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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
| Tracing the star formation history of cluster galaxies using the Hα/UV flux ratio
Since the Hα and UV fluxes from galaxies are sensitive to stellarpopulations of ages <107 and ≈ 108 yrrespectively, their ratio f(Hα)/f(UV) provides us with a tool tostudy the recent t ≤ 108 yr star formation history ofgalaxies, an exercise that we present here applied to 98 galaxies in 4nearby clusters (Virgo, Coma, Abell 1367 and Cancer). The observedf(Hα)/f(UV) ratio is a factor of two smaller than theexpected one as determined from population synthesis models assuming arealistic delayed, exponentially declining star formation history. Wediscuss various mechanisms that may have affected the observedf(Hα)/f(UV) ratio and we propose that the above discrepancy arisesfrom either the absorption of Lyman continuum photons by dust within thestar formation regions or from the occurrence of star formationepisodes. After splitting our sample into different subsamples accordingto evolutionary criteria we find that our reference sample of galaxiesunaffected by the cluster environment show an average value off(Hα)/f(UV) two times lower than the expected one. We argue thatthis difference must be mostly due to absorption of ≈45% of the Lymancontinuum photons within star forming regions. Galaxies with clear signsof an ongoing interaction show average values of f(Hα)/f(UV)slightly higher than the reference value, as expected if those objectshad SFR increased by a factor of ≃4. The accuracy of the currentUV and Hα photometry is not yet sufficient to clearly disentanglethe effect of interactions on the f(Hα)/f(UV) ratio, butsignificant observational improvements are shortly expected to resultfrom the GALEX mission.Tables 1-3 are only available in electronic form athttp://www.edpsciences.org
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| Dust emission in the far-infrared as a star formation tracer at z= 0: systematic trends with luminosity
We investigate whether dust emission in the far-infrared (far-IR)continuum provides a robust estimate of the star formation rate (SFR)for a nearby, normal late-type galaxy. We focus on the ratio of the40-1000 μm luminosity (Ldust) to the far-ultraviolet(far-UV) (0.165 μm) luminosity, which is connected to recent episodesof star formation. Available total photometry at 0.165, 60, 100 and 170μm limits the statistics to 30 galaxies, which, however, span a largerange in observed (and, thus, attenuated by dust) K-band (2.2 μm)luminosity, morphology and inclination (i). This sample shows that theratio of Ldust to the observed far-UV luminosity depends notonly on i, as expected, but also on morphology and, in a tighter way, onobserved K-band luminosity. We find thatLdust/LFUV~ e-τK (α+0.62)LK0.62, where LFUV andLK are the unattenuated stellar luminosities in far-UV and K,respectively, and α is the ratio of the attenuation optical depthsat 0.165 μm (τFUV) and 2.2 μm (τK).This relation is to zeroth order independent of i and morphology. It maybe further expressed asLdust/LFUV~LδK, whereδ= 0.61 - 0.02α, under the observationally motivatedassumption that, for an average inclination,e-τK~L-0.02K. We adoptcalculations of two different models of attenuation of stellar light byinternal dust to derive solid-angle-averaged values of α. We findthat δ is positive and decreases towards 0 from the more luminousto the less luminous galaxies. This means that there is no universalratio of far-IR luminosity to unattenuated far-UV luminosity for nearby,normal late-type galaxies. The far-IR luminosity systematicallyoverestimates SFR in more luminous, earlier-type spirals, owing to theincreased fractional contribution to dust heating of optical/near-IRphotons in these objects. Conversely, it systematically underestimatesSFR in fainter, later-type galaxies, the τFUV of which isreduced. The limited statistics and the uncertainty affecting theprevious scaling relations do not allow us to establish quantitativeconclusions, but an analogous analysis making use of larger data sets,available in the near future (e.g. from GALEX, ASTRO-F and SIRTF), andof more advanced models will allow a quantitative test of ourconclusions.
