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The Pattern Speeds of 38 Barred Galaxies
We estimate the pattern speeds of 38 barred galaxies by simulationmodeling. We construct the gravitational potentials of the galaxies fromnear-IR photometry by assuming that the mass-to-light ratio (M/L) isconstant in the H band and a single pattern speed dominates in thestellar disk. We use the response of gaseous and stellar particle disksto a rigidly rotating potential to determine the pattern speed. If ourassumptions are correct, then the pattern speed depends on themorphological type: the average value of the ratio of the corotationresonance radius to the bar radius, ℛ, increases from about 1.1 intype SB0/a to 1.4 in SBb and 1.7 in SBc. Within the error estimates, allthe bars in galaxies of type SBab or earlier are fast rotators, havingℛ<=1.4, whereas late-type galaxies include both fast and slowrotators.
| The Distribution of Bar and Spiral Arm Strengths in Disk Galaxies
The distribution of bar strengths in disk galaxies is a fundamentalproperty of the galaxy population that has only begun to be explored. Wehave applied the bar-spiral separation method of Buta and coworkers toderive the distribution of maximum relative gravitational bar torques,Qb, for 147 spiral galaxies in the statistically well-definedOhio State University Bright Galaxy Survey (OSUBGS) sample. Our goal isto examine the properties of bars as independently as possible of theirassociated spirals. We find that the distribution of bar strengthdeclines smoothly with increasing Qb, with more than 40% ofthe sample having Qb<=0.1. In the context of recurrent barformation, this suggests that strongly barred states are relativelyshort-lived compared to weakly barred or nonbarred states. We do notfind compelling evidence for a bimodal distribution of bar strengths.Instead, the distribution is fairly smooth in the range0.0<=Qb<0.8. Our analysis also provides a first look atspiral strengths Qs in the OSUBGS sample, based on the sametorque indicator. We are able to verify a possible weak correlationbetween Qs and Qb, in the sense that galaxies withthe strongest bars tend to also have strong spirals.
| Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.
| Formation of inner rings in 3D potentials of barred galaxies
In a 3D analytic potential we find the families of periodic orbits thatsupport the formation of inner rings. These are families at highenergies, between the inner radial ultraharmonic 4:1 (iUHR) resonanceand corotation, influenced by the 4:1, 6:1 and 8:1 resonances. The innerrings they support are mainly ovals and polygons with `corners' on thebar minor axis, on its sides, which correspond to morphologies oftenseen in real galaxies like NGC 6782 and IC 4290. We also investigate theconditions under which less probable shapes of rings may be supported byorbits at the region. Such rings include pentagonal features (NGC 3367)and hexagons with cusps on the major axis of the bar and two sidesparallel to it (NGC 7020).
| Secular Evolution and the Formation of Pseudobulges in Disk Galaxies
The Universe is in transition. At early times, galactic evolution wasdominated by hierarchical clustering and merging, processes that areviolent and rapid. In the far future, evolution will mostly be secularthe slow rearrangement of energy and mass that results from interactionsinvolving collective phenomena such as bars, oval disks, spiralstructure, and triaxial dark halos. Both processes are important now.This review discusses internal secular evolution, concentrating on oneimportant consequence, the buildup of dense central components in diskgalaxies that look like classical, merger-built bulges but that weremade slowly out of disk gas. We call these pseudobulges.
