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Imaging Fabry-Perot Spectroscopy of NGC 5775: Kinematics of the Diffuse Ionized Gas Halo
We present imaging Fabry-Perot observations of Hα emission in thenearly edge-on spiral galaxy NGC 5775. We have derived a rotation curveand a radial density profile along the major axis by examiningposition-velocity (PV) diagrams from the Fabry-Perot data cube, as wellas a CO 2-1 data cube from the literature. PV diagrams constructedparallel to the major axis are used to examine changes in azimuthalvelocity as a function of height above the midplane. The results of thisanalysis reveal the presence of a vertical gradient in azimuthalvelocity. The magnitude of this gradient is approximately 1 kms-1 arcsec-1, or about 8 km s-1kpc-1, although a higher value of the gradient may beappropriate in localized regions of the halo. The evidence for anazimuthal velocity gradient is much stronger for the approaching half ofthe galaxy, although earlier slit spectra are consistent with a gradienton both sides. There is evidence for an outward radial redistribution ofgas in the halo. The form of the rotation curve may also change withheight, but this is not certain. We compare these results with those ofan entirely ballistic model of a disk-halo flow. The model predicts avertical gradient in azimuthal velocity that is shallower than theobserved gradient, indicating that an additional mechanism is requiredto further slow the rotation speeds in the halo.
| The structure of galactic disks. Studying late-type spiral galaxies using SDSS
Using imaging data from the SDSS survey, we present the g' and r' radialstellar light distribution of a complete sample of ~90 face-on tointermediate inclined, nearby, late-type (Sb-Sdm) spiral galaxies. Thesurface brightness profiles are reliable (1 σ uncertainty lessthan 0.2 mag) down to μ27 mag/''. Only ~10% of all galaxies havea normal/standard purely exponential disk down to our noise limit. Thesurface brightness distribution of the rest of the galaxies is betterdescribed as a broken exponential. About 60% of the galaxies have abreak in the exponential profile between 1.5-4.5 times thescalelength followed by a downbending, steeper outer region. Another~30% shows also a clear break between 4.0-6.0 times thescalelength but followed by an upbending, shallower outer region. A fewgalaxies have even a more complex surface brightness distribution. Theshape of the profiles correlates with Hubble type. Downbending breaksare more frequent in later Hubble types while the fraction of upbendingbreaks rises towards earlier types. No clear relation is found betweenthe environment, as characterised by the number of neighbours, and theshape of the profiles of the galaxies.
| The multi-phase gaseous halos of star forming late-type galaxies. I. XMM-Newton observations of the hot ionized medium
This study presents first results from an X-ray mini-survey carried outwith XMM-Newton to investigate the diffuse Hot Ionized Medium in thehalos of nine nearby star-forming edge-on spiral galaxies. Diffusegaseous X-ray halos are detected in eight of our targets, covering awide range of star formation rates from quiescent to starburst cases.For four edge-on spiral galaxies, namely NGC 3044, NGC 3221, NGC 4634,and NGC 5775, we present the first published high resolution/sensitivitydetections of extended soft X-ray halos. EPIC X-ray contour mapsoverlaid onto Hα imaging data reveals that in all cases thepresence of X-ray halos is correlated with extraplanar Diffuse IonizedGas. Moreover, these halos are also associated with non-thermal cosmicray halos, as evidenced by radio continuum observations. SupplementalUV-data obtained with the OM-telescope at 210 nm show Diffuse IonizedGas to be well associated with UV emission originating in the underlyingdisk. Beside NGC 891, NGC 4634 is the second non-starburst galaxy with adiffuse soft X-ray halo (|z|≤ 4 kpc). In case of NGC 3877, for whichwe also present the first high resolution X-ray imaging data, no haloemission is detectable. EPIC pn spectra (0.3-12 keV) of the diffuseX-ray emission are extracted at different offset positions from thedisk, giving evidence to a significant decrease of gas temperatures,electron densities, and gas masses with increasing distance to theplane. A comparison between dynamical and radiative cooling time scalesimplies that the outflow in all targets is likely to be sustained. Wefind very strong indications that spatially correlated multi-phasegaseous halos are created by star forming activity in the disk plane. Ina forthcoming paper, we will present multi-frequency luminosityrelations and evaluate key parameters which might trigger the formationof multi-phase galaxy halos.
