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The Nature of the Peculiar Virgo Cluster Galaxies NGC 4064 and NGC 4424
Using extensive kinematical and morphological data on two Virgo Clustergalaxies undergoing strong nuclear star formation, we show that rampressure stripping and gravitational interactions can act together ongalaxies that have recently fallen into clusters. We present a detailedstudy of the peculiar H I-deficient Virgo Cluster spiral galaxies NGC4064 and NGC 4424 using 12CO 1-0 interferometry, opticalimaging, and integral field spectroscopic observations in order to learnwhat type of environmental interactions have affected these galaxies.Optical imaging reveals that NGC 4424 has a strongly disturbed stellardisk, with banana-shaped isophotes and shells. NGC 4064, which lies inthe cluster outskirts, possesses a relatively undisturbed outer stellardisk and a central bar. In both galaxies Hα emission is confinedto the central kiloparsec and originates in barlike strings of luminousstar-forming complexes surrounded by fainter filaments. Complexes ofyoung blue stars exist beyond the present location of ongoing starformation, indicating rapidly shrinking star-forming disks. Disturbeddust lanes extend out to a radius of 2-3 kpc, much farther than theHα and CO emission detected by us but similar to the blue stellarcomplexes. CO observations reveal bilobal molecular gas morphologies,with Hα emission peaking inside the CO lobes, implying a timesequence in the star formation process. Gas kinematics reveals strongbarlike noncircular motions in the molecular gas in both galaxies,suggesting that the material is radially infalling. In NGC 4064 thestellar kinematics reveals strong barlike noncircular motions in thecentral 1 kpc and stars supported by rotation with V/σ>1 beyonda radius of 15" (1.2 kpc). On the other hand, NGC 4424 has extremelymodest stellar rotation velocities (Vmax~30 kms-1), and stars are supported by random motions as far out aswe can measure, with V/σ=0.6 at r=18'' (1.4 kpc). Theionized gas kinematics in the core are disturbed and possiblycounterrotating. The observations suggest that the peculiarities of NGC4424 are the result of an intermediate-mass merger plus ram pressurestripping. In the case of NGC 4064, the evidence suggests an alreadystripped ``truncated/normal'' galaxy that recently suffered a minormerger or tidal interaction with another galaxy. Observations of thepresent star formation rate and gas content suggest that these galaxieswill become small-bulge S0s within the next 3 Gyr. We propose thatgalaxies with ``truncated/compact'' Hα morphologies such as theseare the result of the independent effects of ram pressure stripping,which removes gas from the outer disk, and gravitational interactionssuch as mergers, which heat stellar disks, drive gas to the centralkiloparsec, and increase the central mass concentrations. Together theseeffects transform the morphology of these galaxies.
| The origin of rR1 ring structures in barred galaxies
We propose a new theory for the formation of rR1 ringstructures, i.e. for ring structures with both an inner and an outerring, the latter having the form of "8". We propose that these rings areformed by material from the stable and unstable invariant manifoldsassociated with the Lyapunov orbits around the equilibrium points of abarred galaxy. We discuss the shape and velocity structure of the ringsthus formed and argue that they agree with the observed properties ofrR1 structures.
| How large are the bars in barred galaxies?
