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|Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies|
Why are the nuclei of some galaxies more active than others? If mostgalaxies harbor a central massive black hole, the main difference isprobably in how well it is fueled by its surroundings. We investigatethe hypothesis that such a difference can be seen in the detailedcircumnuclear morphologies of galaxies using several quantitativelydefined features, including bars, isophotal twists, boxy and diskyisophotes, and strong nonaxisymmetric features in unsharp-masked images.These diagnostics are applied to 250 high-resolution images of galaxycenters obtained in the near-infrared with NICMOS on the Hubble SpaceTelescope. To guard against the influence of possible biases andselection effects, we have carefully matched samples of Seyfert 1,Seyfert 2, LINER, starburst, and normal galaxies in their basicproperties, taking particular care to ensure that each was observed witha similar average scale (10-15 pc pixel-1). Severalmorphological differences among our five different spectroscopicclassifications emerge from the analysis. The H II/starburst galaxiesshow the strongest deviations from smooth elliptical isophotes, whilethe normal galaxies and LINERs have the least disturbed morphology. TheSeyfert 2s have significantly more twisted isophotes than any othercategory, and the early-type Seyfert 2s are significantly more disturbedthan the early-type Seyfert 1s. The morphological differences betweenSeyfert 1s and Seyfert 2s suggest that more is at work than simply theviewing angle of the central engine. They may correspond to differentevolutionary stages.
|An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample|
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
|Companions of Bright Barred Shapley-Ames Galaxies|
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
|The IRAS Revised Bright Galaxy Sample|
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
|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.
|Supernovae in the nuclear regions of starburst galaxies|
The feasibility of using near-infrared observations to discoversupernovae in the nuclear and circumnuclear regions of nearby starburstgalaxies is investigated. We provide updated estimates of the intrinsiccore-collapse supernova rates in these regions. We discuss the problemof extinction, and present new estimates of the extinction towards 33supernova remnants in the starburst galaxy M 82. This is done using Hiand H2 column density measurements. We estimate the molecularto atomic hydrogen mass ratio to be 7.4+/-1.0 in M 82. We have assemblednear-infrared photometric data for a total of 13 core-collapsesupernovae, some unpublished hitherto. This constitutes the largestdatabase of infrared light curves for such events. We show that theinfrared light curves fall into two classes, `ordinary' and `slowlydeclining'. Template JHKL light curves are derived for both classes. Forordinary core-collapse supernovae, the average peak JHKL absolutemagnitudes are -18.4, -18.6, -18.6 and -19.0 respectively. The slowlydeclining core-collapse supernovae are found to be significantly moreluminous than the ordinary events, even at early times, having averagepeak JHKL absolute magnitudes of -19.9, -20.0, -20.0 and -20.4respectively. We investigate the efficiency of a computerized imagesubtraction method in supernova detection. We then carry out a MonteCarlo simulation of a supernova search using K-band images of NGC 5962.The effects of extinction and observing strategy are discussed. Weconclude that a modest observational programme will be able to discovera number of nuclear supernovae.
|Galaxies with Rows|
The results of a search for galaxies with straight structural elements,usually spiral-arm rows (“rows” in the terminology ofVorontsov-Vel'yaminov), are reported. The list of galaxies that possess(or probably possess) such rows includes about 200 objects, of whichabout 70% are brighter than 14m. On the whole, galaxies with rows makeup 6 8% of all spiral galaxies with well-developed spiral patterns. Mostgalaxies with rows are gas-rich Sbc-Scd spirals. The fraction ofinteracting galaxies among them is appreciably higher than amonggalaxies without rows. Earlier conclusions that, as a rule, the lengthsof rows are similar to their galactocentric distances and that theangles between adjacent rows are concentrated near 120° areconfirmed. It is concluded that the rows must be transient hydrodynamicstructures that develop in normal galaxies.
|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.
|Compact Radio Emission from Warm Infrared Galaxies|
In this paper, we present a comparison between the optical spectroscopicdata and the incidence of compact radio emission for a sample of 60 warminfrared galaxies. We find that 80% of optically classified activegalactic nucleus (AGN)-type galaxies contain compact radio sources,while 37% of optically classified starburst galaxies contain compactradio sources. The compact radio luminosity shows a bimodaldistribution, indicating two populations in our sample. The majority ofthe higher radio luminosity class (L>104Lsolar) are AGNs, while the majority of the lower radioluminosity class (L<104 Lsolar) are starbursts.The compact radio emission in the starburst galaxies may be due toeither obscured AGNs or complexes of extremely luminous supernovae suchas that seen in Arp 220. The incidence of optically classified AGNsincreases with increasing far-infrared (FIR) luminosity. Using FIRcolor-color diagrams, we find that globally the energetics of 92% of thegalaxies in our sample are dominated by starburst activity, including60% of galaxies that we find to contain AGNs on the basis of theiroptical classification. The remainder are energetically dominated bytheir AGNs in the infrared. For starburst galaxies, electron densityincreases with dust temperature, consistent with the merger model forinfrared galaxies.
