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|The photometric properties of isolated early-type galaxies|
Isolated galaxies are important because they probe the lowest densityregimes inhabited by galaxies. We define a sample of 36 nearby isolatedearly-type galaxies for further study. Our isolation criteria requirethem to have no comparable-mass neighbours within 2 B-band magnitudes,0.67 Mpc in the plane of the sky and 700 km s-1 in recessionvelocity. New wide-field optical imaging of 10 isolated galaxies withthe Anglo-Australian Telescope confirms their early-type morphology andrelative isolation. We also present imaging of four galaxy groups as acontrol sample. The isolated galaxies are shown to be moregravitationally isolated than the group galaxies. We find that theisolated early-type galaxies have a mean effective colour of(B-R)e= 1.54 +/- 0.14, similar to their high-densitycounterparts. They reveal a similar colour-magnitude relation slope andsmall intrinsic scatter to cluster ellipticals. They also follow theKormendy relation of surface brightness versus size for luminous clustergalaxies. Such properties suggest that the isolated galaxies formed at asimilar epoch to cluster galaxies, such that the bulk of their stars arevery old. However, our galaxy modelling reveals evidence for dust lanes,plumes, shells, boxy and disc isophotes in four out of nine galaxies.Thus at least some isolated galaxies have experienced a recentmerger/accretion event, which may have induced a small burst of starformation. We derive luminosity functions for the isolated galaxies andfind a faint slope of -1.2, which is similar to the `universal' slopefound in a wide variety of environments. We examine the number densitydistribution of galaxies in the field of the isolated galaxies. Only thevery faintest dwarf galaxies (MR>~-15.5) appear to beassociated with the isolated galaxies, whereas anyintermediate-luminosity galaxies appear to lie in the background.Finally, we discuss possible formation scenarios for isolated early-typegalaxies. Early epoch formation and a merger/accretion of galaxies arepossible explanations. The collapse of a large, virialized group is anunlikely explanation, but that of a poor group remains viable.
|Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data|
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
|Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry|
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
|The gas content of peculiar galaxies: Counterrotators and polar rings|
This paper studies the global ISM content in a sample of 104 accretinggalaxies, including counterrotators and polar rings, which spans theentire Hubble sequence. The molecular, atomic and hot gas content ofaccretors is compared to a newly compiled sample of normal galaxies. Wepresent results of a small survey of the J=1-0 line of 12COwith the 15 m SEST telescope on a sample of 11 accretors (10counterrotators and 1 polar ring). The SEST sample is enlarged withpublished data from 48 galaxies, for which observational evidence ofcounterrotation in the gas and/or the stars has been found. Furthermore,the available data on a sample of 46 polar ring galaxies has beencompiled. In order to explore the existence of an evolutionary pathlinking the two families of accretors, the gas content ofcounterrotators and polar rings is compared. It was found that thenormalized content of cold gas (Mgas/LB) in polarrings is ~ 1 order of magnitude higher than the reference value derivedfor normal galaxies. The inferred gas masses are sufficient to stabilizepolar rings through self-gravity. In contrast, it was found that thecold gas content of counterrotators is close to normal for all galaxytypes. Although counterrotators and polar rings probably share a commonorigin, the gas masses estimated here confirm that light gas ringsaccreted by future counterrotators may have evolved faster than theself-gravitating structures of polar rings. In this scenario, thetransformation of atomic into molecular gas could be enhanced near thetransition region between the prograde and the retrograde disks,especially in late-type accretors characterized by a high content ofprimordial gas. This is tentatively confirmed in this work: the measuredH2/HI ratio seems larger in counterrotators than in normal orpolar ring galaxies for types later than S0s. Based on observationscollected at SEST telescope, European Southern Observatory, La Silla,Chile. Table 1 is only available in electronic form athttp://www.edpsciences.org
|The visible environment of galaxies with counterrotation|
In this paper we present a statistical study of the environments of 49galaxies in which there is gas- or stellar-counterrotation. The numberof possible companions in the field (to apparent magnitude 22), theirsize and concentration were considered. All the statistical parameterswere analysed by means of Kolgomorov-Smirnov tests, using a controlsample of 43 galaxies without counterrotation. From our data, nosignificant differences between the counter-rotating and control samplesappear. This is different to Seyfert or radio-loud galaxies which lie inenvironments with a higher density of companions. On the contrary, if aweak tendency exists, for galaxies with gas counterrotation only, it isdiscovered in regions of space where the large scale density of galaxiesis smaller. Our results tend to disprove the hypothesis thatcounterrotation and polar rings derive from a recent interaction with asmall satellite or a galaxy of similar size. To a first approximation,they seem to follow the idea that all galaxies are born through a mergerprocess of smaller objects occurring very early in their life, or thatthey derive from a continuous, non-traumatic infall of gas that formedstars later. Whatever the special machinery is which producescounterrotation or polar rings instead of a co-planar, co-rotatingdistribution of gas and stars, it seems not to be connected to thepresent galaxy density of their environments.
