Keck spectroscopy and imaging of globular clusters in the lenticular galaxy NGC 524

We have obtained Keck Low-Resolution Imaging Spectrometer imaging and spectra for 29 globular clusters associated with the lenticular galaxy NGC 524. Using the empirical calibration of Brodie & Huchra we find that our spectroscopic sample spans a metallicity range of −2.0 ≤[Fe/H]≤ 0 . We have compared the composite spectrum of the metal-poor ([Fe/H] < −1) and metal-rich clusters with stellar population models in order to estimate the ages of the NGC 524 globular clusters. We conclude that the clusters are generally old, and are coeval at the 2σ confidence level. To determine the mean [α/Fe] ratios of the globular clusters, we have employed the Milone et al. α-enhanced stellar population models. We verified the reliability of these models by comparing them with high signal-to-noise Galactic globular cluster spectra. We observe a weak trend of decreasing [α/Fe] ratios with increasing metallicity in the NGC 524 clusters; the metal-poor clusters possess [α/Fe]∼0.3, whilst the metal-rich clusters exhibit [α/Fe] ratios closer to solar-scaled values. Analysis of the cluster system kinematics reveals that the full sample (excluding an outlying cluster) exhibits a rotation of 114 ± 60 km s−1 around a position angle of 22°± 27° , and a velocity dispersion of 186 ± 29 km s−1 at a mean radius of 89 arcsec from the galaxy centre. Subdividing the clusters into metal-poor and metal-rich subcomponents (at [Fe/H]=−1.0 ), we find that the metal-poor (17) clusters and metal-rich (11) clusters have similar velocity dispersions ( 197 ± 40 and 169 ± 47 km s−1 , respectively). However, the metal-poor clusters dominate the rotation in our sample with 147 ± 75 km s−1 , whilst the metal-rich clusters show no significant rotation (68 ± 84 km s−1) . We derive a virial and projected mass estimation for NGC 524 of between 4 and 13 × 1011 M⊙ (depending on the assumed orbital distribution) interior to ∼2 effective radii of this galaxy.