Statistics – Applications
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........12w&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF WATERLOO (CANADA), 1995.Source: Dissertation Abstracts International, Volume: 56-10, Section: B, p
Statistics
Applications
Distance Indicator, Surface Density, Globular Cluster, Galaxy
Scientific paper
This thesis presents a survey of the astronomical applications to which the method of brightness fluctuations may be applied. These applications include the use as an extragalactic distance indicator through surface brightness fluctuations (SBFs), and as a means to measure the surface density of globular clusters around very distant galaxies through single object fluctuations (SOFs). When examining the stellar halo component of a galaxy, SBFs can be used to either measure accurate distances to galaxies or, conversely, measure the apparent magnitude or colour of very narrow range of stellar populations. The former approach requires an accurate knowledge of the galaxy's halo stellar population luminosity function in order to estimate the galaxy's distance. The latter approach requires a distance to the galaxy to be already known together with accurate stellar isochrones in order to match the observed fluctuation stellar brightness with model predictions. Data taken in the Washington Photometric System, a system designed to measure stellar metallicities accurately, were used to derive a distance to the galaxy NGC 1379. The brightness fluctuation technique can be used to measure the total population of globular clusters around distant galaxies. The method relies on measuring fluctuations produced by faint unresolved globular clusters in the host galaxy, the amplitude of which depends on both the specific frequency and the luminosity function of the globular cluster system itself. This technique bypasses the need to obtain counts of globular clusters directly which must then be extrapolated past the limiting magnitude to obtain a total cluster population. Brightness fluctuations sample the integrated globular cluster counts up to ~ 3 magnitudes faintward of the photometric limit and thus provide an improved estimate of total cluster populations over direct counting techniques. The procedure to measure globular cluster brightness fluctuations is described using data of the galaxy M87 as an example and two discrepancies are seen. The results are ~10% less than the globular cluster surface density counts measured by direct identification using the very same data. Secondly, at very low fluctuation levels (i.e. cluster count levels) the small enhancement in surface density seen by McLaughlin et al. (1994) is not seen in the fluctuation results. Finally, the accuracy and reliability of the brightness fluctuation technique in measuring globular clusters in very distant galaxies was tested using simulations. Binning the M87 data by 2 x 2, 4 x 4, and 8 x 8 pixels was done to simulate M87 being 2, 4, and 8 times more distant. The results from the simulated data indicate that, for a galaxy like M87 rich in globular clusters, the SOF method can measure the globular cluster surface density to distances as far as 4 times that of M87 (~50 -60 Mpc) with +/-25% accuracy. The globular cluster surface density derived from the 8 x 8 binned data was significantly underestimated and indicates no useful globular cluster system information can be obtained using the fluctuation method. (Abstract shortened by UMI.).
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