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Structural properties of disk galaxies. I. The intrinsic equatorial ellipticity of bulges
Context: A variety of formation scenarios have been proposed to explainthe diversity of properties observed in bulges. Studying their intrinsicshape can help to constrain the dominant mechanisms at the epochs oftheir assembly. Aims: The structural parameters of a magnitude-limitedsample of 148 unbarred S0-Sb galaxies were derived in order to study thecorrelations between bulges and disks, as well as the probabilitydistribution function of the intrinsic equatorial ellipticity of bulges. Methods: We present a new fitting algorithm (GASP2D) to performtwo-dimensional photometric decomposition of the galaxysurface-brightness distribution. This was assumed to be the sum of thecontribution of a bulge and disk component characterized by ellipticaland concentric isophotes with constant (but possibly different)ellipticity and position angles. Bulge and disk parameters of the samplegalaxies were derived from the J-band images, which were available inthe Two Micron All Sky Survey. The probability distribution function ofthe equatorial ellipticity of the bulges was derived from thedistribution of the observed ellipticities of bulges and misalignmentsbetween bulges and disks. Results: Strong correlations between thebulge and disk parameters were found. About 80% of bulges in unbarredlenticular and early-to-intermediate spiral galaxies are not oblate buttriaxial ellipsoids. Their mean axial ratio in the equatorial plane is< B/A > = 0.85. Their probability distribution function is notsignificantly dependent on morphology, light concentration orluminosity. The possible presence of nuclear bars does not influence ourresults. Conclusions: The interplay between bulge and disk parametersfavors scenarios in which bulges have assembled from mergers and/or havegrown over long times through disk secular evolution. However, all thesemechanisms have to be tested against the derived distribution of bulgeintrinsic ellipticities.Table 3 is only available in electronic form at http://www.aanda.org
| Photometric Decomposition of Barred Galaxies
We present a nonparametric method for decomposition of the light of diskgalaxies into disk, bulge, and bar components. We have developed andtested the method on a sample of 68 disk galaxies for which we haveacquired I-band photometry. The separation of disk and bar light relieson the single assumption that the bar is a straight feature with adifferent ellipticity and position angle from that of the projecteddisk. Here we present the basic method, but we recognize that it can besignificantly refined. We identify bars in only 47% of the more nearlyface-on galaxies in our sample. The fraction of light in the bar has abroad range, from 1.3% to 40% of the total galaxy light. Iflow-luminosity galaxies have more dominant halos, and if haloscontribute to bar stability, the luminosity functions of barred andunbarred galaxies should differ markedly; while our sample is small, wefind only a slight difference of low significance.
| The Survey for Ionization in Neutral Gas Galaxies. I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG),a census of star formation in H I-selected galaxies. The survey consistsof Hα and R-band imaging of a sample of 468 galaxies selected fromthe H I Parkes All Sky Survey (HIPASS). The sample spans three decadesin H I mass and is free of many of the biases that affect otherstar-forming galaxy samples. We present the criteria for sampleselection, list the entire sample, discuss our observational techniques,and describe the data reduction and calibration methods. This paperfocuses on 93 SINGG targets whose observations have been fully reducedand analyzed to date. The majority of these show a single emission linegalaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs ina single field. All of the targets in this sample are detected inHα, indicating that dormant (non-star-forming) galaxies withMHI>~3×107 Msolar are veryrare. A database of the measured global properties of the ELGs ispresented. The ELG sample spans 4 orders of magnitude in luminosity(Hα and R band), and Hα surface brightness, nearly 3 ordersof magnitude in R surface brightness and nearly 2 orders of magnitude inHα equivalent width (EW). The surface brightness distribution ofour sample is broader than that of the Sloan Digital Sky Survey (SDSS)spectroscopic sample, the EW distribution is broader than prism-selectedsamples, and the morphologies found include all common types ofstar-forming galaxies (e.g., irregular, spiral, blue compact dwarf,starbursts, merging and colliding systems, and even residual starformation in S0 and Sa spirals). Thus, SINGG presents a superior censusof star formation in the local universe suitable for further studiesranging from the analysis of H II regions to determination of the localcosmic star formation rate density.
| Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies
This paper is part of a series that focuses on investigating galaxyformation and evolution in small-scale systems of galaxies inlow-density environments. We present results from a study of the NGC4756 group, which is dominated by the elliptical galaxy NGC 4756. Thecharacteristics of the group are investigated through (1) the detailedinvestigation of the morphological, photometric, and spectroscopicproperties of nine galaxies among the dominant members of the group; (2)the determination of the photometric parameters of the faint galaxypopulation in an area of 34'×34' centered onNGC 4756 and (3) an analysis of the X-ray emission in the area based onarchival data.The nine member galaxies are located in the core part of the NGC 4756group (a strip ~300 kpc in diameter, H0=70 km s-1Mpc-1), which has a very loose configuration. The centralpart of the NGC 4756 group contains a significant fraction of early-typegalaxies. Three new group members with previously unknown systemicvelocities are identified, one of which is type dE. At about 7.5 arcminsouthwest of NGC 4756 a substructure of the group is detected, includingIC 829, MCG -2-33-35, MCG -2-33-36, and MCG -2-33-38, that meets theHickson criteria for being a compact group. Most of the galaxies in thissubstructure show interaction signatures. We do not detect apparent finestructure and signatures of recent interaction events in the early-typegalaxy population, with the exception of a strong dust lane in theelliptical galaxy MCG -2-33-38. However, this galaxy displays signaturesof nuclear activity. Strong [O III], [N II], and [S II] line emission,combined with comparatively weak but broad Hα emission, suggestsan intermediate Seyfert type classification. Although the area isheavily contaminated by the background cluster A1631, X-ray data suggestthe presence of a hot intergalactic medium related to the detected X-rayemission of the group. The present results are discussed in the contextof group evolution.Based on observations obtained at the European Southern Observatory, LaSilla, Chile (program 65.P-252).
| The 1000 Brightest HIPASS Galaxies: H I Properties
We present the HIPASS Bright Galaxy Catalog (BGC), which contains the1000 H I brightest galaxies in the southern sky as obtained from the H IParkes All-Sky Survey (HIPASS). The selection of the brightest sourcesis based on their H I peak flux density (Speak>~116 mJy)as measured from the spatially integrated HIPASS spectrum. The derived HI masses range from ~107 to 4×1010Msolar. While the BGC (z<0.03) is complete inSpeak, only a subset of ~500 sources can be consideredcomplete in integrated H I flux density (FHI>~25 Jy kms-1). The HIPASS BGC contains a total of 158 new redshifts.These belong to 91 new sources for which no optical or infraredcounterparts have previously been cataloged, an additional 51 galaxiesfor which no redshifts were previously known, and 16 galaxies for whichthe cataloged optical velocities disagree. Of the 91 newly cataloged BGCsources, only four are definite H I clouds: while three are likelyMagellanic debris with velocities around 400 km s-1, one is atidal cloud associated with the NGC 2442 galaxy group. The remaining 87new BGC sources, the majority of which lie in the zone of avoidance,appear to be galaxies. We identified optical counterparts to all but oneof the 30 new galaxies at Galactic latitudes |b|>10deg.Therefore, the BGC yields no evidence for a population of``free-floating'' intergalactic H I clouds without associated opticalcounterparts. HIPASS provides a clear view of the local large-scalestructure. The dominant features in the sky distribution of the BGC arethe Supergalactic Plane and the Local Void. In addition, one can clearlysee the Centaurus Wall, which connects via the Hydra and Antlia Clustersto the Puppis Filament. Some previously hardly noticable galaxy groupsstand out quite distinctly in the H I sky distribution. Several newstructures, including some not behind the Milky Way, are seen for thefirst time.
| HYPERLEDA. II. The homogenized HI data
After a compilation of HI data from 611 references and new observationsmade in Nançay, we produce a catalog of homogenized HI data for16781 galaxies. The homogenization is made using the EPIDEMIC methodfrom which all data are progressively converted into the adoptedstandard. The result is a catalog giving: 1) the logarithm of twice themaximum rotation velocity, log 2V_Msin i, converted to thesystem of Mathewson et al. (\cite{Mathewson1996}). This quantity isgiven without correction for inclination; 2) the HI magnitude,m21, (area of the 21-cm line width expressed in magnitude)converted to the flux system of Theureau et al. (\cite{Theureau1998});3) the HI velocity, V_HI, expressed with the optical definition (i.e.,using wavelengths instead frequencies). The typical uncertainties are:0.04 for log 2V_Msin i, 0.25 mag for m21 and 9 kms-1 for V_HI.Full Tables \ref{epidemicw}, \ref{epidemicw2}, \ref{epidemicf},\ref{epidemicf2} and Fig. \ref{profiles} are available in electronicform at http://www.edpsciences.org. Full Tables \ref{references},\ref{cataf}, \ref{newdata} and \ref{notes} are available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/57
| 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.
| Galaxy Luminosity Functions from Deep Spectroscopic Samples of Rich Clusters
Using a new spectroscopic sample and methods accounting forspectroscopic sampling fractions that vary in magnitude and surfacebrightness, we present R-band galaxy luminosity functions (GLFs) for sixnearby galaxy clusters with redshifts of 4000 kms-1
| 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.
| 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.
| 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.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| 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.
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