Properties of the cluster population of NGC 1566 and their implications

TL;DR

This study analyzes the properties of star clusters in NGC 1566, revealing consistent mass and luminosity functions across the galaxy, and explores how cluster formation efficiency relates to star formation parameters.

Contribution

It provides detailed measurements of the cluster population, including luminosity and mass functions, and investigates their radial variation and implications for cluster formation theories.

Findings

Luminosity function follows a power law with index ~ -2 at lower luminosities.

Mass distribution shows a slight steepening with galactocentric distance.

Cluster formation efficiency correlates with surface density of star formation, not total star formation rate.

Abstract

We present results of a photometric study into the cluster population of NGC 1566, a nearby grand design spiral galaxy, sampled out to a Galactocentric radius of $\approx 5.5$ kpc. The shape of the mass-limited age distribution shows negligible variation with radial distance from the centre of the galaxy, and demonstrates three separate sections, with a steep beginning, flat middle and steep end. The luminosity function can be approximated by a power law at lower luminosities with evidence of a truncation at higher luminosity. The power law section of the luminosity function of the galaxy is best fitted by an index $\approx -2$, in agreement with other studies, and is found to agree with a model luminosity function, which uses an underlying Schechter mass function. The recovered power law slope of the mass distribution shows a slight steepening as a function of galactocentric distance, but this is within error estimates. It also displays a possible truncation at the high mass end. Additionally, the cluster formation efficiency ($\Gamma$) and the specific U-band luminosity of clusters ($T_L(U)$) are calculated for NGC 1566 and are consistent with values for similar galaxies. A difference in NGC 1566, however, is that the fairly high star formation rate is in contrast with a low $\Sigma_{SFR}$ and $\Gamma$, indicating that $\Gamma$ can only be said to depend strongly on $\Sigma_{SFR}$, not the star formation rate.