Contents
Images
Upload your image
DSS Images Other Images
Related articles
Halo Mass Profiles and Low Surface Brightness Galaxy Rotation Curves
A recent study has claimed that the rotation curve shapes and massdensities of low surface brightness (LSB) galaxies are largelyconsistent with ΛCDM predictions, in contrast to a large body ofobservational work. I demonstrate that the method used to derive thisconclusion is incapable of distinguishing the characteristic steep CDMmass-density distribution from the core-dominated mass-densitydistributions found observationally: even core-dominatedpseudoisothermal halos would be inferred to be consistent with CDM. Thismethod can therefore make no definitive statements regarding the(dis)agreement between the data and CDM simulations. After introducingan additional criterion that does take the slope of the massdistribution into account, I find that only about a quarter of the LSBgalaxies investigated are possibly consistent with CDM. However, formost of these, the fit parameters are so weakly constrained that this isnot a strong conclusion. Of the 20 galaxies with tightly constrained fitparameters, only 3 are consistent with ΛCDM. Two of thesegalaxies are likely dominated by stars, leaving only one possible darkmatter-dominated, CDM-consistent candidate. These conclusions are basedon comparison of data and simulations at identical radii and fits to theentire rotation curves. LSB galaxies that are consistent with CDMsimulations, if they exist, seem to be rare indeed.
| The Molecular Interstellar Medium of Dwarf Galaxies on Kiloparsec Scales: A New Survey for CO in Northern, IRAS-detected Dwarf Galaxies
We present a new survey for CO in dwarf galaxies using the ARO Kitt Peak12 m telescope. This survey consists of observations of the centralregions of 121 northern dwarfs with IRAS detections and no known COemission. We detect CO in 28 of these galaxies and marginally detectanother 16, increasing by about 50% the number of such galaxies known tohave significant CO emission. The galaxies we detect are comparable instellar and dynamical mass to the Large Magellanic Cloud, althoughsomewhat brighter in CO and fainter in the far-IR. Within dwarfs, wefind that the CO luminosity LCO is most strongly correlatedwith the K-band and the far-infrared luminosities. There are also strongcorrelations with the radio continuum (RC) and B-band luminosities andlinear diameter. Conversely, we find that far-IR dust temperature is apoor predictor of CO emission within the dwarfs alone, although a goodpredictor of normalized CO content among a larger sample of galaxies. Wesuggest that LCO and LK correlate well because thestellar component of a galaxy dominates the midplane gravitational fieldand thus sets the pressure and density of the atomic gas, which controlthe formation of H2 from H I. We compare our sample with moremassive galaxies and find that dwarfs and large galaxies obey the samerelationship between CO and the 1.4 GHz RC surface brightness. Thisrelationship is well described by a Schmidt law withΣRC~Σ1.3CO. Therefore,dwarf galaxies and large spirals exhibit the same relationship betweenmolecular gas and star formation rate (SFR). We find that this result isrobust to moderate changes in the RC-to-SFR and CO-to-H2conversion factors. Our data appear to be inconsistent with large (orderof magnitude) variations in the CO-to-H2 conversion factor inthe star-forming molecular gas.
| Detections of CO in Late-Type, Low Surface Brightness Spiral Galaxies
Using the IRAM 30 m telescope, we have obtained 12CO J=1-0and 2-1 spectral line observations toward the nuclear regions of 15edge-on, low surface brightness (LSB) spiral galaxies. Our samplecomprises extreme late-type LSB spirals with disk-dominated morphologiesand rotational velocities Vrot<~120 km s-1. Wereport detections of four galaxies in at least one transition (>~5σ) for the remainder of the sample we provide upper limits on thenuclear CO content. Adopting a standard GalacticICO-to-H2 conversion factor implies molecular gasmasses of (3.3-9.8)×106 Msolar in thenuclear regions (inner 1.1-1.8 kpc) of the detected galaxies. Combiningour new data with samples of late-type spirals from the literature, wefind that CO-detected LSB spirals adhere to the sameMH2-far-infrared correlation as more luminous andhigher surface brightness galaxies. The amount of CO in the centralregions of late-type spirals appears to depend more strongly on massthan on central optical surface brightness, and CO detectabilitydeclines significantly for moderate to low surface brightness spiralswith Vrot<~90 km s-1 no LSB spirals have so farbeen detected in CO below this threshold. Metallicity effects alone areunlikely to account for this trend, and we speculate that we are seeingthe effects of a decrease in the mean fraction of a galaxy disk able tosupport giant molecular cloud formation with decreasing galaxy mass.
