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Late-type galaxies observed with SAURON: two-dimensional stellar and emission-line kinematics of 18 spirals
We present the stellar and gas kinematics of a sample of 18 nearbylate-type spiral galaxies (Hubble types ranging from Sb to Sd), observedwith the integral-field spectrograph SAURON at the 4.2-m WilliamHerschel Telescope. SAURON covers the spectral range 4800-5380Å,allowing us to measure the Hβ, Fe, Mgb absorption features and theemission in the Hβ line and the [OIII]λλ4959,5007Å and [NI]λλ5198, 5200Å doublets over a 33× 41-arcsec2 field of view. The maps cover the nuclearregion of these late-type galaxies and in all cases include the entirebulge. In many cases the stellar kinematics suggests the presence of acold inner region, as visible from a central drop in the stellarvelocity dispersion. The ionized gas is almost ubiquitous and behaves ina complicated fashion: the gas velocity fields often display morefeatures than the stellar ones, including wiggles in the zero-velocitylines, irregular distributions, ring-like structures. The line ratio[OIII]/Hβ often takes on low values over most of the field,probably indicating a wide-spread star formation.
| Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies. II. Surface Photometry and the Properties of the Underlying Stellar Population
We present the results from an analysis of surface photometry of B, R,and Hα images of a total of 114 nearby galaxies(vhelio<4000 km s-1) drawn from the Palomar/LasCampanas Imaging Atlas of blue compact dwarf (BCD) galaxies. Surfacebrightness and color profiles for the complete sample have beenobtained. We determine the exponential and Sérsic profiles thatbest fit the surface brightness distribution of the underlying stellarpopulation detected in these galaxies. We also compute the (B-R) colorand total absolute magnitude of the underlying stellar population andcompared them to the integrated properties of the galaxies in thesample. Our analysis shows that the (B-R) color of the underlyingpopulation is systematically redder than the integrated color, except inthose galaxies where the integrated colors are strongly contaminated byline and nebular-continuum emission. We also find that galaxies withrelatively red underlying stellar populations [typically (B-R)>=1mag] show structural properties compatible with those of dwarfelliptical galaxies (i.e., a smooth light distribution, fainterextrapolated central surface brightness, and larger scale lengths thanBCD galaxies with blue underlying stellar populations). At least ~15% ofthe galaxies in the sample are compatible with being dwarf elliptical(dE) galaxies experiencing a burst of star formation. For the remainingBCD galaxies in the sample we do not find any correlation between therecent star formation activity and their structural differences withrespect to other types of dwarf galaxies.
| Active and Star-forming Galaxies and Their Supernovae
To investigate the extent to which nuclear starbursts or other nuclearactivity may be connected with enhanced star formation activity in thehost galaxy, we perform a statistical investigation of supernovae (SNe)discovered in host galaxies from four samples: the Markarian galaxiessample, the Second Byurakan Survey (SBS) sample, the north Galactic pole(NGP) sample of active or star-forming galaxies, and the NGP sample ofnormal galaxies. Forty-seven SNe in 41 Mrk galaxies, 10 SNe in six SBSgalaxies, 29 SNe in 26 NGP active or star-forming galaxies, and 29 SNein 26 NGP normal galaxies have been studied. We find that the rate ofSNe, particularly core-collapse (Types Ib/c and II) SNe, is higher inactive or star-forming galaxies in comparison with normal galaxies.Active or star-forming host galaxies of SNe are generally of latermorphological type and have lower luminosity and smaller linear sizethan normal host galaxies of SNe. The radial distribution of SNe inactive and star-forming galaxies shows a higher concentration toward thecenter of the active host galaxy than is the case for normal hostgalaxies, and this effect is more pronounced for core-collapse SNe.Ib/c-type SNe have been discovered only in active and star-forminggalaxies of our samples. About 78% of these SNe are associated with H IIregions or are located very close to the nuclear regions of these activegalaxies, which are in turn hosting AGNs or starburst nuclei. Besidesthese new results, our study also supports the conclusions of severalother earlier papers. We find that Type Ia SNe occur in all galaxytypes, whereas core-collapse SNe of Types Ib/c and II are found only inspiral and irregular galaxies. The radial distribution of Type Ib SNe intheir host galaxies is more centrally concentrated than that of Type IIand Ia SNe. The radial distances of Types Ib/c and II SNe, from thenuclei of their host galaxies, is larger for barred spiral hosts.Core-collapse SNe are concentrated in spiral arms and are often close toor in the H II regions, whereas Type Ia SNe show only a looseassociation with spiral arms and no clear association with H II regions.
| GMRT observations of the group Holmberg 124: Evolution by tidal forces and ram pressure?
