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Abstract: We present new ATCA 21-cm line observations of the neutral hydrogen in thenearby radio galaxy Centaurus A. We image in detail with a resolution down to7-, ~100pc the distribution of HI along the dust lane. Our data have bettervelocity resolution and better sensitivity than previous observations. The HIextends for a total of ~15kpc. The data, combined with a titled-ring model ofthe disk, allow to conclude that the kinematics of the HI is that of aregularly rotating, highly warped structure down to the nuclear scale. Theparameters in particular the inclination of our model are somewhat differentfrom some of the previously proposed models but consistent with what wasrecently derived from stellar light in a central ring. The model nicelydescribes also the morphology of the dust lane as observed with Spitzer. Thereare no indications that large-scale anomalies in the kinematics exist thatcould be related to supplying material for the AGN. Large-scale radial motionsdo exist, but these are only present at larger radii r>6kpc. This unsettledgas is mainly part of a tail-arm like structure. The relatively regularkinematics of the gas in this structure suggests that it is in the process ofsettling down into the main disk. The presence of this structure furthersupports the merger-interaction origin of the HI in Cen A. From the structureand kinematics we estimate a timescale of 1.6-3.2*10^{8}yr since the mergingevent. No bar structure is needed to describe the kinematics of the HI. Thecomparison of the timescale derived from the large-scale HI structure and thoseof the radio structure together with the relative regularity of the HI down tothe sub-kpc regions does not suggest a one-to-one correspondence between themerger and the phase of radio activity. Interestingly, the radial motions ofthe outer regions are such that the projected velocities are redshiftedcompared to the regular orbits. This means that the blueshifted absorptiondiscovered earlier and discussed in our previous paper cannot be caused byout-moving gas at large radius projected onto the centre. Therefore, theinterpretation of the blueshifted absorption, together with at least a fractionof the redshifted nuclear absorption, as evidence for a regular inner disk,still holds. Finally, we also report the discovery of two unresolved cloudsdetected at 5.2 and 11kpc away in projection from the HI disk. They arelikely an other example of left-over of the merger that brought the HI gas.

Author: C. Struve 1,2, T.A. Oosterloo 1,2, R. Morganti 1,2, L. Saripalli 3,4 1 Netherlands Institute for Radio Astronomy 2 Kapteyn Instit

Source: https://arxiv.org/


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