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Multiwavelength Star Formation Indicators: Observations
We present a compilation of multiwavelength data on different starformation indicators for a sample of nearby star forming galaxies. Herewe discuss the observations, reductions and measurements of ultravioletimages obtained with STIS on board the Hubble Space Telescope (HST),ground-based Hα, and VLA 8.46 GHz radio images. These observationsare complemented with infrared fluxes, as well as large-apertureoptical, radio, and ultraviolet data from the literature. This databasewill be used in a forthcoming paper to compare star formation rates atdifferent wave bands. We also present spectral energy distributions(SEDs) for those galaxies with at least one far-infrared measurementsfrom ISO, longward of 100 μm. These SEDs are divided in two groups,those that are dominated by the far-infrared emission, and those forwhich the contribution from the far-infrared and optical emission iscomparable. These SEDs are useful tools to study the properties ofhigh-redshift galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| An Atlas of Hα and R Images and Radial Profiles of 29 Bright Isolated Spiral Galaxies
Narrowband Hα+[N II] and broadband R images and surface photometryare presented for a sample of 29 bright (MB<-18 mag)isolated S0-Scd galaxies within a distance of 48 Mpc. These galaxies areamong the most isolated nearby spiral galaxies of their Hubbleclassifications as determined from the Nearby Galaxies Catalog.
| Ultraviolet-to-Far-Infrared Properties of Local Star-forming Galaxies
We present the results of a multiwavelength study of nearby galaxiesaimed at understanding the relation between the ultraviolet andfar-infrared emission in star-forming galaxies. The data set comprisesnew ultraviolet (from HST STIS), ground-based Hα, and radiocontinuum observations, together with archival infrared data (from IRASand ISO). The local galaxies are used as benchmarks for comparison ofthe infrared-to-ultraviolet properties with two populations ofhigh-redshift galaxies: the submillimeter star-forming galaxies detectedby SCUBA and the ultraviolet-selected Lyman break galaxies (LBGs). Inaddition, the long wavelength baseline covered by the present dataenables us to compare the star formation rates (SFRs) derived from theobserved ultraviolet, Hα, infrared, and radio luminosities and togauge the impact of dust opacity in the local galaxies. We also derive anew calibration for the nonthermal part of the radio SFR estimator,based on the comparison of 1.4 GHz measurements with a new estimator ofthe bolometric luminosity of the star-forming regions. We find that moreactively star-forming galaxies show higher dust opacities, which is inline with previous results. We find that the local star-forming galaxieshave a lower Fλ(205 μm)/Fλ(UV)ratio by 2-3 orders of magnitude than the submillimeter-selectedgalaxies and may have a similar or somewhat higherFλ(205 μm)/Fλ(UV) ratio thanLBGs. The Fλ(205 μm)/Fλ(UV) ratioof the local galaxy population may be influenced by the cool dustemission in the far-infrared heated by nonionizing stellar populations,which may be reduced or absent in the LBGs.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| First Detection of PAHs and Warm Molecular Hydrogen in Tidal Dwarf Galaxies
We observed two faint tidal dwarf galaxies (TDGs), NGC 5291 N and NGC5291 S, with the Infrared Spectrograph on the Spitzer Space Telescope.We detect strong polycyclic aromatic hydrocarbon (PAH) emission at 6.2,7.7, 8.6, 11.3, 12.6, and 16.5 μm, which match models of groups of~100 carbon atoms with an equal mixture of neutral and ionized PAHs. TheTDGs have a dominant warm (~140 K) dust component in marked contrast tothe cooler (40-60 K) dust found in starburst galaxies. For the firsttime we detect the low-J rotational lines from molecular hydrogen.Adopting LTE, there is ~105 Msolar of ~400 K gas,which is <0.1% of the cold gas mass inferred from 12CO(1-0) measurements. The combination of one-third solar metallicity witha recent (<5 million year) episode of star formation is reflected inthe S and Ne ratios. The excitation is higher than typical values forstarburst galaxies and similar to that found in BCDs. Using the InfraredArray Camera, we identify an additional 13 PAH-rich candidate TDGs.These sources occupy a distinct region of IRAC color space with[3.6]-[4.5]<0.4 and [4.5]-[8.0]>3.2. Their disturbed morphologiessuggest past merger events between companions; for example, NGC 5291 Shas a projected 11 kpc tail. NGC 5291 N and S have stellar masses of(1.5 and 3.0)×108 Msolar, which iscomparable to BCDs, although still roughly 10% of the LMC's stellarmass. The candidate TDGs are an order of magnitude less massive. Thissystem appears to be a remarkable TDG nursery.
