The Effect of Surface Brightness Dimming in the Selection of High-z Galaxies

TL;DR

This study investigates how surface brightness dimming affects the detection of high-redshift galaxies, revealing that most high-z galaxies likely have compact UV emission regions, which impacts galaxy selection biases.

Contribution

The paper provides empirical analysis of surface brightness dimming effects on high-z galaxy detection using HST data, highlighting the compactness of UV emission in these galaxies.

Findings

No significant trend in total magnitudes across different survey depths.

Most high-z galaxies have a compact UV emission profile.

Surface brightness dimming does not significantly bias high-z galaxy detection.

Abstract

Cosmological surface brightness dimming of the form $(1+z)^{-4}$ affects all sources. The strong dependence of surface brightness dimming on redshift z suggests the presence of a selection bias when searching for high-redshift galaxies, i.e. we tend to detect only those galaxies with a high surface brightness (SB). However, unresolved knots of emission are not affected by SB dimming, thus providing a way to test the clumpiness of high-z galaxies. Our strategy relies on the comparison of the total flux detected for the same source in surveys characterized by different depth. For all galaxies, deeper images permit the better investigation of low-SB features. Cosmological SB dimming makes these low-SB features hard to detect when going to higher and higher redshifts. We used the GOODS and HUDF Hubble Space Telescope legacy datasets to study the effect of SB dimming on low-SB features of high-redshift galaxies and compare it to the prediction for smooth sources. We selected a sample of Lyman-break galaxies at z~4 (i.e. B-band dropouts) detected in all of the datasets and found no significant trend when comparing the total magnitudes measured from images with different depth. Through Monte Carlo simulations we derived the expected trend for galaxies with different SB profiles. The comparison to the datahints at a compact distribution for most of the rest-frame ultraviolet light emitted from high-z galaxies.