| Predicted chemical evolution for spiral disks from their observed rotation curves
The rotation curves for a sample of 67 spiral galaxies have been used asinput for the multiphase chemical evolution model. By using N[II]/Halfaas estimator of the oxygen abundance, we constraint the possible modelsfor each galaxy. We may, then, predict the time evolution of thesegalaxies and the present time radial distribution for gas, stars, andstar formation rate surface densities and elemental abundances.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| The Nature of Ultraluminous X-Ray Sources
We present spectroscopic observations of six optical counterparts ofultraluminous X-ray sources (ULXs) around nearby galaxies. The spectraof the six objects show the presence of broad emission features. Theidentification of these allow us to classify all of the objects asquasars at higher redshift than their assigned parent galaxy. This isone of the first and largest identifications of such objects usingunambigous optical spectral features. These results, in conjuction withprevious similar identifications of other sources, indicate thathigh-redshift quasars represent an important fraction of cataloged ULXsources. We estimate the density of such sources and compare this withexpectations for a population of randomly distributed backgroundquasars.
| The Structural Properties of Isolated Galaxies, Spiral-Spiral Pairs, and Mergers: The Robustness of Galaxy Morphology during Secular Evolution
We present a structural analysis of nearby galaxies in spiral-spiralpairs in optical BVRI bands and compare them with the structures ofisolated spiral galaxies and galaxies in ongoing mergers. We use thesecomparisons to determine how galaxy structure changes during galaxyinteractions and mergers. We analyze light concentration (C), asymmetry(A), and clumpiness (S) parameters, and use the projections of CASparameter space to compare these samples. We find that the CASparameters of paired galaxies are correlated with the projectedseparations of the pair. For the widest and closest pairs, the CASparameters tend to be similar to those of isolated and ongoing majormergers (e.g., ultraluminous infrared galaxies), respectively. Ourresults imply that galaxy morphology is a robust property that onlychanges significantly during a strong interaction or major merger. Thetypical timescale for this change in our paired sample, based ondynamical friction arguments, is short, τ~0.1-0.5 Gyr. We findaverage enhancement factors for the spiral-pair asymmetries andclumpiness values of ~2.2 and 1.5. The S parameter, which is related tostar formation (SF) activity, has a moderate level of enhancement,suggesting that this activity in modern spirals depends more on internalprocesses than on external conditions. We further test the statisticalcriterion for picking up interacting galaxies in an automated way byusing the A-S projection plane. The diversity of our spiral-pair samplein the CAS space suggests that structural/SF/morphological properties ofinteracting galaxies change abruptly only when the interaction becomesvery strong and the criteria given previously by Conselice for findinggalaxies involved in major mergers are effective.
