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from Part 5 - Bulge Phenomenology
Published online by Cambridge University Press: 10 November 2010
We report the case of the geometrical and kinematical decoupling between the bulge and the disk of the Sa galaxy NGC 4698. The R–band isophotal map of this spiral shows that the bulge structure is elongated perpendicularly to the major axis of the disk. At the same time a central stellar velocity gradient is found along the major axis of the bulge. We also present the Sa galaxy NGC 4672 as being a good candidate for a spiral hosting a bulge and a disk that are orthogonally decoupled with respect to one other. This decoupling of the two fundamental stellar components suggests that the disk could represent a second event in the history of early-type spirals.
Introduction
NGC 4698 is classified Sa by Sandage & Tammann (1981) and Sab(s) by de Vaucouleurs et al. (1991; RC3). Sandage & Bedke (1994; CAG) present NGC 4698 as an example of the early-to-intermediate Sa type since it is characterized by a large central bulge and tightly wound spiral arms. In addition to a remarkable geometrical decoupling between the bulge and the disk (whose apparent major axes appear oriented in an orthogonal way upon simple visual inspection of galaxy plates; see Panels 78, 79 and 87 in CAG), a spectrum taken along the minor axis of the disk shows the presence of a stellar velocity gradient which could be ascribed to the bulge.
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