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Two-dimensional warm gas kinematics in interacting galaxy systems
Gas reservoirs, internal or acquired, play an important role in thesecular evolution of interacting galaxies, since they are able toenhance/trigger star formation episodes and, probably, feed the activityof active galactic nuclei. Using Fabry-Perot observations, we havemapped, in the Hα line, the warm (T~ 104) gasdistribution and the velocity fields of the galaxy members of fiveinteracting, gas-rich galaxy systems. We investigated two M51-likesystems (Arp 70 and Arp 74), two systems containing highly disruptedmembers (WBL 366 and RR 24) and a case of merging in progress (Arp 299,one of the nearest luminous infrared objects).We detected gas motions following the elongated arm/tail of Arp 70b,while in the fainter member of the pair of galaxies, Arp 70a, the gasdistribution is off-centred with respect to the stellar isophotes,suggesting an external acquisition. Our kinematic data highlightednon-circular motions in the velocity field of one of the members of Arp74 (Arp 74a). The two galaxies of the RR 24 system are connected by onetidal tail, through which the kinematically disturbed component RR 24bseems to supply warm gas to RR 24a. In spite of the nearly irregular gasdistribution and perturbed morphology, WBL 366a (the star-forming galaxyVV-523) and WBL 366b have nearly regular velocity fields. The velocityfield in the Arp 299 system is irregular, and gas flow between the twonuclei is detected.The present observations, discussed in the light of model predictionsand complementary observations from the literature, suggest that allthese systems are still probably in an early phase of the encounter.However, the ionized gas distribution and kinematics are stronglyinfluenced by tidal forces. In particular, cross-fuelling mechanismsbetween galaxies are in action. In Arp 299 the warm and cold gaseouscomponents show similar kinematic properties, although the cold gasseems to maintain a still better organized motion with respect to thewarm gas.
| Hubble Space Telescope Observations of Star-forming Regions in NGC 3994/3995
We obtained ultraviolet and optical images of star-forming regions inthe interacting galaxy system NGC 3994/3995 using the Space TelescopeImaging Spectrograph on the Hubble Space Telescope. We describe thecharacteristics of 56 detected knots, a majority of which are youngerthan 20 Myr old. There is no discernible pattern of knot age withrespect to position within the galaxies. The knots have masses and radiiranging from 7.2×103 to 4.4×106Msolar and from 4 to 23 pc, respectively. Using aconservative criterion, we find that ~15% of these knots may beproto-globular clusters; the percentage of proto-globular clusters maybe as high as ~70%. The UV flux distribution of the knots in NGC 3995can be fitted with a power law with α=-0.72+/-0.11, with noturnover detected brightward of the completeness limit.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
| Principal component analysis of International Ultraviolet Explorer galaxy spectra
We analyse the UV spectral energy distribution of a sample of normalgalaxies listed in the International Ultraviolet Explorer (IUE) NewlyExtracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principalcomponent analysis. The sample consists of the IUE short-wavelength (SW)spectra of the central regions of 118 galaxies, where the IUE apertureincluded more than 1 per cent of the galaxy size. The principalcomponents are associated with the main components observed in theultraviolet (UV) spectra of galaxies. The first component, accountingfor the largest source of diversity, may be associated with the UVcontinuum emission. The second component represents the UV contributionof an underlying evolved stellar population. The third component issensitive to the amount of activity in the central regions of galaxiesand measures the strength of star-formation events.In all the samples analysed here, the principal component representativeof star-forming activity accounts for a significant percentage of thevariance. The fractional contribution to the spectral energydistribution (SED) by the evolved stars and by the young population aresimilar.Projecting the SEDs on to their eigenspectra, we find that none of thecoefficients of the principal components can outline an internalcorrelation or can correlate with the optical morphological types. In asubsample of 43 galaxies, consisting of almost only compact and BCDgalaxies, the third principal component defines a sequence related tothe degree of starburst activity of the galaxy.
