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|Companions to Isolated Elliptical Galaxies: Revisiting the Bothun-Sullivan Sample|
We investigate the number of physical companion galaxies for a sample ofrelatively isolated elliptical galaxies. The NASA/IPAC ExtragalacticDatabase (NED) has been used to reinvestigate the incidence of satellitegalaxies for a sample of 34 elliptical galaxies, first investigated byBothun & Sullivan using a visual inspection of Palomar Sky Surveyprints out to a projected search radius of 75 kpc. We have repeatedtheir original investigation using data cataloged in NED. Nine of theseelliptical galaxies appear to be members of galaxy clusters; theremaining sample of 25 galaxies reveals an average of +1.0+/-0.5apparent companions per galaxy within a projected search radius of 75kpc, in excess of two equal-area comparison regions displaced by 150-300kpc. This is significantly larger than the +0.12+/-0.42companions/galaxy found by Bothun & Sullivan for the identicalsample. Making use of published radial velocities, mostly availablesince the completion of the Bothun-Sullivan study, identifies thephysical companions and gives a somewhat lower estimate of +0.4companions per elliptical galaxy. This is still 3 times larger than theoriginal statistical study, but given the incomplete and heterogeneousnature of the survey redshifts in NED, it still yields a firm lowerlimit on the number (and identity) of physical companions. An expansionof the search radius out to 300 kpc, again restricted to sampling onlythose objects with known redshifts in NED, gives another lower limit of4.5 physical companions per galaxy. (Excluding five elliptical galaxiesin the Fornax Cluster, this average drops to 3.5 companions perelliptical.) These physical companions are individually identified andlisted, and the ensemble-averaged radial density distribution of theseassociated galaxies is presented. For the ensemble, the radial densitydistribution is found to have a falloff consistent withρ~R-0.5 out to approximately 150 kpc. For non-FornaxCluster companions the falloff continues out to the 300 kpc limit of thesurvey. The velocity dispersion of these companions is found to reach amaximum of 350 km s-1 at around 120 kpc, after which theyfall at a rate consistent with Keplerian falloff. This falloff may thenindicate the detection of a cut-off in the mass-density distribution inthe elliptical galaxies' dark matter halo at ~100 kpc.
|A New Nonparametric Approach to Galaxy Morphological Classification|
We present two new nonparametric methods for quantifying galaxymorphology: the relative distribution of the galaxy pixel flux values(the Gini coefficient or G) and the second-order moment of the brightest20% of the galaxy's flux (M20). We test the robustness of Gand M20 to decreasing signal-to-noise ratio (S/N) and spatialresolution and find that both measures are reliable to within 10% forimages with average S/N per pixel greater than 2 and resolutions betterthan 1000 and 500 pc, respectively. We have measured G andM20, as well as concentration (C), asymmetry (A), andclumpiness (S) in the rest-frame near-ultraviolet/optical wavelengthsfor 148 bright local ``normal'' Hubble-type galaxies (E-Sd) galaxies, 22dwarf irregulars, and 73 0.05
|The Relationship between Stellar Light Distributions of Galaxies and Their Formation Histories|
A major problem in extragalactic astronomy is the inability todistinguish in a robust, physical, and model-independent way how galaxypopulations are physically related to each other and to their formationhistories. A similar, but distinct, and also long-standing question iswhether the structural appearances of galaxies, as seen through theirstellar light distributions, contain enough physical information tooffer this classification. We argue through the use of 240 images ofnearby galaxies that three model-independent parameters measured on asingle galaxy image reveal its major ongoing and past formation modesand can be used as a robust classification system. These parametersquantitatively measure: the concentration (C), asymmetry (A), andclumpiness (S) of a galaxy's stellar light distribution. When combinedinto a three-dimensional ``CAS'' volume all major classes of galaxies invarious phases of evolution are cleanly distinguished. We argue thatthese three parameters correlate with important modes of galaxyevolution: star formation and major merging activity. This is arguedthrough the strong correlation of Hα equivalent width andbroadband colors with the clumpiness parameter S, the uniquely largeasymmetries of 66 galaxies undergoing mergers, and the correlation ofbulge to total light ratios, and stellar masses, with the concentrationindex. As an obvious goal is to use this system at high redshifts totrace evolution, we demonstrate that these parameters can be measured,within a reasonable and quantifiable uncertainty with available data outto z~3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Fieldimages.
