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A Virgo high-resolution Hα kinematical survey - II. The Atlas
A catalogue of ionized gas velocity fields for a sample of 30 spiral andirregular galaxies of the Virgo cluster has been obtained by using 3Doptical data. The aim of this survey is to study the influence ofhigh-density environments on the gaseous kinematics of local clustergalaxies. Observations of the Hα line by means of Fabry-Perotinterferometry have been performed at the Canada-France-HawaiiTelescope, European Southern Observatory 3.6-m telescope, Observatoirede Haute-Provence 1.93-m telescope and Observatoire du montMégantic telescope at angular and spectral samplings from 0.4 to1.6arcsec and 7 to 16kms-1. A recently developed, automaticand adaptive spatial binning technique is used to reach a nearlyconstant signal-to-noise ratio (S/N) over the whole field of view,allowing us to keep a high spatial resolution in high-S/N regions andextend the detection of signal in low-S/N regions. This paper is part ofa series and presents the integrated emission-line and velocity maps ofthe galaxies. Both Hα morphologies and kinematics exhibit signs ofperturbations in the form of, for example, external filaments, inner andnuclear spiral- and ring-like structures, inner kinematical twists,kinematical decoupling of a nuclear spiral, streaming motions alongspiral arms and misalignment between kinematical and photometricorientation axes.
| A Comparison of Hα and Stellar Scale Lengths in Virgo and Field Spirals
The scale lengths of the old stars and ionized gas distributions arecompared for similar samples of Virgo Cluster members and field spiralgalaxies via Hα and broad R-band surface photometry. While theR-band and Hα scale lengths are, on average, comparable for thecombined sample, we find significant differences between the field andcluster samples. While the Hα scale lengths of the field galaxiesare a factor of 1.14+/-0.07 longer, on average, than their R-band scalelengths, the Hα scale lengths of Virgo Cluster members are, onaverage, 20% smaller than their R-band scale lengths. Furthermore, inVirgo, the scale length ratios are correlated with the size of thestar-forming disk: galaxies with smaller overall Hα extents alsoshow steeper radial falloff of star formation activity. At the sametime, we find no strong trends in scale length ratio as a function ofother galaxy properties, including galaxy luminosity, inclination,morphological type, central R-band light concentration, or bar type. Ourresults for Hα emission are similar to other results for dustemission, suggesting that Hα and dust have similar distributions.The environmental dependence of the Hα scale length placesadditional constraints on the evolutionary process(es) that cause gasdepletion and a suppression of the star formation rate in clusters ofgalaxies.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| The Structural Properties of Isolated Galaxies, Spiral-Spiral Pairs, and Mergers: The Robustness of Galaxy Morphology during Secular Evolution
We present a structural analysis of nearby galaxies in spiral-spiralpairs in optical BVRI bands and compare them with the structures ofisolated spiral galaxies and galaxies in ongoing mergers. We use thesecomparisons to determine how galaxy structure changes during galaxyinteractions and mergers. We analyze light concentration (C), asymmetry(A), and clumpiness (S) parameters, and use the projections of CASparameter space to compare these samples. We find that the CASparameters of paired galaxies are correlated with the projectedseparations of the pair. For the widest and closest pairs, the CASparameters tend to be similar to those of isolated and ongoing majormergers (e.g., ultraluminous infrared galaxies), respectively. Ourresults imply that galaxy morphology is a robust property that onlychanges significantly during a strong interaction or major merger. Thetypical timescale for this change in our paired sample, based ondynamical friction arguments, is short, τ~0.1-0.5 Gyr. We findaverage enhancement factors for the spiral-pair asymmetries andclumpiness values of ~2.2 and 1.5. The S parameter, which is related tostar formation (SF) activity, has a moderate level of enhancement,suggesting that this activity in modern spirals depends more on internalprocesses than on external conditions. We further test the statisticalcriterion for picking up interacting galaxies in an automated way byusing the A-S projection plane. The diversity of our spiral-pair samplein the CAS space suggests that structural/SF/morphological properties ofinteracting galaxies change abruptly only when the interaction becomesvery strong and the criteria given previously by Conselice for findinggalaxies involved in major mergers are effective.
