Young clusters in M33 (Sharma et al.)

Vol. 534
In section 4. Extragalactic astronomy

The population of young stellar clusters throughout the disk of M33

The authors have identified 648 young stellar clusters in M33, with typical ages between 3 and 10 Myr, using Spitzer 24 micron images, as well as Hα and GALEX images to help exclude AGB stars. These young star clusters extend out to 12 kpc from the centre of the galaxy, which is about twice as far out as the bright star-forming disk. The clusters in the central region span a wide range of mass (10² < M < 3x10⁵ Msun) and luminosity (10³⁸ < L_bol < 3x10⁴¹ erg s^-1), while at galactocentric radii larger than ~4kpc there is a deficiency of massive clusters. Beyond 7kpc, predominantly low-mass clusters (M<10³ Msun) are found of slightly older age (>10Myr). This implies that about 10 Myr ago star formation was taking place as far out as 10-12kpc from the centre of M33.