| Revised masses of dust and gas of SCUBA Local Universe Survey far-infrared bright galaxies based on a recent CO survey
Recent CO measurements of an essentially complete subsample of galaxiesfrom the SCUBA Local Universe Survey (SLUGS) are used to examine theirimplications for dust and gas masses in this sample. Estimates of dustmasses are affected by a contribution to the SCUBA brightnessmeasurements by CO(3-2) emission, and molecular gas masses by the use ofa modified value of the CO-to-H2 conversion factor X. Theaverage dust mass is reduced by 25-38 per cent, which has no bearing onearlier conclusions concerning the shape of the dust mass luminosityfunction derived from the SLUGS. The value of X found from the COsurvey, when applied together with the reduction in dust masses, leadsto lower estimates for the mean gas-to-dust mass ratios, where the gasincludes both H2 and H I. For the CO sample, the mean globalratio is reduced from approximately 430 to about 320-360, but is furtherreduced to values near 50 when applied to the nuclear regions relevantto the CO observations. We discuss these results and suggest that thedifferences between the nuclear and outer regions may simply reflectdifferences in metallicity or the existence of considerable amounts ofunobserved cold dust in the outer regions of these galaxies.
| An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
| H I Observations of Barred Magellanic Spirals. II. The Frequency and Impact of Companions
The results of an H I 21 cm line survey of a sample of Magellanic spiralgalaxies with apparent optical companions reveal that only four of 13systems have confirmed H I-detected neighbors. The current interactionsare affecting the morphology of the main galaxy in only two cases, NGC3664 and NGC 3995. The presence of companions near NGC 2537 and UGC 5391appears to have no effect on the morphology of those galaxies. Overall,there is little difference between the asymmetry of the H I profiles ofthose galaxies with and without companions, and on average, theseMagellanic spirals have H I profiles that are no more asymmetric than arandom sample of spirals in the field. We conclude that currentinteractions cannot be responsible for the lopsided morphology of mostof the galaxies in this sample and that, whatever its original cause,lopsidedness must be a long-lived characteristic of these galaxies.
| Dust masses and star formation in bright IRAS galaxies. Application of a physical model for the interpretation of FIR observations
We address the problem of modeling the far-infrared (FIR) spectrum andderiving the star-formation rate (SFR) and the dust mass of spiralgalaxies. We use the realistic physical model of Popescu et al.(\cite{popescu}) to describe the overall ultra-violet (UV), optical andFIR spectral energy distribution (SED) of a spiral galaxy. The modeltakes into account the 3-dimensional old and young stellar distributionsin the bulge and the disk of a galaxy, together with the dust geometry.The geometrical characteristics of the galaxy and the intrinsic opticaland near-infrared spectra are determined by the galaxy's observed K-bandphotometry. The UV part of the spectrum is assumed to be proportional tothe SFR through the use of population synthesis models. By solving theradiative transfer equation, we are able to determine the absorbedenergy, the dust temperature and the resulting FIR spectrum. The modelhas only three free parameters: SFR, dust mass, and the fraction of theUV radiation which is absorbed locally by dense dust in the HII regions.Using this model, we are able to fit well the FIR spectra of 62 brightIRAS galaxies from the ``SCUBA Local Universe Galaxy Survey" of Dunne etal. (\cite{dunne1}). As a result, we are able to determine, amongothers, their SFR and dust mass. We find that, on average, the SFR (inabsolute units), the star-formation efficiency, the SFR surface densityand the ratio of FIR luminosity over the total intrinsic luminosity, arelarger than the respective values of typical spiral galaxies of the samemorphological type. We also find that the mean gas-to-dust mass ratio isclose to the Galactic value, while the average central face-on opticaldepth of these galaxies in the V band is 2.3. Finally, we find a strongcorrelation between SFR or dust mass and observed FIR quantities liketotal FIR luminosity or FIR luminosity at 100 and 850 μm. Thesecorrelations yield well-defined relations, which can be used todetermine a spiral galaxy's SFR and dust-mass content from FIRobservations.