| 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.
| Mid-Infrared Galaxy Morphology along the Hubble Sequence
The mid-infrared emission from 18 nearby galaxies were imaged with theInfrared Array Camera (IRAC) on the Spitzer Space Telescope, samplingthe spatial distributions of the reddening-free stellar photosphericemission and the warm dust in the interstellar medium. These twocomponents provide a new framework for galaxy morphology classificationin which the presence of spiral arms and their emission strengthrelative to the starlight can be measured directly and with highcontrast. Four mid-infrared classification methods are explored, threeof which are based on quantitative global parameters (colors andbulge-to-disk ratio) that are similar to those used in the past foroptical studies; in this limited sample, all correlate well withtraditional B-band classification. We suggest reasons why infraredclassification may be superior to optical classification.
| 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
| A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. II. Cluster Sizes and Structural Parameter Correlations
We investigate the structural properties of nuclear star clusters inlate-type spiral galaxies. More specifically, we fit analytical modelsto Hubble Space Telescope images of 39 nuclear clusters in order todetermine their effective radii after correction for the instrumentalpoint-spread function. We use the results of this analysis to comparethe luminosities and sizes of nuclear star clusters to those of otherellipsoidal stellar systems, in particular the Milky Way globularclusters. Our nuclear clusters have a median effective radius ofre=3.5 pc, with 50% of the sample falling in the range2.4pc<=re<=5.0pc. This narrow size distribution isstatistically indistinguishable from that of Galactic globular clusters,even though the nuclear clusters are, on average, 4 mag brighter thanthe old globular clusters. We discuss some possible interpretations ofthis result. From a comparison of nuclear cluster luminosities withvarious properties of their host galaxies, we confirm that more luminousgalaxies harbor more luminous nuclear clusters. It remains unclearwhether this correlation mainly reflects the influence of galaxy size,mass, and/or star formation rate. Since the brighter galaxies in oursample typically have stellar disks with a higher central surfacebrightness, nuclear cluster luminosity also correlates with thisproperty of their hosts. On the other hand, we find no evidence for acorrelation between the presence of a nuclear star cluster and thepresence of a large-scale stellar bar.
| 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
| 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.
| 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.
| Molecular gas in the central regions of the latest-type spiral galaxies
Using the IRAM 30 >m telescope, we have surveyed an unbiased sampleof 47 nearby spiral galaxies of very late (Scd-Sm) Hubble-type foremission in the 12CO(1-0) and (2-1) lines. The sensitivity ofour data (a few mK) allows detection of about 60% of our sample in atleast one of the CO lines. The median detected H2 mass is1.4x 107 >msun within the central few kpc, assuming astandard conversion factor. We use the measured line intensities tocomplement existing studies of the molecular gas content of spiralgalaxies as a function of Hubble-type and to significantly improve thestatistical significance of such studies at the late end of the spiralsequence. We find that the latest-type spirals closely follow thecorrelation between molecular gas content and galaxy luminosityestablished for earlier Hubble types. The molecular gas in late-typegalaxies seems to be less centrally concentrated than in earlier types.We use Hubble Space Telescope optical images to correlate the moleculargas mass to the properties of the central galaxy disk and the compactstar cluster that occupies the nucleus of most late-type spirals. Thereis no clear correlation between the luminosity of the nuclear starcluster and the molecular gas mass, although the CO detection rate ishighest for the brightest clusters. It appears that the central surfacebrightness of the stellar disk is an important parameter for the amountof molecular gas at the galaxy center. Whether stellar bars play acritical role for the gas dynamics remains unclear, in part because ofuncertainties in the morphological classifications of our sample.
