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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.
| The Hα Galaxy Survey . III. Constraints on supernova progenitors from spatial correlations with Hα emission
Aims.We attempt to constrain progenitors of the different types ofsupernovae from their spatial distributions relative to star formationregions in their host galaxies, as traced by Hα + [Nii] lineemission. Methods: .We analyse 63 supernovae which have occurredwithin galaxies from our Hα survey of the local Universe. Threestatistical tests are used, based on pixel statistics, Hα radialgrowth curves, and total galaxy emission-line fluxes. Results:.Many type II supernovae come from regions of low or zero emission lineflux, and more than would be expected if the latter accurately traceshigh-mass star formation. We interpret this excess as a 40% "Runaway"fraction in the progenitor stars. Supernovae of types Ib and Ic doappear to trace star formation activity, with a much higher fractioncoming from the centres of bright star formation regions than is thecase for the type II supernovae. Type Ia supernovae overall show a weakcorrelation with locations of current star formation, but there isevidence that a significant minority, up to about 40%, may be linked tothe young stellar population. The radial distribution of allcore-collapse supernovae (types Ib, Ic and II) closely follows that ofthe line emission and hence star formation in their host galaxies, apartfrom a central deficiency which is less marked for supernovae of typesIb and Ic than for those of type II. Core-collapse supernova ratesoverall are consistent with being proportional to galaxy totalluminosities and star formation rates; however, within this total thetype Ib and Ic supernovae show a moderate bias towards more luminoushost galaxies, and type II supernovae a slight bias towardslower-luminosity hosts.
| 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
| The inner structure of ΛCDM haloes - II. Halo mass profiles and low surface brightness galaxy rotation curves
We use a set of high-resolution cosmological N-body simulations toinvestigate the inner mass profile of galaxy-sized cold dark matter(CDM) haloes. These simulations extend the numerical convergence studypresented in Paper I of this series, and demonstrate that the massprofile of CDM galaxy haloes can be robustly estimated beyond a minimumconverged radius of order rconv~ 1h-1 kpc in ourhighest-resolution runs. The density profiles of simulated haloes becomeprogressively shallower from the virial radius inwards, and show no signof approaching a well-defined power law near the centre. Atrconv, the density profile is steeper than expected from theformula proposed by Navarro, Frenk & White, which has aρ~r-1 cusp, but significantly shallower than the steeplydivergent ρ~r-1.5 cusp proposed by Moore et al. Weperform a direct comparison of the spherically averaged dark mattercircular velocity profiles with Hα rotation curves of a sample oflow surface brightness (LSB) galaxies. We find that most galaxies in thesample (about 70 per cent) have rotation curves that are consistent withthe structure of CDM haloes. Of the remainder, 20 per cent have rotationcurves which cannot be fit by any smooth fitting function with few freeparameters, and 10 per cent are inconsistent with CDM haloes. However,the latter consist mostly of rotation curves that do not extend to largeenough radii to accurately determine their shapes and maximumvelocities. We conclude that the inner structure of CDM haloes is notmanifestly inconsistent with the rotation curves of LSB galaxies.
