WIKISKY.ORG

 Home Baþlangýç Evrende yaþayabilmek için News@Sky Gökyüzü görüntüsü Koleksiyon Forum Blog New! SSS Basýn Giriþ

# NGC 4517

Ýçindekiler

### Görüntüler

Resim Yükleyin

DSS Images   Other Images

### Ýlgili Makaleler

 Interacting galaxies and cosmological parametersWe propose a (physical)-geometrical method to measureΩm° and ΩΛ°, thepresent rates of the density cosmological parameters for aFriedmann-Lemaître universe. The distribution of linearseparations between two interacting galaxies, when both of them undergoa first massive starburst, is used as a standard of length. Statisticalproperties of the linear separations of such pairs of“interactivated” galaxies are estimated from the data in theTwo Degree Field Galaxy Redshift Survey. Synthetic samples ofinteractivated pairs are generated with random orientations and a likelydistribution of redshifts. The resolution of the inverse problemprovides the probability densities of the retrieved cosmologicalparameters. The accuracies that can be achieved by that method onΩm° and ΩΛ° arecomputed depending on the size of ongoing real samples. Observationalprospects are investigated as the foreseeable surface densities on thesky and magnitudes of those objects. A Study of Edge-On Galaxies with the Hubble Space Telescope Advanced Camera for Surveys. I. Initial ResultsWe present the initial results of a Hubble Space Telescope/AdvancedCamera for Surveys snapshot survey of 16 nearby, edge-on, late-typegalaxies covering a range in distance from 2 to 19 Mpc. The images ofthese galaxies show significant resolved stellar populations. We deriveF606W and F814W photometry for more than 1.2 million stars and presentcolor-magnitude diagrams that show a mixture of young, intermediate, andold stars in each galaxy. In one of the fields we serendipitously detectstars from the Large Magellanic Cloud. We also identify a candidateyoung dwarf galaxy lying ~2 kpc above the plane of NGC 4631. For thenearest six galaxies, we derive tip of the red giant branch distancesand demonstrate that these galaxies fall on the K-band Tully-Fisherrelation established in clusters. From the color of the red giantbranch, we also find evidence that these galaxies possess a metal-poorthick-disk or halo population. A search for low surface brightness dwarf galaxies in different environments According to the cold dark matter (CDM) hierarchical clustering theoryof galaxy and large-scale structure formation, there should be numerouslow-mass dark matter haloes present in the Universe today. If thesehaloes contain sufficient stars, they should be detectable aslow-luminosity stellar systems or dwarf galaxies. We have previouslydescribed a new detection method for faint low surface brightnessobjects and we have shown that there are relatively large numbers ofvery faint dwarf galaxies in the nearby Virgo cluster. In this paper, wepresent results from a similar survey carried out on the MillenniumGalaxy strip, which runs along the celestial equator and samples a verydifferent galaxy environment. We show that the dwarf-to-giant galaxynumber ratio along this strip ranges from 0.7:1 to, at most, 6:1,corresponding to a flat luminosity function (α~-0.8 to -1.0). Thisis very different to our value of 20:1 for the Virgo cluster. There isno population of low surface brightness dwarf galaxies in the field thathave gone undetected by the redshift surveys. This result is exactlyopposite to what CDM models predict for the environmental dependence ofthe dark matter mass function, which is that there are proportionallymore small dark matter haloes in lower-density environments. Low-luminosity Type II supernovae: spectroscopic and photometric evolutionIn this paper we present spectroscopic and photometric observations forfour core-collapsed supernovae (SNe), namely SNe 1994N, 1999br, 1999euand 2001dc. Together with SN 1997D, we show that they form a group ofexceptionally low-luminosity events. These SNe have narrow spectrallines (indicating low expansion velocities) and low luminosities atevery phase (significantly lower than those of typical core-collapsedsupernovae). The very-low luminosity during the 56Coradioactive decay tail indicates that the mass of 56Niejected during the explosion is much smaller (MNi~ 2-8× 10-3 Msolar) than the average(MNi~ 6-10 × 10-2 Msolar). Twosupernovae of this group (SN 1999br and SN 2001dc) were discovered veryclose to the explosion epoch, allowing us to determine the lengths oftheir plateaux (~100 d) as well as establishing the explosion epochs ofthe other, less completely observed SNe. It is likely that this group ofSNe represent the extreme low-luminosity tail of a single continuousdistribution of Type II plateau supernovae events. Their kinetic energyis also exceptionally