| 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%.
| 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.
| An Infrared Space Observatory Atlas of Bright Spiral Galaxies
In this first paper in a series we present an atlas of infrared imagesand photometry from 1.2 to 180 μm for a sample of bright spiralgalaxies. The atlas galaxies are an optically selected,magnitude-limited sample of 77 spiral and S0 galaxies chosen from theRevised Shapley-Ames Catalog (RSA). The sample is a representativesample of spiral galaxies and includes Seyfert galaxies, LINERs,interacting galaxies, and peculiar galaxies. Using the Infrared SpaceObservatory (ISO), we have obtained 12 μm images and photometry at60, 100, and 180 μm for the galaxies. In addition to its imagingcapabilities, ISO provides substantially better angular resolution thanis available in the IRAS survey, and this permits discrimination betweeninfrared activity in the central regions and global infrared emission inthe disks of these galaxies. These ISO data have been supplemented withJHK imaging using ground-based telescopes. The atlas includes 2 and 12μm images. Following an analysis of the properties of the galaxies,we have compared the mid-infrared and far-infrared ISO photometry withIRAS photometry. The systematic differences we find between the IRASFaint Source Catalog and ISO measurements are directly related to thespatial extent of the ISO fluxes, and we discuss the reliability of IRASFaint Source Catalog total flux densities and flux ratios for nearbygalaxies. In our analysis of the 12 μm morphological features we findthat most but not all galaxies have bright nuclear emission. We find 12μm structures such as rings, spiral arm fragments, knotted spiralarms, and bright sources in the disks that are sometimes brighter thanthe nuclei at mid-infrared wavelengths. These features, which arepresumably associated with extranuclear star formation, are common inthe disks of Sb and later galaxies but are relatively unimportant inS0-Sab galaxies. Based on observations with the Infrared SpaceObservatory (ISO), an ESA project with instruments funded by ESA MemberStates (especially the PI countries: France, Germany, Netherlands, andUnited Kingdom) and with the participation of ISAS and NASA.
| A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. I. Observations and Image Analysis
We present new Hubble Space Telescope I-band images of a sample of 77nearby late-type spiral galaxies with low inclination. The main purposeof this catalog is to study the frequency and properties of nuclear starclusters. In 59 galaxies of our sample, we have identified a distinct,compact (but resolved), and dominant source at or very close to thephotocenter. In many cases, these clusters are the only prominent sourcewithin a few kiloparsecs from the galaxy nucleus. We present surfacebrightness profiles, derived from elliptical isophote fits, of allgalaxies for which the fit was successful. We use the fitted isophotesat radii larger than 2" to check whether the location of the clustercoincides with the photocenter of the galaxy and confirm that in nearlyall cases, we are truly dealing with ``nuclear'' star clusters. Fromanalytical fits to the surface brightness profiles, we derive thecluster luminosities after subtraction of the light contribution fromthe underlying galaxy disk and/or bulge. Based on observations made withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555. Theseobservations are associated with proposal 8599.
