A Deep Hubble Space Telescope Search for Escaping Lyman Continuum Flux at z ~ 1.3: Evidence for an Evolving Ionizing Emissivity

November 2010 • 2010ApJ...723..241S

Authors • Siana, Brian • Teplitz, Harry I. • Ferguson, Henry C. • Brown, Thomas M. • Giavalisco, Mauro • Dickinson, Mark • Chary, Ranga-Ram • de Mello, Duilia F. • Conselice, Christopher J. • Bridge, Carrie R. • Gardner, Jonathan P. • Colbert, James W. • Scarlata, Claudia

Abstract • We have obtained deep Hubble Space Telescope far-UV images of 15 starburst galaxies at z ~ 1.3 in the GOODS fields to search for escaping Lyman continuum (LyC) photons. These are the deepest far-UV images (m _AB = 28.7, 3σ, 1'' diameter) over this large an area (4.83 arcmin²) and provide some of the best escape fraction constraints for any galaxies at any redshift. We do not detect any individual galaxies, with 3σ limits to the LyC (~700 Å) flux 50-149 times fainter (in f _ν) than the rest-frame UV (1500 Å) continuum fluxes. Correcting for the mean intergalactic medium (IGM) attenuation (factor ~2), as well as an intrinsic stellar Lyman break (factor ~3), these limits translate to relative escape fraction limits of f _esc,rel < [0.03, 0.21]. The stacked limit is f _esc,rel(3σ) < 0.02. We use a Monte Carlo simulation to properly account for the expected distribution of line-of-sight IGM opacities. When including constraints from previous surveys at z ~ 1.3 we find that, at the 95% confidence level, no more than 8% of star-forming galaxies at z ~ 1.3 can have relative escape fractions greater than 0.50. Alternatively, if the majority of galaxies have low, but non-zero, escaping LyC, the escape fraction cannot be more than 0.04. In light of some evidence for strong LyC emission from UV-faint regions of Lyman break galaxies (LBGs) at z ~ 3, we also stack sub-regions of our galaxies with different surface brightnesses and detect no significant LyC flux at the f _esc,rel < 0.03 level. Both the stacked limits and the limits from the Monte Carlo simulation suggest that the average ionizing emissivity (relative to non-ionizing UV emissivity) at z ~ 1.3 is significantly lower than has been observed in LBGs at z ~ 3. If the ionizing emissivity of star-forming galaxies is in fact increasing with redshift, it would help to explain the high photoionization rates seen in the IGM at z>4 and reionization of the IGM at z>6.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 10872.

Links

• PREPRINT http://arxiv.org/abs/1001.3412
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2010ApJ...723..241S
• ELECTR https://doi.org/10.1088%2F0004-637X%2F723%2F1%2F241
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2010ApJ...723..241S
• PDF https://iopscience.iop.org/article/10.1088/0004-637X/723/1/241/pdf
• PDF https://stacks.iop.org/0004-637X/723/241/pdf
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2010ApJ...723..241S
• DATA https://hst.esac.esa.int/ehst/#/pages/search;bibcode=2010ApJ...723..241S
• DATA https://irsa.ipac.caltech.edu/bibdata/2010/S/2010ApJ...723..241S.html