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Scale Heights of Non-Edge-on Spiral Galaxies
We present a method of calculating the scale height of non-edge-onspiral galaxies, together with a formula for errors. The method is basedon solving Poisson's equation for a logarithmic disturbance of matterdensity in spiral galaxies. We show that the spiral arms can not extendto inside the ``forbidden radius'' r0, due to the effect ofthe finite thickness of the disk. The method is tested by re-calculatingthe scale heights of 71 northern spiral galaxies previously calculatedby Ma, Peng & Gu. Our results differ from theirs by less than 9%. Wealso present the scale heights of a further 23 non-edge-on spiralgalaxies.
| Low-Luminosity Active Galaxies and Their Central Black Holes
Central black hole masses for 117 spiral galaxies representingmorphological stages S0/a through Sc and taken from the largespectroscopic survey of Ho et al. are derived using Ks-banddata from the Two Micron All Sky Survey. Black hole masses are foundusing a calibrated black hole-Ks bulge luminosity relation,while bulge luminosities are measured by means of a two-dimensionalbulge-disk decomposition routine. The black hole masses are correlatedagainst a variety of parameters representing properties of the nucleusand host galaxy. Nuclear properties such as line width (FWHM [N II]), aswell as emission-line ratios (e.g., [O III]/Hβ, [O I]/Hα, [NII]/Hα, and [S II]/Hα), show a very high degree ofcorrelation with black hole mass. The excellent correlation with linewidth supports the view that the emission-line gas is in virialequilibrium with either the black hole or bulge potential. The very goodemission-line ratio correlations may indicate a change in ionizingcontinuum shape with black hole mass in the sense that more massiveblack holes generate harder spectra. Apart from theinclination-corrected rotational velocity, no excellent correlations arefound between black hole mass and host galaxy properties. Significantdifferences are found between the distributions of black hole masses inearly-, mid-, and late-type spiral galaxies (subsamples A, B, and C) inthe sense that early-type galaxies have preferentially larger centralblack holes, consistent with observations that Seyfert galaxies arefound preferentially in early-type systems. The line width distributionsshow a marked difference among subsamples A, B, and C in the sense thatearlier type galaxies have larger line widths. There are also cleardifferences in line ratios between subsamples A+B and C that likely arerelated to the level of ionization in the gas. Finally, aKs-band Simien & de Vaucouleurs diagram shows excellentagreement with the original B-band relation, although there is a largedispersion at a given morphological stage.
| The AMIGA sample of isolated galaxies. II. Morphological refinement
We present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies.
| Secular Evolution via Bar-driven Gas Inflow: Results from BIMA SONG
We present an analysis of the molecular gas distributions in the 29barred and 15 unbarred spirals in the BIMA CO (J=1-0) Survey of NearbyGalaxies (SONG). For galaxies that are bright in CO, we confirm theconclusion by Sakamoto et al. that barred spirals have higher moleculargas concentrations in the central kiloparsec. The SONG sample alsoincludes 27 galaxies below the CO brightness limit used by Sakamoto etal. Even in these less CO-bright galaxies we show that high central gasconcentrations are more common in barred galaxies, consistent withradial inflow driven by the bar. However, there is a significantpopulation of early-type (Sa-Sbc) barred spirals (6 of 19) that have nomolecular gas detected in the nuclear region and have very little out tothe bar corotation radius. This suggests that in barred galaxies withgas-deficient nuclear regions, the bar has already driven most of thegas within the bar corotation radius to the nuclear region, where it hasbeen consumed by star formation. The median mass of nuclear moleculargas is over 4 times higher in early-type bars than in late-type (Sc-Sdm)bars. Since previous work has shown that the gas consumption rate is anorder of magnitude higher in early-type bars, this implies that theearly types have significantly higher bar-driven inflows. The loweraccretion rates in late-type bars can probably be attributed to theknown differences in bar structure between early and late types. Despitethe evidence for bar-driven inflows in both early and late Hubble-typespirals, the data indicate that it is highly unlikely for a late-typegalaxy to evolve into an early type via bar-induced gas inflow.Nonetheless, secular evolutionary processes are undoubtedly present, andpseudobulges are inevitable; evidence for pseudobulges is likely to beclearest in early-type galaxies because of their high gas inflow ratesand higher star formation activity.