| The Asymmetry of Galaxies: Physical Morphology for Nearby and High-Redshift Galaxies
We present a detailed study of rotational asymmetry in galaxies for bothmorphological and physical diagnostic purposes. An unambiguous methodfor computing asymmetry is developed, which is robust for both distantand nearby galaxies. By degrading real galaxy images, we test thereliability of this asymmetry measure over a range of observationalconditions, e.g., spatial resolution and signal-to-noise ratio (S/N).Compared to previous methods, this new algorithm avoids the ambiguityassociated with choosing a center by using a minimization method andsuccessfully corrects for variations in S/N. There is, however, a strongrelationship between the rotational asymmetry and physical resolution(distance at fixed spatial resolution): objects become more symmetricwhen less well-resolved. We further investigate asymmetry as a functionof galactic radius and rotation. We find the asymmetry index has astrong radial dependence that differs vastly between Hubble types. As aresult, a meaningful asymmetry index must be specified within awell-defined radius representative of the physical galaxy scale. Weenumerate several viable alternatives, which exclude the use ofisophotes. Asymmetry as a function of angle (Aφ) is alsoa useful indicator of ellipticity and higher order azimuthal structure.In general, we show that the power of asymmetry as a morphologicalparameter lies in the strong correlation with B-V color for galaxiesundergoing normal star formation spanning all Hubble types fromellipticals to irregular galaxies. The few interacting galaxies in ourstudy do not fall on this asymmetry-color ``fiducial sequence,'' asthese galaxies are too asymmetric for their color. We suggest this factcan be used to distinguish between ``normal'' galaxies and galaxiesundergoing an interaction or merger.
| Structural and Photometric Classification of Galaxies. I. Calibration Based on a Nearby Galaxy Sample
In this paper we define an observationally robust, multiparameter spacefor the classification of nearby and distant galaxies. The parametersinclude luminosity, color, and the image-structure parameters: size,image concentration, asymmetry, and surface brightness. Based on aninitial calibration of this parameter space using the ``normal'' Hubbletypes surveyed in 1996 by Frei et al., we find that only a subset of theparameters provide useful classification boundaries for this sample.Interestingly, this subset does not include distance-dependent scaleparameters such as size or luminosity. The essential ingredient is thecombination of a spectral index (e.g., color) with parameters of imagestructure and scale: concentration, asymmetry, and surface brightness.We refer to the image structure parameters (concentration and asymmetry)as indices of ``form.'' We define a preliminary classification based onspectral index, form, and surface brightness (a scale) that successfullyseparates normal galaxies into three classes. We intentionally identifythese classes with the familiar labels of early, intermediate, and late.This classification, or others based on the above four parameters, canbe used reliably to define comparable samples over a broad range inredshift. The size and luminosity distribution of such samples will notbe biased by this selection process except through astrophysicalcorrelations between spectral index, form, and surface brightness.
| H I observations of emission-line galaxies
We present single-dish Lovell telescope H i observations of a sample of67 emission-line and UV-excess galaxies, of which 52 are taken from theUniversity of Michigan (UM) catalogue. In addition, H i observations of24 gas-rich irregular galaxies are presented. We find that emission-linegalaxies are H i-rich with a median H i mass to blue luminosity ratioMHI/LB of ~ 0.45 Msun/Lsun.Within the UM galaxy sample the MHI/LB ratio tendsto increase with decreasing luminosity. Finally, it is found that themost H i-rich UM galaxies are the most metal deficient, implying thatthese objects are less evolved.
