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The Classification of Galaxies: Early History and Ongoing Developments
"You ask what is the use of classification, arrangement,systematization. I answer you; order and simplification are the firststeps toward the mastery of a subject the actual enemy is the unknown."
| Formation of inner rings in 3D potentials of barred galaxies
In a 3D analytic potential we find the families of periodic orbits thatsupport the formation of inner rings. These are families at highenergies, between the inner radial ultraharmonic 4:1 (iUHR) resonanceand corotation, influenced by the 4:1, 6:1 and 8:1 resonances. The innerrings they support are mainly ovals and polygons with `corners' on thebar minor axis, on its sides, which correspond to morphologies oftenseen in real galaxies like NGC 6782 and IC 4290. We also investigate theconditions under which less probable shapes of rings may be supported byorbits at the region. Such rings include pentagonal features (NGC 3367)and hexagons with cusps on the major axis of the bar and two sidesparallel to it (NGC 7020).
| On the 3D dynamics and morphology of inner rings
We argue that inner rings in barred spiral galaxies are associated withspecific 2D and 3D families of periodic orbits located just beyond theend of the bar. These are families located between the inner radialultraharmonic 4:1 resonance and corotation. They are found in the upperpart of a type-2 gap of the x1 characteristic, and can account for theobserved ring morphologies without any help from families of thex1-tree. Due to the evolution of the stability of all these families,the ring shapes that are favoured are mainly ovals, as well as polygonswith `corners' on the minor axis, on the sides of the bar. On the otherhand, pentagonal rings, or rings of the NGC 7020-type hexagon, should beless probable. The orbits that make the rings belong in their vastmajority to 3D families of periodic orbits and orbits trapped aroundthem.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| 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
| Analysis of the distribution of HII regions in external galaxies. IV. The new galaxy sample. Position and inclination angles
We have compiled a new sample of galaxies with published catalogs of HIIregion coordinates. This sample, together with the former catalog ofGarcía-Gómez & Athanassoula (\cite{gga1}), will formthe basis for subsequent studies of the spiral structure in discgalaxies. In this paper we address the problem of the deprojection ofthe galaxy images. For this purpose we use two deprojection methodsbased on the HII region distribution and compare the results with thevalues found in the literature using other deprojection methods. Takinginto account the results of all the methods, we propose optimum valuesfor the position and inclination angles of all the galaxies in oursample. Tables 2 and 3 are only available in electronic form athttp://www.edpsciences.org
| Ultraviolet Signposts of Resonant Dynamics in the Starburst-ringed SAB Galaxy M94 (NGC 4736)
The dynamic orchestration of star-birth activity in the starburst-ringedgalaxy M94 (NGC 4736) is investigated using images from the UltravioletImaging Telescope (UIT; far-ultraviolet [FUV] band), Hubble SpaceTelescope (HST; near-ultraviolet [NUV] band), Kitt Peak 0.9 m telescope(Hα, R, and I bands), and Palomar 5 m telescope (B band), alongwith spectra from the International Ultraviolet Explorer (IUE) and theLick 1 m telescope. The wide-field UIT image shows FUV emission from (1)an elongated nucleus, (2) a diffuse inner disk, where Hα isobserved in absorption, (3) a bright inner ring of H II regions at theperimeter of the inner disk (R=48"=1.1 kpc), and (4) two 500 pc sizeknots of hot stars exterior to the ring on diametrically opposite sidesof the nucleus (R=130"=2.9 kpc). The HST Faint Object Camera imageresolves the NUV emission from the nuclear region into a bright core anda faint 20" long ``minibar'' at a position angle of 30°. Optical andIUE spectroscopy of the nucleus and diffuse inner disk indicates a~107-108 yr old stellar population from low-levelstar-birth activity blended with some LINER activity. Analysis of theHα-, FUV-, NUV-, B-, R-, and I-band emissions, along with otherobserved tracers of stars and gas in M94, indicates that most of thestar formation is being orchestrated via ring-bar dynamics, involvingthe nuclear minibar, inner ring, oval disk, and outer ring. The innerstarburst ring and bisymmetric knots at intermediate radius, inparticular, argue for bar-mediated resonances as the primary drivers ofevolution in M94 at the present epoch. Similar processes may begoverning the evolution of the ``core-dominated'' galaxies that havebeen observed at high redshift. The gravitationally lensed ``PretzelGalaxy'' (0024+1654) at a redshift of ~1.5 provides an importantprecedent in this regard.
| Using Hubble Space Telescope images to identify straight segments in galaxy nuclear spirals
This Letter reports the discovery of straight segments of nuclear spiralarms. Hubble Space Telescope images of Seyfert galaxies are used. Themorphology of the straight features on scales of few hundred parsecsproves to be similar to the morphology of disc-wide polygonal spiralsand rings. This suggests that the straight structures on both nuclearand disc scales may have a common physical nature.