| Light and Motion in the Local Volume
Using high-quality data on 149 galaxies within 10 Mpc, I find nocorrelation between luminosity and peculiar velocity at all. There is nounequivocal sign on scales of 1-2 Mpc of the expected gravitationaleffect of the brightest galaxies, in particular infall toward groups, orof infall toward the supergalactic plane on any scale. Either darkmatter is not distributed in the same way as luminous matter in thisregion, or peculiar velocities are not due to fluctuations in mass. Thesensitivity of peculiar velocity studies to the background model ishighlighted.
| Structure and star formation in disk galaxies. III. Nuclear and circumnuclear Hα emission
From Hα images of a carefully selected sample of 57 relativelylarge, Northern spiral galaxies with low inclination, we study thedistribution of the Hα emission in the circumnuclear and nuclearregions. At a resolution of around 100 parsec, we find that the nuclearHα emission in the sample galaxies is often peaked, andsignificantly more often so among AGN host galaxies. The circumnuclearHα emission, within a radius of two kpc, is often patchy inlate-type, and absent or in the form of a nuclear ring in early-typegalaxies. There is no clear correlation of nuclear or circumnuclearHα morphology with the presence or absence of a bar in the hostgalaxy, except for the nuclear rings which occur in barred hosts. Thepresence or absence of close bright companion galaxies does not affectthe circumnuclear Hα morphology, but their presence does correlatewith a higher fraction of nuclear Hα peaks. Nuclear rings occur inat least 21% (±5%) of spiral galaxies, and occur predominantly ingalaxies also hosting an AGN. Only two of our 12 nuclear rings occur ina galaxy which is neither an AGN nor a starburst host. We confirm thatweaker bars host larger nuclear rings. The implications of these resultson our understanding of the occurrence and morphology of massive starformation, as well as non-stellar activity, in the central regions ofgalaxies are discussed.
| A New Nonparametric Approach to Galaxy Morphological Classification
We present two new nonparametric methods for quantifying galaxymorphology: the relative distribution of the galaxy pixel flux values(the Gini coefficient or G) and the second-order moment of the brightest20% of the galaxy's flux (M20). We test the robustness of Gand M20 to decreasing signal-to-noise ratio (S/N) and spatialresolution and find that both measures are reliable to within 10% forimages with average S/N per pixel greater than 2 and resolutions betterthan 1000 and 500 pc, respectively. We have measured G andM20, as well as concentration (C), asymmetry (A), andclumpiness (S) in the rest-frame near-ultraviolet/optical wavelengthsfor 148 bright local ``normal'' Hubble-type galaxies (E-Sd) galaxies, 22dwarf irregulars, and 73 0.05
| 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.
| A Catalog of Neighboring Galaxies
We present an all-sky catalog of 451 nearby galaxies, each having anindividual distance estimate D<~10 Mpc or a radial velocityVLG<550 km s-1. The catalog contains data onbasic optical and H I properties of the galaxies, in particular, theirdiameters, absolute magnitudes, morphological types, circumnuclearregion types, optical and H I surface brightnesses, rotationalvelocities, and indicative mass-to-luminosity and H I mass-to-luminosityratios, as well as a so-called tidal index, which quantifies the galaxyenvironment. We expect the catalog completeness to be roughly 70%-80%within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr,dIm, and dSph) galaxies with MB>-17.0, which contributeabout 4% to the local luminosity density, and roughly 10%-15% to thelocal H I mass density. The H I mass-to-luminosity and the H Imass-to-total (indicative) mass ratios increase systematically fromgiant galaxies toward dwarfs, reaching maximum values about 5 in solarunits for the most tiny objects. For the Local Volume disklike galaxies,their H I masses and angular momentum follow Zasov's linear relation,expected for rotating gaseous disks being near the threshold ofgravitational instability, favorable for active star formation. We foundthat the mean local luminosity density exceeds 1.7-2.0 times the globaldensity, in spite of the presence of the Tully void and the absence ofrich clusters in the Local Volume. The mean local H I density is 1.4times its ``global'' value derived from the H I Parkes Sky Survey.However, the mean local baryon densityΩb(<8Mpc)=2.3% consists of only a half of the globalbaryon density, Ωb=(4.7+/-0.6)% (Spergel et al.,published in 2003). The mean-square pairwise difference of radialvelocities is about 100 km s-1 for spatial separations within1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. alsoWe calculated the integral area of the sky occupied by the neighboringgalaxies. Assuming the H I size of spiral and irregular galaxies to be2.5 times their standard optical diameter and ignoring any evolutioneffect, we obtain the expected number of the line-of-sight intersectionswith the H I galaxy images to be dn/dz~0.4, which does not contradictthe observed number of absorptions in QSO spectra.
