Spectroscopy of NGC 4258 Globular Cluster Candidates: Membership Confirmation and Kinematics

We present multiobject spectroscopic observations of 23 globular cluster candidates (GCCs) in the prototypical megamaser galaxy NGC 4258, carried out with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy instrument at the 10.4 m Gran Telescopio Canarias. The candidates have been selected based on the (u* − i′) versus (i′ − Ks) diagram, in the first application of the u*i′Ks method to a spiral galaxy. In the spectroscopy presented here, 70% of the candidates are confirmed as globular clusters (GCs). Our results validate the efficiency of the u*i′Ks method in the sparser GC systems of spirals, and given the downward correction to the total number of GCs, the agreement of the galaxy with the correlations between black hole mass and the total number and mass of GCs is actually improved. We find that the GCs, mostly metal-poor, corotate with the H i disk, even at large galactocentric distances.