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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.
| 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.
| Cold dust and molecular gas towards the centers of Magellanic type galaxies and irregulars. I. The data
We present 1300 μm continuum emission measurements and observationsof the 12CO (1-0) and (2-1) transition towards the centers of64 Magellanic type galaxies (Sdm/Sm) and irregulars (Im/I0/Irr). Thesources are selected to have IRAS flux densities S100 μm≥1000 mJy and optical diameters mainly below 180 arcsec. We wereable to detect 12CO towards 41 and the continuum emissiontowards 28 galaxies. In addition, we obtained the corresponding data fora set of 6 complementary galaxies of different morphological type.Based on observations collected at ESO, La Silla, Chile and IRAM, PicoVeleta, Spain.The full version of Figs. \ref{spec1.fig} and \ref{spec2.fig} is onlyavailable in electronic form at http://www.edpsciences.org
| Highly Ionized High-Velocity Gas in the Vicinity of the Galaxy
We report the results of a FUSE study of high-velocity O VI absorptionalong complete sight lines through the Galactic halo in directionstoward 100 extragalactic objects and two halo stars. The high-velocity OVI traces a variety of phenomena, including tidal interactions with theMagellanic Clouds, accretion of gas, outflowing material from theGalactic disk, warm/hot gas interactions in a highly extended Galacticcorona, and intergalactic gas in the Local Group. We identify 84high-velocity O VI features at >=3 σ confidence at velocitiesof -500=40+/-13 kms-1, and an average O VI column density=13.95+/-0.34 with a median value of 13.97. Values of bgreater than the 17.6 km s-1 thermal width expected for O VIat T~3×105 K indicate that additional nonthermalbroadening mechanisms are common. The O VI λ1031.926 absorptionis detected at >=3 σ confidence along 59 of the 102 sight linessurveyed. The high-velocity O VI detections indicate that ~60% of thesky (and perhaps as much as ~85%, depending on data qualityconsiderations) is covered by high-velocity H+ associatedwith the O VI. We find that N(H+)>~1018cm-2 if the high-velocity hot gas has a metallicity similarto that of the Magellanic Stream; this detection rate is considerablyhigher than that of high-velocity warm H I traced through its 21 cmemission at a comparable column density level. Some of the high-velocityO VI is associated with known H I structures (the Magellanic Stream,Complex A, Complex C, the Outer Spiral Arm, and several discrete H IHVCs). Some of the high-velocity O VI features have no counterpart in HI 21 cm emission, including discrete absorption features and positivevelocity absorption wings extending from ~100 to ~300 km s-1that blend with lower velocity absorption produced by the Galactic thickdisk/halo. The discrete features may typify clouds located in the LocalGroup, while the O VI absorption wings may be tidal debris or materialexpelled from the Galactic disk. Most of the O VI features havevelocities incompatible with those of the Galactic halo, even if thehalo has decoupled from the underlying Galactic disk. The reduction inthe dispersion about the mean of the high-velocity O VI centroids whenthe velocities are converted from the LSR to the GSR and LGSR referenceframes is necessary (but not conclusive) evidence that some of theclouds are located outside the Galaxy. Most of the O VI cannot beproduced by photoionization, even if the gas is irradiated byextragalactic ultraviolet background radiation. Several observationalquantities indicate that collisions in hot gas are the primaryionization mechanism responsible for the production of the O VI. Theseinclude the ratios of O VI column densities to those of other highlyionized species (C IV, N V) and the strong correlation between N(O VI)and O VI line width. Consideration of the possible sources ofcollisional ionization favors production of some of the O VI at theboundaries between cool/warm clouds of gas and a highly extended(R>~70 kpc), hot (T>106 K), low-density(n<~10-4-10-5 cm-3) Galactic coronaor Local Group medium. The existence of a hot, highly extended Galacticcorona or Local Group medium and the prevalence of high-velocity O VIare consistent with predictions of current galaxy formation scenarios.Distinguishing between the various phenomena producing high-velocity OVI in and near the Galaxy will require continuing studies of thedistances, kinematics, elemental abundances, and physical states of thedifferent types of high-velocity O VI found in this study. Descriptionsof galaxy evolution will need to account for the highly ionized gas, andfuture X-ray studies of hot gas in the Local Group will need to considercarefully the relationship of the X-ray absorption/emission to thecomplex high-velocity absorption observed in O VI.
