Contents
Images
Upload your image
DSS Images Other Images
Related articles
Objective Classification of Spiral Galaxies Having Extended Rotation Curves Beyond the Optical Radius
We carry out an objective classification of four samples of spiralgalaxies having extended rotation curves beyond the optical radius. Amultivariate statistical analysis (viz., principal component analysis[PCA]) shows that about 96% of the total variation is due to twocomponents, one being the combination of absolute blue magnitude andmaximum rotational velocity beyond the optical region and the otherbeing the central density of the halo. On the basis of PCA a fundamentalplane has been constructed that reduces the scatter in the Tully-Fisherrelation up to a maximum of 16%. A multiple stepwise regression analysisof the variation of the overall shape of the rotation curves shows thatit is mainly determined by the central surface brightness, while theshape purely in the outer part of the galaxy (beyond the optical radius)is mainly determined by the size of the galactic disk.
| The Baryonic Tully-Fisher Relation of Galaxies with Extended Rotation Curves and the Stellar Mass of Rotating Galaxies
I investigate the baryonic Tully-Fisher relation for a sample ofgalaxies with extended 21 cm rotation curves spanning the range 20 kms-1<~Vf<=300 km s-1. A variety ofscalings of the stellar mass-to-light ratio Υ* areconsidered. For each prescription for Υ*, I give fitsof the form Md=AVxf.Presumably, the prescription that comes closest to the correct valuewill minimize the scatter in the relation. The fit with minimum scatterhas A=50 Msolar km-4 s4 andx=4. This relation holds over five decades in mass. Galaxy color,stellar fraction, and Υ* are correlated with eachother and with Md, in the sense that more massivegalaxies tend to be more evolved. There is a systematic dependence ofthe degree of maximality of disks on surface brightness. High surfacebrightness galaxies typically have Υ*~3/4 of themaximum disk value, while low surface brightness galaxies typicallyattain ~1/4 of this amount.
| Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies
Published mass models fitted to galaxy rotation curves are used to studythe systematic properties of dark matter (DM) halos in late-type anddwarf spheroidal (dSph) galaxies. Halo parameters are derived by fittingnon-singular isothermals to (V^2 - Vvis^2)1/2,where V(r) is the observed rotation curve and Vvis is therotation curve of the visible matter. The latter is calculated from thesurface brightness assuming that the mass-to-light ratio M/L is constantwith radius. ``Maximum disk'' values of M/L are adjusted to fit as muchof the inner rotation curve as possible without making the halo have ahollow core. Rotation curve decomposition becomes impossible fainterthan absolute magnitude M_B ≃ -14, where V becomes comparable tothe velocity dispersion of the gas. To increase the luminosity rangefurther, we include dSph galaxies, which are physically related tospiral and irregular galaxies. Combining the data, we find that DM halossatisfy well defined scaling laws analogous to the ``fundamental plane''relations for elliptical galaxies. Halos in less luminous galaxies havesmaller core radii r_c, higher central densities ρ_0, and smallercentral velocity dispersions σ. Scaling laws provide new anddetailed constraints on the nature of DM and on galaxy formation andevolution. Some simple implications include:1 -- A single, continuous physical sequence of increasing mass extendsfrom dSph galaxies with M_B ≃ -7.6 to Sc I galaxies with M_B≃ -22.4.2 -- The high DM densities in dSph galaxies are normal for such tinygalaxies. Since virialised density depends on collapse redshiftzcoll, ρ_0 ∝ (1 + zcoll)^3, the smallestdwarfs formed at least Δ zcoll ≃ 7 earlier thanthe biggest spirals.3 -- The high DM densities of dSphs implies that they are real galaxiesformed from primordial density fluctuations. They are not tidalfragments. Tidal dwarfs cannot retain even the low DM densities of theirgiant-galaxy progenitors. In contrast, dSphs have higher DM densitiesthan do giant-galaxy progenitors.4 -- The fact that, as luminosity decreases, dwarf galaxies become muchmore numerous and also more nearly dominated by DM raises thepossibility that there exists a large population of objects that arecompletely dark. Such objects are a canonical prediction of cold DMtheory. If they exist, ``empty halos'' are likely to be small and dense-- that is, darker versions of Draco and UMi.5 -- The slopes of the DM parameter correlations provide a measure ongalactic mass scales of the slope n of the power spectrum|δk|2 ∝ k^n of primordial densityfluctuations. Our preliminary results, not yet corrected for baryoniccompression of DM, give n ≃ -1.9 ± 0.2. This is consistentwith cold DM theory.