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| CO Molecular Gas in Infrared-luminous Galaxies
We present the first statistical survey of the properties of the12CO(1-0) and 12CO(3-2) line emission from thenuclei of a nearly complete subsample of 60 infrared (IR) luminousgalaxies selected from SCUBA Local Universe Galaxy Survey (SLUGS). Thissubsample is flux limited at S60μm>=5.24 Jy with far-IR(FIR) luminosities mostly at LFIR>1010Lsolar. We compare the emission line strengths of12CO(1-0) and (3-2) transitions at a common resolution of~15". The measured 12CO(3-2) to (1-0) line intensity ratiosr31 vary from 0.22 to 1.72, with a mean value of 0.66 for thesources observed, indicating a large spread of the degree of excitationof CO in the sample. These CO data, together with a wide range of dataat different wavelengths obtained from the literature, allow us to studythe relationship between the CO excitation conditions and the physicalproperties of gas/dust and star formation in the central regions ofgalaxies. Our analysis shows that there is a nonlinear relation betweenCO and FIR luminosities, such that their ratioLCO/LFIR decreases linearly with increasingLFIR. This behavior was found to be consistent with theSchmidt law relating star formation rate to molecular gas content, withan index N=1.4+/-0.3. We also find a possible dependence of the degreeof CO gas excitation on the efficiency of star-forming activity. Usingthe large velocity gradient (LVG) approximation to model the observeddata, we investigate the CO-to-H2 conversion factor X for theSLUGS sample. The results show that the mean value of X for the SLUGSsample is lower by a factor of 10 compared to the conventional valuederived for the Galaxy, if we assume the abundance of CO relative toH2, ZCO=10-4. For a subset of 12galaxies with H I maps, we derive a mean total face-on surface densityof H2+HI of about 42 Msolar pc-2 withinabout 2 kpc of the nucleus. This value is intermediate between that ingalaxies like our own and those with strong star formation.
| Tidally Triggered Star Formation in Close Pairs of Galaxies. II. Constraints on Burst Strengths and Ages
Galaxy-galaxy interactions rearrange the baryons in galaxies and triggersubstantial star formation; the aggregate effects of these interactionson the evolutionary histories of galaxies in the universe are poorlyunderstood. We combine B- and R-band photometry and optical spectroscopyto estimate the strengths and timescales of bursts of triggered starformation in the centers of 190 galaxies in pairs and compact groups.Based on an analysis of the measured colors and EW(Hα), wecharacterize the preexisting and triggered populations separately. Thebest-fitting burst scenarios assume stronger reddening corrections forline emission than for the continuum and continuous star formationlasting for >~100 Myr. The most realistic scenarios require aninitial mass function that is deficient in the highest mass stars. Thecolor of the preexisting stellar population is the most significantsource of uncertainty. Triggered star formation contributessubstantially (probably >~50%) to the R-band flux in the centralregions of several galaxies; tidal tails do not necessarily accompanythis star formation. Many of the galaxies in our sample have bluercenters than outskirts, suggesting that pre- or nonmerger interactionsmay lead to evolution along the Hubble sequence. These objects wouldappear blue and compact at higher redshifts; the older, redder outskirtsof the disks would be difficult to detect. Our data indicate thatgalaxies with larger separations on the sky contain weaker, and probablyolder, bursts of star formation on average. However, confirmation ofthese trends requires further constraints on the colors of the olderstellar populations and on the reddening for individual galaxies.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| Possibly interacting Vorontsov-Velyaminov galaxies. II. The 6-m telescope spectroscopy of VV 080, 131, 499, 523 and 531
In continuation of the program formulated in Paper I we present resultsof long-slit spectroscopy with the Russian 6-m telescope of five moreobjects from the Vorontsov-Velyaminov (hereafter VV) Atlas and Catalogueof Interacting galaxies. These are the galaxies for which theinteraction is not evident, although all of them are classified asmultiple systems (usually as ``nests'', ``chains'' and similar systems).The spectrophotometry data enable us to derive for all galaxiesabundances of O, and for some of them abundances of N, Ne and S. For twoof them chemical abundances are given for the first time. In spectra ofthree of the studied galaxies [O Iii] lambda 4363 line is measured, andT_e and oxygen abundance are derived by the classical method. For thetwo others, empirical methods are used. For all 5 galaxies, the radialvelocity distribution along the slit was obtained in the Hα -line.The studied galaxies represent a rather mixed sample: from very lowluminosity irregular galaxies, like VV 499 (DDO 053), to rather brightVV 523 (NGC 3991). Their metallicities vary from Z ~ 1/25Zsun for VV 499 to ~ 1/2 Zsun for VV 523. Themorphology of these galaxies ranges between typical dIrr (VV 080)through ring-like (VV 131) to clumpy Irr (VV 523). Position-Velocitydiagrams in the Hα -line along the galaxy body imply the existenceof large-scale ionized gas outflows/supershells around the sites ofintense current and/or recent SF activity. Sizes of supershells vary inthe range of several hundred pc to ~ 2 kpc. For all studied galaxies weexamine their local environment and indicate the nearest neighbouringobjects capable of inducing the observed enhanced star formation.
