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Dark and Baryonic Matter in Bright Spiral Galaxies. I. Near-Infrared and Optical Broadband Surface Photometry of 30 Galaxies
We present photometrically calibrated images and surface photometry inthe B, V, R, J, H, and K bands of 25, and in the g, r, and K bands offive nearby bright (B0T<12.5 mag) spiralgalaxies with inclinations of 30°-65° spanning the Hubblesequence from Sa to Scd. Data are from The Ohio State University BrightSpiral Galaxy Survey, the Two Micron All Sky Survey, and the SloanDigital Sky Survey Second Data Release. Radial surface brightnessprofiles are extracted, and integrated magnitudes are measured from theprofiles. Axis ratios, position angles, and scale lengths are measuredfrom the near-infrared images. A one-dimensional bulge/diskdecomposition is performed on the near-infrared images of galaxies witha nonnegligible bulge component, and an exponential disk is fit to theradial surface brightness profiles of the remaining galaxies.Based in part on observations obtained at the Cerro TololoInter-American Observatory, operated by the Association of Universitiesfor Research in Astronomy, Inc., under a cooperative agreement with theNational Science Foundation.
| Dark and Baryonic Matter in Bright Spiral Galaxies. II. Radial Distributions for 34 Galaxies
We decompose the rotation curves of 34 bright spiral galaxies intobaryonic and dark matter components. Stellar mass profiles are createdby applying color-M/L relations to near-infrared and optical photometry.We find that the radial profile of the baryonic-to-dark-matter ratio isself-similar for all galaxies, when scaled to the radius at which thecontribution of the baryonic mass to the rotation curve equals that ofthe dark matter (RX). We argue that this is due to thequasi-exponential nature of disks and rotation curves that are nearlyflat after an initial rise. The radius RX is found tocorrelate most strongly with baryonic rotation speed, such that galaxieswith RX measurements that lie further out in their disksrotate faster. This quantity also correlates very strongly with stellarmass, Hubble type, and observed rotation speed; B-band central surfacebrightness is less related to RX than these other galaxyproperties. Most of the galaxies in our sample appear to be close tomaximal disk. For these galaxies, we find that maximum observed rotationspeeds are tightly correlated with maximum rotation speeds predictedfrom the baryon distributions, such that one can create a Tully-Fisherrelation based on surface photometry and redshifts alone. Finally, wecompare our data to the NFW parameterization for dark matter profileswith and without including adiabatic contraction as it is most commonlyimplemented. Fits are generally poor, and all but two galaxies arebetter fit if adiabatic contraction is not performed. In order to havebetter fits, and especially to accommodate adiabatic contraction,baryons would need to contribute very little to the total mass in theinner parts of galaxies, seemingly in contrast with other observationalconstraints.
| Hubble Space Telescope STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass on Hubble Type
We study the nuclear star clusters (NCs) in spiral galaxies of variousHubble types using spectra obtained with the STIS on board the HubbleSpace Telescope (HST). We observed the nuclear clusters in 40 galaxies,selected from two previous HST WFPC2 imaging surveys. At a spatialresolution of ~0.2" the spectra provide a better separation of clusterlight from underlying galaxy light than is possible with ground-basedspectra. Approximately half of the spectra have a sufficiently highsignal-to-noise ratio for detailed stellar population analysis. For theother half we only measure the continuum slope, as quantified by the B-Vcolor. To infer the star formation history, metallicity, and dustextinction, we fit weighted superpositions of single-age stellarpopulation templates to the high signal-to-noise ratio spectra. We usethe results to determine the luminosity-weighted age, mass-to-lightratio, and masses of the clusters. Approximately half of the sampleclusters contain a population younger than 1 Gyr. Theluminosity-weighted ages range from 10 Myr to 10 Gyr. The stellarpopulations of NCs are generally best fit as a mixture of populations ofdifferent ages. This indicates that NCs did not form in a single event,but that instead they had additional star formation long after theoldest stars formed. On average, the sample clusters in late-typespirals have a younger luminosity-weighted mean age than those inearly-type spirals (L=8.37+/-0.25 vs.9.23+/-0.21). The average mass-weighted ages are older by ~0.7 dex,indicating that there often is an underlying older population that doesnot contribute much light but does contain most of the mass. The averagecluster masses are smaller in late-type spirals than in early-typespirals (logM=6.25+/-0.21 vs. 7.63+/-0.24) and exceed the masses typicalof globular clusters. The cluster mass correlates loosely with totalgalaxy luminosity. It correlates more strongly with both the Hubble typeof the host galaxy and the luminosity of its bulge. The lattercorrelation has the same slope as the well-known correlation betweensupermassive black hole mass and bulge luminosity. The properties ofboth nuclear clusters and black holes in the centers of spiral galaxiesare therefore intimately connected to the properties of the host galaxy,and in particular its bulge component. Plausible formation scenarioshave to account for this. We discuss various possible selection biasesin our results, but conclude that none of them can explain thedifferences seen between clusters in early- and late-type spirals. Theinability to infer spectroscopically the populations of faint clustersdoes introduce a bias toward younger ages, but not necessarily towardhigher masses.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555. These observations areassociated with proposals 9070 and 9783.