| Modified Newtonian Dynamics as an Alternative to Dark Matter
Modified Newtonian dynamics (MOND) is an empirically motivatedmodification of Newtonian gravity or inertia suggested by Milgrom as analternative to cosmic dark matter. The basic idea is that ataccelerations below ao ~ 10-8 cm/s2 ~cHo/6 the effective gravitational attraction approaches√(gnao), where gn is the usualNewtonian acceleration. This simple algorithm yields flat rotationcurves for spiral galaxies and a mass-rotation velocity relation of theform M ∝ V4 that forms the basis for the observedluminosity-rotation velocity relation-the Tully-Fisher law. We reviewthe phenomenological success of MOND on scales ranging from dwarfspheroidal galaxies to superclusters and demonstrate that the evidencefor dark matter can be equally well interpreted as evidence for MOND. Wediscuss the possible physical basis for an acceleration-basedmodification of Newtonian dynamics as well as the extention of MOND tocosmology and structure formation.
| Disc-like objects in hierarchical hydrodynamical simulations: comparison with observations
We present results from a careful and detailed analysis of thestructural and dynamical properties of a sample of 29 disc-like objectsidentified at z=0 in three AP3M-SPH fully consistent cosmologicalsimulations. These simulations are realizations of a CDM hierarchicalmodel, in which an inefficient Schmidt-law-like algorithm to model thestellar formation process has been implemented. We focus on propertiesthat can be constrained with available data from observations of spiralgalaxies, namely the bulge and disc structural parameters and therotation curves. Comparison with data from Broeils, de Jong and Courteaugives satisfactory agreement, in contrast with previous findings usingother codes. This suggests that the stellar formation implementation wehave used has succeeded in forming compact bulges that stabilizedisc-like structures in the violent phases of their assembly, while inthe quiescent phases the gas has cooled and collapsed in accord with theFall & Efstathiou standard model of disc formation.
| On the apparent coupling of neutral hydrogen and dark matter in spiral galaxies
We have studied a mass model for spiral galaxies in which the darkmatter surface density is a scaled version of the observed Hi surfacedensity. Applying this mass model to a sample of 24 spiral galaxies withreliable rotation curves, one obtains good fits for most galaxies. Thescaling factors cluster around 7, after correction for the presence ofprimordial helium. For several cases, however, different, often larger,values are found. For galaxies that cannot be fitted well, thediscrepancy occurs at large radii and results from a fairly rapiddecline of the Hi surface density in the outermost regions. Because ofsuch imperfections and in view of possible selection effects, it is notpossible to conclude here that there is a real coupling between Hi anddark matter in spiral galaxies.
| Producing Disc-Like Objects with Observational Counterparts from Hierarchical Hydrodynamical Simulations
We report some results on the formation of disc-like objects inhierarchical hydrodynamical simulations with characteristics compatiblewith observed spirals.
| A Visual Search for Galaxies in a Milky Way Region around the North Supergalactic Pole
We performed a visual systematic search for galaxies on POSS II(B)plates in a Milky Way region between l~=32deg-68° andb~=-4deg to 19°. This region partly contains the LocalVoid, and the north supergalactic pole exists at the central part. Thesurveyed area was about 560 deg2, and a total of 11,310galaxies and galaxy candidates with sizes of 0.1′ or greater wereidentified. Among the detected objects, 152 have been given in galaxycatalogs and 159, including 49 known galaxies, are associated with IRASpoint sources. We made a catalog of the detected objects, in which theposition in (α, δ) and (l, b), the size, and the features ofthe image and multiplicity are given for each object. The surface numberdensities of the detected objects almost depend on the Galacticlatitude. In the surveyed region, there is no nearby cluster and thereis an outstanding concentration of galaxies at l=7deg-12°and 4000-5000 km s-1.
| Is a Simple Collisionless Relic Dark Matter Particle Ruled Out?
The central densities of dark matter (DM) halos are much lower thanpredicted in cold DM models of structure formation. Confirmation thatthey have cores with a finite central density would allow us to rule outmany popular types of collisionless particles as candidates for DM. Anymodel that leads to cusped halos (such as cold DM) is already facingserious difficulties on small scales, and hot DM models have beenexcluded. Here I show that fermionic warm DM is inconsistent with thewide range of phase-space densities in the DM halos of well-observednearby galaxies.
| The Milky Way as a galaxy.
