Are Hubble Deep Field Galaxy Counts Whole Numbers?

Abstract

We compute the two-point angular correlation function and number-magnitude relation of Hubble Deep Field sources in order to assess their nature. We find that the correlation peaks between 0.25 arcsec and 0.4 arcsec with amplitude of 2 or greater, and much more for the smallest objects. This angular scale corresponds to physical scales of order 1 kpc for redshifts z > 1. The correlation must therefore derive from objects with subgalaxian separations. At faint magnitudes, the counts satisfy the relation Number prop. to 1/flux, expected for images which are subdivisions of larger ones. A conservative conjecture may explain these results. Since high redshift space (z > 0.5) dominates the volume of the sample, observational redshift effects are important. The K-correction and surface brightness dimming of diffuse sources enhances the prominence of compact, unresolved, UV-bright objects, such as star-forming regions within normal gas-rich galaxies. If such regions appear as individual sources, they could explain the subgalaxian correlation.Comment: accepted by ApJL, AASTeX 4.0 preprint style, 2 PostScript figures, Replacing astro-ph/9603020 (major modification: improved detection alg.

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“…), and be counted as several distinct faint sources. As suggested by Colley et al (1996) in this case strong correlations between sources on scales < 10 kpc should be found. A good test is therefore the two-point angular correlation function.…”

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“…The "true" (corrected) number of galaxies in each bin is N =cn, where n is the raw number of detections Abraham et al 1996) and a large number of galaxies display asymmetry and multiple structure. Colley et al (1996) stressed that compact high-redshift objects may appear more prominently than diffuse objects if their angular size is smaller than the point-spread function (PSF). The cosmological dimming in surface brightness for these sources is less significant, leading to an enhancement of compact sources over diffuse, resolved objects.…”

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A Review of High-Redshift Merger Observations

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