| The Ultraluminous X-Ray Source Population from the Chandra Archive of Galaxies
One hundred fifty-four discrete non-nuclear ultraluminous X-ray (ULX)sources, with spectroscopically determined intrinsic X-ray luminositiesgreater than 1039 ergs s-1, are identified in 82galaxies observed with Chandra's Advanced CCD Imaging Spectrometer.Source positions, X-ray luminosities, and spectral and timingcharacteristics are tabulated. Statistical comparisons between theseX-ray properties and those of the weaker discrete sources in the samefields (mainly neutron star and stellar-mass black hole binaries) aremade. Sources above ~1038 ergs s-1 display similarspatial, spectral, color, and variability distributions. In particular,there is no compelling evidence in the sample for a new and distinctclass of X-ray object such as the intermediate-mass black holes.Eighty-three percent of ULX candidates have spectra that can bedescribed as absorbed power laws with index <Γ>=1.74 andcolumn density =2.24×1021cm-2, or ~5 times the average Galactic column. About 20% ofthe ULXs have much steeper indices indicative of a soft, and likelythermal, spectrum. The locations of ULXs in their host galaxies arestrongly peaked toward their galaxy centers. The deprojected radialdistribution of the ULX candidates is somewhat steeper than anexponential disk, indistinguishable from that of the weaker sources.About 5%-15% of ULX candidates are variable during the Chandraobservations (which average 39.5 ks). Comparison of the cumulative X-rayluminosity functions of the ULXs to Chandra Deep Field results suggests~25% of the sources may be background objects, including 14% of the ULXcandidates in the sample of spiral galaxies and 44% of those inelliptical galaxies, implying the elliptical galaxy ULX population isseverely compromised by background active galactic nuclei. Correlationswith host galaxy properties confirm the number and total X-rayluminosity of the ULXs are associated with recent star formation andwith galaxy merging and interactions. The preponderance of ULXs instar-forming galaxies as well as their similarities to less-luminoussources suggest they originate in a young but short-lived populationsuch as the high-mass X-ray binaries with a smaller contribution (basedon spectral slope) from recent supernovae. The number of ULXs inelliptical galaxies scales with host galaxy mass and can be explainedmost simply as the high-luminosity end of the low-mass X-ray binarypopulation.
| A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. II. Cluster Sizes and Structural Parameter Correlations
We investigate the structural properties of nuclear star clusters inlate-type spiral galaxies. More specifically, we fit analytical modelsto Hubble Space Telescope images of 39 nuclear clusters in order todetermine their effective radii after correction for the instrumentalpoint-spread function. We use the results of this analysis to comparethe luminosities and sizes of nuclear star clusters to those of otherellipsoidal stellar systems, in particular the Milky Way globularclusters. Our nuclear clusters have a median effective radius ofre=3.5 pc, with 50% of the sample falling in the range2.4pc<=re<=5.0pc. This narrow size distribution isstatistically indistinguishable from that of Galactic globular clusters,even though the nuclear clusters are, on average, 4 mag brighter thanthe old globular clusters. We discuss some possible interpretations ofthis result. From a comparison of nuclear cluster luminosities withvarious properties of their host galaxies, we confirm that more luminousgalaxies harbor more luminous nuclear clusters. It remains unclearwhether this correlation mainly reflects the influence of galaxy size,mass, and/or star formation rate. Since the brighter galaxies in oursample typically have stellar disks with a higher central surfacebrightness, nuclear cluster luminosity also correlates with thisproperty of their hosts. On the other hand, we find no evidence for acorrelation between the presence of a nuclear star cluster and thepresence of a large-scale stellar bar.
| The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies
We discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/
| A Catalog of Candidate Intermediate-Luminosity X-Ray Objects
ROSAT, and now Chandra, X-ray images allow studies of extranuclear X-raypoint sources in galaxies other than our own. X-ray observations ofnormal galaxies with ROSAT and Chandra have revealed that off-nuclear,compact, intermediate-luminosity(LX[2-10keV]>=1039.0 ergs s-1) X-rayobjects (IXOs, a.k.a. ULXs [ultraluminous X-ray sources]) are quitecommon. Here we present a catalog and finding charts for 87 IXOs in 54galaxies, derived from all of the ROSAT HRI imaging data for galaxieswith cz<=5000 km s-1 from the Third Reference Catalog ofBright Galaxies. We have defined the cutoff LX for IXOs sothat it is well above the Eddington luminosity of a 1.4Msolar black hole (1038.3 ergs s-1), soas not to confuse IXOs with ``normal'' black hole X-ray binaries. Thiscatalog is intended to provide a baseline for follow-up work withChandra and XMM-Newton, and with space- and ground-based survey work atwavelengths other than X-ray. We demonstrate that elliptical galaxieswith IXOs have a larger number of IXOs per galaxy than nonellipticalgalaxies with IXOs and note that they are not likely to be merelyhigh-mass X-ray binaries with beamed X-ray emission, as may be the casefor IXOs in starburst galaxies. Approximately half of the IXOs withmultiple observations show X-ray variability, and many (19) of the IXOshave faint optical counterparts in DSS optical B-band images. Follow-upobservations of these objects should be helpful in identifying theirnature.