|Optical Spectroscopy of the Central Regions of Bright Barred Spiral Galaxies|
Optical red spectra of a set of 18 bright barred spiral galaxies arepresented. The study is aimed at determining the local kinematics, andthe physical conditions of ionized gas in the compact nucleus (inside adiameter of 5") and in the circumnuclear regions (inside a diameter of20"). Only 8 galaxies showed bright emission from their east and westside of the nucleus. The spectrum of each region was analizedseparately. In other 10 galaxies the line emission was so weak that wewere only able to obtain an average spectrum of the central emission. Noemission was detected in the remaining 8 galaxies. An estimate of thedynamical mass is presented based on the observed velocities in thecircumnuclear regions. In NGC 4314 and NGC 6951, that show H_alphaemission distributed in circumnuclear ring structures, we determine the[NII]/H_alpha and [SII]/H_alpha ratios for the eastern and westernregions of the rings. The velocity difference for the two sides is usedto derive the rotation velocity of the gas around the compact nucleus.The ratio [NII]6583/H_alpha is a factor of 2 larger in the compactnucleus of NGC 6951 than in its western side. The electron gas densitieshave been estimated from the [SII] lines ratio.
|K'-Band Observations of Underlying Symmetric Structure in Flocculent Galaxies|
Galaxies classified as flocculent have stochastic spiral structure intheir stellar disks. Recent observations reveal that some opticallyflocculent galaxies have underlying, faint two-arm near-IR symmetricstructure, which is indicative of a density wave. We present K'-bandobservations of 14 flocculent galaxies, of which half show some symmetryin their stellar disks and four have prominent near-IR structure. Theirarm-interarm contrasts increase with radius as they do in grand-designgalaxies, but the contrast is much smaller, indicating that the densitywaves are very weak.
|The Environments of Supernovae in Post-Refurbishment Hubble Space Telescope Images|
The locations of supernovae (SNe) in the local stellar and gaseousenvironment in galaxies contain important clues to their progenitorstars. Access to this information, however, has been hampered by thelimited resolution achieved by ground-based observations. High spatialresolution Hubble Space Telescope (HST) images of galaxy fields in whichsupernovae had been observed can improve the situation considerably. Wehave examined the immediate environments of a few dozen supernovae usingarchival post-refurbishment HST images. Although our analysis is limitedbecause of signal-to-noise ratio and filter bandpass considerations, theimages allow us for the first time to resolve individual stars in, andto derive detailed color-magnitude diagrams for, several environments.We are able to place more rigorous constraints on the masses of thesesupernovae. A search was made for late-time emission from supernovae inthe archival images and for the progenitor stars in presupernova imagesof the host galaxies. We have detected SN 1986J in NGC 891 and,possibly, SN 1981K in NGC 4258. We have also identified the progenitorof the Type IIn SN 1997bs in NGC 3627. By removing younger resolvedstars in the environments of SNe Ia, we can measure the colors of theunresolved stellar background and attribute these colors generally to anolder, redder population. HST images ``accidentally'' caught the Type IaSN 1994D in NGC 4526 shortly after its outburst; we measure itsbrightness. Finally, we add to the statistical inferences that can bemade from studying the association of SNe with recent star-formingregions.
|Look-alike galaxies:. HI observations for look-alike galaxies of four calibrators|
We present a programme aiming at applying the Tully-Fisher relation forgalaxies with the same morphological type and the same inclination(look-alike galaxies or sosie galaxies) as calibrating galaxies. Theadvantage of sosie galaxies is discussed. In particular, it is shownthat using sosies of bright calibrators will allow us to explore theuniverse deeper and more efficiently than the classical TF methodapplied to different morphological types and different inclinations. Asa preliminary part, we report in this paper new HI observationsperformed with the radiotelescope of Nançay (France) for sosiesof four calibrators NGC 224, NGC 3031, NGC 253 and NGC 5457. 82 galaxieswere detected. These observations made use of Nançayradiotelescope. The Nançay Radio Observatory is the Unitéscientifique de Nançay of the Observatoire de Paris,associated asUnité de Service et de Recherche (USR) No. B704 to the FrenchCentre National de la Recherche Scientifique (CNRS). The NançayObservatory also acknowledges the financial support of the ConseilRégional of the Région Centre in France.
