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# NGC 2820

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 Late-type galaxies observed with SAURON: two-dimensional stellar and emission-line kinematics of 18 spiralsWe present the stellar and gas kinematics of a sample of 18 nearbylate-type spiral galaxies (Hubble types ranging from Sb to Sd), observedwith the integral-field spectrograph SAURON at the 4.2-m WilliamHerschel Telescope. SAURON covers the spectral range 4800-5380Å,allowing us to measure the Hβ, Fe, Mgb absorption features and theemission in the Hβ line and the [OIII]λλ4959,5007Å and [NI]λλ5198, 5200Å doublets over a 33× 41-arcsec2 field of view. The maps cover the nuclearregion of these late-type galaxies and in all cases include the entirebulge. In many cases the stellar kinematics suggests the presence of acold inner region, as visible from a central drop in the stellarvelocity dispersion. The ionized gas is almost ubiquitous and behaves ina complicated fashion: the gas velocity fields often display morefeatures than the stellar ones, including wiggles in the zero-velocitylines, irregular distributions, ring-like structures. The line ratio[OIII]/Hβ often takes on low values over most of the field,probably indicating a wide-spread star formation. Highlights from the ObservatoriesNot Available GMRT observations of the group Holmberg 124: Evolution by tidal forces and ram pressure?We report new radio continuum and 21 cm HI observations using the GiantMetrewave Radio Telescope (GMRT) of the group Holmberg 124 (Ho 124)comprising four late-type galaxies, namely NGC 2820, Mrk 108, NGC 2814and NGC 2805. The three galaxies, NGC 2820, Mrk 108 and NGC 2814 whichare closely located in the sky plane have clearly undergone tidalinteractions as seen from the various morphological tidal signatures anddebris. Moreover we note various features in the group members which webelieve might be due to ram pressure. In this paper, we describe fourinteresting results emerging from our observations: a) detection of thetidal radio continuum bridge at 330 MHz connecting the galaxies NGC2820+Mrk 108 with NGC 2814. The radio bridge was discovered at 1465 MHzby van der Hulst & Hummel (1985, A&A, 150, 17). We find that thebridge has a fairly steep spectrum with a spectral index α (S∝ να) of -1.8+0.3-0.2which is much steeper than the -0.8 quoted by van der Hulst & Hummel(1985); b) detection of other tidal features like the tilted HI andradio continuum disk of NGC 2814, a HI streamer and a radio continuumtail arising from the south of NGC 2814. We also report the detection ofa possible tidal dwarf galaxy in HI; c) sharp truncation in the HIdistribution in the south of NGC 2820 and in the HI and radio continuumdistribution in the north of NGC 2814. The optical disks in both thecases look undisturbed. As pointed out by Davis et al. (1997, AJ, 114,613), ram pressure affects different components of the interstellarmedium to varying degrees. Simple estimates of pressure in differentcomponents of the interstellar medium (radio continuum, Hα and HI)in NGC 2820 indicate that ram pressure will significantly influence HI;d) detection of a large one-sided HI loop to the north of NGC 2820. Noradio continuum emission or Hα emission is associated with the HIloop. We discuss various scenarios for the origin of this loop includinga central starburst, ram pressure stripping and tidal interaction. We donot support the central starburst scenario since the loop is notdetected in ionized gas. Using the upper limit on X-ray luminosity of Ho124 (Mulchaey et al. 2003, ApJS, 145, 39), we estimate an upper limit onthe intragroup medium (IGrM) density of 8.8×10-4cm-3. For half this electron density, we estimate the rampressure force of the IGrM to be comparable to the gravitational pull ofthe disk of NGC 2820. Since tidal interaction has obviously influencedthe group, we suggest that the loop could have formed by ram pressurestripping if tidal effects had reduced the surface density of HI in NGC2820. From the complex observational picture of Ho 124 and the numericalestimates, we suggest that the evolution of the Ho 124 group may begoverned by both tidal forces due to the interaction and the rampressure due to motion of the member galaxies in the IGrM and that theIGrM densities should not be too low (i.e. ≥4×10-4). However this needs to be verified by furtherobservations. GHASP: an Hα kinematic survey of spiral and irregular galaxies - III. 15 new velocity fields and study of 46 rotation curvesWe present Fabry-Pérot observations obtained in the frame of theGHASP survey (Gassendi Hα survey of SPirals). We have derived theHα maps, the velocity fields and the rotation curves for a set of15 galaxies. The data presented in this paper are combined with the datapublished in our two previous papers in order to make a preliminaryanalysis of the rotation curves obtained for 46 galaxies. We check theconsistency of our data with the Tully-Fisher relationship and concludethat our Hα rotation curves reach the maximum velocity in most ofthe cases, even with solid-body rotating galaxies. We find that ourrotation curves, on average, almost reach the isophotal radiusR25. We confirm the trend, already mentioned by Rubin,Waterman & Kenney and Márquez et al., that the maximumextension of the Hα rotation curves increases with the type of thespiral galaxy, up to t~ 7-8 and we find that it decreases for magellanicand irregular galaxies. We also confirm the trend seen by Márquezet al. that later types tend to have lower values of the internal slopeof the rotation curve, in agreement with Rubin et al. 