| Kinematics of Diffuse Ionized Gas Halos: A Ballistic Model of Halo Rotation
To better understand diffuse ionized gas (DIG) kinematics and halorotation in spiral galaxies, we have developed a model in which cloudsare ejected from the disk and follow ballistic trajectories through thehalo. The behavior of clouds in this model has been investigatedthoroughly through a parameter space search and a study of individualcloud orbits. Synthetic velocity profiles have been generated in z(height above the plane) from the models for the purpose of comparingwith velocity centroid data from previously obtained long-slit spectraof the edge-on spirals NGC 891 (one slit) and NGC 5775 (two slits). Ineach case, a purely ballistic model is insufficient to explain observedDIG kinematics. In the case of NGC 891, the observed vertical velocitygradient is not as steep as predicted by the model, possibly suggestinga source of coupling between disk and halo rotation or an outwardlydirected pressure gradient. The ballistic model more successfullyexplains DIG kinematics observed in NGC 5775; however, it cannot explainthe observed trend of high-z gas velocities nearly reaching the systemicvelocity. Such behavior can be attributed to either an inwardly directedpressure gradient or a possible tidal interaction with its companion,NGC 5774. In addition, the ballistic model predicts that clouds moveradially outward as they cycle through the halo. The mass and energyfluxes estimated from the model suggest that this radially outward gasmigration leads to a redistribution of material that may significantlyaffect the evolution of the interstellar medium.
| Discovery of High-Latitude CO in an H I Supershell in NGC 5775
We report the discovery of very high latitude molecular gas in theedge-on spiral galaxy NGC 5775. Emission from both the J=1-0 and 2-1lines of 12CO is detected up to 4.8 kpc away from themidplane of the galaxy. NGC 5775 is known to host a number of H Isupershells. The association of the molecular gas(MH2,F2=3.1×107Msolar) reported here with one of the H I supershells(labeled F2) is clear, which suggests that molecular gas may havesurvived the process that originally formed the supershell.Alternatively, part of the gas could have been formed in situ at highlatitude from shock compression of preexisting H I gas. The COJ=2-1/J=1-0 line ratio of 0.34+/-40% is significantly lower than unity,which suggests that the gas is excited subthermally, with gas density afew times 102 cm-3. The molecular gas is likely inthe form of cloudlets that are confined by magnetic and cosmic-raypressure. The potential energy of the gas at high latitude is found tobe 2×1056 ergs, and the total (H I+H2)kinetic energy is 9×1053 ergs. Based on the energeticsof the supershell, we suggest that most of the energy in the supershellis in the form of potential energy and that the supershell is on theverge of falling and returning the gas to the disk of the galaxy.
| 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.
| A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. I. Observations and Image Analysis
We present new Hubble Space Telescope I-band images of a sample of 77nearby late-type spiral galaxies with low inclination. The main purposeof this catalog is to study the frequency and properties of nuclear starclusters. In 59 galaxies of our sample, we have identified a distinct,compact (but resolved), and dominant source at or very close to thephotocenter. In many cases, these clusters are the only prominent sourcewithin a few kiloparsecs from the galaxy nucleus. We present surfacebrightness profiles, derived from elliptical isophote fits, of allgalaxies for which the fit was successful. We use the fitted isophotesat radii larger than 2" to check whether the location of the clustercoincides with the photocenter of the galaxy and confirm that in nearlyall cases, we are truly dealing with ``nuclear'' star clusters. Fromanalytical fits to the surface brightness profiles, we derive thecluster luminosities after subtraction of the light contribution fromthe underlying galaxy disk and/or bulge. Based on observations made withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555. Theseobservations are associated with proposal 8599.
| Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of Hαemission line of a sample of 111 spiral galaxies with recognizable andwell defined spiral morphology and with a well determined environmentalstatus, ranging from isolation to non-disruptive interaction withsatellites or companions. The form and properties of the rotation curvesare considered as a function of the isolation degree, morphological typeand luminosity. The line ratios are used to estimate the metallicity ofall the detected HII regions, thus producing a composite metallicityprofile for different types of spirals. We have found that isolatedgalaxies tend to be of later types and lower luminosity than theinteracting galaxies. The outer parts of the rotation curves of isolatedgalaxies tend to be flatter than in interacting galaxies, but they showsimilar relations between global parameters. The scatter of theTully-Fisher relation defined by isolated galaxies is significantlylower than that of interacting galaxies. The [NII]/Hα ratios, usedas a metallicity indicator, show a clear trend between Z andmorphological type, t, with earlier spirals showing higher ratios; thistrend is tighter when instead of t the gradient of the inner rotationcurve, G, is used; no trend is found with the change in interactionstatus. The Z-gradient of the disks depends on the type, being almostflat for early spirals, and increasing for later types. The[NII]/Hα ratios measured for disk HII regions of interactinggalaxies are higher than for normal/isolated objects, even if all thegalaxy families present similar distributions of Hα EquivalentWidth. Tables 3 and 4 and Figs. 6, 7 and 21 are only available inelectronic form at http://www.edpsciences.org. Table 5 is only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/389 Based on dataobtained Asiago/Ekar Observatory. Also based on observations made withINT operated on the island of La Palma by ING in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias.
| 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 Frequency of Active and Quiescent Galaxies with Companions: Implications for the Feeding of the Nucleus
We analyze the idea that nuclear activity, either active galactic nuclei(AGNs) or star formation, can be triggered by interactions by studyingthe percentage of active, H II, and quiescent galaxies with companions.Our sample was selected from the Palomar survey and avoids selectionbiases faced by previous studies. This sample was split into fivedifferent groups, Seyfert galaxies, LINERs, transition galaxies, H IIgalaxies, and absorption-line galaxies. The comparison between the localgalaxy density distributions of the different groups showed that in mostcases there is no statistically significant difference among galaxies ofdifferent activity types, with the exception that absorption-linegalaxies are seen in higher density environments, since most of them arein the Virgo Cluster. The comparison of the percentage of galaxies withnearby companions showed that there is a higher percentage of LINERs,transition galaxies, and absorption-line galaxies with companions thanSeyfert and H II galaxies. However, we find that when we consider onlygalaxies of similar morphological types (elliptical or spiral), there isno difference in the percentage of galaxies with companions amongdifferent activity types, indicating that the former result was due tothe morphology-density effect. In addition, only small differences arefound when we consider galaxies with similar Hα luminosities. Thecomparison between H II galaxies of different Hα luminositiesshows that there is a significantly higher percentage of galaxies withcompanions among H II galaxies with L(Hα)>1039 ergss-1 than among those with L(Hα)<=1039ergs s-1, indicating that interactions increase the amount ofcircumnuclear star formation, in agreement with previous results. Thefact that we find that galaxies of different activity types have thesame percentage of companions suggests that interactions betweengalaxies is not a necessary condition to trigger the nuclear activity inAGNs. We compare our results with previous ones and discuss theirimplications.
