WIKISKY.ORG
 Home Getting Started To Survive in the Universe News@Sky Astro Photo The Collection Forum Blog New! FAQ Press Login

# NGC 5962

Contents

### Images

DSS Images   Other Images

### Related articles

 Star Formation in Satellite GalaxiesWe present narrowband observations of the Hα emission in a sampleof 31 satellites orbiting isolated giant spiral galaxies. The samplestudied spans the range -19 mag The evolution of actively star-forming galaxies in the mid-infraredIn this paper we analyze the evolution of actively star-forming galaxiesin the mid-infrared (MIR). This spectral region, characterized bycontinuum emission by hot dust and by the presence of strong emissionfeatures generally ascribed to polycyclic aromatic hydrocarbon (PAH)molecules, is the most strongly affected by the heating processesassociated with star formation and/or active galactic nuclei (AGNs).Following the detailed observational characterization of galaxies in theMIR by the Infrared Space Observatory (ISO), we have updated themodelling of this spectral region in our spectrophotometric modelGRASIL. In the diffuse component we have updated the treatment of PAHsaccording to the model by Li & Draine. As for the dense phase of theinterstellar medium associated with the star-forming regions, themolecular clouds, we strongly decrease the abundance of PAHs as comparedto that in the cirrus, based on the observational evidence of the lackor weakness of PAH bands close to the newly formed stars, possibly dueto the destruction of the molecules in strong ultraviolet fields. Therobustness of the model is checked by fitting near-infrared to radiobroad-band spectra and the corresponding detailed MIR spectra of a largesample of galaxies, at once. With this model, we have analyzed thelarger sample of actively star-forming galaxies by Dale et al. We showthat the observed trends of galaxies in the ISO-IRAS-radio colour-colourplots can be interpreted in terms of the different evolutionary phasesof star formation activity, and the consequent different dominance inthe spectral energy distribution of the diffuse or dense phase of theISM. We find that the observed colours indicate a surprising homogeneityof the starburst phenomenon, allowing only a limited variation of themost important physical parameters, such as the optical depth of themolecular clouds, the time-scale of the escape of young stars from theirfor mation sites, and the gas consumption time-scale. In this paper wedo not attempt to reproduce the far-infrared coolest region in thecolour-colour plots, as we concentrate on models meant to reproduceactive star-forming galaxies, but we discuss possible requirements of amore complex modelling for the coldest objects. A wide-field HI study of the NGC 1566 groupWe report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies. Atomic and Molecular Gas in Colliding Galaxy Systems. I. The DataWe present H I and CO (1-0) interferometric observations of 10comparable-mass interacting systems obtained at the Very Large Array(VLA) and the Owens Valley Radio Observatory (OVRO) millimeter array.The primary intent of this study is to investigate the response of coldgas during the early stages of collision of massive disk galaxies. Thesample sources are selected based on their luminosity(MB<=-19), projected separation (5-40 kpc), andsingle-dish CO (1-0) content (SCO>=20 Jy kms-1). These selection criteria result in a sample thatprimarily consists of systems in the early stages of an interaction or amerger. Despite this sample selection, 50% of the systems show long H Itidal tails indicative of a tidal disruption in a prograde orbit. Inaddition, all (4/4) of the infrared luminous pairs (LIRGs) in the sampleshow long H I tails, suggesting that the presence of a long H I tail canbe a possible signature of enhanced star formation activity in acollision of gas-rich galaxies. More than half of the groups show adisplacement of H I peaks from the stellar disks. The CO (1-0)distribution is generally clumpy and widely distributed, unlike in mostIR-selected late stage mergers-in fact, CO peaks are displaced from thestellar nucleus in 20% (4/18) of the galaxies with robust CO detection.H I and CO (1-0) position-velocity diagrams (PVDs) and rotation curvesare also presented, and their comparison with the numerical simulationanalyzed in Paper I show evidence for radial inflow and wide occurrencesof nuclear molecular rings. These results are further quantified byexamining physical and structural parameters derived in comparison withisolated systems in the BIMA SONG sample in our forthcoming paper. Simulating the