| Spectral classification of emission-line galaxies
The main goal of this work is to further investigate the classificationof emission-line galaxies from the ``Spectrophotometric Catalogue of HII galaxies'' by Terlevich et al. (1991) in a homogeneous and objectiveway, using the three line-ratio diagrams, called diagnostic diagrams, ofVeilleux & Osterbrock (1987). On the basis of the resultingcatalogue, we critically discuss the classification methods in theoptical range. In particular we compare our classification scheme to theone done by Rola et al. (1997) which is efficient for the classificationof redshifted galaxies. We also propose a new diagnostic diagraminvolving the known intensity ratio R23=([O II],l 3727+[OIII] l 4959+{[O III] l 5007)/Hb which appears to be a very goodcriterion allowing to discriminate the Seyfert 2 from H ii galaxies. Therevised catalogue including 314 narrow-emission-line galaxies contains HII galaxies, Seyfert 2 galaxies, Low Ionization Nuclear Emission-LineRegions (hereafter LINERs) galaxies and some particular types ofgalaxies with the most intriguing ones, called ``ambiguous'', due to theambiguity of their location in the diagnostic diagrams. These galaxiesappear as H II galaxies and as active galactic nuclei (hereafter AGNs)in different diagrams of Veilleux & Osterbrock and constitutecertainly a sample of particularly interesting candidates for a thoroughstudy of connections between starbursts and AGNs. Available inelectronic form only via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Galaxy Structural Parameters: Star Formation Rate and Evolution with Redshift
The evolution of the structure of galaxies as a function of redshift isinvestigated using two parameters: the metric radius of the galaxy(R_eta) and the power at high spatial frequencies in the disk of thegalaxy (chi). A direct comparison is made between nearby (z~0) anddistant (0.2<~z<~1) galaxies by following a fixed range in restframe wavelengths. The data of the nearby galaxies comprise 136broadband images at ~4500 Å observed with the 0.9 m telescope atKitt Peak National Observatory (23 galaxies) and selected from thecatalog of digital images of Frei et al. (113 galaxies). Thehigh-redshift sample comprises 94 galaxies selected from the Hubble DeepField (HDF) observations with the Hubble Space Telescope using the WideField Planetary Camera 2 in four broad bands that range between ~3000and ~9000 Å (Williams et al.). The radius is measured from theintensity profile of the galaxy using the formulation of Petrosian, andit is argued to be a metric radius that should not depend very stronglyon the angular resolution and limiting surface brightness level of theimaging data. It is found that the metric radii of nearby and distantgalaxies are comparable to each other. The median value of the radius ofthe local sample is ~5+/-1 kpc, and the median radius ofthe HDF sample is ~6+/-2 kpc for q_0=0.5, H_0=65 km s^-1Mpc^-1 however, for q_0=0.1, ~7 kpc and for q_0=1,~5 kpc. In the HDF, galaxies with redshifts larger thanz>0.6 have flatter R_eta distributions than galaxies with redshiftssmaller than z<=0.6. However, the median R_eta values of high- andlow-redshift galaxies are consistent with each other. This result isconsistent with the simulations of galaxy images at redshifts z=0.35,z=0.5, and z=0.9, which show that the metric sizes can be recoveredwithin +/-2 kpc. The flocculency or power at high spatial frequencies isquantified using a simple method that is based on surface photometry inone band and that depends on the size of the star-forming regions and onthe intensity profile of the galaxy. In nearby galaxies, the flocculencyis found to trace the star formation rate as chi is correlated withoptical colors (B-V) and the strength of the hydrogen recombinationlines (Hα). In the HDF, galaxies at redshifts smaller than z~1 andwith fluxes brighter than B=25 have values of chi similar to what ismeasured in nearby galaxies and to what is expected from simulations ofdistant galaxy images. Among the HDF galaxies, I find that at most 4%can be identified as dwarf galaxies with rates of star formation similarto NGC 4449 and NGC 1569. Most HDF galaxies are giants with starformation rates similar to those in nearby giant galaxies. In summary,in this study I have introduced a method to measure the metric sizes andflocculency of the two-dimensional light distribution of galaxies. As aresult, I find that the high spatial frequency power is related to thestar formation rate. Further, I find that the sizes and power at highspatial frequencies of HDF galaxies remain largely unchanged between thepresent epoch and redshifts lower than z~1.