| BVRI surface photometry of (S+S) binary galaxies I. The data
We present multicolour broad band (BVRI) photometry for a sample of 33spiral-spiral (S+S) binary galaxies drawn from the KarachentsevCatalogue of Isolated Pairs of Galaxies (KPG). The data is part of ajoint observational programme devoted to systematic photometric study ofone of the most complete and homogeneous pair samples available in theliterature. We present azimuthally averaged colour and surfacebrightness profiles, colour index (B-I) maps, B band and sharp/filteredB band images as well as integrated magnitudes, magnitudes at differentcircular apertures and integrated colours for each pair. Internal andexternal data comparisons show consistency within the estimated errors.Two thirds of the sample have total aperture parameters homogeneouslyderived for the first time. After reevaluating morphology for all thepairs, we find a change in Hubble type for 24 galaxies compared to theoriginal POSS classifications. More than half of our pairs showmorphological concordance which could explain, in part, the strongcorrelation in the (B-V) colour indices (Holmberg Effect) between paircomponents. We find a tendency for barred galaxies to show grand designmorphologies and flat colour profiles. The measurements will be used ina series of forthcoming papers where we try to identify and isolate themain structural and photometric properties of disk galaxies at differentstages of interaction. Table A.1 is only available in electronic form atthe CDS via anonymous ftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/54 and Tables 2-4 arealso available in electronic form at the CDS. Full Fig. 5 is onlyavailable in electronic form at the http://www.edpsciences.org Based ondata obtained at the 2.1 m telescope of the Observatorio Guillermo Haroat Cananea, Sonora, México, operated by the Instituto Nacional deAstrofísica, Optica y Electrónica.
| NGC 5775: Anatomy of a disk-halo interface
We present the first high-resolution study of the disk-halo interface inan edge-on galaxy (NGC 5775) in which every component of theinterstellar medium is represented and resolved (though not all to thesame resolution). New single-dish CO J=2-1 and CO J=1-0 data, ROSATX-ray data, and HIRES IRAS data are presented along with HI data whichemphasizes the high latitude features. In conjunction with previouslypublished radio continuum (6 and 20 cm) and Hα data, we findspatial correlations between various ISM components in that allcomponents of the ISM are present in the disk-halo features (except forCO for which there is insufficient spatial coverage). The HI featuresextend to ~ 7 kpc above the plane, form loops in position-positionspace, in one case, form a loop in position-velocity space, and are alsoobserved over a large velocity range. This implies that the disk-halofeatures represent expanding supershells. However, the shells may beincomplete and partially open-topped, suggesting that we are observingthe breakup of the supershells as they traverse the disk-halo interface.There is some evidence for acceleration with z and both redshifted andblueshifted velocities are present, although the gas which is laggingwith respect to galactic rotation dominates. The radio continuumspectral index is flatter around the shell rims and we show that thiscannot be due to a contribution from thermal gas but rather is due tointrinsic flattening of the non-thermal spectral index, suggesting thatshocks may be important in these regions. The Hα emission islocated interior to the HI. For feature F3, the Hα emission formsthe interior ``skin" of the HI shell, yet there appears to be a minimumof in-disk star formation immediately below the feature. We present apicture of a ``typical" HI supershell which accelerates and breaks upthrough the disk-halo interface. Such a feature is likely internallygenerated via an energetic event in the disk.
| The second Kiso Survey for ultraviolet-excess galaxies. II.
Not Available
| 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.
| 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.