I present a study of the sizes (semimajor axes) of bars in discgalaxies, combining a detailed R-band study of 65 S0-Sb galaxies withthe B-band measurements of 70 Sb-Sd galaxies from Martin (1995). As hasbeen noted before with smaller samples, bars in early-type (S0-Sb)galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies;this is true both for relative sizes (bar length as fraction ofisophotal radius R25 or exponential disc scalelength h) andabsolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~ 3.3 kpc),~0.2-0.8R25 (mean ~ 0.38R25) and ~0.5-2.5h (mean ~1.4h). Late-type bars extend to only ~0.5-3.5 kpc,~0.05-0.35R25 and 0.2-1.5h their mean sizes are ~1.5 kpc, ~0.14R25 and ~0.6h. Sb galaxies resemble earlier-type galaxiesin terms of bar size relative to h; their smallerR25-relative sizes may be a side effect of higher starformation, which increases R25 but not h. Sbc galaxies form atransition between the early- and late-type regimes. For S0-Sbcgalaxies, bar size correlates well with disc size (both R25and h); these correlations are stronger than the known correlation withMB. All correlations appear to be weaker or absent forlate-type galaxies; in particular, there seems to be no correlationbetween bar size and either h or MB for Sc-Sd galaxies.Because bar size scales with disc size and galaxy magnitude for mostHubble types, studies of bar evolution with redshift should selectsamples with similar distributions of disc size or magnitude(extrapolated to present-day values); otherwise, bar frequencies andsizes could be mis-estimated. Because early-type galaxies tend to havelarger bars, resolution-limited studies will preferentially find bars inearly-type galaxies (assuming no significant differential evolution inbar sizes). I show that the bars detected in Hubble Space Telescope(HST) near-infrared(IR) images at z~ 1 by Sheth et al. have absolutesizes consistent with those in bright, nearby S0-Sb galaxies. I alsocompare the sizes of real bars with those produced in simulations anddiscuss some possible implications for scenarios of secular evolutionalong the Hubble sequence. Simulations often produce bars as large as(or larger than) those seen in S0-Sb galaxies, but rarely any as smallas those in Sc-Sd galaxies.
| An atlas of calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering theregion around the λλ8498, 8542, 8662 calcium triplet(CaT). The sample comprises 78 objects, divided into 43 Seyfert 2s, 26Seyfert 1s, three starburst and six normal galaxies. The spectra pertainto the inner ~300 pc in radius, and thus sample the central kinematicsand stellar populations of active galaxies. The data are used to measurestellar velocity dispersions (σ*) with bothcross-correlation and direct fitting methods. These measurements arefound to be in good agreement with each other and with those in previousstudies for objects in common. The CaT equivalent width is alsomeasured. We find average values and sample dispersions ofWCaT of 4.6 +/- 2.0, 7.0 +/- 1.0 and 7.7 +/- 1.0 Å forSeyfert 1s, Seyfert 2s and normal galaxies, respectively. We furtherpresent an atlas of [SIII]λ9069 emission-line profiles for asubset of 40 galaxies. These data are analysed in a companion paperwhich addresses the connection between stellar and narrow-line regionkinematics, the behaviour of the CaT equivalent width as a function ofσ*, activity type and stellar population properties.
| A wide-field HI study of the NGC 1566 group
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| Hα Imaging of Early-Type Sa-Sab Spiral Galaxies. II. Global Properties
New results, based on one of the most comprehensive Hα imagingsurveys of nearby Sa-Sab spirals completed to date, reveals early-typespirals to be a diverse group of galaxies that span a wide range inmassive star formation rates. While the majority of Sa-Sab galaxies inour sample are forming stars at a modest rate, a significant fraction(~29%) exhibit star formation rates greater than 1 Msolaryr-1, rivaling the most prolifically star-forming late-typespirals. A similar diversity is apparent in the star formation historyof Sa-Sab spirals as measured by their Hα equivalent widths.Consistent with our preliminary results presented in the first paper inthis series, we find giant H II regions [L(Hα)>=1039ergs s-1] in the disks of ~37% of early-type spirals. Wesuspect that recent minor mergers or past interactions are responsiblefor the elevated levels of Hα emission and, perhaps, for thepresence of giant H II regions in these galaxies. Our results, however,are not in total agreement with the Hα study of Kennicutt &Kent, who did not find any early-type spirals with Hα equivalentwidths >14 Å. A close examination of the morphologicalclassification of galaxies, however, suggests that systematicdifferences between the Revised Shapley-Ames Catalog and the SecondReference Catalogue may be responsible for the contrasting results.Based on observations obtained with the 3.5 m telescope at Apache PointObservatory (APO) and the 0.9 m telescope at Kitt Peak NationalObservatory (KPNO). The APO 3.5 m telescope is owned and operated by theAstrophysical Research Consortium.
