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The Cool ISM in S0 Galaxies. II. A Survey of Atomic Gas
The place of lenticular galaxies within the range of types of galaxiesremains unclear. We previously reported the mass of molecular hydrogenfor a volume-limited sample of lenticular galaxies, where we saw thatthe amount of gas was less than that predicted by the return of stellarmass to the interstellar medium. Here we report observations of atomichydrogen (H I) for the same sample. Detections in several galaxies makemore compelling the case presented in our earlier paper that the mass ofcool gas in S0 galaxies cuts off at ~10% of what is expected fromcurrent models of gas return from stellar evolution. The molecular andatomic phases of the gas in our sample galaxies appear to be separateand distinct, both spatially and in velocity space. We propose that themolecular gas arises mostly from the stellar mass returned to thegalaxy, while the atomic hydrogen is mainly accumulated from externalsources (infall, captured dwarfs, etc.). While this proposal fits mostof the observations, it makes the presence of the upper mass cutoff evenmore mysterious.
| Stellar Populations in Nearby Lenticular Galaxies
We have obtained two-dimensional spectral data for a sample of 58 nearbyS0 galaxies with the Multi-Pupil Fiber/Field Spectrograph of the 6 mtelescope of the Special Astrophysical Observatory of the RussianAcademy of Sciences. The Lick indices Hβ, Mg b, and arecalculated separately for the nuclei and for the bulges taken as therings between R=4'' and 7", and the luminosity-weighted ages,metallicities, and Mg/Fe ratios of the stellar populations are estimatedby comparing the data to single stellar population (SSP) models. Fourtypes of galaxy environments are considered: clusters, centers ofgroups, other places in groups, and the field. The nuclei are found tobe on average slightly younger than the bulges in any type ofenvironment, and the bulges of S0 galaxies in sparse environments areyounger than those in dense environments. The effect can be partlyattributed to the well-known age correlation with the stellar velocitydispersion in early-type galaxies (in our sample the galaxies in sparseenvironments are on average less massive than those in denseenvironments), but for the most massive S0 galaxies, withσ*=170-220 km s-1, the age dependence on theenvironment is still significant at the confidence level of 1.5 σ.Based on observations collected with the 6 m telescope (BTA) at theSpecial Astrophysical Observatory (SAO) of the Russian Academy ofSciences (RAS).
| Bar-Halo Friction in Galaxies. II. Metastability
It is well established that strong bars rotating in dense halosgenerally slow down as they lose angular momentum to the halo throughdynamical friction. Angular momentum exchanges between the bar and haloparticles take place at resonances. While some particles gain and otherslose, friction arises when there is an excess of gainers over losers.This imbalance results from the generally decreasing numbers ofparticles with increasing angular momentum, and friction can thereforebe avoided if there is no gradient in the density of particles acrossthe major resonances. Here we show that anomalously weak friction canoccur for this reason if the pattern speed of the bar fluctuates upward.After such an event, the density of resonant halo particles has a localinflexion created by the earlier exchanges, and bar slowdown can bedelayed for a long period; we describe this as a metastable state. Weshow that this behavior in purely collisionless N-body simulations isfar more likely to occur in methods with adaptive resolution. We alsoshow that the phenomenon could arise in nature, since bar-driven gasinflow could easily raise the bar pattern speed enough to reach themetastable state. Finally, we demonstrate that mild external or internalperturbations quickly restore the usual frictional drag, and it isunlikely therefore that a strong bar in a galaxy having a dense halocould rotate for a long period without friction.
| The structure of galactic disks. Studying late-type spiral galaxies using SDSS
Using imaging data from the SDSS survey, we present the g' and r' radialstellar light distribution of a complete sample of ~90 face-on tointermediate inclined, nearby, late-type (Sb-Sdm) spiral galaxies. Thesurface brightness profiles are reliable (1 σ uncertainty lessthan 0.2 mag) down to μ27 mag/''. Only ~10% of all galaxies havea normal/standard purely exponential disk down to our noise limit. Thesurface brightness distribution of the rest of the galaxies is betterdescribed as a broken exponential. About 60% of the galaxies have abreak in the exponential profile between 1.5-4.5 times thescalelength followed by a downbending, steeper outer region. Another~30% shows also a clear break between 4.0-6.0 times thescalelength but followed by an upbending, shallower outer region. A fewgalaxies have even a more complex surface brightness distribution. Theshape of the profiles correlates with Hubble type. Downbending breaksare more frequent in later Hubble types while the fraction of upbendingbreaks rises towards earlier types. No clear relation is found betweenthe environment, as characterised by the number of neighbours, and theshape of the profiles of the galaxies.