|The Contribution of H I-rich Galaxies to the Damped Lyα Absorber Population at z = 0|
We present a study of the expected properties of the low-redshift dampedLyα absorber population determined from a sample of H I-selectedgalaxies in the local universe. Because of a tight correlation betweenthe H I mass and H I cross section, which we demonstrate spans allgalaxy types, we can use our H I-selected sample to predict theproperties of the absorption-line systems. We use measurements of thenumber density and H I cross section of galaxies to show that the totalH I cross section at column densities sufficient to produce dampedLyα absorption is consistent with no evolution of the absorberpopulation. We also find that the dN/dz distribution is dominated bygalaxies with H I masses near 109 Msolar. However,because of the large dispersion in the correlation between H I mass andstellar luminosity, we find that the distribution of dN/dz as a functionof LJ is fairly flat. In addition, we examine the line widthsof the H I-selected galaxies and show that there may be evolution in thekinematics of H I-rich galaxies, but it is not necessary for the higherredshift population to contain a greater proportion of high-massgalaxies than we find locally.
|Galaxy classification using fractal signature|
Fractal geometry is becoming increasingly important in the study ofimage characteristics. For recognition of regions and objects in naturalscenes, there is always a need for features that are invariant and theyprovide a good set of descriptive values for the region. There are manyfractal features that can be generated from an image. In this paper,fractal signatures of nearby galaxies are studied with the aim ofclassifying them. The fractal signature over a range of scales proved tobe an efficient feature set with good discriminating power. Classifierswere designed using nearest neighbour method and neural networktechnique. Using the nearest distance approach, classification rate wasfound to be 92%. By the neural network method it has been found toincrease to 95%.
|Bar strengths in spiral galaxies estimated from 2MASS images|
Non-axisymmetric forces are presented for a sample of 107 spiralgalaxies, of which 31 are barred (SB) and 53 show nuclear activity. As adata base we use JHK images from the 2 Micron All-sky Survey, and thenon-axisymmetries are characterized by the ratio of the tangential forceto the mean axisymmetric radial force field, following Buta & Block.Bar strengths have an important role in many extragalactic problems andtherefore it is important to verify that the different numerical methodsapplied for calculating the forces give mutually consistent results. Weapply both direct Cartesian integration and a polar grid integrationutilizing a limited number of azimuthal Fourier components of density.We find that the bar strength is independent of the method used toevaluate the gravitational potential. However, because of thedistance-dependent smoothing by Fourier decomposition, the polar methodis more suitable for weak and noisy images. The largest source ofuncertainty in the derived bar strength appears to be the uncertainty inthe vertical scaleheight, which is difficult to measure directly formost galaxies. On the other hand, the derived bar strength is ratherinsensitive to the possible gradient in the vertical scaleheight of thedisc or to the exact model of the vertical density distribution,provided that the same effective vertical dispersion is assumed in allmodels. In comparison with the pioneering study by Buta & Block, thebar strength estimate is improved here by taking into account thedependence of the vertical scaleheight on the Hubble type: we find thatfor thin discs bar strengths are stronger than for thick discs by anamount that may correspond to as much as one bar strength class. Weconfirm the previous result by Buta and co-workers showing that thedispersion in bar strength is large among all the de Vaucouleurs opticalbar classes. In the near-infrared 40 per cent of the galaxies in oursample have bars (showing constant phases in the m= 2 Fourier amplitudesin the bar region), while in the optical band one-third of these barsare obscured by dust. Significant non-axisymmetric forces can also beinduced by the spiral arms, generally in the outer parts of the galacticdiscs, which may have important implications on galaxy evolution.Possible biases of the selected sample are also studied: we find thatthe number of bars identified drops rapidly when the inclination of thegalactic disc is larger than 50°. A similar bias is found in theThird Reference Catalogue of Bright Galaxies, which might be of interestwhen comparing bar frequencies at high and low redshifts.