| The I-Band Tully-Fisher Relation for SC Galaxies: 21 Centimeter H I Line Data
A compilation of 21 cm line spectral parameters specifically designedfor application of the Tully-Fisher (TF) distance method is presentedfor 1201 spiral galaxies, primarily field Sc galaxies, for which opticalI-band photometric imaging is also available. New H I line spectra havebeen obtained for 881 galaxies. For an additional 320 galaxies, spectraavailable in a digital archive have been reexamined to allow applicationof a single algorithm for the derivation of the TF velocity widthparameter. A velocity width algorithm is used that provides a robustmeasurement of rotational velocity and permits an estimate of the erroron that width taking into account the effects of instrumental broadeningand signal-to-noise. The digital data are used to establish regressionrelations between measurements of velocity widths using other commonprescriptions so that comparable widths can be derived throughconversion of values published in the literature. The uniform H I linewidths presented here provide the rotational velocity measurement to beused in deriving peculiar velocities via the TF method.
| The I-Band Tully-Fisher Relation for SC Galaxies: Optical Imaging Data
Properties derived from the analysis of photometric I-band imagingobservations are presented for 1727 inclined spiral galaxies, mostly oftypes Sbc and Sc. The reduction, parameter extraction, and errorestimation procedures are discussed in detail. The asymptotic behaviorof the magnitude curve of growth and the radial variation in ellipticityand position angle are used in combination with the linearity of thesurface brightness falloff to fit the disk portion of the profile. TotalI-band magnitudes are calculated by extrapolating the detected surfacebrightness profile to a radius of eight disk scale lengths. Errors inthe magnitudes, typically ~0.04 mag, are dominated by uncertainties inthe sky subtraction and disk-fitting procedures. Comparison is made withthe similar imaging database of Mathewson, Ford, & Buchhorn, both aspresented originally by those authors and after reanalyzing theirdigital reduction files using identical disk-fitting procedures. Directcomparison is made of profile details for 292 galaxies observed incommon. Although some differences occur, good agreement is found,proving that the two data sets can be used in combination with onlyminor accommodation of those differences. The compilation of opticalproperties presented here is optimized for use in applications of theTully-Fisher relation as a secondary distance indicator in studies ofthe local peculiar velocity field.
| A strong correlation between bar strength and global star forming activity in isolated barred galaxies
I have studied the relation between the global star formation activityand the bar structure in a sample of isolated barred galaxies. The starformation activity was quantified via the ratio between the IRAS fluxesat 25 mu m and 100 mu m. Two parameters were chosen to define the barstructure: the strength of the bar and the relative projected barlength. The strength of the bar was defined by epsilon_ {b}=10(1-b/a),where a and b are the projected semi-major and semi-minor bar axis. Therelative bar length was defined as: 2Lb/D25, whereL_ {b} is one half of the projected total bar length and D25is the diameter of the 25 mag arcsec-2 magnitude isophote inthe B band. We found a strong correlation between the star formationactivity and epsilon_ {b}. The regression line is given bylog(I25/I100)=-1.81+0.093 epsilon_ {b}, with acorrelation coefficient of 0.9. The link is not so evident between therelative projected bar length and the star formation activity. But, itis noted that there is enhanced star formation activity in galaxies withstrong bars and small relative bar lengths,0.1<2Lb/D25<0.22.
| Very Wide Galaxy Pairs of the Northern and Southern Sky
We present highly accurate observations of the 21 cm line of hydrogen ingalaxies made at the Arecibo and Parkes Observatories. The galaxiesobserved have been identified, through rigorous selection criteriaapplied to the CfA and SSRS catalogs, as being members of pairs withprojected separations of up to 1.5 Mpc (H0 = 75 km s-1 Mpc-1). Theseobservations form the completion of the Chengalur-Nordgren galaxy pairsample with data previously published by Chengalur, Nordgren andcolleagues. The new selection criteria used in this paper are anextension to larger projected separations of the criteria usedpreviously. Forty-nine new galaxies are observed, while H I is detectedin 41 of them. With the addition of these galaxies, the completed samplehas highly accurate H I velocities for a total of 219 galaxies.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Faint Blue Galaxies
The physical properties of the faint blue galaxy population are reviewedin the context of observational progress made via deep spectroscopicsurveys and Hubble Space Telescope imaging of field galaxies at variouslimits and theoretical models for the integrated star formation historyof the universe. Notwithstanding uncertainties in the properties of thelocal population of galaxies, convincing evidence has emerged fromseveral independent studies for a rapid decline in the volume-averagedstar-formation rate of field galaxies since a redshift z {approximatelyequal to} 1. Together with the small angular sizes and modest meanredshift of the faintest detectable sources, these results can beunderstood in hierarchical models where the bulk of the star formationoccurred at redshifts between z {approximately equal to} 1 - 2. Thephysical processes responsible for the subsequent demise of the faintblue galaxy population remain unclear. Considerable progress will bepossible when the evolutionary trends can be in the context ofindependent physical parameters such as the underlying galactic mass.