| Completing H I observations of galaxies in the Virgo cluster
High sensitivity (rms noise 0.5 mJy) 21-cm H I line observationswere made of 33 galaxies in the Virgo cluster, using the refurbishedArecibo telescope, which resulted in the detection of 12 objects. Thesedata, combined with the measurements available from the literature,provide the first set of H I data that is complete for all 355 late-type(Sa-Im-BCD) galaxies in the Virgo cluster with mp ≤ 18.0mag. The Virgo cluster H I mass function (HIMF) that was derived forthis optically selected galaxy sample is in agreement with the HIMFderived for the Virgo cluster from the blind HIJASS H I survey and isinconsistent with the Field HIMF. This indicates that both in this richcluster and in the general field, neutral hydrogen is primarilyassociated with late-type galaxies, with marginal contributions fromearly-type galaxies and isolated H I clouds. The inconsistency betweenthe cluster and the field HIMF derives primarily from the difference inthe optical luminosity function of late-type galaxies in the twoenvironments, combined with the HI deficiency that is known to occur ingalaxies in rich clusters.Tables \ref{t1, \ref{sample_dat} and Appendix A are only available inelectronic form at http://www.edpsciences.org
| On the alignment between binary spiral galaxies
We show some significance against the null hypothesis of randominteractions of binary spiral galaxies, and in favour of the alternativethat more interactions than expected occur for axes either nearlyparallel (spins being parallel or anti-parallel) or nearly orthogonal.We discuss this in the context of similar prior studies, using adifferent statistical focus in such a way that we are able toincorporate additional data.
| A multibeam HI survey of the Virgo cluster - two isolated HI clouds?
We have carried out a fully sampled large area (4°× 8°)21-cm HI line survey of part of the Virgo cluster using the Jodrell Bankmultibeam instrument. The survey has a sensitivity some three timesbetter than the standard HIJASS (HI Jodrell All Sky Survey) and HIPASS(HI Parkes All Sky Survey) surveys. We detect 31 galaxies, 27 of whichare well-known cluster members. The four new detections have beenconfirmed in the HIPASS data and by follow-up Jodrell Bank pointedobservations. One object lies behind M86, but the other three have noobvious optical counterparts upon inspection of the digital sky surveyfields. These three objects were mapped at Arecibo with a smaller3.6-arcmin half power beam width (HPBW) and a four times bettersensitivity than the Jodrell Bank data, which allow an improveddetermination of the dimensions and location of two of the objects, butsurprisingly failed to detect the third. The two objects are resolved bythe Arecibo beam, giving them a size far larger than any optical imagesin the nearby field. To our mass limit of 5 ×107(Δv/50 km s-1) Msolar andcolumn density limit of 3 × 1018(Δv/50 kms-1) atom cm-2, these new detections representonly about 2 per cent of the cluster atomic hydrogen mass. Ourobservations indicate that the HI mass function of the cluster turnsdown at the low-mass end, making it very different to the field galaxyHI mass function. This is quite different to the Virgo cluster opticalluminosity function, which is much steeper than that in the generalfield. Many of the sample galaxies are relatively gas-poor compared withHI selected samples of field galaxies, confirming the `anaemic spirals'view of Virgo cluster late-type galaxies. The velocity distribution ofthe HI detected galaxies is also very different to that of the clusteras a whole. There are relatively more high-velocity galaxies in the HIsample, suggesting that they form part of a currently infallingpopulation. The HI sample with optical identifications has a minimum HIcolumn density cut-off more than an order of magnitude above thatexpected from the sensitivity of the survey. This observed columndensity is above the normally expected level for star formation tooccur. The two detections with no optical counterparts have very muchlower column densities than that of the rest of the sample, below thestar formation threshold.
