Astron. J., 147, 78 (2014/April-0)
The luminosity function of star clusters in 20 star-forming galaxies based on Hubble Legacy Archive photometry.
WHITMORE B.C., CHANDAR R., BOWERS A.S., LARSEN S., LINDSAY K., ANSARI A. and EVANS J.
Abstract (from CDS):
Luminosity functions (LFs) have been determined for star cluster populations in 20 nearby (4-30 Mpc), star-forming galaxies based on Advanced Camera for Surveys source lists generated by the Hubble Legacy Archive (HLA). These cluster catalogs provide one of the largest sets of uniform, automatically generated cluster candidates available in the literature at present. Comparisons are made with other recently generated cluster catalogs demonstrating that the HLA-generated catalogs are of similar quality, but in general do not go as deep. A typical cluster LF can be approximated by a power law, dN/dL∝L α, with an average value for α of -2.37 and rms scatter = 0.18 when using the F814W ("I") band. A comparison of fitting results based on methods that use binned and unbinned data shows good agreement, although there may be a systematic tendency for the unbinned (maximum likelihood) method to give slightly more negative values of α for galaxies with steeper LFs. We find that galaxies with high rates of star formation (or equivalently, with the brightest or largest numbers of clusters) have a slight tendency to have shallower values of α. In particular, the Antennae galaxy (NGC 4038/39), a merging system with a relatively high star formation rate (SFR), has the second flattest LF in the sample. A tentative correlation may also be present between Hubble type and values of α, in the sense that later type galaxies (i.e., Sd and Sm) appear to have flatter LFs. Hence, while there do appear to be some weak correlations, the relative similarity in the values of α for a large number of star-forming galaxies suggests that, to first order, the LFs are fairly universal. We examine the bright end of the LFs and find evidence for a downturn, although it only pertains to about 1% of the clusters. Our uniform database results in a small scatter (~0.4 to 0.5 mag) in the correlation between the magnitude of the brightest cluster (Mbrightest) and log of the number of clusters brighter than MI= -9 (log N). We also examine the magnitude of the brightest cluster versus log SFR for a sample including both dwarf galaxies and ULIRGs. This shows that the correlation extends over roughly six orders of magnitude but with scatter that is larger than for our spiral sample, probably because of the high levels of extinction in many of the LIRGs.
galaxies: individual: (NGC 45, NGC 406, NGC 628, NGC 1300, NGC 1309, NGC 1313, NGC 1483, NGC 2397, NGC 3627, NGC 4038,sol - 39, NGC 4258, NGC 4394, NGC 4395, NGC 4736, NGC 5055, NGC 5236, NGC 5457, NGC 6217, NGC 6503, NGC 7793) - galaxies: interactions - galaxies: star clusters: general
objects in Figure 2 (from Chandar et al. 2010, 2014) are not yet identified.
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