Not Available
| The Various Kinematics of Dwarf Irregular Galaxies in Nearby Groups and Their Dark Matter Distributions
Eight dwarf irregular galaxies, in the two nearby groups of galaxiesSculptor and Centaurus A (at 2.5 Mpc and 3.5 Mpc), have been imaged inneutral hydrogen (H I) with the Australia Telescope and the Very LargeArray. These galaxies have absolute magnitudes ranging fromMB=-15.7 to -11.3. Yet they are mostly rotationallysupported, with maximum velocities going from 19 to 67 kms-1. Multicomponent mass models have been fitted to therotation curves to investigate the properties of their dark matter halosand the scaling laws of dark matter halo parameters. Dwarf galaxieshave, on average, a higher dark to luminous mass ratio, as well ashigher dark halo central densities than spiral galaxies. They have alarger dispersion of their dark matter properties both in terms of theirtotal dark matter amount and of their dark halo parameters, compared tospiral galaxies. It is therefore very difficult to predict a dwarfgalaxy rotation curve shape based only on its optical properties. Dwarfsare not well fitted by cold dark matter (CDM) halos of the type proposedby Navarro, Frenk, & White, even for ΛCDM models withΩ0 as low as 0.3. For two of our dwarfs we also haveHα rotation curves confirming the H I velocities, so thediscrepancy with the CDM models cannot be attributed to beam-smearingeffects.
| Arcsecond Positions of UGC Galaxies
We 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.
| Central Rotation Curves of Spiral Galaxies
We present high-resolution central-to-outer rotation curves for Sb, SBb,Sc, and SBc galaxies. We discuss their general characteristics,particularly their central behavior, as well as dependencies onmorphological types, activity, and peculiarity. The rotation curvesgenerally show a steep nuclear rise and high-velocity central rotation,followed by a broad maximum in the disk and then a flat rotation due tothe massive halo. Since the central high velocity and steep rise arecommon to all massive galaxies, they cannot be due to noncircularmotions. Disk rotation curves of barred galaxies show larger dispersionthan those of normal galaxies, probably because of noncircular motions.Interacting galaxies often show perturbed outer rotation curves, whiletheir central rotation shows no particular peculiarity. In addition,central activities, such as starbursts and active galactic nuclei,appear to show no particular correlation with the property of rotationcurves. This would suggest that the central activities are triggered bya more local effect than the global dynamical property.
| Extensive Spiral Structure and Corotation Resonance
Spiral density wave theories demand that grand-design spiral structurebe bounded, at most, between the inner and outer Lindblad resonances ofthe spiral pattern. The corotation resonance lies between the outer andthe inner Lindblad resonances. The locations of the resonances are atradii whose ratios to each other are rather independent of the shape ofthe rotation curve. The measured ratio of outer to inner extent ofspiral structure for a given spiral galaxy can be compared to thestandard ratio of corotation to inner Lindblad resonance radius. In thecase that the measured ratio far exceeds the standard ratio, it islikely that the corotation resonance is within the bright optical disk.Studying such galaxies can teach us how the action of resonances sculptsthe appearance of spiral disks. This paper reports observations of 140disk galaxies, leading to resonance ratio tests for 109 qualified spiralgalaxies. It lists candidates that have a good chance of having thecorotation resonance radius within the bright optical disk.
| Testing the Hypothesis of Modified Dynamics with Low Surface Brightness Galaxies and Other Evidence
The rotation curves of low surface brightness galaxies provide a uniquedata set with which to test alternative theories of gravitation over alarge dynamic range in size, mass, surface density, and acceleration.Many clearly fail, including any in which the mass discrepancy appearsat a particular length scale. One hypothesis, Modified NewtonianDynamics (MOND), is consistent with the data. Indeed, it accuratelypredicts the observed behavior. We find no evidence on any scale thatclearly contradicts MOND and much that supports it.
| Testing the Dark Matter Hypothesis with Low Surface Brightness Galaxies and Other Evidence
The severity of the mass discrepancy in spiral galaxies is stronglycorrelated with the central surface brightness of their disks.Progressively lower surface brightness galaxies have ever larger massdiscrepancies. No other parameter (luminosity, size, velocity,morphology) is so well correlated with the magnitude of the massdeficit. The rotation curves of low surface brightness disks thusprovide a unique data set with which to probe the dark matterdistribution in galaxies. The mass discrepancy is apparent from R = 0,giving a nearly direct map of the halo mass distribution. The luminousmass is insignificant. Interpreting the data in terms of dark matterleads to troublesome fine-tuning problems. Different observationsrequire contradictory amounts of dark matter. Structure formationtheories are as yet far from able to explain the observations.
