The large scale structure of the universe

Citation

Picard, Alain (1991) The large scale structure of the universe. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/hv26-2889. https://resolver.caltech.edu/CaltechETD:etd-09172008-084234

Abstract

We present a catalogue of galaxies from COSMOS scans of 16 second epoch Palomar Observatory Sky Survey (POSS-II) plates. The surveys covers an area of 386 square degrees, and covers 150,000 galaxies in the magnitude range 16.5 ≤ r ≤ 19.0. The plates are divided into a north galactic (7 plates, α ≈ 15[superscript h]0[superscript m],δ ≈ +30°(1950.0), b ≈ 65°) and south galactic (9 plates, α ≈ 0[superscript h]20[superscript m], δ ≈ +5°(1950.0), b ≈ -55°) field.

The magnitude scale of each plate was brought to a common photometric system (Gunn r) using extensive CCD photometry. The total error in the zero point of the magnitude scale at the faint end is 0.06[superscript m].

The procedure for separating stars and galaxies is based on image parameters provided by the COSMOS machine and is completely objective. Visual tests indicate that the catalogue is 94% complete.

We have measured the angular correlation function of galaxies w(θ). The north field is in good agreement with the results of the APM survey. The south field exhibits more power on large scales than the north field. We have performed several tests to determine the effect of possible systematic errors between the two fields and do not find any effect sufficiently large to account for the south field's excess power. The measured correlation function for both fields are incompatible with the predictions of the currently most popular model, cold dark matter (CDM).

The number counts of galaxies in the two fields are substantially different. Several tests have been performed to make sure that the effect is not the result of a systematic error in zero point of the magnitude system or due to extinction or obscuration. The natural scale for structures which might be responsible for this difference is 50h[superscript -1] Mpc. We do not know if this difference is a rare event; more fields need to be surveyed to address this important question.

We have developed an objective algorithm for detecting clusters of galaxies from our galaxy catalogue. The algorithm is based on fixed overdensities at varying angular scales, and is well-suited to detecting clusters over a large range of redshifts. We present a catalogue of clusters based on this algorithm, using an overdensity threshold obtained from comparing the cluster's densities to each field's overall back-ground density. The results are very sensitive to the choice of background density. The multiplicity function of the objective clusters agree well when referenced to each field's background density, but disagree sharply when referenced to the overall mean density of the survey.

The objective catalogue is compared with that of Abell's. Poor agreement is found between the two catalogues. It is not possible to choose a set of parameters in our catalogue which reproduces Abell's catalogue well.

The measurement of the galaxy-cluster correlation function w[subscript g-cl](θ) is in good qualitative agreement with predictions of CDM, but more detailed comparisons with theory must wait for the acquisition of redshifts for a large fraction of the clusters.

At present, no theory is able to explain the amount of power on large scale observed in this survey.

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