low. Although an origin from low-mass progenitorshas also been proposed for low-luminosity core-collapsed SNe, recentwork provides evidence in favour of the high-mass progenitor scenario.The incidence of these low-luminosity SNe could be as high as 4-5 percent of all Type II SNe. The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights from Hubble Space Telescope ImagingWe use available multifilter Hubble Space Telescope (HST) WFPC2 imagingof five (M81, M83, NGC 6946, M101, and M51, in order of distance)low-inclination, nearby spiral galaxies to study ancient star clusterpopulations. Combining rigorous selection criteria to rejectcontaminants (individual stars, background galaxies, and blends) withoptical photometry including the U bandpass, we unambiguously detectancient globular cluster (GC) systems in each galaxy. We presentluminosities, colors, and size (effective radius) measurements for ourcandidate GCs. These are used to estimate specific frequencies, toassess whether intrinsic color distributions are consistent with thepresence of both metal-poor and metal-rich GCs, and to compare relativesizes of ancient clusters between different galaxy systems. M81globulars have intrinsic color distributions that are very similar tothose in the Milky Way and M31, with ~40% of sample clusters havingcolors expected for a metal-rich population. The GC system in M51meanwhile, appears almost exclusively blue and metal-poor. This lack ofmetal-rich GCs associated with the M51 bulge indicates that the bulgeformation history of this Sbc galaxy may have differed significantlyfrom that of our own. Ancient clusters in M101 and possibly in NGC 6946,two of the three later type spirals in our sample, appear to haveluminosity distributions that continue to rise to our detection limit(MV~-6.0), well beyond the expected turnover(MV~-7.4) in the luminosity function. This is reminiscent ofthe situation in M33, a Local Group galaxy of similar Hubble type. Thefaint ancient cluster candidates in M101 and NGC 6946 have properties(colors and reff) similar to their more luminouscounterparts, and we suggest that these are either intermediate-age (3-9Gyr) disk clusters or the low-mass end of the original GC population.Potentially, these lower mass clusters were not destroyed because ofdifferent dynamical conditions relative to those present in earlier typegalaxies. If the faint, excess GC candidates are excluded, we find thatthe specific frequency (SN) of ancient clusters formed inlater type spirals is roughly constant, with SN=0.5+/-0.2. Ifwe consider only the blue, metal-poor clusters in the early-type spiralM81, this galaxy is also consistent with having formed a universal''specific frequency of halo GC population, with a value ofSN~0.6. By combining the results of this study withliterature values for other systems, we find that the total GC specificfrequencies in spirals appear to correlate best with Hubble type andbulge/total ratio, rather than with galaxy luminosity or galaxy mass. Spectrophotometry of galaxies in the Virgo cluster. II. The dataDrift-scan mode (3600-6800 Å) spectra with 500 Hubble Space Telescope observations of globular cluster systems along the Hubble sequence of spiral galaxiesWe have studied the globular cluster systems of seven giant, edge-onspiral galaxies using Hubble Space Telescope imaging in V and I. Thegalaxy sample covers the Hubble types Sa to Sc, allowing us to study thevariation of the properties of globular cluster systems along the Hubblesequence. The photometry reaches ~1.5 mag beyond the turn-over magnitudeof the globular cluster luminosity function for each galaxy. Specificfrequencies of globular clusters (SN values) were evaluatedby comparing the numbers of globular clusters found in our WFPC2pointings with those in our Milky Way that would be detected in the samespatial region if placed at the distance of the target galaxies. Resultsfrom this method were found to be consistent with the more commonly usedmethod of constructing radial distribution functions of globularclusters. The SN values of spirals with B/T<~ 0.3 (i.e.spirals with a Hubble type later than about Sb) are consistent with avalue of SN= 0.55 +/- 0.25. We suggest that this populationof globular clusters represents a universal', old halo population thatis present around each galaxy. Most galaxies in our sample haveSN values that are consistent with a scenario in whichglobular cluster systems are made up of (i) the aforementioned halopopulation plus (ii) a population that is associated with bulges, whichgrows approximately linearly with the mass of the bulge. Such scenariosinclude the merger scenario' for the formation of elliptical galaxiesas well as the multi-phase collapse' scenario, but it seemsinconsistent