| Dynamics and Stability of Resonant Rings in Galaxies
We have developed a model for a spheroidal, ring-shaped galaxy. Thestars move in a ring with an elliptical cross section at the 1: 1frequency resonance. The shape of the cross section of the equilibriumring depends on the oblateness of the galaxy itself, so that the ellipseof the ring cross section is radially extended when the oblateness ofthe galaxy is small. If the oblateness of galaxy exceeds some criticalvalue, the ellipse cross section is extended along the Ox 3 axis. Theshape of the ring cross section is circular for a galaxy with criticaleccentricity. The stability of the ring over a wide range ofperturbations is studied. A fundamental bicubic dispersion equation forthe frequencies of small oscillations of a perturbed ring is derived.Application of the model to the ring galaxy NGC 7020 shows that its ringcross section should be approximately circular. Analysis of thedispersion equation demonstrates that stellar orbits in the arm areunstable (but the instability increment is small). We conclude thatstars in the ring of this galaxy should drift from the 1: 1 resonance,and the ring itself should evolve.
| 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.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://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 biconical cavity associated with HD 200775: the formation of a cometary nebula
We have observed with high angular resolution (10'' - 24'') an area of ~18'x15' around HD 200775 in the J=2->1 line of (12) CO and theJ=1->0 lines of (13) CO and C(18) O. An interferometric HI 21cm imagewith similar angular resolution (14'') is also presented. Molecularobservations show that the star is located in a biconical cavity thathas been very likely excavated by an energetic and bipolar outflow in anearlier evolutionary stage. The star is not located at the apex of thiscavity but ~ 50 '' towards the eastern lobe. At the present stage, thereis no evidence for high velocity gas within the lobes of the cavity.However, the morphology of the HI emission, two filaments arranged in a``>'' shape feature, and the bow shock located at the tip of one ofthese filaments, show that high velocity atomic gas is outflowing in ashell adjacent to the walls of the cavity in the eastern lobe. Sincethis high velocity atomic gas has not been detected in the western lobe,the outflow has a cometary shape. We propose that this outflow is formedwhen the atomic gas in the inner walls of the cavity is accelerated bythe stellar wind. The cometary shape is due to the off-center positionof the star. This cometary HI region constitutes the latest evolutionarystage of the bipolar outflow associated with HD 200775. Based on theseresults we propose a simple model to explain the formation of cometarynebulae in massive star forming regions.
| Galactic Rings
About one fifth of all spiral disk galaxies include a ring-shapedpattern in the light distribution, and an additional one third appear tohave broken or partial rings made up of spiral arms (pseudorings). Theserings are a special problem in galaxy morphology with a direct bearingon the internal dynamics and evolution of disk galaxies. Morphologicaldata have shown that rings are most often associated with bars or othercommon nonaxisymmetric perturbations, such as ovals. Kinematic andmetric data have provided considerable evidence for intrinsic ovalshapes and preferred alignments between ring major axes and bars.Photometric data have demonstrated that most rings are sites of currentactive star formation, and in some galaxies a ring is the only placewhere recent star formation is found. A few rings are sites of the mostspectacular "starbursts" known in non-violently interacting galaxies.Though a small fraction of observed rings may be due to collisions ormergers of galaxies, or to accretion of intergalactic gas, the vastmajority of rings are probably simple resonance phenomena, caused by theactions of a rotating bar or other nonaxisymmetic disturbance on themotions of gas clouds in the disk. The evidence in support of this ideahas accumulated steadily during the past 15 years, and our goal in thisreview is to bring together a large body of theoretical andobservational results in one place. We shall see that rings are anatural consequence of barred galaxy dynamics, and that they are moreeasily understood than the bars and ovals which undoubtedly create them.However, there are interesting problems, such as the lack of any ringsin some barred galaxies, the less common but by no means rare cases ofrings in nonbarred galaxies, the role of mild tidal interactions, wherethe gas that fuels star formation in rings actually comes from, theexistence of different ring types of very different time-scales in thesame galaxy. We will discuss these problems in some detail here, andindicated where the solutions may lie.