| A Far Ultraviolet Spectroscopic Explorer Survey of Molecular Hydrogen in Intermediate-Velocity Clouds in the Milky Way Halo
Far Ultraviolet Spectroscopic Explorer (FUSE) data are used toinvestigate the molecular hydrogen (H2) content ofintermediate-velocity clouds (IVCs) in the lower halo of the Milky Way.We analyze interstellar absorption toward 56 (mostly extragalactic)background sources to study H2 absorption in the Lyman andWerner bands in 61 IVC components at H I column densities>=1019 cm-2. For data with good signal-to-noiseratio (S/N) (~9 per resolution element and higher), H2 in IVCgas is convincingly detected in 14 cases at column densities varyingbetween ~1014 and ~1017 cm-2. We findan additional 17 possible H2 detections in IVCs in FUSEspectra with lower S/N. The molecular hydrogen fractions, f, varybetween 10-6 and 10-3, implying a dense, mostlyneutral gas phase that is probably related to the cold neutral medium(CNM) in these clouds. If the H2 stays information-dissociation equilibrium, the CNM in these clouds can becharacterized by compact (D~0.1 pc) filaments with volume densities onthe order of nH~30 cm-3. The relatively highdetection rate of H2 in IVC gas implies that the CNM in theseclouds is ubiquitous. More dense regions with much higher molecularfractions may exist, but it would be difficult to detect them inabsorption because of their small size.
| 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.
| 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.
| 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.
| A New Database of Observed Spectral Energy Distributions of Nearby Starburst Galaxies from the Ultraviolet to the Far-Infrared
We present a database of UV-to-FIR data of 83 nearby starburst galaxies.The galaxies are selected based upon the availability of IUE data. Wehave recalibrated the IUE UV spectra for these galaxies by incorporatingthe most recent improvements. For 45 of these galaxies we useobservations by Storchi-Bergmann et al. and McQuade et al. for thespectra in the optical range. The NIR data are from new observationsobtained at the NASA/IRTF and the Mount Laguna Observatory, combinedwith the published results from observations at the Kitt Peak NationalObservatory. In addition, published calibrated ISO data are included toprovide mid-IR flux densities for some of the galaxies. Theoptical-to-IR data are matched as closely as possible to the IUE largeaperture. In conjunction with IRAS and ISO FIR flux densities, all thesedata form a set of observed spectral energy distributions (SEDs) of thenuclear regions of nearby starburst galaxies. The SEDs should be usefulin studying star formation and dust/gas attenuation in galaxies. We alsopresent the magnitudes in the standard BVRI and various HST/WFPC2bandpasses synthesized from the UV and optical wavelength ranges ofthese SEDs. For some of the galaxies, the HST/WFPC2 magnitudessynthesized from the SEDs are checked with those directly measured fromWFPC2 images to test the photometric errors of the optical data andtheir effective matching of apertures with the UV data. The implicationsof the new SEDs on the star formation rates and dust/gas attenuation arebriefly discussed.