| Oxygen and nitrogen abundances in nearby galaxies. Correlations between oxygen abundance and macroscopic properties
We performed a compilation of more than 1000 published spectra of H IIregions in spiral galaxies. The oxygen and nitrogen abundances in each HII region were recomputed in a homogeneous way, using the P-method. Theradial distributions of oxygen and nitrogen abundances were derived. Thecorrelations between oxygen abundance and macroscopic properties areexamined. We found that the oxygen abundance in spiral galaxiescorrelates with its luminosity, rotation velocity, and morphologicaltype: the correlation with the rotation velocity may be slightlytighter. There is a significant difference between theluminosity-metallicity relationship obtained here and that based on theoxygen abundances determined through the R23-calibrations.The oxygen abundance of NGC 5457 recently determined using directmeasurements of Te (Kennicutt et al. \cite{Kennicutt2003})agrees with the luminosity-metallicity relationship derived in thispaper, but is in conflict with the luminosity-metallicity relationshipderived with the R23-based oxygen abundances. The obtainedluminosity-metallicity relation for spiral galaxies is compared to thatfor irregular galaxies. Our sample of galaxies shows evidence that theslope of the O/H - MB relationship for spirals (-0.079± 0.018) is slightly more shallow than that for irregulargalaxies (-0.139 ± 0.011). The effective oxygen yields wereestimated for spiral and irregular galaxies. The effective oxygen yieldincreases with increasing luminosity from MB -11 toMB -18 (or with increasing rotation velocity fromVrot 10 km s-1 to Vrot 100km s-1) and then remains approximately constant. Irregulargalaxies from our sample have effective oxygen yields lowered by afactor of 3 at maximum, i.e. irregular galaxies usually keep at least1/3 of the oxygen they manufactured during their evolution.Appendix, Tables \ref{table:refero}, \ref{table:referV}, and Figs.\ref{figure:sample2}-\ref{figure:sample5} are only available inelectronic form at http://www.edpsciences.org}
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Deprojecting spiral galaxies using Fourier analysis. Application to the Frei sample
We present two methods that can be used to deproject spirals, based onFourier analysis of their images, and discuss their potential andrestrictions. Our methods perform particularly well for galaxies moreinclined than 50° or for non-barred galaxies moreinclined than 35°. They are fast and straightforward touse, and thus ideal for large samples of galaxies. Moreover, they arevery robust for low resolutions and thus are appropriate for samples ofcosmological interest. The relevant software is available from us uponrequest. We use these methods to determine the values of the positionand inclination angles for a sample of 79 spiral galaxies contained inthe Frei et al. (\cite{frei96}) sample. We compare our results with thevalues found in the literature, based on other methods. We findstatistically very good agreementTable 7 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/415/849
| Structure and star formation in disc galaxies - I. Sample selection and near-infrared imaging
We present near-infrared imaging of a sample of 57 relatively large,northern spiral galaxies with low inclination. After describing theselection criteria and some of the basic properties of the sample, wegive a detailed description of the data collection and reductionprocedures. The Ksλ= 2.2-μm images cover most ofthe disc for all galaxies, with a field of view of at least 4.2 arcmin.The spatial resolution is better than 1 arcsec for most images. We fitbulge and exponential disc components to radial profiles of the lightdistribution. We then derive the basic parameters of these components,and the bulge/disc ratio, and explore correlations of these parameterswith several galaxy parameters.