| The evolution of actively star-forming galaxies in the mid-infrared
In this paper we analyze the evolution of actively star-forming galaxiesin the mid-infrared (MIR). This spectral region, characterized bycontinuum emission by hot dust and by the presence of strong emissionfeatures generally ascribed to polycyclic aromatic hydrocarbon (PAH)molecules, is the most strongly affected by the heating processesassociated with star formation and/or active galactic nuclei (AGNs).Following the detailed observational characterization of galaxies in theMIR by the Infrared Space Observatory (ISO), we have updated themodelling of this spectral region in our spectrophotometric modelGRASIL. In the diffuse component we have updated the treatment of PAHsaccording to the model by Li & Draine. As for the dense phase of theinterstellar medium associated with the star-forming regions, themolecular clouds, we strongly decrease the abundance of PAHs as comparedto that in the cirrus, based on the observational evidence of the lackor weakness of PAH bands close to the newly formed stars, possibly dueto the destruction of the molecules in strong ultraviolet fields. Therobustness of the model is checked by fitting near-infrared to radiobroad-band spectra and the corresponding detailed MIR spectra of a largesample of galaxies, at once. With this model, we have analyzed thelarger sample of actively star-forming galaxies by Dale et al. We showthat the observed trends of galaxies in the ISO-IRAS-radio colour-colourplots can be interpreted in terms of the different evolutionary phasesof star formation activity, and the consequent different dominance inthe spectral energy distribution of the diffuse or dense phase of theISM. We find that the observed colours indicate a surprising homogeneityof the starburst phenomenon, allowing only a limited variation of themost important physical parameters, such as the optical depth of themolecular clouds, the time-scale of the escape of young stars from theirfor mation sites, and the gas consumption time-scale. In this paper wedo not attempt to reproduce the far-infrared coolest region in thecolour-colour plots, as we concentrate on models meant to reproduceactive star-forming galaxies, but we discuss possible requirements of amore complex modelling for the coldest objects.
| Radio Continuum and Far-infrared Emission from the Galaxies in the Eridanus Group
The Eridanus galaxies follow the well-known radio-FIR correlation. Themajority (70%) of these galaxies have their star formation rates belowthat of the Milky Way. The galaxies that have a significant excess ofradio emission are identified as low luminosity AGNs based on theirradio morphologies obtained from the GMRT observations. There are nopowerful AGNs (L20 cm>1023WHz-1) in the group. The twomost far-infrared and radio luminous galaxies in the group have opticaland HI morphologies suggestive of recent tidal interactions. TheEridanus group also has two far-infrared luminous but radio-deficientgalaxies. It is believed that these galaxies are observed within a fewMyr of the onset of an intense star formation episode after beingquiescent for at least a 100 Myr. The upper end of the radio luminositydistribution of the Eridanus galaxies (L20 cm1022WHz-1) isconsistent with that of the field galaxies, other groups, and late-typegalaxies in nearby clusters.
| The HI Content of the Eridanus Group of Galaxies
The HI content of galaxies in the Eridanus group is studied using theGMRT observations and the HIPASS data. A significant HI deficiency up toa factor of 2-3 is observed in galaxies in the high galaxy densityregions. The HI deficiency in galaxies is observed to be directlycorrelated to the local projected galaxy density, and inverselycorrelated to the lineof-sight radial velocity. Furthermore, galaxieswith larger optical diameters are predominantly in the lower galaxydensity regions. It is suggested that the HI deficiency in Eridanus isdue to tidal interactions. In some galaxies, evidences of tidalinteractions are seen. An important implication is that significantevolution of galaxies can take place in the group environment. In thehierarchical way of formation of clusters via mergers of groups, afraction of the observed HI deficiency in clusters could have originatedin groups. The co-existence of S0s and severely HI deficient galaxies inthe Eridanus group suggests that tidal interaction is likely to be aneffective mechanism for transforming spirals to S0s.
| GMRT HI Observations of the Eridanus Group of Galaxies I.