| 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.
| Investigating the Origins of Dark Matter Halo Density Profiles
Although high-resolution N-body simulations make robust empiricalpredictions of the density distribution within cold dark matter halos,these studies have yielded little physical insight into the origins ofthe distribution. We therefore attempt to investigate the problem usinganalytic and semianalytic approaches. Simple analytic considerationssuggest that the inner slope of the central cusps in dark matter haloscannot be steeper than α=2 (where ρ~r-α),with α=1.5-1.7 being a more realistic upper limit. Moreover, ouranalysis suggests that any number of effects, whether real (e.g.,angular momentum imparted by tidal torques and secondary perturbations)or artificial (e.g., two-body interactions, the accuracy of thenumerical integrator, round-off errors) will result in shallower slopes.We also find that the halos should exhibit a well-defined relationshipbetween rperi/rapo andjθ/jr. We derive this relationshipanalytically and speculate that it may be ``universal.'' Using asemianalytic scheme based on Ryden & Gunn, we further explore therelationship between the specific angular momentum distribution in ahalo and its density profile. For present purposes, we restrictourselves to halos that form primarily via the nearly smooth accretionof matter, and consider only the specific angular momentum generated bysecondary perturbations associated with the cold dark matter spectrum ofdensity fluctuations. Compared to those formed in N-body simulations,our ``semianalytic'' halos are more extended, have flatter rotationcurves, and have a higher specific angular momentum, even though we havenot yet taken into account the effects of tidal torques. Whether thedensity profile of numerical halos is indeed the result of loss inangular momentum outside the central region, and whether this loss is afeature of hierarchical merging and major mergers in particular, isunder investigation.
| Properties of isolated disk galaxies
We 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
| Dark Matter in late-type galaxies
High resolution H alpha rotation curves of Low Surface Brightnessgalaxies show that the central slopes of the dark matter density inthose galaxies do not agree with predictions from cosmological numericalsimulations. A comparison of our data with those of other authors showsgood agreement.
| Constraints of the Clumpiness of Dark Matter Halos through Heating of the Disk Galaxies
Motivated by the presence of numerous dark matter clumps in the MilkyWay's halo, as expected from the cold dark matter cosmological model, weconduct numerical simulations to examine the heating of the disk. Weconstruct a fairly realistic initial Galaxy model with a stable thindisk. The disk interacts with dark matter clumps for about 5 Gyr. Threephysical effects are examined: the mass spectrum of the dark matterclumps, the initial thickness of the galactic disk, and the spatialdistribution of the clumps. We find that the massive end of the massspectrum determines the amount of disk heating. Thicker disks sufferless heating. There is a certain thickness at which the heating due tothe interaction with the clumps is saturated. The spatial distributionof the clumps plays an important role in disk heating. We adopt twodifferent spatial distributions of the clumps. The first, which mimicsthe primordial distribution of the clumps at the epoch of the collapseof the halo, is proportional to the underlying halo densitydistribution. Recent cosmological simulations, however, yield depletionof the clumps within the extent of the disk in the present-day galaxies.Therefore, we construct the second distribution, which has the samenumber density of the clumps as the prediction for the cosmologicalsimulations within the disk region. Our numerical simulations show thatthe first distribution produces considerable disk heating, while thelatter does not. These results suggest that at early epochs, or in caseswhere many clumps are surviving until the present, the disk should havesuffered considerable heating in the earlier epochs of their evolution.