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 Extra-Planar Radio Emission from Edge-on Disk GalaxiesNot Available Extraplanar Emission-Line Gas in Edge-On Spiral Galaxies. I. Deep Emission-Line ImagingThe extraplanar diffuse ionized gas (eDIG) in 17 nearby, edge-on diskgalaxies is studied using deep Taurus Tunable Filter Hα and [N II]λ6583 images and conventional interference filter Hα+[N II]λλ6548, 6583 images that reach flux levels generally below~1×10-17 ergs s-1 cm-2arcsec-2. [N II] λ6583/Hα excitation maps areavailable for 10 of these objects. All but one galaxy in the sampleexhibit eDIG. The contribution of the eDIG to the total Hαluminosity is relatively constant, on the order of 12%+/-4%. TheHα scale height of the eDIG derived from a two-exponential fit tothe vertical emission profile ranges from 0.4 to 17.9 kpc, with anaverage of 4.3 kpc. This average value is noticeably larger than theeDIG scale height measured in our Galaxy and other galaxies. Thisdifference in scale height is probably due in part to the lower fluxlimits of our observations. The ionized mass of the extraplanarcomponent inferred by assuming a constant filling factor of 0.2 and aconstant path length through the disk of 5 kpc ranges from1.4×107 to 2.4×108 Msolar,with an average value of 1.2×108 Msolar.Under these same assumptions, the recombination rate required to keepthe eDIG ionized ranges from 0.44×106 to13×106 s-1 cm-2 of the disk, orabout 10%-325% of the Galactic value. A quantitative analysis of thetopology of the eDIG confirms that several galaxies in the sample have ahighly structured eDIG morphology. The distribution of the eDIG emissionis often correlated with the locations of the H II regions in the disk,supporting the hypothesis that the predominant source of ionization ofthe eDIG is photoionization from OB stars located in the H II regions. Astrong correlation is found between the IR (or far-IR) luminosities perunit disk area (basically a measure of the star formation rate per unitdisk area) and the extraplanar ionized mass, further providing supportfor a strong connection between the disk and eDIG components in thesegalaxies. The excitation maps confirm that the [N II]/Hα ratiosare systematically higher in the eDIG than in the disk. Althoughphotoionization by disk OB stars is generally able to explain theseelevated [N II]/Hα ratios, a secondary source of ionizationappears to be needed when one also takes into account other line ratios;more detail is given in a companion paper (our Paper II). Extraplanar Emission-Line Gas in Edge-on Spiral Galaxies. II. Optical SpectroscopyThe results from deep long-slit spectroscopy of nine edge-on spiralgalaxies with known extraplanar line emission are reported. Emissionfrom Hα, [N II] λλ6548, 6583, and [S II]λλ6716, 6731 is detected out to heights of a fewkiloparsecs in all of these galaxies. Several other fainter diagnosticlines such as [O I] λ6300, [O III] λλ4959, 5007,and He I λ5876 are also detected over a smaller scale. Therelative strengths, centroids, and widths of the various emission linesprovide constraints on the electron density, temperature, reddening,source(s) of ionization, and kinematics of the extraplanar gas. In allbut one galaxy, photoionization by massive OB stars alone hasdifficulties explaining all of the line ratios in the extraplanar gas.Hybrid models that combine photoionization by OB stars and anothersource of ionization such as photoionization by turbulent mixing layersor shocks provide a better fit to the data. The (upper limits on the)velocity gradients measured in these galaxies are consistent with thepredictions of the galactic fountain model to within the accuracy of themeasurements. 