|The Supernova Rate in Starburst Galaxies|
We conducted an optical CCD search for supernovae in a sample of 142bright [m(B) <= 16 mag], nearby (z<=0.03) starburst galaxies overthe period 1988 December to 1991 June, to a limiting R-band magnitude of18. Five supernovae were found, in all cases outside the host galaxy'snucleus. We determine supernova rates (in supernova units or SNU) in theextranuclear regions to be 0.7 h^2 SNU for Type Ia, 0.7 h^2 SNU for TypeIb/c, and ~0.6 h^2 SNU for Type II, with large uncertainties but upperlimits of 2.2 h^2, 2.5 h^2, and 1.7 h^2 SNU, respectively. These ratesare similar to those measured in ``normal'' galaxies. We found noevidence for a supernova-induced brightening in any galactic nucleusand, with a few reasonable assumptions, can place upper limits of 9 h^2,12 h^2, and 7 h^2 SNU on the rates of unobscured supernovae Types Ia,Ib/c, and II, respectively, inside the nuclei.
|A Hubble Space Telescope Imaging Survey of Nearby Active Galactic Nuclei|
We have obtained WFPC2 images of 256 of the nearest (z <= 0.035)Seyfert 1, Seyfert 2, and starburst galaxies. Our 500 s broadband(F606W) exposures reveal much fine-scale structure in the centers ofthese galaxies, including dust lanes and patches, bars, rings, wisps,and filaments, and tidal features such as warps and tails. Most of thisfine structure cannot be detected in ground-based images. We haveassigned qualitative classifications for these morphological featuresand a Hubble type for the inner region of each galaxy, and we have alsomeasured quantitative information such as 0."18 and 0."92 aperturemagnitudes, position angles, and ellipticities, where possible. There islittle direct evidence for unusually high rates of interaction in theSeyfert galaxies. Slightly less than 10% of all the galaxies show tidalfeatures or multiple nuclei. The incidence of inner starburst rings isabout 10% in both classes of Seyfert galaxies. In contrast, galaxieswith H II region emission-line spectra appear substantially moreirregular and clumpy because of their much higher rates of current starformation per unit of galactic mass. The presence of an unresolvedcentral continuum source in our Hubble Space Telescope images is avirtually perfect indicator of a Seyfert 1 nucleus as seen byground-based spectroscopy. Fifty-two percent of these Seyfert 1 pointsources are saturated in our images; we use their wings to estimatemagnitudes ranging from 15.8 to 18.5. The converse is not universallytrue, however, as over one-third of Seyferts with direct spectroscopicevidence for broad Balmer wings show no nuclear point source. These 34resolved Seyfert 1's have fainter nonstellar nuclei, which appear to bemore extinguished by dust absorption. Like the Seyfert 2's, they havecentral surface brightnesses consistent with those expected for thebulges of normal galaxies. The rates for the occurrences of bars inSeyfert 1's and 2's and non-Seyferts are the same. We found onesignificant morphological difference between the host galaxies ofSeyfert 1 and Seyfert 2 nuclei. The Seyfert 2 galaxies are significantlymore likely to show nuclear dust absorption, especially in lanes andpatches that are irregular or reach close to the nucleus. A few simpletests show that the difference cannot be explained by different averageredshifts or selection techniques. It is confirmed by our galaxymorphology classifications, which show that Seyfert 1 nuclei reside inearlier type galaxies than Seyfert 2 nuclei. If, as we believe, this isan intrinsic difference in host galaxy properties, it undermines one ofthe postulates of the strong unification hypothesis for Seyfertgalaxies, that they merely appear different because of the orientationof their central engine. The excess galactic dust we see in Seyfert 2'smay cause substantial absorption that obscures their hypothesized broademission line regions and central nonstellar continua. This galacticdust could produce much of the absorption in Seyfert 2 nuclei that hadinstead been attributed to a thick dusty accretion torus forming theouter part of the central engine.
|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.