|The IRAS PSCz dipole|
We use the PSCz IRAS galaxy redshift survey to analyse the cosmologicalgalaxy dipole out to a distance of 300h-1Mpc. The masked areais filled in three different ways, first by sampling the whole sky atrandom, secondly by using neighbouring areas to fill a masked region,and thirdly using a spherical harmonic analysis. The method of treatmentof the mask is found to have a significant effect on the finalcalculated dipole. The conversion from redshift space to real space isaccomplished by using an analytical model of the cluster and voiddistribution, based on 88 nearby groups, 854 clusters and 163 voids,with some of the clusters and all of the voids found from the PSCz database. The dipole for the whole PSCz sample appears to have convergedwithin a distance of 200h-1Mpc and yields a value forβΩ0.6b0.750.11-0.08, consistent with earlier determinations from IRAS samples bya variety of methods. For b=1, the 2σ range forΩ0 is 0.43-1.02. The direction of the dipole is within13° of the cosmic microwave background (CMB) dipole, the mainuncertainty in direction being associated with the masked area behindthe Galactic plane. The improbability of further major contributions tothe dipole amplitude coming from volumes larger than those surveyed heremeans that the question of the origin of the CMB dipole is essentiallyresolved.
|The ROSAT International X-ray/Optical Survey (RIXOS): source catalogue|
We describe the ROSAT International X-ray/Optical Survey (RIXOS), amedium-sensitivity survey and optical identification of X-ray sourcesdiscovered in ROSAT high Galactic latitude fields (|b|>28 deg) andobserved with the Position Sensitive Proportional Counter (PSPC)detector. The survey made use of the central 17arcmin of each ROSATfield. A flux limit of3x10-14ergcm-2s-1 (0.5-2keV) wasadopted for the survey, and a minimum exposure time of 8000s wasrequired for qualifying ROSAT observations. X-ray sources in the surveyare therefore substantially above the detection threshold of each fieldused, and many contain enough counts to allow the X-ray spectral slopeto be estimated. Spectroscopic observations of potential counterpartswere obtained of all sources down to the survey limit in 64 fields,totalling a sky area of 15.77deg2. Positive opticalidentifications are made for 94per cent of the 296 sources thusexamined. A further 18 fields (4.44deg2), containing 105sources above the 3x10-14ergcm-2s-1survey limit, are completely optically identified to a higher flux of8x10-14ergcm-2s-1 (0.5-2keV). Opticalspectroscopic data are supplemented by deep CCD imaging of many sourcesto reveal the morphology of the optical counterparts, and objects toofaint to register on Sky Survey plates. The faintest opticalcounterparts have R~22. This paper describes the survey method, andpresents a catalogue of the RIXOS sources and their opticalidentifications. Finding charts based on Sky Survey data are given foreach source, supplemented by CCD imaging where necessary.
|Nearby Optical Galaxies: Selection of the Sample and Identification of Groups|
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
|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.
|A catalogue of spatially resolved kinematics of galaxies: Bibliography|
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to18.104.22.168) or via http://cdsweb.u-strasbg.fr/Abstract.html
|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.
|The fundamental plane of early-type galaxies: stellar populations and mass-to-light ratio.|
We analyse the residuals to the fundamental plane (FP) of ellipticalgalaxies as a function of stellar-population indicators; these are basedon the line-strength parameter Mg_2_ and on UBVRI broad-band colors, andare partly derived from new observations. The effect of the stellarpopulations accounts for approximately half the observed variation ofthe mass-to-light ratio responsible for the FP tilt. The residual tiltcan be explained by the contribution of two additional effects: thedependence of the rotational support, and possibly that of the spatialstructure, on the luminosity. We conclude to a constancy of thedynamical-to-stellar mass ratio. This probably extends to globularclusters as well, but the dominant factor would be here the luminositydependence of the structure rather than that of the stellar population.This result also implies a constancy of the fraction of dark matter overall the scalelength covered by stellar systems. Our compilation ofinternal stellar kinematics of galaxies is appended.