| Active Nuclei and Star-forming Objects at z>2: Metallicities, Winds, and Formation Histories
We present near-infrared observations of the active galactic nuclei(AGNs) and star-forming objects in the field of the radio galaxy 53W002at z=2.39. The star-forming objects are of special interest as candidateprotogalactic objects. The 1.1-2.2 μm passbands sample theemitted-optical range at this redshift, providing new diagnostics of thestructure, metal abundance, and age of the members of this groupingoriginally selected through Lyα emission. The star-forming objectsare uniformly very blue in continuum slope, which fits with the strongLyα emission in indicating metal abundances that are less thanhalf solar; some are as blue as the most metal-poor local objects. Theyfall in a range of luminosity and metallicity that is not populated bylocal objects, indicating a shorter star-forming history at this earlyepoch. The best local analogs, such as Mrk 66 and 357, either haveseveral times lower luminosity at comparable [O/H] or significantlyhigher [O/H] for comparable luminosity. Spectroscopy from theNear-Infrared Camera and Multi-Object Spectrometer yields detections of[O III] emission for two objects and interesting [O III] and Hβlimits for the rest, augmented by Hα limits from InfraredTelescope Facility imaging. These data are satisfied by model stellarpopulations that have been forming stars for the last2-5×106 yr before z=2.39. We do not see evidence forolder preexisting stellar populations, either in the broadband colors oras redder halos in which the star-forming regions are imbedded. Theseresults suggest that the compact star-forming objects we see atz=2.0-2.5 are indeed early stages in the building of galaxies ratherthan transient star-forming events in larger pre-existing dynamicalsystems. The results also allow an alternative scheme, in which theseare low-mass systems that are blowing winds rather than self-enriching,in which case they should fade rapidly with cosmic epoch. For the threeprominent AGNs at z=2.39, Hα and [O III] emission were measured.Unlike the fainter star-forming objects, their line ratios (specificallyLyα/Hα) show metallicities just as high as in nearbysystems. If the AGNs occur in those systems that started with thehighest density and began active star formation before the less massivesurrounding objects, they will have higher metallicity (as we see intheir emitted-ultraviolet line ratios). The ``ionization cones'' seenprominently in Lyα also appear in [O III] and Hα, with arole for continuum reflection in some cases as well. The contrastbetween the AGNs and fainter star-forming objects can be broadlyaccommodated in a hierarchical formation picture, although there arestill important unknowns as to the fate of the star-forming objects.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| 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.
| The Westerbork HI survey of spiral and irregular galaxies. I. HI imaging of late-type dwarf galaxies
Neutral hydrogen observations with the Westerbork Synthesis RadioTelescope are presented for a sample of 73 late-type dwarf galaxies.These observations are part of the WHISP project (Westerbork H I Surveyof Spiral and Irregular Galaxies). Here we present H I maps, velocityfields, global profiles and radial surface density profiles of H I, aswell as H I masses, H I radii and line widths. For the late-typegalaxies in our sample, we find that the ratio of H I extent to opticaldiameter, defined as 6.4 disk scale lengths, is on average 1.8 +/- 0.8,similar to that seen in spiral galaxies. Most of the dwarf galaxies inthis sample are rich in H I, with a typical Mion {Hi}/L_B of1.5. The relative H I content M_ion {HI}/L_R increases towards fainterabsolute magnitudes and towards fainter surface brightnesses. Dwarfgalaxies with lower average H I column densities also have lower averageoptical surface brightnesses. We find that lopsidedness is as commonamong dwarf galaxies as it is in spiral galaxies. About half of thedwarf galaxies in our sample have asymmetric global profiles, a thirdhas a lopsided H I distribution, and about half shows signs of kinematiclopsidedness.