| A Hubble Space Telescope Study of Star Formation in the Inner Resonance Ring of NGC 3081
We present Hubble Space Telescope Wide Field Planetary Camera 2 imagesof the inner regions of NGC 3081, an absolute magnitudeMB=-20.0 early-type barred spiral having four well-definedresonance rings: a nuclear ring, an inner ring, an outer R1ring, and an outer R'2 pseudoring. Here we focuson a photometric study of the inner ring, a feature likely associatedwith an inner 4:1 resonance near the ends of the bar. The ring isnotable for its high contrast and sharp definition, which is due to asignificant degree of active star formation. The ring is also notablefor its significant intrinsic elongation and parallel alignment with thebar. These characteristics influence the way star-forming sites aredistributed around the ring. The ring is lined by numerous blue sources,many of which appear to be slightly diffuse compared with the stellarpoint-spread function. These blue sources are strongly concentratedwithin +/-60° of the bar axis and follow the Hα distributionwell. The blue sources are much larger than typical Galactic open orglobular clusters and may represent young massive clusters like the``populous clusters'' of the LMC and objects seen previously mainly inintermediate- to late-type spiral galaxies. We also present an analysisof the integrated light of the inner ring, to deduce information on itsstar formation history. A profile analysis is used to separate the ringfrom the background old disk starlight. High-resolution Fourier analysisis used to search for wavelength-dependent phase shifts along the ringto determine if star-forming sites stay in the ring as they age. Theresults give an intriguing picture of a galaxy in an advancedevolutionary state where periodic orbits are clearly manifested in themorphology.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 (AURA), Inc.,under NASA contract NAS 5-26555.
| The Formation of Starburst Ring, Circumnuclear Molecular Disk, and Diamond-shape Structures in Disk Galaxies
Starburst rings are one of most spectacular phenomena observed in thecenter of many nearby galaxies. Recent high resolution observations haverevealed that star burst rings are often composed of two tightly woundspirals. Density wave theory successfully shows that tightly woundspirals can be excited resonantly by a rotating bar potential. We willuse numerical simulations to demonstrate the formation of starburstrings. In addition, we will show for certain galaxies with rapidlyrising rotation curves, a tiny disk of extremely gas high density nearthe center can be formed as well. This disk, with weak star formationactivities, is in close resemblance to the dense circumnuclear moleculardisks seen in the center of many nearby galaxies, which may or may nothave AGN in the nucleus. The simulations to be presented here are usingthe high order Godunov method featured with exact Riemann solver and fftPoisson solver. The simulations use Milky Way's rotation curve todemonstrate the formation of starburt rings and the dense circumnuclearmolecular disk near the center. On the other hand, simulations using anearly-flat rotation curve further result in a diamond-shape structurein addition to starburt rings and the dense circumnuclear moleculardisk. Such results are relevant to galaxy NGC6782, in which adiamond-shaped ring is observed and with the central ring, forms thefamous double-ring structure.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Deprojecting spiral galaxies using Fourier analysis. Application to the Ohio sample
We use two new methods developed recently (Barberàet al.\cite{bar03}, A&A, 415, 849), as well as information obtained fromthe literature, to calculate the orientation parameters of the spiralgalaxies in the Ohio State University Bright Galaxy Survey. We comparethe results of these methods with data from the literature, and find ingeneral good agreement. We provide a homogeneous set of mean orientationparameters which can be used to approximately deproject the disks of thegalaxies and facilitate a number of statistical studies of galaxyproperties.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/421/595
| Double-barred galaxies. I. A catalog of barred galaxies with stellar secondary bars and inner disks
I present a catalog of 67 barred galaxies which contain distinct,elliptical stellar structures inside their bars. Fifty of these aredouble-barred galaxies: a small-scale, inner or secondary bar isembedded within a large-scale, outer or primary bar. I providehomogenized measurements of the sizes, ellipticities, and orientationsof both inner and outer bars, along with global parameters for thegalaxies. The other 17 are classified as inner-disk galaxies, where alarge-scale bar harbors an inner elliptical structure which is alignedwith the galaxy's outer disk. Four of the double-barred galaxies alsopossess inner disks, located in between the inner and outer bars. Whilethe inner-disk classification is ad-hoc - and undoubtedly includes someinner bars with chance alignments (five such probable cases areidentified) - there is good evidence that inner disks form astatistically distinct population, and that at least some are indeeddisks rather than bars. In addition, I list 36 galaxies which may bedouble-barred, but for which current observations are ambiguous orincomplete, and another 23 galaxies which have been previously suggestedas potentially being double-barred, but which are probably not. Falsedouble-bar identifications are usually due to features such as nuclearrings and spirals being misclassified as bars; I provide someillustrated examples of how this can happen.A detailed statistical analysis of the general population of double-barand inner-disk galaxies, as represented by this catalog, will bepresented in a companion paper.Tables \ref{tab:measured} and \ref{tab:deproj} are only available inelectronic form at http://www.edpsciences.org