| The dwarf LSB galaxy population of the Virgo cluster - I. The faint-end slope of the luminosity function
The widely varying dwarf galaxy counts in different environments providea strong challenge to standard hierarchical clustering models. Theluminosity function is not universal, but seems to be strongly dependentupon environment. In this paper we describe an automated procedure fordetecting and measuring very low surface brightness (LSB) features indeep CCD data. We apply this procedure to large-area CCD survey fieldsof the Virgo cluster. We show that there are many more faint (-10>=MB>=-14) LSB galaxies than would be predicted fromextrapolation of the Virgo cluster catalogue luminosity function. Overour limited range of measurement, the faint-end slope of the luminosityfunction becomes α=-1.6. The luminosity function is flatter in theinner regions of the cluster than it is in the outer regions. Althoughthese galaxies contribute a small fraction of the total stellar light ofthe cluster, they may contribute significantly to the mass in galaxiesif they have large mass-to-light ratios similar to those recentlymeasured for Local Group dwarf galaxies.
| Star formation rate in galaxies from UV, IR, and Hα estimators
Infrared (IR) luminosity of galaxies originating from dust thermalemission can be used as an indicator of the star formation rate (SFR).Inoue et al. (\cite{inoue00}, IHK) have derived a formula for theconversion from dust IR luminosity to SFR by using the following threequantities: the fraction of Lyman continuum luminosity absorbed by gas(f), the fraction of UV luminosity absorbed by dust (epsilon ), and thefraction of dust heating from old (ga 108 yr) stellarpopulations (eta ). We develop a method to estimate those threequantities based on the idea that the various way of SFR estimates fromultraviolet (UV) luminosity (2000 Å luminosity), Hαluminosity, and dust IR luminosity should return the same SFR. Afterapplying our method to samples of galaxies, the following results areobtained in our framework. First, our method is applied to a sample ofstar-forming galaxies, finding that f ~ 0.6, epsilon ~ 0.5, and eta ~0.4 as representative values. Next, we apply the method to a starburstsample, which shows larger extinction than the star-forming galaxysample. With the aid of f, epsilon , and eta , we are able to estimatereliable SFRs from UV and/or IR luminosities. Moreover, the Hαluminosity, if the Hα extinction is corrected by using the Balmerdecrement, is suitable for a statistical analysis of SFR, because thesame {correction factor for the Lyman continuum extinction (i.e. 1/f)}is applicable to both normal and starburst galaxies over all the rangeof SFR. The metallicity dependence of f and epsilon is also tested:Only the latter proves to have a correlation with metallicity. As anextension of our result, the local (z=0) comoving density of SFR can beestimated with our dust extinction corrections. We show that all UV,Hα , and IR comoving luminosity densities at z=0 give a consistentSFR per comoving volume ( ~ 3x 10-2h M_sun yr-1Mpc-3). Useful formulae for SFR estimate are listed.Tables 1 and 2, and Appendix A 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
| A New Empirical Method for Estimating the Far-Infrared Flux of Galaxies
We propose a new empirical method to estimate the total far-infraredflux of galaxies from the spectral energy distribution (SED) atwavelengths of λ <= 100 μm. It is difficult to derive thetotal far-infrared luminosity from only the IRAS data, though it is oneof the most important properties of galaxies. Observations by InfraredTelescope in Space (IRTS) indicate that the SED of the diffuse emissionfrom the Galactic plane in this wavelength region can be derived fromthe 60 μm to 100 μm color. This empirical SED relation wasimproved in order to obtain a better fit to the Galactic plane data forIν(60 μm) / Iν(100 μm) > 0.6, andapplied to 96 IRAS galaxies for which ISOPHOT and KAO data are availableat λ > 100 μm. As a result, the empirical relation welldescribes the far-infrared (FIR) SED for a majority of galaxies.Additionally, the total FIR flux for λ >= 40 μm was derivedfrom the flux densities at 60 and 100 μm by using this model. For the96 IRAS galaxies, the uncertainty in the total far-infrared flux of thepresent method is 26%. The present method is more accurate than theprevious one widely used to derive the total infrared flux from the IRAS60 and 100 μm data.