| Dynamical modelling of the remarkable four-armed barred spiral galaxy ESO 566-24
ESO 566-24 is an extraordinary barred galaxy that has four regularlyspaced spiral arms in blue light images. This type of spiral structure,which is rare among the spiral population, is also clearly seen innear-infrared (NIR) images, and thus is present in the old stellarpopulation. We have constructed dynamical models of ESO 566-24. Thegravitational potential is determined using NIR photometry, and the gasdynamics is modelled as inelastically colliding particles. The resultingmorphology and kinematics with different assumed pattern speeds, discvertical thicknesses and dark halo contributions are compared withobservations. Our models reproduce the main morphological features ofthis galaxy: the four-armed spiral, and the inner and nuclear rings. Thepattern speed of the bar is such that the corotation resonance is welloutside the bar radius, rCR/rb= 1.6 +/- 0.3. Thefour-armed spiral resides in the region between inner and outer 4/1resonances. In addition, the main kinematical features, includingbar-induced deviations from circular rotation, are explained by ourmodels. The best fit is obtained when the dark halo contribution is justenough to make the modelled rotation curve match the observed one. Thus,luminous matter dominates the rotation curve within the disc region.
| Gravitational Bar and Spiral Arm Torques from Ks-band Observations and Implications for the Pattern Speeds
We have obtained deep near-infrared Ks-band William HerschelTelescope observations of a sample of 15 nearby spiral galaxies having arange of Hubble types and apparent bar strengths. The near-infraredlight distributions are converted into gravitational potentials, and themaximum relative gravitational torques due to the bars and the spiralsare estimated. We find that spiral strength, Qs, and barstrength, Qb, correlate well with other measures of spiralarm and bar amplitudes and that spiral and bar strengths also correlatewell with each other. We also find a correlation between the positionangle of the end of the bar and the position angle of the inner spiral.These correlations suggest that the bars and spirals grow together withthe same rates and pattern speeds. We also show that the strongest barstend to have the most open spiral patterns. Because open spirals implyhigh disk-to-halo mass ratios, bars and spirals most likely growtogether as a combined disk instability. They stop growing for differentreasons, however, giving the observed variation in bar-spiralmorphologies. Bar growth stops because of saturation when most of theinner disk is in the bar, and spiral growth stops because of increasedstability as the gas leaves and the outer disk heats up.
| 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.
| 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
| Orbital dynamics of three-dimensional bars - IV. Boxy isophotes in face-on views
We study the conditions that favour boxiness of isodensities in theface-on views of orbital 3D models for barred galaxies. Using orbitalweighted profiles we show that boxiness is in general a composite effectthat appears when one considers stable orbits belonging to severalfamilies of periodic orbits. 3D orbits that are introduced due tovertical instabilities play a crucial role in the face-on profiles andenhance their rectangularity. This happens because at the 4:1 radialresonance region we have several orbits with boxy face-on projections,instead of a few rectangular-like x1 orbits, which, in a fair fractionof the models studied so far, are unstable in this region. Massive barsare characterized by rectangular-like orbits. However, we find that itis the pattern speed that affects the elongation of the boxy featuremost, in the sense that fast bars are more elongated than slow ones.Boxiness in intermediate distances between the centre of the model andthe end of the bar can be attributed to x1v1 orbits, or to a combinationof families related to the radial 3:1 resonance.
