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

# NGC 3346

Contents

### Images

DSS Images   Other Images

### Related articles

 Late-type galaxies observed with SAURON: two-dimensional stellar and emission-line kinematics of 18 spiralsWe present the stellar and gas kinematics of a sample of 18 nearbylate-type spiral galaxies (Hubble types ranging from Sb to Sd), observedwith the integral-field spectrograph SAURON at the 4.2-m WilliamHerschel Telescope. SAURON covers the spectral range 4800-5380Å,allowing us to measure the Hβ, Fe, Mgb absorption features and theemission in the Hβ line and the [OIII]λλ4959,5007Å and [NI]λλ5198, 5200Å doublets over a 33× 41-arcsec2 field of view. The maps cover the nuclearregion of these late-type galaxies and in all cases include the entirebulge. In many cases the stellar kinematics suggests the presence of acold inner region, as visible from a central drop in the stellarvelocity dispersion. The ionized gas is almost ubiquitous and behaves ina complicated fashion: the gas velocity fields often display morefeatures than the stellar ones, including wiggles in the zero-velocitylines, irregular distributions, ring-like structures. The line ratio[OIII]/Hβ often takes on low values over most of the field,probably indicating a wide-spread star formation. Hubble Space Telescope STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass on Hubble TypeWe study the nuclear star clusters (NCs) in spiral galaxies of variousHubble types using spectra obtained with the STIS on board the HubbleSpace Telescope (HST). We observed the nuclear clusters in 40 galaxies,selected from two previous HST WFPC2 imaging surveys. At a spatialresolution of ~0.2" the spectra provide a better separation of clusterlight from underlying galaxy light than is possible with ground-basedspectra. Approximately half of the spectra have a sufficiently highsignal-to-noise ratio for detailed stellar population analysis. For theother half we only measure the continuum slope, as quantified by the B-Vcolor. To infer the star formation history, metallicity, and dustextinction, we fit weighted superpositions of single-age stellarpopulation templates to the high signal-to-noise ratio spectra. We usethe results to determine the luminosity-weighted age, mass-to-lightratio, and masses of the clusters. Approximately half of the sampleclusters contain a population younger than 1 Gyr. Theluminosity-weighted ages range from 10 Myr to 10 Gyr. The stellarpopulations of NCs are generally best fit as a mixture of populations ofdifferent ages. This indicates that NCs did not form in a single event,but that instead they had additional star formation long after theoldest stars formed. On average, the sample clusters in late-typespirals have a younger luminosity-weighted mean age than those inearly-type spirals (L=8.37+/-0.25 vs.9.23+/-0.21). The average mass-weighted ages are older by ~0.7 dex,indicating that there often is an underlying older population that doesnot contribute much light but does contain most of the mass. The averagecluster masses are smaller in late-type spirals than in early-typespirals (logM=6.25+/-0.21 vs. 7.63+/-0.24) and exceed the masses typicalof globular clusters. The cluster mass correlates loosely with totalgalaxy luminosity. It correlates more strongly with both the Hubble typeof the host galaxy and the luminosity of its bulge. The lattercorrelation has the same slope as the well-known correlation betweensupermassive black hole mass and bulge luminosity. The properties ofboth nuclear clusters and black holes in the centers of spiral galaxiesare therefore intimately connected to the properties of the host galaxy,and in particular its bulge component. Plausible formation scenarioshave to account for this. We discuss various possible selection biasesin our results, but conclude that none of them can explain thedifferences seen between clusters in early- and late-type spirals. Theinability to infer spectroscopically the populations of faint clustersdoes introduce a bias toward younger ages, but not necessarily towardhigher masses.