| Classifications of the Host Galaxies of Supernovae, Set III
A homogeneous sample comprising host galaxies of 604 recent supernovae,including 212 objects discovered primarily in 2003 and 2004, has beenclassified on the David Dunlap Observatory system. Most SN 1991bg-likeSNe Ia occur in E and E/Sa galaxies, whereas the majority of SN1991T-like SNe Ia occur in intermediate-type galaxies. This differenceis significant at the 99.9% level. As expected, all types of SNe II arerare in early-type galaxies, whereas normal SNe Ia occur in all Hubbletypes. This difference is significant at the 99.99% level. A smallnumber of SNe II in E galaxies might be due to galaxy classificationerrors or to a small young-population component in these mainly oldobjects. No significant difference is found between the distributionsover the Hubble type of SNe Ibc and SNe II. This confirms that both ofthese types of objects have similar (massive) progenitors. The presentdata show that in order to understand the dependence of supernova typeon host-galaxy population, it is more important to obtain accuratemorphological classifications than it is to increase the size of thedata sample.
| 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.
| Multicomponent decompositions for a sample of S0 galaxies
We have estimated the bulge-to-total (B/T) light ratios in theKs band for a sample of 24 S0, S0/a and Sa galaxies byapplying a two-dimensional multicomponent decomposition method. For thedisc an exponential function is used, the bulges are fitted by aSérsic R1/n function and the bars and ovals aredescribed either by a Sérsic or a Ferrers function. In order toavoid non-physical solutions, preliminary characterization of thestructural components is made by inspecting the radial profiles of theorientation parameters and the low azimuthal wavenumber Fourieramplitudes and phases. In order to identify also the inner structures,unsharp masks were created: previously undetected inner spiral arms werefound in NGC 1415 and marginally in NGC 3941. Most importantly, we foundthat S0s have a mean K ratio of 0.24 +/- 0.11,which is significantly smaller than the mean R=0.6 generally reported in the literature. Also, the surface brightnessprofiles of the bulges in S0s were found to be more exponential-likethan generally assumed, the mean shape parameter of the bulge being= 2.1 +/- 0.7. We did not find examples of barred S0s lackingthe disc component, but we found some galaxies (NGC 718, 1452 and 4608)having a non-exponential disc in the bar region. To our knowledge, ourstudy is the first attempt to apply a multicomponent decompositionmethod for a moderately sized sample of early-type disc galaxies.
| On the relation between orbital structure and observed bar morphology
We investigate the morphological relation between the orbits of thecentral family of periodic orbits (x1 family) and the baritself using models of test particles moving in a barred potential. Weshow that different bar morphologies may have as a backbone the same setof x1 periodic orbits. We point out that by populatinginitially axisymmetric stellar discs exponentially with test particlesin circular, or almost circular motion, we may end up with a responsebar which reveals a shape different in crucial details from that of theindividual stable x1 orbits. For example, a bar model inwhich the x1 orbits are pure ellipses may have a much morecomplicated response morphology. This depends on the particularinvariant curves around x1, which are populated in eachmodel.
| On the Relevance of the Tremaine-Weinberg Method Applied to an Hα Velocity Field: Pattern Speed Determination in M100 (NGC 4321)
The relevance of the Tremaine-Weinberg (TW) method is tested formeasuring bar, spiral, and inner structure pattern speeds using agaseous velocity field. The TW method is applied to various simulatedbarred galaxies in order to demonstrate its validity in seven differentconfigurations, including star formation and/or dark matter halo. Thereliability of the different physical processes involved and of thevarious observational parameters is also tested. The simulations showthat the TW method could be applied to gaseous velocity fields to get agood estimate of the bar pattern speed, under the condition that regionsof shocks are avoided and measurements are confined to regions where thegaseous bar is well formed. We successfully apply the TW method to theHα velocity field of the Virgo Cluster galaxy M100 (NGC 4321) andderive pattern speeds of 55+/-5 km s-1 kpc-1 forthe nuclear structure, 30+/-2 km s-1 kpc-1 for thebar, and 20+/-1 km s-1 kpc-1 for the spiralpattern, in full agreement with published determinations using the samemethod or alternative ones.
