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Weak homology of elliptical galaxies.
Studies of the Fundamental Plane of early-type galaxies, from small tointermediate redshifts, are generally carried out under the guidingprinciple that the Fundamental Plane reflects the existence of anunderlying mass-luminosity relation for such galaxies, in a scenariowhere galaxies are homologous systems in dynamical equilibrium. In thispaper we re-examine the question of whether a systematic non-homologycould be partly responsible for the correlations that define theFundamental Plane. We start by studying a small set of objectscharacterized by photometric profiles that have been pointed out todeviate significantly from the standard R1/4 law. For theseobjects we confirm that a generic R1/n law, with n a freeparameter, can provide superior fits (the best-fit value of n can belower than 2.5 or higher than 10), better than those that can beobtained by a pure R1/4 law, by an R1/4 +exponential model, and by other dynamically justified self-consistentmodels. Therefore, strictly speaking, elliptical galaxies should not beconsidered homologous dynamical systems. Still, a case for weakhomology, useful for the interpretation of the Fundamental Plane, couldbe made if the best-fit parameter n, as often reported, correlates withgalaxy luminosity L, provided the underlying dynamical structure alsofollows a systematic trend with luminosity. We demonstrate that thisstatement may be true even in the presence of significant scatter in thecorrelation n(L). Preliminary indications provided by a set of ``datapoints" associated with a sample of 14 galaxies suggest that neither thestrict homology nor the constant stellar mass-to-light solution are asatisfactory explanation of the observed Fundamental Plane. Theseconclusions await further extensions and clarifications, because theclass of low-luminosity early-type galaxies, which contributesignificantly to the Fundamental Plane, falls outside the simpledynamical framework considered here and because dynamical considerationsshould be supplemented with other important constraints derived from theevolution of stellar populations.
| 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.
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