Star clusters in M 33 IV. A new survey from deep HST images

We have detected 102 star clusters in he 33, from 35 deep Hubble Space Telescope (HST) WFPC2 fields taken from our program and from the HST archive. Twenty-eight fields have V and I band imaging, and an additional seven fields are imaged in a single V filter. Eighty-two of the clusters were previously unknown. Integrated photometry reveals that 25 clusters have (V - I) colors typical of those found in Galactic globular clusters (only ten of these objects were previously known). Our discovery of 16 new globular cluster candidates increases previous estimates of the old cluster population in hi 33 by similar to 60%. An additional eleven objects (only two were previously known) have colors expected for intermediate age clusters. The new clusters have a range of ages from 6 million years to >15 Gyrs, and masses between 10(2) M.-10(6) M., although these parameters are estimated from only one color. The number of new clusters detected more than double?; our previous sample (Papers I and II), and extends coverage to older objects and new off-spiral arm locations in M 33. The luminosity function for old hi 33 clusters shows a peak at M-V similar to -7.0, nearly half a magnitude fainter than found in the Galactic and hi 31 globular cluster populations. The luminosity function for intermediate age objects shows no turnover down to M-V similar to -6.6 We estimate the total number of globular clusters in hi 33 to be 75 +/- 14. This gives a specific frequency, S-N, of 2.07 +/- 0.39 - significantly higher than found for other later-type spiral galaxies, but in the range found for ellipticals.