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Nature of Nuclear Rings in Unbarred Galaxies: NGC 7742 and NGC 7217
We have studied an unbarred Sb galaxy with a nuclear star-forming ring,NGC 7742, by means of two-dimensional spectroscopy, long-slitspectroscopy, and imaging and have compared the results with theproperties of another galaxy of this type, NGC 7217, which was studiedby us earlier. Both galaxies have many peculiar features in common: eachhas two global exponential stellar disks with different scale lengths,each possesses a circumnuclear inclined gaseous disk with a radius of300 pc, and each has a global counterrotating subsystem, a gaseous onein NGC 7742 and a stellar one in NGC 7217. We suggest that a past minormerger is the probable cause of all these peculiarities, including theappearance of nuclear star-forming rings without global bars; the ringsmight be produced as resonance features by tidally induced ovaldistortions of the global stellar disks.
| 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
| An Inner Ring and the Microlensing toward the Bulge
All current bulge-disk models for the inner Galaxy fall short ofreproducing self-consistently the observed microlensing optical depth bya factor of 2 (>2 σ). We show that the least mass-consuming wayto increase the microlensing optical depth is to add density roughlyhalfway between the observer and the highest microlensing sourcedensity. We present evidence for the existence of such a densitystructure in the Galaxy: an inner ring, a standard feature of barredgalaxies. Judging from data on similar rings in external galaxies, aninner ring can contribute more than 50% of a pure bulge-disk model tothe microlensing optical depth. We may thus eliminate the need for asmall viewing angle of the bar. The influence of an inner ring on theevent duration distribution, for realistic viewing angles, would be toincrease the fraction of long-duration events toward Baade's window. Thelongest events are expected toward the negative-longitude tangent pointat l~-22°. A properly sampled event duration distribution towardthis tangent point would provide essential information about viewingangle and elongation of the overall density distribution in the innerGalaxy.
| 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.
| Noncircular Gas Kinematics and Star Formation in the Ringed Galaxy NGC 4736
We analyze the gas kinematics and star formation properties of thenearby RSab galaxy NGC 4736 using interferometric and single-dishCO(1-0) data and previously published Hα and H I data. The COmorphology is dominated by a central molecular bar and tightly woundspiral arms associated with a bright ring of star formation. Strong H Iemission is also found in the ring, but H I is absent from the centralregions. Comparison of the H I and Hα distributions suggests thatH I in the ring is primarily dissociated H2. Modeling of theCO kinematics reveals gas motion in elliptical orbits around the centralbar, and we argue that the ring represents both the outer Lindbladresonance of the bar and the inner Lindblad resonance of a larger ovaldistortion. The H I kinematics show evidence for axisymmetric inflowtoward the ring and are inconsistent with streaming in alignedelliptical orbits, but the highly supersonic (~40 km s-1)inflow velocities required, corresponding to mass inflow rates of ~2Msolar yr-1, suggest that more sophisticatedmodels (e.g., gas orbiting in precessed elliptical orbits) should beconsidered. The radial CO and Hα profiles are poorly correlated inthe vicinity of the nuclear bar but show a better correlation (in roughagreement with the Schmidt law) at the ring. Even along the ring,however, the azimuthal correspondence between CO and Hα is poor,suggesting that massive stars form more efficiently at some (perhapsresonant) locations than at others. These results indicate that the starformation rate per unit gas mass exhibits strong spatial variations andis not solely a function of the available gas supply. The localizationof star formation to the ring is broadly consistent with gravitationalinstability theory, although the instability parameter Q~3 on average inthe ring, only falling below 1 in localized regions. Large-scaledynamical effects, by concentrating gas at resonances and influencingthe star formation rate, appear to play a key role in this galaxy'sevolution.