| Hα Morphologies and Environmental Effects in Virgo Cluster Spiral Galaxies
We describe the various Hα morphologies of Virgo Cluster andisolated spiral galaxies and associate the Hα morphologies withthe types of environmental interactions that have altered the clustergalaxies. The spatial distributions of Hα and R-band emission areused to divide the star formation morphologies of the 52 Virgo Clusterspiral galaxies into several categories: normal (37%), anemic (6%),enhanced (6%), and (spatially) truncated (52%). Truncated galaxies arefurther subdivided on the basis of their inner star formation rates intotruncated/normal (37%), truncated/compact (6%), truncated/anemic (8%),and truncated/enhanced (2%). The fraction of anemic galaxies isrelatively small (6%-13%) in both environments, suggesting thatstarvation is not a major factor in the reduced star formation rates ofVirgo spiral galaxies. The majority of Virgo spiral galaxies have theirHα disks truncated (52%), whereas truncated Hα disks arerarer in isolated galaxies (12%). Most of the Hα-truncatedgalaxies have relatively undisturbed stellar disks and normal toslightly enhanced inner disk star formation rates, suggesting thatintracluster medium-interstellar medium (ICM-ISM) stripping is the mainmechanism causing the reduced star formation rates of Virgo spiralgalaxies. Several of the truncated galaxies are peculiar, with enhancedcentral star formation rates, disturbed stellar disks, and barlikedistributions of luminous H II complexes inside the central 1 kpc but nostar formation beyond, suggesting that recent tidal interactions orminor mergers have also influenced their morphology. Two highly inclinedHα-truncated spiral galaxies have numerous extraplanar H IIregions and are likely in an active phase of ICM-ISM stripping. Severalspiral galaxies have one-sided Hα enhancements at the outer edgeof their truncated Hα disks, suggesting modest local enhancementsin their star formation rates due to ICM-ISM interactions. Low-velocitytidal interactions and perhaps outer cluster H I accretion seem to bethe triggers for enhanced global star formation in four Virgo galaxies.These results indicate that most Virgo spiral galaxies experienceICM-ISM stripping, many experience significant tidal effects, and manyexperience both.
| Radio and Far-Infrared Emission as Tracers of Star Formation and Active Galactic Nuclei in Nearby Cluster Galaxies
We have studied the radio and far-infrared (FIR) emission from 114galaxies in the seven nearest clusters (<100 Mpc) with prominentX-ray emission to investigate the impact of the cluster environment onthe star formation and active galactic nucleus (AGN) activity in themember galaxies. The X-ray selection criterion is adopted to focus onthe most massive and dynamically relaxed clusters. A large majority ofcluster galaxies show an excess in radio emission over that predictedfrom the radio-FIR correlation, the fraction of sources with radioexcess increases toward cluster cores, and the radial gradient in theFIR/radio flux ratio is a result of radio enhancement. Of theradio-excess sources, 70% are early-type galaxies, and the same fractionhost an AGN. The galaxy density drops by a factor of 10 from thecomposite cluster center out to 1.5 Mpc, yet galaxies show no change inFIR properties over this region and show no indication of masssegregation. We have examined in detail the physical mechanisms thatmight impact the FIR and radio emission of cluster galaxies. Whilecollisional heating of dust may be important for galaxies in clustercenters, it appears to have a negligible effect on the observed FIRemission for our sample galaxies. The correlations between radio and FIRluminosity and radius could be explained by magnetic compression fromthermal intracluster medium pressure. We also find that simple delayedharassment cannot fully account for the observed radio, FIR, and mid-IRproperties of cluster galaxies.
