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|Formalism and quality of a proper motion link with extragalactic objects for astrometric satellite missions|
The accuracy of the link of the proper motion system of astrometricsatellite missions like AMEX and GAIA is discussed. Monte-Carlo methodswere used to simulate catalogues of positions and proper motions ofquasars and galaxies to test the link. The main conclusion is, thatfuture satellite missions like GAIA may be ``self-calibrated'' by theirmeasurements of QSOs, while additional measurements from radio stars orHST-data are needed to calibrate the less deep reaching astrometricsatellite missions of AMEX type.
|HIDEEP - an extragalactic blind survey for very low column-density neutral hydrogen|
We have carried out an extremely long integration time (9000 sbeam-1) 21-cm blind survey of 60 deg2 in Centaurususing the Parkes multibeam system. We find that the noise continues tofall as throughout, enabling us to reach an HI column-density limit of4.2 × 1018 cm-2 for galaxies with a velocitywidth of 200 km s-1 in the central 32 deg2 region,making this the deepest survey to date in terms of column densitysensitivity. The HI data are complemented by very deep opticalobservations from digital stacking of multi-exposure UK SchmidtTelescope R-band films, which reach an isophotal level of 26.5 R magarcsec-2 (~=27.5 B mag arcsec-2). 173 HI sourceshave been found, 96 of which have been uniquely identified with opticalcounterparts in the overlap area. There is not a single source withoutan optical counterpart. Although we have not measured the columndensities directly, we have inferred them from the optical sizes oftheir counterparts. All appear to have a column density ofNHI= 1020.65+/-0.38. This is at least an order ofmagnitude above our sensitivity limit, with a scatter only marginallylarger than the errors on NHI. This needs explaining. Ifconfirmed it means that HI surveys will only find low surface brightness(LSB) galaxies with high MHI/LB. Gas-rich LSBgalaxies with lower HI mass to light ratios do not exist. The paucity oflow column-density galaxies also implies that no significant populationwill be missed by the all-sky HI surveys being carried out at Parkes andJodrell Bank.
|FLASH redshift survey - I. Observations and catalogue|
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
|The plane W(Na I) X W(Mg I) - Effects of interstellar Na I in a sample of southern galaxies|
Galaxy spectra from a subsample of the Southern Sky Redshift Survey databank were used to study the equivalent width plane for the lines Na Ilambda 5893 A vs Mg I lambda 5175 A. An estimate of how important thecontribution of the interstellar gas for the sodium line is compared tothat of the stellar population. The sample is made up of galaxies withmorphological types from E to Sc and are distributed up to radialvelocities of 25,000 km/s, most of them smaller than 15,000 km/s. Mostearly type galaxies with dust lanes, particularly nearly edge-on So's,present an enhancement of the Na I line. Inclined spiral galaxies tendto present enhanced Na I with respect to face-on spirals. This tendency,previously found in a smaller sample of galaxies limited to V equal toor less than 6000 km/s, is now confirmed for more distant ones. In thelarge velocity sample it shows the global bulge rather than the verynucleus; the persistence of the effect suggests that the scale height ofthe gas layer in the central disk can reach a considerable fraction ofthe bulge radius.
|Redshifts in Klemola 27|
Observational data for galaxies in the galaxy cluster Klemola 27gathered over the last few years are presented. These are mostly newredshifts and further, accurate coordinates and morphological types fora large number of 'prominent' galaxies in the ESO/SRC-Survey fields 444and 445. A few preliminary H I radial velocities are also reported. Thedata available for this cluster are briefly discussed.
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