| A Wide-Field, Broadband Imaging Survey of Butcher-Oemler Cluster Cl 0024+1654: The Catalog
Wide-field (20'×20') UBVI images of intermediate-redshift(z=0.39), Butcher-Oemler cluster Cl 0024+1654 have been obtained. Thesedata probe the rest-frame mid-UV properties over a much larger area thanprevious studies of Cl 0024+1654. Using these data, a multicolor catalogof nonstellar objects, assumed to be galaxies, has been constructed andanalyzed. Using statistical arguments, the observed galaxy sample isseparated into field and cluster populations. The basic photometricproperties of these populations are presented and discussed. The``dropout'' objects (i.e., objects undetected in one or more photometricbands) in our catalog are also discussed. A description of the finalUBVI images, as well as the object catalog, is provided in an appendix.In a second appendix the use of SExtractor in crowded fields, such asthe core of Cl 0024+1654, is discussed. The specific issues of themid-UV properties of red envelope cluster galaxies, as well as thepossible detection of a faint blue cluster population, are discussed ina forthcoming companion paper by Silva, Alexov, & Pierce.The observations described were conducted at Kitt Peak NationalObservatory, National Optical Astronomy Observatory, which is operatedby the Association of Universities for Research in Astronomy (AURA)Inc., under cooperative agreement with the National Science Foundation(NSF).
| An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies. II. The Hα survey atlas and catalog
In this second paper on the investigation of extraplanar diffuse ionizedgas in nearby edge-on spiral galaxies we present the actual results ofthe individual galaxies of our Hα imaging survey. A grand totalof 74 galaxies have been studied, including the 9 galaxies of a recentlystudied sub-sample \citep{Ro00}. 40.5% of all studied galaxies revealextraplanar diffuse ionized gas, whereas in 59.5% of the survey galaxiesno extraplanar diffuse ionized gas could be detected. The averagedistances of this extended emission above the galactic midplane rangefrom 1-2 kpc, while individual filaments in a few galaxies reachdistances of up to |z| ~ 6 kpc. In several cases a pervasive layer ofionized gas was detected, similar to the Reynolds layer in our MilkyWay, while other galaxies reveal only extended emission locally. Themorphology of the diffuse ionized gas is discussed for each galaxy andis compared with observations of other important ISM constituents in thecontext of the disk-halo connection, in those cases where publishedresults were available. Furthermore, we present the distribution ofextraplanar dust in these galaxies, based on an analysis of theunsharp-masked R-band images. The results are compared with thedistribution of the diffuse ionized gas.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).\ref{fig22}-\ref{fig54} are only available in electronic form athttp://www.edpsciences.org
| 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).
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| The Inner Scale Length of Spiral Galaxy Rotation Curves
We use the tapering effect of Hα/[N II] rotation curves of spiralgalaxies first noted by Goad & Roberts to investigate the internalextinction in disks. The scale length of exponential fits to the innerpart of rotation curves depends strongly on the disk axial ratio.Preliminary modeling of the effect implies substantial opacity of thecentral parts of disks at a wavelength of 0.66 μm. In addition, theaverage kinematic scale length of rotation curves, when corrected toface-on perspective, has a nearly constant value of about 1.7h-1 kpc for all luminosity classes. The interpretation ofthat effect, as the result of the increasing dominance of the baryonicmass in the inner parts of galaxies, yields a mean baryonicmass-to-light ratio in the I band of ΥI=2.7 hMsolar/Lsolar,I, within the inner 1.7h-1 kpc of disks.
| Photometric parameters of edge-on galaxies from 2MASS observations
To analyze the vertical structure of edge-on galaxies, we have usedimages of a large uniform sample of flat galaxies that have been takenduring the 2MASS all-sky survey. The photometric parameters, such as theradial scale length, the vertical scale height, and the deprojectedcentral surface brightness of galactic disks have been obtained. We finda strong correlation between the central surface brightness and theratio of the vertical scale height to the vertical scale length: thethinner the galaxy, the lower the central surface brightness of itsdisk. The vertical scale height does not increase systematically withthe distance from the galaxy center in the frames of this sample.