| Stellar populations and star cluster formation in interacting galaxies with the Advanced Camera for Surveys
Pixel-by-pixel colour-magnitude and colour-colour diagrams-based on asubset of the Hubble Space Telescope Advanced Camera for Surveys EarlyRelease Observations-provide a powerful technique to explore and deducethe star and star cluster formation histories of the Mice and the Tadpole interactinggalaxies. In each interacting system we find some 40 bright young starclusters (20<~F606W(mag)<~25, with a characteristic mass of~3×106 Msolar), which are spatiallycoincident with blue regions of active star formation in their tidaltails and spiral arms. We estimate that the main events triggering theformation of these clusters occurred ~(1.5-2.0)×108 yrago. We show that star cluster formation is a major mode of starformation in galaxy interactions, with >~35% of the active starformation in encounters occurring in star clusters. This is the firsttime that young star clusters have been detected along the tidal tailsin interacting galaxies. The tidal tail of the Tadpole system isdominated by blue star forming regions, which occupy some 60% of thetotal area covered by the tail and contribute ~70% of the total flux inthe F475W filter (decreasing to ~40% in F814W). The remaining pixels inthe tail have colours consistent with those of the main disk. Thetidally triggered burst of star formation in the Mice is of similarstrength in both interacting galaxies, but it has affected onlyrelatively small, spatially coherent areas.
| On the 3D dynamics and morphology of inner rings
We argue that inner rings in barred spiral galaxies are associated withspecific 2D and 3D families of periodic orbits located just beyond theend of the bar. These are families located between the inner radialultraharmonic 4:1 resonance and corotation. They are found in the upperpart of a type-2 gap of the x1 characteristic, and can account for theobserved ring morphologies without any help from families of thex1-tree. Due to the evolution of the stability of all these families,the ring shapes that are favoured are mainly ovals, as well as polygonswith `corners' on the minor axis, on the sides of the bar. On the otherhand, pentagonal rings, or rings of the NGC 7020-type hexagon, should beless probable. The orbits that make the rings belong in their vastmajority to 3D families of periodic orbits and orbits trapped aroundthem.
| Ultraviolet-Optical Pixel Maps of Face-on Spiral Galaxies: Clues for Dynamics and Star Formation Histories
Ultraviolet and optical images of the face-on spiral galaxies NGC 6753and NGC 6782 reveal regions of strong ongoing star formation that areassociated with structures traced by the old stellar populations. We usethese images to construct NUV-(NUV-I814) pixelcolor-magnitude diagrams (pCMDs) that reveal plumes of pixels withstrongly varying near-ultraviolet (NUV) surface brightness and nearlyconstant I814 surface brightness. The plumes correspond tosharply bounded radial ranges, with (NUV-I814) at a given NUVsurface brightness being bluer at larger radii. The plumes are parallelto both the reddening vector and simple model mixtures of young and oldpopulations, thus neither reddening nor the fraction of the youngpopulation can produce the observed separation between the plumes. Theimages and radial surface brightness and color plots indicate that theseparate plumes are caused by sharp declines in the surface densities ofthe old populations at radii corresponding to disk resonances. Themaximum surface brightness of the NUV light remains essentially constantwith radius, while the maximum I814 surface brightnessdeclines sharply with radius. A mid-ultraviolet (MUV) image of NGC 6782shows emission from the nuclear ring. The distribution of points in an(MUV-NUV)-(NUV-I814) pixel color-color diagram is broadlyconsistent with the simple mixture model but shows a residual trend thatthe bluest pixels in (MUV-NUV) are the reddest pixels in(NUV-I814). This may be due to a combination of red continuumfrom late-type supergiants and [S III] emission lines associated with HII regions in active star-forming regions. We have shown that pixelmapping is a powerful tool for studying the distribution and strength ofongoing star formation in galaxies. Deep, multicolor imaging can extendthis to studies of extinction and the ages and metallicities ofcomposite stellar populations in nearby galaxies.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Sciences Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| A Hubble Space Telescope Survey of the Mid-Ultraviolet Morphology of Nearby Galaxies