| Far-Infrared Photometry of a Statistical Sample of Late-Type Virgo Cluster Galaxies
We present deep diffraction-limited far-infrared (FIR) strip maps of asample of 63 galaxies later than S0 and brighter thanBT=16.8, selected from the Virgo Cluster Catalogue ofBinggeli, Sandage, & Tammann. The ISOPHOT instrument on board theInfrared Space Observatory was used to achieve sensitivities typicallyan order of magnitude deeper than IRAS in the 60 and 100 μm bands andto reach the confusion limit at 170 μm. The averaged 3 σ upperlimits for integrated flux densities of point sources at 60, 100, and170 μm are 43, 33, and 58 mJy, respectively. A total of 63.5% aredetected at all three wavelengths. The highest detection rate (85.7%) isin the 170 μm band. In many cases the galaxies are resolved, allowingthe scale length of the infrared disks to be derived from theoversampled brightness profiles in addition to the spatially integratedemission. The data presented should provide the basis for a variety ofstatistical investigations of the FIR spectral energy distributions ofgas-rich galaxies in the local universe spanning a broad range in starformation activity and morphological types, including dwarf systems andgalaxies with rather quiescent star formation activity. Based onobservations with the Infrared Space Observatory (ISO), an ESA projectwith instruments funded by ESA member states (especially the PIcountries: France, Germany, the Netherlands, and the United Kingdom) andwith the participation of ISAS and NASA.
| Cold Dust in Late-Type Virgo Cluster Galaxies
We have statistically analyzed the spatially integrated far-infrared(FIR) emissions of the complete volume- and luminosity-limited sample oflate-type (later than S0) Virgo Cluster galaxies measured using theInfrared Space Observatory by Tuffs and coworkers in bands centered on60, 100, and 170 μm. Thirty of 38 galaxies detected at all threewavelengths contain a cold dust emission component, present within allmorphological types of late-type systems ranging from early giant spiralgalaxies to blue compact dwarfs (BCDs) and which could not have beenrecognized by IRAS. We fitted the data with a superposition of twomodified blackbody functions, physically identified with a localizedwarm dust emission component associated with H II regions (whosetemperature was constrained to be 47 K), and a diffuse emissioncomponent of cold dust. The cold dust temperatures were found to bebroadly distributed, with a median of 18 K, some 8-10 K lower than wouldhave been predicted from IRAS. The derived total dust mass iscorrespondingly increased by factors of typically 6-13. A good linearcorrelation is found between the ``warm FIR'' luminosities and theHα equivalent widths (EWs), supporting the assumptions of ourconstrained spectral energy distribution fit procedure. We also found agood nonlinear correlation between the ``cold FIR'' luminosities and theHα EWs, consistent with the prediction of Popescu and coworkersthat the FIR-submillimeter emission should mainly be due to diffusenonionizing UV photons. Both the ``warm'' and the ``cold'' FIRluminosity components are nonlinearly correlated with the (predominantlynonthermal) radio luminosities. There is a tendency for the temperaturesof the cold dust component to become colder and for the cold dustsurface densities (normalized to optical area) to increase for latermorphological types. A particularly significant result concerns the lowdust temperatures (ranging down to less than 10 K) and large dust massesassociated with the Im and BCD galaxies in our sample. We propose twoscenarios to account for the FIR characteristics of these systems.
| 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.
| 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
| Dust-to-gas ratio and star formation history of blue compact dwarf galaxies
This paper investigates the origin of the observed large variety indust-to-gas ratio, D, among blue compact dwarf galaxies (BCDs). Byapplying our chemical evolution model, we find that the dust destructioncan largely suppress the dust-to-gas ratio when the metallicity of a BCDreaches 12+log (O/H) ~ 8, i.e., a typical metallicity level of BCDs. Wealso show that dust-to-gas ratio is largely varied owing to the changeof dust destruction efficiency that has two effects: (i) a significantcontribution of Type Ia supernovae to total supernova rate; (ii)variation of gas mass contained in a star-forming region. While massloss from BCDs was previously thought to be the major cause for thevariance of D, we suggest that the other two effects are also important.We finally discuss the intermittent star formation history, whichnaturally explains the large dispersion of dust-to-gas ratio among BCDs.
