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|Structure and kinematics of edge-on galaxy discs - IV. The kinematics of the stellar discs|
The stellar disc kinematics in a sample of 15 intermediate- to late-typeedge-on spiral galaxies are studied using a dynamical modellingtechnique. The sample covers a substantial range in maximum rotationvelocity and deprojected face-on surface brightness and contains sevenspirals with either a boxy- or peanut-shaped bulge. Dynamical models ofthe stellar discs are constructed using the disc structure from I-bandsurface photometry and rotation curves observed in the gas. Thedifferences in the line-of-sight stellar kinematics between the modelsand absorption-line spectroscopy are minimized using a least-squaresapproach. The modelling constrains the disc surface density and stellarradial velocity dispersion at a fiducial radius through the freeparameter (σz/σR)-1, whereσz/σR is the ratio of vertical andradial velocity dispersion and M/L is the disc mass-to-light ratio. For13 spirals a transparent model provides a good match to the meanline-of-sight stellar velocity dispersion. Models that include arealistic radiative transfer prescription confirm that the effect ofdust on the observable stellar kinematics is small at the observed slitpositions. We discuss possible sources of systematic error and concludethat most of these are likely to be small. The exception is the neglectof the dark halo gravity, which has probably caused an overestimate ofthe surface density in the case of low surface brightness discs.
|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.
|HI observations of loose galaxy groups. I. Data and global properties|
At Nançay, 21-cm H I line observations were made of 15spiral-dominated loose groups of galaxies, divided into two samples: an``interacting'' sample containing at least one pair of interactinggalaxies, and a ``control'' sample having no optical evidence ofinteractions or morphological disturbances among the group members. Theinteracting sample consists of 62 galaxies representing 9 differentgroups, and the control sample contains 40 galaxies representing 6groups. Of the 91 galaxy and galaxy pairs observed, 74 were detected,while upper limits were placed on the remaining 17 objects. Thesehomogeneous H I data, which will be used in future analyses, providecomparative information on the H I content of groups and serve as aprobe of the vicinity of the target spirals for H I clouds or very lowsurface brightness gas-rich galaxies.
|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.
|Seeing Galaxies through Thick and Thin. I. Optical Opacity Measures in Overlapping Galaxies|
We describe the use of partially overlapping galaxies to provide directmeasurements of the effective absorption in galaxy disks, independent ofassumptions about internal disk structure. The nonoverlapping parts ofthe galaxies and symmetry considerations are used to reconstruct, viadifferential photometry, how much background galaxy light is lost inpassing through the foreground disks. Extensive catalog searches andfollow-up imaging yield ~15-25 nearby galaxy pairs suitable for varyingdegrees of our analysis; 11 of the best such examples are presentedhere. From these pairs, we find that interarm extinction is modest,declining from AB~1 mag at 0.3RB25 toessentially zero by RB25; the interarm dust has ascale length consistent with that of the disk starlight. In contrast,dust in spiral arms and resonance rings may be optically thick(AB>2) at virtually any radius. Some disks have flatterextinction curves than the Galaxy, with AB/AI~1.6this is probably the signature of clumpy dust distributions. Even thoughtypical spirals are not optically thick throughout their disks, wherethey are optically thick is correlated with where they are mostluminous: in spiral arms and inner disks. This correlation betweenabsorption and emission regions may account for their apparent surfacebrightness being only mildly dependent on inclination, erroneouslyindicating that spirals are generally optically thick. Taken as anensemble, the opacities of spiral galaxies may be just great enough tosignificantly affect QSO counts, though not enough to cause theirhigh-redshift cutoff. Based in part on archival observations with theNASA/ESA Hubble Space Telescope (HST) obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS5-26555.
|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.
|An X-Ray Survey of Galaxies in Pairs|
Results are reported from the first survey of X-ray emission fromgalaxies in pairs. The sample consists of 52 pairs of galaxies from theCatalog of Paired Galaxies whose coordinates overlap the ROSAT PositionSensitive Proportional Counter pointed observations. The mean observedlogl_X for early-type pairs is 41.35+/-0.21, while the mean logl_Xpredicted using the l_X-l_b relationship for isolated early-typegalaxies is 42.10+/-0.19. With 95% confidence, the galaxies in pairs areunderluminous in the X-ray, compared with isolated galaxies, for thesame l_b. A significant fraction of the mixed pair sample also appearssimilarly underluminous. A spatial analysis shows that the X-rayemission from pairs of both types typically has an extent of ~10-50 kpc,much smaller than the group intergalactic medium, and thus likelyoriginates from the galaxies. CPG 564, the most X-ray luminousearly-type pair, 4.7x10^42 ergs s^-1, is an exception. The extent of itsX-ray emission, greater than 169 kpc, and HWHM, ~80 kpc, is comparableto that expected from an intergalactic medium. The sample shows only aweak correlation, ~81% confidence, between l_X and l_b, presumably dueto variations in gas content within the galaxies. No correlation betweenl_X and the pair velocity difference (Deltav), separation (Deltar), orfar-infrared luminosity (l_fir) is found, although the detection rate islow, 22%.