|Bar Galaxies and Their Environments|
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
|Dark and luminous matter in the NGC 3992 group of galaxies. I. The large barred spiral NGC 3992|
Detailed neutral hydrogen observations have been obtained of the largebarred spiral galaxy NGC 3992 and its three small companion galaxies,UGC 6923, UGC 6940, and UGC 6969. For the main galaxy, the H Idistribution is regular with a low level radial extension outside thestellar disc. However, at exactly the region of the bar, there is apronounced central H I hole in the gas distribution. Likely gas has beentransported inwards by the bar and because of the emptyness of the holeno large accretion events can have happened in recent galactic times.The gas kinematics is very regular and it is demonstrated that theinfluence of the bar potential on the velocity field is negligible. Aprecise and extended rotation curve has been derived showing somedistinct features which can be explained by the non-exponential radiallight distribution of NGC 3992. The decomposition of the rotation curvegives a slight preference for a sub maximal disc, though a range of disccontributions, up to a maximum disc situation fits nearly equally well.For such a maximum disc contribution, which might be expected in orderto generate and maintain the bar, the required mass-to-light ratio islarge but not exceptional.
|A Multivariate Analysis of Galaxies in the Hubble Deep Field-North|
We use the ultraviolet and optical WFPC2 and near-infrared NICMOS imagesof the Hubble Deep Field-North to measure and statistically compare anarray of parameters for over 250 of the galaxies it contains. Theseparameters include redshift, rest-frame visible asymmetry andconcentration, bolometric luminosity, and extinction-corrected starformation rate. We find only one strong correlation, between bolometricluminosity and star formation rate, from which early-type galaxiesnoticeably deviate. When our asymmetry measurements are combined withthose of a sample of nearby galaxies covering the full Hubble sequence,we find a weak correlation between redshift and rest-frame visibleasymmetry, consistent with the qualitative evidence of galaxymorphological evolution from these and other deep Hubble Space Telescopeimages. The mean values of these asymmetry measurements show a monotonicincrease with redshift interval over the range 0<~z<~2, increasingby a factor of approximately 3. If this trend is real, it suggests thatgalaxy morphological evolution within the last ~70% of the Hubble timeis a gradual process that is continuing through the present cosmologicalepoch. There is evidence that the dominant source of this evolution isthe ``minor'' mergers of disk galaxies with smaller companions, whichcould also transform late-type spiral galaxies to early-type spiralgalaxies. Interestingly, in contrast to local galaxies we find nocorrelations between galaxy star formation rate and either UV or visibleasymmetry. This could arise if the star formation of high-redshiftgalaxies proceeds in episodes that are short (~100 Myr) relative to thetimescales over which galaxy mergers produce strong asymmetries (~500Myr), a result suggested by the high star formation rates of Lyman breakgalaxies.
|Nearby Optical Galaxies: Selection of the Sample and Identification of Groups|
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
|The Asymmetry of Galaxies: Physical Morphology for Nearby and High-Redshift Galaxies|
We present a detailed study of rotational asymmetry in galaxies for bothmorphological and physical diagnostic purposes. An unambiguous methodfor computing asymmetry is developed, which is robust for both distantand nearby galaxies. By degrading real galaxy images, we test thereliability of this asymmetry measure over a range of observationalconditions, e.g., spatial resolution and signal-to-noise ratio (S/N).Compared to previous methods, this new algorithm avoids the ambiguityassociated with choosing a center by using a minimization method andsuccessfully corrects for variations in S/N. There is, however, a strongrelationship between the rotational asymmetry and physical resolution(distance at fixed spatial resolution): objects become more symmetricwhen less well-resolved. We further investigate asymmetry as a functionof galactic radius and rotation. We find the asymmetry index has astrong radial dependence that differs vastly between Hubble types. As aresult, a meaningful asymmetry index must be specified within awell-defined radius representative of the physical galaxy scale. Weenumerate several viable alternatives, which exclude the use ofisophotes. Asymmetry as a function of angle (Aφ) is alsoa useful indicator of ellipticity and higher order azimuthal structure.In general, we show that the power of asymmetry as a morphologicalparameter lies in the strong correlation with B-V color for galaxiesundergoing normal star formation spanning all Hubble types fromellipticals to irregular galaxies. The few interacting galaxies in ourstudy do not fall on this asymmetry-color ``fiducial sequence,'' asthese galaxies are too asymmetric for their color. We suggest this factcan be used to distinguish between ``normal'' galaxies and galaxiesundergoing an interaction or merger.
