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Globular clusters (GCs) can be considered discrete, long-lived, dynamical tracers that retain crucial information about the assembly history of their parent galaxy. In this paper, we present a new catalogue of GC velocities and colours for the lenticular galaxy NGC 1023, we study their kinematics and spatial distribution, in comparison with the underlying stellar kinematics and surface brightness profile, and we test a new method for studying GC properties. Specifically, we decompose the galaxy light into its spheroid (assumed to represent the bulge+halo components) and disc components and use it to assign to each GC a probability of belonging to one of the two components. Then we model the galaxy kinematics, assuming a disc and spheroidal component, using planetary nebulae and integrated stellar light. We use this kinematic model and the probability previously obtained from the photometry to recalculate for each GC its likelihood of being associated with the disc, the spheroid, or neither. We find that the reddest GCs are likely to be associated with the disc, as found for faint fuzzies in this same galaxy, suggesting that the disc of this S0 galaxy originated at z ∍ 2. The majority of blue GCs are found likely to be associated with the spheroidal (hot) component. The method also allows us to identify objects that are unlikely to be in equilibrium with the system. In NGC 1023 some of the rejected GCs form a substructure in phase space that is connected with NGC 1023 companion galaxy. [ABSTRACT FROM AUTHOR]

Establishing the reliability with which stellar population parameters can be measured is vital to extragalactic astronomy. Galactic globular clusters (GCs) provide an excellent medium in which to test the consistency of single stellar population (SSP) models as they should be our best analogue to a homogeneous (single) stellar population. Here we present age, metallicity and α-element abundance measurements for 48 Galactic GCs as determined from integrated spectra using Lick indices and SSP models from Thomas, Maraston & Korn, Lee & Worthey and Vazdekis et al. By comparing our new measurements to independent determinations we are able to assess the ability of these SSPs to derive consistent results – a key requirement before application to heterogeneous stellar populations like galaxies. We find that metallicity determinations are extremely robust, showing good agreement for all models examined here, including a range of enhancement methods. Ages and α-element abundances are accurate for a subset of our models, with the caveat that the range of these parameters in Galactic GCs is limited. We are able to show that the application of published Lick index response functions to models with fixed abundance ratios allows us to measure reasonable α-element abundances from a variety of models. We also examine the age–metallicity and [α/Fe]–metallicity relations predicted by SSP models, and characterize the possible effects of varied model horizontal branch morphology on our overall results. [ABSTRACT FROM AUTHOR]

We present radial stellar population parameters for a subsample of 12 galaxies from the 36 isolated early-type galaxies of Reda et al. Using new long-slit spectra, central values and radial gradients for the stellar age, metallicity [Z/H] and α-element abundance [E/Fe] are measured. Similarly, the central stellar population parameters are derived for a further five isolated early-type galaxies using their Lick indices from the literature. On average, the 17 isolated galaxies have mean central [Z/H]o and [E/Fe]o of 0.29 ± 0.03 and 0.17 ± 0.03, respectively, and span a wide range of ages from 1.7 to 15 Gyr. We find that isolated galaxies follow similar scaling relations between central stellar population parameters and galaxy velocity dispersion to their counterparts in high-density environments. However, we note a tendency for isolated galaxies to have slightly younger ages, higher metallicities and lower abundance ratios. Such properties are qualitatively consistent with the expectation of an extended star formation history for galaxies in lower density environments. Generally, we measure constant age and [E/Fe] radial gradients. However, three galaxies show remarkable positive age gradients and two galaxies have negative age gradients. We find that the age gradients anticorrelate with the central galaxy age. Thus as a young starburst evolves, the age gradient flattens from positive to almost zero. Metallicity gradients range from near zero to strongly negative. For our high-mass galaxies metallicity gradients are shallower with increasing mass. Such behaviour is not predicted in dissipational collapse models but might be expected in multiple mergers. The metallicity gradients are also found to be correlated with the central age and metallicity, as well as to the age gradients. In conclusion, our stellar population data for a sample of isolated early-type galaxies are more compatible with an extended merger/accretion history than early dissipative collapse. [ABSTRACT FROM AUTHOR]

We present the analysis of Lick absorption-line indices from three separate long-slit spectroscopic observations of the nearby isolated elliptical galaxy NGC 821. The three data sets present a consistent picture of the stellar population within one effective radius, in which strong gradients are evident in both luminosity-weighted age and metallicity. The central population exhibits a young age of ∼4 Gyr and a metallicity ∼3 times solar. At one effective radius the age has risen to ∼12 Gyr and the metallicity fallen to less than ∼1/3 times solar. The low-metallicity population around one effective radius appears to have an exclusively red horizontal branch (RHB), with no significant contribution from the blue horizontal branch evident in some globular clusters of the same age and metallicity. Despite the strong central age gradient, we demonstrate that only a small fraction (≤10 per cent) of the galaxy's stellar mass can have been created in recent star formation events. We consider possible star formation histories for NGC 821 and find that the most likely cause of the young central population was a minor merger or tidal interaction that caused NGC 821 to consume its own gas in a centrally concentrated burst of star formation 1–4 Gyr ago. [ABSTRACT FROM AUTHOR]