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The stratified two-sided jet of Cygnus A. Acceleration and collimation

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The stratified two-sided jet of Cygnus A. Acceleration and collimation

dc.contributor.author	Boccardi, B.
dc.contributor.author	Krichbaum, T. P.
dc.contributor.author	Bach, U.
dc.contributor.author	Mertens, F.
dc.contributor.author	Ros Ibarra, Eduardo
dc.contributor.author	Alef, W.
dc.contributor.author	Zensus, J. Anton
dc.date.accessioned	2017-07-04T15:03:54Z
dc.date.available	2017-07-04T15:03:54Z
dc.date.issued	2015
dc.identifier.citation	Boccardi, B. Krichbaum, T. P. Bach, U. Mertens, F. Ros Ibarra, Eduardo Alef, W. Zensus, J. Anton 2015 The stratified two-sided jet of Cygnus A. Acceleration and collimation Astronomy and Astrophysics 585 A33 1 9
dc.identifier.uri	http://hdl.handle.net/10550/59338
dc.description.abstract	Aims. High-resolution Very-Long-Baseline Interferometry observations of relativistic jets are essential for constraining the fundamental parameters of jet formation models. At a distance of 249 Mpc, Cygnus A is a unique target for such studies, since it is the only Fanaroff-Riley Class II radio galaxy for which a detailed subparsec scale imaging of the base of both jet and counter-jet can be obtained. Observing at millimeter wavelengths unveils those regions that appear self-absorbed at longer wavelengths and enables an extremely sharp view toward the nucleus to be obtained. Methods. We performed 7 mm Global VLBI observations, achieving ultra-high resolution imaging on scales down to 90uas. This resolution corresponds to a linear scale of only ~400 Schwarzschild radii (for MBH = 2.5 × 109M⊙). We studied the kinematic properties of the main emission features of the two-sided flow and probed its transverse structure through a pixel-based analysis. Results. We suggest that a fast and a slow layer with different acceleration gradients exist in the flow. The extension of the acceleration region is large (~ 104RS), indicating that the jet is magnetically driven. The limb brightening of both jet and counter-jet and their large opening angles (φJ ~ 10°) strongly favour a spine-sheath structure. In the acceleration zone, the flow has a parabolic shape (r ∝ z0.55 ± 0.07). The acceleration gradients and the collimation profile are consistent with the expectations for a jet in "equilibrium", achieved in the presence of a mild gradient of the external pressure (p ∝ z− k,k ≤ 2).
dc.language.iso	eng
dc.relation.ispartof	Astronomy and Astrophysics, 2015, vol. 585, num. A33, p. 1-9
dc.subject	Astrofísica
dc.subject	Astronomia
dc.title	The stratified two-sided jet of Cygnus A. Acceleration and collimation
dc.type	journal article	es_ES
dc.date.updated	2017-07-04T15:03:54Z
dc.identifier.doi	10.1051/0004-6361/201526985
dc.identifier.idgrec	108957
dc.rights.accessRights	open access	es_ES