| Systematics of Dark Halos in High Surface Brightness Spiral Galaxies
A study of mass distributions in 22 spiral galaxies, with rotationcurves taken from the literature and Hubble types ranging from Sa to Sd,is presented. It is demonstrated that a relation of the formM_d(r)=gammaM^1/2(r)r between the mass distribution of the luminouscomponents M(r) and that of the dark halo M_d(r) is consistent with theobserved kinematics with only the dark-to-visible mass ratio displayingsignificant variations between galaxies. The parameter gamma, which iscorrelated with M_dyn/M_lum, characterizes the relative importance ofthe dark-to-luminous mass. The model M/L ratio of the stellar component,M/L_B(stars), is correlated with the observed B - V color. In our samplethe average model of Sb galaxies is 2.7 M_ȯL^-1_solar for an average color <(B - V)_0> = 0.71, that of theSc's is = 1.5 M_solar L^-1_solar for <(B -V)_0> = 0.54, both values being in very good agreement withpopulation synthesis models. A large part of the intrinsic scatter inthe Tully-Fisher relation is due to the spread in gamma. The relation ofcoupling accounts for the disk-halo conspiracy in HSB spirals and isalso valid in LSB dwarf galaxies. Its universality in disk rotatingsystems implies the existence of a physical mechanism responsible forthe continuity between visible and dark mass distributions.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Hubble constant from sosie galaxies and HIPPARCOS geometrical calibration
New distances, larger than previous ones, have been obtained for M 31and M 81 based on the geometrical zero-point of the CepheidPeriod-luminosity relation provided by the HIPPARCOS satellite. Bycombining them with independent determinations we define reasonableranges for the distances of these important calibrating galaxies. Onthis basis, we determine the Hubble constant from the method of sosies(look-alike) galaxies, galaxies having the same characteristics than thecalibrators. The method is quite secure because it is purelydifferential and it does not depend on any assumption (apart from thenatural one that two sosies galaxies have similar absoluteluminosities). Nevertheless, the Malmquist bias has to be taken intoaccount. The observations behave exactly as predicted from theanalytical formulation of the bias. Thus, rejecting galaxies which areaffected by the Malmquist bias we derive the Hubble constant: H_o = 60+/- 10 (external) km.s^{-1}.Mpc^{-1} If we strictly use the calibrationobtained with HIPPARCOS and if the bias found in the Period-LuminosityRelation is considered, the Hubble constant is smaller than this (~ 55km.s(-1}.Mpc({-1)) ). This gives arguments in favour of thelong-distance scale. We briefly discuss possible improvements aiming atstill reducing the uncertainty.
| The dark and visible matter content of low surface brightness disc galaxies
We present mass models of a sample of 19 low surface brightness (LSB)galaxies and compare the properties of their constituent mass componentswith those of a sample of high surface brightness (HSB) galaxies. Wefind that LSB galaxies are dark matter dominated. Their halo parametersare only slightly affected by assumptions on stellar mass-to-lightratios. Comparing LSB and HSB galaxies we find that mass models derivedusing the maximum disc hypothesis result in the discs of LSB galaxieshaving systematically higher stellar mass-to-light ratios than HSBgalaxies of similar rotation velocity. This is inconsistent with allother available evidence on the evolution of LSB galaxies. We arguetherefore that the maximum disc hypothesis does not provide arepresentative description of the LSB galaxies and their evolution. Massmodels with stellar mass-to-light ratios determined by the colours andstellar velocity dispersions of galactic discs imply that LSB galaxieshave dark matter haloes that are more extended and less dense than thoseof HSB galaxies. Surface brightness is thus related to the haloproperties. LSB galaxies are slowly evolving, low-density and darkmatter dominated galaxies.