| Optical and Near-Infrared Color Profiles in Nearby Early-Type Galaxies and the Implied Age and Metallicity Gradients
We present results of an age and metallicity gradient analysis inferredfrom both optical and near-infrared surface photometry. The analysis isbased on a sample of 36 nearby early-type galaxies, obtained from theEarly Data Release of the Sloan Digital Sky Survey and the Two MicronAll Sky Survey. Surface brightness profiles were derived in each bandand used to study the color gradients of the galaxies. Using simplestellar population models with both optical and near-infrared colors, wemay interpret the color gradients in terms of age and metallicitygradients of galaxies. UsinggZ≡dlogZmet/dlogR andgA=dlog(age)/dlogR to represent the metallicity and agegradients, we found a median value of gZ=-0.25+/-0.03 for themetallicity gradient, with a dispersionσgZ=0.19+/-0.02. The corresponding valuesfor the age gradients were gA=0.02+/-0.04 andσgA=0.25+/-0.03. These results are in goodagreement with recent observational results, as well as with recentsimulations that suggest that both monolithic collapse and major mergershave played important roles in the formation of early-type galaxies. Ourresults demonstrate the potential of using multi-wave band colorsobtained from current and future optical and infrared surveys inconstraining the age and metallicity gradients of early-type galaxies.
| The all-sky distribution of 511 keV electron-positron annihilation emission
We present a map of 511 keV electron-positron annihilation emission,based on data accumulated with the SPI spectrometer aboard ESA'sINTEGRAL gamma-ray observatory, that covers approximately ~95% of thecelestial sphere. Within the exposed sky area, 511 keV line emission issignificantly detected towards the galactic bulge region and, at a verylow level, from the galactic disk. The bulge emission is highlysymmetric and is centred on the galactic centre with an extension of ~8° (FWHM). The emission is equally well described by models thatrepresent the stellar bulge or halo populations. The detectionsignificance of the bulge emission is ~ 50σ, that of the galacticdisk is ~ 4σ. The disk morphology is only weakly constrained bythe present data, being compatible with both the distribution of youngand old stellar populations. The 511 keV line flux from the bulge anddisk components is (1.05 ± 0.06) × 10-3 phcm-2 s-1 and (0.7 ± 0.4) ×10-3 ph cm-2 s-1 respectively,corresponding to a bulge-to-disk flux ratio in the range 1-3. Assuming apositronium fraction of f_p=0.93 this translates into annihilation ratesof (1.5 ± 0.1) × 1043 s-1and (0.3± 0.2) × 1043 s-1, respectively. Theratio of the bulge luminosity to that of the disk is in the range 3-9.We find no evidence for a point-like source in addition to the diffuseemission, down to a typical flux limit of ~10-4 phcm-2 s-1. We also find no evidence for thepositive latitude enhancement that has been reported from OSSEmeasurements; our 3σ upper flux limit for this feature is 1.5× 10-4 ph cm-2 s-1. The diskemission can be attributed to the β^+-decay of the radioactivespecies 26 Al and 44Ti. The bulge emission arisesfrom a different source which has only a weak or no disk component. Wesuggest that Type Ia supernovae and/or low-mass X-ray binaries are theprime candidates for the source of the galactic bulge positrons. Lightdark matter annihilation could also explain the observed 511 keV bulgeemission characteristics.
| Photometric properties and origin of bulges in SB0 galaxies
We have derived the photometric parameters for the structural componentsof a sample of fourteen SB0 galaxies by applying a parametricphotometric decomposition to their observed I-band surface brightnessdistribution. We find that SB0 bulges are similar to bulges of theearly-type unbarred spirals, i.e. they have nearly exponential surfacebrightness profiles (< n>=1.48±0.16) and their effectiveradii are strongly coupled to the scale lengths of their surroundingdiscs (< r_e/h>=0.20±0.01). The photometric analysis alonedoes not allow us to differentiate SB0 bulges from unbarred S0 ones.However, three sample bulges have disc properties typical ofpseudobulges. The bulges of NGC 1308 and NGC 4340 rotate faster thanbulges of unbarred galaxies and models of isotropic oblate spheroidswith equal ellipticity. The bulge of IC 874 has a velocity dispersionlower than expected from the Faber-Jackson correlation and thefundamental plane of the elliptical galaxies and S0 bulges. Theremaining sample bulges are classical bulges, and are kinematicallysimilar to lower-luminosity ellipticals. In particular, they follow theFaber-Jackson correlation, lie on the fundamental plane and those forwhich stellar kinematics are available rotate as fast as the bulges ofunbarred galaxies.