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. An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies. I. How common are gaseous halos among non-starburst galaxies?In a series of two papers we present results of a new Hα imagingsurvey, aiming at the detection of extraplanar diffuse ionized gas inhalos of late-type spiral galaxies. We have investigated a sample of 74nearby edge-on spirals, covering the northern and southern hemisphere.In 30 galaxies we detected extraplanar diffuse emission at meandistances of |z| ~ 1-2 kpc. Individual filaments can be traced out to|z|<=6 kpc in a few cases. We find a good correlation between the FIRflux ratio (S60/S100) and the SFR per unit area(LFIR/D225), based on thedetections/non-detections. This is actually valid for starburst, normaland for quiescent galaxies. A minimal SFR per unit area for the lowestS60/S100 values, at which extended emission hasbeen detected, was derived, which amounts to dotEA25thres = (3.2+/-0.5)*E40ergs-1 kpc-2. There are galaxies where extraplanaremission was detected at smaller values ofLFIR/D225, however, only in combinationwith a significantly enhanced dust temperature. The results corroboratethe general view that the gaseous halos are a direct consequence of SFactivity in the underlying galactic disk.Based on observations collected at the European Southern Observatory,Chile (ESO No. 63.N-0070, ESO No. 64.N-0034, ESO No. 65.N.-0002). Narrow Lines in Type II Supernovae: Probing the Circumstellar Nebulae of the ProgenitorsWe have carried out a high-dispersion (R~30,000) echelle spectroscopicsurvey of 16 Type II supernovae (SNe) to search for narrow emissionlines from circumstellar nebulae ejected by their massive progenitors.Circumstellar nebulae, if detected, provide invaluable opportunities toprobe SN progenitors. Of the 16 SNe observed, SN ejecta are clearlydetected in four SNe and possibly in another two SNe, interstellar gasis detected in 12 SNe, and circumstellar material is detected only in SN1978K and SN 1998S. In the case of SN 1978K, we are able to place anupper limit of ~2.2 pc for the size of the circumstellar ejecta nebulaand note that this is more consistent with the typical sizes observedfor ejecta nebulae around luminous blue variables, rather thanWolf-Rayet stars. In the case of SN 1998S, our observations of thenarrow lines ~1 yr after the SN explosion show variations compared toearly epochs. The nebular lines we observe from SN 1998S eitheroriginate from the low-density outer region of a circumstellar nebula orhave become dominated by an interstellar component. Warps and correlations with intrinsic parameters of galaxies in the visible and radioFrom a comparison of the different parameters of warped galaxies in theradio, and especially in the visible, we find that: a) No large galaxy(large mass or radius) has been found to have high amplitude in thewarp, and there is no correlation of size/mass with the degree ofasymmetry of the warp. b) The disc density and the ratio of dark toluminous mass show an opposing trend: smaller values give moreasymmetric warps in the inner radii (optical warps) but show nocorrelation with the amplitude of the warp; however, in the externalradii is there no correlation with asymmetry. c) A third anticorrelationappears in a comparison of the amplitude and degree of asymmetry in thewarped galaxies. Hence, it seems that very massive dark matter haloeshave nothing to do with the formation of warps but only with the degreeof symmetry in the inner radii, and are unrelated to the warp shape forthe outermost radii. Denser discs show the same dependence. 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 New Observations of Extra-Disk Molecular Gas in Interacting Galaxy Systems, Including a Two-Component System in Stephan's QuintetWe present new CO (1-0) observations of 11 extragalactic tails andbridges in nine interacting galaxy systems, almost doubling the numberof such features with sensitive CO measurements. Eight of these 11features were undetected in CO to very low CO/H I limits, with the mostextreme case being the NGC 7714/5 bridge. This bridge contains luminousH II regions and has a very high H I column density(1.6×1021 cm-2 in the 55" CO beam), yet wasundetected in CO to rms T*R=2.4 mK. The H I columndensity is higher than standard H2 and CO self-shieldinglimits for solar-metallicity gas, suggesting that the gas in this bridgeis metal-poor and has an enhancedNH2/ICO ratio compared with theGalactic value. Only one of the 11 features in our sample wasunambiguously detected in CO, a luminous H I-rich star formation regionnear an optical tail in the compact group Stephan's Quintet. We detectCO at two widely separated velocities in this feature, at ~6000 and~6700 km s-1. Both of these components have H I and Hαcounterparts. These velocities correspond to those of galaxies in thegroup, suggesting that this gas is material that has been removed fromtwo galaxies in the group. The CO/H I/Hα ratios for bothcomponents are similar to global values for spiral galaxies. Warm dust as a tracer of galaxies with gaseous halosWe present radio continuum observations conducted with the VLA and ATCAof a sample of 15 edge-on spiral galaxies. 