Departures from axial symmetry, and starburst activity, in the bulge of NGC 4736

Varela, A. M.; Beckman, J. E.; Cepa, J.; Munoz-Tunon, C.; Vilchez, J. M.
Bibliographical reference

(IAU, European Regional Astronomy Meeting, 11th, La Laguna, Spain, July 3-8, 1989) Astrophysics and Space Science (ISSN 0004-640X), vol. 170, no. 1-2, Aug. 1990, p. 305-310.

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Evidence for circumnuclear starbursts in spiral galaxies can take the form of a blue excess near the nucleus, but more frequently (because of dust extinction) H I or radio continuum emission. Such bursts are quite common, even in objects with no interacting companions. One consequence of a burst is to sweep gas outward from the inner zone, so further bursts (and perhaps the initial one) need to be resupplied with gas. This can be effected via a nonaxisymmetric gravitational potential, not necessarily a bar, in the nuclear bulge. Searching for these nonaxisymmetric features, two-dimensional photometry has been obtained from CCD maps in B, V, R, I, and Z bands, for a set of galaxies which have undergone starburst activity.