| Properties of isolated disk galaxies
We present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org
| Radio continuum spectra of galaxies in the Virgo cluster region
New radio continuum observations of galaxies in the Virgo cluster regionat 4.85, 8.6, and 10.55 GHz are presented. These observations arecombined with existing measurements at 1.4 and 0.325 GHz. The sampleincludes 81 galaxies where spectra with more than two frequencies couldbe derived. Galaxies that show a radio-FIR excess exhibit centralactivity (HII, LINER, AGN). The four Virgo galaxies with the highestabsolute radio excess are found within 2° of the centerof the cluster. Galaxies showing flat radio spectra also host activecenters. There is no clear trend between the spectral index and thegalaxy's distance to the cluster center.Figure 3 is only available in electronic form athttp://www.edpsciences.orgTable 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/1
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| Minor-axis velocity gradients in disk galaxies
We present the ionized-gas kinematics and photometry of a sample of 4spiral galaxies which are characterized by a zero-velocity plateau alongthe major axis and a velocity gradient along the minor axis,respectively. By combining these new kinematical data with thoseavailable in the literature for the ionized-gas component of the S0s andspirals listed in the Revised Shapley-Ames Catalog of Bright Galaxies werealized that about 50% of unbarred galaxies show a remarkable gasvelocity gradient along the optical minor axis. This fraction rises toabout 60% if we include unbarred galaxies with an irregular velocityprofile along the minor axis. This phenomenon is observed all along theHubble sequence of disk galaxies, and it is particularly frequent inearly-type spirals. Since minor-axis velocity gradients are unexpectedif the gas is moving onto circular orbits in a disk coplanar to thestellar one, we conclude that non-circular and off-plane gas motions arenot rare in the inner regions of disk galaxies.Based on observations carried out at the European Southern Observatoryin La Silla (Chile) (ESO 69.B-0706 and 70.B-0338), with the MultipleMirror Telescope which is a joint facility of the SmithsonianInstitution and the University of Arizona, and with the ItalianTelescopio Nazionale Galileo (AOT-5, 3-18) at the Observatorio del Roquede los Muchachos in La Palma (Spain).Table 1 is only available in electronic form athttp://www.edpsciences.org. Table 5 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/507
| The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe
The characteristics of the starburst galaxies from the Pico dos Diassurvey (PDS) are compared with those of the nearby ultraviolet (UV)bright Markarian starburst galaxies, having the same limit in redshift(vh < 7500 km s-1) and absolute B magnitude(MB < -18). An important difference is found: theMarkarian galaxies are generally undetected at 12 and 25 μm in IRAS.This is consistent with the UV excess shown by these galaxies andsuggests that the youngest star-forming regions dominating thesegalaxies are relatively free of dust.The far-infrared selection criteria for the PDS are shown to introduce astrong bias towards massive (luminous) and large size late-type spiralgalaxies. This is contrary to the Markarian galaxies, which are found tobe remarkably rich in smaller size early-type galaxies. These resultssuggest that only late-type spirals with a large and massive disc arestrong emitters at 12 and 25 μm in IRAS in the nearby Universe.The Markarian and PDS starburst galaxies are shown to share the sameenvironment. This rules out an explanation of the differences observedin terms of external parameters. These differences may be explained byassuming two different levels of evolution, the Markarian being lessevolved than the PDS galaxies. This interpretation is fully consistentwith the disc formation hypothesis proposed by Coziol et al. to explainthe special properties of the Markarian SBNG.
| 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.
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| 12CO(J= 2->1) and CO(J= 3->2) observations of Virgo Cluster spiral galaxies with the KOSMA telescope: Global properties
We present 12CO (J= 2->1) and CO (J= 3->2) observationsof quiescent Virgo Cluster spiral galaxies with the KOSMA 3 m submmtelescope. The beam sizes of 80\arcsec at 345 GHz and 120 arcsec at 230GHz are well suited for the investigation of global properties of VirgoCluster galaxies. The observed sample was selected based on previous12CO (J=1->0) detections by Stark et al. (\cite{Stark86}),performed with the AT&T Bell Laboratory 7 m telescope (beam size ~100\arcsec). We were able to detect 18 spiral galaxies in12CO (2->1) and 16 in 12CO (3->2). Beammatched observations of the lowest three 12CO transitionsallow us to compare our results with previous high spatial resolutionstudies of (moderate) starburst galaxies and galactic core regions. Wediscuss the global excitation conditions of the ISM in these quiescentspiral galaxies. The resulting CO (3-2)/(1-0) integrated line ratiosvary over a relatively narrow range of values from 0.35 to 0.14 (on a Kkm s-1-scale) with increasing CO (2-1)/(1-0) ratio (from 0.5to 1.1). The line ratios between the three lowest rotational transitionsof CO cannot be fitted by any radiative transfer model with a singlesource component. A two-component model, assuming a warm, dense nuclearand a cold, less dense disc component allows us to fit the observed lineratios for most of the galaxies individually by selecting suitableparameters. The two-component model, however, fails to explain theobserved correlation of the line ratios. This is due to a variation ofthe relative filling factor of the warm gas alone, assuming a typicalset of parameters for the two components common for all galaxies.