| The Tully-Fisher Relation as a Measure of Luminosity Evolution: A Low-Redshift Baseline for Evolving Galaxies
We use optical rotation curves to investigate the R-band Tully-Fisherproperties of a sample of 90 spiral galaxies in close pairs, covering arange of luminosities, morphological types, and degrees of tidaldistortion. The galaxies follow the Tully-Fisher relation remarkablywell, with the exception of eight distinct ~3 σ outliers. Althoughmost of the outliers show signs of recent star formation, gasdynamicaleffects are probably the dominant cause of their anomalous Tully-Fisherproperties. Four outliers with small emission-line widths have verycentrally concentrated line emission and truncated rotation curves; thecentral emission indicates recent gas infall after a close galaxy-galaxypass. These four galaxies may be local counterparts to compact, bluegalaxies at intermediate redshift. The remaining galaxies have anegligible offset from the reference Tully-Fisher relation, but ashallower slope (2.6 σ significance) and a 25% larger scatter. Weargue that triggered star formation is a significant contributor to theslope difference. We characterize the nonoutlier sample with measures ofdistortion and star formation to search for third-parameter dependencein the residuals of the TF relation. Severe kinematic distortion is theonly significant predictor of TF residuals; this distortion is not,however, responsible for the slope difference from the referencedistribution. Because the outliers are easily removed by sigma clipping,we conclude that even in the presence of some tidal distortion,detection of moderate (>~0.5 mag in rest-frame R) luminosityevolution should be possible with high-redshift samples the size of this90-galaxy study. The slope of the TF relation, although difficult tomeasure, is as fundamental for quantifying luminosity evolution as thezero-point offset. Some observations reported in this paper wereobtained at the Multiple Mirror Telescope Observatory, a facilityoperated jointly by the University of Arizona and the SmithsonianInstitution.
| 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.
| Dust Absorption and the Ultraviolet Luminosity Density at Z~3 as Calibrated by Local Starburst Galaxies
We refine a technique to measure the absorption-corrected ultraviolet(UV) luminosity of starburst galaxies using rest-frame UV quantitiesalone and apply it to Lyman-limit U dropouts at z~3 found in the HubbleDeep Field (HDF). The method is based on an observed correlation betweenthe ratio of far-infrared (FIR) to UV fluxes with spectral slope beta (aUV color). A simple fit to this relation allows the UV flux absorbed bydust and reprocessed to the FIR to be calculated, and hence thedust-free UV luminosity to be determined. International UltravioletExplorer spectra and Infrared Astronomical Satellite fluxes of localstarbursts are used to calibrate the F_FIR/F_1600 versus beta relationin terms of A_1600 (the dust absorption at 1600 Å) and thetransformation from broadband photometric color to beta. Bothcalibrations are almost completely independent of theoreticalstellar-population models. We show that the recent marginal andnondetections of HDF U dropouts at radio and submillimeter wavelengthsare consistent with their assumed starburst nature and our calculatedA_1600. This is also true of recent observations of the ratio of opticalemission-line flux to UV flux density in the brightest U dropouts. Thislatter ratio turns out not to be a good indicator of dust extinction. InU dropouts, absolute magnitude M_1600,0 correlates with beta: brightergalaxies are redder, as is observed to be the case for local starburstgalaxies. This suggests that a mass-metallicity relationship is alreadyin place at z~3. The absorption-corrected UV luminosity function of Udropouts extends up to M_1600,0~-24 AB mag, corresponding to a starformation rate ~200 M_solar yr^-1 (H_0=50 km s^-1 Mpc^-3 and q_0=0.5 areassumed throughout). The absorption-corrected UV luminosity density atz~3 is rho_1600,0>=1.4x10^27 ergs^-1 Hz^-1 Mpc^-1. It is still alower limit since completeness corrections have not been done andbecause only galaxies with A_1600<~3.6 mag are blue enough in the UVto be selected as U dropouts. The luminosity-weighted meandust-absorption factor of our sample is 5.4+/-0.9 at 1600 Å.
| The Very Young Starburst Merger System NGC 1741
We use Hubble Space Telescope (HST) Faint Object Camera (FOC)ultraviolet (UV) and WFPC2 optical images in conjunction with UVspectroscopic observations taken with the Goddard High ResolutionSpectrograph to examine the star formation history and properties of theinteracting galaxy system NGC 1741 in the Hickson Compact Group 31. Thehigh spatial resolution afforded by HST has allowed us to identify alarge number of starburst knots, or ``super-star clusters'' (SSCs), inthe starburst regions of this system. Photometry of these SSCs in the UVand optical bands indicates that most of these objects have ages of afew Myr, with a few up to ~100 Myr, and masses between 10^4 and 10^6M_solar. The estimated age is confirmed by a spectral synthesis analysisof one knot for which we have obtained a UV spectrum. The V-bandluminosity function of the SSCs is well represented by a power lawphi(L)~L^-alpha with an index of -1.85, with no evidence of a turnoverbrighter than the completeness limit. These properties are in goodagreement with those found for SSCs in other starburst galaxies. Ourresults support the suggestion that some of these SSCs may be extremelyyoung globular clusters formed in a relatively recent starburst episodethat has been triggered by a merger event.