| SCUBA observations of galaxies with metallicity measurements: a new method for determining the relation between submillimetre luminosity and dust mass
Using a new technique, we have determined a value for the constant ofproportionality between submillimetre emission and dust mass, the dustmass-absorption coefficient (κd) at 850μm. Ourmethod has an advantage over previous methods in that we avoidassumptions about the properties of dust in the interstellar medium. Ouronly assumption is that the fraction of metals incorporated in the dust(ɛ) in galaxies is a universal constant. To implement ourmethod, we require objects that have submillimetre and far-infrared fluxmeasurements as well as gas mass and metallicity estimates. We presentdata for all the galaxies with suitable measurements, including newsubmillimetre maps for five galaxies. We find κ850=0.07 +/- 0.02 m2 kg-1. We have also been able touse our sample to investigate our assumption that ɛ is auniversal constant. We find no evidence that ɛ is different fordwarf and giant galaxies, and show that the scatter in ɛ fromgalaxy to galaxy is apparently quite small.
| The distribution of atomic gas and dust in nearby galaxies - I. Presentation of matched-resolution VLA H I and SCUBA 850-μm maps
We present matched-resolution VLA HI and SCUBA 850-μm maps of 20IRAS-bright galaxies. Of the galaxies observed, two were not detected inHI and two were detected in absorption. The HI distributions of thegalaxies have a range of morphologies. Some of the systems appear HIdeficient in the central regions which could be due to a high conversionrate of HI into molecules or HI absorption. In contrast to the HI, the850-μm emission has a smooth distribution which is concentratedtowards the optical centre of each galaxy. We also find evidence for850-μm emission extending to the periphery of the optical disc insome of the galaxies. Finally, we note that the relative lack of850-μm emission when compared with HI does not necessarily mean thatthe atomic gas and dust do not have similar mass distributions.
| 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.
| Near-infrared template spectra of normal galaxies: k-corrections, galaxy models and stellar populations
We have observed 28 local galaxies in the wavelength range between 1 and2.4μm in order to define template spectra of the normal galaxiesalong the Hubble sequence. Five galaxies per morphological type wereobserved in most cases, and the resulting rms spread of the normalizedspectra of each class, including both intrinsic differences andobservational uncertainties, is about 1 per cent in K, 2 per cent in Hand 3 per cent in J. Many absorption features can be accuratelymeasured. The target galaxies and the spectroscopic aperture(7×53arcsec2) were chosen to be similar to those usedby Kinney et al. to define template UV and optical spectra. The two datasets are matched in order to build representative spectra between 0.1and 2.4μm. The continuum shape of the optical spectra and therelative normalization of the near-IR ones were set to fit the averageeffective colours of the galaxies of the various Hubble classes. Theresulting spectra are used to compute the k-corrections of the normalgalaxies in the near-IR bands, and to check the predictions of variousspectral synthesis models: while the shape of the continuum is generallywell predicted, large discrepancies are found in the absorption lines.Among the other possible applications, here we also show how thesespectra can be used to place constraints on the dominant stellarpopulation in local galaxies. Spectra and k-corrections are publiclyavailable and can be downloaded from the web site http://www.arcetri.astro.it/~filippo/spectra.