| Fast bars in SB0 galaxies
We measured the bar pattern speed in a sample of 7 SB0 galaxies usingthe Tremaine-Weinberg method. This represents the largest sample ofgalaxies for which the bar pattern speed has been measured this way. Allthe observed bars are as rapidly rotating as they can be. We comparedthis result with recent high-resolution N-body simulations of bars incosmologically-motivated dark matter halos, and conclude that these barsare not located inside centrally concentrated halos.
| The Pattern Speeds of M51, M83, and NGC 6946 Using CO and the Tremaine-Weinberg Method
In spiral galaxies in which the molecular phase dominates the ISM, themolecular gas as traced by CO emission will approximately obey thecontinuity equation on orbital timescales. The Tremaine-Weinberg methodcan then be used to determine the pattern speed of such galaxies. Wehave applied the method to single-dish CO maps of three nearby spirals,M51, M83, and NGC 6946, to obtain estimates of their pattern speeds:38+/-7, 45+/-8, and 39+/-8 km s-1 kpc-1,respectively, and we compare these results to previous measurements. Wealso analyze the major sources of systematic errors in applying theTremaine-Weinberg method to maps of CO emission.
| Inner-truncated Disks in Galaxies
We present an analysis of the disk brightness profiles of 218 spiral andlenticular galaxies. At least 28% of disk galaxies exhibit innertruncations in these profiles. There are no significant trends oftruncation incidence with Hubble type, but the incidence among barredsystems is 49%, more than 4 times that for nonbarred galaxies. However,not all barred systems have inner truncations, and not allinner-truncated systems are currently barred. Truncations represent areal dearth of disk stars in the inner regions and are not an artifactof our selection or fitting procedures nor the result of obscuration bydust. Disk surface brightness profiles in the outer regions are wellrepresented by simple exponentials for both truncated and nontruncateddisks. However, truncated and nontruncated systems have systematicallydifferent slopes and central surface brightness parameters for theirdisk brightness distributions. Truncation radii do not appear tocorrelate well with the sizes or brightnesses of the bulges. Thissuggests that the low angular momentum material apparently missing fromthe inner disk was not simply consumed in forming the bulge population.Disk parameters and the statistics of bar orientations in our sampleindicate that the missing stars of the inner disk have not simply beenredistributed azimuthally into bar structures. The sharpness of thebrightness truncations and their locations with respect to othergalactic structures suggest that resonances associated with diskkinematics, or tidal interactions with the mass of bulge stars, might beresponsible for this phenomenon.
| Optical Photometry of SN2003gs
The use of type Ia supernovae (SNeIa) as distance indicators is mademore accurate by the continued acquisition of good photometry on SNeIaevents. As the set of observed events becomes more accurate by includingprecise CCD photometry, use of Phillip's Dm15 parameter gives betterdefined magnitude errors and template fits even with incomplete data,allowing us to estimate the peak magnitude, epoch of peak brightness,and host galaxy reddening. With these considerations it is possible touse the peak brightness of SNeIa to measure luminosity distances despitethe fact that the SNe are imperfect standard candles.For this study, optical UBVRI photometry is carried out using IRAF andStetson's DAOPHOT for the nearby supernova SN2003gs in NGC0936. Thesupernova was caught just at maximum light and the light curve iswell-fit through day 80 since maximum light. This supernova was a raresublumious event with Dm15=1.85m. The absolute magnitude fits well onthe relationship of absolute magnitude versus Dm15 of Phillips et al..(1999).Thanks to the National Science Foundation and to Cerro TololoInter-American Observatory for their support of this study.