| The Relationship between Stellar Light Distributions of Galaxies and Their Formation Histories
A major problem in extragalactic astronomy is the inability todistinguish in a robust, physical, and model-independent way how galaxypopulations are physically related to each other and to their formationhistories. A similar, but distinct, and also long-standing question iswhether the structural appearances of galaxies, as seen through theirstellar light distributions, contain enough physical information tooffer this classification. We argue through the use of 240 images ofnearby galaxies that three model-independent parameters measured on asingle galaxy image reveal its major ongoing and past formation modesand can be used as a robust classification system. These parametersquantitatively measure: the concentration (C), asymmetry (A), andclumpiness (S) of a galaxy's stellar light distribution. When combinedinto a three-dimensional ``CAS'' volume all major classes of galaxies invarious phases of evolution are cleanly distinguished. We argue thatthese three parameters correlate with important modes of galaxyevolution: star formation and major merging activity. This is arguedthrough the strong correlation of Hα equivalent width andbroadband colors with the clumpiness parameter S, the uniquely largeasymmetries of 66 galaxies undergoing mergers, and the correlation ofbulge to total light ratios, and stellar masses, with the concentrationindex. As an obvious goal is to use this system at high redshifts totrace evolution, we demonstrate that these parameters can be measured,within a reasonable and quantifiable uncertainty with available data outto z~3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Fieldimages.
| The BIMA Survey of Nearby Galaxies (BIMA SONG). II. The CO Data
The BIMA Survey of Nearby Galaxies is a systematic imaging study of the3 mm CO J=1-0 molecular emission within the centers and disks of 44nearby spiral galaxies. The typical spatial resolution of the survey is6" or 360 pc at the average distance (12 Mpc) of the sample. Thevelocity resolution of the CO observations is 4 km s-1,though most maps are smoothed to 10 km s-1 resolution. For 33galaxies, multifield observations ensured that a region >~190"(=10 kpc) in diameter was imaged. For the remaining 11galaxies, which had smaller optical diameters and were on averagefarther away, single-pointing observations imaged a 100" diameter(=11 kpc) region. The sample was not chosen based on CO orinfrared brightness; instead, all spirals were included that met theselection criteria of vsolar<=2000 km s-1,δ>=-20deg, i<=70deg,D25<70', and BT<11.0. Thedetection rate was 41/44 sources or 93%; of the three nondetections, one(M81) is known to have CO emission at locations outside the survey fieldof view. Fully sampled single-dish CO data were incorporated into themaps for 24 galaxies; these single-dish data comprise the most extensivecollection of fully sampled, two-dimensional single-dish CO maps ofexternal galaxies to date. We also tabulate direct measurements of theglobal CO flux densities for these 24 sources. For the remaining 20sources, we collected sensitive single-dish spectra in order to evaluatethe large-scale flux recovery. We demonstrate that the measured ratiosof flux density recovered are a function of the signal-to-noise of theinterferometric data. We examine the degree of central peakedness of themolecular surface density distributions and show that the distributionsexhibit their brightest CO emission within the central 6" in only 20/44or 45% of the sample. We show that all three Local Group spiral galaxieshave CO morphologies that are represented in SONG, though the Milky WayCO luminosity is somewhat below the SONG average, and M31 and M33 arewell below average. This survey provides a unique public database ofintegrated intensity maps, channel maps, spectra, and velocity fields ofmolecular emission in nearby galaxies. It also lays the groundwork forextragalactic surveys by more powerful future millimeter-wavelengthinterferometers like CARMA and ALMA.
| 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.
| Revised positions for CIG galaxies
We present revised positions for the 1051 galaxies belonging to theKarachentseva Catalog of Isolated Galaxies (CIG). New positions werecalculated by applying SExtractor to the Digitized Sky Survey CIG fieldswith a spatial resolution of 1 arcsper 2. We visually checked theresults and for 118 galaxies had to recompute the assigned positions dueto complex morphologies (e.g. distorted isophotes, undefined nuclei,knotty galaxies) or the presence of bright stars. We found differencesbetween older and newer positions of up to 38 arcsec with a mean valueof 2 arcsper 96 relative to SIMBAD and up to 38 arcsec and 2 arcsper 42respectively relative to UZC. Based on star positions from the APMcatalog we determined that the DSS astrometry of five CIG fields has amean offset in (alpha , delta ) of (-0 arcsper 90, 0 arcsper 93) with adispersion of 0 arcsper 4. These results have been confirmed using the2MASS All-Sky Catalog of Point Sources. The intrinsic errors of ourmethod combined with the astrometric ones are of the order of 0 arcsper5.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/391
| NIR surface photometry of a sample of nearby spiral galaxies
The first results of an observational programme aimed at mapping asample of face-on spiral galaxies in the NIR are presented. This papershows the surface photometry of the first ten galaxies in the sample.The data were taken in the broad band J (1.2 mu m) and Ks(2.2 mu m) filters. The sources were selected mainly according to theirsize and brightness in order to suit the characteristics of the CAIN 2DNIR camera on the 1.5-m Carlos Sánchez Telescope (Tenerife,Spain). The primary scientific goal is to provide a comprehensive anduniform database of the main structural and photometric parameters ofthe sample members from NIR surface photometry. To this end, ellipticalisophotal fitting was performed on each galaxy image to extractinformation about the size and location of its morphological componentsand provide the azimuthally averaged radial brightness profile.Analytical functions for each component's brightness distribution werethen used to match that profile, and their functional parametersobtained from the global fitting. This first report includes data forNGC 3344, NGC 3686, NGC 3938, NGC 3953, NGC 4254, NGC 4303, NGC 4314,NGC 5248, NGC 6384 and NGC 7479.