Spitzer Mid-Infrared Color-Color DiagramsWe use a simple parameterization of the mid-IR spectra of a wide rangeof galaxy types in order to predict their distribution in the InfraredArray Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 μm and MultibandPhotometer for Spitzer 24 μm color-color diagrams. We distinguishthree basic spectral types by the energetically dominant component inthe 3-12 μm regime: stellar-dominated, polycyclic aromatichydrocarbon (PAH)-dominated, and continuum-dominated. We use a Markovchain Monte Carlo approach to arrive at a more systematic and robustrepresentation of the mid-IR spectra of galaxies than do moretraditional approaches. We find that IRAC color-color plots are wellsuited to distinguishing the above spectral types, while the addition of24 μm data allows us to suggest practical three-color cuts thatpreferentially select higher redshift sources of a specific type. Wecompare our simulations with the color-color plot obtained by theSpitzer First Look Survey and find reasonable agreement. Lastly, wediscuss other applications as well as future directions for this work. The Distribution of Bar and Spiral Arm Strengths in Disk GalaxiesThe distribution of bar strengths in disk galaxies is a fundamentalproperty of the galaxy population that has only begun to be explored. Wehave applied the bar-spiral separation method of Buta and coworkers toderive the distribution of maximum relative gravitational bar torques,Qb, for 147 spiral galaxies in the statistically well-definedOhio State University Bright Galaxy Survey (OSUBGS) sample. Our goal isto examine the properties of bars as independently as possible of theirassociated spirals. We find that the distribution of bar strengthdeclines smoothly with increasing Qb, with more than 40% ofthe sample having Qb<=0.1. In the context of recurrent barformation, this suggests that strongly barred states are relativelyshort-lived compared to weakly barred or nonbarred states. We do notfind compelling evidence for a bimodal distribution of bar strengths.Instead, the distribution is fairly smooth in the range0.0<=Qb<0.8. Our analysis also provides a first look atspiral strengths Qs in the OSUBGS sample, based on the sametorque indicator. We are able to verify a possible weak correlationbetween Qs and Qb, in the sense that galaxies withthe strongest bars tend to also have strong spirals. Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - IBar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies. The distribution of atomic gas and dust in nearby galaxies - III. Radial distributions and metallicity gradients The radial distribution of dust and gas in 38 nearby galaxies isinvestigated, using a sample of galaxies for which matched resolution(25 arcsec) neutral hydrogen (HI) and 850-μm images are available.Most of these radial profiles are fitted well by an exponential model,and the derived 850-μm scalelengths are proportional to the HIscalelengths. From this relation, it is found that the metallicitygradients of these galaxies are much shallower than previous studies,unless the dust temperature is constant within the disc, or asignificant component of molecular gas exists at large radii that is nottraced by CO observations. The distribution of atomic gas and dust in nearby galaxies - II. Further matched-resolution Very Large Array H I and SCUBA 850-μm imagesWe present Very Large Array (VLA) C-array 21-cm HI images of galaxiesfrom the SCUBA Local Universe Galaxy Survey which have been observed at850 μm with the James Clerk Maxwell Telescope. Matched-resolution (~25 arcsec) HI images of 17 galaxies are presented and compared with850-μm images. HI or 850-μm images of an additional six galaxieswhich were detected at only one wavelength are presented. Additionally,lower resolution H I observations of nine galaxies are presented. Theobservations of these galaxies, along with results previously presented,do not show any obvious trends in the HI/dust or H2/dust massratios with morphological type. The Properties of Satellite Galaxies in External Systems. II. Photometry and ColorsIn this second paper dedicated to the study of satellite galaxies wepresent broadband photometry in the B, V, R, and I filters of 49satellite galaxies orbiting giant isolated spiral galaxies. Firstanalysis of the properties of these objects are presented by means ofcolor-color and color-magnitude diagrams for early- and late-typesatellites. Although we find differences in the slope of the V-I versusMv color magnitude diagram, as a whole, the relations are inagreement with the trends known to date for galaxies of similarmagnitudes