The GMRT HI 21cm-line observations of galaxies in the Eridanus group arepresented. The Eridanus group, at a distance of ~23 Mpc, is a loosegroup of ~200 galaxies. The group extends to more than 10 Mpc inprojection. The velocity dispersion of the galaxies in the group is ~240km s-1. The galaxies are clustered into different sub-groups. Theoverall population mix of the group is 30% (E + S0) and 70% (Sp + Irr).The observations of 57 Eridanus galaxies were carried out with the GMRTfor ~ 200 h. HI emission was detected from 31 galaxies. The channel rmsof ~1 mJy beam-1 was achieved for most of the image-cubes made with 4 hof data. The corresponding HI column density sensitivity (3σ) is~1 × 1020 cm-2 for a velocity-width of ~ 13.4 km s-1.The 3σ detection lss surface densities, HI disk parameters and HIrotation curves are presented. The velocity fields are analysedseparately for the approaching and the receding sides of the galaxies.These data will be used to study the HI and the radio continuumproperties, the Tully-Fisher relations, the dark matter halos, and thekinematical and HI lopsidedness in galaxies.
| Simulating the Spitzer Mid-Infrared Color-Color Diagrams
We use a simple parameterization of the mid-IR spectra of a wide rangeof galaxy types in order to predict their distribution in the InfraredArray Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 μm and MultibandPhotometer for Spitzer 24 μm color-color diagrams. We distinguishthree basic spectral types by the energetically dominant component inthe 3-12 μm regime: stellar-dominated, polycyclic aromatichydrocarbon (PAH)-dominated, and continuum-dominated. We use a Markovchain Monte Carlo approach to arrive at a more systematic and robustrepresentation of the mid-IR spectra of galaxies than do moretraditional approaches. We find that IRAC color-color plots are wellsuited to distinguishing the above spectral types, while the addition of24 μm data allows us to suggest practical three-color cuts thatpreferentially select higher redshift sources of a specific type. Wecompare our simulations with the color-color plot obtained by theSpitzer First Look Survey and find reasonable agreement. Lastly, wediscuss other applications as well as future directions for this work.
| 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.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| 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.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Comparison of Bar Strengths and Fractions of Bars in Active and Nonactive Galaxies
Gravitational perturbation strengths and bar fractions in active andnonactive galaxies are compared using the Ohio State University BrightGalaxy Survey, which forms a statistically well defined sample of 180disk galaxies. Bar fractions are studied using (1) the optical andnear-IR classification of bars made by Eskridge and coworkers in 2002and (2) our own bar classification based on Fourier decomposition ofnear-IR images (Fourier bars). The gravitational perturbation strengthsare calculated using the bar torque method, taking the maximum ratioQg of the tangential force to the mean background radialforce as a measure of the nonaxisymmetric perturbation. In addition,two-dimensional bulge-disk-bar decomposition is used to study theproperties of bulges of the sample galaxies. In the near-IR, Seyfertgalaxies, LINERs, and H II/starburst galaxies were found to have asimilar fraction, 72%, of Fourier bars (or SB-type bars), compared to55% in the nonactive galaxies. However, if SAB-type bars are alsoincluded, practically all (95%) H II/starburst galaxies have bars. Inaddition, a large fraction (34%) of bars in LINERs are obscured by dustin the optical region. We find that bars in early-type galaxies are atthe same time long and massive and have weak perturbation strengths.Weak perturbation strengths can be explained by dilution of thenonaxisymmetric forces by the massive bulges: for a bulge-to-disk massratio B/D ranging from 0 to 1, the dilution may reduce Qgfrom as high as 0.6 to as low as 0.1. On the other hand, bar length(relative to disk scale length) is not correlated with B/D, contrary toexpectation. Seyfert- or LINER-type nuclear activity is present in mostgalaxies that have thin and thick planar bar components, whereas nuclearactivity does not appear in those late-type galaxies that have extremelymassive bars and strong perturbation strengths.