We present a systematic imaging survey of 37 nearby galaxies observedwith the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2(WFPC2) in the mid-UV F300W filter, centered at 2930 Å, as well asin the I-band (F814W) filter at 8230 Å. Eleven of these galaxieswere also imaged in the F255W filter, centered at 2550 Å. Oursample is carefully selected to include galaxies of sufficiently smallradius and high predicted mid-UV surface brightness to be detectablewith WFPC2 in one orbit and covers a wide range of Hubble types andinclinations. The mid-UV (2000-3200 Å) spans the gap betweenground-based UBVR(IJHK) images, which are available or were acquired forthe current study, and far-UV images available from the Astro/UITmissions for 15 galaxies in our sample. The first qualitative resultsfrom our study are as follows:1. Early-type galaxies show a significantdecrease in surface brightness going from the red to the mid-UV,reflecting the absence of a dominant young stellar population and insome cases the presence of significant (central) dust lanes. Galaxiesthat are early types in the optical show a variety of morphologies inthe mid-UV that can lead to a different morphological classification,although not necessarily as later type. Some early-type galaxies becomedominated by a blue nuclear feature or a point source in the mid-UV,e.g., as a result of the presence of a Seyfert nucleus or a LINER. Thisis in part due to our mid-UV surface brightness selection, but it alsosuggests that part of the strong apparent evolution of weak AGNs inearly-type galaxies may be due to surface brightness dimming of theirUV-faint stellar population, which renders the early-type host galaxiesinvisible at intermediate to higher redshifts.2. About half of themid-type spiral and star-forming galaxies appear as a latermorphological type in the mid-UV, as Astro/UIT also found primarily inthe far-UV. Sometimes these differences are dramatic (e.g., NGC 6782shows a spectacular ring of hot stars in the mid-UV). However, not allmid-type spiral galaxies look significantly different in the mid-UV.Their mid-UV images show a considerable range in the scale and surfacebrightness of individual star-forming regions. Almost without exception,the mid-type spirals in our sample have their small bulges bisected by adust lane, which often appears to be connected to the inner spiral armstructure.3. The majority of the heterogeneous subset of late-type,irregular, peculiar, and merging galaxies display F300W morphologiesthat are similar to those seen in F814W, but with important differencesdue to recognizable dust features absorbing the bluer light and to hotstars, star clusters, and star formation ``ridges'' that are bright inthe mid-UV. Less than one-third of the galaxies classified as late typein the optical appear sufficiently different in the mid-UV to result ina different classification.Our HST mid-UV survey of nearby galaxiesshows that, when observed in the rest-frame mid-UV, early- to mid-typegalaxies are more likely to be misclassified as later types thanlate-type galaxies are to be misclassified as earlier types. This isbecause the later type galaxies are dominated by the same young and hotstars in all filters from the mid-UV to the red and so have a smaller``morphological K-correction'' than true earlier type galaxies. Themorphological K-correction can thus explain part, but certainly not all,of the excess faint blue late-type galaxies seen in deep HST fields.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute (STScI), which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS 5-26555. Also based in part onobservations made with the Vatican Advanced Technology Telescope: theAlice P. Lennon Telescope and the Thomas J. Bannan AstrophysicsFacility.
| Near-Infrared and Optical Morphology of Spiral Galaxies
We announce the initial release of data from the Ohio State University(OSU) Bright Spiral Galaxy Survey, a BVRJHK imaging survey of awell-defined sample of 205 bright, nearby spiral galaxies. We presentH-band morphological classification on the Hubble sequence for the OSUSurvey sample. We compare the H-band classification to B-bandclassification from our own images and from standard galaxy catalogs.Our B-band classifications match well with those of the standardcatalogs. On average, galaxies with optical classifications from Sathrough Scd appear about one T type earlier in the H band than in the Bband, but with large scatter. This result does not support recent claimsmade in the literature that the optical and near-IR morphologies ofspiral galaxies are uncorrelated. We present detailed descriptions ofthe H-band morphologies of our entire sample, as well as B- and H-bandimages for a set of 17 galaxies chosen as type examples and BRHcolor-composite images of six galaxies chosen to demonstrate the rangein morphological variation as a function of wavelength. Based partiallyon observations obtained at the Cerro Tololo Inter-American Observatory,operated by the Association of Universities for Research in Astronomy(AURA), Inc., under cooperative agreement with the National ScienceFoundation.