in nearby clusters of galaxies. Comparison with the relationsfound for satellites in the Local Group allows us to sample better thebright end of the luminosity function of satellite galaxies and extendsfor brighter objects the validity of the color-magnitude relation foundfor dwarf galaxies in the Local Group. Most of the E/S0 galaxies in oursample show a negative color gradient with values similar to those knownfor early-type galaxies in other environments. Classification of Spectra from the Infrared Space Observatory PHT-S DatabaseWe have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA). The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39 Deprojecting spiral galaxies using Fourier analysis. Application to the Ohio sampleWe use two new methods developed recently (Barberàet al.\cite{bar03}, A&A, 415, 849), as well as information obtained fromthe literature, to calculate the orientation parameters of the spiralgalaxies in the Ohio State University Bright Galaxy Survey. We comparethe results of these methods with data from the literature, and find ingeneral good agreement. We provide a homogeneous set of mean orientationparameters which can be used to approximately deproject the disks of thegalaxies and facilitate a number of statistical studies of galaxyproperties.Table 1 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/421/595 Dust masses and star formation in bright IRAS galaxies. Application of a physical model for the interpretation of FIR observationsWe address the problem of modeling the far-infrared (FIR) spectrum andderiving the star-formation rate (SFR) and the dust mass of spiralgalaxies. We use the realistic physical model of Popescu et al.(\cite{popescu}) to describe the overall ultra-violet (UV), optical andFIR spectral energy distribution (SED) of a spiral galaxy. The modeltakes into account the 3-dimensional old and young stellar distributionsin the bulge and the disk of a galaxy, together with the dust geometry.The geometrical characteristics of the galaxy and the intrinsic opticaland near-infrared spectra are determined by the galaxy's observed K-bandphotometry. The UV part of the spectrum is assumed to be proportional tothe SFR through the use of population synthesis models. By solving theradiative transfer equation, we are able to determine the absorbedenergy, the dust temperature and the resulting FIR spectrum. The modelhas only three free parameters: SFR, dust mass, and the fraction of theUV radiation which is absorbed locally by dense dust in the HII regions.Using this model, we are able to fit well the FIR spectra of 62 brightIRAS galaxies from the SCUBA Local Universe Galaxy Survey" of Dunne etal. (\cite{dunne1}). As a result, we are able to determine, amongothers, their SFR and dust mass. We find that, on average, the SFR (inabsolute units), the star-formation efficiency, the SFR surface densityand the ratio of FIR luminosity over the total intrinsic luminosity, arelarger than the respective values of typical spiral galaxies of the samemorphological type. We also find that the mean gas-to-dust mass ratio isclose to the Galactic value, while the average central face-on opticaldepth of these galaxies in the V band is 2.3. Finally, we find a strongcorrelation between SFR or dust mass and observed FIR quantities liketotal FIR luminosity or FIR luminosity at 100 and 850 μm. Thesecorrelations yield well-defined relations, which can be used todetermine a spiral galaxy's SFR and dust-mass content from FIRobservations. Minor-axis velocity gradients in disk galaxiesWe 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 Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxiesWe discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/ Cirrus models for local and high-z SCUBA galaxiesWe present a model for the ultraviolet to submillimetre emission fromstars embedded in the general interstellar dust in galaxies (theinfrared cirrus' component). Such emission is characterized byrelatively low optical depths of dust and by cool (<30 K) dusttemperatures. The model incorporates the stellar population synthesismodel of Bruzual & Charlot and the dust model of Siebenmorgen &Krügel which includes the effects of small grains/polycyclicaromatic hydrocarbons. We apply the model to fit the optical tosubmillimetre spectral energy distributions (SEDs) of nearby galaxies,which are dominated by cirrus emission, and we find that our simplemodel is quite adequate to explain the observed SEDs.We also, more controversially, apply this cirrus model to the SEDs ofhigh redshift sources detected in blank-field submillimetre surveys withthe