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555. These observations areassociated with proposals 9070 and 9783. The AMIGA sample of isolated galaxies. II. Morphological refinementWe present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies. A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. II. Cluster Sizes and Structural Parameter CorrelationsWe investigate the structural properties of nuclear star clusters inlate-type spiral galaxies. More specifically, we fit analytical modelsto Hubble Space Telescope images of 39 nuclear clusters in order todetermine their effective radii after correction for the instrumentalpoint-spread function. We use the results of this analysis to comparethe luminosities and sizes of nuclear star clusters to those of otherellipsoidal stellar systems, in particular the Milky Way globularclusters. Our nuclear clusters have a median effective radius ofre=3.5 pc, with 50% of the sample falling in the range2.4pc<=re<=5.0pc. This narrow size distribution isstatistically indistinguishable from that of Galactic globular clusters,even though the nuclear clusters are, on average, 4 mag brighter thanthe old globular clusters. We discuss some possible interpretations ofthis result. From a comparison of nuclear cluster luminosities withvarious properties of their host galaxies, we confirm that more luminousgalaxies harbor more luminous nuclear clusters. It remains unclearwhether this correlation mainly reflects the influence of galaxy size,mass, and/or star formation rate. Since the brighter galaxies in oursample typically have stellar disks with a higher central surfacebrightness, nuclear cluster luminosity also correlates with thisproperty of their hosts. On the other hand, we find no evidence for acorrelation between the presence of a nuclear star cluster and thepresence of a large-scale stellar bar. Searching for Bulges at the End of the Hubble SequenceWe investigate the stellar disk properties of a sample of 19 nearbyspiral galaxies with low inclination and late Hubble type (Scd orlater). We combine our high-resolution Hubble Space Telescope I-bandobservations with existing ground-based optical images to obtain surfacebrightness profiles that cover a high dynamic range of galactic radii.Most of these galaxies contain a nuclear star cluster, as discussed in aseparate paper. The main goal of the present work is to constrain theproperties of stellar bulges at these extremely late Hubble types. Wefind that the surface brightness profiles of the latest-type spiralgalaxies are complex, with a wide range in shapes. We have sorted oursample in a sequence, starting with pure'' disk galaxies(approximately 30% of the sample). These galaxies have exponentialstellar disks that extend inward to within a few tens of parsecs fromthe nucleus, where the light from the nuclear cluster starts todominate. They appear to be truly bulgeless systems. Progressing alongthe sequence, the galaxies show increasingly prominent deviations from asimple exponential disk model on kiloparsec scales. Traditionally, suchdeviations have prompted bulge-disk'' decompositions. Indeed, thesurface brightness profiles of these galaxies are generally well fittedby adding a second (exponential) bulge component. However, we find thatmost surface brightness profiles can be fitted equally well (or better)with a single Sérsic-type R1/n profile over the entireradial range of the galaxy without requiring a separate bulge''component. We warn in a general sense against identification of bulgessolely on the basis of single-band surface brightness profiles. Despitethe narrow range of Hubble types in our sample, the surface brightnessprofiles are far from uniform. The differences between the variousgalaxies appear unrelated to their Hubble types, thus questioning theusefulness of the Hubble sequence for the subcategorization of thelatest-type spiral galaxies. A number of galaxies show central excessemission on spatial scales of a few hundred parsecs that cannot beattributed to the nuclear cluster, the Sérsic-type description ofthe stellar disk, or what one would generally consider to be a bulgecomponent. The origin of this light component remains unclear.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555. These observations are associatedwith proposal 8599. Revised positions for CIG galaxiesWe present revised positions for the 1051 galaxies belonging to theKarachentseva Catalog of Isolated Galaxies (CIG). New positions werecalculated by applying SExtractor to the Digitized Sky Survey CIG fieldswith a spatial resolution of 1 arcsper 2. We visually checked theresults and for 118 galaxies had to recompute the assigned positions dueto complex morphologies (e.g. distorted isophotes, undefined nuclei,knotty galaxies) or the presence of bright stars. We found differencesbetween older and newer positions of up to 38 arcsec with a mean valueof 2 arcsper 96 relative to SIMBAD and up to 38 arcsec and 2 arcsper 42respectively relative to UZC. Based on star positions from the APMcatalog we determined that the DSS astrometry of five CIG fields has amean offset in (alpha , delta ) of (-0 arcsper 90, 0 arcsper 93) with adispersion of 0 arcsper 4. These results have been confirmed using the2MASS All-Sky Catalog of Point Sources. The intrinsic errors of ourmethod combined with the astrometric ones are of the order of 0 arcsper5.Full Table 1 is 