Emission line galaxies in the SHARDS Hubble frontier fields. II. Limits on Lyman-continuum escape fractions of lensed emission line galaxies at redshifts 2<z<3.5

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We present an investigation of escape fractions of UV photons from a unique sample of lensed low-mass emission line–selected galaxies at z < 3.5 found in the SHARDS Hubble Frontier Fields medium-band survey. We have used this deep imaging survey to locate 42 relatively low-mass galaxies down to log (M_(*)/M_(ꙩ))= 7 in the redshift range 2.4 <z<3.5 that are candidate line emitters. Using deep multiband Hubble UVIS imaging, we investigate the flux of escaping ionizing photons from these systems, obtaining 1σ upper limits of f^(rel)_(esc) ∼ 7% for individual galaxies and <2% for stacked data. We measure potential escaping Lyman-continuum flux for two low-mass line emitters with values at f^(rel)_(esc) = 0.032^(+0.081)_(-0.009) and 0.021^(+0.101)_(-0.006), both detected at the ∼3.2σ level. A detailed analysis of possible contamination reveals a <0.1% probability that these detections result from line-of-sight contamination. The relatively low Lyman-continuum escape fraction limit and the low fraction of systems detected are an indication that low-mass line-emitting galaxies may not be as important a source of reionization as hoped if these are analogs of reionization sources. We also investigate the structures of our galaxy sample, finding no evidence for a correlation of escape fraction with asymmetric structure.
© 2022. The Author(s). Artículo firmado por 13 autores. We thank the referee for comments that significantly improved the presentation of this paper. This work was supported by the Science and Technology Facilities Council in the form of a studentship to A.G. We also acknowledge support from the ERC Advanced Investigator Grant EPOCHS (788113). L.F. acknowledges funding from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. D.C. is a Ramon-Cajal Researcher and is supported by the Ministerio de Ciencia, Innovación y Universidades (MICIU/FEDER) under research grant PGC2018-094975-C21. L.R.-M. acknowledges the support from grant PRIN MIUR2017-20173ML3WW_001, and D.R.G. thanks CONACyT for research grant CB-A1-S-22784. This paper is (partly) based on SHARDS-FF data. SHARDS-FF is currently funded by Spanish Government grant PGC2018-093499-BI00. Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma. This work is also based partially on data and catalog products from HFF-DeepSpace, funded by the National Science Foundation and Space Telescope Science Institute (operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555). Software: galclean (Ferreira et al. 2018), astropy (Astropy Collaboration et al. 2013), FAST (Kriek et al. 2009), Scipy +Numpy (Virtanen et al. 2020), EAZY (Brammer et al. 2008), OSIRIS pipeline (Pérez-González et al. 2013).
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