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 Late-type galaxies observed with SAURON: two-dimensional stellar and emission-line kinematics of 18 spiralsWe present the stellar and gas kinematics of a sample of 18 nearbylate-type spiral galaxies (Hubble types ranging from Sb to Sd), observedwith the integral-field spectrograph SAURON at the 4.2-m WilliamHerschel Telescope. SAURON covers the spectral range 4800-5380Å,allowing us to measure the Hβ, Fe, Mgb absorption features and theemission in the Hβ line and the [OIII]λλ4959,5007Å and [NI]λλ5198, 5200Å doublets over a 33× 41-arcsec2 field of view. The maps cover the nuclearregion of these late-type galaxies and in all cases include the entirebulge. In many cases the stellar kinematics suggests the presence of acold inner region, as visible from a central drop in the stellarvelocity dispersion. The ionized gas is almost ubiquitous and behaves ina complicated fashion: the gas velocity fields often display morefeatures than the stellar ones, including wiggles in the zero-velocitylines, irregular distributions, ring-like structures. The line ratio[OIII]/Hβ often takes on low values over most of the field,probably indicating a wide-spread star formation. Hubble Space Telescope STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass on Hubble TypeWe study the nuclear star clusters (NCs) in spiral galaxies of variousHubble types using spectra obtained with the STIS on board the HubbleSpace Telescope (HST). We observed the nuclear clusters in 40 galaxies,selected from two previous HST WFPC2 imaging surveys. At a spatialresolution of ~0.2" the spectra provide a better separation of clusterlight from underlying galaxy light than is possible with ground-basedspectra. Approximately half of the spectra have a sufficiently highsignal-to-noise ratio for detailed stellar population analysis. For theother half we only measure the continuum slope, as quantified by the B-Vcolor. To infer the star formation history, metallicity, and dustextinction, we fit weighted superpositions of single-age stellarpopulation templates to the high signal-to-noise ratio spectra. We usethe results to determine the luminosity-weighted age, mass-to-lightratio, and masses of the clusters. Approximately half of the sampleclusters contain a population younger than 1 Gyr. Theluminosity-weighted ages range from 10 Myr to 10 Gyr. The stellarpopulations of NCs are generally best fit as a mixture of populations ofdifferent ages. This indicates that NCs did not form in a single event,but that instead they had additional star formation long after theoldest stars formed. On average, the sample clusters in late-typespirals have a younger luminosity-weighted mean age than those inearly-type spirals (L=8.37+/-0.25 vs.9.23+/-0.21). The average mass-weighted ages are older by ~0.7 dex,indicating that there often is an underlying older population that doesnot contribute much light but does contain most of the mass. The averagecluster masses are smaller in late-type spirals than in early-typespirals (logM=6.25+/-0.21 vs. 7.63+/-0.24) and exceed the masses typicalof globular clusters. The cluster mass correlates loosely with totalgalaxy luminosity. It correlates more strongly with both the Hubble typeof the host galaxy and the luminosity of its bulge. The lattercorrelation has the same slope as the well-known correlation betweensupermassive black hole mass and bulge luminosity. The properties ofboth nuclear clusters and black holes in the centers of spiral galaxiesare therefore intimately connected to the properties of the host galaxy,and in particular its bulge component. Plausible formation scenarioshave to account for this. We discuss various possible selection biasesin our results, but conclude that none of them can explain thedifferences seen between clusters in early- and late-type spirals. Theinability to infer spectroscopically the populations of faint clustersdoes introduce a bias toward younger ages, but not necessarily towardhigher masses.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555. These observations areassociated with proposals 9070 and 9783. A Comparison of Hα and Stellar Scale Lengths in Virgo and Field SpiralsThe 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. GHASP: an Hα kinematic survey of spiral and irregular galaxies - IV. 44 new velocity fields. Extension, shape and asymmetry of Hα rotation curvesWe present Fabry-Perot observations obtained in the frame of the GHASPsurvey (Gassendi HAlpha survey of SPirals). We have derived the Hαmap, the velocity field and the rotation curve for a new set of 44galaxies. The data presented in this paper are combined with the datapublished in the three previous papers providing a total number of 85 ofthe 96 galaxies observed up to now. This sample of kinematical data hasbeen divided into two groups: isolated (ISO) and softly