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The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35
| The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data
We present the spectroscopic data for the galaxies studied in the EFARproject, which is designed to measure the properties and peculiarmotions of early-type galaxies in two distant regions. We have obtained1319 spectra of 714 early-type galaxies over 33 observing runs on 10different telescopes. We describe the observations and data reductionsused to measure redshifts, velocity dispersions and the Mgb and Mg_2Lick linestrength indices. Detailed simulations and intercomparison ofthe large number of repeat observations lead to reliable error estimatesfor all quantities. The measurements from different observing runs arecalibrated to a common zero-point or scale before being combined,yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgblinestrengths and 582 Mg_2 linestrengths. The median estimated errors inthe combined measurements are Delta cz=20 km s^-1, Delta sigma sigma=9.1 per cent, Delta Mgb Mgb=7.2 per cent and Delta Mg_2=0.015 mag.Comparison of our measurements with published data sets shows nosystematic errors in the redshifts or velocity dispersions, and onlysmall zero-point corrections to bring our linestrengths on to thestandard Lick system. We have assigned galaxies to physical clusters byexamining the line-of-sight velocity distributions based on EFAR andZCAT redshifts, together with the projected distributions on the sky. Wederive mean redshifts and velocity dispersions for these clusters, whichwill be used in estimating distances and peculiar velocities and to testfor trends in the galaxy population with cluster mass. The spectroscopicparameters presented here for 706 galaxies combine high-quality data,uniform reduction and measurement procedures, and detailed erroranalysis. They form the largest single set of velocity dispersions andlinestrengths for early-type galaxies published to date.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| The peculiar motions of early-type galaxies in two distant regions. III - The photometric data
We present R-band CCD photometry for 776 galaxies observed in the EFARproject. The photometry is compared with photoelectric data, showingthat a common zero-point good to better than 1 per cent and a precisionof 0.03 mag per zero-point have been achieved. We give the circularlyaveraged surface brightness profiles and the photometric parameters ofthe 762 program galaxies, D(n) diameters, half-luminosity radii, totalmagnitudes, and average effective surface brightnesses. More than 80percent of the profiles have a global S/N ratio larger than 300. Theextrapolation needed to derive total magnitudes is less than 10 percentfor 80 percent of the fits. More than 80 percent of the galaxies havemean effective surface brightness larger than the observed skybrightness. In 90 percent of the profiles the estimate of thecontamination of the sky by the galaxy light is less than 1 percent. Wederive total magnitudes and half-luminosity radii to better than 0.15mag and 25 percent, respectively, for 90 percent of our sample. Incontrast, external comparisons show that data in the literature can bestrongly affected by systematic errors due to large extrapolations,small radial range, sky subtraction errors, seeing effects, and the useof a simple R exp 1/4 fit. The resulting errors can easily amount tomore than 0.5 mag in the total magnitudes and 50 percent in thehalf-luminosity radii.
| Soft excesses of hard X-ray selected Seyfert 1 galaxies studied with the ROSAT-PSPC
The nature of the soft X-ray excess in Seyfert 1 galaxies is still anopen issue. In order to derive some general properties we analysed theROSAT PSPC archive observations of the Seyfert galaxies in the\cite[Nandra & Pounds (1994)]{Nan94} Ginga sample. The use of thissample ensures a reliable estimate (under the assumption of lack ofintrinsic spectral variability) of the slope of the underlying powerlaw, which instead cannot be well measured using ROSAT data alone. Wetested three different models for the soft excess: emission fromaccretion disk (described by a black body), absorption from ionized gas(``warm absorber'', described by an absorption edge), and reflectionfrom mildly ionized material (described by a step function). The mainresult is that no model gives a satisfactory fit for all sources.Furthermore for two sources none of these models provides an acceptablefit. In these cases a physically meaningful combination of twocomponents (e.g. warm absorber plus black body) gives a good fit. Weconclude that several different effects concur to the soft excessphenomenon in Seyfert galaxies.
| Axel: A balloon-borne X-ray astronomy experiment
Following a successful programme to investigate the physics of ultrahigh pressure proportional counters, a counter array has been developedfor hard X-ray astronomy. A parallel investigation has evaluated theperformance of a large area phoswich scintillator detector for the samepurpose. The two detectors have been integrated in a balloon-bornepayload, the Astrophysical X-ray Experimental Laboratory (AXEL) Thispaper describes the instrumentation aboard the payload.
| Soft excesses of hard X-ray selected Seyfert 1 galaxies.