| High-resolution rotation curves of low surface brightness galaxies
We present high-resolution rotation curves of a sample of 26 low surfacebrightness galaxies. From these curves we derive mass distributionsusing a variety of assumptions for the stellar mass-to-light ratio. Weshow that the predictions of current Cold Dark Matter models for thedensity profiles of dark matter halos are inconsistent with the observedcurves. The latter indicate a core-dominated structure, rather than thetheoretically preferred cuspy structure. based on observations at theObservatoire de Haute Provence.
| Mass Density Profiles of Low Surface Brightness Galaxies
We derive the mass density profiles of dark matter halos that areimplied by high spatial resolution rotation curves of low surfacebrightness galaxies. We find that, at small radii, the mass densitydistribution is dominated by a nearly constant density core with a coreradius of a few kiloparsecs. For ρ(r)~rα, thedistribution of inner slopes α is strongly peaked aroundα=-0.2. This is significantly shallower than the cuspyα<=-1 halos found in cold dark matter simulations. While theobserved distribution of α does have a tail toward such extremevalues, the derived value of α is found to depend on the spatialresolution of the rotation curves: α~-1 is found only for theleast well resolved galaxies. Even for these galaxies, our data are alsoconsistent with constant-density cores (α=0) of modest (~1 kpc)core radius, which can give the illusion of steep cusps wheninsufficiently resolved. Consequently, there is no clear evidence for acuspy halo in any of the low surface brightness galaxies observed.
| The Evolutionary Status of Isolated Dwarf Irregular Galaxies. II. Star Formation Histories and Gas Depletion
The results of UBV and Hα imaging of a large sample of isolateddwarf irregular galaxies are interpreted in the context of compositestellar population models. The observed optical colors are best fittedby composite stellar populations that have had approximately constantstar formation rates for at least 10 Gyr. The galaxies span a range ofcentral surface brightness, from 20.5 to 25.0 mag arcsec-2there is no correlation between surface brightness and star formationhistory. Although the current star formation rates are low, it ispossible to reproduce the observed luminosities without a majorstarburst episode. The derived gas depletion timescales are long,typically ~20 Gyr. These results indicate that dwarf irregular galaxies(dI's) will be able to continue with their slow, but constant, starformation activity for at least another Hubble time. The sample ofisolated dI's is compared with a sample of starbursting dwarf galaxiestaken from the literature. The starbursting dwarf galaxies have manysimilar properties; the main difference between these two types ofgas-rich dwarf galaxies is that the current star formation isconcentrated in the center of the starbursting systems, while it is muchmore distributed in the quiescent dI's. This results in pronounced colorgradients for the starbursting dwarf galaxies, while the majority of thequiescent dwarf irregular galaxies have minor or nonexistent colorgradients. Thus, the combination of low current star formation rates,blue colors, and the lack of significant color gradients indicates thatstar formation percolates slowly across the disks of normal dwarfgalaxies in a quasi-continuous manner.
| Properties of tidally-triggered vertical disk perturbations
We present a detailed analysis of the properties of warps andtidally-triggered perturbations perpendicular to the plane of 47interacting/merging edge-on spiral galaxies. The derived parameters arecompared with those obtained for a sample of 61 non-interacting edge-onspirals. The entire optical (R-band) sample used for this study waspresented in two previous papers. We find that the scale height of disksin the interacting/merging sample is characterized by perturbations onboth large ( =~ disk cut-off radius) and short ( =~ z0)scales, with amplitudes of the order of 280 pc and 130 pc on average,respectively. The size of these large (short) -scale instabilitiescorresponds to 14% (6%) of the mean disk scale height. This is a factorof 2 (1.5) larger than the value found for non-interacting galaxies. Ahallmark of nearly all tidally distorted disks is a scale height thatincreases systematically with radial distance. The frequent occurrenceand the significantly larger size of these gradients indicate that diskasymmetries on large scales are a common and persistent phenomenon,while local disturbances and bending instabilities decline on shortertimescales. Nearly all (93%) of the interacting/merging and 45% of thenon-interacting galaxies studied are noticeably warped. Warps ofinteracting/merging galaxies are ~ 2.5 times larger on average thanthose observed in the non-interacting sample, with sizes of the order of340 pc and 140 pc, respectively. This indicates that tidal distortionsdo considerably contribute to the formation and size of warps. However,they cannot entirely explain the frequent occurrence of warped disks.Based on observations obtained at the European Southern Observatory(ESO, La Silla, Chile), Calar Alto Observatory operated by the MPIA(DSAZ, Spain), Lowell Observatory (Flagstaff,AZ, USA), and Hoher ListObservatory (Germany).
