Kinematics, ages and metallicities of star clusters in NGC 1316: A 3-Gyr-old merger remnant

Abstract

We report on multi-object spectroscopy in the red spectral region of 37 candidate star clusters in an ∼8 × aarcmin2 field centred on the giant early-type radio galaxy NGC 1316 (Fornax A), the brightest galaxy in the Fornax cluster. Out of this sample, 24 targets are found to be genuine star clusters associated with NGC 1316, and 13 targets are Galactic foreground stars. For the star cluster sample, we measure a mean heliocentric velocity υhel = 1698 ± 46 km s-1 and a velocity dispersion σ = 227 ± 33 km s-1 within a galacto-centric radius of 24 kpc. Partly responsible for the velocity dispersion is a significant rotation in the star cluster system, with a mean velocity of ∼175 ± 70 km s-1 along a position angle of ∼6° ± 18°. Using the projected mass estimator and assuming isotropic orbits, the estimated total mass is (6.6 ± 1.V) × 1011 M⊙ within a radius of 24 kpc. The mass is uncertain by about a factor of 2, depending on the orbital assumptions. The implied M/LB ratio is in the range 3-6. Four star clusters in our sample are exceptionally luminous (MV