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J/AJ/107/135 Colors and color gradients in bulges of galaxies (Balcells+ 1994)
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Colors and color gradients in bulges of galaxies
Balcells M., Peletier R.F.
<Astron. J. 107, 135 (1994)>
=1994AJ....107..135B
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Keywords: photometry: galaxies - galaxies: spiral - galaxies: early-type
Abstract:
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.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1 87 32 Photometric data
table2 123 18 Central colors and color gradients
table3 53 6 Comparison with aperture photometry
table4 23 4 Integrated colors of single burst models
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Byte-by-byte Description of file: table1
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Bytes Format Units Label Explanations
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2- 6 I5 --- UGC UGC denomination
9- 10 A2 --- IC When IC, the following number is the IC name
11- 14 I4 --- NGC NGC denomination
18- 19 I2 --- Type Numerical morphological type from the RC3
23- 26 F4.2 --- epsilon Disk ellipticity (1-b/a)
29- 34 F6.2 mag Mtot(R) R luminosity of the galaxy
38- 43 F6.2 mag Mbul(R) []? R luminosity of the bulge
47- 51 F5.2 --- D/B Bulge to disk ratio in R color
55- 59 F5.2 mag/arcsec2 mu0(R) Central surface brightness of the disk
in R color
62- 66 F5.2 --- h_UR []? Ratio of the scale lengths of the disk
in U and R minus 1 (h_U/h_R - 1)
70- 89 A20 --- RR Reason why a galaxy did not qualify for the
dustfree sample
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Byte-by-byte Description of file: table2
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Bytes Format Units Label Explanations
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3- 6 I4 --- NGC NGC name
10- 13 F4.2 mag (B-R)0 B-R central color
17- 20 F4.2 mag e_(B-R)0 rms uncertainty on (B-R)0
23- 27 F5.2 --- d(B-R)/dr B-R color gradient
31- 34 F4.2 --- e_d(B-R)/dr rms uncertainty on d(B-R)/dr
38- 41 F4.2 mag (U-R)0 U-R central color
45- 48 F4.2 mag e_(U-R)0 rms uncertainty on (U-R)0
52- 56 F5.2 --- d(U-R)/dr U-R color gradient
60- 63 F4.2 --- e_d(U-R)/dr rms uncertainty on d(U-R)/dr
67- 70 F4.2 mag (R-I)0 R-I central color
74- 77 F4.2 mag e_(R-I)0 rms uncertainty on (R-I)0
81- 85 F5.2 --- d(R-I)/dr R-I color gradient
89- 92 F4.2 --- e_d(R-I)/dr rms uncertainty on d(R-I)/dr
96- 99 F4.2 mag (U-B)0 U-B central color
103-106 F4.2 mag e_(U-B)0 rms uncertainty on (U-B)0
110-114 F5.2 --- d(U-B)/dr U-B color gradient
118-121 F4.2 --- e_d(U-B)/dr rms uncertainty on d(U-B)/dr
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Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1- 8 A8 --- NGC Galaxy name
11- 15 F5.2 mag DeltaU []? Average difference between the artificial
aperture measurement and the literature
photometry, in U
19- 22 F4.2 mag e_DeltaU []? rms uncertainty on DeltaU
25- 29 F5.2 mag DeltaB Average difference between the artificial
aperture measurement and the literature
photometry, in B
33- 36 F4.2 mag e_DeltaB rms uncertainty on DeltaB
39- 43 F5.2 mag DeltaR Average difference between the artificial
aperture measurement and the literature
photometry, in R
47- 50 F4.2 mag e_DeltaR []? rms uncertainty on DeltaR
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byte-by-byte Description of file: table4
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Bytes Format Units Label Explanations
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3- 7 F5.2 Sun [Fe/H] Metallicity
11- 15 F5.3 mag (B-R)20 Integrated B-R color for an age of 20 Gyr
19- 23 F5.3 mag (B-R)12 Integrated B-R color for an age of 12 Gyr
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(End) Patricia Bauer [CDS] 22-Feb-1993