| The SCUBA Local Universe Galaxy Survey - I. First measurements of the submillimetre luminosity and dust mass functions
This is the first of a series of papers presenting results from theSCUBA Local Universe Galaxy Survey (SLUGS), the first statistical surveyof the submillimetre properties of the local Universe. As the initialpart of this survey, we have used the SCUBA camera on the James ClerkMaxwell Telescope to observe 104 galaxies from the IRAS Bright GalaxySample. We present here the 850-μm flux measurements. The 60-, 100-,and 850-μm flux densities are well fitted by single-temperature dustspectral energy distributions, with the sample mean and standarddeviation for the best-fitting temperature beingTd=35.6+/-4.9K and for the dust emissivity indexβ=1.3+/-0.2. The dust temperature was found to correlate with60-μm luminosity. The low value of β may simply mean that thesegalaxies contain a significant amount of dust that is colder than thesetemperatures. We have estimated dust masses from the 850-μm fluxesand from the fitted temperature, although if a colder component ataround 20K is present (assuming a β of 2), then the estimated dustmasses are a factor of 1.5-3 too low. We have made the first directmeasurements of the submillimetre luminosity function (LF) and of thedust mass function. Unlike the IRAS 60-μm LF, these are well fittedby Schechter functions. The slope of the 850-μm LF at lowluminosities is steeper than -2, implying that the LF must flatten atluminosities lower than we probe here. We show that extrapolating the60-μm LF to 850μm using a single temperature and β does notreproduce the measured submillimetre LF. A population of `cold' galaxies(Td<25K) emitting strongly at submillimetre wavelengthswould have been excluded from the 60-μm-selected sample. If suchgalaxies do exist, then this estimate of the 850-μm flux is biased(it is underestimated). Whether such a population does exist is unknownat present. We correlate many of the global galaxy properties with theFIR/submillimetre properties. We find that there is a tendency for lessluminous galaxies to contain hotter dust and to have a greater starformation efficiency (cf. Young). The average gas-to-dust ratio for thesample is 581+/-43 (using both the atomic and molecular hydrogen), whichis significantly higher than the Galactic value of 160. We believe thatthis discrepancy is probably due to a `cold dust' component atTd<=20K in our galaxies. There is a surprisingly tightcorrelation between dust mass and the mass of molecular hydrogen,estimated from CO measurements, with an intrinsic scatter of ~=50percent.
| The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the Very Large Array (VLA) FIRST survey and the AutomatedPlate Measuring Facility (APM) catalog of the Palomar Observatory SkySurvey I (POSS-I) plates as the basis for constructing a newradio-selected sample of optically bright quasars. This is the firstradio-selected sample that is competitive in size with current opticallyselected quasar surveys. Using only two basic criteria, radio-opticalpositional coincidence and optical morphology, quasars and BL Lacobjects can be identified with 60% selection efficiency; the efficiencyincreases to 70% for objects fainter than 17 mag. We show that a moresophisticated selection scheme can predict with better than 85%reliability which candidates will turn out to be quasars. This paperpresents the second installment of the FIRST Bright Quasar Survey(FBQS), with a catalog of 636 quasars distributed over 2682deg2. The quasar sample is characterized and all spectra aredisplayed. The FBQS detects both radio-loud and radio-quiet quasars outto redshift z>3. We find a large population of objects ofintermediate radio loudness; there is no evidence in our sample for abimodal distribution of radio characteristics. The sample includes ~29broad absorption line quasars, both high and low ionization, and anumber of new objects with remarkable optical spectra.
| 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.
