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[57.05] Discovery of the Galaxy Proximity Effect and Implications for the Intensity of the Ionizing Background Radiation

S. M. Pascarelle, K. M. Lanzetta (SUNY Stony Brook), H.-W. Chen (OCIW), J. K. Webb (University of New South Wales)

We present an analysis of galaxy and QSO absorption line pairs from 24 z\lesssim 1 QSO fields. We demonstrate the existence of a galaxy proximity effect, in that galaxies in the vicinity of QSOs do not show the same incidence and extent of gaseous envelopes as galaxies far from QSOs. We show that the scale over which the galaxy proximity effect exists lies within QSO-galaxy separations of <3000 km s^-1 rather than \lesssim 1000 km s^-1, i.e., it is comparable to the scale of the QSO ionizing radiation rather than the scale of galaxy clustering. Finally, we combine previous findings that (1) many or most Lyman-\alpha absorption lines arise in extended galaxy envelopes, and (2) galaxies are known to cluster around QSOs to show that the magnitude of the proximity effect has likely been underestimated. Consequently, determinations of the far-ultraviolet ionizing background intensity using the proximity effect may have been overestimated. We use the QSO-galaxy cross-correlation function from our galaxy sample to estimate the magnitude of this overestimate and find it could be as high as a factor of 20 at z\lesssim 1.