| 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.
| 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
| Infrared Emission of Normal Galaxies from 2.5 to 12 Micron: Infrared Space Observatory Spectra, Near-Infrared Continuum, and Mid-Infrared Emission Features
We present ISOPHOT spectra of the regions 2.5-4.9 μm and 5.8-11.6μm for a sample of 45 disk galaxies from the US Infrared SpaceObservatory Key Project on Normal Galaxies. The galaxies were selectedto span the range in global properties of normal, star-forming diskgalaxies in the local universe. The spectra can be decomposed into threespectral components: (1) continuum emission from stellar photospheres,which dominates the near-infrared (NIR; 2.5-4.9 μm) spectral region;(2) a weak NIR excess continuum, which has a color temperature of~103 K, carries a luminosity of a few percent of the totalfar-infrared (FIR) dust luminosity LFIR and most likelyarises from the interstellar medium (ISM); and (3) the well-known broademission features at 6.2, 7.7, 8.6, and 11.3 μm, which are generallyattributed to aromatic carbon particles. These aromatic features inemission (AFEs) dominate the mid-infrared (MIR; 5.8-11.6 μm) part ofthe spectrum and resemble the so-called type A spectra observed in manynonstellar sources and the diffuse ISM in our own Galaxy. The fewnotable exceptions include NGC 4418, where a dust continuum replaces theAFEs in MIR, and NGC 1569, where the AFEs are weak and the strongestemission feature is [S IV] 10.51 μm. The relative strengths of theAFEs vary by 15%-25% among the galaxies. However, little correlation isseen between these variations and either IRAS 60 μm/100 μm fluxdensity ratio R(60/100) or the FIR/blue luminosity ratioLFIR/LB, two widely used indicators of the currentstar formation activity, suggesting that the observed variations are nota consequence of the radiation field differences among the galaxies. Wedemonstrate that the NIR excess continuum and AFE emission arecorrelated, suggesting that they are produced by similar mechanisms andsimilar (or the same) material. On the other hand, as the current starformation activity increases, the overall strengths of the AFEs and theNIR excess continuum drop significantly with respect to that of the FIRemission from large dust grains. In particular, the summed luminosity ofthe AFEs falls from ~0.2 LFIR for the most ``IR-quiescent''galaxies to ~0.1 LFIR for the most ``IR-active'' galaxies.This is likely a consequence of the preferential destruction in intenseradiation fields of the small carriers responsible for the NIR/AFEemission.Based on observations with ISO, an ESA project with instruments fundedby ESA member states (especially the PI countries, France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| Bar 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.
| A GMRT HI imaging survey of the ERIDANUS group of galaxies.
This project aims to image a subset of galaxies in the nearby groupEridanus in HI emission and in radio continuum using the GMRT. Thetypical resolution of HI images will be $\sim$1 kpc with a 3$\sigma$sensitivity to HI mass of a few times 10$^{7}$ M$_\odot$. The rotationcurves obtained using the HI velocity field together with the 2MASSmagnitudes in the near infrared will be used to construct theTully-Fisher relation for this group. High resolution (sub-kpc)multi-frequency radio continuum images will be used to studystar-formation rates, radio morphologies and spectral indices ofEridanus galaxies. About half of the galaxies have already been observedand further observations on some late type galaxies are proposed withthe GMRT. We present here the HI image and the rotation curve for amember of this group viz. NGC 1385.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| The Visibility of Galactic Bars and Spiral Structure at High Redshifts