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/411/391 Molecular gas in the central regions of the latest-type spiral galaxiesUsing the IRAM 30 >m telescope, we have surveyed an unbiased sampleof 47 nearby spiral galaxies of very late (Scd-Sm) Hubble-type foremission in the 12CO(1-0) and (2-1) lines. The sensitivity ofour data (a few mK) allows detection of about 60% of our sample in atleast one of the CO lines. The median detected H2 mass is1.4x 107 >msun within the central few kpc, assuming astandard conversion factor. We use the measured line intensities tocomplement existing studies of the molecular gas content of spiralgalaxies as a function of Hubble-type and to significantly improve thestatistical significance of such studies at the late end of the spiralsequence. We find that the latest-type spirals closely follow thecorrelation between molecular gas content and galaxy luminosityestablished for earlier Hubble types. The molecular gas in late-typegalaxies seems to be less centrally concentrated than in earlier types.We use Hubble Space Telescope optical images to correlate the moleculargas mass to the properties of the central galaxy disk and the compactstar cluster that occupies the nucleus of most late-type spirals. Thereis no clear correlation between the luminosity of the nuclear starcluster and the molecular gas mass, although the CO detection rate ishighest for the brightest clusters. It appears that the central surfacebrightness of the stellar disk is an important parameter for the amountof molecular gas at the galaxy center. Whether stellar bars play acritical role for the gas dynamics remains unclear, in part because ofuncertainties in the morphological classifications of our sample. A new catalogue of ISM content of normal galaxiesWe have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of normality''. Thedefinition of a normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5 Mass-to-light ratios from the fundamental plane of spiral galaxy discsThe best-fitting two-dimensional plane within the three-dimensionalspace of spiral galaxy disc observables (rotational velocityvrot, central disc surface brightnessμ0=-2.5logI0 and disc scalelength h) has beenconstructed. Applying the three-dimensional bisector method ofregression analysis to a sample of ~100 spiral galaxy discs that spanmore than 4magarcsec-2 in central disc surface brightnessyields vrot\proptoI0.50\pm0.050\,h0.77\pm 0.07 (B band)and vrot\proptoI0.43\pm0.040\,h0.69\pm 0.07 (R band).Contrary to popular belief, these results suggest that in the B band,the dynamical mass-to-light ratio (within four disc scalelengths) islargely independent of the surface brightness, varying as I0.00\pm0.100\,h0.54\pm 0.14. Consistentresults were obtained when the range of the analysis was truncated byexcluding the low-surface-brightness galaxies. Previous claims thatM/LBvaries withI-1/20,Bareshown to be misleading and/or caused by galaxy selection effects - notall low-surface-brightness disc galaxies are dark matter dominated. Thesituation is, however, different in the near-infrared whereLK'~v4 and M/LK' is shown to vary asI-1/20,K\prime. Theoretical studies ofspiral galaxy discs should therefore not assume a constant M/L ratiowithin any given passband. The B-band dynamical mass-to-light ratio(within four disc scalelengths) has no obvious correlation with (B-R)disc colour, while in the K' band it varies as -1.25+/-0.28(B-R).Combining the present observational data with recent galaxy modelpredictions implies that the logarithm of the stellar-to-dynamical massratio is not a constant value, but increases as discs become redder,varying as 1.70+/-0.28(B-R). Bar Galaxies and Their EnvironmentsThe prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment. A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. I. Observations and Image AnalysisWe present new Hubble Space Telescope I-band images of a sample of 77nearby late-type spiral galaxies with low inclination. The main purposeof this catalog is to study the frequency and properties of nuclear starclusters. In 59 galaxies of our sample, we have identified a distinct,compact (but resolved), and dominant source at or very close to thephotocenter. In many cases, these clusters are the only prominent sourcewithin a few kiloparsecs from the galaxy nucleus. We present surfacebrightness profiles, derived from elliptical isophote fits, of allgalaxies for which the fit was successful. We use the fitted isophotesat radii larger than 2" to check whether the location of the clustercoincides with the photocenter of the galaxy and confirm that in nearlyall cases, we are truly dealing with nuclear'' star clusters. Fromanalytical fits to the surface brightness profiles, we derive thecluster luminosities