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 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. The Molecular Interstellar Medium of Dwarf Galaxies on Kiloparsec Scales: A New Survey for CO in Northern, IRAS-detected Dwarf GalaxiesWe present a new survey for CO in dwarf galaxies using the ARO Kitt Peak12 m telescope. This survey consists of observations of the centralregions of 121 northern dwarfs with IRAS detections and no known COemission. We detect CO in 28 of these galaxies and marginally detectanother 16, increasing by about 50% the number of such galaxies known tohave significant CO emission. The galaxies we detect are comparable instellar and dynamical mass to the Large Magellanic Cloud, althoughsomewhat brighter in CO and fainter in the far-IR. Within dwarfs, wefind that the CO luminosity LCO is most strongly correlatedwith the K-band and the far-infrared luminosities. There are also strongcorrelations with the radio continuum (RC) and B-band luminosities andlinear diameter. Conversely, we find that far-IR dust temperature is apoor predictor of CO emission within the dwarfs alone, although a goodpredictor of normalized CO content among a larger sample of galaxies. Wesuggest that LCO and LK correlate well because thestellar component of a galaxy dominates the midplane gravitational fieldand thus sets the pressure and density of the atomic gas, which controlthe formation of H2 from H I. We compare our sample with moremassive galaxies and find that dwarfs and large galaxies obey the samerelationship between CO and the 1.4 GHz RC surface brightness. Thisrelationship is well described by a Schmidt law withΣRC~Σ1.3CO. Therefore,dwarf galaxies and large spirals exhibit the same relationship betweenmolecular gas and star formation rate (SFR). We find that this result isrobust to moderate changes in the RC-to-SFR and CO-to-H2conversion factors. Our data appear to be inconsistent with large (orderof magnitude) variations in the CO-to-H2 conversion factor inthe star-forming molecular gas. Inner-truncated Disks in GalaxiesWe present an analysis of the disk brightness profiles of 218 spiral andlenticular galaxies. At least 28% of disk galaxies exhibit innertruncations in these profiles. There are no significant trends oftruncation incidence with Hubble type, but the incidence among barredsystems is 49%, more than 4 times that for nonbarred galaxies. However,not all barred systems have inner truncations, and not allinner-truncated systems are currently barred. Truncations represent areal dearth of disk stars in the inner regions and are not an artifactof our selection or fitting procedures nor the result of obscuration bydust. Disk surface brightness profiles in the outer regions are wellrepresented by simple exponentials for both truncated and nontruncateddisks. However, truncated and nontruncated systems have systematicallydifferent slopes and central surface brightness parameters for theirdisk brightness distributions. Truncation radii do not appear tocorrelate well with the sizes or brightnesses of the bulges. Thissuggests that the low angular momentum material apparently missing fromthe inner disk was not simply consumed in forming the bulge population.Disk parameters and the statistics of bar orientations in our sampleindicate that the missing stars of the inner disk have not simply beenredistributed azimuthally into bar structures. The sharpness of thebrightness truncations and their locations with respect to othergalactic structures suggest that resonances associated with diskkinematics, or tidal interactions with the mass of bulge stars, might beresponsible for this phenomenon. The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxiesWe discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/ 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 A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sampleA sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org 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. 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. Star-forming Complexes in a Sample of Spiral and Irregular GalaxiesOver 300 star-forming complexes in 11 intermediate- and late-type spiraland irregular galaxies have been observed in the B, I, and Hαbands to determine their luminosity functions, ages, sizes, and masses.The total Hα luminosity from complexes compared with the totalgalaxy Hα luminosity ranges from 20% to 70%, but the percentage isnearly constant at 7% in the B band for most galaxies. A comparison ofthe colors and luminosities of the complexes with published clusterevolutionary models suggests that the complexes range in age from a fewtimes 10^6 yr to nearly 10^9 yr; the majority have ages of less than 1to 2x10^7 yr. The complex masses range from 10^4 to 10^7 M_solar. Theluminosity functions for the complexes follow a power law with anexponent of approximately -2 late-type galaxies have slightly shallowerslopes than intermediate-type galaxies. The sizes of the largestcomplexes in each galaxy scale approximately with the square root of thegalaxy luminosity, confirming previous studies. The complexes may have afractal size distribution that is consistent with values predicted bytheoretical turbulence models of the interstellar medium. The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XII. The Discovery of Cepheids and a New Distance to NGC 2541We report the detection of Cepheids and a new distance to the spiralgalaxy NGC 2541, based on data obtained with the Wide Field PlanetaryCamera 2 on board the Hubble Space Telescope (HST). A total of 25exposures (divided into 13 epochs) were obtained using the F555W filter(transformed to Johnson V), and nine exposures were obtained (dividedinto five epochs) using the F814W filter (transformed to Cousins I).Photometric reduction of the data is performed using two independentpackages, DoPHOT and DAOPHOT II/ALLFRAME, which give very good agreementin the measured magnitudes. A total of 34 bona fide Cepheids, withperiods ranging from 12 to over 60 days, are identified based on bothsets of photometry. By fitting V and I period-luminosity relations,apparent distance moduli are derived assuming a Large Magellanic Clouddistance modulus and mean color excess of mu_LMC = 18.50 +/- 0.10 magand E(B-V) = 0.10 mag, respectively. Adopting A(V)/E(V-I) = 2.45, weobtain a true distance modulus to NGC 2541 of mu_0 = 30.47 +/- 0.11(random) +/- 0.12 (systematic) mag (D = 12.4 +/- 0.6 [random] +/- 0.7[systematic] Mpc), and a total (Galactic plus internal) mean colorexcess E(B-V) = 0.08 +/- 0.05 (internal error) mag. 