| Search and Redshift Survey for IRAS Galaxies behind the Milky Way and Structure of the Local Void
This is the third and final paper of our systematic visual search forIRAS galaxies behind the Milky Way at |b| <= 15 deg. This paperpresents a catalog of 950 IRAS galaxies with 60 mu m flux densitieslarger than 0.6 Jy located between l = 0 deg and 150 deg, of which 293are newly identified by this search. We made a redshift survey for theidentified galaxies and obtained new redshift data of 171 galaxies. Wealso present newly measured redshifts of 27 IRAS galaxies between l =150 deg and 225 deg at |b| <= 15 deg. In this paper we studied thestructure of the Local void using IRAS galaxies and galaxies from theThird Reference Catalogue of Bright Galaxies in the region l = 30deg--120 deg and b = -50 deg to +30 deg. The center of the Local voidturned out to be located at l ~ 60 deg, b ~ -15 deg, and cz ~ 2500 kms-1, and the size is about 2500 km s-1 along the direction toward thecenter.
| Nuclear Rotation Curves of Galaxies in the Co-Line Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2428S&db_key=AST
| Neutral Hydrogen Distributions and Kinematics of Giant Low Surface=20 Brightness Disk Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1858P&db_key=AST
| Short 21-cm WSRT observations of spiral and irregular galaxies. HI properties.
We present the analysis of neutral hydrogen properties of 108 galaxies,based on short 21-cm observations with the Westerbork Synthesis RadioTelescope (WSRT). The results of two HI surveys are analysed toinvestigate the existence of relations between optical and HIproperties, like diameters, hydrogen masses and average surfacedensities. For all galaxies in our sample we find that the HI diameter,defined at a surface density level of 1Msun_/pc^2^, is largerthan the optical diameter, defined at the 25^th^mag/arcsec^2^ isophotallevel. The Hi-to-optical-diameter ratio does not depend on morphologicaltype or luminosity. The strongest, physically meaningful, correlationfor the sample of 108 galaxies is the one between logM_HI_ and logD_HI_,with a slope of 2. This implies that the HI surface density averagedover the whole HI disc is constant from galaxy to galaxy, independent ofluminosity or type. The radial HI surface density profiles are studiedusing the technique of principal component analysis. We find that about81% of the variation in the density profiles of galaxies can beexplained by two dimensions. The most dominant component can be relatedto "scale" and the second principal component accounts for the variancein the behaviour of the radial profile in the central parts of galaxies(i.e. "peak or depression") . The third component accounts for 7% of thevariation and is most likely responsible for bumps and wiggles in theobserved density profiles.
| HI observations of low surface brightness galaxies: probing low-density galaxies
We present Very Large Array (VLA) and Westerbork Synthesis RadioTelescope (WSRT) 21-cm Hi observations of 19 late-type low surfacebrightness (LSB) galaxies. Our main findings are that these galaxies, aswell as having low surface brightnesses, have low Hi surface densities,about a factor of ~3 lower than in normal late-type galaxies. We showthat LSB galaxies in some respects resemble the outer parts of late-typenormal galaxies, but may be less evolved. LSB galaxies are more gas-richthan their high surface brightness counterparts. The rotation curves ofLSB galaxies rise more slowly than those of HSB galaxies of the sameluminosity, with amplitudes between 50 and 120 km s^-1, and are oftenstill increasing at the outermost measured point. The shape of therotation curves suggests that LSB galaxies have low matter surfacedensities. We use the average total mass surface density of a galaxy asa measure for the evolutionary state, and show that LSB galaxies areamong the least compact, least evolved galaxies. We show that bothM_Hi/L_B and M_dyn/L_B depend strongly on central surface brightness,consistent with the surface brightness-mass-to-light ratio relationrequired by the Tully-Fisher relation. LSB galaxies are therefore slowlyevolving galaxies, and may well be low surface density systems in allrespects.
| The Published Extended Rotation Curves of Spiral Galaxies: Confrontation with Modified Dynamics
A sample of 22 spiral galaxy rotation curves, measured in the 21 cm lineof neutral hydrogen, is considered in the context of Milgrom's modifieddynamics (MOND). Combined with the previous, highly selected sample ofBegeman et al., this constitutes the current total sample of galaxieswith published (or available) extended rotation curves and photometricobservations of the light distribution. This is the observational basisof present quantitative understanding of the discrepancy between thevisible mass and classical dynamical mass in galaxies. It is found thatthe gravitational force calculated from the observed distribution ofluminous material and gas by use of the simple MOND formula can accountfor the overall shape and amplitude of these 22 rotation curves, and insome cases, the predicted curve agrees with the observed rotation curvein detail. The fitted rotation curves have, in 13 cases, only one freeparameter, which is the mass-to-light ratio of the luminous disk; innine cases, there is an additional free parameter, which is M/L of acentral bulge or light concentration. The values of the global M/L(bulge plus disk) are reasonable and, when the gas mass is alsoincluded, show a scatter consistent with that in the Tully-Fisherrelation. The success of the MOND prescription in predicting therotation curves in this larger, less stringently selected sample lendsfurther support to the idea that dynamics or gravity is non-Newtonian inthe limit of low acceleration and that it is unnecessary to invoke thepresence of large quantities of unseen matter.