| When Is a Bulge Not a Bulge? Inner Disks Masquerading as Bulges in NGC 2787 and NGC 3945
We present a detailed morphological, photometric, and kinematic analysisof two barred S0 galaxies with large, luminous inner disks inside theirbars. We show that these structures, in addition to being geometricallydisklike, have exponential profiles (scale lengths ~300-500 pc) distinctfrom the central, nonexponential bulges. We also find them to bekinematically disklike. The inner disk in NGC 2787 has a luminosityroughly twice that of the bulge; but in NGC 3945, the inner disk isalmost 10 times more luminous than the bulge, which itself is extremelysmall (half-light radius ~100 pc, in a galaxy with an outer ring ofradius ~14 kpc) and has only ~5% of the total luminosity-a bulge/totalratio much more typical of an Sc galaxy. We estimate that at least 20%of (barred) S0 galaxies may have similar structures, which means thattheir bulge/disk ratios may be significantly overestimated. These innerdisks dominate the central light of their galaxies; they are at least anorder of magnitude larger than typical ``nuclear disks'' found inelliptical and early-type spiral galaxies. Consequently, they mustaffect the dynamics of the bars in which they reside.
| X-Ray Emission from a Sample of Young Supernovae
When a massive star produces a powerful stellar wind prior to itssupernova event, theory predicts that the collision of the explodedstellar ejecta with the wind leads to a reverse shock, creating softX-ray emission. To understand the frequency at which luminous youngX-ray supernovae occur, we used ROSAT to observe a complete sample ofnearby supernovae (vhelio<1700 km s-1) thatoccurred in the period 1985.5 through 1994.3, which included eight TypeIa supernovae and 19 Type Ib and Type II events. Three supernovae aredetected in this time frame, SN 1987A (LMC), SN 1993J (NGC 3031), and apreviously unreported source, SN 1992ad, a Type II supernova in NGC4411b. No supernova had 0.5-2 keV luminosities exceeding2×1039 ergs s-1, so at the 95% confidencelevel, the probability of an individual supernova exceeding thisluminosity limit is less than 12%. Two of these supernovae hadluminosities brighter than 6×1038 ergs s-1and at the 95% confidence level, the probability of a supernova beingdetected above this luminosity is in the range 8.7%-51%. It is unlikelyfor young supernovae to be a large component of the IntermediateLuminosity X-Ray Object (IXO or ULX) class, where the luminosity exceeds2×1039 ergs s-1. The rate of successfuldetections appears to increase for sensitivities in the 1037ergs s-1 range, especially when obtained close to the time ofthe event.
| Anillos Adentro: Las Regiones Centrales de NGC 1433
Not Available
| Bar strengths in spiral galaxies estimated from 2MASS images
Non-axisymmetric forces are presented for a sample of 107 spiralgalaxies, of which 31 are barred (SB) and 53 show nuclear activity. As adata base we use JHK images from the 2 Micron All-sky Survey, and thenon-axisymmetries are characterized by the ratio of the tangential forceto the mean axisymmetric radial force field, following Buta & Block.Bar strengths have an important role in many extragalactic problems andtherefore it is important to verify that the different numerical methodsapplied for calculating the forces give mutually consistent results. Weapply both direct Cartesian integration and a polar grid integrationutilizing a limited number of azimuthal Fourier components of density.We find that the bar strength is independent of the method used toevaluate the gravitational potential. However, because of thedistance-dependent smoothing by Fourier decomposition, the polar methodis more suitable for weak and noisy images. The largest source ofuncertainty in the derived bar strength appears to be the uncertainty inthe vertical scaleheight, which is difficult to measure directly formost galaxies. On the other hand, the derived bar strength is ratherinsensitive to the possible gradient in the vertical scaleheight of thedisc or to the exact model of the vertical density distribution,provided that the same effective vertical dispersion is assumed in allmodels. In comparison with the pioneering study by Buta & Block, thebar strength estimate is improved here by taking into account thedependence of the vertical scaleheight on the Hubble type: we find thatfor thin discs bar strengths are stronger than for thick discs by anamount that may correspond to as much as one bar strength class. Weconfirm the previous result by Buta and co-workers showing that thedispersion in bar strength is large among all the de Vaucouleurs opticalbar classes. In the near-infrared 40 per cent of the galaxies in oursample have bars (showing constant phases in the m= 2 Fourier amplitudesin the bar region), while in the optical band one-third of these barsare obscured by dust. Significant non-axisymmetric forces can also beinduced by the spiral arms, generally in the outer parts of the galacticdiscs, which may have important implications on galaxy evolution.Possible biases of the selected sample are also studied: we find thatthe number of bars identified drops rapidly when the inclination of thegalactic disc is larger than 50°. A similar bias is found in theThird Reference Catalogue of Bright Galaxies, which might be of interestwhen comparing bar frequencies at high and low redshifts.