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. Asymmetry in high-precision global H I profiles of isolated spiral galaxiesNew high-SNR 21 cm H I line profiles have been obtained for 104 galaxieswith the Green Bank 43 m telescope. The primary sample is composed ofisolated spirals with no known optical companions within a 1 radius anda median ratio of optical diameter to beamwidth of 0.17. An effort wasmade to ensure linearity of baseline fitting and precise flux densitycalibration to better than 5 percent. Two quantitative measures ofasymmetry are applied to assess the occurrence of lopsidedness in theglobal H I profiles. In agreement with previous estimates, half thegalaxies show significant H I profile asymmetries. The lopsidednesscannot be explained by pointing offsets but, rather, must result fromnoncircular motions, confusion with unidentified companions within thetelescope beam, or true distortions in the H I distribution. 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. The Absence of X-Ray Flashes from Nearby Galaxies and the Gamma-Ray Burst Distance ScaleIf typical gamma-ray bursts (GRBs) have X-ray counterparts similar tothose detected by Ginga, then sensitive-focusing X-ray telescopes willbe able to detect GRBs 3 orders of magnitude fainter than the detectionlimit of the Burst and Transient Source Experiment (BATSE). If asubstantial portion of the burst population detected by BATSE originatesin a Galactic halo at distances greater than or equal to 150 kpc,existing X-ray telescopes will be able to detect GRBs in externalgalaxies out to a distance of at least 4.5 Mpc. As reported in Gotthelf,Hamilton, & Helfand, the imaging proportional counter (IPC) on boardthe Einstein Observatory detected 42 transient events with pointlikespatial characteristics and timescales of less than 10 s. These eventsare distributed isotropically on the sky; in particular, they are notconcentrated in the directions of nearby external galaxies. For halomodels of the BATSE bursts with radii of 150 kpc or greater, we wouldexpect to see several burst events in observations pointed toward nearbygalaxies. We see none. We therefore conclude that if the Gingadetections are representative of the population of GRBs sampled byBATSE, GRBs cannot originate in a Galactic halo population with limitingradii between 150 and 400 kpc. Inasmuch as halos with limiting radiioutside of this range have been excluded by the BATSE isotropymeasurements, our result indicates that all halo models are excluded.This result is independent of whether the flashes we do detect have anastronomical origin. Light Profiles and Pattern Speeds for Bars in Early- and Late-Type GalaxiesJ, H, and K infrared band observations of 11 barred galaxies, and B andI band observations of 8 barred galaxies, spanning a wide range ofHubble types, confirm the trend found earlier that early types tend tohave flat light profiles along the bars and late types have exponentiallight profiles. Both types have nearly continuous exponential lightprofiles when azimuthally averaged. The flat profiles arise from excessold and young stars at the bar ends, presumably where the orbits crowdtogether near the inner 4:1 resonance. The exponential profiles have nosuch crowding and also lack offset leading dustlanes as if there is noinner Lindblad resonance inside the bar. Arm/interarm contrasts in Jband increase with radius near the center and then become constant ordecrease with radius at a value of arm/interarm ~6. This saturation ofwave amplitude tends to occur at the same radius where the armsbifurcate or become multiple, suggesting that spiral waves limit theirown amplitudes at large radii by coupling to higher order modes. Acompilation of bar pattern speeds from the literature, mostly coveringearly types, generally puts corotation at a distance between 1.2 and 1.4times the bar semi-major axis length, usually in the middle of thestrong part of the spiral arms. These observations imply that early-typebars end because of orbit resonance scattering slightly beyond theirinner 4:1 resonances; the spirals and rings in these galaxies appear tocorotate with the bars. Patterns speeds in late type bars remainunknown. Near-Infrared Observations of Isophotal Twists in Barred Spiral GalaxiesWe present observations in JHK passbands for 12 barred galaxies and inBI passbands for 9 galaxies in order to study isophotal twists in early-and late-type barred spirals. We also summarize previous observationsand examine high-resolution atlas images to compile data on twists as afunction of Hubble type. Twists have been detected only in early-typespirals. This result is consistent with the hypothesis that only early-type bars have inner Lindblad resonances and that twists are associatedwith ILRs. The transition occurs around type SBbc and parallels thetransition from bars with relatively flat intensity profiles to barswith exponential profiles in later types. Nuclei of Nearby Disk Galaxies.I.A Hubble Space Telescope Imaging SurveyWe present deconvolved images of the central regions of 20 nearby diskgalaxies, obtained with the original Planetary Camera of the HubbleSpace Telescope. The galaxies span a range in Hubble type