| A Search for Active Galactic Nuclei in Sc Galaxies with H II Spectra
We have searched for nuclear radio emission from a statisticallycomplete sample of 40 Sc galaxies within 30 Mpc that are opticallyclassified as star-forming objects, in order to determine whether weakactive galactic nuclei might be present. Only three nuclear radiosources were detected, in NGC 864, NGC 4123, and NGC 4535. Thesegalaxies have peak 6 cm radio powers of ~1020 WHz-1 at arcsecond resolution, while upper limits of thenondetected galaxies typically range from 1018.4 to1020 W Hz-1. The three nuclear radio sources areall resolved and appear to have diffuse morphologies, with linear sizesof ~300 pc. This strongly indicates that circumnuclear star formationhas been detected in these three H II galaxies. Comparisons withprevious 20 cm Very Large Array (VLA) results for the detected galaxiesshow that the extended nuclear radio emission has a flat spectrum in twoobjects and is almost certainly generated by thermal emission from gasionized by young stars in the centers of those galaxies. The 6 cm radiopowers are comparable to predictions for thermal emission that are basedon the nuclear Hα luminosities and imply nuclear star formationrates of 0.08-0.8 Msolar yr-1, while thelow-resolution NRAO VLA Sky Survey implies galaxy-wide star formationrates of 0.3-1.0 Msolar yr-1 in stars above 5Msolar. In a few of the undetected galaxies, the upper limitsto the radio power are lower than predicted from the Hαluminosity, possibly because of overresolution of central star-formingregions. Although the presence of active nuclei powered by massive blackholes cannot be definitively ruled out, the present results suggest thatthey are likely to be rare in these late-type galaxies with H IIspectra.
| The Three-dimensional Structure of the Virgo Cluster Region from Tully-Fisher and H I Data
The distances and H I contents of 161 spiral galaxies in the region ofthe Virgo cluster are used to gain insight into the complicatedstructure of this galaxy system. Special attention has been paid to theinvestigation of the suggestion presented in an earlier work that someperipheral Virgo groups may contain strongly gas-deficient spiralgalaxies. The three-dimensional galaxy distribution has been inferredfrom quality distance estimates obtained by averaging distance modulibased on the Tully-Fisher relationship taken from eight published datasets previously homogenized, resulting in a relation with a dispersionof 0.41 mag. Previous findings that the spiral distribution issubstantially more elongated along the line of sight than in the planeof the sky are confirmed by the current data. In addition, an importanteast-west disparity in this effect has been detected. The overallwidth-to-depth ratio of the Virgo cluster region is about 1:4, with themost distant objects concentrated in the western half. The filamentarystructure of the spiral population and its orientation are alsoreflected by the H I-deficient objects alone. The H I deficiency patternshows a central enhancement extending from ~16 to 22 Mpc inline-of-sight distance; most of this enhancement arises from galaxiesthat belong to the Virgo cluster proper. However, significant gasdeficiencies are also detected outside the main body of the cluster in aprobable group of galaxies at line-of-sight distances ~25-30 Mpc, lyingin the region dominated by the southern edge of the M49 subcluster andclouds W' and W, as well as in various foreground galaxies. In the Virgoregion, the H I content of the galaxies then is not a straightforwardindicator of cluster membership.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| 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.
