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The rotation curves shapes of late-type dwarf galaxies
We present rotation curves derived from H I observations for a sample of62 galaxies that have been observed as part of the Westerbork H I Surveyof Spiral and Irregular Galaxies (WHISP) project. These rotation curveshave been derived by interactively fitting model data cubes to theobserved cubes. This procedure takes the rotation curve shape, the H Idistribution, the inclination, and the size of the beam into account,and makes it possible to correct for the effects of beam smearing. Acomparison with higher spatial resolution Hα rotation curvesavailable in the literature shows that there is general agreementbetween the two. The late-type dwarf galaxies in our sample haverotation-curve shapes that are similar to those of late-type spiralgalaxies, in the sense that their rotation curves, when expressed inunits of disk scale lengths, rise as steeply in the inner parts andstart to flatten at two disk scale lengths. None of the galaxies in oursample have solid-body rotation curves that extend beyond three diskscale lengths. The logarithmic slopes between two disk scale lengths andthe last measured point on the rotation curve is similar betweenlate-type dwarf and spiral galaxies. Thus, whether the flat part of therotation curve is reached or not seems to depend more on the extent ofthe rotation curve than on its amplitude. We also find that the outerrotation curve shape does not strongly depend on luminosity, at leastfor galaxies fainter than MR ~ -19. We find that in spiralgalaxies and even in the central regions of late-type dwarf galaxies,the shape of the central distribution of light and the inner rise of therotation curve are related. This implies that galaxies with strongercentral concentrations of light also have higher central mass densities,and it suggests that the luminous mass dominates the gravitationalpotential in the central regions, even in low surface brightness dwarfgalaxies.
| GHASP: an Hα kinematic survey of 203 spiral and irregular galaxies - VII. Revisiting the analysis of Hα data cubes for 97 galaxies
The Gassendi HAlpha survey of SPirals survey (GHASP) consists of 3DHα data cubes for 203 spiral and irregular galaxies, covering alarge range in morphological types and absolute magnitudes, forkinematics analysis. It is the largest sample of Fabry-Perot datapublished up to now. In order to provide an homogenous sample, reducedand analysed using the same procedure, we present in this paper the newreduction and analysis for a set of 97 galaxies already published inprevious papers but now using the new data reduction procedure adoptedfor the whole sample. The GHASP survey is now achieved and the wholesample is reduced using the adaptive binning techniques based on Voronoitessellations. We have derived Hα data cubes from which arecomputed Hα maps, radial velocity fields as well as residualvelocity fields, position-velocity diagrams, rotation curves andkinematical parameters for almost all galaxies. The rotation curves, thekinematical parameters and their uncertainties are computedhomogeneously using the new method based on the power spectrum of theresidual velocity field. This paper provides the kinematical parametersfor the whole sample. For the first time, the integrated Hαprofiles have been computed and are presented for the whole sample. Thetotal Hα fluxes deduced from these profiles have been used inorder to provide a flux calibration for the 203 GHASP galaxies. Thispaper confirms the conclusions already drawn from half the sampleconcerning (i) the increased accuracy of position angles measurementsusing kinematical data, (ii) the difficulty to have robustdeterminations of both morphological and kinematical inclinations inparticular for low-inclination galaxies and (iii) the very goodagreement between the Tully-Fisher relationship derived from our dataand previous determinations found in the literature.
| Diffuse H I Disks in Isolated Galaxies
In order to investigate the contribution of diffuse components to theirtotal H I emission, we have obtained high-precision H I line fluxdensities with the 100 m Green Bank Telescope for a sample of 100isolated spiral and irregular galaxies which we have previously observedwith the 43 m telescope. A comparison of the observed H I line fluxesobtained with the two different telescopes, characterized by half-powerbeam widths of 9' and 21', respectively, exploits a ``beam-matching''technique to yield a statistical determination of the occurrence ofdiffuse H I components in their disks. A simple model of the H Idistribution within a galaxy well describes ~75% of the sample andaccounts for all of the H I line flux density. The remaining galaxiesare approximately evenly divided into two categories: those which appearto possess a significantly more extensive H I distribution than themodel predicts, and those for which the H I distribution is morecentrally concentrated than predicted. Examples of both extremes can befound in the literature, but little attention has been paid to thecentrally concentrated H I systems. Our sample has demonstrated thatgalaxies do not commonly possess extended regions of low surfacebrightness H I gas which is not accounted for by our currentunderstanding of the structure of H I disks. Eight H I-rich companionsto the target objects are identified, and a set of extragalactic H Iline flux density calibrators is presented.
