A DIRECT MEASUREMENT OF THE INTERGALACTIC MEDIUM OPACITY TO H I IONIZING PHOTONS

Journal Article · Tue Nov 10 04:00:00 EST 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/705/2/L113· OSTI ID:21378339

Prochaska, J Xavier; Worseck, Gabor ^[1]; O'Meara, John M ^[2]

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1. Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
2. Department of Chemistry and Physics, Saint Michael's College, One Winooski Park, Colchester, VT 05439 (United States)

We present a new method to directly measure the opacity from H I Lyman limit (LL) absorption kappa{sub LL} along quasar sight lines by the intergalactic medium (IGM). The approach analyzes the average ('stacked') spectrum of an ensemble of quasars at a common redshift to infer the mean free path lambda{sup 912}{sub mfp} to ionizing radiation. We apply this technique to 1800 quasars at z = 3.50-4.34 drawn from the Sloan Digital Sky Survey (SDSS), giving the most precise measurements on kappa{sub LL} at any redshift. From z = 3.6 to 4.3, the opacity increases steadily as expected and is well parameterized by lambda{sup 912}{sub mfp} = lambda{sub 0} - b {sub l}ambda(z - 3.6) with lambda{sub 0} = (48.4 +- 2.1) h{sup -1}{sub 72} Mpc and b{sub l}ambda = (38.0 +- 5.3) h {sup -1}{sub 72} Mpc (proper distance). The relatively high lambda{sup 912} {sub mfp} values indicate that the incidence of systems which dominate kappa{sub LL} evolves less strongly at z > 3 than that of the Lyalpha forest. We infer a mean free path three times higher than some previous estimates, a result which has important implications for the photoionization rate derived from the emissivity of star-forming galaxies and quasars. Finally, our analysis reveals a previously unreported, systematic bias in the SDSS quasar sample related to the survey's color targeting criteria. This bias potentially affects all z approx 3 IGM studies using the SDSS database.

• OSTI ID: 21378339
• Journal Information: Astrophysical Journal (Online), Journal Name: Astrophysical Journal (Online) Journal Issue: 2 Vol. 705; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
BOSONS
COLOR
COSMIC RADIO SOURCES
ELEMENTARY PARTICLES
EMISSIVITY
GALAXIES
IONIZATION
IONIZING RADIATIONS
MASSLESS PARTICLES
MEAN FREE PATH
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHOTOIONIZATION
PHOTONS
PHYSICAL PROPERTIES
QUASARS
RADIATIONS
RED SHIFT
SORPTION
STARS
SURFACE PROPERTIES
UNIVERSE