Submillimetre Common User Bolometer Array (SCUBA). Surprisingly, anexcellent fit is found for many of these sources, with typical valuesfor the optical depth AV and the surface brightness of thestellar radiation field ψ being only a factor of 2-3 higher than fornearby galaxies. This increase is not unreasonable given the expectedevolution of dust optical depth in currently favoured star-formationhistory models.We conclude that the tendency to interpret the high-z SCUBA galaxies asvery highly obscured starbursts may be premature and that these galaxiesmay be more closely linked to optically selected high redshift galaxiesthan previously assumed. CO Molecular Gas in Infrared-luminous GalaxiesWe present the first statistical survey of the properties of the12CO(1-0) and 12CO(3-2) line emission from thenuclei of a nearly complete subsample of 60 infrared (IR) luminousgalaxies selected from SCUBA Local Universe Galaxy Survey (SLUGS). Thissubsample is flux limited at S60μm>=5.24 Jy with far-IR(FIR) luminosities mostly at LFIR>1010Lsolar. We compare the emission line strengths of12CO(1-0) and (3-2) transitions at a common resolution of~15". The measured 12CO(3-2) to (1-0) line intensity ratiosr31 vary from 0.22 to 1.72, with a mean value of 0.66 for thesources observed, indicating a large spread of the degree of excitationof CO in the sample. These CO data, together with a wide range of dataat different wavelengths obtained from the literature, allow us to studythe relationship between the CO excitation conditions and the physicalproperties of gas/dust and star formation in the central regions ofgalaxies. Our analysis shows that there is a nonlinear relation betweenCO and FIR luminosities, such that their ratioLCO/LFIR decreases linearly with increasingLFIR. This behavior was found to be consistent with theSchmidt law relating star formation rate to molecular gas content, withan index N=1.4+/-0.3. We also find a possible dependence of the degreeof CO gas excitation on the efficiency of star-forming activity. Usingthe large velocity gradient (LVG) approximation to model the observeddata, we investigate the CO-to-H2 conversion factor X for theSLUGS sample. The results show that the mean value of X for the SLUGSsample is lower by a factor of 10 compared to the conventional valuederived for the Galaxy, if we assume the abundance of CO relative toH2, ZCO=10-4. For a subset of 12galaxies with H I maps, we derive a mean total face-on surface densityof H2+HI of about 42 Msolar pc-2 withinabout 2 kpc of the nucleus. This value is intermediate between that ingalaxies like our own and those with strong star formation. Infrared Emission of Normal Galaxies from 2.5 to 12 Micron: Infrared Space Observatory Spectra, Near-Infrared Continuum, and Mid-Infrared Emission FeaturesWe present ISOPHOT spectra of the regions 2.5-4.9 μm and 5.8-11.6μm for a sample of 45 disk galaxies from the US Infrared SpaceObservatory Key Project on Normal Galaxies. The galaxies were selectedto span the range in global properties of normal, star-forming diskgalaxies in the local universe. The spectra can be decomposed into threespectral components: (1) continuum emission from stellar photospheres,which dominates the near-infrared (NIR; 2.5-4.9 μm) spectral region;(2) a weak NIR excess continuum, which has a color temperature of~103 K, carries a luminosity of a few percent of the totalfar-infrared (FIR) dust luminosity LFIR and most likelyarises from the interstellar medium (ISM); and (3) the well-known broademission features at 6.2, 7.7, 8.6, and 11.3 μm, which are generallyattributed to aromatic carbon particles. These aromatic features inemission (AFEs) dominate the mid-infrared (MIR; 5.8-11.6 μm) part ofthe spectrum and resemble the so-called type A spectra observed in manynonstellar sources and the diffuse ISM in our own Galaxy. The fewnotable exceptions include NGC 4418, where a dust continuum replaces theAFEs in MIR, and NGC 1569, where the AFEs are weak and the strongestemission feature is [S IV] 10.51 μm. The relative strengths of theAFEs vary by 15%-25% among the galaxies. However, little correlation isseen between these variations and either IRAS 60 μm/100 μm fluxdensity ratio R(60/100) or the FIR/blue luminosity ratioLFIR/LB, two widely used indicators of the currentstar formation activity, suggesting that the observed variations are nota consequence of the radiation field differences among the galaxies. Wedemonstrate that the NIR excess continuum and AFE emission arecorrelated, suggesting that they are produced by similar mechanisms andsimilar (or the same) material. On the other hand, as