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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.
| A Comparison of Hα and Stellar Scale Lengths in Virgo and Field Spirals
The scale lengths of the old stars and ionized gas distributions arecompared for similar samples of Virgo Cluster members and field spiralgalaxies via Hα and broad R-band surface photometry. While theR-band and Hα scale lengths are, on average, comparable for thecombined sample, we find significant differences between the field andcluster samples. While the Hα scale lengths of the field galaxiesare a factor of 1.14+/-0.07 longer, on average, than their R-band scalelengths, the Hα scale lengths of Virgo Cluster members are, onaverage, 20% smaller than their R-band scale lengths. Furthermore, inVirgo, the scale length ratios are correlated with the size of thestar-forming disk: galaxies with smaller overall Hα extents alsoshow steeper radial falloff of star formation activity. At the sametime, we find no strong trends in scale length ratio as a function ofother galaxy properties, including galaxy luminosity, inclination,morphological type, central R-band light concentration, or bar type. Ourresults for Hα emission are similar to other results for dustemission, suggesting that Hα and dust have similar distributions.The environmental dependence of the Hα scale length placesadditional constraints on the evolutionary process(es) that cause gasdepletion and a suppression of the star formation rate in clusters ofgalaxies.
| 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.
| Integral Field Spectroscopy of 23 Spiral Bulges
We have obtained integral-field spectroscopy for 23 spiral bulges usingINTEGRAL on the William Herschel Telescope and SPIRAL on theAnglo-Australian Telescope. This is the first two-dimensional surveydirected solely at the bulges of spiral galaxies. Eleven galaxies of thesample do not have previous measurements of the stellar velocitydispersion (σ*). These data are designed to complementour Space Telescope Imaging Spectrograph program for estimating blackhole masses in the range 106-108 Msolarusing gas kinematics from nucleated disks. These observations will serveto derive the stellar dynamical bulge properties using the traditionalMg b and Ca II triplets. We use both cross-correlation and maximumpenalized likelihood to determine projected σ* in thesesystems and present radial velocity fields, major axis rotation curves,curves of growth, and σ* fields. Usingcross-correlation to extract the low-order two-dimensional stellardynamics we generally see coherent radial rotation and irregularvelocity dispersion fields suggesting that σ* is anontrivial parameter to estimate.
| The Pattern Speeds of 38 Barred Galaxies
We estimate the pattern speeds of 38 barred galaxies by simulationmodeling. We construct the gravitational potentials of the galaxies fromnear-IR photometry by assuming that the mass-to-light ratio (M/L) isconstant in the H band and a single pattern speed dominates in thestellar disk. We use the response of gaseous and stellar particle disksto a rigidly rotating potential to determine the pattern speed. If ourassumptions are correct, then the pattern speed depends on themorphological type: the average value of the ratio of the corotationresonance radius to the bar radius, ℛ, increases from about 1.1 intype SB0/a to 1.4 in SBb and 1.7 in SBc. Within the error estimates, allthe bars in galaxies of type SBab or earlier are fast rotators, havingℛ<=1.4, whereas late-type galaxies include both fast and slowrotators.
| The Distribution of Bar and Spiral Arm Strengths in Disk Galaxies
The distribution of bar strengths in disk galaxies is a fundamentalproperty of the galaxy population that has only begun to be explored. Wehave applied the bar-spiral separation method of Buta and coworkers toderive the distribution of maximum relative gravitational bar torques,Qb, for 147 spiral galaxies in the statistically well-definedOhio State University Bright Galaxy Survey (OSUBGS) sample. Our goal isto examine the properties of bars as independently as possible of theirassociated spirals. We find that the distribution of bar strengthdeclines smoothly with increasing Qb, with more than 40% ofthe sample having Qb<=0.1. In the context of recurrent barformation, this suggests that strongly barred states are relativelyshort-lived compared to weakly barred or nonbarred states. We do notfind compelling evidence for a bimodal distribution of bar strengths.Instead, the distribution is fairly smooth in the range0.0<=Qb<0.8. Our analysis also provides a first look atspiral strengths Qs in the OSUBGS sample, based on the sametorque indicator. We are able to verify a possible weak correlationbetween Qs and Qb, in the sense that galaxies withthe strongest bars tend to also have strong spirals.
| Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.
| Nuclear Properties of a Sample of Nearby Spiral Galaxies from Hubble Space Telescope STIS Imaging
We present surface photometry for the central regions of a sample of 48spiral galaxies (mostly unbarred and barred of type Sbc or Sc) observedwith the Space Telescope Imaging Spectrograph on board the Hubble SpaceTelescope. Surface brightness profiles (SBPs) were derived and modeledwith a Nuker law. We also analyzed archival Wide Field Planetary Camera2 images with a larger field of view, which are available for 18galaxies in our sample. We modeled the extracted bulge SBPs with anexponential, an r1/4, or an rn profile. Inagreement with previous studies, we find that bulges of Sbc galaxiesfall into two categories: bulges well described by an exponentialprofile and those well described by an r1/4 profile. Only onegalaxy requires the use of a more general Sérsic profile toproperly describe the bulge. Nuclear photometrically distinct componentsare found in ~55% of the galaxies. For those that we classify as starclusters on the basis of their resolved extent, we find absolutemagnitudes that are brighter on average than those previously identifiedin spiral galaxies. This might be due to a bias in our sample towardstar-forming galaxies, combined with a trend for star-forming galaxiesto host brighter central clusters.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| 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
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| Chemically consistent evolution of galaxies. II. Spectrophotometric evolution from zero to high redshift
The composite stellar populations of galaxies comprise stars of a widerange of metallicities. Subsolar metallicities become increasinglyimportant, both in the local universe when going from early towardslater galaxy types as well as for dwarf galaxies and for all types ofgalaxies towards higher redshifts.We present a new generation of chemically consistent evolutionarysynthesis models for galaxies of various spectral types from E throughSd. The models follow the chemical enrichment of the ISM and take intoaccount the increasing initial metallicity of successive stellargenerations using recently published metallicity dependent stellarevolutionary isochrones, spectra and yields.Our first set of closed-box 1-zone models does not include any spatialresolution or dynamics. For a Salpeter initial mass function (IMF) thestar formation rate (SFR) and its time evolution are shown tosuccessfully parameterise spectral galaxy types E, ..., Sd. We show howthe stellar metallicity distribution in various galaxy types build upwith time to yield after 12 Gyr agreement with stellar metallicitydistributions observed in our and other local galaxies.The models give integrated galaxy spectra over a wide wavelength range(90.9 Å-160 μm), which for ages of 12 Gyr are in goodagreement not only with observed broad band colours but also withtemplate spectra for the respective galaxy types.Using filter functions for Johnson-Cousins U, B, V, RC,IC, as well as for HST broad band filters in the optical andBessel & Brett's NIR J, H, K filter system, we calculate theluminosity and colour evolution of model galaxies over a Hubble time.Including a standard cosmological model (H0 = 65,Ω0 = 0.1) and the attenuation by intergalactic hydrogenwe present evolutionary and cosmological corrections as well as apparentluminosities in various filters over the redshift range from z 5to the present for our galaxy types and compare to earlier models usingsingle (=solar) metallicity input physics only. We also resent a firstcomparison of our cc models to HDF data. A more detailed comparison withHubble Deep Field (HDF) and other deep field data and an analysis andinterpretation of high redshift galaxies in terms of ages,metallicities, star formation histories and, galaxy types will be thesubject of a forthcoming paper.
| Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
| 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.