interacting(SOFT) galaxies. In this paper, the extension of the Hα discs, theshape of the rotation curves, the kinematical asymmetry and theTully-Fisher relation have been investigated for both ISO and SOFTgalaxies. The Hα extension is roughly proportional toR25 for ISO as well as for SOFT galaxies. The smallestextensions of the ionized disc are found for ISO galaxies. The innerslope of the rotation curves is found to be correlated with the centralconcentration of light more clearly than with the type or thekinematical asymmetry, for ISO as well as for SOFT galaxies. The outerslope of the rotation curves increases with the type and with thekinematical asymmetry for ISO galaxies but shows no special trend forSOFT galaxies. No decreasing rotation curve is found for SOFT galaxies.The asymmetry of the rotation curves is correlated with themorphological type, the luminosity, the (B-V) colour and the maximalrotational velocity of galaxies. Our results show that the brightest,the most massive and the reddest galaxies, which are fast rotators, arethe least asymmetric, meaning that they are the most efficient withwhich to average the mass distribution on the whole disc. Asymmetry inthe rotation curves seems to be linked with local star formation,betraying disturbances of the gravitational potential. The Tully-Fisherrelation has a smaller slope for ISO than for SOFT galaxies. Neon abundance in discs of spiral galaxies.Not Available GMRT observations of the group Holmberg 124: Evolution by tidal forces and ram pressure?We report new radio continuum and 21 cm HI observations using the GiantMetrewave Radio Telescope (GMRT) of the group Holmberg 124 (Ho 124)comprising four late-type galaxies, namely NGC 2820, Mrk 108, NGC 2814and NGC 2805. The three galaxies, NGC 2820, Mrk 108 and NGC 2814 whichare closely located in the sky plane have clearly undergone tidalinteractions as seen from the various morphological tidal signatures anddebris. Moreover we note various features in the group members which webelieve might be due to ram pressure. In this paper, we describe fourinteresting results emerging from our observations: a) detection of thetidal radio continuum bridge at 330 MHz connecting the galaxies NGC2820+Mrk 108 with NGC 2814. The radio bridge was discovered at 1465 MHzby van der Hulst & Hummel (1985, A&A, 150, 17). We find that thebridge has a fairly steep spectrum with a spectral index α (S∝ να) of -1.8+0.3-0.2which is much steeper than the -0.8 quoted by van der Hulst & Hummel(1985); b) detection of other tidal features like the tilted HI andradio continuum disk of NGC 2814, a HI streamer and a radio continuumtail arising from the south of NGC 2814. We also report the detection ofa possible tidal dwarf galaxy in HI; c) sharp truncation in the HIdistribution in the south of NGC 2820 and in the HI and radio continuumdistribution in the north of NGC 2814. The optical disks in both thecases look undisturbed. As pointed out by Davis et al. (1997, AJ, 114,613), ram pressure affects different components of the interstellarmedium to varying degrees. Simple estimates of pressure in differentcomponents of the interstellar medium (radio continuum, Hα and HI)in NGC 2820 indicate that ram pressure will significantly influence HI;d) detection of a large one-sided HI loop to the north of NGC 2820. Noradio continuum emission or Hα emission is associated with the HIloop. We discuss various scenarios for the origin of this loop includinga central starburst, ram pressure stripping and tidal interaction. We donot support the central starburst scenario since the loop is notdetected in ionized gas. Using the upper limit on X-ray luminosity of Ho124 (Mulchaey et al. 2003, ApJS, 145, 39), we estimate an upper limit onthe intragroup medium (IGrM) density of 8.8×10-4cm-3. For half this electron density, we estimate the rampressure force of the IGrM to be comparable to the gravitational pull ofthe disk of NGC 2820. Since tidal interaction has obviously influencedthe group, we suggest that the loop could have formed by ram pressurestripping if tidal effects had reduced the surface density of HI in NGC2820. From the complex observational picture of Ho 124 and the numericalestimates, we suggest that the evolution of the Ho 124 group may begoverned by both tidal forces due to the interaction and the rampressure due to motion of the member galaxies in the IGrM and that theIGrM densities should not be too low (i.e. ≥4×10-4). However this needs to be verified by furtherobservations. Structure and star formation in disk galaxies. III. Nuclear and circumnuclear Hα emissionFrom Hα images of a carefully selected sample of 57 relativelylarge, Northern spiral galaxies with low inclination, we study thedistribution of the Hα emission in the circumnuclear and nuclearregions. At a resolution of around 100 parsec, we find that the nuclearHα emission in the sample galaxies is often