We investigate the visibility of galactic bars and spiral structure inthe distant universe by artificially redshifting 101 B-band CCD imagesof local spiral galaxies from the Ohio State University Bright SpiralGalaxy Survey. These local galaxy images represent a much fairerstatistical baseline than the galaxy atlas images presented by Frei etal. in 1995, the most commonly used calibration sample for morphologicalwork at high redshifts. Our artificially redshifted images correspond toHubble Space Telescope I814-band observations of the localgalaxy sample seen at z=0.7, with integration times matching those ofboth the very deep northern Hubble Deep Field (HDF) data and the muchshallower HDF flanking field observations. The expected visibility ofgalactic bars is probed in two ways: (1) using traditional visualclassification and (2) by charting the changing shape of the galaxydistribution in ``Hubble space,'' a quantitative two-parameterdescription of galactic structure that maps closely onto Hubble'soriginal tuning fork. Both analyses suggest that over two-thirds ofstrongly barred luminous local spirals (i.e., objects classified as SBin the Third Reference Catalogue) would still be classified as stronglybarred at z=0.7 in the HDF data. Under the same conditions, most weaklybarred spirals (classified SAB in the Third Reference Catalogue) wouldbe classified as regular spirals. The corresponding visibility of spiralstructure is assessed visually, by comparing luminosity classificationsfor the artificially redshifted sample with the corresponding luminosityclassifications from the Revised Shapley-Ames Catalog. We find that forexposure times similar to that of the HDF, spiral structure should bedetectable in most luminous (MB~M*) low-inclination spiralgalaxies at z=0.7 in which it is present. However, obvious spiralstructure is only detectable in ~30% of comparable galaxies in the HDFflanking field data using the Wide Field Planetary Camera 2. Our studyof artificially redshifted local galaxy images suggests that, whenviewed at similar resolution, noise level, and redshift-correctedwavelength, barred spirals are less common at z~0.7 than they are atz=0.0, although more data are needed to definitively rule out thepossibility that cosmic variance is responsible for much of this effect.
| Far-Infrared Spectroscopy of Normal Galaxies: Physical Conditions in the Interstellar Medium
The most important cooling lines of the neutral interstellar medium(ISM) lie in the far-infrared (FIR). We present measurements by theInfrared Space Observatory Long Wavelength Spectrometer of seven linesfrom neutral and ionized ISM of 60 normal, star-forming galaxies. Thegalaxy sample spans a range in properties such as morphology, FIR colors(indicating dust temperature), and FIR/blue ratios (indicating starformation activity and optical depth). In two-thirds of the galaxies inthis sample, the [C II] line flux is proportional to FIR dust continuum.The other one-third show a smooth decline inL[CII]/LFIR with increasing Fν(60μm)/Fν(100 μm) and LFIR/LB,spanning a range of a factor of more than 50. Two galaxies at the warmand active extreme of the range haveL[CII]/LFIR<2×10-4 (3 σupper limit). This is due to increased positive grain charge in thewarmer and more active galaxies, which leads to less efficient heatingby photoelectrons from dust grains. The ratio of the two principalphotodissociation region (PDR) cooling linesL[OI]/L[CII] shows a tight correlation withFν(60 μm)/Fν(100 μm), indicating thatboth gas and dust temperatures increase together. We derive atheoretical scaling between [N II] (122 μm) and [C II] from ionizedgas and use it to separate [C II] emission from neutral PDRs and ionizedgas. Comparison of PDR models of Kaufman et al. with observed ratios of(1) L[OI]/L[CII] and(L[CII]+L[OI])/LFIR and (2)L[OI]/LFIR and Fν(60μm)/Fν(100 μm) yields far-UV flux G0 andgas density n. The G0 and n values estimated from the twomethods agree to better than a factor of 2 and 1.5, respectively, inmore than half the sources. The derived G0 and n correlatewith each other, and G0 increases with n asG0~nα, where α~1.4 . We interpret thiscorrelation as arising from Strömgren sphere scalings if much ofthe line and continuum luminosity arises near star-forming regions. Thehigh values of PDR surface temperature (270-900 K) and pressure(6×104-1.5×107 K cm-3)derived also support the view that a significant part of grain and gasheating in the galaxies occurs very close to star-forming regions. Thedifferences in G0 and n from galaxy to galaxy may be due todifferences in the physical properties of the star-forming clouds.Galaxies with higher G0 and n have larger and/or denserstar-forming clouds.
| 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.