| Analysis of the distribution of HII regions in external galaxies. IV. The new galaxy sample. Position and inclination angles
We have compiled a new sample of galaxies with published catalogs of HIIregion coordinates. This sample, together with the former catalog ofGarcía-Gómez & Athanassoula (\cite{gga1}), will formthe basis for subsequent studies of the spiral structure in discgalaxies. In this paper we address the problem of the deprojection ofthe galaxy images. For this purpose we use two deprojection methodsbased on the HII region distribution and compare the results with thevalues found in the literature using other deprojection methods. Takinginto account the results of all the methods, we propose optimum valuesfor the position and inclination angles of all the galaxies in oursample. Tables 2 and 3 are only available in electronic form athttp://www.edpsciences.org
| FAUST observations of ultraviolet sources in the directions of NGC 4038-39 and 6752
Analysis of ultraviolet (UV) observations with the FAUST shuttle-bornetelescope toward the Antennae and NGC 6752 celestial regions resulted inthe detection of 46 and 221 candidate sources respectively, for asignal-to-noise ratio of 8. We discuss the source detection process andthe identification of UV sources with optical counterparts. Usingcorrelations with existing catalogues, we present reliableidentifications for approximately 60 per cent of the sources. We findthat most identified objects are B, A and F stars. The remainingidentified objects are galaxies, a white dwarf in a binary system, andtwo K-type stars. Nearly all of the remaining unidentified objects haveassigned optical counterparts but, lacking additional information, wegive these only as best estimates. With help from new diagnosticdiagrams, we suggest that these unclassified objects are main-sequence(or giant) stars within the local spiral arm or halo; or other hotevolved objects within the local spiral arm. We discuss the nature ofthe objects found and compare our results with those predicted fromspectral and Galactic models.
| A Dust-penetrated Classification Scheme for Bars as Inferred from Their Gravitational Force Fields
The division of galaxies into ``barred'' (SB) and ``normal'' (S) spiralsis a fundamental aspect of the Hubble galaxy classification system. This``tuning fork'' view was revised by de Vaucouleurs, whose classificationvolume recognized apparent ``bar strength'' (SA, SAB, SB) as acontinuous property of galaxies called the ``family.'' However, the SA,SAB, and SB families are purely visual judgments that can have littlebearing on the actual bar strength in a given galaxy. Until veryrecently, published bar judgments were based exclusively on blue lightimages, where internal extinction or star formation can either mask abar completely or give the false impression of a bar in a nonbarredgalaxy. Near-infrared camera arrays, which principally trace the oldstellar population in both normal and barred galaxies, now facilitate aquantification of bar strength in terms of their gravitationalpotentials and force fields. In this paper, we show that the maximumvalue, Qb, of the ratio of the tangential force to the meanaxisymmetric radial force in a barred disk galaxy is a quantitativemeasure of the strength of a bar. Qb does not measure barellipticity or bar shape but rather depends on the actual forcing due tothe bar embedded in its disk. We show that a wide range of true barstrengths characterizes the category ``SB,'' while the de Vaucouleurscategory ``SAB'' corresponds to a narrower range of bar strengths. Wepresent Qb values for 36 galaxies, and we incorporate our barclasses into a dust-penetrated classification system for spiralgalaxies.