Not Available
| The Peculiar Motions of Early-Type Galaxies in Two Distant Regions. I. Cluster and Galaxy Selection
The EFAR project is a study of 736 candidate elliptical galaxies in 84clusters lying in two regions, toward Hercules-Corona Borealis andPerseus-Pisces-Cetus, at distances cz ~ 6000-15,000 km s^-1^. In thispaper (the first of a series), we present an introduction to the EFARproject and describe in detail the selection of the clusters andgalaxies in our sample. Fundamental data for the galaxies and clustersare given, including accurate new positions for each galaxy andredshifts for each cluster. The galaxy selection functions aredetermined by using diameters measured from Schmidt sky survey imagesfor 2185 galaxies in the cluster fields. Future papers in this serieswill present the spectroscopic and photometric observations of thissample, investigate the properties of the fundamental plane forelliptical galaxies, and determine the large- scale peculiar velocityfields in these two regions of the universe.
| 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.
| Emission Spectrum Integrated over an Accretion Disk: Comparison with Observations of Active Galactic Nuclei
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...440..610S&db_key=AST
| The EXOSAT GSPC iron line catalog.
We report on the global properties of the Fe feature seen in the 6-7keVspectra of X-ray sources observed with the EXOSAT Gas ScintillationProportional Counter (GSPC). Of a total of 431 spectra extracted fromthe EXOSAT archive, 205 required the addition of a Gaussian emissionline to the continuum spectrum in order to obtain satisfactory fits. Themajority of these sources are X-ray binaries. The best fit lineproperties are given for each of these spectra as well as beingsummarized by source class. For the 226 spectra which did not requirethe addition of an emission feature, upper limit equivalent widths fornarrow and broad lines are presented.
| Nonthermal pair models reflection and X-ray spectral variability of active galaxies
Standard nonthermal electron-positron pair cascades, including theeffects of reflection from an accretion disk, can explain reasonablywell the mean spectra of low-luminosity, Seyfert-type active galaxies.We test this model using the spectral variability observed by EXOSATbetween 0.05 and 10 keV in five active galaxies: NGC 5548, 3C 120, 3C273, NGC 7469, and MCG 2-58-22. We find that pair-reflection models failto reproduce the full range of spectra observed, particularly very hardspectra with a strong soft X-ray excess. Either the pair-reflectionmodel is not an accurate description of the emission process in theseobjects or extrinsic effects, such as enhancement of the reflectioncomponent and/or a partially ionized absorber with a large columndensity, are responsible for much of the observed spectral variability.
| On the nature of rapid X-ray variability in active galactic nuclei
We systematically analyze all (110) EXOSAT AGN medium-energy lightcurves of length greater than 20 ks to search for and quantify theirflux variability. We also perform extensive simulations to quantify theselection effects (such as the source brightness or the length ofobservation) that might prevent the detection of variability. Wequantify variability in terms of a 'normalized variability amplitude'(NVA) derived from the power spectrum of each light curve. Of the 32sources observed, we detect variability in 12. We find that, contrary tosome previous claims, there is no evidence that sources change thecharacter of their variability between observations. We confirm thatthere is a strong inverse correlation between NVA and source luminositywhich can be simply explained if source size scales with luminosity. Afurther result is that the sources with the steepest energy spectra arepossibly the most variable. One explanation of the latter result, in thecontext of reprocessing models, might be that sources with steeperenergy spectra contain a smaller reflected or reprocessed component,which might be expected to vary less rapidly than the direct component.We briefly discuss a small number of light curves obtained using thelow-energy telescope on EXOSAT, and confirm that their power spectra aresteeper than those of the corresponding medium-energy light curves.
| Photoelectric and CCD photometry of E and S0 galaxies
We present BR photoelectric photometry for 352 E and S0 galaxies thatare part of a large survey of the properties and peculiar motions ofgalaxies in distant clusters. Repeat measurements show our internalerrors to be 2-3 percent in B and R and 1-2 percent in B-R. Comparisonsof BR and BVR reductions for 10 galaxies also observed in V show smallsystematic errors due to differences between the spectral energydistributions of stars and galaxies. External comparisons with B-Vcolors in the literature confirm that these colors are good to 1percent. We also describe R-band CCD observations for 95 of the galaxiesand place these on a BR photometric system for photoelectric and CCDphotomerry, with a common zero-point good to better than 1 percent. Wefind the rms precision of both our photoelectric and CCD R magnitudes tobe 2-3 percent for galaxies as faint as R = 15.