after subtraction of the light contribution fromthe underlying galaxy disk and/or bulge. Based on observations made withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555. Theseobservations are associated with proposal 8599. Galaxies with RowsThe results of a search for galaxies with straight structural elements,usually spiral-arm rows (“rows” in the terminology ofVorontsov-Vel'yaminov), are reported. The list of galaxies that possess(or probably possess) such rows includes about 200 objects, of whichabout 70% are brighter than 14m. On the whole, galaxies with rows makeup 6 8% of all spiral galaxies with well-developed spiral patterns. Mostgalaxies with rows are gas-rich Sbc-Scd spirals. The fraction ofinteracting galaxies among them is appreciably higher than amonggalaxies without rows. Earlier conclusions that, as a rule, the lengthsof rows are similar to their galactocentric distances and that theangles between adjacent rows are concentrated near 120° areconfirmed. It is concluded that the rows must be transient hydrodynamicstructures that develop in normal galaxies. A Dust-penetrated Classification Scheme for Bars as Inferred from Their Gravitational Force FieldsThe division of galaxies into barred'' (SB) and normal'' (S) spiralsis a fundamental aspect of the Hubble galaxy classification system. Thistuning fork'' view was revised by de Vaucouleurs, whose classificationvolume recognized apparent bar strength'' (SA, SAB, SB) as acontinuous property of galaxies called the family.'' However, the SA,SAB, and SB families are purely visual judgments that can have littlebearing on the actual bar strength in a given galaxy. Until veryrecently, published bar judgments were based exclusively on blue lightimages, where internal extinction or star formation can either mask abar completely or give the false impression of a bar in a nonbarredgalaxy. Near-infrared camera arrays, which principally trace the oldstellar population in both normal and barred galaxies, now facilitate aquantification of bar strength in terms of their gravitationalpotentials and force fields. In this paper, we show that the maximumvalue, Qb, of the ratio of the tangential force to the meanaxisymmetric radial force in a barred disk galaxy is a quantitativemeasure of the strength of a bar. Qb does not measure barellipticity or bar shape but rather depends on the actual forcing due tothe bar embedded in its disk. We show that a wide range of true barstrengths characterizes the category SB,'' while the de Vaucouleurscategory SAB'' corresponds to a narrower range of bar strengths. Wepresent Qb values for 36 galaxies, and we incorporate our barclasses into a dust-penetrated classification system for spiralgalaxies. An Investigation into the Prominence of Spiral Galaxy BulgesFrom a diameter-limited sample of 86 low-inclination (face-on) spiralgalaxies, the bulge-to-disk size and luminosity ratios and otherquantitative measurements for the prominence of the bulge are derived.The bulge and disk parameters have been estimated using aseeing-convolved Sérsic r1/n bulge and aseeing-convolved exponential disk that were fitted to the optical (B, R,and I) and near-infrared (K) galaxy light profiles. In general,early-type spiral galaxy bulges have Sérsic values of n>1, andlate-type spiral galaxy bulges have values of n<1. In the B band,only eight galaxies have a bulge shape parameter n consistent with theexponential value 1, and only five galaxies do in the K band. Use of theexponential bulge model is shown to restrict the range ofre/h and B/D values by more than a factor of 2. Applicationof the r1/n bulge models, unlike exponential bulge models,results in a larger mean re/h ratio for the early-type spiralgalaxies than for the late-type spiral galaxies, although this result isshown not to be statistically significant. The mean B/D luminosity ratiois, however, significantly larger (>3 σ) for the early-typespirals than for the late-type spirals. Two new parameters areintroduced to measure the prominence of the bulge. The first is thedifference between the central surface brightness of the galaxy and thesurface brightness level at which the bulge and disk contribute equally.The other test uses the radius at which the contribution from the diskand bulge light are equal, normalized for the effect of intrinsicallydifferent galaxy sizes. Both of these parameters reveal that theearly-type spiral galaxies appear'' to have significantly (more than 2σ in all passbands) bigger and brighter bulges than late-typespiral galaxies. This apparent contradiction with the re/hvalues can be explained with an iceberg-like scenario, in which thebulges in late-type spiral galaxies are relatively submerged in theirdisk. This can be achieved by varying the relative