| The Disk and Dark Halo Mass of the Barred Galaxy NGC 4123. II. Fluid-Dynamical Models
We report a dynamical determination of the separate contributions ofdisk and dark halo masses to the rotation curve of a spiral galaxy. Weuse fluid-dynamical models of gas flow in the barred galaxy NGC 4123 toconstrain the dynamical properties of the galaxy: disk M/L, bar patternspeed, and the central density and scale radius of the dark halo. Wederive a realistic barred potential directly from the lightdistribution. For each model we assume a value of the stellar M/L and abar pattern speed Ωp and add a dark halo to fit therotation curve. We then compute the gas flow velocities with atwo-dimensional gasdynamical code and compare the model flow patterns toa two-dimensional velocity field derived from Fabry-Perot observations.The strong shocks and noncircular motions in the observed gas flowrequire a high stellar M/L and a fast-rotating bar. Models with I-banddisk M/L of 2.0-2.5 h75, or 80%-100% of the maximum diskvalue, are highly favored. The corotation radius of the bar must be<=1.5 times the bar semimajor axis. These results contradict somerecent claimed ``universal'' galaxy disk/halo relations, since NGC 4123is of modest size (rotation curve maximum 145 km s-1 andVflat=130 km s-1) yet quite disk-dominated. Thedark halo of NGC 4123 is less concentrated than favored by currentmodels of dark halos based on cosmological simulations. Since some 30%of bright disk galaxies are strongly barred and have dust lanesindicating shock morphology similar to that of NGC 4123, it is likelythat they also have high stellar M/L and low-density halos. We suggestthat luminous matter dominates inside the optical radius R25of high surface brightness disk galaxies.
| Using Hubble Space Telescope images to identify straight segments in galaxy nuclear spirals
This Letter reports the discovery of straight segments of nuclear spiralarms. Hubble Space Telescope images of Seyfert galaxies are used. Themorphology of the straight features on scales of few hundred parsecsproves to be similar to the morphology of disc-wide polygonal spiralsand rings. This suggests that the straight structures on both nuclearand disc scales may have a common physical nature.
| 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.
| Molecular Gas, Dust, and Star Formation in the Barred Spiral NGC 5383
We have mapped the barred spiral NGC 5383 using theBerkeley-Illinois-Maryland Association millimeter-wave array forobservations of CO (J=1-0), the Palomar 1.5 m telescope for Hα andoptical broadband, and the Kitt Peak 1.3 m telescope for near-IRbroadband. We compare the observed central gas and dust morphology tothe predictions of recent hydrodynamic simulations calculated using thePiner, Stone, and Teuben code. In the nuclear region, our observationsreveal three peaks lying along an S-shaped gas and dust distribution:two of these are at the inner end of offset bar dust lanes at thepresumed location of the inner Lindblad resonance (ILR), and the otherlies closer to the nucleus. In contrast, the model predicts acircumnuclear ring, not the observed S-shaped distribution; moreover,the predicted surface density contrast between the central gasaccumulation and the bar dust lanes is an order of magnitude larger thanobserved. These discrepancies remain for all our simulations whichproduce offset bar dust lanes and indicate that the model is missing anessential process or component. A small nuclear bar might account forthe discrepancy, but we rule this out using a Hubble Space TelescopeNICMOS (near-IR camera and multiobject spectrometer) image: this revealsa nuclear trailing spiral, not a bar; we show that coarser resolution(i.e., ground-based images) can produce artifacts that resemble bars orrings. We conclude that the discrepancies in morphology and contrast aredue to the omission of star formation from the model; this is supportedby the observed high rate of central star formation (7 Msolaryr-1), a rate that can consume most of the accumulating gas.As is common in similar bars, the star formation rate in the bar betweenthe bar ends and the central region is low (0.5 Msolaryr-1), despite the high gas column density in the bar dustlanes; this is generally attributed to shear and shocks. We note atendency for the H II regions to be associated with the spurs feedingthe main bar dust lanes, but these are located on the leading side ofthe bar. We propose that stars form in the spurs, which provide a highcolumn density but low shear environment. H II regions can therefore befound even on the leading side of the bar because the ionizing starspass ballistically through the dust lane. 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 NAS5-26555.