| Hα surface photometry of galaxies in the Virgo cluster. IV. The current star formation in nearby clusters of galaxies
Hα +[NII] imaging observations of 369 late-type (spiral) galaxiesin the Virgo cluster and in the Coma/A1367 supercluster are analyzed,covering 3 rich nearby clusters (A1367, Coma and Virgo) and nearlyisolated galaxies in the Great-Wall. They constitute an opticallyselected sample (mp<16.0) observed with ~ 60 %completeness. These observations provide us with the current(T<107 yrs) star formation properties of galaxies that westudy as a function of the clustercentric projected distances (Theta ).The expected decrease of the star formation rate (SFR), as traced by theHα EW, with decreasing Theta is found only when galaxies brighterthan Mp ~ -19.5 are considered. Fainter objects show no orreverse trends. We also include in our analysis Near Infrared data,providing information on the old (T>109 yrs) stars. Puttogether, the young and the old stellar indicators give the ratio ofcurrently formed stars over the stars formed in the past, or``birthrate'' parameter b. For the considered galaxies we also determinethe ``global gas content'' combining HI with CO observations. We definethe ``gas deficiency'' parameter as the logarithmic difference betweenthe gas content of isolated galaxies of a given Hubble type and themeasured gas content. For the isolated objects we find that b decreaseswith increasing NIR luminosity. In other words less massive galaxies arecurrently forming stars at a higher rate than their giant counterpartswhich experienced most of their star formation activity at earliercosmological epochs. The gas-deficient objects, primarily members of theVirgo cluster, have a birthrate significantly lower than the isolatedobjects with normal gas content and of similar NIR luminosity. Thisindicates that the current star formation is regulated by the gaseouscontent of spirals. Whatever mechanism (most plausibly ram-pressurestripping) is responsible for the pattern of gas deficiency observed inspiral galaxies members of rich clusters, it also produces the observedquenching of the current star formation. A significant fraction of gas``healthy'' (i.e. with a gas deficiency parameter less than 0.4) andcurrently star forming galaxies is unexpectedly found projected near thecenter of the Virgo cluster. Their average Tully-Fisher distance isfound approximately one magnitude further away (muo = 31.77)than the distance of their gas-deficient counterparts (muo =30.85), suggesting that the gas healthy objects belong to a cloudprojected onto the cluster center, but in fact lying a few Mpc behindVirgo, thus unaffected by the dense IGM of the cluster. Based onobservations taken at the Observatorio Astronómico Nacional(Mexico), the OHP (France), Calar Alto and NOT (Spain) observatories.Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org
| Hα surface photometry of galaxies in the Virgo cluster. II. Observations with the OHP and Calar Alto 1.2 m telescopes
We present Hα line imaging observations of 122 galaxies obtainedwith the 1.20 m telescopes of the Observatoire de Haute Provence (OHP)and of Calar Alto. The observed galaxies are mostly Virgo clustermembers (95), along with 10 objects in the Coma/A1367 supercluster, 6 inthe clusters A2197 and A2199, and 11 nearby galaxies taken as fillers.Hα +[NII] fluxes and equivalent widths, as well as images of allthe detected targets, are presented. Based on observations taken at theObservatoire de Haute Provence (OHP) (France), operated by the FrenchCNRS, and Calar Alto Observatory (Spain), operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy. Figure 1 is only available inelectronic form at http://www.edpsciences.org
| Star formation and dust extinction in nearby star-forming and starburst galaxies
We study the star formation rate and dust extinction properties of asample of nearby star-forming galaxies as derived from Hα and UV (~ 2000 Å) observations and we compare them to those of a sample ofstarburst galaxies. The dust extinction in Hα is estimated fromthe Balmer decrement and the extinction in UV using the FIR to UV fluxratio or the attenuation law for starburst galaxies of Calzetti et al.(\cite{calzetti5}). The Hα and UV emissions are stronglycorrelated with a very low scatter for the star-forming objects and witha much higher scatter for the starburst galaxies. The Hα to UVflux ratio is found to be larger by a factor ~ 2 for the starburstgalaxies. We compare both samples with a purely UV selected sample ofgalaxies and we conclude that the mean Hα and UV properties ofnearby star-forming galaxies are more representative of UV-selectedgalaxies than starburst galaxies. We emphasize that the Hα to UVflux ratio is strongly dependent on the dust extinction: the positivecorrelation found between FHα/FUV andFFIR/FUV vanishes when the Hα and UV fluxare corrected for dust extinction. The Hα to UV flux ratiosconverted into star formation rate and combined with the Balmerdecrement measurements are tentatively used to estimate the dustextinction in UV.
| An Atlas of Hα and R Images and Radial Profiles of 63 Bright Virgo Cluster Spiral Galaxies
Narrowband Hα and broadband R images and radial profiles arepresented for 63 bright spiral galaxies in the Virgo Cluster. The sampleis complete for Sb-Scd galaxies with B0T<=12and inclination <=75°. Isophotal radii, disk scale lengths,concentration parameters, and integrated fluxes are derived for thesample galaxies.