with the secular evolution' scenario of Pfenniger &Norman, in which bulges are formed from disc stars by means of theredistribution of angular momentum through bar instabilities and/orminor perturbations. However, there is one bulge-dominated spiral galaxyin our sample (NGC7814) with a low SN value that isconsistent with those of the latest-type spirals. This means that thesecular evolution' scenario can still be viable for somebulge-dominated spirals. Thus, our results suggest that the formationhistories of galaxy bulges of early-type spirals can be significantlydifferent from one galaxy to another. A Survey for H2O Megamasers. III. Monitoring Water Vapor Masers in Active GalaxiesWe present single-dish monitoring of the spectra of 13 extragalacticwater megamasers taken over a period of 9 years and a single epoch ofsensitive spectra for seven others. The primary motivation is a searchfor drifting line velocities analogous to those of the systemic featuresin NGC 4258, which are known to result from centripetal acceleration ofgas in an edge-on, subparsec molecular disk. We detect a velocity driftanalogous to that in NGC 4258 in only one source, NGC 2639. Another, themaser source in NGC 1052, exhibits erratic changes in its broad maserprofile over time. Narrow maser features in all of the other diskgalaxies discussed here either remain essentially constant in velocityover the monitoring period or are sufficiently weak or variable inintensity that individual features cannot be traced reliably from oneepoch to the next. In the context of a circumnuclear, molecular diskmodel, our results suggest that either (a) the maser lines seen aresystemic features subject to a much smaller acceleration than present inNGC 4258, presumably because the gas is farther from the nuclear blackhole, or (b) we are detecting satellite'' lines for which theacceleration is in the plane of the sky.Our data include the first K-band science observations taken with thenew 100 m Green Bank Telescope (GBT). The GBT data were taken duringtesting and commissioning of several new components and so are subjectto some limitations; nevertheless, they are in most cases the mostsensitive H2O spectra ever taken for each source and cover800 MHz (~=10,800 km s-1) of bandwidth. Many new maserfeatures are detected in these observations. Our data also include atentative and a clear detection of the megamaser in NGC 6240 at epochs ayear and a few months, respectively, prior to the detections reported byHagiwara et al. and Nakai et al.We also report a search for water vapor masers toward the nuclei of 58highly inclined (i>80deg), nearby galaxies. These sourceswere selected to investigate the tendency that H2O megamasersfavor inclined galaxies. None were detected, confirming that megamasersare associated exclusively with active galactic nuclei. The IRAS Revised Bright Galaxy SampleIRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above thecharacteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs. The 2MASS Large Galaxy AtlasWe present the largest galaxies as seen in the near-infrared (1-2μm), imaged with the Two Micron All Sky Survey (2MASS), ranging inangular size from 1' to 1.5d. We highlight the 100 largest in thesample. The galaxies span all Hubble morphological types, includingelliptical galaxies, normal and barred spirals, and dwarf and peculiarclasses. The 2MASS Large Galaxy Atlas provides the necessary sensitivityand angular resolution to examine in detail morphologies in thenear-infrared, which may be radically different from those in theoptical. Internal structures such as spirals, bulges, warps, rings,bars, and star formation regions are resolved by 2MASS. In addition tolarge mosaic images, the atlas includes astrometric, photometric, andshape global measurements for each galaxy. A comparison of fundamentalmeasures (e.g., surface brightness, Hubble type) is carried out for thesample and compared with the Third Reference Catalogue. We furthershowcase NGC 253 and M51 (NGC 5194/5195) to demonstrate the quality anddepth of the data. The atlas represents the first uniform, all-sky,dust-penetrated view of galaxies of every type, as seen in thenear-infrared wavelength window that is most sensitive to the dominantmass component of galaxies. The images and catalogs are availablethrough the NASA/IPAC Extragalactic Database and Infrared ScienceArchive and are part of the 2MASS Extended Source Catalog. 