Title: A study of inclination effects on galaxy surface brightness
Abstract: The inclination effects due to the internal absorption on the surface brightness of spiral galaxies at the center (μ_0_) and at the equivalent radius (μ_e_) are investigated using the V-band data obtained with the KISO Schmidt telescope. The results confirm the general trend of the inclination effect from the ESO Schmidt data in the B band, in particular, the small inclination effect on μ_e_ (C_e_ ~0) for middle-type spirals (T = 3-5), upon which the current argument of highly opaque nature of galaxy disks by Valentijin is based. Those empirical results are compared with predictions from simple models of disks and bulges obscured by an exponential absorbing layer with various optical thickness (0<=τ_0_<= infinity) and relative scale height (0<=ζ= β_d_/β_s_ <= infinity). The general trends of variation in μ_e_ and μ_0_ over various types of spiral galaxies are interpreted in terms of increasing bulge/disk ratio, and of decreasing ζ with decreasing type index, without assuming highly opaque disks. When the height of absorbing layer is restricted to ζ <= 1, the layer must be highly opaque for a pure-disk galaxy of C~O. However, the small inclination effect (C_e_~0) can also be reconciled with an extended absorbing disk (ζ> 1) of moderate or small optical thickness (τ_0_ < 1). One needs to investigate more in details of bulge/disk ratio and of scale height ζ in order to determine the optical thickness τ_0_ from this kind of study.