We report new radio continuum and 21 cm HI observations using the GiantMetrewave Radio Telescope (GMRT) of the group Holmberg 124 (Ho 124)comprising four late-type galaxies, namely NGC 2820, Mrk 108, NGC 2814and NGC 2805. The three galaxies, NGC 2820, Mrk 108 and NGC 2814 whichare closely located in the sky plane have clearly undergone tidalinteractions as seen from the various morphological tidal signatures anddebris. Moreover we note various features in the group members which webelieve might be due to ram pressure. In this paper, we describe fourinteresting results emerging from our observations: a) detection of thetidal radio continuum bridge at 330 MHz connecting the galaxies NGC2820+Mrk 108 with NGC 2814. The radio bridge was discovered at 1465 MHzby van der Hulst & Hummel (1985, A&A, 150, 17). We find that thebridge has a fairly steep spectrum with a spectral index α (S∝ να) of -1.8+0.3-0.2which is much steeper than the -0.8 quoted by van der Hulst & Hummel(1985); b) detection of other tidal features like the tilted HI andradio continuum disk of NGC 2814, a HI streamer and a radio continuumtail arising from the south of NGC 2814. We also report the detection ofa possible tidal dwarf galaxy in HI; c) sharp truncation in the HIdistribution in the south of NGC 2820 and in the HI and radio continuumdistribution in the north of NGC 2814. The optical disks in both thecases look undisturbed. As pointed out by Davis et al. (1997, AJ, 114,613), ram pressure affects different components of the interstellarmedium to varying degrees. Simple estimates of pressure in differentcomponents of the interstellar medium (radio continuum, Hα and HI)in NGC 2820 indicate that ram pressure will significantly influence HI;d) detection of a large one-sided HI loop to the north of NGC 2820. Noradio continuum emission or Hα emission is associated with the HIloop. We discuss various scenarios for the origin of this loop includinga central starburst, ram pressure stripping and tidal interaction. We donot support the central starburst scenario since the loop is notdetected in ionized gas. Using the upper limit on X-ray luminosity of Ho124 (Mulchaey et al. 2003, ApJS, 145, 39), we estimate an upper limit onthe intragroup medium (IGrM) density of 8.8×10-4cm-3. For half this electron density, we estimate the rampressure force of the IGrM to be comparable to the gravitational pull ofthe disk of NGC 2820. Since tidal interaction has obviously influencedthe group, we suggest that the loop could have formed by ram pressurestripping if tidal effects had reduced the surface density of HI in NGC2820. From the complex observational picture of Ho 124 and the numericalestimates, we suggest that the evolution of the Ho 124 group may begoverned by both tidal forces due to the interaction and the rampressure due to motion of the member galaxies in the IGrM and that theIGrM densities should not be too low (i.e. ≥4×10-4). However this needs to be verified by furtherobservations.
| Principal component analysis of International Ultraviolet Explorer galaxy spectra
We analyse the UV spectral energy distribution of a sample of normalgalaxies listed in the International Ultraviolet Explorer (IUE) NewlyExtracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principalcomponent analysis. The sample consists of the IUE short-wavelength (SW)spectra of the central regions of 118 galaxies, where the IUE apertureincluded more than 1 per cent of the galaxy size. The principalcomponents are associated with the main components observed in theultraviolet (UV) spectra of galaxies. The first component, accountingfor the largest source of diversity, may be associated with the UVcontinuum emission. The second component represents the UV contributionof an underlying evolved stellar population. The third component issensitive to the amount of activity in the central regions of galaxiesand measures the strength of star-formation events.In all the samples analysed here, the principal component representativeof star-forming activity accounts for a significant percentage of thevariance. The fractional contribution to the spectral energydistribution (SED) by the evolved stars and by the young population aresimilar.Projecting the SEDs on to their eigenspectra, we find that none of thecoefficients of the principal components can outline an internalcorrelation or can correlate with the optical morphological types. In asubsample of 43 galaxies, consisting of almost only compact and BCDgalaxies, the third principal component defines a sequence related tothe degree of starburst activity of the galaxy.
