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Spitzer Space Telescope IRAC and MIPS Observations of the Interacting Galaxies IC 2163 and NGC 2207: Clumpy Emission
IC 2163 and NGC 2207 are interacting galaxies that have been wellstudied at optical and radio wavelengths and simulated in numericalmodels to reproduce the observed kinematics and morphological features.Spitzer IRAC and MIPS observations reported here show over 200 brightclumps from young star complexes. The brightest IR clump is amorphologically peculiar region of star formation in the western arm ofNGC 2207. This clump, which dominates the Hα and radio continuumemission from both galaxies, accounts for ~12% of the total 24 μmflux. Nearly half of the clumps are regularly spaced along somefilamentary structure, whether in the starburst oval of IC 2163 or inthe thin spiral arms of NGC 2207. This regularity appears to influencethe clump luminosity function, making it peaked at a value nearly afactor of 10 above the completeness limit, particularly in the starburstoval. This is unlike the optical clusters inside the clumps, which havea luminosity function consistent with the usual power-law form. Thegiant IR clumps presumably formed by gravitational instabilities in thecompressed gas of the oval and the spiral arms, whereas the individualclusters formed by more chaotic processes, such as turbulencecompression, inside these larger scale structures.
| The grazing encounter between IC 2163 and NGC 2207: pushing the limits of observational modelling
We present numerical hydrodynamical models of the collision between thegalaxies IC 2163 and NGC 2207. These models extend the results ofearlier work in which the galaxy discs were modelled one at a time. Weconfirm the general result that the collision is primarily planar, thatis, at moderate inclination relative to the two discs, and prograde forIC 2163, but retrograde for NGC 2207. We list 34 specific morphologicalor kinematic features on a variety of scales, found with multiwavebandobservations, which we use to constrain the models. The models are ableto reproduce most of these features, with a relative orbit in which thecompanion (IC 2163) disc first side-swipes the primary (NGC 2207) discon the west side, then moves around the edge of the primary disc to thenorth and to its current position on the east side. The models alsoprovide evidence that the dark matter halo of NGC 2207 has only moderateextent. For IC 2163, the prolonged prograde disturbance in the modelproduces a tidal tail, and an oval or ocular waveform very much like theobserved ones, including some fine structure. The retrograde disturbancein the model produces no strong waveforms within the primary galaxy.This suggests that the prominent spiral waves in NGC 2207 were presentbefore the collision, and models with waves imposed in the initialconditions confirm that they would not be disrupted by the collision.With an initial central hole in the gas disc of the primary, and imposedspirals, the model also reproduces the broad ring seen in HIobservations. Model gas disc kinematics compare well to the observed(HI) kinematics, providing further confirmation of its validity. Analgorithm for feedback heating from young stars is included, and thefeedback models suggest the occurrence of a moderate starburst in IC2163 about 250 Myr ago.We believe that this is now one of the best-modelled systems ofcolliding galaxies, though the model could still be improved byincluding full disc self-gravity. The confrontation between observationsand models of so many individual features provides one of the strongesttests of collision theory. The success of the models affirms thistheory, but the effort required to achieve this, and the sensitivity ofmodels to initial conditions, suggests that it will be difficult tomodel specific structures on scales smaller than about a kiloparsec inany collisional system.
| Spatial distribution of galaxies in the Puppis region
We determine the spatial distribution of the galaxies located behind thepart of the zone of avoidance of the Milky Way defined by 220°
| 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.
| The unexpected youth of globular clusters.
Not Available
| Supernova 2003H in NGC 2207
IAUC 8046 available at Central Bureau for Astronomical Telegrams.
| 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.
