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A Comparison of Hα and Stellar Scale Lengths in Virgo and Field Spirals
The scale lengths of the old stars and ionized gas distributions arecompared for similar samples of Virgo Cluster members and field spiralgalaxies via Hα and broad R-band surface photometry. While theR-band and Hα scale lengths are, on average, comparable for thecombined sample, we find significant differences between the field andcluster samples. While the Hα scale lengths of the field galaxiesare a factor of 1.14+/-0.07 longer, on average, than their R-band scalelengths, the Hα scale lengths of Virgo Cluster members are, onaverage, 20% smaller than their R-band scale lengths. Furthermore, inVirgo, the scale length ratios are correlated with the size of thestar-forming disk: galaxies with smaller overall Hα extents alsoshow steeper radial falloff of star formation activity. At the sametime, we find no strong trends in scale length ratio as a function ofother galaxy properties, including galaxy luminosity, inclination,morphological type, central R-band light concentration, or bar type. Ourresults for Hα emission are similar to other results for dustemission, suggesting that Hα and dust have similar distributions.The environmental dependence of the Hα scale length placesadditional constraints on the evolutionary process(es) that cause gasdepletion and a suppression of the star formation rate in clusters ofgalaxies.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| Diffuse Light in the Virgo Cluster
We present deep optical imaging of the inner ~1.5d×1.5d of theVirgo Cluster to search for diffuse intracluster light (ICL). Our imagereaches a 1 σ depth of μV=28.5 magarcsec-2, which is 1.5 mag arcsec-2 deeper thanprevious surveys, and reveals an intricate web of diffuse ICL. We seeseveral long (>100 kpc) tidal streamers, as well as a myriad ofsmaller scale tidal tails and bridges between galaxies. The diffuse haloof M87 is traced out to nearly 200 kpc, appearing very irregular onthese scales, while significant diffuse light is also detected aroundthe M84/M86 pair. Several galaxies in the core are embedded in commonenvelopes, suggesting they are true physical subgroups. The complexsubstructure of Virgo's diffuse ICL reflects the hierarchical nature ofcluster assembly, rather than being the product of smooth accretionaround a central galaxy.
| 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
| Hα Morphologies and Environmental Effects in Virgo Cluster Spiral Galaxies
We describe the various Hα morphologies of Virgo Cluster andisolated spiral galaxies and associate the Hα morphologies withthe types of environmental interactions that have altered the clustergalaxies. The spatial distributions of Hα and R-band emission areused to divide the star formation morphologies of the 52 Virgo Clusterspiral galaxies into several categories: normal (37%), anemic (6%),enhanced (6%), and (spatially) truncated (52%). Truncated galaxies arefurther subdivided on the basis of their inner star formation rates intotruncated/normal (37%), truncated/compact (6%), truncated/anemic (8%),and truncated/enhanced (2%). The fraction of anemic galaxies isrelatively small (6%-13%) in both environments, suggesting thatstarvation is not a major factor in the reduced star formation rates ofVirgo spiral galaxies. The majority of Virgo spiral galaxies have theirHα disks truncated (52%), whereas truncated Hα disks arerarer in isolated galaxies (12%). Most of the Hα-truncatedgalaxies have relatively undisturbed stellar disks and normal toslightly enhanced inner disk star formation rates, suggesting thatintracluster medium-interstellar medium (ICM-ISM) stripping is the mainmechanism causing the reduced star formation rates of Virgo spiralgalaxies. Several of the truncated galaxies are peculiar, with enhancedcentral star formation rates, disturbed stellar disks, and barlikedistributions of luminous H II complexes inside the central 1 kpc but nostar formation beyond, suggesting that recent tidal interactions orminor mergers have also influenced their morphology. Two highly inclinedHα-truncated spiral galaxies have numerous extraplanar H IIregions and are likely in an active phase of ICM-ISM stripping. Severalspiral galaxies have one-sided Hα enhancements at the outer edgeof their truncated Hα disks, suggesting modest local enhancementsin their star formation rates due to ICM-ISM interactions. Low-velocitytidal interactions and perhaps outer cluster H I accretion seem to bethe triggers for enhanced global star formation in four Virgo galaxies.These results indicate that most Virgo spiral galaxies experienceICM-ISM stripping, many experience significant tidal effects, and manyexperience both.
