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FLAIR II Spectroscopy of Two DENIS J Band Galaxy Samples
As a pilot survey for the forthcoming 6dF Galaxy Redshift Survey,spectroscopy of galaxies selected in the 1.2 micron J waveband with theDENIS imaging survey was performed atthe UKST using the FLAIR IImulti-object spectroscope. Sixty-nine galaxy redshifts were obtained ina high galactic latitude field and an additional 12 redshifts in a lowgalactic latitude (b=-17°), obscured field. This spectroscopicfollowup of NIR selected galaxies illustrates the feasibility ofobtaining redshifts with optical spectra on galaxies selected at muchlonger wavelengths. It validated a very preliminary algorithm forstar/galaxy separation for high galactic latitude DENIS objects, with99% reliability for J<13.9. The FLAIR redshifts are in excellentagreement with those, previously published, of 20 common galaxies.However, the redshift determinations presented here requiredsubstantially longer integration times to achieve 90% completeness thanexpected from previous optical surveys at comparable depth. This ismainly due to a degradation in overall fibre throughput due to knownproblems with ageing of the prism-cement-fibre interface with exposureto UV light. In comparison to our high galactic latitude field, our lowlatitude (high extinction) field required 2.5 times more exposure timefor less than 50% of successful redshift measurements. Among theJ≤13.9 galaxies with measured redshifts, only 37+/-6% displayemission lines, in comparison with 60% of emission line galaxies inoptical samples of comparable depth. These galaxies are, on average,half a magnitude bluer in B-J than galaxies of the same luminositywithout emission lines. We confirm a previous optically-based resultthat the fraction of galaxies with emission lines increases rapidly withdecreasing galaxy luminosity. The J band luminosity function isestimated. Our high latitude field displays a concentration of galaxiesat cz≃38000kms-1 suggesting a possible supercluster. Aradial velocity is reported for a galaxy lying near the projected centreof the Abell 1434 cluster of galaxies, for which no cluster redshift iscurrently available.
| 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.
| A comparative study of morphological classifications of APM galaxies
We investigate the consistency of visual morphological classificationsof galaxies by comparing classifications for 831 galaxies from sixindependent observers. The galaxies were classified on laser print copyimages or on computer screen using scans made with the Automated PlateMeasuring (APM) machine. Classifications are compared using the RevisedHubble numerical type index T. We find that individual observers agreewith one another with rms combined dispersions of between 1.3 and 2.3type units, typically about 1.8 units. The dispersions tend to decreaseslightly with increasing angular diameter and, in some cases, withincreasing axial ratio (b/a). The agreement between independentobservers is reasonably good but the scatter is non-negligible. In spiteof the scatter, the Revised Hubble T system can be used to train anautomated galaxy classifier, e.g. an artificial neural network, tohandle the large number of galaxy images that are being compiled in theAPM and other surveys.
| Molecules in galaxies. IV - Molecular and atomic hydrogen in Virgo cluster galaxies
If gas and dust are well mixed in a galaxy, the dust mass should beproportional to the sum of the masses of atomic and molecular gas. Thisassumption has been used to estimate the mean conversion ratio betweenthe flux in the CO J = 1-0 line and the molecular gas mass of a galaxyusing a set of observations of the 100 microns continuum flux density,the H I 21 cm line flux and the CO line flux for a sample of spiralgalaxies in the Virgo cluster; these galaxies have a wide variation inthe ratio of CO to H I line flux. The result, N(H2) = 6.3 + or - 3.5 x10 to the 20th mol/sq cm/(K x km/s), is in agreement with valuesinferred from observations of the molecular interstellar medium in theGalaxy.
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