New Constraints on the Lyman Continuum Escape Fraction at z~1.3

October 2007 • 2007ApJ...668...62S

Authors • Siana, Brian • Teplitz, Harry I. • Colbert, James • Ferguson, Henry C. • Dickinson, Mark • Brown, Thomas M. • Conselice, Christopher J. • de Mello, Duilia F. • Gardner, Jonathan P. • Giavalisco, Mauro • Menanteau, Felipe

Abstract • We examine deep far-UV (1600 Å) imaging of the HDF-N and the HUDF to search for leaking Lyman continuum radiation from starburst galaxies at z~1.3. There are 21 (primarily sub-L^*) galaxies with spectroscopic redshifts between 1.1<z<1.5, and none are detected in the far-UV. We fit stellar population templates to the galaxies' optical/near-infrared SEDs to determine the starburst age and level of dust attenuation for each individual galaxy, giving a more accurate estimate of the intrinsic Lyman continuum ratio, f₁₅₀₀/f₇₀₀, and allowing a conversion from f₇₀₀ to relative escape fraction (f_esc,rel). We show that previous high-redshift studies may have underestimated the amplitude of the Lyman break, and thus the relative escape fraction, by a factor ~2. Once the starburst age and intergalactic H I absorption are accounted for, 18 galaxies in our sample have limits to the relative escape fraction, f_esc,rel<1.0 with some limits as low as f_esc,rel<0.10 and a stacked limit of f_esc,rel<0.08. This demonstrates, for the first time, that most sub-L^* galaxies at this redshift do not have large escape fractions. When combined with a similar study of more luminous galaxies at the same redshift, we show that, if all star-forming galaxies at z~1 have similar relative escape fractions, the value must be less than 0.14 (3 σ). We also show that less than 20% (3 σ) of star-forming galaxies at z~1 have relative escape fractions near unity. These limits contrast with the large escape fractions found at z~3 and suggest that the average escape fraction has decreased between z~3 and z~1.

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 programs 7410, 9478, and 10403 (as well as 6337 HDF-WFPC2, 7817 HDF-NICMOS, 9978, 10086 HUDF-ACS, 9803 HUDF-NICMOS).

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IPAC Authors
(alphabetical)

James Colbert

Associate Scientist

Harry Teplitz

Senior Scientist