|Structural and Photometric Classification of Galaxies. I. Calibration Based on a Nearby Galaxy Sample|
In this paper we define an observationally robust, multiparameter spacefor the classification of nearby and distant galaxies. The parametersinclude luminosity, color, and the image-structure parameters: size,image concentration, asymmetry, and surface brightness. Based on aninitial calibration of this parameter space using the ``normal'' Hubbletypes surveyed in 1996 by Frei et al., we find that only a subset of theparameters provide useful classification boundaries for this sample.Interestingly, this subset does not include distance-dependent scaleparameters such as size or luminosity. The essential ingredient is thecombination of a spectral index (e.g., color) with parameters of imagestructure and scale: concentration, asymmetry, and surface brightness.We refer to the image structure parameters (concentration and asymmetry)as indices of ``form.'' We define a preliminary classification based onspectral index, form, and surface brightness (a scale) that successfullyseparates normal galaxies into three classes. We intentionally identifythese classes with the familiar labels of early, intermediate, and late.This classification, or others based on the above four parameters, canbe used reliably to define comparable samples over a broad range inredshift. The size and luminosity distribution of such samples will notbe biased by this selection process except through astrophysicalcorrelations between spectral index, form, and surface brightness.
|Radio Emission from Galaxies in the Las Campanas Redshift Survey|
To increase the redshift range and look-back time over which the radioluminosity function can be measured directly, we identified 1157galaxies in the Las Campanas Redshift Survey (LCRS) having isophotal(red) magnitudes m_iso<=18.0 with radio sources brighter than 2.5 mJybeam^-1 in the 1.4 GHz NRAO VLA Sky Survey (NVSS). Since the NVSS has45" FWHM angular resolution, these radio and optical limits includenearly all LCRS galaxies with 1.4 GHz luminosities L>=10^22.4 W Hz^-1at z~0.05 to L>=10^23.6 W Hz^-1 at z~0.2. The mean redshift~0.14 of the radio-detected galaxies is higher than the meanredshift ~0.10 of the optical sample. This indicates that,statistically, the radio emission was detected from galaxies with thehighest optical luminosities. Of the 1157 galaxies, 261 were alsoidentified with far-infrared (FIR) sources in the IRAS Point SourceCatalog and Faint Source Catalog. The principal radio energy sources inall identified galaxies were classified as either ``starburst'' or``AGN'' on the basis of their FIR-radio flux ratios, FIR spectralindices, and radio-optical flux ratios. We show that the radio-opticalflux ratio can be effectively used to classify the dominant energysource for the radio emission even if FIR fluxes and radio morphologicaldata are not available.