| Catalog of Multicolor Profiles of Galaxies
A catalog of multicolor photometric profiles derived from aperturephotometry for a selected sample of galaxies is given. The data sources,homogenization procedures and selection criteria used are described.
| Discovery and Implications of a New Large-Scale Stellar Bar in NGC 5248
For decades, the grand-design SAB spiral galaxy NGC 5248 has beenpostulated to host a short bar of semimajor axis 22" (1.6 kpc). Fromdynamical and morphological arguments, however, we argue that its spiralstructure is being driven by a large-scale bar whose corotation radiuslies at ~115" (8.6 kpc). Our estimate is based partially on a deepR-band image, which reveals that the feature previously thought to be aninclined disk is in fact an extended stellar bar. The bar is embeddedwithin a fainter outer disk visible out to a radius of 230" (17.2 kpc).The bar has a deprojected ellipticity of 0.44 and a semimajor axis of95" (7.1 kpc). The classical grand-design spirals of NGC 5248, prominentin B, R, and K light, lie on the leading edge of the large-scale stellarbar and are accompanied by concave dust lanes out to at least 70". Theoffset between the dust and young stars is consistent with ourunderstanding of gas flows in barred galaxies, where shocks along theleading edges of a moderately strong bar compress the gas to formmassive young stars. While in many strongly barred galaxies, opticalspiral arms are prominent outside the bar but not within it, NGC 5248illustrates how intense star formation along a moderately strong bar canlead to conspicuous open spiral arms within the bar itself. NGC 5248also provides a clear example of how a large-scale stellar bar embeddedwithin a faint outer optical disk can be misidentified as an inclineddisk when imaging studies lack the sensitivity to detect the actualouter disk. We discuss the implications for the estimated bar fractionat higher redshifts.
| Magnetic fields in barred galaxies. I. The atlas
The total and polarized radio continuum emission of 20 barred galaxieswas observed with the Very Large Array (VLA) at lambda 3, 6, 18 and 22cm and with the Australia Telescope Compact Array (ATCA) at lambda 6 cmand 13 cm. Maps at 30\arcsec angular resolution are presented here.Polarized emission (and therefore a large-scale regular magnetic field)was detected in 17 galaxies. Most galaxies of our sample are similar tonon-barred galaxies with respect to the radio/far-infrared fluxcorrelation and equipartition strength of the total magnetic field.Galaxies with highly elongated bars are not always radio-bright. Wediscuss the correlation of radio properties with the aspect ratio of thebar and other measures of the bar strength. We introduce a new measureof the bar strength, Lambda , related to the quadrupole moment of thebar's gravitational potential. The radio surface brightness I of thebarred galaxies in our sample is correlated with Lambda , I~Lambda0.4+/-0.1, and thus is highest in galaxies with a long barwhere the velocity field is distorted by the bar over a large fractionof the disc. In these galaxies, the pattern of the regular field issignificantly different from that in non-barred galaxies. In particular,field enhancements occur upstream of the dust lanes where the fieldlines are oriented at large angles to the bar's major axis. Polarizedradio emission seems to be a good indicator of large-scalenon-axisymmetric motions. Tables 3, 4 and Figs. 8-10, 13, 15, 16, 18 and22 are only available in electronic form at http://www.edpsciences.org
| 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
| High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample - II. The properties of compact radio components
We discuss the properties of compact nuclear radio components in Seyfertgalaxies from the extended 12-μm AGN sample of Rush et al. Our mainresults can be summarized as follows. Type 1 and type 2 Seyferts producecompact radio components which are indistinguishable in strength andaspect, indicating that their central engines are alike, as proposed bythe unification model. Infrared IRAS fluxes are more closely correlatedwith low-resolution radio fluxes than high-resolution radio fluxes,suggesting that they are dominated by kiloparsec-scale, extranuclearemission regions; extranuclear emission may be stronger in type 2Seyferts. Early-type Seyfert galaxies tend to have stronger nuclearradio emission than late-type Seyfert galaxies. V-shaped extendedemission-line regions, indicative of `ionization cones', are usuallyfound in sources with large, collimated radio outflows. Hidden broadlines are most likely to be found in sources with powerful nuclear radiosources. Type 1 and type 2 Seyferts selected by their IRAS 12-μm fluxdensities have well-matched properties.