peaked, andsignificantly more often so among AGN host galaxies. The circumnuclearHα emission, within a radius of two kpc, is often patchy inlate-type, and absent or in the form of a nuclear ring in early-typegalaxies. There is no clear correlation of nuclear or circumnuclearHα morphology with the presence or absence of a bar in the hostgalaxy, except for the nuclear rings which occur in barred hosts. Thepresence or absence of close bright companion galaxies does not affectthe circumnuclear Hα morphology, but their presence does correlatewith a higher fraction of nuclear Hα peaks. Nuclear rings occur inat least 21% (±5%) of spiral galaxies, and occur predominantly ingalaxies also hosting an AGN. Only two of our 12 nuclear rings occur ina galaxy which is neither an AGN nor a starburst host. We confirm thatweaker bars host larger nuclear rings. The implications of these resultson our understanding of the occurrence and morphology of massive starformation, as well as non-stellar activity, in the central regions ofgalaxies are discussed. GHASP: an Hα kinematic survey of spiral and irregular galaxies - III. 15 new velocity fields and study of 46 rotation curvesWe present Fabry-Pérot observations obtained in the frame of theGHASP survey (Gassendi Hα survey of SPirals). We have derived theHα maps, the velocity fields and the rotation curves for a set of15 galaxies. The data presented in this paper are combined with the datapublished in our two previous papers in order to make a preliminaryanalysis of the rotation curves obtained for 46 galaxies. We check theconsistency of our data with the Tully-Fisher relationship and concludethat our Hα rotation curves reach the maximum velocity in most ofthe cases, even with solid-body rotating galaxies. We find that ourrotation curves, on average, almost reach the isophotal radiusR25. We confirm the trend, already mentioned by Rubin,Waterman & Kenney and Márquez et al., that the maximumextension of the Hα rotation curves increases with the type of thespiral galaxy, up to t~ 7-8 and we find that it decreases for magellanicand irregular galaxies. We also confirm the trend seen by Márquezet al. that later types tend to have lower values of the internal slopeof the rotation curve, in agreement with Rubin et al. A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. II. Cluster Sizes and Structural Parameter CorrelationsWe investigate the structural properties of nuclear star clusters inlate-type spiral galaxies. More specifically, we fit analytical modelsto Hubble Space Telescope images of 39 nuclear clusters in order todetermine their effective radii after correction for the instrumentalpoint-spread function. We use the results of this analysis to comparethe luminosities and sizes of nuclear star clusters to those of otherellipsoidal stellar systems, in particular the Milky Way globularclusters. Our nuclear clusters have a median effective radius ofre=3.5 pc, with 50% of the sample falling in the range2.4pc<=re<=5.0pc. This narrow size distribution isstatistically indistinguishable from that of Galactic globular clusters,even though the nuclear clusters are, on average, 4 mag brighter thanthe old globular clusters. We discuss some possible interpretations ofthis result. From a comparison of nuclear cluster luminosities withvarious properties of their host galaxies, we confirm that more luminousgalaxies harbor more luminous nuclear clusters. It remains unclearwhether this correlation mainly reflects the influence of galaxy size,mass, and/or star formation rate. Since the brighter galaxies in oursample typically have stellar disks with a higher central surfacebrightness, nuclear cluster luminosity also correlates with thisproperty of their hosts. On the other hand, we find no evidence for acorrelation between the presence of a nuclear star cluster and thepresence of a large-scale stellar bar. Oxygen and nitrogen abundances in nearby galaxies. Correlations between oxygen abundance and macroscopic propertiesWe performed a compilation of more than 1000 published spectra of H IIregions in spiral galaxies. The oxygen and nitrogen abundances in each HII region were recomputed in a homogeneous way, using the P-method. Theradial distributions of oxygen and nitrogen abundances were derived. Thecorrelations between oxygen abundance and macroscopic properties areexamined. We found that the oxygen abundance in spiral galaxiescorrelates with its luminosity, rotation velocity, and morphologicaltype: the correlation with the rotation velocity may be slightlytighter. There is a significant difference between theluminosity-metallicity relationship obtained here and that based on theoxygen abundances determined through the R23-calibrations.The oxygen abundance of NGC 5457 recently determined using directmeasurements of Te (Kennicutt et al. \cite{Kennicutt2003})agrees with the luminosity-metallicity relationship