A bottom-up search for Lyman-continuum leakage in the Hubble Ultra Deep Field

Abstract

Context: Studies of the production and escape of Lyman Continuum from galaxies often rely on array of indirect observational tracers in preselection of candidate leakers. Aims: Here, we investigate how much ionizing radiation might be missed due to these selection criteria by completely removing them and performing a search selected purely from rest-frame LyC emission; and how that affects our estimates of the ionizing background. Methods: We invert the conventional method and perform a bottom-up search for Lyman-continuum leaking galaxies at redshifts $2<z<3.5$. Using archival data from HST and VLT/MUSE, we run source finding software on UV-filter HST images from the HUDF, and subject all detected sources to a series of tests to eliminate those that are inconsistent with being ionizing sources. Results: We find 6 new and one previously identified candidate leakers with absolute escape fractions ranging from 36% to 100%. Our filtering criteria eliminate one object previously reported as a candidate ionizing emitter in the literature, while we report non-detection in the rest frame Lyman continuum of two other previously reported sources. We find that our candidates make a contribution to the metagalactic ionizing field of ${\log }_{10}({\epsilon }_{\nu })=25.32(+0.25)(-0.21)$ and $25.29(+0.27)(-0.22)$ erg/s/Hz/cMpc${}^3$ for the full set of candidates and for the 4 strongest candidates only; both values are higher than but consistent with other recent figures in the literature. Conclusions: Our findings suggest that galaxies that do not meet the usual selection criteria may make a non-negligible contribution to the cosmic ionizing field. We recommend that similar searches be carried out on a larger scale in well-studied fields with both UV and large ancillary data coverage, for example in the full set of CANDELS fields.

22 pages, 8 tables, 12 figures. This is the version accepted for publication in A&A. Contains only minor edits from v1

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• The Lyman-alpha and Continuum Origins Survey II: the connection between the escape of ionizing radiation and Lyman-alpha halos in star-forming galaxies
• Photometric IGM tomography with Subaru/HSC: the large-scale structure of Ly$\alpha$ emitters and IGM transmission in the COSMOS field at $z\sim 5$
• A Lyman continuum analysis for $\sim 100$ galaxies at $z_{\text{spec}}\sim 3$ in the Abell 2744 Cluster Field
• Lyman Continuum escaping from in-situ formed stars in a tidal bridge at z = 3