On the heterogeneity of metal-line and Lyα absorption in galaxy halos at z∼0.7

We examine the properties of two galaxy '' halos '' at z similar to 0: 7 in the Ton 153 (Z(em) = 1: 01) quasar field. The first absorber-galaxy pair ( G1) is a z = 0: 672, L-B = 4: 3L(B)(*), E/ S0 galaxy probed at D = 58 kpc. G1 is associated with a remarkable five-component Ly alpha complex having tau LL <= 0: 4, W-r( Ly alpha) = 2: 8 angstrom, and a velocity spread of Delta v = 1420 km s(-1). We find no Mg II, C IV, N V, nor O VI absorption in these clouds and infer metallicity upper limits of - 3 <= log Z/Z circle dot <= - 1, depending on assumptions of photoionized or collisionally ionized gas. The second absorber-galaxy pair (G2) is a z = 0: 661, L-B = 1: 8L(B)(*), Sab galaxy probed at D = 103 kpc. G2 is associated with metal- enriched (log Z/Z circle dot similar or equal to -0: 4) photoionized gas having N(HI) similar or equal to 18: 3 (cm (-2)) and a velocity spread of Delta v = 200 km s(-1). The very different G1 and G2 systems both have gas-galaxy properties inconsistent with the standard luminosity-dependent galaxy halo model commonly invoked for quasar absorption line surveys. We emphasize that mounting evidence is revealing that extended galactic gaseous envelopes in the regime of D <= 100 kpc do not exhibit a level of homogeneity supporting a standardized halo model. Selection effects may have played a central role in the development of a simple model. We discuss the G1 and G2 systems in the context of Lambda CDM models of galaxy formation and suggest that the heterogeneous properties of absorber-galaxy pairs is likely related to the range of overdensities from which galaxies and gas structures arise.