derived in thispaper, but is in conflict with the luminosity-metallicity relationshipderived with the R23-based oxygen abundances. The obtainedluminosity-metallicity relation for spiral galaxies is compared to thatfor irregular galaxies. Our sample of galaxies shows evidence that theslope of the O/H - MB relationship for spirals (-0.079± 0.018) is slightly more shallow than that for irregulargalaxies (-0.139 ± 0.011). The effective oxygen yields wereestimated for spiral and irregular galaxies. The effective oxygen yieldincreases with increasing luminosity from MB  -11 toMB  -18 (or with increasing rotation velocity fromVrot  10 km s-1 to Vrot  100km s-1) and then remains approximately constant. Irregulargalaxies from our sample have effective oxygen yields lowered by afactor of 3 at maximum, i.e. irregular galaxies usually keep at least1/3 of the oxygen they manufactured during their evolution.Appendix, Tables \ref{table:refero}, \ref{table:referV}, and Figs.\ref{figure:sample2}-\ref{figure:sample5} are only available inelectronic form at http://www.edpsciences.org} Structure and star formation in disc galaxies - I. Sample selection and near-infrared imagingWe present near-infrared imaging of a sample of 57 relatively large,northern spiral galaxies with low inclination. After describing theselection criteria and some of the basic properties of the sample, wegive a detailed description of the data collection and reductionprocedures. The Ksλ= 2.2-μm images cover most ofthe disc for all galaxies, with a field of view of at least 4.2 arcmin.The spatial resolution is better than 1 arcsec for most images. We fitbulge and exponential disc components to radial profiles of the lightdistribution. We then derive the basic parameters of these components,and the bulge/disc ratio, and explore correlations of these parameterswith several galaxy parameters. First results from the HI Jodrell All Sky Survey: inclination-dependent selection effects in a 21-cm blind surveyDetails are presented of the HI Jodrell All Sky Survey (HIJASS). HIJASSis a blind neutral hydrogen (HI) survey of the northern sky (δ> 22°), being conducted using the multibeam receiver on theLovell Telescope (full width at half-maximum beamwidth 12 arcmin) atJodrell Bank. HIJASS covers the velocity range -3500 to 10 000 kms-1, with a velocity resolution of 18.1 km s-1 andspatial positional accuracy of ~2.5 arcmin. Thus far about 1115deg2 of sky have been surveyed. The average rms noise duringthe early part of the survey was around 16 mJy beam-1.Following the first phase of the Lovell Telescope upgrade (in 2001), therms noise is now around 13 mJy beam-1. We describe themethods of detecting galaxies within the HIJASS data and of measuringtheir HI parameters. The properties of the resulting HI-selected sampleof galaxies are described. Of the 222 sources so far confirmed, 170 (77per cent) are clearly associated with a previously catalogued galaxy. Afurther 23 sources (10 per cent) lie close (within 6 arcmin) to apreviously catalogued galaxy for which no previous redshift exists. Afurther 29 sources (13 per cent) do not appear to be associated with anypreviously catalogued galaxy. The distributions of peak flux, integratedflux, HI mass and cz are discussed. We show, using the HIJASS data, thatHI self-absorption is a significant, but often overlooked, effect ingalaxies with large inclination angles to the line of sight. Properlyaccounting for it could increase the derived HI mass density of thelocal Universe by at least 25 per cent. The effect that this will haveon the shape of the HI mass function will depend on how self-absorptionaffects galaxies of different morphological types and HI masses. We alsoshow that galaxies with small inclinations to the line of sight may alsobe excluded from HI-selected samples, since many such galaxies will haveobserved velocity widths that are too narrow for them to bedistinguished from narrow-band radio-frequency interference. This effectwill become progressively more serious for galaxies with smallerintrinsic velocity widths. If, as we might expect, galaxies with smallerintrinsic velocity widths have smaller HI masses, then compensating forthis effect could significantly steepen the faint-end slope of thederived HI mass function. An X-Ray Atlas of Groups of GalaxiesA search was conducted for a hot intragroup medium in 109 low-redshiftgalaxy groups observed with the ROSAT PSPC. Evidence for diffuse,extended X-ray emission is found in at least 61 groups. Approximatelyone-third of these detections have not been previously reported in theliterature. Most of the groups are detected out to less than half of thevirial radius with ROSAT. Although some spiral-rich groups do contain anintragroup medium, diffuse emission is restricted to groups that containat least one early-type galaxy. Searching for Bulges at the End of the Hubble SequenceWe