| Galaxy classification using fractal signature
Fractal geometry is becoming increasingly important in the study ofimage characteristics. For recognition of regions and objects in naturalscenes, there is always a need for features that are invariant and theyprovide a good set of descriptive values for the region. There are manyfractal features that can be generated from an image. In this paper,fractal signatures of nearby galaxies are studied with the aim ofclassifying them. The fractal signature over a range of scales proved tobe an efficient feature set with good discriminating power. Classifierswere designed using nearest neighbour method and neural networktechnique. Using the nearest distance approach, classification rate wasfound to be 92%. By the neural network method it has been found toincrease to 95%.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| The Luminosity-Metallicity Relation, Effective Yields, and Metal Loss in Spiral and Irregular Galaxies
I present results on the correlation between galaxy mass, luminosity,and metallicity for a sample of spiral and irregular galaxies havingwell-measured abundance profiles, distances, and rotation speeds.Additional data for low surface brightness galaxies from the literatureare also included for comparison. These data are combined to study themetallicity-luminosity and metallicity-rotation speed correlations forspiral and irregular galaxies. The metallicity-luminosity correlationshows its familiar form for these galaxies, a roughly uniform change inthe average present-day O/H abundance of about a factor of 100 over 11mag in B luminosity. However, the O/H-Vrot relation shows achange in slope at a rotation speed of about 125 km s-1. Atfaster Vrot, there appears to be no relation between averagemetallicity and rotation speed. At lower Vrot, themetallicity correlates with rotation speed. This change in behaviorcould be the result of increasing loss of metals from the smallergalaxies in supernova-driven winds. This idea is tested by looking atthe variation in effective yield, derived from observed abundances andgas fractions assuming closed box chemical evolution. The effectiveyields derived for spiral and irregular galaxies increase by a factor of10-20 from Vrot~5 to 300 km s-1, asymptoticallyincreasing to approximately constant yeff forVrot>~150 km s-1. The trend suggests thatgalaxies with Vrot<~100-150 km s-1 may lose alarge fraction of their supernova ejecta, while galaxies above thisvalue tend to retain metals.
| Inner Molecular Rings in Barred Galaxies: BIMA Survey of Nearby Galaxies CO Observations
Although inner star-forming rings are common in optical images of barredspiral galaxies, observational evidence for the accompanying moleculargas has been scarce. In this paper we present images of molecular innerrings, traced using the CO (1-0) emission line, from theBerkeley-Illinois-Maryland-Association Survey of Nearby Galaxies (BIMASONG). We detect inner-ring CO emission from all five SONG barredgalaxies classified as inner ring [type (r)]. We also examine the sevenSONG barred galaxies classified as inner spiral [type (s)]; in one ofthese, NGC 3627, we find morphological and kinematic evidence for amolecular inner ring. Inner-ring galaxies have been classified as suchbased on optical images, which emphasize recent star formation. Weconsider the possibility that there may exist inner rings in which starformation efficiency is not enhanced. However, we find that in NGC 3627the inner-ring star formation efficiency is enhanced relative to mostother regions in that galaxy. We note that the SONG (r) galaxies have apaucity of CO and Hα emission interior to the inner ring (exceptnear the nucleus), while NGC 3627 has relatively bright bar CO andHα emission; we suggest that galaxies with inner rings such as NGC3627 may be misclassified if there are significant amounts of gas andstar formation in the bar.