| 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.
| 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.
| 1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxies
We present near-infrared H-band (1.65 μm) surface brightness profiledecomposition for 1157 galaxies in five nearby clusters of galaxies:Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma andA1367 in the ``Great Wall". The optically selected (mpg≤16.0) sample is representative of all Hubble types, from E to Irr+BCD,except dE and of significantly different environments, spanning fromisolated regions to rich clusters of galaxies. We model the surfacebrightness profiles with a de Vaucouleurs r1/4 law (dV), withan exponential disk law (E), or with a combination of the two (B+D).From the fitted quantities we derive the H band effective surfacebrightness (μe) and radius (re) of each component, theasymptotic magnitude HT and the light concentration indexC31. We find that: i) Less than 50% of the Ellipticalgalaxies have pure dV profiles. The majority of E to Sb galaxies is bestrepresented by a B+D profile. All Scd to BCD galaxies have pureexponential profiles. ii) The type of decomposition is a strong functionof the total H band luminosity (mass), independent of the Hubbleclassification: the fraction of pure exponential decompositionsdecreases with increasing luminosity, that of B+D increases withluminosity. Pure dV profiles are absent in the low luminosity rangeLH<1010 L\odot and become dominantabove 1011 L\odot . Based on observations taken atTIRGO, Gornergrat, Switzerland (operated by CAISMI-CNR, Arcetri,Firenze, Italy) and at the Calar Alto Observatory (operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy). Table 2 and Figs. 2, 3, 4are available in their entirety only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Dust-to-Gas Ratio and Metal Abundance in Dwarf Galaxies
We have compared the metallicity (represented by oxygen abundance), Xo,and the dust-to-gas ratio, D , in a sample of dwarf galaxies. For dwarfirregulars (dIrrs) we find a good correlation between the twoquantities, with a power-law index of 0.52 +/- 0.25. Blue compact dwarf(BCD) galaxies do not show such a good correlation; in addition, boththe dust-to-gas ratio and the metallicity tend to be higher than fordIrrs. We have then developed a simple but physical analytical model forthe above relation. Comparing the model results with the data, weconclude that (i) for low values of D , the D-Xo relation isquasi-linear, whereas for higher values, the curve strongly deviatesfrom the linear behavior, implying that the commonly used power-lawapproximation is very poor; (ii) the deviation from the linear behaviordepends critically on the parameter chi , the "differential" massoutflow rate from the galaxy in units of the star formation rate, psi ;(iii) the shape of the D-Xo curve does not depend on psi ,but only on chi ; however, the specific location of a given galaxy onthe curve does depend on psi ; and (iv) the BCD metallicity segregationis the result of a higher psi , together with a significant differentialmass outflow. Thus, the lack of correlation can be produced by largelydifferent star formation rates and values of chi in these objects.
| The Virgo Cluster Distance from 21 Centimeter Line Widths
The distance of the Virgo cluster is derived in the B band from the 21cm line width-absolute magnitude relation. This relation is calibratedusing 18 spirals with Cepheid distances, mainly from the Hubble SpaceTelescope. The calibration is applied to a complete sample ofnonpeculiar spirals with i > 45 deg lying within the optical (n = 49)or X-ray (n = 35) contour of the cluster, resulting in a mean clusterdistance of (m - M)0 = 31.58 +/- 0.24 mag (external error), or 20.7 +/-2.4 Mpc. The mean distance of subcluster A is 0.46 +/- 0.18 mag smallerthan that of subcluster B, but the individual distances of the membersof the two substructures show considerable overlap. Cluster spirals with30 deg < i < 45 deg yield distances almost as good as those ofmore inclined galaxies. H I-truncated galaxies are overluminous by 0.8mag