| 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
| 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
| The origin of H I-deficiency in galaxies on the outskirts of the Virgo cluster. II. Companions and uncertainties in distances and deficiencies
The origin of the deficiency in neutral hydrogen of 13 spiral galaxieslying in the outskirts of the Virgo cluster is reassessed. If thesegalaxies have passed through the core of the cluster, their interstellargas should have been lost through ram pressure stripping by the hotX-ray emitting gas of the cluster. We analyze the positions of these HI-deficient and other spiral galaxies in velocity-distance plots, inwhich we include our compilation of velocity-distance data on 61elliptical galaxies, and compare with simulated velocity-distancediagrams obtained from cosmological N-body simulations. We find that20% relative Tully-Fisher distance errors are consistent with thegreat majority of the spirals, except for a small number of objectswhose positions in the velocity-distance diagram suggest grosslyincorrect distances, implying that the Tully-Fisher error distributionfunction has non-Gaussian wings. Moreover, we find that the distanceerrors may lead to an incorrect fitting of the Tolman-Bondi solutionthat can generate significant errors in the distance and especially themass estimates of the cluster. We suggest 4 possibilities for theoutlying H I-deficient spirals (in decreasing frequency): 1) they havelarge relative distance errors and are in fact close enough (atdistances between 12.7 and 20.9 Mpc from us) to the cluster to havepassed through its core and seen their gas removed by ram pressurestripping; 2) their gas is converted to stars by tidal interactions withother galaxies; 3) their gas is heated during recent mergers withsmaller galaxies; and 4) they are not truly H I-deficient (e.g. S0/amisclassified as Sa).Appendix A is 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.
| 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
| UV to radio centimetric spectral energy distributions of optically-selected late-type galaxies in the Virgo cluster
We present a multifrequency dataset for an optically-selected,volume-limited, complete sample of 118 late-type galaxies (>=S0a) inthe Virgo cluster. The database includes UV, visible, near-IR, mid-IR,far-IR, radio continuum photometric data as well as spectroscopic dataof Hα , CO and HI lines, homogeneously reduced, obtained from ourown observations or compiled from the literature. Assuming the energybalance between the absorbed stellar light and that radiated in the IRby dust, we calibarte an empirical attenuation law suitable forcorrecting photometric and spectroscopic data of normal galaxies. Thedata, corrected for internal extinction, are used to construct thespectral energy distribution (SED) of each individual galaxy, andcombined to trace the median SED of galaxies in various classes ofmorphological type and luminosity. Low-luminosity, dwarf galaxies haveon average bluer stellar continua and higher far-IR luminosities perunit galaxy mass than giant, early-type spirals. If compared to nearbystarburst galaxies such as M 82 and Arp 220, normal spirals haverelatively similar observed stellar spectra but 10-100 times lower IRluminosities. The temperature of the cold dust component increases withthe far-IR luminosity, from giant spirals to dwarf irregulars. The SEDare used to separate the stellar emission from the dust emission in themid-IR regime. We show that the contribution of the stellar emission at6.75 mu m to the total emission of galaxies is generally important, from~ 80% in Sa to ~ 20% in Sc.Tables 2-5, 7, 8, and Fig. 2 are only available in electronic form athttp://www.edpsciences.orgTables 10-12 are only available in electronic form 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/402/37
| 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.
| 1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0
We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.
| 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.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Hα surface photometry of galaxies in the Virgo cluster. IV. The current star formation in nearby clusters of galaxies
Hα +[NII] imaging observations of 369 late-type (spiral) galaxiesin the Virgo cluster and in the Coma/A1367 supercluster are analyzed,covering 3 rich nearby clusters (A1367, Coma and Virgo) and nearlyisolated galaxies in the Great-Wall. They constitute an opticallyselected sample (mp<16.0) observed with ~ 60 %completeness. These observations provide us with the current(T<107 yrs) star formation properties of galaxies that westudy as a function of the clustercentric projected distances (Theta ).The expected decrease of the star formation rate (SFR), as traced by theHα EW, with decreasing Theta is found only when galaxies brighterthan Mp ~ -19.5 are considered. Fainter objects show no orreverse trends. We also include in our analysis Near Infrared data,providing information on the old (T>109 yrs) stars. Puttogether, the young and the old stellar indicators give the ratio ofcurrently formed stars over the stars formed in the past, or``birthrate'' parameter b. For the considered galaxies we also determinethe ``global gas content'' combining HI with CO observations. We definethe ``gas deficiency'' parameter as the logarithmic difference betweenthe gas content of isolated galaxies of a given Hubble type and themeasured gas content. For the isolated objects we find that b decreaseswith increasing NIR luminosity. In