| 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.
| Integral Field Near-Infrared Spectroscopy of a Sample of Seyfert and LINER Galaxies. I. The Data
We present near-IR integral field spectroscopy of a sample of 31 Seyfertand LINER galaxies which were selected both to span a wide range ofnuclear magnitudes and to possess roughly equal numbers of Seyfert type1 and 2 nuclei. Moderate resolution (R~1000 R~2000 for three cases)integral field K-band spectra were obtained for all 31 galaxies in oursample and for 18 galaxies (R~1000 R~2000 for four cases) H-bandintegral field spectra were also obtained. In each case, we presentnuclear, larger aperture, and difference spectra with correspondinginformation about emission line wavelengths, fluxes, and widths.Line-free H- and K-band continuum images as well as [Fe II]λ1.644 μm, Brγ, and H2 1-0 S(1) emissionlines are also presented. In addition, we provide extensive informationabout each galaxy obtained from the literature that will be usefulsubsequently for characterizing the sample and for comparison with ournear-IR data. Based on observations obtained with the Anglo-AustralianTelescope, Siding Spring, Australia, the European Southern Observatory,La Silla, the William Herschel Telescope operated on the island of LaPalma by the Isaac Newton Group in the Spanish Observatorio del Roque delos Muchachos of the Instituto de Astrofísica de Canarias, andthe Calar Alto 3.5 m, which is operated by the Max-Planck-Institutfür Astronomie, Heidelberg, Germany, jointly with the SpanishNational Commission for Astronomy.
| Strömgren Photometry from z=0 to z~1. I. The Method
We use rest-frame Strömgren photometry to observe clusters ofgalaxies in a self-consistent manner from z=0 to z=0.8. Strömgrenphotometry of galaxies is intended as a compromise between standardbroadband photometry and spectroscopy, in the sense that it is moresensitive to subtle variations in spectral energy distributions than theformer, yet much less time-consuming than the latter. principalcomponent analysis is used to facilitate extraction of information fromthe Strömgren data. By calibrating the principal components usingwell-studied galaxies, as well as models of stellar populations, wedevelop a purely empirical method to detect, and subsequently classify,cluster galaxies at all redshifts smaller than 0.8. Interlopers arediscarded with unprecedented efficiency (up to 100%). The firstprincipal component essentially reproduces the Hubble sequence and canthus be used to determine the global star formation history of clustermembers. The (PC2, PC3) plane allows us to identify Seyfert galaxies(and distinguish them from starbursts) based on photometric colorsalone. In the case of E/S0 galaxies with known redshift, we are able toresolve the age-dust-metallicity degeneracy, albeit at the accuracylimit of our present observations. We use this technique in later papersto probe galaxy clusters well beyond their cores and to faintermagnitudes than spectroscopy can achieve, because the faint end of theluminosity function as well as the outer cluster regions seem to exhibitthe strongest evolutionary trends. We are able to directly compare thesedata over the entire redshift range without a priori assumptions becauseour observations do not require first-order k-corrections. Thecompilation of such data for different cluster types over a wideredshift range is likely to set important constraints on the evolutionof galaxies and on the clustering process.
