Late-type Spiral Galaxy Disk Colors And Color Gradients

The formation and evolution of disks are important for the formation and evolution of spiral galaxies, for disks are important components of the galaxies and the most baryons are in disks. We discussed the color gradients of disks for 395 late-type spiral galaxies brighter than 15~m in r-band that selected from Data Release Two of Slogan Digital Sky Survey. We decomposed their bulges and disks through one-dimensional fitting of the surface brightness profile of the sample galaxies, and statistically analyzed the color gradients of their disks. We also analyzed the correlations among the color, color gradients and other structural parameters .We got the following conclusions : (1) Color gradients were found in the disks of the late-type spirals . The gradients in the colors of r-z and g-z are roughly constants when expressed in Δc/ΔR, while g-r favors the form of Δc/Δlog R. (2) The values of color gradients are: Δ(g - r)/ΔR= -0.048 ± 0.003, Δ(r - z)/Δ R=-0.166 ± 0.088, Δ(g - r)/ΔR=-0.245 ± 0.011; Δ(g - r)/ΔlogR= -0.152 ± 0.010, Δ(r - z)/ΔlogR=-0.377 ± 0.019, Δ(g - z)/ΔlogR=-0.590 ± 0.026 , the values in the form Δc/Δlog R are in good agreement with previous results. (3)There are strong correlations between the absolute magnitude and the color of the disks: the brighter the disks, the redder they are, but no significant correlations were found between the color gradients and the absolute magnitude of the disks. (4) There are the correlations between the size and the color of the disks: the bigger the disks, the bluer they are, with fixed luminosity. We also found the correlations between the size and the color gradients: the bigger the disks, the steeper color gradients are .(5) The correlations between the color and color gradients were found, the bluer the disks and the steeper the color gradients are.(6) There are weak correlations between the color and the B/D (bulge-to-disk ratio),between the color gradients and the B/D, which maybe was only one reflection of the correlations between the B/D and the color and between the B/D and the color gradients. (7) Our statistical conclusions strongly implied that the color and the color gradients can...