The Size and Pervasiveness of Ly$alpha$-UV Spatial Offsets in Star-Forming Galaxies at $zsim6$. (arXiv:2007.01310v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lemaux_B/0/1/0/all/0/1">B. C. Lemaux</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fuller_S/0/1/0/all/0/1">S. Fuller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bradac_M/0/1/0/all/0/1">M. Bradač</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pentericci_L/0/1/0/all/0/1">L. Pentericci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hoag_A/0/1/0/all/0/1">A. Hoag</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Strait_V/0/1/0/all/0/1">V. Strait</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Treu_T/0/1/0/all/0/1">T. Treu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alvarez_C/0/1/0/all/0/1">C. Alvarez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bolan_P/0/1/0/all/0/1">P. Bolan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gandhi_P/0/1/0/all/0/1">P. J. Gandhi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jones_T/0/1/0/all/0/1">T. Jones</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mason_C/0/1/0/all/0/1">C. Mason</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pelliccia_D/0/1/0/all/0/1">D. Pelliccia</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ribeiro_B/0/1/0/all/0/1">B. Ribeiro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ryan_R/0/1/0/all/0/1">R. E. Ryan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schmidt_K/0/1/0/all/0/1">K. B. Schmidt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vanzella_E/0/1/0/all/0/1">E. Vanzella</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Khusanova_Y/0/1/0/all/0/1">Y. Khusanova</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fevre_O/0/1/0/all/0/1">O. Le Fèvre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guaita_L/0/1/0/all/0/1">L. Guaita</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hathi_N/0/1/0/all/0/1">N. P. Hathi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koekemoer_A/0/1/0/all/0/1">A. Koekemoer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pforr_J/0/1/0/all/0/1">J. Pforr</a>
We study the projected spatial offset between the ultraviolet continuum and
Ly$alpha$ emission for a sample of 65 lensed and unlensed galaxies in the
Epoch of Reionization (5<z<7), 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
($|Delta_{Lyalpha-UV}|$), 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 $|Delta_{Lyalpha-UV}|$ 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$0.05
kpc, respectively. We argue that offsets are likely not the result of merging
processes, but are rather due to anisotropic internal processes internal to the
galaxies as a result of stellar feedback, which facilitates Ly$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 $le$1” were employed, such as those
planned for James Webb Space Telescope/NIRSpec observations. (abridged)
We study the projected spatial offset between the ultraviolet continuum and
Ly$alpha$ emission for a sample of 65 lensed and unlensed galaxies in the
Epoch of Reionization (5<z<7), 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
($|Delta_{Lyalpha-UV}|$), 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 $|Delta_{Lyalpha-UV}|$ 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$0.05
kpc, respectively. We argue that offsets are likely not the result of merging
processes, but are rather due to anisotropic internal processes internal to the
galaxies as a result of stellar feedback, which facilitates Ly$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 $le$1” were employed, such as those
planned for James Webb Space Telescope/NIRSpec observations. (abridged)
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