| Panchromatic Study of Nearby Ultraviolet-bright Starburst Galaxies: Implications for Massive Star Formation and High-Redshift Galaxies
We present a panchromatic study of nearby starburst galaxies from theultraviolet to the visible, including narrowband Hα usingWisconsin-Indiana-Yale-NOAO (WIYN) and Hubble Space Telescope data, todetermine how star formation processes affect the morphologies andintegrated fluxes of nearby starbursts. We find that the UV and Hαmorphologies of starbursts tend to differ, although not in a standard orpredictable manner. From our sample of six nearby starbursts, threesystems show good correlations between UV and Hα fluxes, but wefind differences in UV and Hα morphology among the other three.Occasionally we find systems with well-defined H II regions without thecorresponding brightness in the UV, and vice versa. We discuss thelikely mechanisms behind these differences, which include starburstages, dust absorption, stellar energy ejecta through supernovae andwinds, and leakage of UV photons from stellar clusters. We conclude thatthe large-scale morphological features in starbursts are primarily dueto both age and absorption from a ``picket-fence'' dust distribution. Wefurther demonstrate the similarity and differences between these nearbystarbursts and high-redshift star-forming galaxies. The overallmorphology of our sample of starbursts changes little between UV andvisible wavelengths. If high-redshift galaxies are similar to thesestarbursts, their morphologies should change little between rest-frameUV and optical. We also show that FIR and UV spectral energydistributions and slopes can be used to determine large-scalemorphological features for extreme starbursts, with the steepest FIRslopes correlating with the most disturbed galaxies.
| Young, Star Forming Regions in NGC 3994 and NGC 3995
NGC 3991, NGC 3994, and NGC 3995 comprise a small group of interactinggalaxies. Groundbased images indicate significantly distorted morphologyin NGC 3991 and NGC 3995, while NGC 3994 appears to be a normal,inclined spiral. Spectra of NGC 3991 and NGC 3995 have features typicalof strong HII regions. NGC 3994 is a LINER. All three galaxies havestrong ultraviolet emission and have been observed with IUE (Kinney, etal. 1993). As part of an investigation of star formation in interactinggalaxies, we have obtained ultraviolet and visible images of the centralregions of NGC 3994 and 3995 with the Space Telescope ImagingSpectrograph on HST. Imaging was obtained in two ultraviolet(FUV-MAMA+F25QTZ, NUV-MAMA+F25CN182) and one visible (CCD+F28X50LP)band. Individual star forming knots (at HST resolution) have beenidentified in both galaxies. In NGC 3994 star-forming knots are foundtracing the spiral arms. Results from ground based spectroscopy indicatenuclear reddening of E(B-V) ~ 0.3- 0.4, suggesting that the lack ofUV-bright knots in the center is real and not due to extinction. Theknots in NGC 3995 have a distorted, 'hook shaped' distribution. Theknots are typically 12 - 45 pc in diameter (FWHM), with observed FUVfluxes of approximately 10-17 to 10-16 ergscm-2sec-1 Å-1. We compare ourimaging and spectroscopy data to current starburst models to constrainknot ages and masses. Knot characteristics as a function of location inthe galaxy will also be discussed. This work has been supported in partby NASA, under contract NAS5-31231, and through the Nevada Space GrantConsortium.
| The FIR-radio correlation of Wolf-Rayet galaxies and the role of star formation in LINERs
We find that a preliminary classification of LINERs' energetics may bemade in terms of the FIR-radio correlation of Wolf-Rayet galaxies. TheAGN- or starburst-supported LINERs can be distinguished by theirFIR-to-radio ratio, Qequiv L(1.4GHz)/ L(60mum )> or <0.01. It isinteresting to note that almost all the LINERs with inner rings might bestarburst-supported, indicating reduced AGN activities compared withthose of the AGN-supported ones. We also find that a shock-heating phasefor the warm dust component might be important for some starbursts atthe burst age of >= 107 yr, with Q<0.001.
| The role of star formation in liners.