investigate the stellar disk properties of a sample of 19 nearbyspiral galaxies with low inclination and late Hubble type (Scd orlater). We combine our high-resolution Hubble Space Telescope I-bandobservations with existing ground-based optical images to obtain surfacebrightness profiles that cover a high dynamic range of galactic radii.Most of these galaxies contain a nuclear star cluster, as discussed in aseparate paper. The main goal of the present work is to constrain theproperties of stellar bulges at these extremely late Hubble types. Wefind that the surface brightness profiles of the latest-type spiralgalaxies are complex, with a wide range in shapes. We have sorted oursample in a sequence, starting with pure'' disk galaxies(approximately 30% of the sample). These galaxies have exponentialstellar disks that extend inward to within a few tens of parsecs fromthe nucleus, where the light from the nuclear cluster starts todominate. They appear to be truly bulgeless systems. Progressing alongthe sequence, the galaxies show increasingly prominent deviations from asimple exponential disk model on kiloparsec scales. Traditionally, suchdeviations have prompted bulge-disk'' decompositions. Indeed, thesurface brightness profiles of these galaxies are generally well fittedby adding a second (exponential) bulge component. However, we find thatmost surface brightness profiles can be fitted equally well (or better)with a single Sérsic-type R1/n profile over the entireradial range of the galaxy without requiring a separate bulge''component. We warn in a general sense against identification of bulgessolely on the basis of single-band surface brightness profiles. Despitethe narrow range of Hubble types in our sample, the surface brightnessprofiles are far from uniform. The differences between the variousgalaxies appear unrelated to their Hubble types, thus questioning theusefulness of the Hubble sequence for the subcategorization of thelatest-type spiral galaxies. A number of galaxies show central excessemission on spatial scales of a few hundred parsecs that cannot beattributed to the nuclear cluster, the Sérsic-type description ofthe stellar disk, or what one would generally consider to be a bulgecomponent. The origin of this light component remains unclear.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555. These observations are associatedwith proposal 8599. Molecular gas in the central regions of the latest-type spiral galaxiesUsing the IRAM 30 >m telescope, we have surveyed an unbiased sampleof 47 nearby spiral galaxies of very late (Scd-Sm) Hubble-type foremission in the 12CO(1-0) and (2-1) lines. The sensitivity ofour data (a few mK) allows detection of about 60% of our sample in atleast one of the CO lines. The median detected H2 mass is1.4x 107 >msun within the central few kpc, assuming astandard conversion factor. We use the measured line intensities tocomplement existing studies of the molecular gas content of spiralgalaxies as a function of Hubble-type and to significantly improve thestatistical significance of such studies at the late end of the spiralsequence. We find that the latest-type spirals closely follow thecorrelation between molecular gas content and galaxy luminosityestablished for earlier Hubble types. The molecular gas in late-typegalaxies seems to be less centrally concentrated than in earlier types.We use Hubble Space Telescope optical images to correlate the moleculargas mass to the properties of the central galaxy disk and the compactstar cluster that occupies the nucleus of most late-type spirals. Thereis no clear correlation between the luminosity of the nuclear starcluster and the molecular gas mass, although the CO detection rate ishighest for the brightest clusters. It appears that the central surfacebrightness of the stellar disk is an important parameter for the amountof molecular gas at the galaxy center. Whether stellar bars play acritical role for the gas dynamics remains unclear, in part because ofuncertainties in the morphological classifications of our sample. On the origin of nitrogenThe problem of the origin of nitrogen is considered within the frameworkof an empirical approach. The oxygen abundances and nitrogen to oxygenabundances ratios are derived in H II regions of a number of spiralgalaxies through the recently suggested P-method using more than sixhundred published spectra. The N/O-O/H diagram for H II regions inirregular and spiral galaxies is constructed. It is found that the N/Ovalues in H II regions of spiral galaxies of early morphological typesare higher than those in H II regions with the same metallicity inspiral galaxies of late morphological types. This suggests along-time-delayed contribution to the nitrogen production. The N/O ratioof a galaxy can then be used as an indicator of the time that haselapsed since the bulk of star formation occurred, or in