Star-forming complexes in a sample of spiral and irregular galaxies

Over 300 star-forming complexes in 11 intermediate- and late-type spiral and irregular galaxies have been observed in the B, I, and Ha bands to determine their luminosity functions, ages, sizes, and masses. The total Ha luminosity from complexes compared with the total galaxy H alpha luminosity ranges from 20% to 70%, but the percentage is nearly constant at 7% in the B band for most galaxies. A comparison of the colors and luminosities of the complexes with published cluster evolutionary models suggests that the complexes range in age from a few times 10(6) yr to nearly 10(9) yr; the majority have ages of less than 1 to 2 x 10(7) yr. The complex masses range from 10(4) to 10(7) M-. The luminosity functions for the complexes follow a power law with an exponent of approximately -2; late-type galaxies have slightly shallower slopes than intermediate-type galaxies. The sizes of the largest complexes in each galaxy scale approximately with the square root of the galaxy luminosity, confirming previous studies. The complexes may have a fractal size distribution that is consistent with values predicted by theoretical turbulence models of the interstellar medium.