|Kinematics of the local universe. VII. New 21-cm line measurements of 2112 galaxies|
This paper presents 2112 new 21-cm neutral hydrogen line measurementscarried out with the meridian transit Nan\c cay radiotelescope. Amongthese data we give also 213 new radial velocities which complement thoselisted in three previous papers of this series. These new measurements,together with the HI data collected in LEDA, put to 6 700 the number ofgalaxies with 21-cm line width, radial velocity, and apparent diameterin the so-called KLUN sample. Figure 5 and Appendices A and B forcorresponding comments are available in electronic form at thehttp://www.edpsciences.com
|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 (to188.8.131.52) or via http://cdsweb.u-strasbg.fr/Abstract.html
|Mid-Infrared Continuum of Starburst Nuclei: Contribution from Hot Large Grains within H II Regions?|
The IRAS 12 and 25 mu m fluxes are compared with the Br gamma flux in asample of starburst nuclei. Good correlations are found between them.The subsequent analysis indicates the presence of two components in themid-infrared continuum: the nonthermal emission from "small grains"(<=100 A) which are heated transiently by nonionizing photons outsidethe H II regions and the thermal emission from "large grains" which areheated to ~140 K by ionizing, nonionizing, and Ly alpha photons insidethe H II regions. The small grains emitting at 12 mu m are depleted by~20% with respect to cirrus clouds in our Galaxy. The ratio of amountsof large grains to gas in the H II regions is comparable to the standardinterstellar value. The emission from hot large grains appears to bemore enhanced over the emission from small grains in starburst nucleiwith higher excitations.
|Scaleheights of 486 southern spiral galaxies and some statistical correlation|
Based on Peng's method (1988), we obtain scaleheights of 486 southernspiral galaxies, the images of which are taken from the Digitized SkySurvey at Xinglong Station of Beijing Astronomical Observatory. Thefitted spiral arms of 70 galaxies are compared with their images to gettheir optimum inclinations. The scaleheights of other 416 ones arelisted in Table A1 in Appendix. After compiling and analyzing the data,we find some statistical correlations. The most interesting results arethat a flatter galaxy is bluer and looks brighter, and galaxies becomeflatter along the Hubble sequence Sab -- Scd. Based on photographic dataof the National Geographic Society -- Palomar Observatory Sky Survey(NGS-POSS) obtained using the Oschin Telescope Palomar Mountain. TheNGS-POSS was funded by a grant from the National Geographic Society tothe California Institute of Technology. The plates were processed intothe present compressed digital form with their permission. The DigitizedSky Survey was produced at the Space Telescope Science Institute underUS Government grant NAG W-2166. Table A1 is available in electronic fromonly, via anonymous ftp 184.108.40.206 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|Spatial Distribution of Ionized Gas in Bright Barred Spiral Galaxies: H(alpha) Images|
Charged Coupled Detector (CCD) images of a set of 52 bright barredspiral galaxies in the narrow band filter H(alpha) and in the broadbandI filter are presented. The sample was selected from the Shapley AmesCatalog, with IRAS fluxes characteristic of star formation and a dusttemperature above Td greater than or equal to 25 K. The study is aimedat identifying the global distribution and the underlying symmetries ofthe structures of ionized gas in barred galaxies. Thirty-two galaxiespresent H(alpha) emission from the innermost central regions, but theemission from nuclear rings is observed only in ten galaxies. About halfof the observed galaxies show H(alpha) emission from several regions inthe disk, and 18 galaxies display emission from along the bar. TheH(alpha) emission from inner and outer rings are easily identified insome galaxies. Some other galaxies present more complicated spatialdistributions, probably due to tidal or direct encounters withneighboring galaxies.
|Constraining the Ages of Supernova Progenitors. I. Supernovae and Spiral Arms|
We present the first results of a three-part study of supernova (SN)ages using positional age indicators in spiral galaxies. We havemeasured the positions of 90 Spectroscopically identified Type Ia andType II SNs (SNs Ia and SNs II) relative to spiral arms in their hostgalaxies, making a special effort to reduce inhomogeneity in the processof arm tracing for different galaxies. We find that SNs II are moretightly concentrated to the arms than SNs Ia, but both kinds of SNsoccur closer to arms than a random disk population. However, whencompared with the distribution of V and I light relative to the arms,the SNs Ia are no more tightly concentrated than the general stellarpopulation. This indicates that SNs Ia occur in a population old enoughto have diffused away from their formation regions.