| Detailed comparison of the structures and kinematics of simulated and observed barred galaxies
We examine the observable properties of simulated barred galaxies,including radial mass profiles, edge-on structure and kinematics, barlengths and pattern speed evolution for detailed comparison to realsystems. We have run several simulations in which bars are createdthrough inherent instabilities in self-consistent simulations of arealistic disc+halo galaxy model with a disc-dominated, flat rotationcurve. These simulations were run at high (N= 20 million particles) andlow (N= 500000 particles) resolution to test numerical convergence. Wedetermine the pattern speeds in simulations directly from the phaseangle of the bar versus time and the Tremaine-Weinberg method.Fundamental dynamics do not change between the high and low resolution,suggesting that convergence has been reached in this case. We find thatthe higher resolution is needed to simulate structural and kinematicproperties accurately. The edge-on view of the higher-resolution systemshows the bending instability and formation of a peanut-shaped bulgeclearly. We determined bar lengths by different means to determine thatthe simulated bar is fast, with a corotation to bar length ratio ofunder 1.5. Simulated bars in these models form with pattern speedsslower than those observed and slow-down during their evolution.Dynamical friction between the bar and dark halo is responsible for thisdeceleration, as revealed by the transfer of angular momentum betweenthe disc and the halo. However, even though the pattern speed is reducedat later times, the instantaneous scalelength of the disc has grownsufficiently for the bar motion to agree with many observations. Byusing a different model and simulation technique than other authors, weare able to compare the robustness of these methods. An animation of theface-on and edge-on views of the 20-million-particle simulation isavailable at http://www.astro.utoronto.ca/~oneill.
| Secular bar formation in galaxies with a significant amount of dark matter
Using high-resolution N-body simulations of stellar discs embedded incosmologically motivated dark matter haloes, we study the evolution ofbars and the transfer of angular momentum between haloes and bars. Wefind that dynamical friction results in some transfer of angularmomentum to the halo, but the effect is much smaller than previouslyfound in low-resolution simulations and is incompatible with earlyanalytical estimates. After 5 Gyr of evolution the stellar componentloses only 5-7 per cent of its initial angular momentum.Mass and force resolutions are crucial for the modelling of bardynamics. In low-resolution (300-500 pc) simulations we find that thebar slows down and angular momentum is lost relatively fast. Insimulations with millions of particles reaching a resolution of 20-40pc, the pattern speed may not change over billions of years. Ourhigh-resolution models produce bars that are fast rotators, where theratio of the corotation radius to the bar semi-major axis lies in therange , marginally compatible with observational results. In contrast tomany previous simulations, we find that bars are relatively short. As inmany observed cases, the bar semi-major axis is close to the exponentiallength of the disc.The transfer of angular momentum between inner and outer parts of thedisc plays a very important role in the secular evolution of the discand the bar. The bar formation increases the exponential length of thedisc by a factor of 1.2-1.5. The transfer substantially increases thestellar mass in the centre of the galaxy and decreases the dark matterto baryon ratio. As the result, the central 2-kpc region is alwaysstrongly dominated by the baryonic component. At intermediate (3-10 kpc)scales the disc is sub-dominant. These models demonstrate that theefficiency of angular momentum transfer to the dark matter has beengreatly overestimated. More realistic models produce bar structure instriking agreement with observational results.
| Model-independent measurements of bar pattern speeds
The pattern speed is one of the fundamental parameters that determinesthe structure of barred galaxies. This quantity is usually derived fromindirect methods or by employing model assumptions. The number of barpattern speeds derived using the model-independent Tremaine &Weinberg technique is still very limited. We present the results ofmodel-independent measurements of the bar pattern speed in four galaxiesranging in Hubble type from SB0 to SBbc. Three of the four galaxies inour sample are consistent with bars being fast rotators. The lack ofslow bars is consistent with previous observations and suggests thatbarred galaxies do not have centrally concentrated dark matter haloes.This contradicts simulations of cosmological structure formation andobservations of the central mass concentration in nonbarred galaxies.
| On position angle errors in the Tremaine-Weinberg method
I show that Tremaine-Weinberg (TW) measurements of bar pattern speedsare sensitive to errors in the position angle of the disc,PAdisc. I use an N-body experiment to measure these errors;for typical random PAdisc errors, the resulting scatter inthe measured values of the dimensionless bar speed parameter (defined asthe ratio of the corotation radius to the bar semi-major axis) is of theorder of the scatter in the observed values.I also consider how the systematic PAdisc errors produced bydisc ellipticities affect TW measurements. The scatter produced by theseerrors may be significant, depending on the ellipticity distribution.Conversely, by using the sample of TW observations, I find that an upperlimit of the typical disc (density) ellipticity is 0.07 at the 90 percent confidence level, which is in good agreement with previousmeasurements.Taken together, the random and systematic scatter suggest that theintrinsic distribution of of gas-poor early-type barred galaxies may beas narrow as that of the gas-rich later types.
