Bibcode
DOI
Balcells, Marc; Peletier, Reynier F.
Referencia bibliográfica
The Astronomical Journal, vol. 107, no. 1, p. 135-152
Fecha de publicación:
1
1994
Número de citas
142
Número de citas referidas
116
Descripción
We have obtained surface photometry in U, B, R, and I for a complete
optically selected sample of 45 early-type spiral galaxies, to
investigate the colors and color gradients of spiral bulges. Color
profiles in U-R, B-R, U-B, and R-I have been determined in wedges
opening on the semiminor axes. Based on several criteria, like the
smoothness of the color profiles, the absence of dust lanes, and the
central colors, we have defined a subsample of 18 objects whose colors
are largely unaffected by dust. We believe such colors are suitable for
inferring properties of the stellar populations of bulges. We find that
the colors of bulges are predominantly bluer than those of ellipticals.
This result holds even when bulges are compared to ellipticals of the
same luminosity, and indicates that bulges are younger and/or more metal
poor than old elliptical galaxies. Most bulges do not reach solar
metallicities. Bulges show predominantly negative color gradients (bluer
outward). For bright bulges (MBulgeR is less than
-20.0), the magnitude of the gradient increases with bulge luminosity.
For fainter bulges, gradients scatter around large negative values. The
behavior of color gradients as a function of bulge luminosity suggests
different formation mechanisms for faint and bright spheroids. For
bright bulges, the scaling of gradients with luminosity suggests a
formation process involving dissipation. The similarity with ellipticals
suggests that the formation of the disk did not affect the stellar
populations of the bulge in a major way. For small bulges (MR
is greater than -20), the existence of pronounced color gradients
suggests a different formation mechanism. For these objects, the
presence of the disk may have severely affected the radial population
distribution in the bulge.