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The kinematics and ionization of nuclear gas clouds in centaurus A

Bicknell, Geoffrey; Sutherland, Ralph; Neumayer, Nadine

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Neumayer et al. established the existence of a blueshifted cloud in the core of Centaurus A, within a few parsecs of the nucleus and close to the radio jet. We propose that the cloud has been impacted by the jet, and that it is in the foreground of the jet, accounting for its blueshifted emission on the southern side of the nucleus. We consider both shock excitation and photoionization models for the excitation of the cloud. Shock models do not account for the [Si VI] and [Ca VIII] emission...[Show more]

dc.contributor.authorBicknell, Geoffrey
dc.contributor.authorSutherland, Ralph
dc.contributor.authorNeumayer, Nadine
dc.date.accessioned2015-12-13T22:19:04Z
dc.identifier.issn0004-637X
dc.identifier.urihttp://hdl.handle.net/1885/71627
dc.description.abstractNeumayer et al. established the existence of a blueshifted cloud in the core of Centaurus A, within a few parsecs of the nucleus and close to the radio jet. We propose that the cloud has been impacted by the jet, and that it is in the foreground of the jet, accounting for its blueshifted emission on the southern side of the nucleus. We consider both shock excitation and photoionization models for the excitation of the cloud. Shock models do not account for the [Si VI] and [Ca VIII] emission line fluxes. However, X-ray observations indicate a source of ionizing photons in the core of Centaurus A; photoionization by the inferred flux incident on the cloud can account for the fluxes in these lines relative to Brackett-γ. The power-law slope of the ionizing continuum matches that inferred from synchrotron models of the X-rays. The logarithm of the ionization parameter is -1.9, typical of that in Seyfert galaxies and consistent with the value proposed for dusty ionized plasmas. The model cloud density depends upon the Lorentz factor of the blazar and the inclination of our line of sight to the jet axis. For acute inclinations, the inferred density is consistent with expected cloud densities. However, for moderate inclinations of the jet to the line of sight, high Lorentz factors imply cloud densities in excess of 105 cm-3 and very low filling factors, suggesting that models of the gamma-ray emission should incorporate jet Lorentz factors ≲ 5.
dc.publisherIOP Publishing
dc.rightsAuthor/s retain copyright
dc.sourceAstrophysical Journal, The
dc.subjectKeywords: black hole physics; galaxies: active; galaxies: individual (Centaurus A); galaxies: jets; line: formation; relativistic processes
dc.titleThe kinematics and ionization of nuclear gas clouds in centaurus A
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume766
dc.date.issued2013
local.identifier.absfor020100 - ASTRONOMICAL AND SPACE SCIENCES
local.identifier.ariespublicationf5625xPUB2803
local.type.statusPublished Version
local.contributor.affiliationBicknell, Geoffrey, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationSutherland, Ralph, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationNeumayer, Nadine, European Southern Observatory
local.bibliographicCitation.issue1
local.bibliographicCitation.startpage9
local.identifier.doi10.1088/0004-637X/766/1/36
dc.date.updated2016-02-24T09:02:35Z
local.identifier.scopusID2-s2.0-84875014654
local.identifier.thomsonID000316054000036
dcterms.accessRightsOpen Access
CollectionsANU Research Publications

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