New Constraints on the Lyman Continuum Escape Fraction at z similar to 1.3 super(1)

We examine deep far-UV (1600 AA) imaging of the HDF-N and the HUDF to search for leaking Lyman continuum radiation from starburst galaxies at z similar to 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, integral of sub(1500)/ integral of sub(700), and allowing a conversion from integral of sub(700) to relative escape fraction ( [unk]). 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 similar to 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, [unk] < 1.0 with some limits as low as [unk] < 0.10 and a stacked limit of [unk] < 0.08. This demonstrates, for the first time, that most sub-L [unk] 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 similar to 1 have similar relative escape fractions, the value must be less than 0.14 (3 sigma ). We also show that less than 20% (3 sigma ) of star-forming galaxies at z similar to 1 have relative escape fractions near unity. These limits contrast with the large escape fractions found at z similar to 3 and suggest that the average escape fraction has decreased between z similar to 3 and z similar to 1.