|Dust in Spiral Galaxies: Comparing Emission and Absorption to Constrain Small-Scale and Very Cold Structures|
The detailed distribution of dust in the disks of spiral galaxies isimportant to understanding the radiative transfer within disks and tomeasuring overall dust masses if significant quantities of dust areeither very opaque or very cold. We address this issue by comparingmeasures of dust absorption, using the galaxy-overlap technique in theoptical, with measures of the dust grains' thermal emission from 50-2000μm, using ISOPHOT on board Infrared Space Observatory (ISO) and SCUBAat the James Clerk Maxwell Telescope. We examine three spiral galaxiesprojected partially in front of E/S0 galaxies: AM 1316-241, NGC 5545,and NGC 5091 (for NGC 5091 we have only optical and ISO data). Adoptingan empirical exponential model for the dust distribution, we comparecolumn densities and dust masses derived from the absorption andemission techniques. This comparison is sensitive to the amount of dustmass in small, opaque structures, which would not contribute strongly toarea-weighted absorption measures, and to very cold dust, which wouldcontribute to optical absorption but provide only a small fraction ofthe submillimeter emission. In AM 1316-241, we find global dust massesof 2-5x10^7 M_solar, with the two techniques agreeing at the 50% level.NGC 5545 has about half this dust mass. The concordance of dust massesis well within the errors expected from our knowledge of the radialdistribution of dust and argues against any dominant part of the dustmass being so cold or opaque. The 50-2000 μm data are well fitted bymodified Planck functions with an emissivity law β=-2, at 21+/-2 K;a modest contribution from warmer dust is required to fit only the 50μm measurement of NGC 5545. We incorporate empirical corrections tothe flux scale of ISOPHOT P32 data, which can reach a factor 2 fromcomparison of IRAS and ISO fluxes for objects in two programs. We alsopresent 12 μm ISOCAM observations of these pairs. The light profilesat this wavelength exhibit shorter disk scale lengths than in theoptical. Comparison of Hα and 12 μm images of NGC 5545 indicatethat ISOCAM images are reliable tracers of star formation.
|Formation of a Polar Ring Galaxy in a Galaxy Merger|
We numerically investigate stellar and gas dynamics in star-forming anddissipative galaxy mergers between two disk galaxies with specificorbital configurations. We find that violent relaxation combined withgaseous dissipation in galaxy merging transforms two disk galaxies intoone S0 galaxy with polar rings; both the central S0-like host and thepolar ring component in a polar ring galaxy are originally diskgalaxies. We also find that morphology of the developed polar ringsreflects both the initial orbit configuration of galaxy merging and theinitial mass ratio of the two merger progenitor disk galaxies. Basedupon these results, we discuss the origin of the fundamentalobservational properties of polar ring galaxies, such as the prevalenceof S0 galaxies among polar ring galaxies, the rarity of polar ringgalaxies among S0 galaxies, the dichotomy between narrow polar rings andannular ones, the shapes of polar ring warps, and an appreciably largeramount of interstellar gas in the polar ring component.
|Groups of galaxies. III. Some empirical characteristics.|
|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 CfA Redshift Survey: Data for the NGP +36 Zone|
We have assembled redshifts for a complete sample of 719 galaxies withm_zw_ <= 15.5 in the declination range 32.5^deg^ <= δ <=38.5^deg^ and right ascension range 8^h^ <= α <= 17^h^. Wehave determined morphological types for all galaxies in the magnitudelimited sample by direct inspection of the POSS-O plates. 576 of theredshifts are measurements from Mount Hopkins, and 405 are newredshifts. We also include new redshifts for 77 fainter galaxies in thesame strip.
|Neutral hydrogen observations of galaxies in the Hercules supercluster. III. CGCG fields at the edge of the void.|
The third installment of a HI redshift survey in the region of theHercules supercluster is presented. This part of the survey presents HIspectra of 84 galaxies selected from the UGC and CGCG which extends thepreviously begun survey of late-type spiral galaxies in that region.Measured HI parameters from the spectra are given. For about 20% of thesample, these parameters are compared to those measured previously byother workers.
|A revised catalog of CfA1 galaxy groups in the Virgo/Great Attractor flow field|
A new identification of groups and clusters in the CfA1 Catalog ofHuchra et al. is presented, using a percolation algorithm to identifydensity enhancements. It is shown that in the resulting catalog,contamination by interlopers is significantly reduced. The Schechterluminosity function is redetermined, including the Malmquist bias.
