A Measurement of The Faint Source Correlation Function in the GOODS and UDF Survey

TL;DR

This paper introduces a method to measure the angular autocorrelation function of very faint, barely resolved sources in HST surveys, revealing new clustering behavior on subarcsecond scales that informs galaxy formation models.

Contribution

It presents a stable procedure for measuring the faint source correlation function and reports the first detection of correlation exceeding unity on subarcsecond scales.

Findings

Correlation function exceeds unity on subarcsecond scales

Correlation function follows a power law with index 2.5

Characteristic angular scale decreases with magnitude

Abstract

We present a stable procedure for defining and measuring the two point angular autocorrelation function, w, of faint (25 < V < 29), barely resolved and unresolved sources in the HST GOODS and UDF datasets. We construct catalogs that include close pairs and faint detections. We show for the first time that on subarcsecond scales, the correlation function exceeds unity. This correlation function is well fit by a power law with index of 2.5 and a characteristic angular scale that decrease slowly with magnitude. This is very different from the purely gravitationalcorrelation function of brighter galaxies which has a index of 0.7 and a characteristic angular scale which decreases quickly with magnitude. This observed clustering probably reflects the presence of giant star-forming regions within galactic-scale potential wells. Its measurement enables a new approach to measuring the redshift distribution of the faintest sources in the sky.