|Galaxy Structural Parameters: Star Formation Rate and Evolution with Redshift|
The evolution of the structure of galaxies as a function of redshift isinvestigated using two parameters: the metric radius of the galaxy(R_eta) and the power at high spatial frequencies in the disk of thegalaxy (chi). A direct comparison is made between nearby (z~0) anddistant (0.2<~z<~1) galaxies by following a fixed range in restframe wavelengths. The data of the nearby galaxies comprise 136broadband images at ~4500 Å observed with the 0.9 m telescope atKitt Peak National Observatory (23 galaxies) and selected from thecatalog of digital images of Frei et al. (113 galaxies). Thehigh-redshift sample comprises 94 galaxies selected from the Hubble DeepField (HDF) observations with the Hubble Space Telescope using the WideField Planetary Camera 2 in four broad bands that range between ~3000and ~9000 Å (Williams et al.). The radius is measured from theintensity profile of the galaxy using the formulation of Petrosian, andit is argued to be a metric radius that should not depend very stronglyon the angular resolution and limiting surface brightness level of theimaging data. It is found that the metric radii of nearby and distantgalaxies are comparable to each other. The median value of the radius ofthe local sample is ~5+/-1 kpc, and the median radius ofthe HDF sample is ~6+/-2 kpc for q_0=0.5, H_0=65 km s^-1Mpc^-1 however, for q_0=0.1, ~7 kpc and for q_0=1,~5 kpc. In the HDF, galaxies with redshifts larger thanz>0.6 have flatter R_eta distributions than galaxies with redshiftssmaller than z<=0.6. However, the median R_eta values of high- andlow-redshift galaxies are consistent with each other. This result isconsistent with the simulations of galaxy images at redshifts z=0.35,z=0.5, and z=0.9, which show that the metric sizes can be recoveredwithin +/-2 kpc. The flocculency or power at high spatial frequencies isquantified using a simple method that is based on surface photometry inone band and that depends on the size of the star-forming regions and onthe intensity profile of the galaxy. In nearby galaxies, the flocculencyis found to trace the star formation rate as chi is correlated withoptical colors (B-V) and the strength of the hydrogen recombinationlines (Hα). In the HDF, galaxies at redshifts smaller than z~1 andwith fluxes brighter than B=25 have values of chi similar to what ismeasured in nearby galaxies and to what is expected from simulations ofdistant galaxy images. Among the HDF galaxies, I find that at most 4%can be identified as dwarf galaxies with rates of star formation similarto NGC 4449 and NGC 1569. Most HDF galaxies are giants with starformation rates similar to those in nearby giant galaxies. In summary,in this study I have introduced a method to measure the metric sizes andflocculency of the two-dimensional light distribution of galaxies. As aresult, I find that the high spatial frequency power is related to thestar formation rate. Further, I find that the sizes and power at highspatial frequencies of HDF galaxies remain largely unchanged between thepresent epoch and redshifts lower than z~1.
|Satellites as Probes of the Masses of Spiral Galaxies|
We present H I observations and analyses of the kinematics of 24satellite-primary galaxy pairs with projected separations between 4.9and 240 kpc. The satellites have masses of less than 3% of their primaryspirals. Two estimates for the masses of the primaries are available,one from their rotation curves and one from the orbital properties ofthe satellites. Defining chi as the ratio of these two mass estimates,it is a measure of the presence, or absence, of a significant halo. Thechi-distribution for these 24 pairs is presented and the selectioneffects are discussed. Moreover, we show that the chi-distribution ofmore numerous pairs, with projected separations of less than 200 kpc,identified by Zaritsky et al., after adopting selection criteria quitedifferent from ours, is similar to our chi-distribution. We show thatthe observational biases have a negligible effect; the biased andunbiased distributions are essentially identical. In order to understandthis distribution, N-body calculations were executed to simulate thedynamical behavior of relatively low mass satellites orbiting primarydisk galaxies with and without extended halos. The models and the realgalaxies were ``observed'' in the same fashion. In addition, we made apartially analytical analysis of the behavior of orbits in a logarithmicpotential. We find that a ``generic'' model, characterized by a singledisk/halo combination, cannot reproduce the observed P(chi)distribution. However, a simple two-component population of galaxies,composed of not more than 60% with halos and 40% without halos, issuccessful, if galaxies have dimensions of order 200 kpc. If galaxiesare considerably larger with sizes extending to 400 kpc or more, theconstraints become more onerous. No generic model can describe the fullrange of the observed P(chi), particularly if the distribution forr_p<200 kpc is compared with that for r_p>200 kpc. Regardless ofthe mix of orbital eccentricities, neither pure halo, nor canonical(disk and halo masses are comparable within the disk radius) models willwork. A multicomponent approximation to reality can be constructed forwhich the canonical model must be mixed with a small fraction of systemsessentially devoid of a massive dark halo. Only by including thesecomplexities can the full range of P(chi) be modeled with any degree ofsuccess over all radial extents. We show that dynamical friction cannotbe ignored in these explorations and that the average mass of a galaxyis in the range of (1-5)x10^12 M_solar, with a mass-to-luminosity ratioof at most a few hundred. This is insufficient to close the universe.