| Identification and classification of galaxies using a biologically-inspired neutral network
Recognition/Classification of galaxies is an important issue in thelarge-scale study of the Universe; it is not a simple task. According toestimates computed from the Hubble Deep Field (HDF), astronomers predictthat the universe may potentially contain over 100 billion galaxies.Several techniques have been reported for the classification ofgalaxies. Parallel developments in the field of neural networks havecome to a stage that they can participate well in the recognition ofobjects. Recently, the Pulse-Coupled Neural Network (PCNN) has beenshown to be useful for image pre-processing. In this paper, we present anovel way to identify optical galaxies by presenting the images of thegalaxies to a hierarchical neural network involving two PCNNs. The imageis presented to the network to generate binary barcodes (one periteration) of the galaxies; the barcodes are unique to the inputgalactic image. In the current study, we exploit this property toidentify optical galaxies by comparing the signatures (binary barcode)from a corresponding database.
| 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.
| A morphological comparison between the central region in AGN and normal galaxies using HST data
We study the morphology of the central region of a sample of ActiveGalactic Nuclei (AGN) and a ``control'' sample of normal galaxies usingarchival observations of the WFPC2 instrument onboard the Hubble SpaceTelescope (HST). We use the ellipse fitting technique in order to get agood description of the inner ``smooth'' light distribution of thegalaxy. We then divide the observed galaxy image by the artificial imagefrom the fitted ellipses in order to detect morphological signatures inthe central region around the nucleus of the galaxy. We performquantitative comparisons of different subgroups of our sample ofgalaxies (according to the Hubble type and the nuclear activity of thegalaxies) by calculating the average amplitude of the structures thatare revealed with the ellipse fitting technique. Our main conclusionsare as follows: 1) All AGNs show significant structure in their inner100 pc and 1 kpc regions whose amplitude is similar in all of them,independent of the Hubble type of the host galaxy. 2) When consideringearly-type galaxies, non-AGN galaxies show no structure at all, contraryto what we find for AGN. 3) When considering late-type galaxies, bothAGN and non-AGN galaxies show significant structure in their centralregion. Our results are consistent with the hypothesis that allearly-type galaxies host a supermassive black hole, but only those thathave enough material in the central regions to fuel it show an activenucleus. The situation is more complicated in late-type galaxies. Eithernot all of them host a central black hole, or, in some of them, thematerial inside the innermost 100 pc region is not transported to thescales of the central engine for some reason, or the large amount of gasand dust hides the active nucleus from our sight. Based on observationsmade with the NASA/ESA Hubble Space Telescope, obtained from the dataarchive at the Space Telescope Science Institute. STScI is operated bythe Association of Universities for Research in Astronomy, Inc., underthe NASA contract NAS5-26555.
| Star Formation in Extragalactic HII Regions. Determination of Parameters of the Initial Mass Function
A method for using the colors of star-forming complexes to derive theslope and upper mass limit of the initial mass function (IMF) and theage of the complex is proposed in the framework of syntheticevolutionary models of star-cluster populations. The star-formationparameters of 105 complexes in 20 spiral and irregular galaxies aredetermined. The IMF slopes in different star-forming complexes differappreciably, and their dependence on the luminosities and masses of thecomplexes is derived. The duration of the star-formation periodincreases with the luminosity of the complex, and complexes with longerstar-formation periods are richer in metals. The slope of the integratedIMF in a Galaxy depends on the mass spectrum of its complexes, and theupper mass limit of the IMF is lower in early-type spirals.