| Tides, Interactions, and Fine-Scale Substructures in Galaxy Clusters
We present the results of a study on galaxy interactions, tides, andother processes that produce luminous fine-scale substructures in thegalaxy clusters: Coma, Perseus, Abell 2199, AWM 3, and AWM 5. Allunusual structures in these clusters can be categorized into sevenmorphologies: interacting galaxies, multiple galaxies (noninteracting),distorted galaxies, tailed galaxies, line galaxies, dwarf galaxy groups,and galaxy aggregates. The various morphologies are described, and acatalog is presented, of 248 objects in these five clusters along withcolor, and positional information obtained from CCD images taken withthe WIYN 3.5 m telescope in broadband B and R filters. Distorted,interacting, and fine-scale substructures have a range of colorsextending from blue objects with B-R~0 to redder colors at B-R~2.5. Wealso find that the structures with the most disturbed morphology havethe bluest colors. In addition, the relative number distributions ofthese structures suggest that two separate classes of galaxy clustersexist: one dominated by distorted structures and the other dominated bygalaxy associations. The Coma and Perseus clusters, respectively, areproposed as models for these types of clusters. These structures avoidthe deep potentials of the dominant D or cD galaxies in the Coma andPerseus clusters, and tend to clump together. Possible mechanisms forthe production of fine-scale substructure are reviewed and compared withobservations of z~0.4 Butcher-Oemler clusters. We conclude, based oncolor, positional, and statistical data, that the most likely mechanismfor the creation of these structures is through an interaction with thegravitational potential of the cluster, possibly coupled with effects ofweak interactions with cluster ellipticals.
| 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).
| 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 Ultraviolet Spectroscopic Properties of Local Starbursts: Implications at High Redshift
We report the results of a systematic study of the vacuum ultraviolet (lambda ~= 1150-2000 Angstroms) spectra of a sample of 45 starburst andrelated galaxies observed with the IUE satellite. These span broadranges in metallicity (from 0.02 to 3 times solar), bolometricluminosity (~107-4 x 1011 Lȯ), and galaxy properties (e.g.,including low-mass dwarf galaxies, normal disk galaxies, and massivegalactic mergers). The projected size of the IUE spectroscopic apertureis typically 1 to several kpc and therefore usually encompasses theentire starburst and is similar to the aperture sizes used forspectroscopy of high-redshift galaxies. Our principal conclusion is thatlocal starbursts occupy a very small fractional volume in themultidimensional manifold defined by such fundamental parameters as theextinction, metallicity, and vacuum-UV line strengths (both stellar andinterstellar) of the starburst and the rotation speed (mass) andabsolute magnitude of the starburst's "host" galaxy. More metal-richstarbursts are redder and more heavily extinguished in the UV, are moreluminous, have stronger vacuum-UV lines, and occur in more massive andoptically brighter host galaxies. We advocate using these localstarbursts as a "training set" to learn how to interpret the rest frameUV spectra of star-forming galaxies at high redshift better, and westress that the degree of similarity between local starbursts andhigh-redshift galaxies in this multidimensional parameter space canalready be tested empirically. The results on local starbursts suggestthat the high- redshift "Lyman Dropout" galaxies are typically highlyreddened and extinguished by dust (by an average factor of 5-10 in theUV), may have moderately high metallicities (0.1-1 times solar?), areprobably building galaxies with stellar surface-mass densities similarto present-day ellipticals, and may be suffering substantial losses ofmetal-enriched gas that can "pollute" the intergalactic medium.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| 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
| Galaxies : colliding in the night.
Not Available
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