Specific Frequency Values Research Articles

The Globular Cluster System in the Outer Regions of NGC 4472

We have undertaken a study of the globular cluster (GC) systems of a large sample of elliptical and spiral galaxies in order to test specific predictions of galaxy formation models. Here we present results for the first elliptical in the study, the giant Virgo cluster galaxy NGC 4472 (M49). The galaxy was observed in three filters (BVR) using the wide-field Mosaic Imager on the Kitt Peak 4 m telescope. The Mosaic images roughly double the radial coverage of previous CCD observations of NGC 4472. We have combined the Mosaic data with published spectroscopic data and archival HST observations in order to study NGC 4472's GC system in detail, and to fully characterize the amount of contamination in our sample of GC candidates. We find that the radial profile of the GC system is fit fairly well by a de Vaucouleurs law of the form log σGC = (3.38 ± 0.08) - (1.56 ± 0.05) r1/4 out to 17' (~80 kpc), but that the observed profile falls slightly below the de Vaucouleurs law between 17' and 23', the limit of the data. The bimodal color distribution observed in previous studies is apparent in our data. We find a small metallicity gradient in the inner 8' of the total GC system due to the increasing ratio of blue to red clusters, consistent with results from past studies. The gradient vanishes, however, when the entire radial extent of the data is taken into account. We estimate a total of ~5900 GCs in NGC 4472 out to 23', yielding a specific frequency of 3.6 ± 0.6 within this radius. This specific frequency value is smaller than that found by previous studies of NGC 4472. We examine the implications of these results with regard to predictions made by four different galaxy formation models, and we find that all four models have at least one inconsistency with the data.

On the linear and nonlinear refractive index of F colour centres as a function of temperature

The linear and nonlinear refractive indices of alkali halide crystals containing F colour centres is considered. The refractive indices vary as a function of temperature and angular frequency. The linear and nonlinear indices are constants at a specific frequency value which seems to be very near the 0K resonance frequency of the F band.