| Massive Star Clusters in Ongoing Galaxy Interactions: Clues to Cluster Formation
We present HST WFPC2 observations, supplemented by ground-based Hαdata, of the star-cluster populations in two pairs of interactinggalaxies selected for being in very different kinds of encounters seenat different stages. Dynamical information and n-body simulationsprovide the details of encounter geometry, mass ratio, and timing. InNGC 5752/4 we are seeing a weak encounter, well past closest approach,after about 2.5×108 yr. The large spiral NGC 5754 has anormal population of disk clusters, while the fainter companion NGC 5752exhibits a rich population of luminous clusters with a flatterluminosity function. The strong, ongoing encounter in NGC 6621/2, seenabout 1.0×108 yr past closest approach between roughlyequal-mass galaxies, has produced an extensive population of luminousclusters, particularly young and luminous in a small region between thetwo nuclei. This region is dynamically interesting, with such a strongperturbation in the velocity field that the rotation curve reversessign. From these results, in comparison with other strongly interactingsystems discussed in the literature, cluster formation requires athreshold level of perturbation, with stage of the interaction a lessimportant factor. The location of the most active star formation in NGC6621/2 draws attention to a possible role for the Toomre stabilitythreshold in shaping star formation in interacting galaxies. The richcluster populations in NGC 5752 and NGC 6621 show that direct contactbetween gas-rich galaxy disks is not a requirement to form luminousclusters and that they can be triggered by processes happening within asingle galaxy disk (albeit triggered by external perturbations).Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The Mysteries of Galaxy Spirals
Not Available
| NGC 4314. IV. Photometry of Star Clusters with the Hubble Space Telescope: History of Star Formation in the Vicinity of a Nuclear Ring
Using Hubble Space Telescope (HST) WFPC2 images, we have obtained U, B,V, I, and Hα photometry for 76 star clusters in the nuclearstar-forming ring of the barred spiral galaxy NGC 4314. These clustersare likely associated with an inner inner Lindblad resonance (IILR). Theblue colors and Hα emission for most of these clusters imply veryyoung ages of 1-15 Myr. Age estimates based on several reddening-freeparameters indicate that the present epoch of star formation has lastedat least 30 Myr. By estimating the masses of stars in the clusters andcomparing with the Hα luminosity, we conclude that a significantfraction of ongoing star formation in the nuclear ring of NGC 4314occurs in clusters. The cluster masses identify these as young openclusters, not young globular clusters. Farther out in the galaxy, justexterior to the ring of young stars, previous ground-based observationsrevealed two symmetric stellar spiral arms that may be associated withan outer inner Lindblad resonance (OILR). With our HST data, we haverevealed part of this structure and its colors in more detail. Thespiral arm colors are consistent with stellar ages between 40 and 200Myr. The age difference between the inner ring of young stars (IILR) andthe larger oval-like feature containing the blue arms (OILR) supports aninterpretation of the morphology of the nuclear region of NGC 4314 thatrequires a reservoir of gas that becomes more compact over time. Wespeculate that as the gas distribution becomes more centrallyconcentrated, it interacts with these two resonances. Each resonancetriggers star formation, resulting in two distinct epochs of starformation. Based on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| Circumnuclear Star Formation in the Spiral Galaxy NGC 3310
The star-forming properties of the circumnuclear ring in the starburstspiral galaxy NGC 3310 have been studied in B, I, J, H, and K bandsusing images from KPNO and from the HST archives. The colors andmagnitudes of the star-forming regions indicate ages less than 10 Myrand masses of 104 to 105 Msolar for thelargest clumps. The luminosity distribution function of the diffusecircumnuclear clusters has a slope of about -2, which is typical ofresults both in circumnuclear rings and in the main disks of othergalaxies. There are 17 candidate super star clusters (SSCs), primarilyin the innermost southern spiral arm. The broad wavelength coverageallows a determination of reddening in the vicinity of the SSCs, whichappears to be small. The locations of the SSCs in the circumnuclear ringand in an inner spiral are coincident with radio continuum and emissionpeaks, and may be the result of a suspected cannibalization of a dwarfgalaxy in the last 10 Myr.