| The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies
We discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/
| First results from the HI Jodrell All Sky Survey: inclination-dependent selection effects in a 21-cm blind survey
Details are presented of the HI Jodrell All Sky Survey (HIJASS). HIJASSis a blind neutral hydrogen (HI) survey of the northern sky (δ> 22°), being conducted using the multibeam receiver on theLovell Telescope (full width at half-maximum beamwidth 12 arcmin) atJodrell Bank. HIJASS covers the velocity range -3500 to 10 000 kms-1, with a velocity resolution of 18.1 km s-1 andspatial positional accuracy of ~2.5 arcmin. Thus far about 1115deg2 of sky have been surveyed. The average rms noise duringthe early part of the survey was around 16 mJy beam-1.Following the first phase of the Lovell Telescope upgrade (in 2001), therms noise is now around 13 mJy beam-1. We describe themethods of detecting galaxies within the HIJASS data and of measuringtheir HI parameters. The properties of the resulting HI-selected sampleof galaxies are described. Of the 222 sources so far confirmed, 170 (77per cent) are clearly associated with a previously catalogued galaxy. Afurther 23 sources (10 per cent) lie close (within 6 arcmin) to apreviously catalogued galaxy for which no previous redshift exists. Afurther 29 sources (13 per cent) do not appear to be associated with anypreviously catalogued galaxy. The distributions of peak flux, integratedflux, HI mass and cz are discussed. We show, using the HIJASS data, thatHI self-absorption is a significant, but often overlooked, effect ingalaxies with large inclination angles to the line of sight. Properlyaccounting for it could increase the derived HI mass density of thelocal Universe by at least 25 per cent. The effect that this will haveon the shape of the HI mass function will depend on how self-absorptionaffects galaxies of different morphological types and HI masses. We alsoshow that galaxies with small inclinations to the line of sight may alsobe excluded from HI-selected samples, since many such galaxies will haveobserved velocity widths that are too narrow for them to bedistinguished from narrow-band radio-frequency interference. This effectwill become progressively more serious for galaxies with smallerintrinsic velocity widths. If, as we might expect, galaxies with smallerintrinsic velocity widths have smaller HI masses, then compensating forthis effect could significantly steepen the faint-end slope of thederived HI mass function.
| The Central Mass Distribution in Dwarf and Low Surface Brightness Galaxies
We present high-resolution Hα rotation curves for a sample of 15dwarf and low surface brightness galaxies. From these we derive limitson the slopes of the central mass distributions, using both a directinversion of the rotation curves and detailed mass models. Assuming thatthe density distributions of dark matter halos follow a power law atsmall radii, ρ(r)~r-α, we find inner slopes in therange 0<~α<~1 for most galaxies. Thus, even with therelatively high spatial resolution of the Hα rotation curvespresented here, the inner slopes are poorly constrained. In generalhalos with constant density cores (α=0) provide somewhat betterfits, but the majority of our galaxies (~75%) are also consistent withα=1, as long as the R-band stellar mass-to-light ratios aresmaller than about 2. Halos with α=1.5, however, are ruled out invirtually every case. In order to investigate the robustness of theseresults we discuss and model several possible causes of systematicerrors, including noncircular motions, galaxy inclination, slit width,seeing, and slit alignment errors. Taking the associated uncertaintiesinto account, we conclude that even for the ~25% of the cases whereα=1 seems inconsistent with the rotation curves, we cannot ruleout cusp slopes this steep. Inclusion of literature samples similar tothe one presented here leads to the same conclusion when the possibilityof systematic errors is taken into account. In the ongoing debate onwhether the rotation curves of dwarf and low surface brightness galaxiesare consistent with predictions for a cold dark matter universe, weargue that our sample and the literature samples discussed in this paperprovide insufficient evidence to rule out halos with α=1. At thesame time, we note that none of the galaxies in these samples requirehalos with steep cusps, as most are equally well or better explained byhalos with constant density cores.
| An H I/Optical Atlas of Isolated Galaxies
We present an H I and optical survey of 41 extremely isolated galaxiesin an attempt to search for the gaseous remnants of the galaxy formationprocess, predicted to exist by hierarchical models of galaxy formation.By observing extremely isolated, quiescent, nonpeculiar galaxies weminimize the chances that any extragalactic H I found will be anothergalaxy, tidal debris, or ejecta from a galactic fountain or superwind.We have obtained new and archival data from the VLA and ATCA in a searchfor H I clouds down to MHI~107 Msolararound these galaxies. We found 13 H I-rich companions around 10 of the41 galaxies surveyed. Optical imaging finds spatially coincident starsassociated with all 13 companions. We find that the isolated galaxieshave properties fairly similar to those of field galaxies, while thecompanions are similar to dwarf irregular galaxies. The presence ofstars in all 13 companions suggests that H I clouds without starsdiscovered by other authors around field galaxies are not primordial andmost likely have either a tidal or ejecta origin.
