Are the HDF Galaxy Counts Whole Numbers?

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  • 6 March 1996
Abstract
The Hubble Deep Field (HDF) offers the best view to date of the optical sky at faint magnitudes and small angular scales. Early reports suggested that faint source counts continue to rise to the completeness limit of the data. In this letter, we investigate the possibility that some of these sources are in fact giant H-II regions or merger fragments within the same galaxy, rather than individual galaxies. To test this hypothesis, we have created a catalog of objects in the Hubble Deep Field. From it, we derive the two point angular correlation function, number-magnitude relation, and magnitude-radius relation. The angular correlation function for all objects is consistent with that obtained from ground-based efforts. For objects with high color redshift (U-B > 2), however, the correlation amplitude increases by nearly an order of magnitude at 1". The magnitude-radius relation shows a significant clump at the small, faint end, with implied physical size below that expected for a fully-formed galaxy at z similar to 2. The number-magnitude relation shows increasing counts to the faintness limit with shallow power-law behavior, which combined with the number-radius relation, implies continuously increasing fragmentation toward high redshift.

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