at a given line width. The distance modulus is corrected by -0.07mag for the fact that cluster members have lower H I surface fluxes andare redder in (B-I) at a given line width than the (field) calibrators.Different sources for the B magnitudes and line widths have littleeffect on the resulting distance. Different precepts for the internalabsorption correction change the result by no more than +/-0.17 mag. Theindividual distances of the cluster members do not show any dependenceon recession velocity, inclination, Hubble type, or line width. Thedependence on apparent magnitude reflects the considerable depth effectof the cluster. The adopted distance is in good agreement withindependent distance determinations of the cluster. Combining thecluster distance with the corrected cluster velocity of 1142 +/- 61 kms-1 gives H0 = 55 +/- 7 km s-1 Mpc-1 (external error). If the Virgocluster distance is inserted into the tight Hubble diagram of clustersout to 11,000 km s-1 using relative distances to the Virgo cluster, oneobtains a global value of H0 = 57 +/- 7 km s-1 Mpc-1.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| The ``Virgo photometry catalogue''; a catalogue of 1180 galaxies in the direction of the Virgo Cluster's core
We present a new catalogue of galaxies in the direction of the VirgoCluster's core: the Virgo Photometry Catalogue (VPC)*. This cataloguecontains 1180 galaxies (including background objects) within a 23square-degree area of the sky centred on R.A._{1950.0} = 12h 26m anddec._{1950.0} = 13(deg) 08'. The VPC galaxy sample comprises ofnon-stellar objects brighter than B_J25 = 19.0; thecompleteness limits being B_J25 ~18.5 for the northern halfof the survey area and B_J25 ~18.0 for the southern half.Independently-calibrated photographic surface photometry is presentedfor over 1000 galaxies in the U, B_J and R_C bands. Parameters listedfor catalogued galaxies include: equatorial coordinates, morphologicaltypes, surface-brightness profile parameters (which preserve themajority of the original surface photometry information), U, B_J &R_C isophotal magnitudes, B_J and [transformed] B total magnitudes,(U-B_J) and (B_J-R_C) equal-area and total colours, apparent angularradii, ellipticities, position angles, heliocentric radial velocitiesand alternative designations. All total magnitudes and total colours areextrapolated according to a new system denoted t in order to distinguishit from the T system already in use. The VPC is based primarily on four(one U, two B_J and one R_C) UK-Schmidt plates, all of which weredigitised using the Royal Observatory Edinburgh's (ROE) COSMOS measuringmachine. All magnitudes, colours and surface-brightness parameters arederived from numerical integrations of segmented plate-scan data, exceptfor (in 109 cases) saturated or (in 51 cases) inextricably-mergedimages; our segmentation software being able to cope with the vastmajority of image mergers. * Appendices B, C and E, which contain thesurface photometry, the main catalogue and the summary cataloguerespectively, are only available in electronic form. They can beobtained from La Centre des Donees astronomiques de Strasbourg (CDS) viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
| Mid-IR emission of galaxies in the Virgo cluster. II. Integrated properties
We analyse the integrated properties of the Mid-IR emission of acomplete, optically selected sample of galaxies in the Virgo clusterobserved with the ISOCAM instrument on board the ISO satellite. TheISOCAM data allows us to construct the luminosity distribution at 6.75and 15 mu m of galaxies for different morphological classes. These dataare used to study the spectral energy distribution of galaxies ofdifferent type and luminosity in the wavelength range 2000 Angstroms -100 mu m. The analysis shows that the Mid-IR emission up to 15 mu m ofoptically-selected, normal early-type galaxies (E, S0 and S0a) isdominated by the Rayleigh-Jeans tail of the cold stellar component. TheMid-IR emission of late-type galaxies is instead dominated by thethermal emission from dust. As in the Milky Way, the small dust