| Hα Rotation Curves: The Soft Core Question
We present high-resolution Hα rotation curves of four late-typedwarf galaxies and two low surface brightness (LSB) galaxies, for whichaccurate H I rotation curves are available from the literature.Observations are carried out at Telescopio Nazionale Galileo. For LSBF583-1 an innovative dispersing element was used, the Volume PhaseHolographic, with a dispersion of about 0.35 Å pixel-1.We find good agreement between the Hα data and the H Iobservations and conclude that the H I data for these galaxies suffervery little from beam smearing. We show that the optical rotation curvesof these dark matter-dominated galaxies are best fitted by the Burkertprofile. In the centers of galaxies, where the N-body simulationspredict cuspy cores and fast rising rotation curves, our data seem to bein better agreement with the presence of soft cores.
| 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.
| The Distribution of Atomic Hydrogen around Two Irregular Galaxies
We present radio interferometric observations of two irregular galaxiesthat were candidates for having unusually extended H I emission. Thegalaxies, UGC 199 and DDO 26, otherwise appeared to be normal,low-luminosity systems with modest star formation rates. To a detectionlimit of (2-3)×1019 cm-2 at a resolution ofabout 50", however, the H I around neither galaxy is unusually extendedcompared with other irregular galaxies. The H I around UGC 199 appearsas a regular, symmetric distribution with regular rotation and a maximumrotation speed of about 80 km s-1. By contrast, the H Iaround DDO 26 shows a concentration into two blobs with an arm in theouter parts to the northwest and some additional emission to thenorthwest of that. The kinematical major axis is approximately 75°from the H I and optical morphological axis, which is unusual for Imgalaxies. In addition the velocity field in the outer parts of thegalaxy is messy, and the velocity profiles at the two H I peaks arebroad. We suggest that DDO 26 has been perturbed externally or may betwo dwarfs in the process of merging.
| The angular momentum content of dwarf galaxies: new challenges for the theory of galaxy formation
We compute the specific angular momentum distributions for a sample oflow-mass disc galaxies observed by Swaters. We compare thesedistributions to those of dark matter haloes obtained by Bullock et al.from high-resolution N-body simulations of structure formation in aΛCDM universe. We find that although the disc mass fractions aresignificantly smaller than the universal baryon fraction, the totalspecific angular momenta of the discs are in good agreement with thoseof dark matter haloes. This suggests that discs form out of only a smallfraction of the available baryons, but yet manage to draw most of theavailable angular momentum. In addition we find that the angularmomentum distributions of discs are clearly distinct from those of thedark matter; discs lack predominantly both low and high specific angularmomenta. Understanding these findings in terms of a coherent picture fordisc formation is challenging. Cooling, feedback and stripping, whichare the main mechanisms to explain the small disc mass fractions found,seem unable to simultaneously explain the angular momentum distributionsof the discs. In fact, it seems that the baryons that make up the discsmust have been born out of angular momentum distributions that areclearly distinct from those of ΛCDM haloes. However, the dark andbaryonic mass components experience the same tidal forces, and it istherefore expected that they should have similar angular momentumdistributions. Therefore, understanding the angular momentum content ofdisc galaxies remains an important challenge for our picture of galaxyformation.
| Dwarf galaxy rotation curves and the core problem of dark matter haloes
The standard cold dark matter (CDM) model has recently been challengedby the claim that dwarf galaxies have dark matter haloes withconstant-density cores, whereas CDM predicts haloes with steeply cuspeddensity distributions. Consequently, numerous alternative dark mattercandidates have recently been proposed. In this paper we scrutinize theobservational evidence for the incongruity between dwarf galaxies andthe CDM model. To this end, we analyse the rotation curves of 20late-type dwarf galaxies studied by Swaters. Taking the effects of beamsmearing and adiabatic contraction into account, we fit mass models tothese rotation curves with dark matter haloes with different cuspslopes, ranging from constant-density cores to r-2 cusps.Even though the effects of beam smearing are small for these data, theuncertainties in the stellar mass-to-light ratio and the limited spatialsampling of the halo's density distribution hamper a unique massdecomposition. Consequently, the rotation curves in our sample cannot beused to discriminate between dark haloes with constant-density cores andr-1 cusps. We show that the dwarf galaxies analysed here areconsistent with CDM haloes in a ΛCDM cosmology, and that there isthus no need to abandon the idea that dark matter is cold andcollisionless. However, the data are also consistent with anyalternative dark matter model that produces dark matter haloes withcentral cusps less steep than r-1.5. In fact, we argue thatbased on existing Hi rotation curves alone, at best weak limits can beobtained on cosmological parameters and/or the nature of the darkmatter. In order to make progress, rotation curves with higher spatialresolution and independent measurements of the mass-to-light ratio ofthe disc are required.
