Computer Science
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007hst..prop11236t&link_type=abstract
HST Proposal ID #11236. Cycle 16
Computer Science
Scientific paper
Lyman continuum photons produced in massive starbursts may have played a dominant role in the reionization of the Universe. Starbursts are important contributors to the ionizing metagalactic background at lower redshifts as well. However, their contribution to the background depends upon the fraction of ionizing radiation that escapes from the intrinsic opacity of galaxies below the Lyman limit. Current surveys suggest that the escape fraction is close to zero in most galaxies, even among young starbursts, but is large in 15-25% of them. Non-uniform escape fractions are expected as a result of violent events creating clear paths in small parts of galaxies. The number of galaxies observed with high escape fraction will result from the combination of the intrinsic number with clear lines of sight and their orientation with respect to the observer. We propose to measure the fraction of escaping Lyman continuum radiation in a large sample 47 of z~0.7 starbursts in the COSMOS field. These compact UV-lumnious galaxies are good analogs to high redshift LBGs. Using the SBC/PR130L we can quickly 1-4 orbits detect relative escape fractions f_LC/f_1500 of 25% or more. This will be the first measurement of the escape fraction in sources between z=1 and the local universe. We expect ~10 detections. Stacking will set limits of <4% on the relative escape fraction in the rest. We will correlate the LC detections with the properties of the galaxies. By targetting z~0.7 in COSMOS, we will have tremendous ancillary information on those sources. A non-detection in all sources would be significant 99% confidence. This would imply that QSOs provide the overwhelming majority of ionizing radtion at z<1, requiring substantial evolution in the processes within Lyman break galaxies which allow large escape fractions at high redshift.;
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