Astronomy Research Works
Permanent URI for this collectionhttp://hdl.handle.net/1903/1587
Browse
20 results
Search Results
Item Two Dimensional Velocity Fields of Low Surface Brightness Galaxies(EDP Sciences, 2005) Kuzio de Naray, R.; McGaugh, S. S.; de Blok, W. J. G.; Bosma, A.We present high resolution two dimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for CDM.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 Simulating Observations of Dark Matter Dominated Galaxies: Towards the Optimal Halo Profile(Blackwell, 2007) de Blok, W.J.G.; Bosma, Albert Bosma; McGaugh, StacyLow Surface Brightness (LSB) galaxies are dominated by dark matter, and their rotation curves thus reflect their dark matter distribution. Recent high-resolution rotation curves suggest that their dark matter mass-density distributions are dominated by a constant-density core. This seems inconsistent with the predictions of Cold Dark Matter (CDM) models which produce halos with compact density cusps and steep mass-density profiles. However, the observationally determined mass profiles may be affected by non-circular motions, asymmetries and offsets between optical and dynamical centres, all of which tend to lower the observed slopes. Here we determine the impact of each of these effects on a variety of halo models, and compare the results with observed mass-density profiles. Our simulations suggest that no single systematic effect can reconcile the data with the cuspy CDM halos. The data are best described by a model with a soft core with an inner power-law mass-density slope ⍺ = −0.2±0.2. However, no single universal halo profile provides a completely adequate description of the data.Item The AGN and Gas Disk in the Low Surface Brightness Galaxy PGC045080(Blackwell, 2007) Das, M.; Kantharia, N.; Ramya, S.; Prabhu, T. P.; McGaugh, S. S.; Vogel, S. N.We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC 045080 (or 1300+0144). PGC 045080 is a moderately distant galaxy having a highly inclined optical disk and massive HI gas content. Radio continuum observations of the galaxy were carried out at 320 MHz, 610 MHz and 1.4 GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disk at all three frequencies. At 1.4 GHz and 610 MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with AGN activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the H flux and radio continuum at 1.4 GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC 045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centers can host significant AGN activity. We also mapped the HI gas disk and velocity field in PGC 045080. The HI disk extends well beyond the optical disk and appears warped. In the HI intensity maps, the disk appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disk but is fairly uniform in the other half. We derived the HI rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of 190km s−1.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.