Here is a 2004 review paper about Young and Massive & Compact star clusters in galaxies, by Soren S. Larsen:
[ This is catalogued at //arxiv.org as the preprint astro-ph/ 0403244 ]
____Young Massive clusters_Larsen review_astro-ph 0403244.pdf
And here is a study of two galaxies (NGC 1569 and NGC 1313) which are known to contain newly-formed star clusters having masses of 100,000 solar masses or more;
____Young massive clusters in N1569 and N1313.pdf
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The following are a few points which I have extracted from Section 3 of A.Adamo et al. (2011, MNRAS, Vol.417, p.1904) , regarding the circumstances in which particularly massive star clusters can form:
- Mergers of two galaxies produce more numerous and more massive clusters than quiescent spiral galaxies.
- Another effect that leads to more high-mass clusters forming is: a galaxy that forms very large numbers of star clusters will also form greater numbers of star clusters that are of very high mass.
- As one might expect, the total number of young and massive star clusters that are found within a galaxy is likely to be positively correlated with the total star-formation rate of that galaxy; a larger total number of formed Star Clusters will, all else being equal, lead to a larger number of massive clusters existing.
For instance, some studies have found that the brightest star cluster within a galaxy is likely to be outstandingly luminous if the host galaxy has a particularly high star-formation rate; a positive correlation has been found between the star-formation rate of a galaxy and the absolute brightness of its brightest star cluster.
- Here is Figure 6 from the paper by Adamo et al. , demonstrating the strong positive correlation between the Star-Formation Rate of the host galaxy and the visual luminosity of its brightest star cluster:
- Shear forces within rotationally-supported Disk Galaxies (such as spirals) favour the formation of low-mass star clusters, as this encourages fragmentation of Giant Molecular Clouds.
- The lack of rotation in dwarf irregular galaxies, and the high gas pressures in merging galaxies, tend to favour the formation of very-massive star clusters. While not all Dwarf Irregular galaxies have a lot of star clusters, it is remarkably common to find a dwarf irregular galaxy that contains one or two very-massive star clusters. (an easily observable example of a dwarf galaxy with a single super-luminous star cluster is NGC 1705 ).
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Bad Galaxy Man's comments of the day:
(1)
You will note that some of the star clusters plotted in Figure 6 are easily as luminous as an entire dwarf galaxy! The most luminous of these star clusters have a luminosity of absolute V magnitude –17, which is over 100 times the luminosity of the most luminous globular star clusters that are found in M31 and our own Galaxy.
(2) Regarding cluster formation in dwarf galaxies;
Certainly, there are many dwarf irregular galaxies which have one or two supergiant nebular/star-forming complexes that can potentially contain very-massive new star clusters; a good example of this is the small irregular galaxy known as IC 4662 which has two complexes that are approximately on the same scale as the Tarantula Nebula.
On the other hand, contrary to the appearance of the High Surface Brightness examples of dwarf irregular galaxies that we are all very familiar with, the majority of dwarf irregular galaxies are actually of extremely low surface brightness, with an extremely low star-formation rate.
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