| High-Resolution Optical Velocity Fields of 11 Low Surface Brightness Galaxies
We present high-resolution two-dimensional velocity fields from integralfield spectroscopy, along with derived rotation curves for 11 lowsurface brightness galaxies. We fit NFW and pseudoisothermal halo modelsto the new data combined with previous long-slit and H I data. In mostcases, we find the pseudoisothermal halo to better represent the datathan the NFW halo, as the NFW concentrations are often lower thanexpected for a ΛCDM cosmology. We also compare our results toprevious studies and find that including the new two-dimensional opticaldata does not significantly alter the halo parameters but does decreasethe uncertainties by roughly a factor of 2.
| 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.
| GHASP: an Hα kinematic survey of spiral and irregular galaxies - IV. 44 new velocity fields. Extension, shape and asymmetry of Hα rotation curves
We present Fabry-Perot observations obtained in the frame of the GHASPsurvey (Gassendi HAlpha survey of SPirals). We have derived the Hαmap, the velocity field and the rotation curve for a new set of 44galaxies. The data presented in this paper are combined with the datapublished in the three previous papers providing a total number of 85 ofthe 96 galaxies observed up to now. This sample of kinematical data hasbeen divided into two groups: isolated (ISO) and softly interacting(SOFT) galaxies. In this paper, the extension of the Hα discs, theshape of the rotation curves, the kinematical asymmetry and theTully-Fisher relation have been investigated for both ISO and SOFTgalaxies. The Hα extension is roughly proportional toR25 for ISO as well as for SOFT galaxies. The smallestextensions of the ionized disc are found for ISO galaxies. The innerslope of the rotation curves is found to be correlated with the centralconcentration of light more clearly than with the type or thekinematical asymmetry, for ISO as well as for SOFT galaxies. The outerslope of the rotation curves increases with the type and with thekinematical asymmetry for ISO galaxies but shows no special trend forSOFT galaxies. No decreasing rotation curve is found for SOFT galaxies.The asymmetry of the rotation curves is correlated with themorphological type, the luminosity, the (B-V) colour and the maximalrotational velocity of galaxies. Our results show that the brightest,the most massive and the reddest galaxies, which are fast rotators, arethe least asymmetric, meaning that they are the most efficient withwhich to average the mass distribution on the whole disc. Asymmetry inthe rotation curves seems to be linked with local star formation,betraying disturbances of the gravitational potential. The Tully-Fisherrelation has a smaller slope for ISO than for SOFT galaxies.
| A Digital Archive of H I 21 Centimeter Line Spectra of Optically Targeted Galaxies
We present a homogeneous compilation of H I spectral parametersextracted from global 21 cm line spectra for some 9000 galaxies in thelocal universe (heliocentric velocity-200
| GHASP: an Hα kinematic survey of spiral and irregular galaxies - III. 15 new velocity fields and study of 46 rotation curves
We 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.