other words ofthe nominal age'' of the galaxy as suggested by Edmunds & Pagelmore than twenty years ago. The scatter in N/O values at a given O/H canbe naturally explained by differences in star formation histories ingalaxies. While low-metallicity dwarf galaxies with low N/O do notcontain an appreciable amount of old stars, low-metallicity dwarfgalaxies with an appreciable fraction of old stars have high N/O.Consideration of planetary nebulae in the Small Magellanic Cloud and inthe Milky Way Galaxy suggests that the contribution of low-mass stars tothe nitrogen production is significant, confirming the conclusion thatthere is a long-time-delayed contribution to the nitrogen production. The bends in the slopes of radial abundance gradients in the disks of spiral galaxies - Do they exist?Spiral galaxies with a reported bend in the slope of gradient in theoxygen abundances (O/H)R_23, derived with traditionally usedR23-method, were examined. It is shown that the artificialorigin of the reported bends can be naturally explained. Two situationsthat result in a false bend in the slope of (O/H)R_23gradient are indicated. It is concluded that at the present time thereis no example of a galaxy with an undisputable established bend in theslope of the oxygen abundance gradient. The Luminosity-Metallicity Relation, Effective Yields, and Metal Loss in Spiral and Irregular GalaxiesI present results on the correlation between galaxy mass, luminosity,and metallicity for a sample of spiral and irregular galaxies havingwell-measured abundance profiles, distances, and rotation speeds.Additional data for low surface brightness galaxies from the literatureare also included for comparison. These data are combined to study themetallicity-luminosity and metallicity-rotation speed correlations forspiral and irregular galaxies. The metallicity-luminosity correlationshows its familiar form for these galaxies, a roughly uniform change inthe average present-day O/H abundance of about a factor of 100 over 11mag in B luminosity. However, the O/H-Vrot relation shows achange in slope at a rotation speed of about 125 km s-1. Atfaster Vrot, there appears to be no relation between averagemetallicity and rotation speed. At lower Vrot, themetallicity correlates with rotation speed. This change in behaviorcould be the result of increasing loss of metals from the smallergalaxies in supernova-driven winds. This idea is tested by looking atthe variation in effective yield, derived from observed abundances andgas fractions assuming closed box chemical evolution. The effectiveyields derived for spiral and irregular galaxies increase by a factor of10-20 from Vrot~5 to 300 km s-1, asymptoticallyincreasing to approximately constant yeff forVrot>~150 km s-1. The trend suggests thatgalaxies with Vrot<~100-150 km s-1 may lose alarge fraction of their supernova ejecta, while galaxies above thisvalue tend to retain metals. GHASP: A 3-D Survey of Spiral and Irregular Galaxies at HαNot Available A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. I. Observations and Image AnalysisWe present new Hubble Space Telescope I-band images of a sample of 77nearby late-type spiral galaxies with low inclination. The main purposeof this catalog is to study the frequency and properties of nuclear starclusters. In 59 galaxies of our sample, we have identified a distinct,compact (but resolved), and dominant source at or very close to thephotocenter. In many cases, these clusters are the only prominent sourcewithin a few kiloparsecs from the galaxy nucleus. We present surfacebrightness profiles, derived from elliptical isophote fits, of allgalaxies for which the fit was successful. We use the fitted isophotesat radii larger than 2" to check whether the location of the clustercoincides with the photocenter of the galaxy and confirm that in nearlyall cases, we are truly dealing with nuclear'' star clusters. Fromanalytical fits to the surface brightness profiles, we derive thecluster luminosities after subtraction of the light contribution fromthe underlying galaxy disk and/or bulge. Based on observations made withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555. Theseobservations are associated with proposal 8599. Compact groups in the UZC galaxy sampleApplying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35 Hα surface photometry of galaxies in the Virgo cluster. II. Observations with the OHP and Calar Alto 1.2 m telescopesWe 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 Arm and Interarm Star Formation in Spiral GalaxiesWe present an outline of our study of the effects of star formation onthe different components of the interstellar medium in the discs ofspiral galaxies, both globally and as a function of arm and interarmenvironment. We are in the process of obtaining images of 57 spiralgalaxies at low inclinations, and analysing them to study thedistribution