| 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.
| Gas-Rich Companions of Isolated Galaxies
We have used the VLA to search for gaseous remnants of the galaxyformation process around six extremely isolated galaxies. We found twodistinct H I clouds around each of two galaxies in our sample (UGC 9762and UGC 11124). These clouds are rotating and appear to have opticalcounterparts, strongly implying that they are typical dwarf galaxies.The companions are currently weakly interacting with the primary galaxybut look to be in stable orbits as they have dynamical frictiontimescales of 5-100 Gyr. In one case, (UGC 11124N), we see ongoingaccretion of the companion onto the primary galaxy. The small mass ratioinvolved in this interaction means that the resulting merger will be aminor one. The companion does, however, contain enough gas that themerger will represent a significant infusion of fuel to drive futurestar formation in UGC 11124 while building up the mass of the disk.
| 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.
| Supernova 1997db in UGC 11861
IAUC 6711 available at Central Bureau for Astronomical Telegrams.
| Supernova 1995ag in UGC 11861
IAUC 6244 available at Central Bureau for Astronomical Telegrams.
| Northern dwarf and low surface brightness galaxies. II - The Green Bank neutral hydrogen survey
The paper reports neutral hydrogen observations of a large sample ofdwarf and other low surface brightness galaxies. A detailed discussionand error analysis of the observations are presented, and spectra aredisplayed for 329 galaxies detected for the first time, or detected withsubstantially better signal-to-noise ratios than achieved previously.The positions on the sky of 667 galaxies meeting the present selectioncriteria north of delta = 38 deg are shown. The distribution of theredshifts of galaxies detected at Green Bank is illustrated. The GreenBank detections tapered off strongly below the median H I flux of 3.7 Jykm/s detected at Arecibo: only 12 percent of the Green Bank sample wasdetected with smaller fluxes.
| Hydroxyl in galaxies. I - Surveys with the NRAO 300 FT telescope
Results are presented of a search for 1667- and 1665-MHz mainline OHtransitions for 321 galaxies, which were observed during four separatesessions at the NRAO 300-ft telescope in the period 1984-1987. Threedetections of OH megamasers are reported, as well as detections of threenew OH absorption sources. The observational sample contains sourcesfrom a variety of catalogs and represents different criteria. Theresults for the whole sample confirm that FIR luminosity and colorcriteria used for these surveys are indeed optimized for findingmegamasers. The results also confirm that detecting distant highluminosity OH megamasers is considerably more successful than findingnearby weak masers.
| Properties of the redshift. I - Data and calibrations
Data at 21 cm are presented for 100 galaxies intended to be used forsystem comparisons between the NRAO 140 and 300 foot telescope and the100 m Effelsberg telescope. Data from the 300 foot telescope are alsogiven for galaxies selected for overlap comparisons with older studies.Flux calibrations and measurement uncertainties in flux, redshifts,profile width, and profile shape are discussed.
| Comparisons between 21 CM data from Effelsberg and Greenbank
Comparison of 21-cm data from the Effelsberg 100-m and NRAO Greenbank91-m telescopes are used to find the limiting precision for redshiftmeasurement. At SNR levels of 10 or above, the random uncertaintyactually achieved in a single redshift measurement is demonstrated to be0.85 km/s at a bandwidth of 6.25 MHz. Uncertainty in other bands scalesas the square root of the bandwidth relative to 6.25 MHz. Random erroris also found to be independent of which telescope or software is usedas long as the SNR is large. At low SNR the choice of software affectsprecision. Substantial systematic errors are shown to be present in someexisting systems or software, due to errors in specifying the locationof the center frequency. Such errors can easily be eliminated withstandardized intercomparisons.
| 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.
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