Observational evidence for triaxiality, and for relatively recent star formation in the bulge of NGC 4736

Beckman, J. E.; Varela, A. M.; Munoz-Tunon, C.; Vilchez, J. M.; Cepa, J.
Referencia bibliográfica

Astronomy and Astrophysics (ISSN 0004-6361), vol. 245, no. 2, May 1991, p. 436-448.

Fecha de publicación:
5
1991
Número de autores
5
Número de autores del IAC
5
Número de citas
23
Número de citas referidas
22
Descripción
CCD maps are presented of the inner 1.4 kpc of NGC 4736 in the B, V, R, I and Z bands, along with an ellipticity analysis of these, in which the ellipticities and position angles of isophotal best-fit ellipses are given as functions of galactocentric radius in each band. Also provided are calibrated profiles through the nucleus in individual bands, and in the B-V, V-R, and F-I color indices, as well as isochromal maps in these colors. The ellipticity analysis reveals the presence of three zones: an inner bulge, out to some 400 pc from the nucleus, a transition zone from 400 to 800 pc, and the disk, beyond 800 pc radius, marked by distinct regimes of ellipticity and position angle of the elliptical isophotes. The underlying differences in position angle between bulge and disk strongly indicate bulge triaxiality in NGC 4736, while the variations in ellipticity in the inner bulge and their color dependence point to recent star-forming activity.