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# NGC 3757

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 Properties of isolated disk galaxiesWe present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org Star Formation Histories of Early-Type Galaxies. I. Higher Order Balmer Lines as Age IndicatorsWe have obtained blue integrated spectra of 175 nearby early-typegalaxies, covering a wide range in galaxy velocity dispersion andemphasizing those with σ<100 km s-1. Galaxies havebeen observed both in the Virgo Cluster and in lower densityenvironments. The main goals are the evaluation of higher order Balmerlines as age indicators and differences in stellar populations as afunction of mass, environment, and morphology. In this first paper, ouremphasis is on presenting the methods used to characterize the behaviorof the Balmer lines through evolutionary population synthesis models.Lower σ galaxies exhibit a substantially greater intrinsicscatter, in a variety of line-strength indicators, than do higherσ galaxies, with the large intrinsic scatter setting in below aσ of 100 km s-1. Moreover, a greater contrast inscatter is present in the Balmer lines than in the lines of metalfeatures. Evolutionary synthesis modeling of the observed spectralindexes indicates that the strong Balmer lines found primarily among thelow-σ galaxies are caused by young age, rather than by lowmetallicity. Thus we find a trend between the population age and thecentral velocity dispersion, such that low-σ galaxies have youngerluminosity-weighted mean ages. We have repeated this analysis usingseveral different Balmer lines and find consistent results from onespectral indicator to another. 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 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. Groups of galaxies. III. Some empirical characteristics.Not Available 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. A revised catalog of CfA1 galaxy groups in the Virgo/Great Attractor flow fieldA new identification of groups and clusters in the CfA1 Catalog ofHuchra et al. is presented, using a percolation algorithm to identifydensity enhancements. It is shown that in the resulting catalog,contamination by interlopers is significantly reduced. The Schechterluminosity function is redetermined, including the Malmquist bias. General study of group membership. II - Determination of nearby groupsWe present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog. Far-infrared luminosity functions of normal galaxiesA volume-limited sample is constructed from the Zwicky catalog and IRASdata base to examine the FIR luminosity functions of normal galaxies,and to investigate possible relationships between FIR emission andgalaxy morphology. Quantitative and unbiased treatment is provided by'survival analysis' statistical methods. It is found that the FIRdistributions of normal galaxies are better fit by lognormal thanSchechter functions. The total FIR emissivity (8 to 115 microns) ofnormal galaxies is approximately equal to half their emission in the Bplus V optical bands. Normal galaxy FIR emission is uncorrelated withthe basic S0-Sm Hubble sequence of spiral galaxy morphology, but appearsto be affected by de Vaucouleurs' (1959) revised morphologicalclassifications based on inner rings and S-shaped arms. Spirals withbars and inner rings are systematically fainter than unbarred spirals.It is suggested that bars and rings reduce the amount or spatiallyconfine the dust in spiral disks, resulting in lower efficiencyconversion of optical and UV photons into the IR. Radio-continuum sources in nearby and bright E/S0 galaxies - Active nuclei versus star formationResults of a sensitive VLA survey of nearby E/S0 galaxies are presented.The 204 galaxies surveyed, plus 12 additional galaxies with existing VLAimages, comprise a volume- and optical magnitude-limited sample. Thediscussion focuses on the relation between radio powers and opticalluminosities, whether the radio emission is driven by an active nucleusor by recent star formation, and what galaxian properties might enhancenuclear activity in an elliptical galaxy. It is suggested that the 67ellipticals in the sample should be targets of sensitive searches forHI, optical emission-line gas, and X-ray emitting gas. Radio-continuum sources in nearby and bright E/S0 galaxies - Sample selection and well-studied casesA volume-limited sample of 216 nearby and optically bright E/S0 galaxieshas been compiled. Twelve of the galaxies are confirmed radio sourcesfor which VLA images are available. Most of the remaining galaxies havepowers less than or of the order of 10 to the 21st-22nd W/Hz, and thisinformation is used to establish the parameters of a new VLA survey ofthese galaxies. The basic optical properties of the galaxies in thesample are tabulated. The influence of environment on gas and dust in S0 galaxiesConsideration is given to the effect of local environemnt on the gas anddust content of S0 galaxies relative to other spiral systems in theLocal Supercluster. The optical properties, H I content, and FIRcontinuum properties of a complete sample of Local Supercluster S0galaxies are analyzed. The characteristics of S0 galaxies are comparedwith those of Sa and Sc galaxies. It is concluded that, like otherspiral galaxies, S0's undergo continuing gas removal when they passthrough high-density regions. Cosmology from a galaxy group catalog. I - BinariesA new, completely objective group-finding algorithm is described andapplied to the CfA redshift catalog. The binary galaxies are isolatedfor analysis. The assumptions underlying the analysis are (1) that lighttraces mass, (2) that our binary galaxy subsets are representative lighttracers, and (3) that the binary orbits are circular. The primary resultof the work is that the resulting bias-free binary catalogs are afunction of the assumed cosmological model. For virtually any inputvalue of Omega(0) in the range 0.01-5.00, there is a reasonablyconsistent interpretation of the CfA survey such that the specifiedvalue of Omega(0) can be derived from the binary sample obtained underthat interpretation. A secondary result is that the higher the inputvalue of Omega(0), the broader the intrinsic distribution in M/L, andhence the less valid the assumption that light traces mass. A survey of galaxy redshifts. IV - The dataThe complete list of the best available radial velocities for the 2401galaxies in the merged Zwicky-Nilson catalog brighter than 14.5mz and with b (II) above +40 deg or below -30 deg ispresented. Almost 60 percent of the redshifts are from the CfA surveyand are accurate to typically 35 km/s. A catalog of hierarchical subclustering in the Turner-Gott groupsInformation on the substructure, to four levels of hierarchy, ispresented for the 103 groups listed by Turner and Gott (TG) in theircatalog of groups of galaxies. All galaxies brighter than Mpg= 14.0 in the region delta is 0 deg or greater and b(II) is 40 deg orgreater that have been assigned group memberships by TG are included.Also listed is the local environmental information for each of thegalaxies, giving the surface density enhancement beta in the galaxy'sneighborhood, calculated at 15 levels in the range beta = 4.6 to 10,000.
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