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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.
|The Arizona-New Mexico Spectroscopic Survey of Galaxies. I. Data for the Western End of the Perseus Supercluster|
We present new optical spectroscopic data for 347 galaxies in the regionof the Perseus supercluster. The new data were obtained using theSteward Observatory 2.3 m telescope and cover the whole optical window.Included are redshifts (for 345 objects), absorption-line equivalentwidths, a continuum index measuring the 4000 Å break, andemission-line flux ratios. After 11 objects are rejected for being toofaint and redshifts for 26 objects are added from the literature, wearrive at a complete sample of 361 galaxies. The distribution ofredshifts for the whole sample is examined, and we show the relationshipof the continuum index to morphology.
|Arcsecond Positions of UGC Galaxies|
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|Galaxy Alignments in the Pisces-Perseus Supercluster Revisited|
A search for preferential galaxy alignments in the Pisces-PerseusSupercluster (PPS) is made using the Minnesota Automated Plate ScannerPisces-Perseus Survey (MAPS-PP). The MAPS-PP is a catalog of ~1400galaxies with a (roughly) isophotal diameter greater than 30"constructed from digitized scans of the blue and red plates of thePalomar Observatory Sky Survey covering the PPS. This is the largestsample of galaxies applied to a search of galaxy alignments in thissupercluster, and it has been used in combination with previouslypublished redshifts to construct the deepest PPS galaxy luminosityfunction to date. While previous studies have relied extensively oncatalogs with visually estimated parameters for both sample selectionand determination of galaxy orientation, the MAPS-PP uses selectioncriteria and measurements that are entirely machine and computer based.Therefore, it is not susceptible to some of the biases, such as thediameter inclination effect, known to exist in some other galaxycatalogs. The presence of anisotropic galaxy distributions is determinedby use of the Kuiper statistic, a robust alternative to the chi^2statistic more traditionally used in these studies. Three statisticallysignificant anisotropic distributions are observed. The reddest galaxiesare observed to be oriented preferentially perpendicular to the locallarge-scale structure. The bluest galaxies near the supercluster planeare observed to have an anisotropic position angle distribution.Finally, a weak trend for the median position angle of color-selectedgalaxy subsamples to ``twist'' with increasing distance from the PPSplane is observed. These position angle distribution anisotropies areweak and are not consistent with any single primordial or modern-eragalaxy alignment mechanism, although a mixture of such mechanisms is notruled out.
|A survey of the Pisces-Perseus supercluster. V - The declination strip +33.5 deg to +39.5 deg and the main supercluster ridge|
Measurements of 544 radial velocities, 229 optical and 315 in the 21 cmH I line, are presented for galaxies, mostly in the declination stripbetween +33.5 and +39.5 deg in the region of the Pisces-Perseussupercluster. These are combined with other available data toinvestigate the linear structure identified as the main superclusterridge. The main ridge of the supercluster extends at least 50/h Mpcbefore it disappears into the zone of avoidance east of Perseus.Confinement both on the plane of the sky and in the velocity dimensionimply an axial ratio of greater than 10:1 and an inclination withrespect to the plane of the sky of less than about 12 degrees. Therelative proximity, low inclination to the plane of the sky, and highcontrast relative to the foreground and background, help to make thePisces-Perseus filament one of the most prominent features in theextragalactic sky on large scales.
|Redshifts of galaxies in the south west region of the Perseus supercluster|
Redshifts for 33 galaxies have been measured making it possible to studythe spatial distribution of a complete sample of 125 galaxies brighterthan the 14.5 mag in a large area west of the Perseus supercluster. Itis shown that the Perseus supercluster connects to another large scalestructure: the A 2634-A 2666 supercluster.
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