of recent massive star formation, old stars, young stars,gas and dust. We will dissect the images into arm and interarm regionsand compare and contrast the morphology and scale lengths within theseregions in H_α, HI, the near infrared, optical and (whereavailable) CO. Modelling will show how the scale lengths are affected bystar formation, how this differs between arms and interarms, and whetherthe Schmidt Law varies from the global values in the arm and interarmregions. The gravitational torque of bars in optically unbarred and barred galaxiesThe relative bar torques for 45 galaxies observed at K-band with the 4.2m William Herschel Telescope are determined by transforming the lightdistributions into potentials and deriving the maximum ratios of thetangential forces relative to the radial forces. The results arecombined with the bar torques for 30 other galaxies determined from ourprevious K-band survey (Buta & Block \cite{buta01}). Relative bartorques determine the degree of spiral arm forcing, gas accretion, andbar evolution. They differ from other measures of bar strength, such asthe relative amplitude of the bar determined photometrically, becausethey include the bulge and other disk light that contributes to theradial component of the total force. If the bulge is strong and theradial forcing large, then even a prominent bar can have a relativelyweak influence on the azimuthal motions in the disk. Here we find thatthe relative bar torque correlates only weakly with the optical bar typelisted in the Revised Shapley-Ames and de Vaucouleurs systems. In fact,some classically barred galaxies have weaker relative bar torques thanclassically unbarred galaxies. The optical class is a poor measure ofazimuthal disk forcing for two reasons: some infrared bars are not seenoptically, and some bars with strong bulges have their azimuthal forcesso strongly diluted by the average radial force that they exert onlysmall torques on their disks. The Hubble classification scheme poorlyrecognizes the gravitational influence of bars. Applications of our bartorque method to the high-redshift universe are briefly discussed. Basedon observations made with the William Herschel Telescope, operated onthe island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias. On the oxygen abundance determination in HII regions. High-metallicity regionsThis is our second paper devoted to the problem of line intensity -oxygen abundance calibration starting from the idea of McGaugh(\cite{mcg91}) that the strong oxygen lines ([OII] lambda lambda 3727,3729 and [OIII] lambda lambda 4959, 5007) contain the necessaryinformation to determine accurate abundances in HII regions. In theprevious study (Pilyugin 2000) the corresponding relations were obtainedfor the low-metallicity HII regions (12+log O/H <= 7.95, the lowerbranch of the O/H - R23 diagram). The high-metallicity HIIregions (12+log O/H >= 8.2, the upper branch of the O/H -R23 diagram) are considered in the present study. A relationof the type O/H=f(P, R23) between oxygen abundance and thevalue of abundance index R23, introduced by Pagel et al.(\cite{pag79}), and the excitation parameter P (which is defined here asthe contribution of the radiation in [OIII] lambda lambda 4959, 5007lines to the total" oxygen radiation) has been derived empiricallyusing the available oxygen abundances determined via measurement of atemperature-sensitive line ratio [OIII]4959,5007/[OIII]4363(Te-method). By comparing oxygen abundances inhigh-metallicity HII regions derived with the Te-method andthose derived with the suggested relations (P-method), it was found thatthe precision of oxygen abundance determination with the P-method isaround 0.1 dex (the mean difference for the 38 HII regions considered is~ 0.08 dex) and is comparable to that of the Te-method. Arelation of the type Te=f(P, R23) between electrontemperature and the values of abundance index R23 and theexcitation parameter P was derived empirically using the availableelectron temperatures determined via measurement oftemperature-sensitive line ratios. The maximum value of differencesbetween electron temperatures determined via measurement oftemperature-sensitive line ratios and those derived with the suggestedrelation is around 1000 K for HII regions considered here, the meanvalue of differences for 38 HII regions is ~ 500 K, which is the sameorder of magnitude as the uncertainties of electron temperaturedeterminations in high-metallicity HII regions via measuredtemperature-sensitive line ratios. Vorontsov-Velyaminov Rows: Straight Segments in the Spiral Arms of GalaxiesThe phenomenon of rows-straight features in the spiral patterns ofgalaxies, which was discovered by Vorontsov-Velyaminov, is investigated.The rows are not artifacts; in several cases, they outline regularspiral arms almost over their entire lengths. The galaxies M101, M51,and a number of more