Astronomy
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Item The Tully-Fisher Relation for Low Surface Brightness Galaxies - Implications for Galaxy Evolution(Blackwell, 1995) Zwaan, M. A.; van der Hulst, J. M.; de Blok, W. J. G.; McGaugh, S. S.Item HI Observations of Low Surface Brightness Galaxies: Probing Low Density Galaxies(Blackwell, 1996) de Blok, W.J.G.; McGaugh, S.S.; van der Hulst, J.M.We present Very Large Array (vla) and Westerbork Synthesis Radio Telescope (wsrt) 21-cm Hi observations of 19 late-type low surface brightness (LSB) galaxies. Our main findings are that these galaxies, as well as having low surface brightnesses, have low Hi surface densities, about a factor of ~ 3 lower than in normal late-type galaxies. We show that LSB galaxies in some respects resemble the outer parts of late-type normal galaxies, but may be less evolved. LSB galaxies are more gas-rich than their high surface brightness counterparts. The rotation curves of LSB galaxies rise more slowly than those of HSB galaxies of the same luminosity, with amplitudes between 50 and 120 km s−1, and are often still increasing at the outermost measured point. The shape of the rotation curves suggests that LSB galaxies have low matter surface densities. We use the average total mass surface density of a galaxy as a measure for the evolutionary state, and show that LSB galaxies are among the least compact, least evolved galaxies. We show that both MHI/LB and Mdyn/LB depend strongly on central surface brightness, consistent with the surface brightness–mass-to-light ratio relation required by the Tully-Fisher relation. LSB galaxies are therefore slowly evolving galaxies, and may well be low surface density systems in all respects.Item The Dark and Baryonic Matter Content of Low Surface Brightness Galaxies(Blackwell, 1997) de Blok, W.J.G.; McGaugh, S.S.We present mass models of a sample of 19 low surface brightness (LSB) galaxies and compare the properties of their constituent mass components with those of a sample of high surface brightness (HSB) galaxies. We find that LSB galaxies are dark matter dominated. Their halo parameters are only slightly affected by assumptions on stellar mass-to-light ratios. Comparing LSB and HSB galaxies we find that mass models derived using the maximum disk hypothesis result in the disks of LSB galaxies having systematically higher stellar mass-to-light ratios than HSB galaxies of similar rotation velocity. This is inconsistent with all other available evidence on the evolution of LSB galaxies. We argue therefore that the maximum disk hypothesis does not provide a representative description of the LSB galaxies and their evolution. Mass models with stellar mass-to-light ratios determined by the colors and stellar velocity dispersions of galactic disks imply that LSB galaxies have dark matter halos that are more extended and less dense than those of HSB galaxies. Surface brightness is thus related to the halo properties. LSB galaxies are slowly evolving, low density and dark matter dominated galaxies.Item The Number, Luminosity, and Mass Density of Spiral Galaxies as a Function of Surface Brightness(Blackwell, 1996) McGaugh, Stacy S.Item Stellar Populations in Shell Galaxies(Copyright: American Astronomical Society, 1990-10) McGaugh, Stacy S.; Bothun, Gregory D.Item A Catalog of Low Surface Brightness Galaxies: List II(Copyright American Astronomical Society, 1992-04) SCHOMBERT, JAMES M.; BOTHUN, GREGORY D.; SCHNEIDER, STEPHEN E.; MCGAUGH, STACY S.Item Star Formation Thresholds in Low Surface Brightness Galaxies(Copyright: American Astronomical Society, 1993-08) VAN DER HULST, J. M.; SKILLMAN, E. D.; SMITH, T. R.; BOTHUN, G. D.; MCGAUGH, S. S.; DE BLOK, W. J. G.Item From Sir Isaac Newton to the Sloan survey: calculating the structure and chaos owing to gravity in the universe(Copyright: SIAM, 1997-01) Lake, George; Quinn, Thomas; Richardson, Derek C.Item Cross talk in 1872 Reticon diode arrays(University of Chicago Press, 1990) Walker, G. A. H.; Johnson, R.; Richardson, D.; Campbell, B.; Irwin, A. W.; Yang, S.Item 1620 GEOGRAPHOS AND 433 EROS: SHAPED BY PLANETARY TIDES?(University of Chicago Press, 1999) BOTTKE, W. F. JR.; RICHARDSON, D. C.; MICHEL, P.; LOVE, S. G.Until recently, most asteroids were thought to be solid bodies whose shapes were determined largely by collisions with other asteroids. Recent work by Burns and others has shown that many asteroids may be little more than rubble piles, held together by self-gravity ; this means that their shapes may be strongly distorted by tides during close encounters with planets. Here we report on numerical simulations of encounters between an ellipsoid-shaped rubble-pile asteroid and Earth. After an encounter, many of the simulated asteroids develop the same rotation rate and distinctive shape as 1620 Geographos (i.e., highly elongated with a single convex side, tapered ends, and small protuberances swept back against the rotation direction). Since our numerical studies show that these events occur with some frequency, we suggest that Geographos may be a tidally distorted object. In addition, our work shows that 433 Eros, which will be visited by the NEAR spacecraft in 1999, is much like Geographos, suggesting that it too may have been molded by tides in the past.