11 of these galaxies, withinclination angles of i >~ 75o and neither active galacticnuclei nor nearby interaction partners, are suitable for studies of haloproperties in relation to the level of star formation in their disks. In6 of these 11 galaxies radio halos were detected at the angularresolution of the current data. In the remaining cases the presence ofhalo emission could not be proven unambiguously, partly due torelatively low angular resolution. A clear trend was found that galaxieswith radio halos are those with the highest far-infrared 60 mu m to 100mu m flux ratios. This shows the suitability of highf60/f100 ratios of >=0.4 as a reliable tracerof galaxies with high star formation rates and related disk-halointeractions, leading to the presence of extraplanar emission, e.g. fromcosmic ray electrons. The measured exponential scale heights of those 6radio halos that were clearly detected range from about 1.4 to 3.1 kpc.All 4 physically small galaxies in our sample do show extraplanarsynchrotron radio emission, indicating that their more shallowgravitational potential compared to normal-sized spirals mightfacilitate the escape of cosmic-ray electrons from the sites of starformation in their disks. Although the galaxies with the highest energyinput rates into the ISM of their disks are those that have the mostprominent radio halos, there is no direct relation between the haloscale heights and the energy input rates. Instead, the scale heights ofthe radio halos are dominated by the energy losses of the cosmic rayelectrons on their way out of the galaxy disks. 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. 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 The influence of interactions and minor mergers on the structure of galactic disks I. Observations and disk modelsThis paper is the first part in our series on the influence of tidalinteractions and minor mergers on the radial and vertical disk structureof spiral galaxies. We report on the sample selection, our observations,and data reduction. Surface photometry of the optical and near infrareddata of a sample of 110 highly-inclined/edge-on disk galaxies arepresented. This sample consists of two subsamples of 61 non-interactinggalaxies (control sample) and of 49 interacting galaxies/minor mergingcandidates. Additionally, 41 of these galaxies were observed in the nearinfrared. We show that the distribution of morphological types of bothsubsamples is almost indistinguishable, covering the range between 0<= T <= 9. An improved, 3-dimensional disk modelling- and fittingprocedure is described in order to analyze and to compare the diskstructure of our sample galaxies by using characteristic parameters. Wefind that the vertical brightness profiles of galactic disks respondvery sensitive even to small deviations from the perfect edge-onorientation. Hence, projection effects of slightly inclined disks maycause substantial changes in the value of the disk scale height and musttherefore be considered in the subsequent study. Based on observationsobtained at the European Southern Observatory (ESO, La Silla, Chile),Calar Alto Observatory operated by the MPIA (DSAZ, Spain), LowellObservatory (Flagstaff/AZ, USA), and Hoher List Observatory (Germany). The influence of interactions and minor mergers on the structure of galactic disks. II. Results and interpretationsWe present the second part of a detailed statistical study focussed onthe effects of tidal interactions and minor mergers on the radial andvertical disk structure of spiral galaxies. In the first part wereported on the sample selection, observations, and applied disk models.In this paper the results are presented, based on disk parametersderived from a sample of 110 highly-inclined/edge-on galaxies. Thissample consists of two subsamples of 49 interacting/merging and 61non-interacting galaxies. Additionally, 41 of these galaxies wereobserved in the NIR. We find significant changes of the disk structurein vertical direction, resulting in ~ 1.5 times larger scale heights andthus vertical velocity dispersions. The radial disk structure,characterized by the cut-off radius and the scale length, shows nostatistically significant changes. Thus, the ratio of radial to verticalscale parameters, h/z0, is ~ 1.7 times smaller for the sampleof interacting/merging galaxies. The total lack of typical flat diskratios h/z0 > 7 in the latter sample implies that verticaldisk heating is most efficient for (extremely) thin disks. Statisticallynearly all galactic disks in the sample (93%) possess non-isothermalvertical luminosity profiles like the sech (60%) and exp (33%)distribution, independent of the sample and passband investigated. Thisindicates that, in spite of tidal perturbations and disk thickening, theinitial vertical distribution of disk stars is not destroyed byinteractions or minor mergers. Based on observations obtained at theEuropean Southern Observatory (ESO, La Silla, Chile), Calar AltoObservatory operated by the MPIA (DSAZ, Spain), Lowell Observatory(Flagstaff/AZ, USA), and