|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.
|Effects of Interactions on the Nuclear Near Infrared Properties of Spiral Galaxies|
Using JHKL photometric measures available in the literature, we havecompared the near-infrared colour indices and central luminosities ofsamples of relatively isolated spiral galaxies with LINER and H IIregion-like nuclei (hereafter called L and H) with corresponding samplesof interacting galaxies, in order to explore the effects of interactionson their near-infrared properties. We have found that the L galaxies andthe isolated H galaxies have, in general, normal near-infrared colourswhich are fully explainable in terms of emission from late-type evolvedstars. On the other hand, the sample of interacting H galaxies displays,on average, somewhat peculiar near-infrared colours (specifically,normal J - H colours, but redward H - K and, especially, K - Lexcesses), which very probably indicate the presence of thermal emissionfrom hot dust, presumably related to intense star formation activityinduced by the interactions. Furthermore, for the same galaxy samplethere is some evidence that the emission at λ ~ 2.2 microns issomewhat more centrally concentrated than that at shorter wavelengths.Interestingly, the L galaxies appear to have greater centralnear-infrared luminosities than the H galaxies, for the samemorphological-type interval.
|The far-infrared properties of the CfA galaxy sample. I - The catalog|
IRAS flux densities are presented for all galaxies in the Center forAstrophysics magnitude-limited sample (mB not greater than 14.5)detected in the IRAS Faint Source Survey (FSS), a total of 1544galaxies. The detection rate in the FSS is slightly larger than in thePSC for the long-wavelength 60- and 100-micron bands, but improves by afactor of about 3 or more for the short wavelength 12- and 25-micronbands. This optically selected sample consists of galaxies which are, onaverage, much less IR-active than galaxies in IR-selected samples. Itpossesses accurate and complete redshift, morphological, and magnitudeinformation, along with observations at other wavelengths.
|KISO survey for ultraviolet-excess galaxies. XIII.|
|HI observations of galaxies in nearby Zwicky clusters|
The results of a long term project of H I observations of galaxieswithin the boundaries of nearby Zwicky clusters are presented. Thedetection rate is rather low (233 out of 618, i.e., 38 percent) ascompared to other surveys carried out recently. Most of the radialvelocities of the detected galaxies are new determinations. The largespread in radial velocities for many of these clusters is a strongindication for the presence of several foreground and/or backgroundgalaxies.
|Effects of Interactions on the Radio Properties of Non-Seyfert Galaxies|
On the basis of radio surveys published in the literature we havecompared the radio properties of samples of relatively isolated spiralgalaxies with LINER- and H II- region-like nuclei (hereafter called Land H galaxies) with corresponding samples of non-Seyfert interactinggalaxies, in order to explore the effects of interactions on their radioproperties. Basically, we have found enhanced total and central radioemission (per light unit) in interacting H galaxies (compared with theirrelatively isolated counterparts) and enhanced central radio emission(per light unit) in interacting L galaxies. Analogous enhancements inthe strength of the total and nuclear Hα emission lines areobserved in interacting galaxies. Furthermore, within a sample ofinteracting galaxies, there appears to be evidence of enhanced total andcentral radio emission (per light unit) in strongly interacting galaxieswhich are likely to have H II-region-like nuclei, compared withmoderately interacting objects of the same nuclear type. Interacting Hgalaxies contain more extended central radio sources than isolatedgalaxies, whereas no difference in this sense is observed in the case ofL galaxies. L galaxies which contain, on average, weaker total andcentral radio sources than the H galaxies have, on average, smallercentral radio sources (of greater radio surface brightness) than the Hgalaxies and follow a less-steep logarithmic radio power-radio sizerelation. As regards the Seyfert galaxies, which are known to becharacterized by powerful central radio emission, we have found thatthey contain, on average, central radio sources of intermediate size,which obey a power-size relation of intermediate steepness (with respectto the L and H galaxies). Thus our statistical study reveals basicstructural differences between the radio properties of the L, H andSeyfert galaxies, and between the effects of interactions on the radioproperties of the three classes of galaxies.
|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.
|Gaseous content of galaxies inside groups|
The gaseous content of a sample constituted of 84 Sb and 95 Sc galaxiesinside groups has been analyzed. After correcting for the luminosityeffect, no gas deficiency was found for those galaxies in spite of aspan of about 2 orders of magnitude in the galaxy density. Anyintergalactic gas present in the considered groups must have densitiessmaller than 0.0003/cu cm.
