Probing the role of the galactic environment in the formation of stellar clusters, using M83 as a test bench

Abstract

We present a study of the M83 cluster population, covering the disc of the\ngalaxy between radii of 0.45 and 4.5 kpc. We aim to probe the properties of the\ncluster population as a function of distance from the galactic centre. We\nobserve a net decline in cluster formation efficiency ($\\Gamma$, i.e. the\namount of star formation happening in bound clusters) from about 26 % in the\ninner region to 8 % in the outer part of the galaxy. The recovered $\\Gamma$\nvalues within different regions of M83 follow the same $\\Gamma$ versus star\nformation rate density relation observed for entire galaxies. We also probe the\ninitial cluster mass function (ICMF) as a function of galactocentric distance.\nWe observe a significant steepening of the ICMF in the outer regions (from\n$-1.90\\pm0.11$ to $-2.70\\pm0.14$) and for the whole galactic cluster population\n(slope of $-2.18\\pm0.07$) of M83. We show that this change of slope reflects a\nmore fundamental change of the 'truncation mass' at the high-mass end of the\ndistribution. This can be modelled as a Schechter function of slope $-2$ with\nan exponential cut-off mass ($M_{\\rm c}$) that decreases significantly from the\ninner to the outer regions (from 4.00 to $0.25\\times 10^5$ M$_\\odot$) while the\ngalactic $M_{\\rm c}$ is $\\approx1.60\\times10^5$ M$_\\odot$. The trends in \\Gamma\nand ICMF are consistent with the observed radial decrease of the $\\Sigma({\\rm\nH}_2)$, hence in gas pressure. As gas pressure declines cluster formation\nbecomes less efficient. We conclude that the host galaxy environment appears to\nregulate 1) the fraction of stars locked in clusters; 2) the upper mass limit\nof the ICMF, consistently described by a near-universal slope $-2$ truncated at\nthe high-mass end.\n