| A Search for ``Dwarf'' Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies
We have completed an optical spectroscopic survey of the nuclear regions(r <~ 200 pc) of a large sample of nearby galaxies. Although the mainobjectives of the survey are to search for low-luminosity activegalactic nuclei and to quantify their luminosity function, the databasecan be used for a variety of other purposes. This paper presentsmeasurements of the spectroscopic parameters for the 418 emission-linenuclei, along with a compilation of the global properties of all 486galaxies in the survey. Stellar absorption generally poses a seriousobstacle to obtaining accurate measurement of emission lines in nearbygalactic nuclei. We describe a procedure for removing the starlight fromthe observed spectra in an efficient and objective manner. The mainparameters of the emission lines (intensity ratios, fluxes, profilewidths, and equivalent widths) are measured and tabulated, as areseveral stellar absorption-line and continuum indices useful forstudying the stellar population. Using standard nebular diagnostics, wedetermine the probable ionization mechanisms of the emission-lineobjects. The resulting spectral classifications provide extensiveinformation on the demographics of emission-line nuclei in the nearbyregions of the universe. This new catalog contains over 200 objectsshowing spectroscopic evidence for recent star formation and an equallylarge number of active galactic nuclei, including 46 that show broad Halpha emission. These samples will serve as the basis of future studiesof nuclear activity in nearby galaxies.
| The Morphologies of Distant Galaxies. II. Classifications from the Hubble Space Telescope Medium Deep Survey
The morphological properties of high-redshift galaxies are investigatedusing a sample of 507 objects (I < 22.0 mag) from the Hubble SpaceTelescope (HST) Medium Deep Survey. Independent visual morphologicalclassifications for each galaxy are used to quantify the statisticaluncertainties in the galaxy classifications. Visual classifications arefound to agree well for I < 21 mag. Fainter than I = 21 magsignificant disagreements are seen in the independent visualclassifications of late-type systems with T > 7, merging systems, andpeculiar galaxies. The classifications of these systems are shown to besome- what subjective. Objective classifications based upon measurementsof central concentration and asymmetry for the Medium Deep Survey sampleare presented. These classifications are calibrated using measurementsof structural parameters for an artificially redshifted sample of localobjects. Morphologically segregated number counts using both sets ofvisual classifications and objective classifications support theconclusion that the observed galaxy counts agree with no-evolutionpredictions for the elliptical and spiral populations, as reported inGlazebrook et al. (1995a). A major conclusion is that the largeoverdensity of merging/peculiar/irregular galaxies relative to thepredictions of no-evolution models (reported by Glazebrook et al. 1995a)is confirmed. However, the shape of the faint-end (I > 21.0 mag)number count relation for peculiar objects is sensitive to the largesystematic uncertainties inherent in the visual classification of theseobjects. Despite this caveat, the frequency of objects showing clearevidence for tidal interactions (e.g., tidal tails) in the HST sample isat least 50% larger than it is among nearby galaxies, at the 2 σlevel. Relatively few "chain galaxies" are seen among the sample ofpeculiar objects, suggesting that these systems do not form a largecomponent of the peculiar galaxy population at I < 22 mag.
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