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 1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history. Flat Galaxies of the RFGC Catalog Detected in the HIPASS SurveyData from the H I Parkes All-Sky Survey (HIPASS) of the southern sky inthe neutral hydrogen line are used to determine the radial velocitiesand widths of the H I line for flat spiral galaxies of the RevisedFlat-Galaxy Catalog (RFGC) seen edge-on. The sample of 103 flat galaxiesdetected in HIPASS is characterized by a median radial velocity of +2037km/sec and a median width of the H I line at the level of 50% of maximumof 242 km/sec. For RFGC galaxies the 50% detection level in HIPASScorresponds to an apparent magnitude B t = 14 m .5 or an angulardiameter a = 2.9. The relative number of detected galaxies increasesfrom 2% for the morphological types Sbc and Sc to 41% for the type Sm.The median value of the ratio of hydrogen mass to total mass for RFGCgalaxies is 0.079. With allowance for the average internal extinctionfor edge-on galaxies, B t m .75, the median ratio of hydrogen mass toluminosity, M H I/L B = 0.74 M ȯ/L ȯ, is typical for late-typespirals. Because of its small depth, HIPASS reveals only a few RFGCgalaxies with previously unknown velocities and line widths. 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. Hα surface photometry of galaxies in the Virgo cluster. IV. The current star formation in nearby clusters of galaxiesHα +[NII] imaging observations of 369 late-type (spiral) galaxiesin the Virgo cluster and in the Coma/A1367 supercluster are analyzed,covering 3 rich nearby clusters (A1367, Coma and Virgo) and nearlyisolated galaxies in the Great-Wall. They constitute an opticallyselected sample (mp<16.0) observed with ~ 60 %completeness. These observations provide us with the current(T<107 yrs) star formation properties of galaxies that westudy as a function of the clustercentric projected distances (Theta ).The expected decrease of the star formation rate (SFR), as traced by theHα EW, with decreasing Theta is found only when galaxies brighterthan Mp ~ -19.5 are considered. Fainter objects show no orreverse trends. We also include in our analysis Near Infrared data,providing information on the old (T>109 yrs) stars. Puttogether, the young and the old stellar indicators give the ratio ofcurrently formed stars over the stars formed in the past, orbirthrate'' parameter b. For the considered galaxies we also determinethe global gas content'' combining HI with CO observations. We definethe gas deficiency'' parameter as the logarithmic difference betweenthe gas content of isolated galaxies of a given Hubble type and themeasured gas content. For the isolated objects we find that b decreaseswith increasing NIR luminosity. In other words less massive galaxies arecurrently forming stars at a higher rate than their giant counterpartswhich experienced most of their star formation activity at earliercosmological epochs. The gas-deficient objects, primarily members of theVirgo cluster, have a birthrate significantly lower than the isolatedobjects with normal gas content and of similar NIR luminosity. Thisindicates that the current star formation is regulated by the gaseouscontent of spirals. Whatever mechanism (most plausibly ram-pressurestripping) is responsible for the pattern of gas deficiency observed inspiral galaxies members of rich clusters, it also produces the observedquenching of the current star formation. A significant fraction of gashealthy'' (i.e. with a gas deficiency parameter less than 0.4) andcurrently star forming galaxies is unexpectedly found projected near thecenter of the Virgo cluster. Their average Tully-Fisher distance isfound approximately one magnitude further away (muo = 31.77)than the distance of their gas-deficient counterparts (muo =30.85), suggesting that the gas healthy objects belong to a cloudprojected onto the cluster center, but in fact lying a few Mpc behindVirgo, thus unaffected by the dense IGM of the cluster. Based onobservations taken at the Observatorio Astronómico Nacional(Mexico), the OHP (France), Calar Alto and NOT (Spain) observatories.Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org Compact groups in the UZC galaxy sampleApplying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35 Photometric parameters of edge-on galaxies from 2MASS observationsTo analyze the vertical structure of edge-on galaxies, we have usedimages of a large uniform sample of flat galaxies that have been takenduring the 2MASS all-sky survey. The photometric parameters, such as theradial scale length, the vertical scale height, and the deprojectedcentral surface brightness of galactic disks have been obtained. We finda strong correlation between the central surface brightness and theratio of the vertical scale height to the vertical scale length: thethinner the galaxy, the lower the central surface brightness of itsdisk. The vertical scale height does not increase systematically withthe distance from the galaxy center in the frames of this sample. Hα surface photometry of galaxies in the Virgo cluster. II. Observations