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|The Southern Sky Redshift Survey|
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
|Gas streaming along the bar in NGC 1808. A combination of high-resolution Hα and HI data.|
High-resolution Hα observations reveal the existence of an unusualbar in the disk of NGC 1808 at a position angle of 155deg, about 20degoffset from the major axis. The bar, which is dominated by a chain ofHII regions along a line of 6kpc length, rotates with a pattern speed of~40km/s/kpc. Its axial ratio appears very large, whereas the bar-to-disklength ratio of ~0.3 is average. A remarkably similar bar has been foundin the galaxy NGC 7479. The outer parts of the HII region chain in NGC1808 coincide with maxima in the HI gas distribution and further outconnect to the outer spiral arms. The streaming of gas along the bar isclearly seen in the HI velocity field. Isovelocity contours nearlyperpendicular to the leading side of the bar point out shocked gasregions, and contours which are almost parallel to the bar on itstrailing side indicate gas is streaming inwards. The shock fronts canalso be observed as broad dust lanes emerging near the nuclear regionand curved along the leading sides of the bar. Inside the corotationradius the gas accumulates at the inner Lindblad resonances which arefound within a radius of 1kpc where they coincide with a nuclear ring orspiral measured in HI absorption and CO emission. Using a corotationradius of 1.2 times the bar radius the outer Lindblad resonance is foundat a radius of ~7kpc, not coincident with the location of the outerspiral arms.
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