| An Atlas of Hubble Space Telescope Spectra and Images of Nearby Spiral Galaxies
We have observed 54 nearby spiral galaxies with the Space TelescopeImaging Spectrograph (STIS) on the Hubble Space Telescope to obtainoptical long-slit spectra of nuclear gas disks and STIS optical (~Rband) images of the central 5''×5'' of thegalaxies. These spectra are being used to determine the velocity fieldof nuclear disks and hence to detect the presence of central massiveblack holes. Here we present the spectra for the successfulobservations. Dust obscuration can be significant at opticalwavelengths, and so we also combine the STIS images with archivalNear-Infrared Camera and Multi-Object Spectrometer H-band images toproduce color maps to investigate the morphology of gas and dust in thecentral regions. We find a great variety in the different morphologies,from smooth distributions to well-defined nuclear spirals and dustlanes.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| 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.
| 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.
| Local velocity field from sosie galaxies. I. The Peebles' model
Pratton et al. (1997) showed that the velocity field around clusterscould generate an apparent distortion that appears as tangentialstructures or radial filaments. In the present paper we determine theparameters of the Peebles' model (1976) describing infall of galaxiesonto clusters with the aim of testing quantitatively the amplitude ofthis distortion. The distances are determined from the concept of sosiegalaxies (Paturel 1984) using 21 calibrators for which the distanceswere recently calculated from two independent Cepheid calibrations. Weuse both B and I-band magnitudes. The Spaenhauer diagram method is usedto correct for the Malmquist bias. We give the equations for theconstruction of this diagram. We analyze the apparent Hubble constant indifferent regions around Virgo and obtain simultaneously the Local Groupinfall and the unperturbed Hubble constant. We found:[VLG-infall = 208 ± 9 km s-1] [\log H =1.82 ± 0.04 (H ≈ 66 ± 6 km s-1Mpc-1).] The front side and backside infalls can be seenaround Virgo and Fornax. In the direction of Virgo the comparison ismade with the Peebles' model. We obtain: [vinfall} =CVirgo/r0.9 ± 0.2] withCVirgo=2800 for Virgo and CFornax=1350 for Fornax,with the adopted units (km s-1 and Mpc). We obtain thefollowing mean distance moduli: [μVirgo=31.3 ± 0.2(r=18 Mpc )] [μFornax=31.7 ± 0.3 (r=22 Mpc). ] Allthese quantities form an accurate and coherent system. Full Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/57
| 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
| Recovering physical parameters from galaxy spectra using MOPED
We derive physical parameters of galaxies from their observed spectrausing MOPED, the optimized data compression algorithm of Heavens,Jimenez & Lahav. Here we concentrate on parametrizing galaxyproperties, and apply the method to the NGC galaxies in Kennicutt'sspectral atlas. We focus on deriving the star formation history,metallicity and dust content of galaxies. The method is very fast,taking a few seconds of CPU time to estimate ~17 parameters, and istherefore specially suited to studying large data sets, such as theAnglo-Australian two-degree-field (2dF) galaxy survey and the SloanDigital Sky Survey (SDSS). Without the power of MOPED, the recovery ofstar formation histories in these surveys would be impractical. InKennicutt's atlas, we find that for the spheroidals a small recent burstof star formation is required to provide the best fit to the spectrum.There is clearly a need for theoretical stellar atmospheric models withspectral resolution better than 1Å if we are to extract all therich information that large redshift surveys contain in their galaxyspectra.
