Computer Science
Scientific paper
Jul 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009hst..prop12249z&link_type=abstract
HST Proposal ID #12249. Cycle 18
Computer Science
Scientific paper
In recent years, the number of quasars with clear sightlines to HeII Ly-alpha has more than tripled, enabling us to map IGM reionization between z=2.5-3.9. We propose COS/G140L spectroscopy for four quasars at z 3.5-3.9, as the brightest in the highest redshift range ever studied. We aim to probe the "penumbra" of the IGM's "dark ages" at the epoch of He II reionization, providing the longest trace yet of reionization history. The proposed quality COS spectra will reveal features of the patchy and rapidly evolving IGM helium ionization near this epoch; COS resolution may also reveal a predicted spectral signature that would establish the redshift of HeII reionization, disentangling the effects of damped absorption, associated absorbers, and proximity zones. The broad wavelength coverage of G140L will enable us to trace helium absorption all the way to the Lyman limit at 228*{1+z} A, and comparison of the four sightlines will unravel the effects of cosmic variance.Our proposed study of z>3.4 quasars complements ongoing COS GTO and GO programs for z<3.3, and will add enormously to our understanding of the fluctuations in the patchy HeII Ly-alpha IGM optical depth, the growth in opacity to higher redshifts, and may reveal the onset epoch/redshift of IGM HeII reionization. By analogy, our study of HeII reionization may also shed light on the morphology of hydrogen reionization between z 6-10.;
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