| The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties
We study the mid-infrared properties of a sample of 69 nearby spiralgalaxies, selected to avoid Seyfert activity contributing a significantfraction of the central energetics, or strong tidal interaction, and tohave normal infrared luminosities. These observations were obtained withISOCAM, which provides an angular resolution of the order of 10arcsec(half-power diameter of the point spread function) and low-resolutionspectro-imaging information. Between 5 and 18 mu m, we mainly observetwo dust phases, aromatic infrared bands and very small grains, both outof thermal equilibrium. On this sample, we show that the globalF15/F_7 colors of galaxies are very uniform, the onlyincrease being found in early-type strongly barred galaxies, consistentwith previous IRAS studies. The F15/F_7 excesses areunambiguously due to galactic central regions where bar-inducedstarbursts occur. However, the existence of strongly barred early-typegalaxies with normal circumnuclear colors indicates that therelationship between a distortion of the gravitational potential and acentral starburst is not straightforward. As the physical processes atwork in central regions are in principle identical in barred andunbarred galaxies, and since this is where the mid-infrared activity ismainly located, we investigate the mid-infrared circumnuclear propertiesof all the galaxies in our sample. We show how surface brightnesses andcolors are related to both the available molecular gas content and themean age of stellar populations contributing to dust heating. Therefore,the star formation history in galactic central regions can beconstrained by their position in a color-surface brightness mid-infrareddiagram. Based on observations with ISO, an ESA project with instrumentsfunded by ESA Member States (especially the PI countries: France,Germany, the Netherlands and the UK) and with the participation of ISASand NASA.
| 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.
| ISO Mid-Infrared Observations of Normal Star-Forming Galaxies: The Key Project Sample
We present mid-infrared maps and preliminary analysis for 61 galaxiesobserved with the ISOCAM instrument aboard the Infrared SpaceObservatory. Many of the general features of galaxies observed atoptical wavelengths-spiral arms, disks, rings, and bright knots ofemission-are also seen in the mid-infrared, except the prominent opticalbulges are absent at 6.75 and 15 μm. In addition, the maps are quitesimilar at 6.75 and 15 μm, except for a few cases where a centralstarburst leads to lower Iν(6.75μm)/Iν(15 μm) ratios in the inner region. We alsopresent infrared flux densities and mid-infrared sizes for thesegalaxies. The mid-infrared color Iν(6.75μm)/Iν(15 μm) shows a distinct trend with thefar-infrared color Iν(60 μm)/Iν(100μm). The quiescent galaxies in our sample [Iν(60μm)/Iν(100 μm)<~0.6] show Iν(6.75μm)/Iν(15 μm) near unity, whereas this ratio dropssignificantly for galaxies with higher global heating intensity levels.Azimuthally averaged surface brightness profiles indicate the extent towhich the mid-infrared flux is centrally concentrated, and provideinformation on the radial dependence of mid-infrared colors. Thegalaxies are mostly well resolved in these maps: almost half of themhave <10% of their flux in the central resolution element. Acomparison of optical and mid-infrared isophotal profiles indicates thatthe flux at 4400 Å near the optical outskirts of the galaxies isapproximately 8 (7) times that at 6.75 μm (15 μm), comparable toobservations of the diffuse quiescent regions of the Milky Way. Thispaper is based on observations with the Infrared Space Observatory(ISO). ISO is an ESA project with instruments funded by ESA memberstates (especially the PI countries: France, Germany, The Netherlands,and the United Kingdom) and with the participation of ISAS and NASA.
| The Centers of Early- to Intermediate-Type Spiral Galaxies: A Structural Analysis
A recent Hubble Space Telescope (HST)/WFPC2 visual survey of early- andintermediate-type spiral galaxies has unveiled a great complexity in theinner regions of these systems, which include a high fraction ofphotometrically distinct compact sources sitting at the galactic centers(``nuclei''). The faint nuclei (M_V>~-12) are typically hosted byrather amorphous, quiescent, bulgelike structures with an exponential(rather than the classical R^1/4) light profile. These ``exponentialbulges'' are commonly found inside the intermediate-type disks,consistent with previous studies. Brighter nuclei (M_V<~-12) aretypically found instead in the centers of galaxies with circumnuclearrings/arms of star formation or dust and an active, i.e., H II- orAGN-type, central spectrum at ground-based resolution. On the structuralplane of half-light radius (R_e) versus mean surface brightness withinthe half-light radius (mu_e), faint and bright nuclei overlap with, andfill the region of parameter space between, the old Milky Way globularclusters and the young star clusters, respectively, with typical R_e ofabout a few up to ~20 pc. On the same plane, the exponential bulges havesignificantly fainter mu_e than R^1/4 bulges for any given radius andfollow a mu_e-R_e relation typical of disks, which strengthens thesuggestion that the exponential bulges grow inside the disks as a resultof the secular evolution of the latter. Under the likely assumption thatthe visual light from the faint nuclei embedded in the quiescentexponential bulges is of stellar origin and of a similar (>~1 Gyr)age for the central star clusters and their host bulges, the massesinferred for the former agree with those required to disrupt barscomparable in size to the latter. This offers support to scenarios inwhich the exponential bulges grow inside the disks owing to the orbitaldisruption of progenitor bars caused by the growth of a centralconcentration of mass and suggests that this specific mode of bulgeformation is (still) active in the present-day universe. On the otherhand, the presence of the massive clusters at the very center of thelow-density exponential bulges should prevent any other ``nuclear'' barfrom forming, thereby preventing further infall of dissipative fuel tothe nuclear regions. This may argue against the possibility of evolvingthe exponential bulges into denser, R^1/4 bulges by a simple looping forseveral cycles of the bar formation/disruption mechanism.