| The Westerbork HI survey of spiral and irregular galaxies. II. R-band surface photometry of late-type dwarf galaxies
R-band surface photometry is presented for 171 late-type dwarf andirregular galaxies. For a subsample of 46 galaxies B-band photometry ispresented as well. We present surface brightness profiles as well asisophotal and photometric parameters including magnitudes, diameters andcentral surface brightnesses. Absolute photometry is accurate to 0.1 magor better for 77% of the sample. For over 85% of the galaxies the radialsurface brightness profiles are consistent with published data withinthe measured photometric uncertainty. For most of the galaxies in thesample H I data have been obtained with the Westerbork Synthesis RadioTelescope. The galaxies in our sample are part of the WHISP project(Westerbork H I Survey of Spiral and Irregular Galaxies), which aims atmapping about 500 nearby spiral and irregular galaxies in H I. Theavailability of H I data makes this data set useful for a wide range ofstudies of the structure, dark matter content and kinematics oflate-type dwarf galaxies. Based on observations made with INT operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias. The tables in Appendix A are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/863. Thefigures in Appendix B are only available in electronic formhttp://www.edpsciences.org
| The Westerbork HI survey of spiral and irregular galaxies. I. HI imaging of late-type dwarf galaxies
Neutral hydrogen observations with the Westerbork Synthesis RadioTelescope are presented for a sample of 73 late-type dwarf galaxies.These observations are part of the WHISP project (Westerbork H I Surveyof Spiral and Irregular Galaxies). Here we present H I maps, velocityfields, global profiles and radial surface density profiles of H I, aswell as H I masses, H I radii and line widths. For the late-typegalaxies in our sample, we find that the ratio of H I extent to opticaldiameter, defined as 6.4 disk scale lengths, is on average 1.8 +/- 0.8,similar to that seen in spiral galaxies. Most of the dwarf galaxies inthis sample are rich in H I, with a typical Mion {Hi}/L_B of1.5. The relative H I content M_ion {HI}/L_R increases towards fainterabsolute magnitudes and towards fainter surface brightnesses. Dwarfgalaxies with lower average H I column densities also have lower averageoptical surface brightnesses. We find that lopsidedness is as commonamong dwarf galaxies as it is in spiral galaxies. About half of thedwarf galaxies in our sample have asymmetric global profiles, a thirdhas a lopsided H I distribution, and about half shows signs of kinematiclopsidedness.
| GHASP: A 3-D Survey of Spiral and Irregular Galaxies at Hα
Not Available
| 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.
| Asymmetry in high-precision global H I profiles of isolated spiral galaxies
New high-SNR 21 cm H I line profiles have been obtained for 104 galaxieswith the Green Bank 43 m telescope. The primary sample is composed ofisolated spirals with no known optical companions within a 1 radius anda median ratio of optical diameter to beamwidth of 0.17. An effort wasmade to ensure linearity of baseline fitting and precise flux densitycalibration to better than 5 percent. Two quantitative measures ofasymmetry are applied to assess the occurrence of lopsidedness in theglobal H I profiles. In agreement with previous estimates, half thegalaxies show significant H I profile asymmetries. The lopsidednesscannot be explained by pointing offsets but, rather, must result fromnoncircular motions, confusion with unidentified companions within thetelescope beam, or true distortions in the H I distribution.
| Optical positions and 327 MHz flux-densities of UGC galaxies in selected Westerbork fields
The study presents accurate optical positions of 421 UGC galaxies whichare used to search for 30 92-cm WSRT fields observed for emission fromthese galaxies. Good 92-cm flux densities were obtained for 140galaxies, marginal flux densities for 71 galaxies, and upper limits for210 galaxies. For 35 galaxies, spectral indices in the decimeterwavelength range are determined. The mean spectral index for spiralgalaxies (0.72 +/- 0.03) is very similar to that of elliptical galaxies(0.64 +/- 0.10). The four multiple systems in the sample have a muchflatter spectral index (-0.21 +/- 0.07), from which the presence of asignificant thermal component in their total radio emission issuggested. Comparison with IRAS results show that about half of thegalaxies detected at radio wavelengths are detected in the FIR. It isproposed that some spiral galaxies are anomalously weak in the IR ascompared with their radio brightness.
| Uncertainties in 21 centimeter redshifts. I - Data
High-precision data on the 21-cm redshifts, profile widths, and shapesfor 625 galaxies are presented. Each galaxy is listed in across-identification and morphology table. High-resolution spectra arealso given for each galaxy. Internal redshift consistency is roughly 1km/s for galaxies for which the S/N is above 15. No systematic effectshave been found which might influence the observed redshift quantizationat 72.5 km/s or its submultiples.
| Neutral hydrogen in two extremely isolated galaxies
Maps made with the Westerbork Synthesis Radio Telescope of 21-cm lineemission from NGC 2712 and 5301 are presented; these spirals are the twomost isolated galaxies ever to have been studied in this way. It istentatively concluded that isolated galaxies do not have more extended HI distributions than nonisolated galaxies; hence, tidal stripping maynot be an important factor in the history of most present-day spirals.In addition, it is suggested that warps and asymmetries in the gasdistributions of spirals can be internally generated and sustained,since they are found in isolated as well as nonisolated galaxies. It isnoted that there remain differences between isolated and nonisolatedgalaxies which deserve further study.
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