Friday, 1 August 2008

On the SFR-brightest cluster relation: estimating the peak SFR in post-merger galaxies

Nate Bastian: astro-ph/0807.4687

He does Monte Carlo simulations and comparisons to observations of star cluster formation in galaxies. It appears thet there is quite a tight relation between the magnitude of the brightest young cluster present, and the current SFR, because the brightest cluster often is young (<15Myr) and the mass of the most massive cluster is determined by the number of clusters formed, which is strongly related to the SFR. In the figure, the colored lines are lines of different cluster mass functions (schechter with some M*. ). The gamma indicates the factor between star formation rate and cluster formation rate, i.e. they find that CFR = 0.08 SFR, which is sort of low. This SFR indicator agrees well with other indicators.

Using the fading of clusters, an old cluster that is very bright can indicate a burst in SFR some time ago, and its luminosity and age give an estimate of the peak SFR of that galaxy (or galaxy merger). Here cluster disruption effects need to be taken into account (which is difficult).

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