| N-body simulations of resonance rings in galactic disks
We have studied the formation of rings in the disks of galaxies by usingtwo-dimensional N-body simulations where the gas component is modelledas dissipatively colliding test particles. Our results support thestandard hypothesis that ring formation occurs when gas is driven toresonances by the gravitational torque of a rotating stellar bar. Whenthe bar is absent, a weaker oval-shaped mode or a spiral mode can havethe same effect. Typical locations of the rings are as follows: theouter rings are usually near the outer Lindblad resonances, the innerrings near the inner 4/1-resonance and the nuclear rings near the innerLindblad resonances. However, we have also found a few exceptions tothese rules. We also have studied why a significant fraction of barredgalaxies lack one, two or all ring types. Our models suggest that theabsence of rings may be related to timescales of ring formation: theinner and nuclear rings usually form faster than the outer rings. Thelack of inner and nuclear rings can be related to the strength of thebar: in high amplitude cases, one or both of these ring types areabsent. Also, bars may rotate fast enough such that they lack the innerLindblad resonance and thus cannot form nuclear rings. The potentialouter ring region is often dominated by a slower spiral mode, which inprinciple could inhibit or delay ring formation. However, we found thatwhen both the bar mode and the slower spiral mode coexist in the outerdisk, there can be almost cyclic alternation between different outerring morphologies. In addition to the outer Lindblad resonance of thebar, certain resonances of the slower mode can also exist near the ringradius. The deceleration of the bar rotation rate and the correspondingchange in the resonance positions did not inhibit ring formation ordestroy an existing ring. The presence of more than one mode could alsoaffect the region of inner or nuclear rings. This can explain part ofthe case in which the ring is misaligned with respect to the main barcomponent.
| The ISOPHOT 170 μ m serendipity survey. I. Compact sources with galaxy associations
The first set of compact sources observed in the ISOPHOT 170 μmSerendipity Survey is presented. From the slew data with low(I100 μm <= 15 MJy/sr) cirrus background, 115well-observed sources with a high signal-to-noise ratio in all detectorpixels having a galaxy association were extracted. Of the galaxies withknown optical morphologies, the vast majority are classified as spirals,barred spirals, or irregulars. The 170 μm fluxes measured from theSerendipity slews have been put on an absolute flux level by usingcalibration sources observed additionally with the photometric mappingmode of ISOPHOT. For all but a few galaxies, the 170 μm fluxes aredetermined for the first time, which represents a significant increasein the number of galaxies with measured Far-Infrared (FIR) fluxes beyondthe IRAS 100 μm limit. The 170 μm fluxes cover the range 2 <~F170 μm la 100 Jy. Formulae for the integrated FIR fluxesF40-220μm and the total infrared fluxesF1-1000μm incorporating the new 170 μm fluxes areprovided. The large fraction of sources with a high F170μm / F100 μm flux ratio indicates that a cold(TDust la 20 K) dust component is present in many galaxies.The detection of such a cold dust component is crucial for thedetermination of the total dust mass in galaxies, and, in cases with alarge F170 μm / F100 μm flux ratio,increases the dust mass by a significant factor. The typical mass of thecoldest dust component is MDust = 107.5 +/- 0.5Msun , a factor 2-10 larger than that derived from IRASfluxes alone. As a consequence, the majority of the derived gas-to-dustratios are much closer to the canonical value of ~ 160 for the MilkyWay. By relaxing the selection criteria, it is expected that theSerendipity Survey will eventually lead to a catalog of 170 μm fluxesfor ~ 1000 galaxies. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. Members of the Consortium on the ISOPHOTSerendipity Survey (CISS) are MPIA Heidelberg, ESA ISO SOC Villafranca,AIP Potsdam, IPAC Pasadena, Imperial College London.
| Gas dynamics in the barred Seyfert galaxy NGC 4151 - I. HI streaming shocks and inflow along the bar
We present sensitive, high-resolution observations of neutral hydrogen(HI) in the unusually gas-rich, oval distortion of the Seyfert galaxyNGC 4151. The gas dynamics of the oval are found to be consistent withthose of a kinematically weak bar, fully confirming previous suggestionsfor the presence of a fat bar, and, for the first time, individualgaseous features in the bar are spatially resolved. In particular, thetwo bright regions close to the leading edges of the bar in NGC 4151exhibit kinematics strikingly similar to the signature of bar shocksseen in gas-dynamical simulations, and demonstrate how strong thegaseous response may be even in such a weak bar potential. The residualvelocity field, showing deviations from circular motion, is largelyconsistent with streaming in a bar potential, and, in addition, clearlyshows that inflow is concentrated in narrow regions originating in theshocks. This inflow may represent an early stage in the fuelling processof the AGN. The presence and properties of the shocks in NGC 4151indicate that, in addition to the x_1 orbits, the family of x_2 orbitsexists and is of significant extent in the bar of NGC 4151, with gasstreaming from the shocks making the transition between the twofamilies. We therefore suggest that the circumnuclear ellipse,identified optically by previous authors and associated with gas flowingin x_2 orbits, has formed as a natural consequence of the gas flows inthe bar without the requirement for a second, inner bar. Observations ofHI were previously thought to be ill-suited to the study of bar shocksbecause of limitations in angular resolution and sensitivity. However,our observations show that, following recent instrumental enhancements,such measurements are now feasible, albeit at the limits of instrumentalcapability.