the current starformation activity increases, the overall strengths of the AFEs and theNIR excess continuum drop significantly with respect to that of the FIRemission from large dust grains. In particular, the summed luminosity ofthe AFEs falls from ~0.2 LFIR for the most IR-quiescent''galaxies to ~0.1 LFIR for the most IR-active'' galaxies.This is likely a consequence of the preferential destruction in intenseradiation fields of the small carriers responsible for the NIR/AFEemission.Based on observations with ISO, an ESA project with instruments fundedby ESA member states (especially the PI countries, France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA. The IRAS Revised Bright Galaxy SampleIRAS 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 thecharacteristic'' 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. The luminous and dark matter content of disk galaxiesWe have compiled a sample of disk galaxies with available photometry inthe B and K bands, velocity line-widths and HI integral fluxes. Severalparameters that trace the luminous, baryonic and dark matter contentswere inferred. We investigated how these parameters vary with differentgalaxy properties, and compared the results with predictions of galaxyevolutionary models in the context of the Λ Cold Dark Matter(ΛCDM) cosmogony. The ratio of disk-to-total maximum circularvelocity, (Vd,m/Vt,m), depends mainly on thecentral disk surface density Σd,0 (or surfacebrightness, SB), increasing roughly asΣd,00.15. While a fraction of high SBgalaxies have a (Vd,m/Vt,m) ratio corresponding tothe maximum disk solution, the low SB are completely dark matterdominated. The trend is similar for the models, although they haveslightly smaller (Vd,m/Vt,m) ratios thanobservations, in particular at the highest SBs and when small baryonfractions are used. The scatter in the(Vd,m/Vt,m)- Σd,0 plot is large.An analysis of residuals shows that (Vd,m/Vt,m)tends to decrease as the galaxy is redder, more luminous (massive), andof earlier type. The models allow us to explain the physics of theseresults, which imply a connexion between halo structure and luminousproperties. The dynamical-to-baryon mass and dynamical mass-to-light (Band K) ratios at a given radius were also estimated. All these ratios,for observations and models, decrease with Σd,0; (orSB) and do not correlate significantly with the galaxy scale, contraryto what has been reported in previous works, based on the analysis ofrotation curve shapes. We discuss this difference and state theimportance of solving the controversy of whether the dark and luminouscontents in disk galaxies depend on SB or luminosity. The broadagreement between the models and observations presented here regardingthe trends of the dynamical-to-baryon matter and mass-to-light ratioswith several galaxy properties favors the ΛCDM scenario. However,the excess of dark matter inside the optical region of disk galaxiesremains the main difficulty.Appendices A and B are only available in electronic form athttp://www.edpsciences.org. Table 1 is only available at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/633 A new catalogue of ISM content of normal galaxiesWe 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 Bar strengths in spiral galaxies estimated from 2MASS imagesNon-axisymmetric forces are presented for a sample of 107 spiralgalaxies, of which 31 are barred (SB) and 53 show nuclear activity. As adata base we use JHK images from the 2 Micron All-sky Survey, and thenon-axisymmetries are characterized by the ratio of the tangential forceto the mean axisymmetric radial force field, following Buta & Block.Bar strengths have an important role in many extragalactic problems andtherefore it is important to verify that the different numerical methodsapplied for calculating the forces give mutually consistent results. Weapply both direct Cartesian integration and a polar grid integrationutilizing a limited number of azimuthal Fourier components of density.We find that the bar strength is independent of the method used toevaluate the gravitational potential. However, because of thedistance-dependent smoothing by Fourier decomposition, the polar methodis more suitable for weak and noisy images. The largest source ofuncertainty in the derived bar strength appears to be the uncertainty inthe vertical scaleheight, which is difficult to measure directly formost galaxies. On the other hand, the derived bar strength is ratherinsensitive to the possible gradient in the vertical scaleheight of thedisc or to the exact model of the vertical density distribution,provided that the same