We find that the structure of the line emitting cold envelope of the jet cocoon is strongly dependent on the non-stationary dynamics of the jet head as it propagates through the ambient medium. We observe the formation of cloud-like high density regions which we associate with NLR clouds and filaments. We find that some of these clouds might be partially neutral and represent sites of jet induced star formation. The calculated Hα flux and the spectral line width are consistent with NLR observations. The simulation of the radio-optical emission with radiative cooling confirms the basic result of the geometric bowshock model developed by Taylor et al. (1989) that the start of noticeable optical line emission can be significantly offset from the hotspot of the radio emission. However, the time-dependent nature of the jet dynamics implies significant differences from their geometric bowshock model.

“…It should be noted that an ENLR is physically distinct from a Narrow Line Region (NLR), which has broader emission lines (several hundred kms −1 ), is more directly affected by the active nucleus and may involve different physical processes to the ENLR. In some Seyferts, the optical emission may be a signature of the physical interaction between the radio ejecta and the surrounding medium (e.g., Whittle et al 1986) as in the model proposed by Taylor, Dyson & Axon (1992). Therefore, any detection of emission line regions, consistent with a cone of ionising UV, should be considered carefully together with kinematic information to determine its true nature.…”

Section: Introductionmentioning

confidence: 99%

Evidence for an outflow from the Seyfert galaxy NGC

Christopoulou

Holloway

Monthly Notices of the Royal Astronomical Society

et al. 1997

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 ′′ from the core, show the [O iii] 5007-Å emission line to consist of two velocity components, both blue-shifted from the systemic radial velocity, with velocity widths of 140 kms −1 and separated by 120 kms −1 . This region is co-spatial with weak extended radio emission and is suggestive of a centrally driven outflow. The [O iii] 5007-Å line spectrum and image of this region have been modelled as an outflowing conical structure at 50 • to the line of sight with a half opening angle of 23 • .In addition to the extended structure, high resolution MERLIN observations of the 18-cm nuclear radio emission reveal a compact (1 ′′ ) radio triple source in PA 73 • . 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.