grainsemitting in the Mid-IR have an excess of emission if compared to biggrains emitting in the Far-IR. While the Far-IR emission of galaxiesincreases with the intensity of the interstellar radiation field, theirMid-IR emission is non-linearly related to the UV radiation field. Thespectral energy distributions of the target galaxies indicate that thereis a linear relationship between the UV radiation field and the Mid-IRemission of galaxies for low or intermediate activities of starformation, while the emission from the hot dust seems to drop for strongUV fields. The Mid-IR colour of late-type galaxies is not related totheir activity of star formation. The properties of the dust emission inthe Mid-IR seem more related to the mass than to the morphological typeof the target galaxy. Since the activity of star formation isanticorrelated to the mass of galaxies, this reflects a relationshipbetween the emission of dust in the Mid-IR and the UV radiation field:galaxies with the lowest Mid-IR emission for a given UV field are lowmass, dwarf galaxies. These observational evidences are easily explainedif the carriers of the Unidentified Infrared Bands that dominate the6.75 mu m emission are destroyed by the intense UV radiation field ofdwarf galaxies, although abundance effects can also play a role. Basedon observations with ISO, an ESA project with instruments founded by ESAmember states (especially the PI countries: France, Germany, theNetherlands and the United Kingdom) and with participation of ISAS andNASA
| The observation of the nearby universe in UV and in FIR: an evidence for a moderate extinction in present day star forming galaxies
We study the FIR and UV-visible properties of star forming galaxies inthe nearby Universe. This comparison is performed using the localluminosity functions at UV and FIR wavelengths and on individualstarburst galaxies for which photometric data from UV to NIR and FIR areavailable. The FIR and UV luminosity functions have quite differentshapes : the UV function exhibits a strong increase for low luminositygalaxies whereas the FIR tail towards ultra luminous galaxies (L >10(11) Lsun) is not detected in UV. The comparison of the FIR and UVlocal luminosity densities argues for a rather moderate extinction innearby disk galaxies. The galaxies selected to be detected in FIR and UVare found to be located in the medium range of both luminosityfunctions. An emphasis is made on starburst galaxies. For a sample of 22of these objects, it is found that the UV (912-3650 Angstroms), thevisible (3600-12500 Angstroms) and the NIR (12500-22000 Angstroms)wavelength range contribute ~ 30%, ~ 50% and ~ 20% respectively to thetotal emerging stellar emission (for a subsample of 12 galaxies for theNIR and visible light). The mean ratio of the dust to bolometricluminosity of these galaxies is 0.37+/-0.22 similar to the ratio foundfor normal spiral galaxies. Only 4 out of the 22 galaxies exhibit a verylarge extinction with more than 60% of their energy emitted in theFIR-submm range. The mean extinction at 2000Angstroms is found to be ~1.2 mag although with a large dispersion. The UV, visible and NIRemissions of our sample galaxies are consistent with a burst lastingover ~ 1 Gyr. The conversion factor of the stellar emission into dustemission is found to correlate with the luminosity of the galaxies,brighter galaxies having a higher conversion factor. Since our sampleappears to be representative of the mean properties of the galaxypopulation in FIR and UV, a very large conversion of the stellar lightinto dust emission can no longer be assumed as a general property ofstarburst galaxies at least in the local Universe. Instead a largeramount of energy emerging from the present starburst galaxies seems tocome from the stars rather than from the dust. We compare the UVproperties of our local starburst galaxies to those of recently detectedhigh redshift galaxies. The larger extinction found in the distantgalaxies is consistent with the trend we find for the nearby starburstgalaxies namely the brighter the galaxies the lower the escape fractionof stellar light.
