Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...432..518t&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 432, no. 2, p. 518-546
Astronomy and Astrophysics
Astrophysics
56
Galactic Bulge, Galactic Structure, Infrared Imagery, Infrared Photometry, Spiral Galaxies, Stellar Color, Stellar Luminosity, Interstellar Extinction, Metallicity, Star Formation, Stellar Composition
Scientific paper
We present surface photometry of 43 SO and spiral galaxies in the K band with a subset also observed in J. Most of the data are photometrically calibrated. We combine our data with published optical major-axis profiles to construct a set of galaxies with rJK colors, divide the major-axis profiles into bulge-dominated and disk-dominated regions, and compute mean colors and color gradients separately for bulges and disks. Typically the disk colors are measured from 0.8 to 1.8 scale lengths. The colors of the bulge and disk components are strongly correlated, indicating that both components have a red stellar content that is similar in both age and metallicity. In the mean the disks are 0.1 mag bluer in r - K than bulges; this color difference would arise if the disks are 2-4 x 109 yr younger or have lower metallicities by Delta(Fe/H) is approximately equal to -0.1 to -0.2. Many of the bulges exhibit negative color gradients (bluer outward), which indicate that metallicity gradients of order Delta(Fe/H) is approximately -0.2 may be common in bulges. Bulges of late-type galaxies are bluer on average than those of early types, probably a consequence of lower metallicity. About 25% of the galaxies have especially red bulge and disk colors, which we interpret as arising from large internal extinction rather than from an enhanced star-formation rate.
Davies Roger L.
DePoy Darren L.
Frogel Jay. A.
Terndrup Donald M.
Wells Lisa A.
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