A test of the foreground proximity effect at z=1.2

Details A test of the foreground proximity effect at z=1.2 A test of the foreground proximity effect at z=1.2

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9877w&link_type=abstract

HST Proposal ID #9877

Mathematics

Logic

Hst Proposal Id #9877 Quasar Absorption Lines And Igm

Scientific paper

The diffuse UV background flux J is a crucial component for cosmological evolution models, though few determinations have been made. The prox- imity effect, the thinning out of the Lyman alpha forest near a sight- line's background quasar and explained at least partly by the enhanced ionization from the quasar, is a key method to measure J. A foreground proximity effect {FPE} should exist from quasars close on the sky but at different z; it can constrain J and test the enhanced ionization model. Galaxy clustering around the quasar may modify the effect, but knowing the galaxy density around the Lya forest should allow for corrections. We propose to measure the FPE at z=1.2, which is advantageous because 1} the diffuse UV flux is lower, and thus contrast with the UV flux of neighboring quasars is higher, and 2} galaxies are easier to identify at z=1.2. We have good knowledge of the physical volume we wish to study through surveys for quasars, MgII absorbers and galaxies, to constrain the redshift-dependent galaxy density along the line of sight. We will analyze the results based on pixel opacities, which is more sensitive to fluctuations in J than traditional line counting, and will compare our results with cosmological simulations to derive estimates of the UV background in the context of available physical models.

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