with the OHP and Calar Alto 1.2 m telescopesWe present Hα line imaging observations of 122 galaxies obtainedwith the 1.20 m telescopes of the Observatoire de Haute Provence (OHP)and of Calar Alto. The observed galaxies are mostly Virgo clustermembers (95), along with 10 objects in the Coma/A1367 supercluster, 6 inthe clusters A2197 and A2199, and 11 nearby galaxies taken as fillers.Hα +[NII] fluxes and equivalent widths, as well as images of allthe detected targets, are presented. Based on observations taken at theObservatoire de Haute Provence (OHP) (France), operated by the FrenchCNRS, and Calar Alto Observatory (Spain), operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy. Figure 1 is only available inelectronic form at http://www.edpsciences.org The Frequency of Active and Quiescent Galaxies with Companions: Implications for the Feeding of the NucleusWe analyze the idea that nuclear activity, either active galactic nuclei(AGNs) or star formation, can be triggered by interactions by studyingthe percentage of active, H II, and quiescent galaxies with companions.Our sample was selected from the Palomar survey and avoids selectionbiases faced by previous studies. This sample was split into fivedifferent groups, Seyfert galaxies, LINERs, transition galaxies, H IIgalaxies, and absorption-line galaxies. The comparison between the localgalaxy density distributions of the different groups showed that in mostcases there is no statistically significant difference among galaxies ofdifferent activity types, with the exception that absorption-linegalaxies are seen in higher density environments, since most of them arein the Virgo Cluster. The comparison of the percentage of galaxies withnearby companions showed that there is a higher percentage of LINERs,transition galaxies, and absorption-line galaxies with companions thanSeyfert and H II galaxies. However, we find that when we consider onlygalaxies of similar morphological types (elliptical or spiral), there isno difference in the percentage of galaxies with companions amongdifferent activity types, indicating that the former result was due tothe morphology-density effect. In addition, only small differences arefound when we consider galaxies with similar Hα luminosities. Thecomparison between H II galaxies of different Hα luminositiesshows that there is a significantly higher percentage of galaxies withcompanions among H II galaxies with L(Hα)>1039 ergss-1 than among those with L(Hα)<=1039ergs s-1, indicating that interactions increase the amount ofcircumnuclear star formation, in agreement with previous results. Thefact that we find that galaxies of different activity types have thesame percentage of companions suggests that interactions betweengalaxies is not a necessary condition to trigger the nuclear activity inAGNs. We compare our results with previous ones and discuss theirimplications. A list of peculiar velocities of RFGC galaxiesA list of radial velocities, HI line widths and peculiar velocities of1327 galaxies from the RFGC catalogue has been compiled using actualobservations and literature data. The list can be used for studying bulkmotions of galaxies, construction of the field of peculiar velocitiesand other tasks. 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. High-Resolution Radio Continuum Observations of Edge-on Spiral GalaxiesRadio continuum emission at 20 cm has been observed in a sample of 16edge-on galaxies, using the VLA in its A configuration. These galaxieswere observed recently at lower resolution by Irwin et al., who foundevidence for extraplanar disk-halo features in 15 of the 16 galaxies.Twelve of the galaxies are detected in the new high-resolutionobservations. Of these, only two, which were previously known Seyferts,show convincing evidence for AGNs. For six of the galaxies, we provideimproved positions for the galaxy nuclei. In four galaxies, radiocontinuum loops extending perpendicular to the major axis have beendiscovered, confirming previous conclusions from lower resolutionobservations that extraplanar emission is present, as well as providingfurther evidence that radio halos'' consist, at least in part, ofunderlying discrete features. For several galaxies, the resolution issufficient to reveal individual star-forming regions in the disk. Weexamine NGC 3556 in detail since this galaxy has been shown by King& Irwin to display extremely large H I supershells. The estimatedinput energy from supernovae in the brightest radio component of thisgalaxy is insufficient to drive the observed H I supershells. We explorepossible resolutions to this energy deficit. Box- and peanut-shaped bulges. I. StatisticsWe present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html 1.65 ^mum (H-band) surface