| CO Observations of the Interacting Galaxy Pair NGC 5394/95
BIMA 12CO J=1-->0 observations are presented of the spiralgalaxies NGC 5394 and NGC 5395 that have undergone a recent, grazingencounter. In NGC 5394 approximately 80% of the CO emission detected byBIMA is concentrated in the central 800 pc (FWHM) starburst region, andthe rest is from a portion of the inner disk south and west of thecentral starburst. In an encounter simulation that reproduces some ofthe main features of this galaxy pair, a considerable amount of gas inNGC 5394 falls into the central region early in the collision. Theobserved total gas distribution in the disk of NGC 5394 is lopsided,with more H I, CO, and Hα emission coming from the western orsouthwestern side. The innermost western arm of NGC 5394 is seen in COand Hα emission, but the eastern inner-disk arm, which is verybright in the optical continuum, is not detected in CO or Hαemission. The NGC 5394 starburst region is similar in radio continuumluminosity and size to the M82 starburst and has a CO luminosity ~4times greater. A CO position-velocity diagram of the NGC 5394 nucleusreveals two separate velocity features very close to the center. Thismay indicate a nuclear ring or the ``twin peaks'' of an ILR or somedepletion of 12CO J=1-->0 at the nucleus. From acomparison of the radio continuum, Hα, 60 μm, and COluminosities, we estimate that the average extinction Av ofthe starburst nucleus is 3-4 mag, the star formation rate is ~6Msolar yr-1, and the conversion factorN(H2)/ICO in the starburst is a factor of 3-4below the standard value. Comparison of NGC 5394 with two other systemspreviously studied suggests that in prograde grazing encounters acentral starburst may not develop until near the end of the ocularphase. Very little of the CO emission from NGC 5395 found in previoussingle-dish observations is detected in the BIMA data; thus moleculargas in NGC 5395 does not appear to be strongly concentrated incompressed ridges.
| H i observations of interacting galaxy pair NGC 4038/9
We present the results of new radio interferometer Hi line observationsfor the merging galaxy pair NGC 4038/9 (`The Antennae'), obtained usingthe Australia Telescope Compact Array. The results improve substantiallywith respect to those of van der Hulst and show in detail the twomerging galactic discs and the two tidal tails produced by theirinteraction. The small edge-on spiral dwarf galaxy ESO 572-G045 is alsoseen near the tip of the southern tail, but distinct from it. It showsno signs of tidal interaction. The northern tidal tail of the Antennaeshows no Hi connection to the discs and has an extension towards thewest. The southern tidal tail is continuous, with a prominent Hiconcentration at its tip, roughly at the location of the tidal dwarfgalaxy observed optically by Mirabel, Dottori & Lutz. Clear velocitystructure is seen along the tidal tails and in the galactic discs. Radiocontinuum images at 20 and 13cm are also presented, showing the discs indetail.
| Le dernier repas de la Voie lactee.
Not Available
| Arc-Shaped and Spheroidal Stellar Complexes
Complexes of young clusters and high-luminosity stars in the shape ofregular, circular arcs have been found in a number of galaxies, firstand foremost the LMC, NGC 6946, and M83. These shapes are found even instrongly inclined galaxies, suggesting that the observed arcs areprojections of partial spherical shells. Obviously, these stellar shellsmust have formed from gaseous shells swept up by some source of centralpressure and become gravitationally unstable. The power of this sourcecorresponds to several dozen supernova explosions; however, its natureremains unclear. A central cluster providing a source of O stars andsupernovae is usually absent. The presence of multiple arcs locatedclose to each other can be explained by the fall of a swarm of fragmentsor by the progenitor stars originating in a single peculiar starcluster, implying the existence of stellar objects capable of givingrise to explosions with energies an order of magnitude higher than thoseof individual supernovae. The same objects may be responsible forgamma-ray bursts. It may be that only the most massive clusters withfrequent or especially powerful supernova explosions are capable ofproducing HI supershells. Otherwise, it is impossible to explain why nosupershells have been found around numerous clusters that should becapable of producing them according to current theories. The presence ofstar clusters in shell-like structures provides extremely importantinformation about the physical conditions in and the ages of the initialgaseous shells, making stellar arcs the best available laboratory forstudies of triggered star formation.