Hoher List Observatory (Germany). The star formation history in the interacting galaxies NGC 4490 and 4485We present the results of radio continuum observations of theinteracting galaxies NGC 4490 and 4485. Observations have been made inthe B-, C- and D-array configurations of the VLA at 1.49, 4.86 and8.44GHz, and with the Ryle Telescope at 15.2GHz. The radio continuummaps have been fitted with a model spectrum consisting of an agedsynchrotron and a thermal component, and have been decomposed into mapsof each component. We find that the data are consistent with a high,ongoing star formation rate over the entire disc of NGC 4490, and thatthe electron age across NGC 4490 is consistent with a scenario in whichNGC 4490 has been undergoing star formation at a constant rate for atleast 10^8yr. Combined with other evidence, we suggest that NGC 4490 isa young galaxy with an age of approximately 2x10^9yr, and that it hashad an approximately constant star formation rate during this periodequal to the current rate of ~4.7M_solaryr^-1. Furthermore, the effectsof the interaction have not had sufficient time to affect the starformation rate in NGC 4490 significantly, although NGC 4485 has beenseverely affected by the interaction. 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. Neutral Hydrogen and Dark Matter in Spiral GalaxiesThe first part presents a brief review of the main HI properties ofisolated, normal spiral galaxies and of the phenomena which seem tocharacterize and dominate their internal metabolism. In the second partattention is drawn to all those processes, such as tidal interactions,accretion and mergers, that depend on the galaxy environment and mayplay a significant role in galaxy formation and evolution. In the thirdpart the observational evidence for the dark matter component of spiralgalaxies is discussed. A Near- and Mid-Infrared Study of the Interacting Galaxy Pair UGC 12914/12915: Taffy''We report on an infrared 1 to 17 μm study of the nearby (cz=4600 kms-1) interacting spiral galaxy system UGC 12914/12915, usingthe ground-based Palomar 200 inch (5 m) telescope and PFIRCAMnear-infrared detector and space-based mid-infrared imaging and spectralobservations using ISOCAM and PHT-S on the Infrared Space Observatory.The system consists of two counterrotating spirals having suffered anearly face-on collision only ~2x107 yr ago. In conjunctionwith radio observations we explore the complex gas/dust morphology ofthe postcollision disks, ring structures, current epoch of starformation, and the remnant connecting bridge: It is the unusual radiosynchrotron bridge that this study was largely aimed at understanding.Strong line emission from aromatic band features at 6.2, 7.7, and 11.3μm are seen in both the mid-IR imaging and PHT-S spectrophotometrycentered on the nuclei. Theaverage mid-IR (5-17 μm) flux density is~0.42 Jy, or about 7% of the 60 μm IRAS flux density. Ournear-/mid-IRdata support the hypothesis that the restricted form of galaxy-galaxyinteraction-counterrotating direct head-on collision among comparablymassed spirals-has produced a large-scale dynamically expanding ring''of recent star formation and gas bar'' structure within the disk ofUGC 12914. The nucleus and northwestern disk of UGC 12915 are undergoingvigorous star formation probably triggered by the interaction. UGC 12914appears to be more quiescent in comparison, although there aresignatures of massive star formation as revealed in direct comparisonbetween the radio, mid-IR, and Hα imaging. Within the connectingbridge region, the mid-IR imaging reveals dust grains intermixed withthe atomic hydrogen gas. The heating mechanism for the hot dust islikely to be UV photons diffusing out from the galactic disks and the HII complex located along the extreme northeastern portion of the bridge:The dust emission, or mid-IR intensity per atomic hydrogen columndensity ratio, is consistent with heating from the local (bridge)interstellar radiation field. An Infrared Search for Extinguished Supernovae in Starburst GalaxiesIR and radio-band observations of heavily extinguished regions instarburst galaxies suggest a high supernova (SN) rate associated withsuch regions. Optically measured SN rates may therefore underestimatethe total SN rate by factors of up to 10, as a result of the very highextinction (A_B~10-20 mag) to core-collapse SNe in starburst regions.The IR/radio SN rates come from a variety of indirect means, however,which suffer from model dependence and other problems. We describe adirect measurement of the SN rate from a regular patrol of starburstgalaxies done with K'-band imaging to minimize the effects ofextinction. A collection of K'-band measurements of core-collapse SNenear maximum light is presented. Such measurements (excluding 1987A) arenot well reported in the literature. Results of a preliminary K'-bandsearch, using the MIRC camera