| The Distribution and Properties of H II Regions in Early-to-Intermediate Hubble Type Ringed Galaxies
This paper presents a study of the H II regions in 32 ringed andpseudo-ringed galaxies having Hubble types in the range S0 + to Sc. Theobjective is to illustrate the distributions of H II regions in classicexamples of ringed galaxies and to relate the observed properties toresonance theory. The sample is selected from the Catalog of SouthernRinged Galaxies and includes examples covering a range of ring andgalaxy morphological properties. We find that the distribution ofHα luminosity around inner rings is sensitive to the intrinsicshape of the rings. Extremely oval inner rings show a greaterconcentration of H II regions near the intrinsic ring major axiscompared to more circular rings. Nuclear rings are present in several ofthe sample galaxies and show a range of morphological properties, from adouble nuclear ring in NGC 1317 to an irregular feature in NGC 1433. Wefind also that in galaxies in which an R_1_ outer ring is prominent inthe continuum image, the H II regions follow an R^'^_2_ morphology. Inseveral cases, the observed distribution of H II regions stronglysupports the idea that the rings are linked to specific orbitalresonances with the bar. H II region luminosity functions have beenderived for all of the sample galaxies. The functions can be representedby power laws whose exponents are very similar to those found fornonringed galaxies. In a few cases, a luminous nuclear ring produces asecondary peak in the luminosity function. One galaxy shows a break inthe luminosity function similar to that observed in other galaxies byKennicutt, Edgar, & Hodge. The most unusual Hα distribution inthe sample was found in the large outer-ringed galaxy NGC 1291. Theprimary bar, lens, and secondary bar regions of this SO/a galaxy arefilled with a wispy pattern of ionized gas filaments very reminiscent ofwhat is seen in the bulge of M31.
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| NGC 7217: A Spheroid-dominated, Early-Type Resonance Ring Spiral Galaxy
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...450..593B&db_key=AST
| Total and effective colors of 501 galaxies in the Cousins VRI photometric system
Total color indices (V-R)T, (V-I)T and effectivecolor indices (V-R)e, (V-I)e in the Cousins VRIphotometric system are presented for 501 mostly normal galaxies. Thecolors are computed using a procedure outlined in the Third ReferenceCatalogue of Bright Galaxies (RC3) whereby standard color curvesapproximated by Laplace-Gauss integrals are fitted to observedphotoelectric multiaperture photometry. 11 sources of such photometrywere used for our analysis, each source being assigned an appropriateweight according to a rigorous analysis of residuals of the data fromthe best-fitting standard color curves. Together with the integrated B-Vand U-B colors provided in RC3, our analysis widens the range ofwavelength of homogeneously defined colors of normal galaxies of allHubble types. We present color-color and color-type relations that canbe modeled to understand the star formation history of galaxies.
| Disc galaxies with multiple triaxial structures. I. BVRI and Hα surface photometry.
We present a BVRI survey of 36 galaxies selected as candidates forhaving a misaligned secondary bar or a triaxial bulge inside the primarybar. Fifteen galaxies have also been observed in Hα. A positivedetection of more than one triaxial structure has been found in 22galaxies shared out as follows: 13 double-barred galaxies, 3triple-barred galaxies, 3 double-barred galaxies with an additionalstructure with twisted isophotes, and 3 galaxies with a bar and astructure with twisted isophotes. Triaxial deformation(s) have beenfound in 6 galaxies classified as unbarred in RC3. The number of Seyfertnuclei amongst double-barred systems is high (6 over 13).
| Photometrically distinct nuclei in elliptical and early-type disks galaxies.
Not Available
| Pattern speed domains in ringed disk galaxies from observational and simulational databases
New test-particle simulations have been carried out to learn more aboutthe secular evolution and morphology of the gaseous and stellardistributions in barred galaxies. We verify the previous results of M.P. Schwarz that gas clouds will tend to collect into ring-like patternsnear major orbit resonances, owing to gravity torques. However, weimprove on these results in several ways. Firstly, we use more gasclouds (10000 vs 2000) than Schwarz and track individual clouds todetermine when they collide, rather than using a collision box as didSchwarz. Secondly, besides Schwarz's isochrone rotation curve, we alsouse a flat rotation curve. Thirdly, we consider more bar pattern speedsand strengths than did Schwarz. Finally, unlike Schwarz and othersimulators, we have a large database of images and color index maps ofnearly 140 ringed galaxies that can be compared to the simulations toevaluate their significance. We confirm the two types of outer Lindbladresonance rings that Schwarz discovered, but find that their existenceis not due so much to the initial density distribution of gas clouds asto pattern speed and the time interval since the bar potential wasimposed. The simulations and the images lead us to suggest that we candivide barred galaxies according to the resonances which the bar patternspeed and rotation curve allow in the disk. We illustrate specificgalaxies that we believe belong to fast, medium, and slow bar patternspeed 'domains' and match them to particular simulation frames. We alsodiscuss alternative hypotheses in which the pattern speed is such thatall resonances are present but the gas has been depleted or wasdistributed differently in various galaxies to produce the threeclassification domains.