| A study of the core of the Shapley Concentration - VI. Spectral properties of galaxies*
We present the results of a study of the spectral properties of galaxiesin the central part of the Shapley Concentration, covering an extremelywide range of densities, from the rich cluster cores to the underlyingsupercluster environment. Our sample is homogeneous, in a well definedmagnitude range (17<=bJ<=18.8) and contains ~1300spectra of galaxies at the same distance, covering an area of~26deg2. These characteristics allowed an accurate spectralclassification that we performed using a principal components analysistechnique. This spectral classification, together with the [Oii]equivalent widths and the star formation rates, has been used to studythe properties of galaxies at different densities: cluster, intercluster(i.e. galaxies in the supercluster but outside clusters) and fieldenvironment. No significant differences are present between samples atlow density regimes (i.e. intercluster and field galaxies). Clustergalaxies, instead, not only have values that are significantly differentfrom the field ones, but also show a dependence on the local density.Moreover, a well defined morphology-density relation is present in thecluster complexes, although these structures are known to be involved inmajor merging events. Also the mean equivalent width of [Oii] shows atrend with the local environment, decreasing at increasing densities,even if it is probably induced by the morphology-density relation.Finally we analysed the mean star formation rate as a function of thedensity, finding again a decreasing trend (at ~3σ significancelevel). Our analysis is consistent with the claim of Balogh et al. thatthe star formation in clusters is depressed.
| Nebular emission from star-forming galaxies
We present a new model for computing consistently the line and continuumemission from galaxies, based on a combination of recent populationsynthesis and photoionization codes. We use effective parameters todescribe the Hii regions and the diffuse gas ionized by single stellargenerations in a galaxy, among which the most important ones are thezero-age effective ionization parameter, the effective gas metallicityand the effective dust-to-heavy element ratio. We calibrate the nebularproperties of our model using the observed [Oiii]/Hβ, [Oii]/[Oiii],[Sii]/Hα and [Nii]/[Sii] ratios of a representative sample ofnearby spiral and irregular, starburst and Hii galaxies. To computewhole (line plus continuum) spectral energy distributions, we includethe absorption by dust in the neutral interstellar medium (ISM) using arecent simple prescription, which is consistent with observations ofnearby starburst galaxies. Our model enables us to interpretquantitatively the observed optical spectra of galaxies in terms ofstars, gas and dust parameters. We find that the range of ionized-gasproperties spanned by nearby galaxies implies factors of 3.5 and 14variations in the Hα and [Oii] luminosities produced per unit starformation rate (SFR). When accounting for stellar Hα absorptionand absorption by dust in the neutral ISM, the actual uncertainties inSFR estimates based on the emergent Hα and [Oii] luminosities areas high as several decades. We derive new estimators of the SFR, thegas-phase oxygen abundance and the effective absorption optical depth ofthe dust in galaxies. We show that, with the help of other lines such as[Oii], Hβ, [Oiii], [Nii] or [Sii], the uncertainties in SFRestimates based on Hα can be reduced to a factor of only 2-3, evenif the Hα line is blended with the adjacent [Nii] lines. WithoutHα, however, the SFR is difficult to estimate from the [Oii],Hβ and [Oiii] lines. The reason for this is that the absorption bydust in the neutral ISM and the ionized-gas parameters are thendifficult to constrain independently. This suggests that, whileinsufficient by itself, the Hα line is essential for estimatingthe star formation rate from the optical emission of a galaxy.
| 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.
| Analysis of Resonances in Grand Design Spiral Galaxies
We have searched for corotation resonances (CRs) in three southern granddesign spiral galaxies: NGC 1365, NGC 1566, and NGC 2997. We have alsointroduced a method of quantifying errors in the phase diagram used todetect CRs. We established the m=2 pattern CR at 12.1, 9.4, and 7 kpcfor NGC 1365, NGC 1566, and NGC 2997, respectively. By using publishedrotation curves, we could determine spiral pattern angular speeds of25.0, 12.2, and 17.6 km s-1 kpc-1, respectively. Athree-armed component has been detected in NGC 2997, with the CR placedat 8.7 kpc with a pattern angular speedΩCR3=12.7 km s-1kpc-1. An m=1 component was detected in NGC 1566. We warilylocate the CR at 7.1 kpc, with a pattern angular speedΩCR~=16.6 km s-1 kpc-1. Thispattern does not present inner Lindblad resonance. Ages have beendetermined by studying the radial density profile of the m=2 Fouriercomponents in g (newly formed stars) and i (perturbing spiral densitywave supported by the disk of old stars), aided by the global aspect ofthe real spiral pattern in comparison with numerical simulations. Thepattern is ~1200 Myr old in NGC 1365, ~800 Myr old in NGC 1566, andyounger than 80 Myr in NGC 2997.