| Seeing Galaxies through Thick and Thin. IV. The Superposed Spiral Galaxies of NGC 3314
The superposed pair of spiral galaxies making up NGC 3314 offers aunique opportunity to trace the dust properties in a spiral galaxy. Weanalyze multicolor Hubble Space Telescope imaging, supported byground-based near-IR imaging and fiber-array spectroscopy, to measuredust extinction in the foreground Sc galaxy NGC 3314A, which is backlitby the Sb system NGC 3314B. The superposition allows us to measureextinctions over a wide range of galactocentric radii in the foregroundgalaxy from 0.4-4.5 kpc. In the outer half of the disk, the extinctionis strongly localized in discrete dust lanes, including some patcheswhose galactic setting is clear only because of associated Hαemission at the foreground velocity. These dust features show anextinction curve with a slope close to the Galactic mean (R=3.5+/-0.3)over a range in galactocentric radius from 1.6 to 3.8 kpc, with noradial trend. Using the I-K color of the background nucleus, we derivean extinction of AI=3.3 through the disk at a projecteddistance of 400 pc from the nucleus of NGC 3314A. The extinction in eventhe inner disk of NGC 3314A is quite patchy, since background Hαemission is detected from all parts of the system. Localanticorrelations between foreground and background line emissiondemonstrate that the dust is concentrated in star-forming regions, ashas been found for the blue light in several systems. The colors of thedust lanes in NGC 3314A that are projected only partially against thebackground disk indicate that the dust scale height in the foregrounddisk is substantially smaller than that of the stars. Thecolor-intensity behavior of the net light in these regions tracks thepredictions of a thin-layer model closely. Based on observations withthe NASA/ESA Hubble Space Telescope obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555.
| Fractal Structure in Galactic Star Fields
The fractal structure of star formation on large scales in disk galaxiesis studied using the size distribution function of stellar aggregates inkiloparsec-scale star fields. Archival Hubble Space Telescope images of10 galaxies are Gaussian-smoothed to define the aggregates, and a countof these aggregates versus smoothing scale gives the fractal dimension.Fractal and Poisson models confirm the procedure. The fractal dimensionof star formation in all of the galaxies is ~2.3. This is the same asthe fractal dimension of interstellar gas in the Milky Way and nearbygalaxies, suggesting that star formation is a passive tracer of gasstructure defined by self-gravity and turbulence. Dense clusters such asthe Pleiades form at the bottom of the hierarchy of structures, wherethe protostellar gas is densest. If most stars form in such clusters,then the fractal arises from the spatial distribution of theirpositions, giving dispersed star fields from continuous clusterdisruption. Dense clusters should have an upper mass limit thatincreases with pressure, from ~103 Msolar inregions like the solar neighborhood to ~106 Msolarin starbursts.
| Hubble Space Telescope Observations of Dust and Star-forming Regions in the Ocular Galaxy IC 2163 and Its Spiral Companion NGC 2207
Hubble Space Telescope observations in U, B, V, and I passbands of theinteracting spiral galaxies IC 2163 and NGC 2207 are used to measureextinctions in the cloud and intercloud regions and ages andluminosities of the star-forming regions. The extinction in the part ofNGC 2207 seen in projection against IC 2163 was determined by using themethod of White & Keel. The extinctions there and elsewhere werealso determined from radiative transfer models of the magnitudedifferences between clouds and their surroundings. The intercloudextinction in V band ranges from 0.5 to 1 mag on the line of sight, andthe cloud extinction ranges from 1 to 2 mag. The measured star-formingregions in these galaxies have a power-law relation between size andluminosity and a power-law luminosity distribution function. These powerlaws are consistent with a fractal dimension for the star formation thatis the same as that for interstellar gas, D~2.2, extending over scalesranging from 20 to 1000 pc. Fifteen compact massive star clusters thatare analogous to super-star clusters found in starburst regions are inthe spiral arms of NGC 2207. Nothing is peculiar about these regionsexcept for a high H I velocity dispersion (~50 km s-1). Twomore super-star clusters are in the tidally compressed oval of IC 2163.These clusters have masses ranging from ~104 to2×105 Msolar and ages of a few times106 yr.