|Physical Morphology of Galaxies using Asymmetry|
We demonstrate in this paper the use of asymmetry in conjunction withthe integrated (B-V) color of galaxies for physical morphologicalpurposes. We show how color-asymmetry diagrams can be used todistinguish between various types of galaxies, including ellipticals,late and early type disks, irregulars and interacting/merging galaxies.We also show how asymmetry can be used to help decipher the morphologyof nearby starbursts, and galaxies in the Hubble Deep Field.
|Star formation in bar environments regions. II. Physical properties, age and abundances of H II|
The nebular properties (electronic density, extinction, age, O/Habundances) of H ii regions found along the bars of the sample of barredspiral galaxies studied by Martin & Friedli (1997) are examined.From line ratio diagnostic diagrams, it is showed that regions locatedalong the major axis of the bars have a normal photoionization spectrum,that is, line ratios reproductible from nebular conditions and ionizingstar radiation field normally encountered in extragalactic H ii regions.There is an indication, however, that their degree of ionization mightbe somewhat different. Another ionization mechanism (high-velocityshocks or hard UV radiation) is clearly present for regions found nearbythe centers of the galaxies. The electronic density of the regions alongthe bars is very close to that of disc regions (< N_e> ~ 80 cm(-3)). On average, bar and disc regions have a similar visual extinction(A_V ~ 1 mag) with exceptions for some regions located near the bar dustlanes of the earlier types of galaxies in our sample. Although theaverage Hα equivalent width of bar H ii regions ( ~ 250 Å)is half that of disc regions, this disparity could be due touncertainties in the galactic continuum and does not translate into asignificant age difference. The oxygen abundance distribution was alsoinvestigated in the bar of these galaxies. The O/H scatter was found tobe very small (<0.1 dex) indicating that mixing of the chemicalcomposition by gas flows is very efficient in a barred structure.Observations reported in this paper were obtained at the Multiple MirrorTelescope Observatory, a facility operated jointly by the University ofArizona and the Smithsonian Institution Physical properties, age andabundances of H ii
|Starbursts in barred spiral galaxies. V. Morphological analysis of bars|
We have measured the bar lengths and widths of 125 barred galaxiesobserved with CCDs. The dependence of bar strength (identified with baraxis ratio) on morphological type, nuclear activity, central and mid-barsurface brightness is investigated. The properties of the bars are bestexplained if the sample is divided into early- (< SBbc) and late-typegalaxies, and into active (starburst, Seyfert or LINER) and normalgalaxies. We find that galaxies with very long bars are mostly activeand that normal late-type galaxies have a distinct behavior from thethree other groups of galaxies. We confirm earlier findings that activelate-type galaxies tend to have both stronger and longer bars thannormal ones. An important result of this paper is that early-typegalaxies do not share this behavior: they all tend to have strong bars,whether they are active or not. We also find correlations between barstrength and relative surface brightness in the middle and at the edgeof the bar, which are not followed by normal late-type galaxies. Theseresults are interpreted in the light of recent numerical simulations andparadigms about galaxy evolution. They suggest that normal late-typegalaxies represent the first stage of galaxy evolution, and that bars inearly- and late-type galaxies do not have the same properties becausethey have a different origin. Based on observations obtained at the 2meter telescope of Observatoire du Pic du Midi, operated by INSU (CNRS)
|A neutral hydrogen study of the barred spiral galaxy NGC 3319|