| Resonance Rings and Galaxy Morphology
Rings of star formation are a common phenomenon of early to intermediateHubble type disk galaxies. Most rings form by gas accumulation atresonances, usually under the continuous action of gravity torques froma bar pattern, but sometimes in response to a mild tidal interactionwith a nearby companion. In either case, a resonance is a very specialplace in any galaxy where star formation can be enhanced and may proceedeither as a starburst or continuously over a long time period. Thisarticle describes the characteristic morphologies of bar-driven andtidally-driven resonance rings.
| Multiple pattern speeds in barred galaxies. I. Two-dimensional models
We have studied the coexistence of several modes with different patternspeeds in barred galaxies, by a simulation survey exploring a wide rangeof initial conditions. The high resolution two-dimensional experimentscover the dynamical evolution for about one Hubble time. A remarkablefeature of these simulations is that in many cases the spiral structureis clearly visible in the stellar component for several gigayears andweakens so slowly that it can take more than 10 gigayears to becomeindiscernable even in the direct density plots. We confirm Sellwood andSparke's (\cite{sellwood88}) results that the pattern speed of thespiral arms may differ from that of the bar. However, we find severaldifferent variations. There are systems where the bar and the spiralstructure are clearly corotating, whereas in others they have differentpattern speeds but are probably connected by a non-linear mode couplingas was suggested by Tagger et al. (\cite{tagger87}). We have also foundmodels with separate pattern speeds, but without evident mode coupling.Several simultaneous spiral modes can also coexist in the disk, evenoverlapping in radius. Sometimes the systems have separate inner andouter spirals, the inner corotating with the bar and the outer having alower pattern speed. We conclude that similar variation can exist inreal galaxies. Some morphological features, like distinct spiralstructures with large size differences, can be best explained byseparate coexisting patterns. However, there are cases where most of thedisk is dominated by one mode. For example, galaxies with well developedouter rings are probably genuine examples of corotating features. It isalso possible that in the presence of two or more modes, the appearanceof the spiral structure changes considerably in a time scale of aboutone gigayear while the Hubble type of the galaxy stays the same.
| 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 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.
| 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.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| 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
| 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.
| 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.
| 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.
| Weakly barred early-type ringed galaxies. IV - The double-ringed SO(+) galaxy NGC 7702
UBVRI surface photometry of NGC 7702, obtained with a CCD detector onthe 3.9-m Anglo-Australian Telescope and with photographic plates on the4-m telescope at CTIO, is reported. The data are presented in tables,graphs, and contour maps and characterized in detail. NGC 7702 is foundto be a true S0(+) galaxy with a bright high-contrast inner ring and afaint low-contrast outer ring; the inner ring is significantly elongatedrelative to typical SB inner rings and has colors which suggest a burstof star formation less than 2 Gyr ago. A small oval revealed by thebulge isophotes in the inner 4 arcsec radius is attributed to a nuclearbar.
| The plane W(Na I) X W(Mg I) - Effects of interstellar Na I in a sample of southern galaxies
Galaxy spectra from a subsample of the Southern Sky Redshift Survey databank were used to study the equivalent width plane for the lines Na Ilambda 5893 A vs Mg I lambda 5175 A. An estimate of how important thecontribution of the interstellar gas for the sodium line is compared tothat of the stellar population. The sample is made up of galaxies withmorphological types from E to Sc and are distributed up to radialvelocities of 25,000 km/s, most of them smaller than 15,000 km/s. Mostearly type galaxies with dust lanes, particularly nearly edge-on So's,present an enhancement of the Na I line. Inclined spiral galaxies tendto present enhanced Na I with respect to face-on spirals. This tendency,previously found in a smaller sample of galaxies limited to V equal toor less than 6000 km/s, is now confirmed for more distant ones. In thelarge velocity sample it shows the global bulge rather than the verynucleus; the persistence of the effect suggests that the scale height ofthe gas layer in the central disk can reach a considerable fraction ofthe bulge radius.
