SIMBAD references

We report a new Fabry-Perot search for Hα emission from the intergalactic cloud H I 1225+01 in an attempt to measure the low-redshift ionizing background radiation. We set a new 2 σ upper limit on Hα emission of 8 mR (5x10^–20 ergs cm^–2.s^–1.arcsec^–2). Conversion of this limit to limits on the strength of the ionizing background requires knowledge of the ratio of the projected to total surface area of this cloud, which is uncertain. We discuss the plausible range of this ratio and within this range find that the strength of the ionizing background is in the lower range of, but consistent with, previous observational and theoretical estimates.