| Seeing Galaxies through Thick and Thin. II. Direct Measures of Extinction in Spiral Disks through Spectroscopy of Overlapping Galaxies
We use slit spectroscopy of overlapping pairs of galaxies to directlydetermine the extinction in disks of foreground spiral galaxies. TheDoppler shifts of pair members are determined via cross-correlation, andtheir relative correlation amplitudes are used to separate theircontributions to the combined spectra in regions of overlap. Thisspectroscopic approach is less subject to stringent symmetry constraintsthan our previous, purely photometric analyses. Extinctions offoreground members were obtained for six of the candidates in our sampleof 18 mostly spiral/spiral pairs, when the signal-to-noise-ratio andvelocity differences were suitable. In agreement with our previousimaging results, we find that the extinction in interarm regions is verymodest, typically AB~0.1 mag (corrected to face-on), whilespiral arms exhibit higher extinctions of ~0.3 mag.
| Hubble Space Telescope Observations of the Interacting Galaxies NGC 2207 and IC 2163
Hubble Space Telescope (HST) images of the galaxies NGC 2207 and IC 2163show star formation and dust structures in a system that has experienceda recent grazing encounter. Tidal forces from NGC 2207 compressed andelongated the disk of IC 2163, forming an oval ridge of star formationalong a caustic where the perturbed gas rebounded after its inwardexcursion. Gas flowing away from this ridge has a peculiar structurecharacterized by thin parallel dust filaments transverse to thedirection of motion. The filaments become thicker and longer as the gasapproaches the tidal arm. Star formation that occurs in the filamentsconsistently lags behind, as if the exponential disk pressure gradientpushes outward on the gas but not on the young stars. Numerical modelssuggest that the filaments come from flocculent spiral arms that werepresent before the interaction. The arms stretch out into parallelfilaments as the tidal tail forms. A dust lane at the outer edge of thetidal tail is a shock front where the flow abruptly changes direction.Gas at small-to-intermediate radii along this edge flows back toward thegalaxy, while elsewhere in the tidal arm, the gas flows outward. Aspiral arm of NGC 2207 that is backlit by IC 2163 is seen with HST tocontain several parallel, knotty filaments spanning the full width ofthe arm. These filaments are probably shock fronts in a density wave.The parallel structure suggests that the shocks occur in several placesthroughout the arm, or that the interarm gas is composed of spiral-likewisps that merge together in the arms. Blue clusters of star formationinside the clumps of these dust lanes show density-wave triggering inunprecedented detail. The star formation process seems to be one oflocal gravitational collapse, rather than cloud collisions. Spiral armsinside the oval of IC 2163 have a familiar geometry reminiscent of abar, although there is no obvious stellar bar. The shape and orientationof these arms suggest they could be the result of inner Lindbladresonance-related orbits in the cos2θ tidal potential that formedthe oval. Their presence suggests that tidal forces alone may initiate atemporary nuclear gas flow and eventual starburst without first forminga stellar bar. Several emission structures resembling jets or conicalflows that are 100-1000 pc long appear in these galaxies. In the westernarm of NGC 2207, there is a dense dark cloud with a conical shape 400 pclong and a bright compact cluster at the tip, and there is a conicalemission nebula of the same length that points away from the cluster inthe other direction. This region also coincides with a nonthermal radiocontinuum source that is ~1000 times the luminosity of Cas A atλ=20 cm. Surrounding clusters in arclike patterns may have beentriggered by enormous explosions. Based on observations with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| 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
| Supernova 1999ec in NGC 2207
IAUC 7268 available at Central Bureau for Astronomical Telegrams.
| Galaxy collisions.
Theories of how galaxies, the fundamental constituents of large-scalestructure, form and evolve have undergone a dramatic paradigm shift inthe last few decades. Earlier views were of rapid, early collapse andformation of basic structures, followed by slow evolution of the stellarpopulations and steady buildup of the chemical elements. Currenttheories emphasize hierarchical buildup via recurrent collisions andmergers, separated by long periods of relaxation and secularrestructuring. Thus, collisions between galaxies are now seen as aprimary process in their evolution. This article begins with a briefhistory; we then tour parts of the vast array of collisional forms thathave been discovered to date. Many examples are provided to illustratehow detailed numerical models and multiwaveband observations haveallowed the general chronological sequence of collisional morphologiesto be deciphered, and how these forms are produced by the processes oftidal kinematics, hypersonic gas dynamics, collective dynamical frictionand violent relaxation. Galaxy collisions may trigger the formation of alarge fraction of all the stars ever formed, and play a key role infueling active galactic nuclei. Current understanding of the processesinvolved is reviewed. The last decade has seen exciting new discoveriesabout how collisions are orchestrated by their environment, howcollisional processes depend on environment, and how these environmentsdepend on redshift or cosmological time.