| Weakly barred early-type ringed galaxies. II - The double-ringed S0(+) galaxy NGC 7187
CCD surface photometry of the southern ringed S0(+) galaxy NGC 7187, aparticularly good example of a system with two bright clear rings withsignificantly different apparent shapes and almost no sign of a bar, ispresented. The galaxy has below average luminosity and the rings aresmall compared to those observed in more typical (R)SB(r) type galaxies,even though the ratio of their sizes is similar to those in suchgalaxies. Bulge isophotes reveal the existence of two nearly orthogonalovals, one having the same shape and position angle as isophotes of theouter disk. The central oval shows significant m = 4 deviations fromelliptical isophote shapes and could be a nuclear bar. The rings areslightly blue enhancements compared to their surroundings. The meancolors of both rings do not imply exceptionally high star formation atthe present time.
| On the relationship between radio emission and optical properties in early-type galaxies
To study the origin of radio activity in early-type galaxies, thepossible dependence of their radio emission on basic optical parameters,such as the absolute magnitude, the central velocity dispersion sigma,and the mean surface brightness mu is explored. A sample of 743 E and SOgalaxies is used which is based on three independent radio surveys ofoptically selected galaxies with virtually complete information onmagnitudes, morphological types, redshift distances, diameters, andradio fluxes. For both E and SO galaxies, only the absolute magnitudeappears to be directly related to the radio activity, while sigma and mudo not. Also, a significant dependence of the apparent flattening onradio power is confirmed for E galaxies. Some relevant implications ofthese results are discussed.
| UBVRI aperture photometry of early-type galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988A&AS...72..215P&db_key=AST
| Surface Brightness and Color Properties of Early-Type Ringed Galaxies
Not Available
| Southern Galaxy Catalogue.
Not Available
| A comparison of distance scales for early-type galaxies
The distance scales of elliptical and lenticular galaxies areintercompared, based on the velocity dispersion indicator derived from arevised Faber-Jackson relation. The scales are found to be in nearperfect agreement with scales derived from the luminosity index and fromthe 21 cm line width indicator. The scales are also in excellentagreement with the distance scale derived by Michard (1979). Additionsare offered for the general catalog of 424 early-type galaxies, and aseries of reduction equations is presented which reduces the externalerrors in the distance moduli.
| UBV photometry of 262 southern galaxies
Multiaperture photometry of 262 bright southern galaxies in the JohnsonUBV system is given. Most of these are south of -30 deg declination,although some northward to -10 deg are included. A total of 169 objectshave published radial-velocity determinations. These provide distancesand enable construction of color-magnitude diagrams for this subset ofobjects through a physical diameter of 2.0 kpc (with H = 100). Thetwo-color diagrams for the inner regions of the galaxies differ fromthose of integrated galaxies due to the color changes towards theircenters. Comparison with theoretical models of Larson and Tinsley (1978)suggest that the colors of the inner portions of most ellipticals andlenticulars are consistent with their having all stars formed at nearlyone epoch with little subsequent star formation, while for spiralslarger amounts of star formation, either in bursts or continuously, aresuggested. This simple picture is complicated by the presence of certainobjects having peculiar colors indicative of large amounts of recentstar formation.
| A 5-GHz survey of bright Southern elliptical and S0 galaxies
The Parkes 64-m telescope has been used in a 5.0-GHz survey of 181Southern E and S0 galaxies from the Reference catalogue of brightgalaxies. Of the 39 detections above the nominal limit of 12 mJy, 15 arenew, several have radio spectra indicating membership in the activeclass, and two have shown intensity variations at centimeterwavelengths. The results of this survey combined with results fromearlier surveys of lower sensitivity suggest that only about 40 per centof the E/S0 galaxies in the Reference catalogue have a flux density at 5GHz exceeding 1 mJy.
| Contributions to galaxy photometry. II - Standard total magnitudes and colors of bright galaxies from multiaperture photoelectric photometry in the UBV system
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJS...33..219D&db_key=AST
| Radial Velocities of Southern Galaxies
Not Available
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