| Empirical Diagnostics of the Starburst-AGN Connection
We examine a representative sample of 35 Seyfert 2 nuclei. Previous workhas shown that nearly half (15) of these nuclei show the direct (butdifficult to detect) spectroscopic signature at optical/near-UVwavelengths of the hot massive stars that power circumnuclearstarbursts. In the present paper we examine a variety of more easilymeasured quantities for this sample, such as the equivalent widths ofstrong absorption features, continuum colors, emission line equivalentwidths, emission line ratios and profiles, far-IR luminosities, andnear-UV surface brightness. We compare the composite starburst+Seyfert 2nuclei to ``pure'' Seyfert 2 nuclei, Starburst galaxies, and normalgalactic nuclei. Our goals are to verify whether the easily measuredproperties of the composite nuclei are consistent with the expectedimpact of a starburst and to investigate alternative less demandingmethods to infer the presence of starbursts in Seyfert 2 nuclei,applicable to larger or more distant samples. We show that starbursts doindeed leave clear and easily quantifiable imprints on the near-UV tooptical continuum and emission line properties of Seyfert 2's. Compositestarburst+Seyfert 2 systems can be recognized by: (1) a strong``featureless continuum'' (FC), which dilutes the Ca II K line from oldstars in the host's bulge to an equivalent width WK<10Å (2) emission lines whose equivalent widths are intermediatebetween starburst galaxies and ``pure'' Seyfert 2's (3) relatively lowexcitation line ratios, which indicate that part of the gas ionizationin these Seyfert 2's (typically ~50% of Hβ) is due tophotoionization by OB stars; (4) large far-IR luminosities(>~1010 Lsolar) (5) high near-UV surfacebrightness (~103 Lsolar pc-2). Thesecharacteristics are all consistent with the expected impact ofcircumnuclear starbursts on the observed properties of Seyfert 2's.Furthermore, they offer alternative empirical diagnostics of thepresence of circumnuclear starbursts from a few easily measuredquantities.
| 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.
| Ultraviolet Signposts of Resonant Dynamics in the Starburst-ringed SAB Galaxy M94 (NGC 4736)
The dynamic orchestration of star-birth activity in the starburst-ringedgalaxy M94 (NGC 4736) is investigated using images from the UltravioletImaging Telescope (UIT; far-ultraviolet [FUV] band), Hubble SpaceTelescope (HST; near-ultraviolet [NUV] band), Kitt Peak 0.9 m telescope(Hα, R, and I bands), and Palomar 5 m telescope (B band), alongwith spectra from the International Ultraviolet Explorer (IUE) and theLick 1 m telescope. The wide-field UIT image shows FUV emission from (1)an elongated nucleus, (2) a diffuse inner disk, where Hα isobserved in absorption, (3) a bright inner ring of H II regions at theperimeter of the inner disk (R=48"=1.1 kpc), and (4) two 500 pc sizeknots of hot stars exterior to the ring on diametrically opposite sidesof the nucleus (R=130"=2.9 kpc). The HST Faint Object Camera imageresolves the NUV emission from the nuclear region into a bright core anda faint 20" long ``minibar'' at a position angle of 30°. Optical andIUE spectroscopy of the nucleus and diffuse inner disk indicates a~107-108 yr old stellar population from low-levelstar-birth activity blended with some LINER activity. Analysis of theHα-, FUV-, NUV-, B-, R-, and I-band emissions, along with otherobserved tracers of stars and gas in M94, indicates that most of thestar formation is being orchestrated via ring-bar dynamics, involvingthe nuclear minibar, inner ring, oval disk, and outer ring. The innerstarburst ring and bisymmetric knots at intermediate radius, inparticular, argue for bar-mediated resonances as the primary drivers ofevolution in M94 at the present epoch. Similar processes may begoverning the evolution of the ``core-dominated'' galaxies that havebeen observed at high redshift. The gravitationally lensed ``PretzelGalaxy'' (0024+1654) at a redshift of ~1.5 provides an importantprecedent in this regard.