| The dependence of the cool matter content on galaxy morphology in galaxies of types E/S0, S0, and SA
Using the material assembled in earlier papers, we examine the manner inwhich the interstellar matter content varies along the Hubble sequencefrom S0 galaxies to Sa galaxies selected from the RSA2 compilation. Forthis we make use of a new and more detailed classification which isdescribed here as applied to these early disk/spiral galaxies. Theprominence of the disk in S0's and the visibility of features (H IIregions) in the Sa's serve as the basis for the subtypes. Three S0categories: subtle, intermediate, and pronounced, and four Sadescriptors: very early, early, intermediate, and late are assigned tothe galaxies. It is found that the total amount of hydrogen (H I + H2)is a function of subtype, being low in the S0's and rising smoothly fromthe early Sa's to the later Sa's. The average surface density ofhydrogen exceeds 3 solar masses/pc-squared only in the latest subtypesof the Sa's. We conclude that the prominence of the disk of a galaxyclosely follows the amount of cool gas which the disk contains.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| Ring structure in disk galaxies
The properties of the solutions to the equations of motion of a gas diskwith dispersion are investigated. The rotation curve of the disk isdivided into two parts and each is considered separately. First, if therotation speed is an increasing function of radius, it is shown thatconcentric rings are possible. Second, if the rotation curve is flat ora decreasing function of radius, there is at most one ring possible inthis region. Previously, galactic ring structure was considered to arisefrom a forcing bar or oval distortion. This work shows that rings arepossible in high symmetry systems such as NGC 7020 with no observablebar.
| Near Infrared Spectral Synthesis in Giant Early Type Galaxies
Not Available
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| Southern Sky Redshift Survey - The catalog
The catalog of radial velocities for galaxies which comprise thediameter-limited sample of the Southern Sky Redshift Survey ispresented. It consolidates the data of observations carried out at theLas Campanas Observatory, Observatorio Nacional, and South AfricanAstronomical Observatory. The criteria used for the sample selection aredescribed, as well as the observational procedures and the techniqueutilized to obtain the final radial velocities. The intercomparisonbetween radial velocity measurements from different telescopes indicatesthat the final data base is fairly homogeneous with a typical error ofabout 40 km/s. The sample is at present 90 percent complete, and themissing galaxies are predominantly objects with very low surfacebrightness for which it is very difficult to obtain optical redshifts.
| Interstellar matter in early-type galaxies. I - The catalog
A catalog is given of the currently available measurements ofinterstellar matter in the 467 early-type galaxies listed in the secondedition of the Revised Shapley-Ames Catalog of Bright Galaxies. Themorphological type range is E, SO, and Sa. The ISM tracers are emissionin the following bands: IRAS 100 micron, X-ray, radio, neutral hydrogen,and carbon monoxide. Nearly two-thirds of the Es and SOs have beendetected in one or more of these tracers. Additional observed quantitiesthat are tabulated include: magnitude, colors, radial velocity, centralvelocity dispersion, maximum of the rotation curve, angular size, 60micron flux, and supernovae. Qualitative statements as to the presenceof dust or emission lines, when available in the literature, are given.Quantities derivative from the observed values are also listed andinclude masses of H I, CO, X-ray gas, and dust as well as an estimate ofthe total mass and mass-to-luminosity ratio of the individual galaxies.
| H I content and FIR emission of S0 galaxies
A sample of 252 S0 galaxies is used to study the relationship between HI content and far-IR emission. Logarithms of the H I content versus thefar-IR emission are employed statistically to develop a best-fit linearregression line which is compared to a slope of approximately unity. Theslopes are different for S0 and SB0 galaxies versus S0/a and SB0/agalaxies. The distribution of the 60-100 micron flux ratio is notsignificantly affected by the presence or absence of bars nor by thedifferences between the S0 and S0/a systems. The flux ratio is higherthan the critical value of Helou in 34 percent of the cases, and thevalue holds when nuclear emission is taken into account. In cases wherethe critical value is exceeded, most far-IR emissions are expected to bedue to star formation. S0 galaxies are generally found to have a normalISM, except where the systems have accreted their H I gas. Systems withdisproportionate FIR emission can be considered galaxies that areexperiencing enhanced star formation or that have had their H I gasswept away.
| Weakly barred early-type ringed galaxies. III - The remarkable outer-ringed S0+ galaxy NGC 7020
The southern S0+ galaxy NGC 7020 presents an unusual morphology: itincludes a very regular outer ring which is completely detached andwhich envelops an inner ring/lens zone with an exotic hexagonal shape.The ring has a high contrast compared with those usually observed inbarred galaxies, yet NGC 7020 is not obviously barred. In this paper,the structure of this galaxy is studied by means of UBVRI CCD surfacephotometry. The photometry reveals a complex system and shows that mostof the recent star formation in the galaxy has taken place in the outerring. Two bright knots are found on the major axis of the hexagonal zonethat appear to be true enhancements of old stars rather than youngassociations. Between these knots and the bulge there are dips in thesurface brightness and a clear zone of rectangular isophotes.
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