| Resonance Rings and Galaxy Morphology
Rings of star formation are a common phenomenon of early to intermediateHubble type disk galaxies. Most rings form by gas accumulation atresonances, usually under the continuous action of gravity torques froma bar pattern, but sometimes in response to a mild tidal interactionwith a nearby companion. In either case, a resonance is a very specialplace in any galaxy where star formation can be enhanced and may proceedeither as a starburst or continuously over a long time period. Thisarticle describes the characteristic morphologies of bar-driven andtidally-driven resonance rings.
| A Hubble Space Telescope Optical and Ground-based Near-Infrared Study of the Giant Nuclear Ring in ESO 565-11
We present multiband Wide Field Planetary Camera 2 images of the centralregions of ESO 565-11, a peculiar southern barred galaxy recently shownto have the largest known example of a circumnuclear starburst ring. Wealso present ground-based near-infrared H-band imaging and photometry ofthe galaxy. The results provide an interesting picture of thestar-forming ring and its environment. Dust connected with the nuclearring lies mainly in a symmetric two-armed spiral pattern. More than 700point sources, mostly unresolved clusters, lie on a highly ellipticalring whose major axis is rotated by more than 20 deg from that of theisophotes of the background starlight. The luminosity function of theseclusters follows a power law with slope a=-2.18+/-0.06, typical of youngcluster systems. Most of the clusters lie in the age range 4-6 Myr, andmost may be metal-rich compared with the Sun. The nuclear ring is stillclearly seen in the H band, revealing a knotty appearance indicatingthat young stars continue to have a significant impact on its brightnessin this passband. Numerical simulations are used to show that thenuclear ring of ESO 565-11 has likely formed between two allowed innerLindblad resonances with the relatively weak primary bar. The resultsindicate that the excessive size of the ring may be due to an extendedhump in the variation of the parameter Ω-κ/2 with radius.The extreme elongation of the ring and its misalignment with the bar mayindicate that it is in an early phase of development. At later times,the simulations suggest that the ring could evolve to a rounder shape.The models do not account for star formation or gas recycling.
| L'histoire mouvementee des formes galactiques.
Not Available
| NGC 3081 - Surface photometry and kinematics of a classic resonance ring barred galaxy
This paper presents a detailed photometric and kinematic study of thewell-known Seyfert 2 galaxy NGC 3081, one of the best examples of aresonance ring barred galaxy in the sky. Improved optical imagescompared to previous studies reveal that NGC 3081 is a classic R1R'2galaxy, a type that shows a distinctive outer ring/pseudoring pattern atlarge radii that can be linked to orbit families at the outer Lindbladresonance (OLR). Together with an exceptionally strong inner ring and ablue nuclear ring, NGC 3081 has the rare distinction of having all fourof the main types of resonance rings that have been predicted bytest-particle models of barred spirals. NIR imaging of NGC 3081 revealsclear old rings connected to the inner ring and the R1 outer ring.Objective comparison of the B- and H-band positions of the inner ringindicates no significant difference in shape, major-axis position angle,or major-axis radius between the two passbands, in spite of thedifferent stellar populations each band emphasizes. Imaging Fabry-Perotinterferometry provides an intriguing picture of star formation in thegalaxy and of the dynamics of the system. H-alpha emission is strong inthe inner ring and is confined to a bounded elliptical annulus ofdiffuse emission whose ellipticity increases from the inner edge to theouter edge. A few H II regions are connected to the strong R1-type outerring, particularly just off the major axis of the inner ring where'dimples', typical of the R1 morphology, are found.
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