| An Infrared Search for Extinguished Supernovae in Starburst Galaxies
IR and radio-band observations of heavily extinguished regions instarburst galaxies suggest a high supernova (SN) rate associated withsuch regions. Optically measured SN rates may therefore underestimatethe total SN rate by factors of up to 10, as a result of the very highextinction (A_B~10-20 mag) to core-collapse SNe in starburst regions.The IR/radio SN rates come from a variety of indirect means, however,which suffer from model dependence and other problems. We describe adirect measurement of the SN rate from a regular patrol of starburstgalaxies done with K'-band imaging to minimize the effects ofextinction. A collection of K'-band measurements of core-collapse SNenear maximum light is presented. Such measurements (excluding 1987A) arenot well reported in the literature. Results of a preliminary K'-bandsearch, using the MIRC camera at the Wyoming Infrared Observatory and animproved search strategy using the new ORCA optics, are described. Amonthly patrol of a sample of IRAS bright (mostly starburst) galaxieswithin 25 Mpc should yield 1-6 SNe yr^-1, corresponding to the range ofestimated SN rates. Our initial MIRC search with low resolution (2.2"pixels) failed to find extinguished SNe in the IRAS galaxies, limitingthe SN rate outside the nucleus (at greater than 15" radius) to lessthan 3.8 far-IR SN rate units (SNe per century per 10^10 L_solarmeasured at 60 and 100 mum, or FIRSRU) at 90% confidence. The MIRCcamera had insufficient resolution to search nuclear starburst regions,where starburst and SN activity is concentrated; therefore, we wereunable to rigorously test the hypothesis of high SN rates in heavilyobscured star-forming regions. We conclude that high-resolution nuclearSN searches in starburst galaxies with small fields are more productivethan low-resolution, large-field searches, even for our sample of large(often several arcminutes) galaxies. With our ORCA high-resolutionoptics, we could limit the total SN rate to less than 1.3 FIRSRU at 90%confidence in 3 years of observations, lower than most estimates.
| A Study of External Galaxies Detected by the COBE Diffuse Infrared Background Experiment
A comparison of the COBE 1 Diffuse Infrared Background Experiment(DIRBE) all-sky survey with the locations of known galaxies in the IRASCatalog of Extragalactic Objects and the Center for Astrophysics Catalogof Galaxies led to the detection of as many as 57 galaxies. In thispaper, we present the photometric data for these galaxies and ananalysis of the seven galaxies that were detected at lambda > 100 mum. Estimates of the ratio of the mass of the cold dust (CD) componentdetected at Td = 20-30 K to a very cold dust (VCD) component with Td ~10-15 K suggest that between 2%-100% of the cirrus-like CD mass can alsoexist in many of these galaxies as VCD. In one galaxy, M33, the DIRBEphotometry at 240 mu m suggests as much as 26 times as much VCD may bepresent as compared to the cirrus-like component. Further submillimetermeasurements of this galaxy are required to verify such a largepopulation of VCD. We also present 10 galaxies that were detected in thesky region not previously surveyed by IRAS and that can be used toconstruct a flux-limited all-sky catalog of galaxies brighter than 1000Jy with a modest completeness limit of about 65%.
| Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.
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