J/AJ/107/135 J/AJ/107/135 Colors and color gradients in bulges of galaxies M Balcells R F Peletier Astron. J. 107 135 1994 1994AJ....107..135B photometry: galaxies: early-type galaxies: spiral galaxies: photometry 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 (M(sup Bulge sub R) 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 (M(sub R) 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.

UGC UGC denomination --- IC When IC, the following number is the IC name --- NGC NGC denomination --- Type Numerical morphological type from the RC3 --- epsilon Disk ellipticity (1-b/a) --- Mtot(R) R luminosity of the galaxy mag Mbul(R) R luminosity of the bulge mag D/B Bulge to disk ratio in R color --- mu0(R) Central surface brightness of the disk in R color mag/arcsec2 h_UR Ratio of the scale lengths of the disk in U and R minus 1 (h_U/h_R - 1) --- RR Reason why a galaxy did not qualify for the dustfree sample --- NGC NGC name --- (B-R)0 B-R central color mag e_(B-R)0 rms uncertainty on (B-R)0 mag d(B-R)/dr B-R color gradient --- e_d(B-R)/dr rms uncertainty on d(B-R)/dr --- (U-R)0 U-R central color mag e_(U-R)0 rms uncertainty on (U-R)0 mag d(U-R)/dr U-R color gradient --- e_d(U-R)/dr rms uncertainty on d(U-R)/dr --- (R-I)0 R-I central color mag e_(R-I)0 rms uncertainty on (R-I)0 mag d(R-I)/dr R-I color gradient --- e_d(R-I)/dr rms uncertainty on d(R-I)/dr --- (U-B)0 U-B central color mag e_(U-B)0 rms uncertainty on (U-B)0 mag d(U-B)/dr U-B color gradient --- e_d(U-B)/dr rms uncertainty on d(U-B)/dr --- NGC Galaxy name --- DeltaU Average difference between the artificial aperture measurement and the literature photometry, in U mag e_DeltaU rms uncertainty on DeltaU mag DeltaB Average difference between the artificial aperture measurement and the literature photometry, in B mag e_DeltaB rms uncertainty on DeltaB mag DeltaR Average difference between the artificial aperture measurement and the literature photometry, in R mag e_DeltaR rms uncertainty on DeltaR mag [Fe/H] Metallicity Sun (B-R)20 Integrated B-R color for an age of 20 Gyr mag (B-R)12 Integrated B-R color for an age of 12 Gyr mag Patricia Bauer CDS 1993Feb22 J_AJ_107_135.xml