| X-ray luminosity and spectral variability of hard X-ray-selected active galactic nuclei
Luminosity and spectral variability are analyzed in a sample of AGNsfrom Exosat data based on the soft (LE: 0.05-2 keV) and hard (ME: 1-8keV) light curves. Specific attention is given to flux variability notedin the objects that are observed at least twice, and time variations andfast variability are also reported. The 14 sources that showsimultaneous long time variations in both light-curve ranges are alsoinvestigated in terms of spectral variability. Flux variability is shownto be very common in AGNs, and a subsample of the AGNs demonstratedchanges in spectral shape with flux. Variations in the ratio of thehard/soft light curves are found to be present in 63 percent of theobjects investigated. The study of X-ray luminosity and spectralvariability in hard-X-ray-selected AGNs shows that no unique spectralbehavior can be associated with the objects. Source spectra can bedominated by either a soft independent component or by a variableabsorber when ME/LE color steepens.
| X-ray observations of the Seyfert 1 galaxy MCG 2-58-22
Results of the detailed X-ray (0.1-10 keV) spectral analysis of theSeyfert 1 galaxy, MGC 2-58-22, are presented based on the Exosatobservations on 1984 November 16-26. X-ray spectra of this source wereobtained from the Exosat archives. Weak, soft flux (0.1-2 keV)variations were found on time scales of 2-3 days, and no variations ofthe hard flux were found during the Exosat observations. Variable softexcesses have been detected in this source. A two power-law modelprovides good fits to the soft excesses. Variations of the LE count rateare correlated with the variations of the soft spectral index (obtainedfrom the two power-law fit) and anticorrelated with the hardness ratioof this source. A highly significant (99.9 percent) emission line at 5.8+/- 0.7 keV with the measured equivalent width as 160 +/- 110 eV hasbeen detected in the X-ray spectra of MCG 2-58-22. The significance ofthese results are discussed.
| On the ratio of the infrared-to-ultraviolet continuum to the X-rays in quasars and active galaxies
A sample of 122 quasars and Seyfert galaxies was analyzed and it wasfound that the NIR 7500 A rest frame luminosity is more linearly relatedto the X-ray luminosity than is the optical luminosity. It is also foundthat the mean spectral slope between 7500 and 4200 A in the rest framemonotonically flattens with luminosity over more than three orders ofmagnitude. The present results support models which attribute the IR andX-ray continua to linked nonthermal processes such as synchrotronself-Compton, while the blue-UV bump comes from a different source, suchas an accretion disk.
| Central Parts of Some Irregular Type-II Candidate Galaxies
Not Available
| Determination of the relative spectrophotometric gradients of galaxies. IV
Relative spectrophotometric gradients of continua are determined for 195galaxies. The spectra have been obtained with the 70-cm meniscustelescope of the Abastumani Astrophysical Observatory using a 2-degpreobjective prism (the reverse linear dispersion was 1200 A/mm inH-gamma). The gradient values were reduced to the AO spectral class andcorrected for light absorption in the Galaxy.
| X-ray, optical, and infrared luminosity correlations in radio-quiet quasars
Published UV, optical, and infrared photometry for a sample of X-rayobserved, radio-quiet quasars are analyzed. The criteria used to selectthe sample are discussed, and the general shape of the IR/opticalcontinuum is examined. Correlations among the various wavebands areanalyzed, and the implications for the empirical shape of theX-ray-to-infrared continuum in quasars and of possible energy generationmechanisms are considered.
| The contribution from active galactic nuclei to the diffuse 1 MeV background
A method is proposed to estimate the contribution from Seyfert galaxiesand quasars to the diffuse 1 MeV background. The contribution from theseAGNs to the 2 keV background is first calculated using traditionalmethods. Then a suitable spectral X-ray index, which is found to beuniversal, is chosen to find the 1 MeV contribution from these AGNs byextrapolation. Results show that quasars generate about 40 percent ofthe 1 MeV background while Seyfert galaxies produce more than 40 percenttaking into account the Penrose Compton Scattering gamma ray emissions.These results indicate that the 1 MeV background is likely to begenerated by discrete objects.
| More Seyfert galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978MNRAS.184P..11W&db_key=AST
| Spectroscopic study of two clusters of galaxies: Abell 2634 and ZW 2247+11
Results are reported for spectroscopic observations of 17 galaxies inAbell 2634 and 16 galaxies in Zwicky 2247+11, both of which clusterscontain radio-tail galaxies. The radial-velocity distributions for theobserved samples in each cluster are determined; a mean velocity of 9372km/s with a dispersion in the line-of-sight velocities of 927 km/s and acorresponding total dispersion of 1610 km/s is obtained for the 17galaxies in Abell 2634, and a mean velocity of 7577 km/s with acorresponding total dispersion of 965 km/s is found for 14 galaxies inZwicky 2247+11. Calculations performed for the parameters of theradio-tail galaxies in the clusters strongly indicate that significantin situ relativistic-particle acceleration is occurring in the radiotails.
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