Use of an Automated Photographic Object Detection System to Analyse the Effect of Magnitude on the Angular Correlation Function of Galaxies

Author: Sebok, William Lawrence

Year: 1982

Degree: Dissertation (Ph.D.)

Advisor: Oke, J. Beverley

Committee Members: Oke, J. Beverly; Gunn, James E.; Young, Peter J.; Lo, Kwok-Yung

Option: Astronomy

DOI: 10.7907/179j-3364

Abstract

An automated system is created which scans photographic plates, locating, measuring, and identifying the objects on these plates. Four deep red sensitive plates from the Palomar 1.2 m. telescope are examined with this system. The objects classified as galaxies are divided into subcatalogs of different apparent magnitudes. The angular correlation function w(θ) (a measure of how galaxies cluster) is computed for each subcatalog for galaxy separations between 18" and 4'32". This enables an analysis of the behavior of the angular correlation function with changing apparent magnitude.

The slope of log correlation function versus log angle, for galaxies 16 < mr < 20.5, is measured to be -1.23 ± 0.18, with a hint of higher negative slopes at fainter magnitudes. This is inconsistent at the 2σ level with the standard slope of -0.8, but may be possible if the slope is a function of magnitude or an effect of the smaller angular size (~ 1 arc. min.) used here.

The slope of the log correlation function as a function of magnitude is most consistent with the slope of the log correlation function as a function of angle for bright galaxies being about -1.1, consistent with the above result.

If this slope is -0.8, then moderate to strong correlation function evolution is favored. If the slope of the log correlation function versus angle is higher then less correlation function evolution is needed.

If the slope is allowed to float to its preferred higher value, then amount of correlation function evolution cannot be distinguished.

No luminosity or color evolution is included in the models, but the models have no trouble fitting the data without it.

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