photometry of galaxies. IV. observations of 170 galaxies with the Calar Alto 2.2 m telescopeWe present near-infrared (H band) surface photometry of 170 galaxies,obtained in 1997 using the Calar Alto 2.2 m telescope equipped with theNICMOS3 camera MAGIC. The majority of our targets are selected amongbright members of the Virgo cluster, however galaxies in the A262 andCancer clusters and in the Coma/A1367 supercluster are also included.This data set is aimed at complementing the NIR survey in the Virgocluster discussed in \cite[Boselli et al. (1997)]{B97} and in the ComaSupercluster, presented in Papers I, II and III of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derivedTables 1 and 2 (full version) are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.Based on observations taken at the Calar Alto Observatory, operated bythe Max-Planck-Institut für Astronomie (Heidelberg) jointly withthe Spanish National Commission for Astronomy. The Revised Flat Galaxy Catalogue.We present a new improved and completed version of the Flat GalaxyCatalogue (FGC) named the Revised Flat Galaxy Catalogue (RFGC)containing 4236 thin edge-on spiral galaxies and covering the whole sky.The Catalogue is intended to study large-scale cosmic streamings as wellas other problems of observational cosmology. The dipole moment ofdistribution of the RFGC galaxies (l = 273 degr; b =+19 degr) lieswithin statistical errors (+/-10 degr) in the direction of the LocalGroup motion towards the Microwave Background Radiation (MBR). 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. High-Latitude Radio Emission in a Sample of Edge-on Spiral GalaxiesWe have mapped 16 edge-on galaxies at 20 cm using the Very Large Arrayin its C configuration, and a subset of these galaxies in the Dconfiguration at 6 and/or 20 cm, in a search for extended (>~1 kpc)radio continuum emission above and below the plane. For five galaxies,we could form spectral index, energy, and magnetic field maps (assumingminimum energy). While the galaxies were partly chosen by radio fluxdensity, they span a variety of star formation rates (SFRs), and onlysix might be considered starburst'' galaxies. A range of Hubble typeand degree of isolation are also represented. The galaxies largely fallon the FIR-radio continuum correlation. They also display a correlationbetween IR surface brightness and warmth, extending the previouslyobserved relation of Lehnert & Heckman to galaxies with lower starformation rates. We find that all but one galaxy show evidence fornonthermal high-latitude radio continuum emission, suggesting thatcosmic-ray (CR) halos are common in star-forming galaxies. Of these,eight galaxies are new detections. The high-latitude emission is seenover a variety of spatial scales and in discrete and/or smooth features.In some cases, discrete features are seen on large scales, suggestingthat smooth radio halos may consist, in part, of discrete featurescombined with low spatial resolution. In general, the discrete featuresemanate from the disk, but estimates of CR diffusion lengths suggestthat diffusion alone is insufficient to transport the particles to thehigh latitudes seen (>15 kpc in one case). Thus CRs likely diffusethrough low-density regions and/or are assisted by other mechanisms(e.g., winds). We searched for correlations between the prevalence ofhigh-latitude radio emission and a number of other properties, includingthe global SFR, supernova input rate per unit star-forming area, E_A,and environment, and do not find clear correlations with any of theseproperties. A subset of the data allows, at best, for only a weakcorrelation with E_A. Our one nondetection (NGC 4517), however, occursat a threshold level consistent with that found by Dahlem, Lisenfeld,& Golla. The lack of a good correlation with star formationindicators could be the result of the different timescales for starformation processes compared with the duration of the radio emission.Correlations with other properties, such as environment, are moredifficult to assess. However, a few isolated galaxies display strongradio halos, indicating that an interaction is not necessary to producethe extraplanar emission. A Search for Extraplanar Dust in Nearby Edge-on SpiralsWe present high-resolution (0.6" to ~1.0") BV images of 12 edge-onspiral galaxies observed with the WIYN 3.5 m telescope. These imageswere obtained to search for extraplanar (|z|>0.4 kpc) absorbing duststructures similar to those previously found in NGC 891 (Howk &Savage). Many of these galaxies have been previously searched fordiffuse ionized gas at high z. Our imaged galaxies include a sample ofseven massive L_*-like spiral galaxies within D<~25 Mpc that haveinclinations i>~87^deg from the plane of the sky. We find that fiveof