Paper

The Size and Pervasiveness of Ly\\(\\alpha\\)-UV Spatial Offsets in Star-Forming Galaxies at \\(z\\sim6\\)

Vanzella, E, Hathi, N P, Pforr, J, Ribeiro, B, Khusanova, Y, Alvarez, C, Pelliccia, D, Strait, V, Bolan, P, Bradač, M, Ryan, R E, Guaita, L, Jones, T, Pentericci, L, Treu, T, Schmidt, K B, Lemaux, B C, Hoag, A, Mason, C, Fuller, S, O Le Fèvre, Koekemoer, A, Gandhi, P J

2021

Overview

We study the projected spatial offset between the ultraviolet continuum and Ly\\(\\alpha\\) emission for 65 lensed and unlensed galaxies in the Epoch of Reionization (\\(5\\leq z\\leq7\\)), the first such study at these redshifts, in order to understand the potential for these offsets to confuse estimates of the Ly\\(\\alpha\\) properties of galaxies observed in slit spectroscopy. While we find that ~40% of galaxies in our sample show significant projected spatial offsets (\\(|\\Delta_{Ly\\alpha-UV}|\\)), we find a modest average offset of 0.61\\(\\pm\\)0.08 kpc. A small fraction of our sample, ~10%, exhibits offsets of 2-4 kpc, sizes that are larger than the effective radii of typical galaxies at these redshifts. An internal comparison and a comparison to studies at lower redshift yielded no significant evidence of evolution of \\(|\\Delta_{Ly\\alpha-UV}|\\) with redshift. In our own sample, UV-bright galaxies showed offsets a factor of three greater than their fainter counterparts, 0.89\\(\\pm\\)0.18 vs. 0.27\\(\\pm\\)0.05 kpc, respectively. We argue that offsets are likely not the result of merging processes, but are rather due to internal anisotropic processes resulting from stellar feedback facilitates Ly\\(\\alpha\\) fluorescence and/or backscattering from nearby or outflowing gas. The reduction in the Ly\\(\\alpha\\) flux due to offset effects for various observational setups was quantified through mock observations of simple simulations. It was found that the loss of Ly\\(\\alpha\\) photons for galaxies with average offsets is not, if corrected for, a limiting factor for all but the narrowest slit widths (<0.4''). However, for the largest offsets, if such offsets are mostly perpendicular to the slit major axis, slit losses were found to be extremely severe in cases where slit widths of \\(\\leq\\)1'' were employed, such as those planned for James Webb Space Telescope/NIRSpec observations. (abridged)

• Publisher: Cornell University Library, arXiv.org
• Subject: Backscattering / Fluorescence / Galaxies / Ionization / James Webb Space Telescope / Offsets / Red shift / Space telescopes / Star formation