Galaxy Alignments in the Pisces-Perseus Supercluster

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Session 62 -- Large Scale Structures
Display presentation, Thursday, 2, 1994, 10:00-11:30

[62.08] Galaxy Alignments in the Pisces-Perseus Supercluster

J.E.Cabanela (U Minn), G.Aldering (U Minn)

We describe the early stages of our investigation into possible mechanisms influencing galaxy orientations using position angles and inclinations for a sample of $\sim500$ spiral galaxies located in the Pisces-Perseus supercluster. Our data consists of digitized scans of POSS I blue and red plates obtained with the Automated Plate Scanner (APS). With these data, we investigate whether there is a preferred galaxy orientation with respect to the major axis of the Pisces-Perseus supercluster, as might be expected if this structure formed from a Zeldovich pancake. If instead, galaxy orientation is influenced by the tidal field due to nearby neighbors, we might find a preference for a galaxy's major-axis to point towards it's nearest massive neighbor. N-body simulations for bottom-up scenarios indicate that tidally induced alignments can survive the process of galaxy formation at a weak, but detectable, level.

Previous work in the Local Supercluster and in Pisces-Perseus indicates that the signal for large-scale alignments is weak, if present at all. The expected subtleness of any alignment demands that we eliminate all sources of bias. To this end, we determine galaxy orientations from ellipse fits to the outer isophotes of our digitized scans. Work by Kashikawa and Okamura (1992) demonstrates that isophotal ellipse-fitting to digital images not only gives orientations of higher precision, but is less susceptable to bias. Moreover, the large APS database will allow us to determine the signal due to chance alignments and systematic errors using unassociated galaxies in the field. By minimizing sources of bias in the measured orientations, and using a sample some five times larger, we expect to significantly improve on the ambiguous results obtained by Flin (1988) in his study of alignments in Pisces-Perseus.

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