these seven systems show extraplanar dust, visible as highlystructured absorbing clouds against the background stellar light of thegalaxies. These dust structures lie at heights |z|>~0.4 kpc, whichshould be above most of the thin disk molecular material in thesegalaxies. The more prominent structures are estimated to have associatedgas masses >~10^5 M_solar the implied potential energies are>~10^52 ergs. All of the galaxies in our sample that show detectableHα emission at large z also show extraplanar dust structures. Noneof those galaxies for which extraplanar Hα searches were negativeshow evidence for extensive high-z dust. The existence of extraplanardust is a common property of massive spiral galaxies. We discuss severalmechanisms for shaping the observed dust features. We emphasize in thisdiscussion the possibility that these dusty clouds represent the densephase of a multiphase medium at high z in spiral galaxies. In a fewcases interactions with close galaxy companions could be responsible forthe high-z dust, either through dynamical stripping or triggered starformation. We can rule out warps as the source of the observed high-zdust. Flaring gas layers seem an unlikely source of the observedmaterial but cannot be ruled out at this time, except for those featuresthat clearly connect to energetic processes in the disk. The correlationbetween high-z dust and extraplanar Hα emission may simply suggestthat both trace the high-z interstellar medium in its various forms (orphases), the existence of which may ultimately be driven by vigorousstar formation in the underlying disk. The absorption produced by high-zdust and associated gas in spiral galaxies must be accounted for whenstudying extraplanar emission from spiral galaxies over much of theelectromagnetic spectrum. The distribution of far-infrared emission from edge-on galaxiesWe use resolution-enhanced IRAS images (HiRes) to study the distributionof far-infrared (FIR) emission in 20 edge-on, disc galaxies. Half of oursample are selected as infrared-bright galaxies which emit most of theirenergy at wavelengths longer than a few mum. The remaining 10 objectsare normal' (quiescent) galaxies. The distribution of FIR emissionalong the major axis of the infrared-bright galaxies tends to be farmore centrally concentrated than that detected in quiescent discs.Indeed, many of the infrared-bright objects are dominated by a luminous,compact or unresolved source (<3 kpc) located in the nuclear region.It is known from emission-line studies carried out in the past (Hαimaging and long-slit spectroscopy) that most of the galaxies that wehave selected as infrared-bright possess an energetic outflow or`superwind', which is powered by enhanced, circumnuclear star formation.We believe, therefore, that the compact FIR emission that we havedetected arises from dust enclosing the central starburst.Low-resolution radio continuum maps for the same galaxies show astriking morphological similarity to the IRAS images, confirming thepresence of enhanced, recent star formation at the centre of theinfrared-bright galaxies. The wider availability of higher resolutionFIR images, such as HiRes, also invites an investigation into whetheredge-on discs are resolved along the minor axis. In particular, weexplore the possibility that the starburst-driven superwinds, presentwithin many of our infrared-bright galaxies, are transporting dustgrains out of the disc. None of the objects that we have examined(infrared-bright or quiescent) exhibits structure that can be reliablyinterpreted as dust outflow. Various artefacts of the HiRes data,specifically those which produce faint, spurious structure in thevicinity of bright FIR sources, ultimately constrain the sensitivity ofour images to about 1 MJy sr^-1 at 60 mum. Thus, if the grains entrainedin the outflow are too cold (<=15 K), we cannot expect to detect themwith the present study. A Complete Redshift Survey to the Zwicky Catalog Limit in a 2^h X 15 deg Region around 3C 273We compile 1113 redshifts (648 new measurements, 465 from theliterature) for Zwicky catalog galaxies in the region (-3.5d <= delta<= 8.5d, 11h5 <= alpha <= 13h5). We include redshifts for 114component objects in 78 Zwicky catalog multiplets. The redshift surveyin this region is 99.5% complete to the Zwicky catalog limit, m_Zw =15.7. It is 99.9% complete to m_Zw = 15.5, the CfA Redshift Survey(CfA2) magnitude limit. The survey region is adjacent to the northernportion of CfA2, overlaps the northernmost slice of the Las CampanasRedshift Survey, includes the southern extent of the Virgo Cluster, andis roughly centered on the QSO 3C 273. As in other portions of theZwicky catalog, bright and faint galaxies trace the same large-scalestructure.
Yeni bir Makale Öner