from S0 to Sm.We have measured surface brightness profiles, and inverted these toestimate luminosity-density profiles. Surface brightness profiles in thecentral regions show a variety of forms, sometimes clearly affected byheavy dust obscuration. All galaxies in the sample earlier than type Scshow a continuing rise in surface brightness up to the resolution limitin the deconvolved images. Later types show shallower slopes, consistentwith exponential disks either continuing into the center or elseflattening in the central regions. These galaxies often, but not always,exhibit an unresolved nucleus which is likely a dense nuclear starcluster. Luminosity densities in the earlier-type galaxies reach orexceed 10^4^ L_sun_,V_ pc^-3^, and the nuclei of the later-type galaxiesoccasionally approach the same level. The dS0 galaxies in our samplehave central characteristics most closely resembling the late-typegalaxies. A comparison of the central luminosity and central surfacebrightness of our galaxies with elliptical galaxies and nucleated dwarfssupports an association of late-type disks systems and such dwarfs. 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. On the size and formation mechanism of the largest star-forming complexes in spiral and irregular galaxiesThe average diameters of the largest star complexes in most of thespiral and irregular galaxies in the Sandage and Bedke Atlas of Galaxieswere measured from the Atlas photographs. The complex diametersDc correlate with galaxy magnitude as Dc = 0.18 -0.14MB, which has about the same slope as the correlation forthe largest H II regions studied by Kennicutt. There is no obviouscorrelation between Dc and either Hubble type or spiral armclass at a given magnitude. The variation of Dc withMB closely matches the expected variation in thecharacteristic length of the gaseous gravitational instabilityconsidering that the rotation curve varies with MB and thatthe stability parameter Q is about 1 in the outer regions of the disk.This match corresponds to an effective velocity dispersion of 6.1 km/sthat is about the same for all spiral and irregular galaxies. Arm structure in normal spiral galaxies, 1: Multivariate data for 492 galaxiesMultivariate data have been collected as part of an effort to develop anew classification system for spiral galaxies, one which is notnecessarily based on subjective morphological properties. A sample of492 moderately bright northern Sa and Sc spirals was chosen for futurestatistical analysis. New observations were made at 20 and 21 cm; thelatter data are described in detail here. Infrared Astronomy Satellite(IRAS) fluxes were obtained from archival data. Finally, new estimatesof arm pattern radomness and of local environmental harshness werecompiled for most sample objects. Mean galaxy luminosity classificationsTo prepare a catalog of weighted means on the classification system ofvan den Bergh, we have combined eight independent lists of luminosityclass estimates, L. Luminosity class values from each set weretransformed to the standard system and weighted according to the errorsderived through a statistical comparison of L differences betweencatalog pairs. Relations were derived for predicting accidental errorsassociated with galaxy diameter and inclination. In addition, we presentformulas for correcting systematic errors associated with diameter andinclination. Finally, we tabulate a high weight subsample of the meanluminosity classes usable as standards. Most values are tabulated in theThird Reference Catalog of Bright Galaxies. Groups of galaxies within 80 Mpc. II - The catalogue of groups and group membersThis 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. Evidence for redshift periodicity in nearby field galaxiesThe present study investigates the notion that extragalactic redshiftsare periodic in ranges around 24.2, 36.3, or 72.5 km/s for anindependent sample of 89 nearby spirals, in the general field, withaccurately determined heliocentric redshifts. A strong periodicity ofabout 37.2 km/s is found, against a white noise background, for anassumed solar vector coincidental, within the uncertainties, with thatcorresponding to the sun's probable motion around the Galactic Center.Comparison with sets of synthetic data simulating the overallcharacteristics of the real data show the periodicity to be present at ahigh confidence level. As an independent test, the sample was dividedinto two groups of 40 and 49 galaxies with more and less accuratelydetermined redshifts, respectively. The measured strength of theperiodicity is significantly greater for the group of 40 galaxies. Theoverall probability that the periodicity of 37.2 km/s arises by chanceis in the range of 3 x 10 exp -6 and exp -4. Properties of the redshift. I - Data and calibrationsData at 21 cm are presented for 100 galaxies intended to be used forsystem comparisons between the NRAO 140 and 300 foot telescope and the100 m Effelsberg telescope. Data from the 300 foot telescope are alsogiven for galaxies selected for overlap comparisons with older studies.Flux calibrations and measurement uncertainties in flux, redshifts,profile width, and profile shape are discussed. Properties of H II region populations in galaxies. I - The first-ranked H II regionsH-alpha photometry of the brightest H II regions in 95 nearby spiral andirregular galaxies has been analyzed in order to study the dependence ofthe H II region populations on the properties of their parent galaxies.It is found that the brightest H II regions in Magellanic irregulargalaxies are about 50 times brighter than those in early-type spirals ofthe same absolute magnitude. It is suggested that this difference is dueto both an increase in the numbers of H II regions in late-type galaxiesand a physical change in the characteristic sizes of the star-formingregions.
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