The nature of the optical filaments in Centaurus A. Evidence for a beamed ionizing continuum⋆

Morganti, R.; Robinson, Andrew; Fosbury, R. A. E.; Alighieri, S. di Serego; Tadhunter, C. N.; Malin, D. F.

doi:10.1093/mnras/249.1.91

Cited by 92 publications

(162 citation statements)

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“…If the dense cloudlets have a fractal structure and a distribution of sizes, then the clouds will cover a range of velocities and degrees of shredding. The outer Ðla-ments do indeed show such a range of morphologiesÈfrom large arcs to elongated smears distributed in the direction away from the galaxy nucleus (Morganti et al 1991 ;Graham 1998). We attribute the former to clouds in the initial stages of acceleration ; in this case the shapes of the emission-line arcs trace the outline of the cloud.…”

Section: T He Outer Filamentsmentioning

confidence: 76%

“…R c D 10È20 We now consider some of the features in the outer Ðla-ment region that enable us to estimate the density and cloud shock velocities. The largest distinct structures amongst the outer Ðlaments are arcs with D70 pc radii of curvature (Morganti et al 1991 ;Graham 1998). By integrating the [O III] surface brightness contours in Morganti et al (1991), the luminosity of the prominent arc at the southern end of the outer Ðlaments is found to be L *OIII+ B ergs s~1.…”

Section: T He Outer Filamentsmentioning

confidence: 98%

“…We attribute the smeared features to the shredded remnants of previously accelerated clouds. At the available resolution in the images of Morganti et al (1991) and Graham (1998), the smallest visible knots are D1AÈ2A wide, corresponding to a radial scale pc. R c D 10È20 We now consider some of the features in the outer Ðla-ment region that enable us to estimate the density and cloud shock velocities.…”

Section: T He Outer Filamentsmentioning

confidence: 99%

“…Its proximity means that various physical processes can be studied in detail with high spatial resolution, and from time to time new observational data appear that confront our understanding of this object and the physical processes occurring in radio galaxies generally. The recent observations of the northern middle lobe (NML) of Cen A by Morganti et al (1999) and the related observations of star formation and emission-line clouds in its vicinity (Graham & Price 1981 ;Morganti et al 1991 ;Graham 1998 ;Sutherland et al 1993 ;Mould et al 2000) fall into this category. The radio observations of the NML are the Ðrst published observations of the NML and Ðll in the spatial gap between the extant Very Large Array images of the inner lobe and the large-scale structure.…”

Section: Introductionmentioning

confidence: 99%

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The Centaurus A Northern Middle Lobe as a Buoyant Bubble

Saxton

Sutherland

Bicknell

2001

ApJ

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We model the northern middle radio lobe of Centaurus A (NGC 5128) as a buoyant bubble of plasma deposited by an intermittently active jet. The extent of the rise of the bubble and its morphology imply that the ratio of its density to that of the surrounding ISM is less than 10~2, consistent with our knowledge of extragalactic jets and minimal entrainment into the precursor radio lobe. Using the morphology of the lobe to date the beginning of its rise through the atmosphere of Cen A, we conclude that the bubble has been rising for approximately 140 Myr. This timescale is consistent with that proposed by Quillen and coworkers for the settling of postmerger gas into the presently observed large-scale disk in NGC 5128, suggesting a strong connection between the delayed reestablishment of radio emission and the merger of NGC 5128 with a small gas-rich galaxy. This suggests a connection, for radio galaxies in general, between mergers and the delayed onset of radio emission. In our model, the elongated X-ray emission region discovered by Feigelson and coworkers, part of which coincides with the northern middle lobe, is thermal gas that originates from the interstellar medium below the bubble and that has been uplifted and compressed. The "" large-scale jet ÏÏ appearing in the radio images of Morganti and coworkers may be the result of the same pressure gradients that cause the uplift of the thermal gas, acting on much lighter plasma, or may represent a jet that did not turn o † completely when the northern middle lobe started to buoyantly rise. We propose that the adjacent emission-line knots (the "" outer Ðlaments ÏÏ) and star-forming regions result from the disturbance, in particular the thermal trunk, caused by the bubble moving through the extended atmosphere of NGC 5128.

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Section: T He Outer Filamentsmentioning

confidence: 76%

Section: T He Outer Filamentsmentioning

confidence: 98%

Section: T He Outer Filamentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Centaurus A Northern Middle Lobe as a Buoyant Bubble

Saxton

Sutherland

Bicknell

2001

ApJ

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“…Some of the pioneering models (e,g., Tadhunter, Robinson, & Morganti 1989, Morganti et al 1991 of EELRs attempted to reproduce the optical emission-line spectra of the optical filaments observed associated with the powerful radio galaxy Cen A. These models invoke beamed photoionization from the nucleus.…”

Section: Excitation Of Extended Emission-line Regions 387mentioning

confidence: 99%

Excitation Mechanism of Extended Emission-Line Regions in Active Galaxies

Evans¹,

Koratkar

Allen

et al. 1997

International Astronomical Union Colloquium

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Abstract. Photoionization and shock models of the extended emissionline regions (EELRs) in active galaxies demonstrate that the optical emission lines alone are a poor discriminant of the excitation mechanism. Combining optical and UV data provides a discriminant between nuclear photoionization and autoionizing shock models. Hubble Space Telescope UV spectrophotometry of two Seyferts suggests that the EELRs in these objects are probably photoionized by the nucleus.

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