other words less massive galaxies arecurrently forming stars at a higher rate than their giant counterpartswhich experienced most of their star formation activity at earliercosmological epochs. The gas-deficient objects, primarily members of theVirgo cluster, have a birthrate significantly lower than the isolatedobjects with normal gas content and of similar NIR luminosity. Thisindicates that the current star formation is regulated by the gaseouscontent of spirals. Whatever mechanism (most plausibly ram-pressurestripping) is responsible for the pattern of gas deficiency observed inspiral galaxies members of rich clusters, it also produces the observedquenching of the current star formation. A significant fraction of gas``healthy'' (i.e. with a gas deficiency parameter less than 0.4) andcurrently star forming galaxies is unexpectedly found projected near thecenter of the Virgo cluster. Their average Tully-Fisher distance isfound approximately one magnitude further away (muo = 31.77)than the distance of their gas-deficient counterparts (muo =30.85), suggesting that the gas healthy objects belong to a cloudprojected onto the cluster center, but in fact lying a few Mpc behindVirgo, thus unaffected by the dense IGM of the cluster. Based onobservations taken at the Observatorio Astronómico Nacional(Mexico), the OHP (France), Calar Alto and NOT (Spain) observatories.Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org
| Hα surface photometry of galaxies in the Virgo cluster. II. Observations with the OHP and Calar Alto 1.2 m telescopes
We present Hα line imaging observations of 122 galaxies obtainedwith the 1.20 m telescopes of the Observatoire de Haute Provence (OHP)and of Calar Alto. The observed galaxies are mostly Virgo clustermembers (95), along with 10 objects in the Coma/A1367 supercluster, 6 inthe clusters A2197 and A2199, and 11 nearby galaxies taken as fillers.Hα +[NII] fluxes and equivalent widths, as well as images of allthe detected targets, are presented. Based on observations taken at theObservatoire de Haute Provence (OHP) (France), operated by the FrenchCNRS, and Calar Alto Observatory (Spain), operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy. Figure 1 is only available inelectronic form at http://www.edpsciences.org
| Star formation and dust extinction in nearby star-forming and starburst galaxies
We study the star formation rate and dust extinction properties of asample of nearby star-forming galaxies as derived from Hα and UV (~ 2000 Å) observations and we compare them to those of a sample ofstarburst galaxies. The dust extinction in Hα is estimated fromthe Balmer decrement and the extinction in UV using the FIR to UV fluxratio or the attenuation law for starburst galaxies of Calzetti et al.(\cite{calzetti5}). The Hα and UV emissions are stronglycorrelated with a very low scatter for the star-forming objects and witha much higher scatter for the starburst galaxies. The Hα to UVflux ratio is found to be larger by a factor ~ 2 for the starburstgalaxies. We compare both samples with a purely UV selected sample ofgalaxies and we conclude that the mean Hα and UV properties ofnearby star-forming galaxies are more representative of UV-selectedgalaxies than starburst galaxies. We emphasize that the Hα to UVflux ratio is strongly dependent on the dust extinction: the positivecorrelation found between FHα/FUV andFFIR/FUV vanishes when the Hα and UV fluxare corrected for dust extinction. The Hα to UV flux ratiosconverted into star formation rate and combined with the Balmerdecrement measurements are tentatively used to estimate the dustextinction in UV.
| An Atlas of Hα and R Images and Radial Profiles of 63 Bright Virgo Cluster Spiral Galaxies
Narrowband Hα and broadband R images and radial profiles arepresented for 63 bright spiral galaxies in the Virgo Cluster. The sampleis complete for Sb-Scd galaxies with B0T<=12and inclination <=75°. Isophotal radii, disk scale lengths,concentration parameters, and integrated fluxes are derived for thesample galaxies.
| The relationship between star formation rates and mid-infrared emission in galactic disks
The Hα and mid-infrared mean disk surface brightnesses arecompared in a sample of nearby spirals observed by ISOCAM. This showsthat, in spiral disks, dust emission at 7 and 15 mu m provides areasonable star formation tracer. The fact that the 15 to 7 mu m fluxratio is nearly constant in various global exciting conditions indicatesa common origin, namely the aromatic infrared band carriers, and impliesthat at these wavelengths, dust emission from the disks of normalgalaxies is dominated by photodissociation regions and not by H Iiregions themselves. We use this newly-found correlation between themid-infrared and the Hα line to investigate the nature of the linkbetween the far-infrared (60 and 100 mu m) and Hα . Although theseparation of the central regions from the disk is impossible to achievein the far-infrared, we show that a circumnuclear contribution to thedust emission, having no equivalent counterpart in Hα , is mostlikely responsible for the well-known non-linearity between far-infraredand Hα fluxes in spiral galaxies. We derive a calibration of 7 and15 mu m fluxes in terms of star formation rates from a primarycalibration of Hα in the literature, and also outline theapplicability limits of the proposed conversion, which should not beblindly extrapolated to objects whose nature is unknown. Based onobservations with ISO, an ESA project with instruments funded by ESAMember States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.