stellar density whilemaintaining the same effective bulge-to-disk ratio. The B/D luminosityratio and the concentration index C31, in agreement with paststudies, are positively correlated and decrease as one moves along thespiral Hubble sequence toward later spiral galaxy types, although forgalaxies with large extended bulges the concentration index no longertraces the B/D luminosity ratio in a one-to-one fashion. A strong(Spearman's rank-order correlation coefficient, rs=0.80) andhighly significant positive correlation exists between the shape, n, ofthe bulge light profile and the bulge-to-disk luminosity ratio. Theabsolute bulge magnitude-logn diagram is used as a diagnostic tool forcomparative studies with dwarf elliptical and ordinary ellipticalgalaxies. At least in the B band these objects occupy distinctlydifferent regions of this parameter space. While the dwarf ellipticalgalaxies appear to be the faint extension to the brighter ellipticalgalaxies, the bulges of spiral galaxies do not; for a given luminositythey have a noticeably smaller shape parameter and hence a more dramaticdecline of stellar density at large radii. Nearby Optical Galaxies: Selection of the Sample and Identification of GroupsIn 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. Arcsecond Positions of UGC GalaxiesWe 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. Cosmic Masks Still DanceThe Hubble classification scheme of galaxies is based on their opticalappearance or masks'. As one goes from early to late type spirals, bothbarred and unbarred, the optical appearance will be dominated more andmore by the young Population I, i.e., blue stars and dust. Atlasesreveal the rich variety of responses of the Population I component ofgas and dust (the mask) to the underlying, older, stellar population.However, the gaseous Population I component, may only constitute 5percent of the dynamical mass of the galaxy. Masks of negligible massmay conceal the human face - and that of galaxy. In the near-infrared,the morphology of older star-dominated disk indicates a simpleclassification scheme: the dominant Fourier m-mode in the dustpenetrated regime, and the associated pitch angle. A ubiquity of low m=1and m=2 modes is confirmed. On the basis of deprojected H (1.65 μm)and K' (2.1μm) images, we propose that the evolved stellar disks maybe grouped into three principal dust penetrated archetypes: those withtightly wound stellar arms characterised by pitch angles at K' of ~10^° (the α class), an intermediate group with pitch angles of~ 25^° (the β class) and thirdly, those with open spiralsdemarcated by pitch angles at K' of ~ 40^° (the γ bin). Flator falling rotation curves give rise to the tightly wound α class;rising rotation curves are associated with the open γ class. Theobserved dust penetrated classes are inextricably related to the rate ofshear in the stellar disk, as determined by A/ω. Here A is thefirst Oort constant andω denotes the angular velocity. There is nocorrelation between our dust penetrated classes and optical Hubblebinning; the Hubble tuning fork does not constrain the morphology of theold stellar Population II disks. NGC 3223 and NGC 7083 (both SbI-II andalmost the same absolute blue magnitude) have identical Hubble types andidentical luminosity classes; the dust penetrated disk of NGC 3223 hastightly wrapped arms of class α, whereas the near-infrared disk ofNGC 7083 has open arms of class γ. This is in turn associated withtheir very different rotation curve shapes yielding different rates ofshear A/ω in their stellar disks. Any specific dust penetratedarchetype may be the resident disk of both an early or late type galaxy.The number of arms and the pitch angle of the arms at K' of theearly-type a' spiral NGC 718 are almost identical to those for thelate-type c' spiral NGC 309. We demonstrate that galaxies on oppositeends of the tuning fork can display remarkably similar evolved diskmorphologies and belong to the same dust penetrated class. In thissense, there is no differentiation between an early and late typegalaxy: the Hubble tuning fork becomes a circle. Furthermore, aprototypically flocculent galaxy such as NGC 5055 (Elmegreen arm class3) can have an evolved disk morphology almost identical to that of NGC5861, characterised in the optical as having one of the most regularspiral patterns known and of Elmegreen class 12. Both opticallyflocculent or grand design galaxies can reside within the same dustpenetrated morphological bin. As was suggested by Block et al. (1994a),it is the gas dominated Population I component which determines theoptical types (a, b, c). This may be partially or even fully decoupledfrom the Population II disk. Those L=lopsided galaxies (where m=1 is adominant mode) are