|A comparative study of morphological classifications of APM galaxies|
We investigate the consistency of visual morphological classificationsof galaxies by comparing classifications for 831 galaxies from sixindependent observers. The galaxies were classified on laser print copyimages or on computer screen using scans made with the Automated PlateMeasuring (APM) machine. Classifications are compared using the RevisedHubble numerical type index T. We find that individual observers agreewith one another with rms combined dispersions of between 1.3 and 2.3type units, typically about 1.8 units. The dispersions tend to decreaseslightly with increasing angular diameter and, in some cases, withincreasing axial ratio (b/a). The agreement between independentobservers is reasonably good but the scatter is non-negligible. In spiteof the scatter, the Revised Hubble T system can be used to train anautomated galaxy classifier, e.g. an artificial neural network, tohandle the large number of galaxy images that are being compiled in theAPM and other surveys.
|Multiwavelength Energy Distributions and Bolometric Luminosities of the 12 Micron Galaxy Sample|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...453..616S&db_key=AST
|A Preliminary Classification Scheme for the Central Regions of Late-Type Galaxies|
The large-scale prints in The Carnegie Atlas of Galaxies have been usedto formulate a classification scheme for the central regions oflate-type galaxies. Systems that exhibit small bright central bulges ordisks (type CB) are found to be of earlier Hubble type and of higherluminosity than galaxies that do not contain nuclei (type NN). Galaxiescontaining nuclear bars, or exhibiting central regions that are resolvedinto individual stars and knots, and galaxies with semistellar nuclei,are seen to have characteristics that are intermediate between those oftypes CB and NN. The presence or absence of a nucleus appears to be auseful criterion for distinguishing between spiral galaxies andmagellanic irregulars.
|Optical studies of galaxies in clusters. Observations of spirals in Virgo. III.|
We present the analysis of the rotation curves of a sample of 32 spiralgalaxies derived from the spectroscopic observations of a sample of 47galaxies. For 15 galaxies we were either unable to detect emission linesor measure a reasonably good rotation curve. Of the 32 rotation curves23 are of galaxies member of the Virgo Cluster and 9 selected from the"field". Analysis of mass and density distribution have been obtained.The mass distribution of cluster galaxies belongs to the Type IIIproposed by Burstein & Rubin (1985) with few exceptions (NGC 4519Type I, NGC 2280, NGC 4189, NGC 5861, NGC 6070 Type II) and, isunrelated to the morphological type. Density distribution curves fromequidensity surface spheroids model, computed for the Virgo sample,result to be primarily composed of three classes. Rotation curves, noneof which shows a peculiar trend, have been parametrized using thecriteria introduced by Whitmore et al. (1984). The clustercentricdistance of Virgo spirals does not correlate neither with OG nor withOGML in agreement with the findings of Distefano et al. (1990) and Amramet al. (1993, 1994) for other clusters.
|The spatial distribution of supernovae in paired and interacting galaxies|
In order to investigate the location of supernovae (SNe) in paired andinteracting galaxies, the 54 supernovae discovered up to May 1993 in 14Isolated Pairs of Galaxies and the 32 Interacting Systems were taken asa sample and studied. The whole sample of SNe, as well as a subsampleformed of type II, and Ib SNe, whose progenitors are young massivestars, do not appear in any one particluar direction with respect to thecompanion. On paired and interacting galaxies, the radial distributionof type Ib and II SNe peaks more toward the galaxy centers than it doesin isolated galaxies, indicating an enhanced Star Formation Rate (SFR)around the nuclei and in the inner disks. The distribution of SNIaappear similar in both samples, confirming that their progenitors arenot the same as those of SNII and IB. The SN rates are related to galaxyluminosity and, as expected, the discovery of SNe is twice more frequentin the brighter galaxy of the pair than in fainter ones. We did not findany relation between the locations of SNe in parent galaxies, the totalStar Formation activity and the kinematics of paired and interactinggalaxies.
|Distribution of supernovae relative to spiral arms and H II regions|
We have studied the association of supernovae in spiral galaxies withsites of recent stars formation -- sprial arms and H II regions. It isshown that supernovae (SNe) of Types Ia, Ib, and II exhibitconcentration to spiral arms and their distributions over the distanceto the nearest spiral arm do not differ significantly. This result isconfirmed by a Kolmogorov-Smirnov test comparison with the distancedistributions, expected if SNe are distributed randomly inside the modelgalaxy. SNe of types Ib and II show a strong concentration towards H IIregions, while distribution of SNe Ia can be explained by chancesuperposition. All studied distributions of SNe Ib and II show strikingsimilarity, which suggests that their progenitors are massive stars withsimilar ages and initial masses. The association of SNe Ia with spiralarms suggests that their progenitors in spiral galaxies are likely to beintermediate mass stars.
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