| The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties
We study the mid-infrared properties of a sample of 69 nearby spiralgalaxies, selected to avoid Seyfert activity contributing a significantfraction of the central energetics, or strong tidal interaction, and tohave normal infrared luminosities. These observations were obtained withISOCAM, which provides an angular resolution of the order of 10arcsec(half-power diameter of the point spread function) and low-resolutionspectro-imaging information. Between 5 and 18 mu m, we mainly observetwo dust phases, aromatic infrared bands and very small grains, both outof thermal equilibrium. On this sample, we show that the globalF15/F_7 colors of galaxies are very uniform, the onlyincrease being found in early-type strongly barred galaxies, consistentwith previous IRAS studies. The F15/F_7 excesses areunambiguously due to galactic central regions where bar-inducedstarbursts occur. However, the existence of strongly barred early-typegalaxies with normal circumnuclear colors indicates that therelationship between a distortion of the gravitational potential and acentral starburst is not straightforward. As the physical processes atwork in central regions are in principle identical in barred andunbarred galaxies, and since this is where the mid-infrared activity ismainly located, we investigate the mid-infrared circumnuclear propertiesof all the galaxies in our sample. We show how surface brightnesses andcolors are related to both the available molecular gas content and themean age of stellar populations contributing to dust heating. Therefore,the star formation history in galactic central regions can beconstrained by their position in a color-surface brightness mid-infrareddiagram. Based on observations with ISO, an ESA project with instrumentsfunded by ESA Member States (especially the PI countries: France,Germany, the Netherlands and the UK) and with the participation of ISASand NASA.
| An atlas of mid-infrared dust emission in spiral galaxies
We present maps of dust emission at 7 mu m and 15 mu m/7 mu m intensityratios of selected regions in 43 spiral galaxies observed with ISOCAM.This atlas is a complement to studies based on these observations,dealing with star formation in centers of barred galaxies and in spiraldisks. It is accompanied by a detailed description of data reduction andan inventory of generic morphological properties in groups definedaccording to bar strength and HI gas content. Based on observations withISO, an ESA project with instruments funded by ESA Member States(especially the PI countries: France, Germany, The Netherlands and theUK) and with the participation of ISAS and NASA.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Luminosity versus Phase-Space-Density Relation of Galaxies Revisited
We reexamined the correlation between the BTmagnitude and the phase-space-density parameterw=(D225vc)-1 of galaxies forthe Virgo, the Coma, the Fornax, and the Perseus clusters in an effortto better understand the physical underpinning of the fundamental plane.A tight correlation (BT=alog w+b) common to differentmorphological types of galaxies (E, S0, S) was found for the Virgo andthe Coma clusters, with a=1.87+/-0.10 and 1.33+/-0.11, respectively. Aninvestigation using only E galaxies was made for the four clusters. Theresults indicated that the empirical linear relation might be commonamong the Coma, the Fornax, and the Perseus clusters, with the VirgoCluster showing deviation. This relation, which is another way toproject the fundamental plane, has an expression insensitive to themorphology and may be suitable for treating galaxies of differentmorphological types collectively.
| 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
| The 3D structure of the Virgo cluster from H-band Fundamental Plane and Tully-Fisher distance determinations
We undertook a surface photometry survey of 200 galaxies in the Virgocluster (complete to B<14.0 mag) carried out in the near-infrared(NIR) H band. Combining velocity dispersion measurements from theliterature with new spectroscopic data for 11 galaxies, we derivedistances of 59 early-type galaxies using the Fundamental Plane (FP)method. The distances of another 75 late-type galaxies are determinedusing the Tully-Fisher (TF) method. For this purpose we use the maximumrotational velocity, as derived from HI spectra from the literature,complemented with new Hα rotation curves of eight highlyHI-deficient galaxies. The zero-points of the FP and TF templaterelations are calibrated assuming the distance modulus of Virgomu_0=31.0, as determined with the Cepheids method. Using these 134distance determinations (with individual uncertainties of 0.35 mag (TF)and 0.45 mag (FP)) we find that the distance of cluster A, associatedwith M87, is mu_0=30.84 +/- 0.06. Cluster B, offset to the south, isfound at mu_0=31.84 +/- 0.10. This subcluster is falling on to A atabout 750 km s^-1. Clouds W and M are at twice the distance of A.Galaxies on the north-west and south-east of the main cluster A belongto two clouds composed almost exclusively of spiral galaxies withdistances consistent with A, but with significantly different velocitydistributions, suggesting that they are falling on to cluster A atapproximately 770 km s^-1 from the far side and at 200 km s^-1 from thenear side respectively. The mass of Virgo inferred from the peculiarmotions induced on its vicinity is consistent with the virialexpectation.
| 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.
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