| Investigation of Barred Galaxies. V. Surroundings of SB and SA Galaxies
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| The Interacting Galaxies NGC 5394/5395: A Post-Ocular Galaxy and Its Ring/Spiral Companion
H I, radio continuum, Fabry-Perot Hα, and ^12CO J=1-->0observations and broadband optical and near infrared images arepresented of the interacting spiral galaxies NGC 5395 and NGC 5394.Kinematically, there are three important, separate components to the H Igas associated with this galaxy pair: (1) the main disk of NGC 5395, (2)a long, northern tidal arm of NGC 5395 distinct in velocity from itsmain disk, and (3) the disk of NGC 5394. The H I northern tidal arm ofNGC 5395 has a line of-sight velocity as much as 75-100 km s^-1 greaterthan the main disk of NGC 5395 at the same projected location and thusis not in the same plane as the disk. The velocity field of the disk ofNGC 5395 is asymmetric and distorted by large-scale and small-scalenoncircular motions. In NGC 5395, the encounter appears to be excitingm=1 and m=0 modes in what had been a two-armed spiral. The dominantspiral arm of NGC 5395 forms a large ring or pseudo-ring of Hα,radio continuum, and H I emission, somewhat off center with respect tothe nucleus. The H I trough in the center of NGC 5395 is not filled inby molecular gas. The Hα velocity contours exhibit an organizedpattern of kinks in crossing the ring and also show streaming motions ina large stellar caustic feature. The eastern side of the ring isbrighter in radio continuum and Hα the western side is brighter inH I and contains massive (10^8 M_solar) H I clouds not associated withthe most luminous H II regions. The smaller galaxy NGC 5394 is in animmediate post-ocular phase, with a central starburst, an intrinsicallyoval disk, two long, fairly symmetric, open tidal arms with higharm-interarm contrast, and very bright inner spiral arms, disjoint fromthe outer tidal arms. Most of the gas in NGC 5394 is in molecular formand concentrated within 3.8 kpc of the center, so is suitable forfueling the starburst. Despite the presence of H I gas, two of the threeoptically bright inner spiral arms of NGC 5394 show no evidence ofongoing star formation. A galaxy encounter simulation reproduces some ofthe main features of this system with a collision that is prograderelative to NGC 5394 and retrograde at a high tilt angle relative to NGC5395. The model finds that the inner spiral structure of NGC 5394developed from an eye-shaped (``ocular'') structure at slightly earliertimes. NGC 5394 and the two ocular galaxies IC 2163 and NGC 2535,studied earlier, form an evolutionary sequence of structures resultingfrom prograde encounters and thus confirm the generic models of suchcollisions. The agreement between the model for NGC 5394/95 and thering/spiral structures seen in NGC 5395 extends our understanding ofcollisional ring galaxies.
| Groups of galaxies. III. Some empirical characteristics.
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| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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 (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| The radio continuum halo of NGC 5775
Sensitive, scaled-array VLA radio-continuum observations of the edge-ongalaxy NGC 5775, at 6 and 20 cm, show evidence of a radio-continuum halothat is detected up to 10-15 kpc above and below the plane. In addition,the presence of a radio continuum bridge connecting NGC 5775 toneighbouring NGC 5774 is confirmed, lending further support to reportsthat these galaxies form an interacting pair. Detailed analysis of theradio continuum halo of NGC 5775 indicates that it is characterized by arelatively steep spectrum with a spectral index of ~ 1.0. The spectralindex of the disk is significantly flatter, averaging ~ 0.6. To firstorder, there is no evidence for large-scale spectral changes as afunction of distance from the mid-plane in either component. Thesuperposition of the disk and halo components, with distinctly differentspectral indices, accounts for the apparent spectral steepening of theobserved (total) emission with distance from the mid-plane. The spectralresults presented here are consistent with the findings for NGC 3556(Bloemen et al. 1993), which could be studied with a 2-3 times betterlinear resolution. As with NGC 3556 the relatively flat spectrum of thedisk of NGC 5775 appears to be the result of an ensemble of discretesources, embedded in diffuse steep-spectrum emission as found in thehalo. It appears that the gradual spectral steepening away from themid-plane found in previous studies of edge-on galaxies may beattributed to insufficient angular resolution, supplemented by themissing-flux problem. In contrast to the absence of global spectralchanges in the disk and halo there are localized features of flatterspectral index that appear to connect the disk to the halo. These``tentacles" of flatter spectral index are roughly vertical and mayrepresent chimneys of localized convection.
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