| Study of the Virgo Cluster Using the B-Band Tully-Fisher Relation
The distances to spiral galaxies of the Virgo cluster are estimatedusing the B-band Tully-Fisher (TF) relation, and the three-dimensionalstructure of the cluster is studied. The analysis is made for a completespiral sample taken from the Virgo Cluster catalog of Binggeli, Sandage,& Tammann. The sample contains virtually all spiral galaxies down toM_{BT}=-15 mag at 40 Mpc. A careful examination is made ofthe selection effect and errors of the data. We estimate distance to 181galaxies, among which distances to 89 galaxies are reasonably accurate.We compare these distances to those obtained by other authors on agalaxy-by-galaxy basis. We find reasonable consistency of theTully-Fisher distance among various authors. In particular, it is foundthat the discrepancy in the distance among the different analyses withdifferent data is about 15%, when good H I and photometric data areavailable. We clarify that the different results on the Virgo distanceamong authors arise from the choice of the sample and interpretation ofthe data. We confirm that the Tully-Fisher relation for the Virgocluster shows an unusually large scatter sigma = 0.67 mag, compared tothat for other clusters. We conclude that this scatter is not due to theintrinsic dispersion of the Tully-Fisher relation, but due to a largedepth effect of the Virgo cluster, which we estimate to be extended from12 Mpc to 30 Mpc. The distribution of H I--deficient galaxies isconcentrated at around 14--20 Mpc, indicating the presence of a core atthis distance, and this agrees with the distance estimated for M87 andother elliptical galaxies with other methods. We show also that thespatial number density of spiral galaxies takes a peak at this distance,while a simple average of all spiral galaxy distances gives 20 Mpc. Thefact that the velocity dispersion of galaxies takes a maximum at 14--18Mpc lends an additional support for the distance to the core. Thesefeatures cannot be understood if the large scatter of the TF relation ismerely due to the intrinsic dispersion. The structure of the VirgoCluster we infer from the Tully-Fisher analysis looks like a filamentwhich is familiar to us in a late phase of structure formation in thepancake collapse in hierarchical clustering simulations. This Virgofilament lies almost along the line of sight, and this is the originthat has led a number of authors to much confusion in the Virgo distancedeterminations. We show that the M87 subcluster is located around 15--18Mpc, and it consists mainly of early-type type spiral galaxies inaddition to elliptical and S0 galaxies. There are very few late-typespiral galaxies in this subcluster. The spiral rich M49 subclusterconsists of a mixture of all types of spiral galaxies and is located atabout 22 Mpc. The two other known clouds, W and M, are located at about30--40 Mpc and undergo infall toward the core. The M cloud contains fewearly type spirals. We cannot discriminate, however, whether thesesubclusters or clouds are isolated aggregates or merely parts offilamentary structure. Finally, we infer the Hubble constant to be 82+/- 10 km s-1 Mpc-1.
| Near infrared surface photometry of late-type Virgo cluster galaxies
Near Infrared (K' band) surface photometry has been obtained for 102 (88late-type) Virgo cluster galaxies. A subset of 20 galaxies was alsoimaged in the H band. Magnitudes and diameters within the 21.5 and 22.0mag arcsec$^{-2}$ isophote, concentration indices and total H and K'magnitudes are derived. Basic statistical properties of a completesample of spiral galaxies spanning the range 6.3 < K'_T < 13.5 aregiven. Tables 3, 5 and 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/Abstract.html} Based on observations taken atthe Calar Alto Observatory, operated by the Max-Planck-Institut furAstronomie (Heidelberg) jointly with the Spanish National Commission forAstronomy.
| On the Size and Formation Mechanism of Star Complexes in Sm, Im, and BCD Galaxies
The diameters D_c_ of the largest star-forming complexes in 67Magellanic spiral and irregular galaxies and 16 blue compact dwarf (BCD)galaxies are found to scale approximately with the square root of thegalaxy luminosity for each type, i.e., smaller galaxies haveproportionately smaller star-forming regions. This is the same relationas for the largest complexes in bright spiral galaxies found previously,although Sm/Im galaxies have complexes that, on average, are a factor of2 larger than the extrapolation for spiral galaxies at the same absolutemagnitude, and the BCD galaxies have complexes that are ~2 times largerthan those typical of the Sm/Im galaxies at the same absolute magnitude.These results are consistent with the interpretation that the largestcomplexes form at the gravitational length scale in a marginally stableinterstellar medium with a nearly constant velocity dispersion c ~ 5-10km s^-1^. The luminosity scaling is then the result of higher averagetotal densities in smaller galaxies compared with the outer regions ofgiant spirals. This total density correlation is shown using published HI line widths and optical galaxy sizes. The implication of these resultsis that star formation begins when the ratio of the gas density ρ tothe total density (gas + stars + dark matter) exceeds several tenths. Ifstar formation lasts for a time scaling with (Grho_)^-1/2^ ~D_c_/c, then the main morphological differences between star formationin galaxies of various sizes can be explained: large galaxies have largestar complexes that form groups of OB associations slowly for up to 50Myr; small galaxies have small complexes (in terms of absolute size)that form dense associations quickly, in bursts spanning less than 5Myr.
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