Cluster kinematics and stellar rotation in NGC 419 with MUSE and adaptive optics

Abstract

We present adaptive optics (AO) assisted integral-field spectroscopy of the\nintermediate-age star cluster NGC 419 in the Small Magellanic Cloud. By\ninvestigating the cluster dynamics and the rotation properties of main sequence\nturn-off stars (MSTO), we demonstrate the power of AO-fed MUSE observations for\nthis class of objects. Based on 1 049 radial velocity measurements, we\ndetermine a dynamical cluster mass of 1.4+/-0.2x10^5 M_sun and a dynamical\nmass-to-light ratio of 0.67+/-0.08, marginally higher than simple stellar\npopulation predictions for a Kroupa initial mass function. A stacking analysis\nof spectra at both sides of the extended MSTO reveals significant rotational\nbroadening. Our analysis further provides tentative evidence that red MSTO\nstars rotate faster than their blue counterparts. We find average V sin i\nvalues of 87+/-16 km/s and 130+/-22 km/s for blue and red MSTO stars,\nrespectively. Potential systematic effects due to the low spectral resolution\nof MUSE can reach 30 km/s but the difference in V sin i between the populations\nis unlikely to be affected.\n