| 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.
| Measurement of fast bars in a sample of early-type barred galaxies
We present surface photometry and stellar kinematics of a sample of fiveSB0 galaxies: ESO 139-G009, IC 874, NGC 1308, NGC 1440 and NGC 3412. Wemeasured their bar pattern speed using the Tremaine-Weinberg method, andderived the ratio, , of the corotation radius to the length of the barsemimajor axis. For all the galaxies, is consistent with being in therange from 1.0 to 1.4, i.e. that they host fast bars. This representsthe largest sample of galaxies for which has been measured in this way.Taking into account the measured distribution of and our measurementuncertainties, we argue that this is probably the true distribution of .If this is the case, then the Tremaine-Weinberg method finds adistribution of which is in agreement with that obtained byhydrodynamical simulations. We compare this result with recenthigh-resolution N-body simulations of bars in cosmologically motivateddark matter haloes, and we conclude that these bars are not locatedinside centrally concentrated dark matter haloes.
| Fast bars in early-type barred galaxies
We measured the bar pattern speed of a sample of 6 SB0 galaxies usingthe Tremaine-Weinberg method. We derived the ratio, {cal R}, of thecorotation radius to the length of the bar semi-major axis. For all thegalaxies, {cal R} is consistent with being in the range from 1.0 and1.4, i.e. that they host fast bars. This represents the largest sampleof galaxies for which {cal R} has been measured this way. We comparedthis result with recent high-resolution N-body simulations of bars incosmologically-motivated dark matter halos, and conclude that these barsare not located inside centrally concentrated dark matter halos.
| Supernova 2003gs in NGC 936
IAUC 8175 available at Central Bureau for Astronomical Telegrams.
| Supernova 2003gs in NGC 936.
Not Available
| Supernova 2003gs in NGC 936
IAUC 8172 available at Central Bureau for Astronomical Telegrams.
| Supernova 2003gs in NGC 936
IAUC 8171 available at Central Bureau for Astronomical Telegrams.
| An Imaging Survey of Early-Type Barred Galaxies
This paper presents the results of a high-resolution imaging survey,using both ground-based and Hubble Space Telescope images, of a completesample of nearby barred S0-Sa galaxies in the field, with a particularemphasis on identifying and measuring central structures within thebars: secondary bars, inner disks, nuclear rings and spirals, andoff-plane dust. A discussion of the frequency and statistical propertiesof the various types of inner structures has already been published.Here we present the data for the individual galaxies and measurements oftheir bars and inner structures. We set out the methods we use to findand measure these structures, and how we discriminate between them. Inparticular, we discuss some of the deficiencies of ellipse fitting ofthe isophotes, which by itself cannot always distinguish between bars,rings, spirals, and dust, and which can produce erroneous measurementsof bar sizes and orientations.
| 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.
| The Cool Interstellar Medium in S0 Galaxies. I. A Survey of Molecular Gas
Lenticular galaxies remain remarkably mysterious as a class.Observations to date have not led to any broad consensus about theirorigins, properties, and evolution, although they are often thought tohave formed in one big burst of star formation early in the history ofthe universe and to have evolved relatively passively since then. Inthat picture, current theory predicts that stellar evolution returnssubstantial quantities of gas to the interstellar medium; most isejected from the galaxy, but significant amounts of cool gas might beretained. Past searches for that material, though, have provided unclearresults. We present results from a survey of molecular gas in avolume-limited sample of field S0 galaxies selected from the NearbyGalaxies Catalog. CO emission is detected from 78% of the samplegalaxies. We find that the molecular gas is almost always located insidethe central few kiloparsecs of a lenticular galaxy, meaning that ingeneral it is more centrally concentrated than in spirals. We combineour data with H I observations from the literature to determine thetotal masses of cool and cold gas. Curiously, we find that, across awide range of luminosity, the most gas-rich galaxies have ~10% of thetotal amount of gas ever returned by their stars. That result isdifficult to understand within the context of either monolithic orhierarchical models of evolution of the interstellar medium.
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