|CCD calibration of the magnitude scale for the SSRS2 sample: The equatorial region|
In this paper we continue our investigation on the isophotal nature,accuracy, and uniformity of the magnitude system adopted in the SouthernSky Redshift Survey extension (SSRS2). Extending our earlier work, weexamine galaxies in the equatorial region, primarily in the declinationrange delta greater than or equal to -17.5 deg and less than or equal to0 deg, over a large range of right ascension, covering the southern andnorthern Galactic caps. For this purpose, we have obtained CCD isophotalmagnitudes in the B and R bands for 265 galaxies of differentmorphological types. Using the larger sample we confirm our earlierclaim that the mSSRS2 magnitudes are very nearly themagnitude measured within the isophote muB = 26 mag/sqarcsec, with a dispersion of about 0.30 mag. The relative zero-pointoffset between our mSSRS2 magnitudes and the CCD photometryis -0.02 mag from all data we have obtained. However, we detect avariation of the zero-point across different regions of the sky of +/-0.10 mag for regions at large angular separations. We also estimate thatthe zero-point offset between the mSSRS2 and Zwicky systemsis relatively small (approximately 0.10 mag), which should allow us tocombine the data from the SSRS2 and the CfA2 Redshift Survey.
|Redshift observations in the Hydra-Centaurus region|
The paper reports 406 redshifts for galaxies in the northern galactichemisphere, south of delta = 0 deg. A substantial fraction of theobserved galaxies are located in the equatorial zone between deltavalues of -17.5 and 0 deg. By combining these new data with thoseavailable in the literature, it is possible to extend the original CfAredshift survey of galaxies brighter than m(B(0)) = 14.5 to b = 30 deg,south of delta = 0. New data taken at lower galactic latitudes alsocontribute to the existing surveys of the Hydra-Centaurus complex.
|New observations and a photographic atlas of polar-ring galaxies|
A photographic atlas of polar-ring galaxies and related objects ispresented. The atlas includes kinematically confirmed polar-ringgalaxies (category A), good condidates based on their morphologicalappearance (category B), possible candidates (category C), and possiblyrelated objects (category D). New photometric and kinematic observationsare reported for several galaxies in the catalog, including observationsthat show that UGC 7576 and UGC 9796 ( = II ZW 73) are S0 galaxies withpolar rings. Roughly 0.5 percent of all nearby S0 galaxies appear tohave polar rings. When corrected for various selection effects (e.g.,nonoptimal viewing orientation, possible dimming, or limited lifetime ofthe ring) the percentage increases to about 5 percent of S0 galaxieswhich have, or have had a polar ring.
|A southern redshift survey. I - Accurate redshifts for 500 galaxies observed at SAAO|
Radial velocities are presented for about 500 galaxies observed with anintensified Reticon photon-counting detector attached to the 1.9 mtelescope at the Sutherland field station of SAAO. The velocities weredetermined by cross correlation with standard velocity templates, fromthe measured wavelengths of emission lines, or from both techniques,with spectra covering the wavelength range from 3700 to 5400 A. Thefinal velocities appear to have the same zero point as H I radiovelocities, and have standard deviations of the order of 35 km/s, thoughcross-correlation velocities on their own may have significantly largererrors.
|Counter-rotation in dust-lane ellipticals and the implications for accretion events in galaxies|
Decoupling of angular momenta of gas and stars in elliptical galaxiesconstitutes evidence for the acquisition of external material by thesegalaxies later in their history. New observations on four major-axisdust-lane ellipticals Anon 1029-459, NGC3528, NGC4370, and NGC5745, arepresented. In the first two of these, counterrotation of gas and starsis observed, whereas the two components are corotating in NGC4370 andNGC5745; these results are consistent with the acquisition hypothesis.The same accretion events occur also in S0 galaxies, where they giverise to polar rings or to counter- and corotating as in the equatorialplane. As dynamic decoupling in these latter galaxies appears common, itis suggested that in all S0s with extended emission lines the gas is ofexternal origin.
|A study of major-axis dust-lane ellipticals|
Kinematical and photometric observations of four early-type galaxieswith dust lanes along the major axes are presented. They are Anon1029-459, NGC 3528, 4370 and 5745. For Anon 1029-459 radio observationsare also presented. All the systems but NGC 4370 show relatively highstellar rotational velocities similar to those observed in SOs. The dustlanes in Anon 1029-459 and NGC 5745 are warped, suggesting that they arerelatively young. There are contradictory indications that these systemsare elliptical galaxies. The class of major-axis dust-lane ellipticalsis not yet as well defined as the class of minor-axis dust-lanegalaxies.
|Southern Galaxy Catalogue.|
|A catalog of dusty elliptical galaxies|
A catalog of about 100 dusty elliptical galaxies and some relatedobjects is presented. A morphological classification system is proposed,and the observed dust lane characteristics of some of the individualgalaxies are described. The properties of the galaxies are discussed,including the distribution of morphological types, their radioproperties, radio source orientation, neutral hydrogen, kinematics anddynamics, and relationship to other types of peculiar galaxies.
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