distant spirals are used as examples to demonstratemajor geometrical and physical properties of these structures. It isshown that the row lengths increase nearly linearly with distance fromthe disk center, and that the angle between adjacent rows is almostalways close to 2pi/3. The galaxies with rows generally belong tomoderate-luminosity Sbc-Sc systems with low rotational velocities,regular spiral patterns (Grand Design), and an HI content normal forthese types of galaxies. Two types of rows are shown to exist, whichdiffer in thickness and appear to be evolutionarily related. Theformation mechanism of the rows should probably be sought in thepeculiar behavior of the gas-compression wave in spiral density waves. Nearby Optical Galaxies: Selection of the Sample and Identification of GroupsIn 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. The QDOT all-sky IRAS galaxy redshift surveyWe describe the construction of the QDOT survey, which is publiclyavailable from an anonymous FTP account. The catalogue consists ofinfrared properties and redshifts of an all-sky sample of 2387 IRASgalaxies brighter than the IRAS PSC 60-μm completeness limit(S_60>0.6Jy), sparsely sampled at a rate of one-in-six. At |b|>10deg, after removing a small number of Galactic sources, the redshiftcompleteness is better than 98per cent (2086/2127). New redshifts for1401 IRAS sources were obtained to complete the catalogue; themeasurement and reduction of these are described, and the new redshiftstabulated here. We also tabulate all sources at |b|>10 deg with noredshift so far, and sources with conflicting alternative redshiftseither from our own work, or from published velocities. A list of 95ultraluminous galaxies (i.e. with L_60μm>10^12 L_solar) is alsoprovided. Of these, ~20per cent are AGN of some kind; the broad-lineobjects typically show strong Feii emission. Since the publication ofthe first QDOT papers, there have been several hundred velocity changes:some velocities are new, some QDOT velocities have been replaced by moreaccurate values, and some errors have been corrected. We also present anew analysis of the accuracy and linearity of IRAS 60-μm fluxes. Wefind that the flux uncertainties are well described by a combination of0.05-Jy fixed size uncertainty and 8per cent fractional uncertainty.This is not enough to cause the large Malmquist-type errors in the rateof evolution postulated by Fisher et al. We do, however, find marginalevidence for non-linearity in the PSC 60-μm flux scale, in the sensethat faint sources may have fluxes overestimated by about 5per centcompared with bright sources. We update some of the previous scientificanalyses to assess the changes. The main new results are as follows. (1)The luminosity function is very well determined overall but is uncertainby a factor of several at the very highest luminosities(L_60μm>5x10^12L_solar), as this is where the remainingunidentified objects are almost certainly concentrated. (2) Thebest-fitting rate of evolution is somewhat lower than our previousestimate; expressed as pure density evolution with density varying as(1+z)^p, we find p=5.6+/-2.3. Making a rough correction for the possible(but very uncertain) non-linearity of fluxes, we find p=4.5+/-2.3. (3)The dipole amplitude decreases a little, and the implied value of thedensity parameter, assuming that IRAS galaxies trace the mass, isΩ=0.9(+0.45, -0.25). (4) Finally, the estimate of density varianceon large scales changes negligibly, still indicating a significantdiscrepancy from the predictions of simple cold dark matter cosmogonies. Spiral patterns with straight arm segmentsThe phenomenon of `rows', which are straight geometrical segments in thespiral arms of galaxies, is studied. The Whirlpool nebula, Messier 51(NGC 5194) in Canes Venatici, is considered to be an example of a giantgrand design galaxy. Optical photographs, Hα, ultraviolet andfar-ultraviolet images, CO, 21-cm and synchrotron emission maps, and aK_s-band mosaic of M51 are studied. With this observational material,multiple rows can be recognized in the spiral arms of the galaxy. Therows comprise a major part of the arms. The lengths of the rows increasealmost linearly with distance from the centre. They intersect oneanother at an (average) angle ~2π/3. A possible physical explanationof the phenomenon of rows is discussed on the basis of the assumptionthat the formation of straight arm segments might be due to thegas-dynamical effect of stability of flat shock fronts, and the tendencyof a slightly curved shock front to become flat. A quantitativeflattening criterion enables an explanation of the geometricalproperties of the arm patterns found in M51 and also in M101. A brieflist of spirals with rows is given. Arcsecond Positions of UGC GalaxiesWe 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.
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