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The Lyman Alpha Reference Sample XII. Morphology of extended Lyman alpha emission in star-forming galaxies
Journal article   Open access   Peer reviewed

The Lyman Alpha Reference Sample XII. Morphology of extended Lyman alpha emission in star-forming galaxies

Armin Rasekh, Jens Melinder, Göran Östlin, Matthew J. Hayes, E. C. Herenz, Axel Runnholm, D. Kunth, J. M. Mas Hesse, A. Verhamme and J. M. Cannon
Astronomy and astrophysics (Berlin), Vol.662, p.A64
06/01/2022
DOI: 10.1051/0004-6361/202140734
url
https://doi.org/10.1051/0004-6361/202140734View
Published (Version of record) Open Access

Abstract

Aims.  We use  Hubble  Space Telescope data of 45 nearby star-forming galaxies to investigate properties of Lyman-alpha (Ly α ) halos, Ly α  morphology, and the star-forming characteristics of galaxies. We study how the morphology of Ly α  emission is related to other Ly α  observables. Furthermore, we study the interdependencies of Ly α  morphological quantities. Methods.  We studied the spatial extent of Ly α  using surface brightness profiles in the following two ways (i) using circular apertures and (ii) within faint Ly α  isophotes. We also measured the average intensity and the size of the regions with a high star formation rate density. The morphology of the galaxies was quantified by computing centroid position, axis ratio, and position angle in the Ly α , ultraviolet continuum, and  I  band maps. Results.  We found that galaxies with more extended star-forming regions possess larger Ly α  halos. Furthermore, galaxies with more elongated Ly α  morphology are also more extended in Ly α . Our data suggest that Ly α  bright galaxies appear rounder in their Ly α  morphology, and there is less of a contribution from their Ly α  halo to their overall luminosity. We compared our results with studies at high redshift and found that whilst the Ly α  extent in the inner regions of the galaxies in our sample are similar to the high- z  Ly α  emitters (LAEs), Ly α  halos are more extended in high- z  LAEs. Conclusions.  Our analysis suggests that the Ly α  morphology affects the measurement of other observable quantities concerning Ly α  emission, and some of the conclusions drawn from high redshift LAEs might be biased towards galaxies with specific Ly α  shapes. In particular, faint Ly α  emitters have larger Ly α  scale lengths and halo fractions. This implies that faint Ly α  emitters are harder to detect at high redshift than previously believed.
 evolution Galaxy halo structure

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