Neutral hydrogen line observations of the late-type barred spiral galaxyNGC 3319 are presented. The distribution and kinematics of the galaxyare studied using the Very Large Array, with spatial resolutions between11 and 50 arcsec and a channel separation of 10.33 km/s. As is typicalfor late-type galaxies, NGC 3319 is rich in H I, with a gaseous bar andspiral features. Several large, low-density regions are present, and theH I spiral structure is distorted, especially in the south. The gasdistribution is asymmetric and extends significantly further to thesoutheast due to a long, off-center tail. Noncircular motions caused bythe bar, spiral structure, and low-density regions are present in theradial velocity field, complicating the rotation curve analysis. Thesenonaxisymmetric structures cause the values of the position angle andinclination derived from the velocity field to vary across the disk. Inaddition, beyond a radius of 180 arcsec, the velocity field is severelyperturbed on the approaching (southern) side of the galaxy, and the diskbecomes nonplanar. However, the galaxy does not show the typical'integral sign' shape of a warped system. We detect a small systemapproximately 11 arcmin south of the center of NGC 3319. It is seen ineight velocity channels and is coincident with a small, resolved objectin the Palomar Sky Survey. A tidal interaction between this object andNGC 3319 is the most likely cause of the distorted spiral structure, theH I tail, and the velocity perturbations found in the southern half ofthe galaxy. Infalling tidal debris from such an event may account forthe large, low-density regions found in the disk, several of which showkinematic evidence that suggest they are expanding superstructures.
|Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles|
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.
|The Southern Sky Redshift Survey|
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
|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 22.214.171.124 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 (to126.96.36.199) or via http://cdsweb.u-strasbg.fr/Abstract.html
|Near-IR photometry of disk galaxies: Search for nuclear isophotal twist and double bars|
We present a near-IR, mainly $H$ band, photometry of 72 nearby (d <40 Mpc) disk galaxies. The main goal of the survey was to search forisophotal twist inside their nuclear regions. As the twist can be due insome cases to projection effects, rather than resulting from a dynamicalphenomenon, we deproject -- under the simplifying assumption of a 2Dgeometry -- all galaxies whose disk position angle and inclination areknown, the latter not exceeding 75 degrees. We show the ellipticity,position angle and surface brightness radial profiles, and discuss how aprojection of 2D and 3D bars can distort the isophotes, give an illusionof a non-existing double bar or mask a real one. We report 15 newdouble-barred galaxies and confirm 2 detected previously. We identify 14additional twists not known before and we also find nuclear triaxialstructures in three SA galaxies. The frequency of Seyferts amonggalaxies with nuclear bars or twists is high. Since these observationsare part of a larger survey, the interpretation of the results will begiven in a future paper, as soon as the number of objects grows enoughto permit meaningful statistics. As a secondary product, we publishstructural parameters (length and axis ratio) of large-scale bars inorder to extend still scarce data on bars in the near-IR.
|Star formation in bar environments. I. Morphology, star formation rates and general properties.|
A study of the morphological properties and star formation rates (SFRs)of HII regions located along the bars of a sample of eleven late-typebarred systems is presented and compared with numerical simulations.According to the relative intensity of star formation along the bar withrespect to that of the nuclear region, three types of distributions areobserved. They may be related to the age of the bar. Other importantcharacteristics include angular misalignments (up to 15°) betweenthe stellar bar and the ``Hα bar'', a correlation between thelocation of the HII regions and dust lanes in certain bars (mostlyearly-type spirals), and a difference in axial ratio and length betweenstellar and Hα bars. A wide range of SFRs (from 0.03 to1.44Msun_/yr) is observed, and star formation is generallyhighly asymmetric with respect to the bar minor axis. All these featurescan be reproduced in numerical models provided that the globalmechanical energy release remains low (but non-zero). In NGC 7479, thetotal gas-to-star transformation efficiency inside the bar is estimatedat about 0.26, meaning that, at present, maybe as nearly as 75% of thegas flowing into the bar region is not transformed into stars.