| A list of peculiar velocities of RFGC galaxies
A 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.
| The Evolutionary Status of Isolated Dwarf Irregular Galaxies. I. UBV and Hα Imaging Observations
The results of UBV and Hα imaging of a large sample of gas-rich,isolated, dwarf irregular galaxies are presented. The majority of thelow-luminosity systems in this sample have no known neighbors within200-400 kpc and thus are unlikely to have had significant interactionswithin the last several gigayears. The new observations confirm thatdwarf irregular galaxies are blue systems, with median values for thesample of 0.42+/-0.040.05 in B-V and-0.22+/-0.040.07 in U-B. Analysis of the derivedsurface photometry indicates that most of these systems can be wellfitted by single exponential disks and have only minor color gradients.Furthermore, the observed H II regions are distributed sparsely acrossthe optical disk. H II region luminosity functions were constructed forthose systems with a sufficient number of H II regions; the derivedpower-law indices are generally shallow, with a median value of-1.61+/-0.310.24.
| Box- and peanut-shaped bulges. I. Statistics
We 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 models
This 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 interpretations
We 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 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 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.
| Confirmation of a faint red halo around NGC 5907
We report the detection of extended infrared emission 5.2kpc above theplane of the edge-on spiral galaxy NGC 5907 in the JK bands. Thisprovides confirmation at two other wavelengths of the R-band result ofSackett et al. The halo J-K colour is found to be 1.3+/-0.3. If we makethe assumption that the halo emission is of the form necessary to give aflat rotation curve at large radii, with a power-law index in projectionof -1.0, the K surface brightness, M/L_K ratio and R-K colour are foundto be 23.0mag arcsec^-2, 100 and 3.5 respectively, at 95-arcsec radius.Adopting a halo index of -2.5 in projection, typical of known stellarhaloes but inconsistent with the halo measured by Sackett et al., the Ksurface brightness at 95 arcsec drops to 24.0mag arcsec^-2 and the J-Kcolour to 2.5, while the M/L_K ratio is undetermined since such a halowould be unrelated to the dark matter component. If the emission isinterpreted as arising from the massive halo, then it is broadlyconsistent with a population of stars at the very lowest masses,possibly extending into the brown dwarf regime.
| Disk Galaxies in the Outer Local Supercluster: Optical CCD Surface Photometry and Distribution of Galaxy Disk Parameters
We report new B-band CCD surface photometry on a sample of 76 diskgalaxies brighter than B_T = 14.5 mag in the Uppsala General Catalogueof Galaxies that are confined within a volume located in the outer partof the Local Supercluster. With our earlier published I-band CCD andhigh signal-to-noise ratio 21 cm H I data, this paper completes ouroptical surface photometry campaign on this galaxy sample. As anapplication of this data set, the B-band photometry is used here toillustrate two selection effects that have been somewhat overlooked inthe literature but that may be important in deriving the distributionfunction of disk central surface brightness (CSB) of disk galaxies froma diameter- and/or flux-limited sample: a Malmquist-type bias againstdisk galaxies with small disk scale lengths (DSLs) at a given CSB and adisk inclination-dependent selection effect that may, for example, biastoward inclined disks near the threshold of a diameter-limited selectionif disks are not completely opaque in the optical. Taking intoconsideration these selection effects, we present a method ofconstructing a volume-sampling function and a way to interpret thederived distribution function of CSB and DSL. Application of this methodto our galaxy sample implies that if galaxy disks are optically thin,CSB and DSL may well be correlated in the sense that, up to aninclination-corrected limiting CSB of about 24.5 mag arcsec^-2 that isadequately probed by our galaxy sample, the DSL distribution of galaxieswith a lower CSB may have a longer tail toward large values unless thedistribution of disk galaxies as a function of CSB rises rapidly towardfaint values.
| 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.
| 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
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