at the Wyoming Infrared Observatory and animproved search strategy using the new ORCA optics, are described. Amonthly patrol of a sample of IRAS bright (mostly starburst) galaxieswithin 25 Mpc should yield 1-6 SNe yr^-1, corresponding to the range ofestimated SN rates. Our initial MIRC search with low resolution (2.2"pixels) failed to find extinguished SNe in the IRAS galaxies, limitingthe SN rate outside the nucleus (at greater than 15" radius) to lessthan 3.8 far-IR SN rate units (SNe per century per 10^10 L_solarmeasured at 60 and 100 mum, or FIRSRU) at 90% confidence. The MIRCcamera had insufficient resolution to search nuclear starburst regions,where starburst and SN activity is concentrated; therefore, we wereunable to rigorously test the hypothesis of high SN rates in heavilyobscured star-forming regions. We conclude that high-resolution nuclearSN searches in starburst galaxies with small fields are more productivethan low-resolution, large-field searches, even for our sample of large(often several arcminutes) galaxies. With our ORCA high-resolutionoptics, we could limit the total SN rate to less than 1.3 FIRSRU at 90%confidence in 3 years of observations, lower than most estimates. The I-Band Tully-Fisher Relation for SC Galaxies: 21 Centimeter H I Line DataA compilation of 21 cm line spectral parameters specifically designedfor application of the Tully-Fisher (TF) distance method is presentedfor 1201 spiral galaxies, primarily field Sc galaxies, for which opticalI-band photometric imaging is also available. New H I line spectra havebeen obtained for 881 galaxies. For an additional 320 galaxies, spectraavailable in a digital archive have been reexamined to allow applicationof a single algorithm for the derivation of the TF velocity widthparameter. A velocity width algorithm is used that provides a robustmeasurement of rotational velocity and permits an estimate of the erroron that width taking into account the effects of instrumental broadeningand signal-to-noise. The digital data are used to establish regressionrelations between measurements of velocity widths using other commonprescriptions so that comparable widths can be derived throughconversion of values published in the literature. The uniform H I linewidths presented here provide the rotational velocity measurement to beused in deriving peculiar velocities via the TF method. The I-Band Tully-Fisher Relation for SC Galaxies: Optical Imaging DataProperties derived from the analysis of photometric I-band imagingobservations are presented for 1727 inclined spiral galaxies, mostly oftypes Sbc and Sc. The reduction, parameter extraction, and errorestimation procedures are discussed in detail. The asymptotic behaviorof the magnitude curve of growth and the radial variation in ellipticityand position angle are used in combination with the linearity of thesurface brightness falloff to fit the disk portion of the profile. TotalI-band magnitudes are calculated by extrapolating the detected surfacebrightness profile to a radius of eight disk scale lengths. Errors inthe magnitudes, typically ~0.04 mag, are dominated by uncertainties inthe sky subtraction and disk-fitting procedures. Comparison is made withthe similar imaging database of Mathewson, Ford, & Buchhorn, both aspresented originally by those authors and after reanalyzing theirdigital reduction files using identical disk-fitting procedures. Directcomparison is made of profile details for 292 galaxies observed incommon. Although some differences occur, good agreement is found,proving that the two data sets can be used in combination with onlyminor accommodation of those differences. The compilation of opticalproperties presented here is optimized for use in applications of theTully-Fisher relation as a secondary distance indicator in studies ofthe local peculiar velocity field. Abundances in Spiral Galaxies: Evidence for Primary Nitrogen ProductionWe present the results of nitrogen and oxygen abundance measurements for185 H II regions spanning a range of radii in 13 spiral galaxies. Asexpected, the nitrogen-to-oxygen ratio increases linearly with theoxygen abundance for high-metallicity H II regions, indicating thatnitrogen is predominantly a secondary element. However, thenitrogen-to-oxygen ratio plateaus for oxygen abundances less than \frac{1}{3} solar [12 + log (O/H) < 8.45], as is also seen inlow-metallicity dwarf galaxies. This result suggests that the observedtrend in dwarf galaxies is not due to the outflow of enriched materialin a shallow gravitational potential. While the effects of the infall ofpristine material and delayed nitrogen delivery are still unconstrained,nitrogen does appear to have both a primary and a secondary component atlow metallicities in all types of galaxies. Groups of galaxies. III. Some empirical characteristics.Not Available
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