|Groups of galaxies in the Center for Astrophysics redshift survey|
By applying the Huchra and Geller (1982) objective group identificationalgorithm to the Center for Astrophysics' redshift survey, a catalog of128 groups with three or more members is extracted, and 92 of these areused as a statistical sample. A comparison of the distribution of groupcenters with the distribution of all galaxies in the survey indicatesqualitatively that groups trace the large-scale structure of the region.The physical properties of groups may be related to the details oflarge-scale structure, and it is concluded that differences among groupcatalogs may be due to the properties of large-scale structures andtheir location relative to the survey limits.
|Observations of galaxies in groups at 102 MHz|
Observations of 325 galaxies in groups were carried out at a frequencyof 102 MHz via the scintillation method. Radio emission was found in 42of these components. Eleven of these have a meridional component.
|The effects of interactions on spiral galaxies. II - Disk star-formation rates|
H-alpha emission-line and IRAS far-IR observations of interacting spiraland irregular galaxies are here used to assess the influence ofinteractions on their global star-formation rates. Two samples ofinteracting galaxies were observed: a complete sample of close pairs,and an Arp atlas sample of peculiar systems. When compared to a controlsample of single galaxies, both samples of interacting systems exhibitsystematically higher levels of H-alpha and infrared emission onaverage, and a larger dispersion in emission properties. Emission levelsin the very active system are much more strongly correlated with theproperties of the interaction than with the internal properties of thegalaxies themselves. Strong disk emission is almost always accompaniedby unusually strong nuclear activity. Simple star-formation burst modelscan reproduce the observed H-alpha equivalent widths and broadbandcolors of most of the galaxies. The bursts are relatively short (fewtimes 10 million yr) and rarely involve more than 1-2 percent of agalaxy's total mass.
|The effects of interactions on spiral galaxies. III - A radio continuum survey of galactic nuclei at 1.49 GHz|
The radio continuum emission from the central region of a sample ofinteracting spiral galaxies (92 galaxies of which 60 in a completesample) and of a control sample of more isolated spiral galaxies (94)was observed with the Very Large Array at 1.49 GHz. The angularresolution of the observations is about 1.3 arcsec, and the detectionlimits are about 0.6 and 1.5 mJy for point sources and extended sourceswith a half power size of 10 arcsec, respectively. This survey, incombination with published optical spectroscopy, provides the data for adetailed comparison of the central region in interacting and moreisolated spiral galaxies.
|The effects of interactions on spiral galaxies. I - Nuclear activity and star formation|
When the present results of spectrophotometry for the nuclei of 161(mostly spiral) galaxies with bright companions and emission lineimaging of 63 galaxies were compared to a similarly observed sample ofisolated-spiral nuclei, both samples of interacting galaxies exhibitedsignificant excesses of nuclear emission. The rate of nuclear starformation is significantly above average even in systems withoutnoticeable tidal distortion in the outer disks, suggesting that thenear-nuclear gas is only marginally stable in isolated galaxies. Theresults obtained suggest that nuclear phenomena are triggered by atidally induced influx of gas from the disk into the nuclear regions,rather than gas transfer between the galaxies.
|A search for environmental effects on the optical properties of galaxies in groups|
Environmental density-related modifications of basic optical properties(luminosities, sizes, axial ratios, and colors) of galaxies belonging toGeller and Huchra's (1983) groups have been investigated. Remarkably, itis found that the broad maxima of the distributions of luminosities anddiameters of spirals and the whole corresponding distributions oflenticulars tend to move to lower values as one goes to groups of highcompactness, whereas the luminosity-diameter relationship of spiralstends to become flatter. No color and axial ratio differences betweengalaxies of high- and low-compactness groups have been detected.
|Recent star formation in interacting galaxies. I - Evidence from JHKL photometry|
A survey has been carried out using JHKL photometry to investigaterecent star formation in interacting galaxies. The objective was to lookfor a K-L excess produced by 'warm' dust heated by a putative burst ofstar formation. K-L excesses are found suggesting that interactionsinduce starbursts with an efficiency approaching 100 percent. Theappearance of these inferred starbursts in interacting systems ofdifferent morphological types is qualitatively consistent with dynamicalstudies of galaxy interactions. However, the common occurrence of suchstarbursts shows that interactions have implications for theastrophysics of galaxies well beyond purely morphological effects.
|H I line studies of galaxies. III - Distance moduli of 822 disk galaxies|
The distance scale established on the basis of a distance moduli catalog(for 822 galaxies) that was derived from 21-cm line widths via theB-band Tully-Fisher relation is compared with several independent scaleshaving a common zero point, that are based on the indicators forluminosity index, redshift, ring diameters, brightest superassociations,and effective diameters. These are in excellent systematic agreement,and confirm the linearity of the H I scale in the 24-35 modulusinterval, but indicate a small systematic zero point difference of about0.2 mag, which must be added to the H I moduli to place them on the same'short' distance scale defined by the others.
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