| The Interacting Galaxies NGC 5394/5395: A Post-Ocular Galaxy and Its Ring/Spiral Companion
H I, radio continuum, Fabry-Perot Hα, and ^12CO J=1-->0observations and broadband optical and near infrared images arepresented of the interacting spiral galaxies NGC 5395 and NGC 5394.Kinematically, there are three important, separate components to the H Igas associated with this galaxy pair: (1) the main disk of NGC 5395, (2)a long, northern tidal arm of NGC 5395 distinct in velocity from itsmain disk, and (3) the disk of NGC 5394. The H I northern tidal arm ofNGC 5395 has a line of-sight velocity as much as 75-100 km s^-1 greaterthan the main disk of NGC 5395 at the same projected location and thusis not in the same plane as the disk. The velocity field of the disk ofNGC 5395 is asymmetric and distorted by large-scale and small-scalenoncircular motions. In NGC 5395, the encounter appears to be excitingm=1 and m=0 modes in what had been a two-armed spiral. The dominantspiral arm of NGC 5395 forms a large ring or pseudo-ring of Hα,radio continuum, and H I emission, somewhat off center with respect tothe nucleus. The H I trough in the center of NGC 5395 is not filled inby molecular gas. The Hα velocity contours exhibit an organizedpattern of kinks in crossing the ring and also show streaming motions ina large stellar caustic feature. The eastern side of the ring isbrighter in radio continuum and Hα the western side is brighter inH I and contains massive (10^8 M_solar) H I clouds not associated withthe most luminous H II regions. The smaller galaxy NGC 5394 is in animmediate post-ocular phase, with a central starburst, an intrinsicallyoval disk, two long, fairly symmetric, open tidal arms with higharm-interarm contrast, and very bright inner spiral arms, disjoint fromthe outer tidal arms. Most of the gas in NGC 5394 is in molecular formand concentrated within 3.8 kpc of the center, so is suitable forfueling the starburst. Despite the presence of H I gas, two of the threeoptically bright inner spiral arms of NGC 5394 show no evidence ofongoing star formation. A galaxy encounter simulation reproduces some ofthe main features of this system with a collision that is prograderelative to NGC 5394 and retrograde at a high tilt angle relative to NGC5395. The model finds that the inner spiral structure of NGC 5394developed from an eye-shaped (``ocular'') structure at slightly earliertimes. NGC 5394 and the two ocular galaxies IC 2163 and NGC 2535,studied earlier, form an evolutionary sequence of structures resultingfrom prograde encounters and thus confirm the generic models of suchcollisions. The agreement between the model for NGC 5394/95 and thering/spiral structures seen in NGC 5395 extends our understanding ofcollisional ring galaxies.
| Dust Spirals and Acoustic Noise in the Nucleus of the Galaxy NGC 2207
Observations with the Hubble Space Telescope reveal an irregular networkof dust spiral arms in the nuclear region of the interacting disk galaxyNGC 2207. The spirals extend from ~50 to ~300 pc in galactocentricradius, with a projected width of ~20 pc. Radiative transfercalculations determine the gas properties of the spirals and the innerdisk and imply a factor of ~4 local gas compression in the spirals. Thegas is not strongly self-gravitating, nor is there a nuclear bar, so thespirals could not have formed by the usual mechanisms applied to maingalaxy disks. Instead, they may result from acoustic instabilities thatamplify at small galactic radii. Such instabilities may promote gasaccretion into the nucleus.
| 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 130.79.128.5 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 (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| The Ocular Galaxy NGC 2535 and its Small Starburst Companion NGC 2536
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INHABITED SKY
