Are Lyman-alpha clouds associated with low surface brightness galaxies?

We have searched for low surface brightness (LSB)galaxies near the line of sight to QSO 3C 273 in two mosaic images covering a maximum area of 53' x 52' on the sky down to a limiting central surface brightness of 26.4 (in Gunn r). From trials to detect simulated LSB galaxies of various sizes and appearances, we conclude that known types of such objects cannot be causing the two absorption lines at the lowest redshifts (cz = 1012 km s(-1) and cz = 1582 km s(-1)) if within 106 h(75)(-1) kpc and 164 h(75)(-1) kpc, respectively, of the line of 75 sight. If galaxies are responsible for these two clouds, they must be either fainter than our detection limits or lie beyond the edges of our images. Galaxies close in velocity to one or the other of the two absorption systems occurring out to at least 1.1 h(75)(-1) Mpc (projected transverse separation) are found from the literature. 75 We find mounting evidence that many Ly alpha absorption systems are tracing the same large-scale structures as galaxies although it is not clear whether in the majority of cases there is a physical connection between absorbers and galaxies other than association in redshift. Coherent absorption on Mpc scales is unlikely to be associated with a single galaxy.