| The Frequency of Active and Quiescent Galaxies with Companions: Implications for the Feeding of the Nucleus
We analyze the idea that nuclear activity, either active galactic nuclei(AGNs) or star formation, can be triggered by interactions by studyingthe percentage of active, H II, and quiescent galaxies with companions.Our sample was selected from the Palomar survey and avoids selectionbiases faced by previous studies. This sample was split into fivedifferent groups, Seyfert galaxies, LINERs, transition galaxies, H IIgalaxies, and absorption-line galaxies. The comparison between the localgalaxy density distributions of the different groups showed that in mostcases there is no statistically significant difference among galaxies ofdifferent activity types, with the exception that absorption-linegalaxies are seen in higher density environments, since most of them arein the Virgo Cluster. The comparison of the percentage of galaxies withnearby companions showed that there is a higher percentage of LINERs,transition galaxies, and absorption-line galaxies with companions thanSeyfert and H II galaxies. However, we find that when we consider onlygalaxies of similar morphological types (elliptical or spiral), there isno difference in the percentage of galaxies with companions amongdifferent activity types, indicating that the former result was due tothe morphology-density effect. In addition, only small differences arefound when we consider galaxies with similar Hα luminosities. Thecomparison between H II galaxies of different Hα luminositiesshows that there is a significantly higher percentage of galaxies withcompanions among H II galaxies with L(Hα)>1039 ergss-1 than among those with L(Hα)<=1039ergs s-1, indicating that interactions increase the amount ofcircumnuclear star formation, in agreement with previous results. Thefact that we find that galaxies of different activity types have thesame percentage of companions suggests that interactions betweengalaxies is not a necessary condition to trigger the nuclear activity inAGNs. We compare our results with previous ones and discuss theirimplications.
| BVRI surface photometry of (S+S) binary galaxies I. The data
We present multicolour broad band (BVRI) photometry for a sample of 33spiral-spiral (S+S) binary galaxies drawn from the KarachentsevCatalogue of Isolated Pairs of Galaxies (KPG). The data is part of ajoint observational programme devoted to systematic photometric study ofone of the most complete and homogeneous pair samples available in theliterature. We present azimuthally averaged colour and surfacebrightness profiles, colour index (B-I) maps, B band and sharp/filteredB band images as well as integrated magnitudes, magnitudes at differentcircular apertures and integrated colours for each pair. Internal andexternal data comparisons show consistency within the estimated errors.Two thirds of the sample have total aperture parameters homogeneouslyderived for the first time. After reevaluating morphology for all thepairs, we find a change in Hubble type for 24 galaxies compared to theoriginal POSS classifications. More than half of our pairs showmorphological concordance which could explain, in part, the strongcorrelation in the (B-V) colour indices (Holmberg Effect) between paircomponents. We find a tendency for barred galaxies to show grand designmorphologies and flat colour profiles. The measurements will be used ina series of forthcoming papers where we try to identify and isolate themain structural and photometric properties of disk galaxies at differentstages of interaction. Table A.1 is only available in electronic form atthe CDS via anonymous ftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/54 and Tables 2-4 arealso available in electronic form at the CDS. Full Fig. 5 is onlyavailable in electronic form at the http://www.edpsciences.org Based ondata obtained at the 2.1 m telescope of the Observatorio Guillermo Haroat Cananea, Sonora, México, operated by the Instituto Nacional deAstrofísica, Optica y Electrónica.
| 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.
| Luminosity versus Phase-Space-Density Relation of Galaxies Revisited
We reexamined the correlation between the BTmagnitude and the phase-space-density parameterw=(D225vc)-1 of galaxies forthe Virgo, the Coma, the Fornax, and the Perseus clusters in an effortto better understand the physical underpinning of the fundamental plane.A tight correlation (BT=alog w+b) common to differentmorphological types of galaxies (E, S0, S) was found for the Virgo andthe Coma clusters, with a=1.87+/-0.10 and 1.33+/-0.11, respectively. Aninvestigation using only E galaxies was made for the four clusters. Theresults indicated that the empirical linear relation might be commonamong the Coma, the Fornax, and the Perseus clusters, with the VirgoCluster showing deviation. This relation, which is another way toproject the fundamental plane, has an expression insensitive to themorphology and may be suitable for treating galaxies of differentmorphological types collectively.
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