| Homogenization of the Stellar Population along Late-Type Spiral Galaxies
We present a study of the broadband UBV color profiles for 257 Sbcbarred and nonbarred galaxies, using photoelectric aperture photometrydata from the literature. Using robust statistical methods, we haveestimated the color gradients of the galaxies, as well as the total andbulge mean colors. A comparative photometric study using CCD images wasdone. In our sample, the color gradients are negative (reddish inward)in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. The results do not change, essentially,when we include the edge-on galaxies. As a consequence of this study wehave also found that barred galaxies are overrepresented among theobjects having null or positive gradients, indicating that bars act as amechanism of homogenization of the stellar population. This effect ismore evident in the U-B color index, although it can also be detected inthe B-V color. A correlation between the total and bulge colors wasfound that is a consequence of an underlying correlation between thecolors of bulges and disks found by other authors. Moreover, the meantotal color is the same irrespective of the gradient regime, whilebulges are bluer in galaxies with null or positive gradients, whichindicates an increase of the star formation rate in the central regionsof these objects. We have also made a quantitative evaluation of theamount of extinction in the center of these galaxies. This was doneusing the Wide Field Planetary Camera 2 (WFPC2) and the Near InfraredCamera and Multi-Object Spectrometer (NICMOS) Hubble Space Telescope(HST) archival data, as well as CCD B, V, and I images. We show thatalthough the extinction in the V-band can reach values up to 2 mag inthe central region, it is unlikely that dust plays a fundamental role inglobal color gradients. We found no correlation between color and O/Habundance gradients. This result could suggest that the color gradientsare more sensitive to the age rather than to the metallicity of thestellar population. However, the absence of this correlation may becaused by dust extinction. We discuss this result by considering apicture in which bars are a relatively fast, recurrent phenomenon. Theseresults are not compatible with a pure classical monolithic scenario forbulge and disk formation. On the contrary, they favor a scenario inwhich both these components are evolving in a correlated process inwhich stellar bars play a crucial role. Based partly on observationsmade at the Pico dos Dias Observatory (PDO/LNA-CNPq), Brazil.
| The mass distribution in the innermost regions of spiral galaxies
We use high-spatial resolution ( ~ 100 pc) rotation curves of 83 spiralgalaxies to investigate the mass distribution of their innermost kpc. Weshow that in this region the luminous matter completely accounts for thegravitational potential and no dark component is required. The derivedI-band disk mass-to-light ratios Y_I agree well with those obtained frompopulation synthesis models and correlate with color in a similar way.We find strict upper limits of ~ 10^7 M_Sun for the masses of compactbodies at the center of spirals ruling out that these systems host theremnants of the quasar activity.
| A new model for the infrared brightness of the Galaxy
We present a model that reproduces the near-infrared brightnessdistribution of the Galaxy, and we compare its predictions with theresults of the Spacelab observations obtained by Kent et al. and theCOBE DIRBE experiment. We examine characteristics of nearby spiralgalaxies as a guide for a consistent description of the bulge, the barand spiral arms. A Monte Carlo method is used to generate a 3D model ofeach component of the Galaxy; the density flux contribution of thepseudo-stars created in this way is then added in a longitude versuslatitude grid to produce contour maps and brightness profiles. Weestimate the mass of the components, based on a calibration of the fluxdensity per unit mass for the characteristic stellar population of eachcomponent. We find that the brightness of the disc is better reproducedby the Freeman radial density profile, which presents a central hole,than by a classical disc with exponential profile extending to thecentre. We show that the rotation curve obtained from the massdistribution of the model is consistent with the observed one.
| 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.
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