designated Lα, Lβ and Lγ accordingto the dust penetrated pitch angle; E=evensided galaxies (where m=2 isthe dominant Fourier mode) are classified into classes Eα, Eβand Eγ, according to our three principal dust penetratedarchetypes. The L and E modes are the most common morphologies in oursample, which spans a range of Hubble types from early (a) to late(irregular). Groups of galaxies. III. Some empirical characteristics.Not Available Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness ProfilesWe present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it. Catalogue of HI maps of galaxies. I.A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html Total magnitude, radius, colour indices, colour gradients and photometric type of galaxiesWe 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. A Search for `Dwarf'' Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host GalaxiesWe have completed an optical spectroscopic survey of the nuclear regions(r <~ 200 pc) of a large sample of nearby galaxies. Although the mainobjectives of the survey are to search for low-luminosity activegalactic nuclei and to quantify their luminosity function, the databasecan be used for a variety of other purposes. This paper presentsmeasurements of the spectroscopic parameters for the 418 emission-linenuclei, along with a compilation of the global properties of all 486galaxies in the survey. Stellar absorption generally poses a seriousobstacle to obtaining accurate measurement of emission lines in nearbygalactic nuclei. We describe a procedure for removing the starlight fromthe observed spectra in an efficient and objective manner. The mainparameters of the emission lines (intensity ratios, fluxes, profilewidths, and equivalent widths) are measured and tabulated, as areseveral stellar absorption-line and continuum indices useful forstudying the stellar population. Using standard nebular diagnostics, wedetermine the probable ionization mechanisms of the emission-lineobjects. The resulting spectral classifications provide extensiveinformation on the demographics of emission-line nuclei in the nearbyregions of the universe. This new catalog contains over 200 objectsshowing spectroscopic evidence for recent star formation and an equallylarge number of active galactic nuclei, including 46 that show broad Halpha emission. These samples will serve as the basis of future studiesof nuclear activity in nearby galaxies. An Einstein X-Ray Survey of Optically Selected Galaxies. I. DataWe present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies. Gas Mass Fractions and the Evolution of Spiral GalaxiesWe show that the gas mass fraction of spiral galaxies is stronglycorrelated with luminosity and surface brightness. It is not correlatedwith linear size. Gas fraction varies with luminosity and surfacebrightness at the same rate, indicating evolution at fixed size. Dimgalaxies are clearly less evolved than bright ones, having consumed only~ \frac {1}{2} of their gas. This resolves the gas consumption paradox,since there exist many galaxies with large gas reservoirs. Thesegas-rich galaxies must have formed the bulk of their stellar populationsin the last half of a Hubble time. The existence of such immaturegalaxies at z = 0 indicates that either galaxy formation is a lengthy oreven ongoing process, or the onset of significant star formation can bedelayed for arbitrary periods in tenuous gas disks. Near-infrared and optical broadband surface photometry of 86 face-on disk dominated galaxies. II. A two-dimensional method to determine bulge and disk parameters.In this Paper I present a new two-dimensional decomposition technique,which models the surface photometry of a galaxy with an exponentiallight profile for both bulge and disk and, when necessary, with aFreeman bar. The new technique was tested for systematic errors on bothartificial and real data and compared with widely used one-dimensionaldecomposition techniques, where the luminosity profile of the galaxy isused. The comparisons indicate that a decomposition of thetwo-dimensional image of the galaxy with an exponential light profilefor both bulge and disk yields the most reproducible and representativebulge and disk parameters. An extensive error analysis was made todetermine the reliability of the model parameters. If the model with anexponential bulge profile is a reasonable description of a galaxy, themaximum errors in the derived model parameters are of order 20%. Theuncertainties in the model parameters will increase, if the exponentialbulge function is replaced by other often used bulge functions as the deVaucouleurs law. All decomposition methods were applied to the opticaland near-infrared data set presented by de Jong & van der Kruit(1994), which