| Large-Scale Structure at Low Galactic Latitude
We have extended the CfA Redshift Survey to low galactic latitudes toinvestigate the relation between the Great Wall in the North GalacticCap and the Perseus-Pisces chain in the South Galactic Cap. We presentredshifts for 2020 galaxies in the Catalogue of Galaxies and of Clustersof Galaxies (Zwicky et al. 1961-68, CGCG) in the following regions: 4^h^<= α <= 8^h^, 17^h^ <= α <= 20^h^, 0^deg^ <=δ <= 45^deg^. In these regions, the redshift catalogue includes1664 galaxies with B(0) <= 15.5 (of which 820 are newly measured) andis 97% complete. We also include redshifts for an additional 356galaxies in these regions with B(O) > 15.5; of these, 148 werepreviously unmeasured. The CGCG samples the galaxy distribution down tob_II_ = 10^deg^. In this paper, we discuss the acquisition and reductionof the spectra, and we examine the qualitative features of the redshiftdistribution. The Great Wall and the Perseus-Pisces chain are not simplyconnected across the Zone of Avoidance. These structures, which at firstappear to be coherent on scales of ~100 h^-1^ Mpc or more, actually formthe boundaries of neighboring voids of considerably smaller scale,approximately 50h^-1^ Mpc. The structures delineated by ouroptically-selected sample are qualitatively similar to those detected bythe far-infrared-selected IRAS 1.2 Jansky Survey (Fisher et al. 1995).Although the IRAS survey probes more deeply into the Zone of Avoidance,our optically-selected survey provides better sampling of structures atb_II_ >= 10^deg^.
| High Resolution Neutral Hydrogen Observations of the Barred Spiral Galaxy NGC 1365
We have observed the barred spiral galaxy NGC 1365 with the VLA in theBnA, CnB, and DnC configurations. We have refined the flux determinationfor partially cleaned images of very non-Gaussian VLA multiconfigurationnaturally weighted beams as described in the Appendix. NGC 1365 is foundto contain 15.2 x 1O^9^M_sun_ of HI. The velocity field is stronglyaffected by the bar in the inner parts, but it is relatively undisturbedin the outer parts. The H I morphology is similar to that in theoptical, but the HI is more uniformly distributed and there is no traceof the bar. NGC 1365 is found to have four well developed arms and tworudimentary ones. The inclination of the inner disk is determined to be40^deg^, substantially different from that obtained by optical means(55^deg^). There is a central H I hole which is filled with moleculargas. We find that NGC 1365 has the most strongly dropping rotation curveknown to us, falling to 63% of its peak value. It starts to drop alreadyat 2/3 of R_25_. In the outer 40% it is well modeled by a Keplerian. Wededuce a total mass for NGC 1365 of 3.9 x 10^11^ M_sun_, resulting in aM/L_B_ of 4.8. Strongly noncircular motions (radial velocity residualsup to 100 km s^-1^) are seen in the bar region. The influence of the bardrops rapidly outside of it and the orbits become rather circular. Theratio between H I diameter and R_25_ is unusually small and NGC 1365lacks a extended H I halo. A similar behavior is displayed by NGC 1300,data for which we have reduced anew, and we discuss whether this couldbe common among strongly barred galaxies. NGC 1365 has a warp whichstarts already at 2/3 of R_25_. The classical resonances may beidentified with kinematical and morphological features of the spiralarms. The good agreement with gas dynamical models give strong supportto this identification. We find a common corotation radius of arms andbar at 1.4 times the bar major axis. This corresponds to a patternvelocity of 21 +/- I km s^-`^ kpc^-1^. The -4/1 resonance is the mostclearly seen feature. The corotation radius corresponds to the maximumdeviation from circular motion in the arms. The bright parts of the armsend at the OLR. The spiral arms of NGC 1365 have a very circularsymmetry when viewed face on, and are substantially more tightly woundthan they appear in the sky plane. NGC 1365 shows a straight front onthe W side, which may be a sign of interaction with the intergalacticmedium. The H I is elongated in the direction of the Fornax clustercenter.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