effective vertical dispersion is assumed in allmodels. In comparison with the pioneering study by Buta & Block, thebar strength estimate is improved here by taking into account thedependence of the vertical scaleheight on the Hubble type: we find thatfor thin discs bar strengths are stronger than for thick discs by anamount that may correspond to as much as one bar strength class. Weconfirm the previous result by Buta and co-workers showing that thedispersion in bar strength is large among all the de Vaucouleurs opticalbar classes. In the near-infrared 40 per cent of the galaxies in oursample have bars (showing constant phases in the m= 2 Fourier amplitudesin the bar region), while in the optical band one-third of these barsare obscured by dust. Significant non-axisymmetric forces can also beinduced by the spiral arms, generally in the outer parts of the galacticdiscs, which may have important implications on galaxy evolution.Possible biases of the selected sample are also studied: we find thatthe number of bars identified drops rapidly when the inclination of thegalactic disc is larger than 50°. A similar bias is found in theThird Reference Catalogue of Bright Galaxies, which might be of interestwhen comparing bar frequencies at high and low redshifts. Mass-to-light ratios from the fundamental plane of spiral galaxy discsThe best-fitting two-dimensional plane within the three-dimensionalspace of spiral galaxy disc observables (rotational velocityvrot, central disc surface brightnessμ0=-2.5logI0 and disc scalelength h) has beenconstructed. Applying the three-dimensional bisector method ofregression analysis to a sample of ~100 spiral galaxy discs that spanmore than 4magarcsec-2 in central disc surface brightnessyields vrot\proptoI0.50\pm0.050\,h0.77\pm 0.07 (B band)and vrot\proptoI0.43\pm0.040\,h0.69\pm 0.07 (R band).Contrary to popular belief, these results suggest that in the B band,the dynamical mass-to-light ratio (within four disc scalelengths) islargely independent of the surface brightness, varying as I0.00\pm0.100\,h0.54\pm 0.14. Consistentresults were obtained when the range of the analysis was truncated byexcluding the low-surface-brightness galaxies. Previous claims thatM/LBvaries withI-1/20,Bareshown to be misleading and/or caused by galaxy selection effects - notall low-surface-brightness disc galaxies are dark matter dominated. Thesituation is, however, different in the near-infrared whereLK'~v4 and M/LK' is shown to vary asI-1/20,K\prime. Theoretical studies ofspiral galaxy discs should therefore not assume a constant M/L ratiowithin any given passband. The B-band dynamical mass-to-light ratio(within four disc scalelengths) has no obvious correlation with (B-R)disc colour, while in the K' band it varies as -1.25+/-0.28(B-R).Combining the present observational data with recent galaxy modelpredictions implies that the logarithm of the stellar-to-dynamical massratio is not a constant value, but increases as discs become redder,varying as 1.70+/-0.28(B-R). The Properties of Satellite Galaxies in External Systems. I. Morphology and Structural ParametersWe present the first results of an ongoing project to study themorphological, kinematical, dynamical, and chemical properties ofsatellite galaxies of external giant spiral galaxies. The sample ofobjects has been selected from the catalog by Zaritsky et al. The paperanalyzes the morphology and structural parameters of a subsample of 60such objects. The satellites span a great variety of morphologies andsurface brightness profiles. About two-thirds of the sample are spiralsand irregulars, the remaining third being early-types. Some casesshowing interaction between pairs of satellites are presented andbriefly discussed. Bar Galaxies and Their EnvironmentsThe 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. Hot dust in normal star-forming galaxies: JHKL' photometry of the ISO Key Project sampleWe present JHK and 3.8 mu m (L') photometry of 26 galaxies in theInfrared Space Observatory (ISO) Normal Galaxy Key Project (KP) sampleand of seven normal ellipticals with the aim of investigating the originof the 4 mu m emission. The majority of the KP galaxies, and all theellipticals, have K-L<~ 1.0, consistent with stellar photospheresplus moderate dust extinction. Ten of the 26 KP galaxies have K-L>~1.0, corresponding to a flat or rising 4 mu m continuum, consistent withsignificant emission from hot dust at 600-1000 K. K-L is anticorrelatedwith ISO flux ratio F6.75/F15, weakly correlatedwith line ratio [O I]/[C II], but not with [C II]/FIR or IRAS ratioF60/F100. Photodissociation-region models forthese