comprises 86 galaxies in six passbands. An image database. II. Catalogue between δ=-30deg and δ=70deg.A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect. Redshift periodicity in the Local Supercluster.Persistent claims have been made over the last ~15yr that extragalacticredshifts, when corrected for the Sun's motion around the Galacticcentre, occur in multiples of ~24 or ~36km/s. A recent investigation byus of 40 spiral galaxies out to 1000km/s, with accurately measuredredshifts, gave evidence of a periodicity ~37.2-37.7km/s. Here we extendour enquiry out to the edge of the Local Supercluster (~2600km/s),applying a simple and robust procedure to a total of 97 accuratelydetermined redshifts. We find that, when corrected for related vectorsclose to recent estimates of the Sun's galactocentric motion, theredshifts of spirals are strongly periodic (P~37.6km/s). The formalconfidence level of the result is extremely high, and the signal is seenindependently with different radio telescopes. We also examine a furthersample of 117 spirals observed with the 300-foot Green Bank telescopealone. The periodicity phenomenon appears strongest for the galaxieslinked by group membership, but phase coherence probably holds overlarge regions of the Local Supercluster. A search for 'dwarf' Seyfert nuclei. 2: an optical spectral atlas of the nuclei of nearby galaxiesWe present an optical spectral atlas of the nuclear region (generally 2sec x 4 sec, or r approximately less than 200 pc) of a magnitude-limitedsurvey of 486 nearby galaxies having BT less than or = 12.5mag and delta greater than 0 deg. The double spectrograph on the Hale 5m telescope yielded simultaneous spectral coverage of approximately4230-5110 A and approximately 6210-6860 A, with a spectral resolution ofapproximately 4 A in the blue half and approximately 2.5 A in the redhalf. This large, statistically significant survey contains uniformlyobserved and calibrated moderate-dispersion spectra of exceptionallyhigh quality. The data presented in this paper will be used for varioussystematic studies of the physical properties of the nuclei of nearbygalaxies, with special emphasis on searching for low-luminosity activegalactic nuclei, or 'dwarf' Seyferts. Our survey led to the discovery offour relatively obvious but previously uncataloged Seyfert galaxies (NGC3735, 492, 4639, and 6951), and many more galactic nuclei showingevidence for Seyfert activity. We have also identified numerouslow-ionization nuclear emission-line regions (LINERs), some of which maybe powered by nonstellar processes. Of the many 'starburst' nuclei inour sample, several exhibit the spectral features of Wolf-Rayet stars. A Preliminary Classification Scheme for the Central Regions of Late-Type GalaxiesThe large-scale prints in The Carnegie Atlas of Galaxies have been usedto formulate a classification scheme for the central regions oflate-type galaxies. Systems that exhibit small bright central bulges ordisks (type CB) are found to be of earlier Hubble type and of higherluminosity than galaxies that do not contain nuclei (type NN). Galaxiescontaining nuclear bars, or exhibiting central regions that are resolvedinto individual stars and knots, and galaxies with semistellar nuclei,are seen to have characteristics that are intermediate between those oftypes CB and NN. The presence or absence of a nucleus appears to be auseful criterion for distinguishing between spiral galaxies andmagellanic irregulars. Quantitative Morphology of Bars in Spiral GalaxiesAs suggested by numerical simulations, the axis ratio of the bar is afundamental parameter to describe the dynamical evolution of a barredgalaxy. In a first-order approximation considering bars as ellipticalfeatures, visual measurements of bar axis ratios and lengths of 136spiral galaxies were performed on photographs of good linear scale.Despite the limitations affecting such measurements, morphologicalproperties of bars in spirals along the Hubble sequence as well as therelationship between the bar axis ratio and nuclear star formationactivity are studied. It is found that the relative length of bars inearly-type galaxies is, on average, about a factor of 3 larger than thelength observed in late-type spirals. Also, a relation between barlengths and bulge diameters is observed for both early-type andlate-type spirals, confirming results from previous works. Furthermore,although the number of objects is small, there is an apparentcorrelation between the presence of nuclear star formation activity andthe bar axis ratio: about 71% of the starburst galaxies included in thesample have a strong bar (b/a < 0.6). The introduction of thesequantitative parameters in galaxy classification schemes is discussed.
Submit a new article