Not Available
| 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 coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| AGNs with composite spectra. II. Additional data
In a previous paper \cite[(Véron et al. 1997)]{ver97} wepresented medium resolution (3.4 Angstroms FWHM) spectroscopicobservations of 15 ``transition objects'', selected for having anambiguous location in the \cite[Veilleux & Osterbrock (1987)]{vei87}diagnostic diagrams, and showed that most of them were in fact``composite'', this being due to the simultaneous presence on the slitof both a Seyfert or Liner nucleus and a H Ii region. Here, we reportnew spectroscopic observations of 53 emission-line galaxies with a``transition'' spectrum, bringing up to 61 the total number of observedobjects in an unbiased sample of 88 ``transition objects''. Almost allof the observed galaxies have a ``composite" nature, confirming thefinding that true ``transition'' spectra may not exist at all. Byeliminating ``composite objects'' from the diagnostic diagrams, a clearseparation between the different classes of nuclear emission-lineregions (Seyfert 2s, Liners and H Ii regions) becomes apparent; byrestricting the volume occupied by the different line-emitting regionsin the 3-dimensional diagnostic diagrams, we are also restricting therange of possible physical parameters in these regions. There seems tobe no continuity between Seyfert 2s and Liners, the two classesoccupying distinct volumes in the 3-dimensional space defined by lambda6300/Hα ii, lambda 6583/Hα , and lambda 6300/Hα .Based on observations collected at the Observatoire de Haute-Provence(CNRS), France, and Hubble Space Telescope (HST) data obtained from theSpace Telescope European Coordinating Facility (ST-ECF) archive. Tables5 and 6 are also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Ultraviolet spectral properties of magellanic and non-magellanic irregulars, H BT II and starburst galaxies
This paper presents the results of a stellar population analysisperformed on nearby (V_R<=5 000 km s^{-1}) star-forming galaxies,comprising magellanic and non-magellanic irregulars, H Ii and starburstgalaxies observed with the IUE satellite. Before any comparison ofgalaxy spectra, we have formed subsets according to absolute magnitudeand morphological classification. Subsequently, we have coadded thespectra within each subset into groups of similar spectral properties inthe UV. As a consequence, high signal-to-noise ratio templates have beenobtained, and information on spectral features can now be extracted andanalysed. Seven groups resulted from this procedure: the magellanicirregulars (including H Ii galaxies) produced two different bluespectral groups; the non-magellanic irregulars could be grouped into twospectral groups with rather peculiar properties; and the luminousstarbursts produced one flat and two blue template spectra. Theirstellar populations are analysed by means of a population synthesisalgorithm based on star cluster spectral components. The syntheticspectra reproduce the observed ones successfully (except thenon-magellanic irregular groups) both in terms of continuum distributionand spectral features. The synthesis flux fractions of different agegroups were transformed into mass fractions, allowing inferences on thestar formation histories. Young stellar populations (age <500 Myrs)are the main flux contributors; in a few cases the intermediate agepopulation (age~1 M_B-2 Myrs) is important, while the old bulgepopulation contributes at most with ~2 % of the lambda2646 Angstromsflux in the case of starburst galaxies, and is negligible in themagellanic irregulars. We also study the reddening values and theextinction law: an SMC-like extinction law is appropriate for all cases.Based upon data collected with the International Ultraviolet Explorer(IUE) Satellite, supported by NASA, SERC and ESA.
| The Supernova Rate in Starburst Galaxies
We conducted an optical CCD search for supernovae in a sample of 142bright [m(B) <= 16 mag], nearby (z<=0.03) starburst galaxies overthe period 1988 December to 1991 June, to a limiting R-band magnitude of18. Five supernovae were found, in all cases outside the host galaxy'snucleus. We determine supernova rates (in supernova units or SNU) in theextranuclear regions to be 0.7 h^2 SNU for Type Ia, 0.7 h^2 SNU for TypeIb/c, and ~0.6 h^2 SNU for Type II, with large uncertainties but upperlimits of 2.2 h^2, 2.5 h^2, and 1.7 h^2 SNU, respectively. These ratesare similar to those measured in ``normal'' galaxies. We found noevidence for a supernova-induced brightening in any galactic nucleusand, with a few reasonable assumptions, can place upper limits of 9 h^2,12 h^2, and 7 h^2 SNU on the rates of unobscured supernovae Types Ia,Ib/c, and II, respectively, inside the nuclei.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| Kinematics of the local universe. VII. New 21-cm line measurements of 2112 galaxies
This paper presents 2112 new 21-cm neutral hydrogen line measurementscarried out with the meridian transit Nan\c cay radiotelescope. Amongthese data we give also 213 new radial velocities which complement thoselisted in three previous papers of this series. These new measurements,together with the HI data collected in LEDA, put to 6 700 the number ofgalaxies with 21-cm line width, radial velocity, and apparent diameterin the so-called KLUN sample. Figure 5 and Appendices A and B forcorresponding comments are available in electronic form at thehttp://www.edpsciences.com
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