galaxies show that the hot dust responsible for red K-L resides inregions of high pressure and intense far-ultraviolet radiation field.Taken together, these results suggest that star formation in normalstar-forming galaxies can assume two basic forms: an active'',relatively rare, mode characterized by hot dust, suppressed AromaticFeatures in Emission (AFEs), high pressure, and intense radiation field;and the more common passive'' mode that occurs under more quiescentphysical conditions, with AFEs, and without hot dust. The occurrence ofthese modes appears to only weakly depend on the star-formation rate perunit area. Passive star formation over large scales makes up the bulk ofstar-forming activity locally, while the active'' regime may dominateat high redshifts. Based on data obtained at TIRGO, Gornergrat,Switzerland. Rotation curves and metallicity gradients from HII regions in spiral galaxiesIn this paper we study long slit spectra in the region of Hαemission line of a sample of 111 spiral galaxies with recognizable andwell defined spiral morphology and with a well determined environmentalstatus, ranging from isolation to non-disruptive interaction withsatellites or companions. The form and properties of the rotation curvesare considered as a function of the isolation degree, morphological typeand luminosity. The line ratios are used to estimate the metallicity ofall the detected HII regions, thus producing a composite metallicityprofile for different types of spirals. We have found that isolatedgalaxies tend to be of later types and lower luminosity than theinteracting galaxies. The outer parts of the rotation curves of isolatedgalaxies tend to be flatter than in interacting galaxies, but they showsimilar relations between global parameters. The scatter of theTully-Fisher relation defined by isolated galaxies is significantlylower than that of interacting galaxies. The [NII]/Hα ratios, usedas a metallicity indicator, show a clear trend between Z andmorphological type, t, with earlier spirals showing higher ratios; thistrend is tighter when instead of t the gradient of the inner rotationcurve, G, is used; no trend is found with the change in interactionstatus. The Z-gradient of the disks depends on the type, being almostflat for early spirals, and increasing for later types. The[NII]/Hα ratios measured for disk HII regions of interactinggalaxies are higher than for normal/isolated objects, even if all thegalaxy families present similar distributions of Hα EquivalentWidth. Tables 3 and 4 and Figs. 6, 7 and 21 are only available inelectronic form at http://www.edpsciences.org. Table 5 is only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/389 Based on dataobtained Asiago/Ekar Observatory. Also based on observations made withINT operated on the island of La Palma by ING in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias. 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 The SCUBA Local Universe Galaxy Survey - II. 450-μm data: evidence for cold dust in bright IRAS galaxiesThis is the second in a series of papers presenting results from theSCUBA Local Universe Galaxy Survey. In our first paper we provided850-μm flux densities for 104 galaxies selected from the IRAS BrightGalaxy Sample and we found that the 60-, 100-μm (IRAS) and 850-μm(SCUBA) fluxes could be adequately fitted by emission from dust at asingle temperature. In this paper we present 450-μm data for thegalaxies. With the new data, the spectral energy distributions of thegalaxies can no longer be fitted with an isothermal dust model - twotemperature components are now required. Using our 450-μm data andfluxes from the literature, we find that the 450/850-μm flux ratiofor the galaxies is remarkably constant, and this holds from objects inwhich the star formation rate is similar to our own Galaxy, toultraluminous infrared galaxies (ULIRGs) such as Arp 220. The onlypossible explanation for this is if the dust emissivity index for all ofthe galaxies is ~2 and the cold dust component has a similar temperaturein all galaxies [formmu3](Tc~20-21K). The 60-μmluminosities of the galaxies were found to depend on both the dust massand the relative amount of energy in the warm component, with a tendencyfor the temperature effects to dominate at the highest L60.The dust masses estimated using the new temperatures are higher by afactor of ~2 than those determined previously using a singletemperature. This brings the gas-to-dust ratios of the IRAS galaxiesinto agreement with those of the Milky Way and other spiral galaxieswhich have been intensively studied in the submm.
Submit a new article