|Global morphology and physical relations between the stars, gas and dust in the disc and arms of M100.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.283..251K&db_key=AST
|The Morphologies of Distant Galaxies. II. Classifications from the Hubble Space Telescope Medium Deep Survey|
The morphological properties of high-redshift galaxies are investigatedusing a sample of 507 objects (I < 22.0 mag) from the Hubble SpaceTelescope (HST) Medium Deep Survey. Independent visual morphologicalclassifications for each galaxy are used to quantify the statisticaluncertainties in the galaxy classifications. Visual classifications arefound to agree well for I < 21 mag. Fainter than I = 21 magsignificant disagreements are seen in the independent visualclassifications of late-type systems with T > 7, merging systems, andpeculiar galaxies. The classifications of these systems are shown to besome- what subjective. Objective classifications based upon measurementsof central concentration and asymmetry for the Medium Deep Survey sampleare presented. These classifications are calibrated using measurementsof structural parameters for an artificially redshifted sample of localobjects. Morphologically segregated number counts using both sets ofvisual classifications and objective classifications support theconclusion that the observed galaxy counts agree with no-evolutionpredictions for the elliptical and spiral populations, as reported inGlazebrook et al. (1995a). A major conclusion is that the largeoverdensity of merging/peculiar/irregular galaxies relative to thepredictions of no-evolution models (reported by Glazebrook et al. 1995a)is confirmed. However, the shape of the faint-end (I > 21.0 mag)number count relation for peculiar objects is sensitive to the largesystematic uncertainties inherent in the visual classification of theseobjects. Despite this caveat, the frequency of objects showing clearevidence for tidal interactions (e.g., tidal tails) in the HST sample isat least 50% larger than it is among nearby galaxies, at the 2 σlevel. Relatively few "chain galaxies" are seen among the sample ofpeculiar objects, suggesting that these systems do not form a largecomponent of the peculiar galaxy population at I < 22 mag.
|H i and the Maffei 2 Starburst: A Merger Scenario|
We present high-resolution H I maps of the nearby starburst galaxyMaffei 2. These VLA maps have maximum resolutions of 20" and showemission extending across 15', well beyond the optical extent of thegalaxy. The radio continuum emission matches the barred asymmetricmorphology seen in the infrared. The asymmetries in the outer disk arealso evident in H I, although the nucleus, which exhibits strong COemission, is deficient in atomic gas. The total H I mass of the galaxyis 1.1 x 10^9^ M_sun_, accounting for ~1.5% of its total inferreddynamical mass. Its velocity field is, to first, order, typical ofsymmetrical barred galaxies, although there is a 10 km s^-1^ differencein systemic velocity between the disk and nucleus. Maffei 2 has amarkedly disturbed appearance with an unusual H I "double arc" to thenorth that is probably a tidal feature indicating a recent or ongoinginteraction. We propose that the asymmetries in the galaxy as well asits nuclear starburst are driven by an ongoing merger with a smallsatellite companion galaxy.
|A Catalog of Digital Images of 113 Nearby Galaxies|
We present a digital catalog of images of 113 galaxies in this paper.These galaxies are all nearby, bright, large, and well resolved. Allimages were recorded with charge coupled devices (CCDs) at the PalomarObservatory with the 1.5 m telescope and at the Lowell Observatory withthe 1.1 m telescope. At Palomar we used the Thuan-Gunn g,r, and iphotometric bands [Thuan & Gunn, PASP, 88,543(1976)] to take 3images each of 31 spiral galaxies; at Lowell we used the B_J_ and Rbands (2 images per galaxy) of the photometric system by Gullixson etal. [ApJS, 99, 281(1995)] to observe 82 spirals and ellipticals. Thegalaxies were selected to span the Hubble classification classes. Alldata are photometrically calibrated with foreground stars removed.Important data on these galaxies published in the Third ReferenceCatalog of Bright Galaxies (de Vaucouleurs et al. 1991) are recorded inthe FITS file headers. All files are available through www athttp://astro.princeton.edu/~frei/galaxy-catalog.html, and PrincetonUniversity Press will soon publish the data on CD-ROM.
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