| GHASP: an Hα kinematic survey of spiral and irregular galaxies - III. 15 new velocity fields and study of 46 rotation curves
We present Fabry-Pérot observations obtained in the frame of theGHASP survey (Gassendi Hα survey of SPirals). We have derived theHα maps, the velocity fields and the rotation curves for a set of15 galaxies. The data presented in this paper are combined with the datapublished in our two previous papers in order to make a preliminaryanalysis of the rotation curves obtained for 46 galaxies. We check theconsistency of our data with the Tully-Fisher relationship and concludethat our Hα rotation curves reach the maximum velocity in most ofthe cases, even with solid-body rotating galaxies. We find that ourrotation curves, on average, almost reach the isophotal radiusR25. We confirm the trend, already mentioned by Rubin,Waterman & Kenney and Márquez et al., that the maximumextension of the Hα rotation curves increases with the type of thespiral galaxy, up to t~ 7-8 and we find that it decreases for magellanicand irregular galaxies. We also confirm the trend seen by Márquezet al. that later types tend to have lower values of the internal slopeof the rotation curve, in agreement with Rubin et al.
| The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe
The characteristics of the starburst galaxies from the Pico dos Diassurvey (PDS) are compared with those of the nearby ultraviolet (UV)bright Markarian starburst galaxies, having the same limit in redshift(vh < 7500 km s-1) and absolute B magnitude(MB < -18). An important difference is found: theMarkarian galaxies are generally undetected at 12 and 25 μm in IRAS.This is consistent with the UV excess shown by these galaxies andsuggests that the youngest star-forming regions dominating thesegalaxies are relatively free of dust.The far-infrared selection criteria for the PDS are shown to introduce astrong bias towards massive (luminous) and large size late-type spiralgalaxies. This is contrary to the Markarian galaxies, which are found tobe remarkably rich in smaller size early-type galaxies. These resultssuggest that only late-type spirals with a large and massive disc arestrong emitters at 12 and 25 μm in IRAS in the nearby Universe.The Markarian and PDS starburst galaxies are shown to share the sameenvironment. This rules out an explanation of the differences observedin terms of external parameters. These differences may be explained byassuming two different levels of evolution, the Markarian being lessevolved than the PDS galaxies. This interpretation is fully consistentwith the disc formation hypothesis proposed by Coziol et al. to explainthe special properties of the Markarian SBNG.
| Extra-Planar Radio Emission from Edge-on Disk Galaxies
Not Available
| Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies. I. Images and Integrated Photometry
We present B, R, and Hα images for a total of 114 nearby galaxies(vhelio<4000 km s-1) that, with exception ofnine objects, are classified as blue compact dwarfs (BCDs). BRintegrated magnitudes, Hα fluxes and Hα equivalent widthsfor all the objects in the sample are presented. A new set ofquantitative, observational criteria for a galaxy to be classified as aBCD is proposed. These criteria include a limit on the K-band luminosity(i.e., stellar mass; MK>-21 mag), peak surface brightness(μB,peak<22 mag arcsec-2), and color at thepeak surface brightness(μB,peak-μR,peak<~1). Hα emissionis detected in all but three sample galaxies. Typical color, absolutemagnitude, and Hα luminosity are (B-R)=0.7+/-0.3 mag,MB=-16.1+/-1.4 mag, and log (LHα)=40.0+/-0.6(ergs s-1). Galaxies morphologically classified as nE and iEBCDs within our sample show lower Hα equivalent widths and reddercolors, on average, than the iI- and i0-type BCDs. For most of thegalaxies the presence of an evolved stellar population is required toexplain their observed properties; only the most metal-poor BCDs (e.g.,I Zw 18, Tol 65) are still compatible with a pure, young burst. Theflux-calibrated and WCS-compliant images in this Atlas are individuallyavailable through the NASA/IPAC Extragalactic Database (NED) imageserver and collectively through a dedicated Web page.
| Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177supernovae (SNe) that have been discovered since 1997 during the courseof the Lick Observatory Supernova Search with the Katzman AutomaticImaging Telescope. Whereas SNe Ia occur in all galaxy types, it isfound, at a high level of statistical confidence, that SNe Ib, Ic, andII are strongly concentrated in late-type galaxies. However, attentionis drawn to a possible exception provided by SN 2001I. This SN IInoccurred in the E2 galaxy UGC 2836, which was not expected to harbor amassive young supernova progenitor.