| The BIMA Survey of Nearby Galaxies. I. The Radial Distribution of CO Emission in Spiral Galaxies
We present the first results of the Berkeley-Illinois-MarylandAssociation Survey of Nearby Galaxies (BIMA SONG), an imaging survey ofthe CO J=1-0 emission in 44 nearby spiral galaxies at a typicalresolution of 6". BIMA SONG differs from previous high-resolution COsurveys in that (1) CO brightness was not an explicit selectioncriterion, (2) a larger area (200" diameter for most galaxies) of eachgalaxy was imaged, and (3) fully sampled single-dish CO data (55"resolution) were obtained for over half of the sample galaxies, so allof the CO flux is imaged in these galaxies. Here we present CO maps fora subsample of 15 BIMA SONG galaxies for which we have also obtainednear-infrared or optical broadband data. The CO maps display aremarkable variety of molecular gas morphologies, and, as expected, theCO surface brightness distributions show considerably more substructurethan the stellar light distributions, even when averaged over kiloparsecscales. The radial distribution of stellar light in galactic disks isgenerally characterized as an exponential. It is, therefore, of interestto investigate whether the molecular gas, which is the star-formingmedium, has a similar distribution. Though our low-resolutionsingle-dish radial profiles of CO emission can be described by simpleexponentials, this is not true for the emission at our full 6"resolution. The scale lengths of the CO disks are correlated with thescale lengths of the stellar disks, with a mean ratio of the scalelengths of about 1. There is, however, considerable intrinsic scatter inthe correlation. We also find that (1) there is also a weak correlationbetween the ratio of K-band to CO luminosity and Hubble type; (2) inhalf of the galaxies presented here, CO emission does not peak at thelocation of the stellar nucleus; (3) averaged over the inner kiloparsec,the CO emission in one-half of the galaxies exhibits an excess over thatexpected from an exponential disk, which is similar to the excess instellar light caused by the bulge stars; and (4) this excess CO emissionmay be due to an increase in the total molecular gas content in thebulge region, or alternatively, to an increase in the CO emissivitycaused by the increased pressure of the bulge region.
| The BIMA Survey of Nearby Galaxies (BIMA SONG)
BIMA SONG is a systematic imaging study of the 3 mm CO J = 1 --> 0molecular emission within the centres and discs of 44 nearby spiralgalaxies on size scales of a few hundred parsecs (6-9``). The overallgoal of the survey is to study the role of molecular gas in theevolution of spiral galaxies. To this end, BIMA SONG addresses 1) thedistribution and physical conditions of the molecular gas in galacticdiscs and its relation to star formation, 2) the effects of a stellarbar on the kinematics of molecular gas, including the possible inflow ofgas along a bar, and 3) the distribution and role of molecular gas inthe central few hundred parsecs of active and quiescent galaxies. Thesource list includes all (except M33 and M31) 44 galaxies of Hubbletypes Sa-Sd, with declinations δ > -20^°, visual magnitudesB < 11.0, velocities v_hel < 2000 km s^-1, and inclinations i <70^°. Beyond the specific scientific questions we will address, thissurvey will provide a unique database for astronomers who study galaxiesat all wavelengths.
| Arm and Interarm Star Formation in Spiral Galaxies
We present an outline of our study of the effects of star formation onthe different components of the interstellar medium in the discs ofspiral galaxies, both globally and as a function of arm and interarmenvironment. We are in the process of obtaining images of 57 spiralgalaxies at low inclinations, and analysing them to study thedistribution of recent massive star formation, old stars, young stars,gas and dust. We will dissect the images into arm and interarm regionsand compare and contrast the morphology and scale lengths within theseregions in H_α, HI, the near infrared, optical and (whereavailable) CO. Modelling will show how the scale lengths are affected bystar formation, how this differs between arms and interarms, and whetherthe Schmidt Law varies from the global values in the arm and interarmregions.
| The gravitational torque of bars in optically unbarred and barred galaxies
The relative bar torques for 45 galaxies observed at K-band with the 4.2m William Herschel Telescope are determined by transforming the lightdistributions into potentials and deriving the maximum ratios of thetangential forces relative to the radial forces. The results arecombined with the bar torques for 30 other galaxies determined from ourprevious K-band survey (Buta & Block \cite{buta01}). Relative bartorques determine the degree of spiral arm forcing, gas accretion, andbar evolution. They differ from other measures of bar strength, such asthe relative amplitude of the bar determined photometrically, becausethey include the bulge and other disk light that contributes to theradial component of the total force. If the bulge is strong and theradial forcing large, then even a prominent bar can have a relativelyweak influence on the azimuthal motions in the disk. Here we find thatthe relative bar torque correlates only weakly with the optical bar typelisted in the Revised Shapley-Ames and de Vaucouleurs systems. In fact,some classically barred galaxies have weaker relative bar torques thanclassically unbarred galaxies. The optical class is a poor measure ofazimuthal disk forcing for two reasons: some infrared bars are not seenoptically, and some bars with strong bulges have their azimuthal forcesso strongly diluted by the average radial force that they exert onlysmall torques on their disks. The Hubble classification scheme poorlyrecognizes the gravitational influence of bars. Applications of our bartorque method to the high-redshift universe are briefly discussed. Basedon observations made with the William Herschel Telescope, operated onthe island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.
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