| Dynamics of Ringed Barred Spiral Galaxies. I. Surface Photometry and Kinematics of NGC 1433 and NGC 6300
This paper presents new near-infrared images and surface photometry andHα Fabry-Perot radial velocities for NGC 1433 and NGC 6300, twolarge and previously well-studied nearby ringed barred spiral galaxies.Stellar absorption-line radial velocities and new optical surfacephotometry are also presented for NGC 1433. The data are intended to setthe stage for dynamical modeling of the two galaxies, with the principalgoals being to derive mass distributions, bar mass-to-light ratios, barpattern speeds, and resonance locations, parameters which have beenderived for very few ringed disk galaxies. The presence of strong ringsand pseudorings in the two galaxies allows the possibility to linkspecific orbital resonances with the observed rings. The new data allowus to derive a fairly complete composite rotation curve of NGC 1433,leading us to make some interesting preliminary judgments about thestructure of the galaxy. The new data also verify the previous findingthat the radial velocity of the Seyfert nucleus in NGC 6300 differs fromthe actual systemic velocity of the galaxy by nearly 100 kms-1. We demonstrate in this paper that the offset is not anartifact of significant extinction in the inner regions of the galaxy.
| Searching for the in-plane Galactic bar and ring in DENIS
New evidence for a long thin Galactic bar (in contradistinction to thebulge), as well as for the existence of the ring and the truncation ofthe inner disc, are sought in the DENIS survey. First, we examine DENISand Two Micron Galactic Survey star counts for the characteristicsignatures of an in-plane bar and ring. The star counts in the plane for30o>l>-30o are shown to be highly asymmetricwith considerably more sources at positive than at negative longitudes.At |b|~ 1.5o, however, the counts are nearly symmetric.Therefore, the asymmetry is not due to the disc, which is shown to havean inner truncation, or to the bulge, so there has to be another majorcomponent in the inner Galaxy that is causing the asymmetries. Thiscomponent provides up to 50% of the detected sources in the planebetween the bulge and l=27o or l=-14o. Thiscomponent is shown to be consistent with an in-plane bar with a positionangle of 40o and half-length of 3.9 kpc. However, there isalso a major peak in the counts at l=-22o, which coincideswith the tangential point of the so-called 3 kpc arm. This is shown tobe most probably a ring or a pseudo-ring. The extinction in the plane isalso shown to be asymmetric with more extinction at negative than atpositive longitudes. For l<8o the extinction is shown tobe slightly tilted with respect to b=0o in the same manner asthe HI disc. We conclude that the Galaxy is a fairly typical ringedbarred spiral galaxy.
| The relationship between star formation rates and mid-infrared emission in galactic disks
The Hα and mid-infrared mean disk surface brightnesses arecompared in a sample of nearby spirals observed by ISOCAM. This showsthat, in spiral disks, dust emission at 7 and 15 mu m provides areasonable star formation tracer. The fact that the 15 to 7 mu m fluxratio is nearly constant in various global exciting conditions indicatesa common origin, namely the aromatic infrared band carriers, and impliesthat at these wavelengths, dust emission from the disks of normalgalaxies is dominated by photodissociation regions and not by H Iiregions themselves. We use this newly-found correlation between themid-infrared and the Hα line to investigate the nature of the linkbetween the far-infrared (60 and 100 mu m) and Hα . Although theseparation of the central regions from the disk is impossible to achievein the far-infrared, we show that a circumnuclear contribution to thedust emission, having no equivalent counterpart in Hα , is mostlikely responsible for the well-known non-linearity between far-infraredand Hα fluxes in spiral galaxies. We derive a calibration of 7 and15 mu m fluxes in terms of star formation rates from a primarycalibration of Hα in the literature, and also outline theapplicability limits of the proposed conversion, which should not beblindly extrapolated to objects whose nature is unknown. Based onobservations with ISO, an ESA project with instruments funded by ESAMember States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.
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