| A New Database of Observed Spectral Energy Distributions of Nearby Starburst Galaxies from the Ultraviolet to the Far-Infrared
We present a database of UV-to-FIR data of 83 nearby starburst galaxies.The galaxies are selected based upon the availability of IUE data. Wehave recalibrated the IUE UV spectra for these galaxies by incorporatingthe most recent improvements. For 45 of these galaxies we useobservations by Storchi-Bergmann et al. and McQuade et al. for thespectra in the optical range. The NIR data are from new observationsobtained at the NASA/IRTF and the Mount Laguna Observatory, combinedwith the published results from observations at the Kitt Peak NationalObservatory. In addition, published calibrated ISO data are included toprovide mid-IR flux densities for some of the galaxies. Theoptical-to-IR data are matched as closely as possible to the IUE largeaperture. In conjunction with IRAS and ISO FIR flux densities, all thesedata form a set of observed spectral energy distributions (SEDs) of thenuclear regions of nearby starburst galaxies. The SEDs should be usefulin studying star formation and dust/gas attenuation in galaxies. We alsopresent the magnitudes in the standard BVRI and various HST/WFPC2bandpasses synthesized from the UV and optical wavelength ranges ofthese SEDs. For some of the galaxies, the HST/WFPC2 magnitudessynthesized from the SEDs are checked with those directly measured fromWFPC2 images to test the photometric errors of the optical data andtheir effective matching of apertures with the UV data. The implicationsof the new SEDs on the star formation rates and dust/gas attenuation arebriefly discussed.
| Narrow Lines in Type II Supernovae: Probing the Circumstellar Nebulae of the Progenitors
We have carried out a high-dispersion (R~30,000) echelle spectroscopicsurvey of 16 Type II supernovae (SNe) to search for narrow emissionlines from circumstellar nebulae ejected by their massive progenitors.Circumstellar nebulae, if detected, provide invaluable opportunities toprobe SN progenitors. Of the 16 SNe observed, SN ejecta are clearlydetected in four SNe and possibly in another two SNe, interstellar gasis detected in 12 SNe, and circumstellar material is detected only in SN1978K and SN 1998S. In the case of SN 1978K, we are able to place anupper limit of ~2.2 pc for the size of the circumstellar ejecta nebulaand note that this is more consistent with the typical sizes observedfor ejecta nebulae around luminous blue variables, rather thanWolf-Rayet stars. In the case of SN 1998S, our observations of thenarrow lines ~1 yr after the SN explosion show variations compared toearly epochs. The nebular lines we observe from SN 1998S eitheroriginate from the low-density outer region of a circumstellar nebula orhave become dominated by an interstellar component.
| Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35
| The Morphologies of Dwarf Markarian Galaxies
The morphologies of the 96 dwarf (M(B) -17m) galaxies in the Markariancatalog are determined from the digitized Schmidt plates obtained forthe construction of the Hubble Space Telescope Guide Star Catalog. Thefraction of double nucleus galaxies within the dwarf Markarian galaxiesis determined to be twice that found for all galaxies in the Markariancatalog. In addition to the 12 previously known cases, four definite andtwo probable galaxies with double nuclei are identified. The fraction ofdwarf Markarian galaxies with bright star forming regions is found to betwice that of Virgo cluster dwarf galaxies. No Elliptical galaxies arefound in the sample. Galaxies with blue compact dwarf and S0morphologies are more often found to contain unresolved regions of UVexcess emission. Dwarf Markarian galaxies with different morphologicalstructures and spectral classes are found to have similar FIRproperties.
| New Observations of Extra-Disk Molecular Gas in Interacting Galaxy Systems, Including a Two-Component System in Stephan's Quintet
We present new CO (1-0) observations of 11 extragalactic tails andbridges in nine interacting galaxy systems, almost doubling the numberof such features with sensitive CO measurements. Eight of these 11features were undetected in CO to very low CO/H I limits, with the mostextreme case being the NGC 7714/5 bridge. This bridge contains luminousH II regions and has a very high H I column density(1.6×1021 cm-2 in the 55" CO beam), yet wasundetected in CO to rms T*R=2.4 mK. The H I columndensity is higher than standard H2 and CO self-shieldinglimits for solar-metallicity gas, suggesting that the gas in this bridgeis metal-poor and has an enhancedNH2/ICO ratio compared with theGalactic value. Only one of the 11 features in our sample wasunambiguously detected in CO, a luminous H I-rich star formation regionnear an optical tail in the compact group Stephan's Quintet. We detectCO at two widely separated velocities in this feature, at ~6000 and~6700 km s-1. Both of these components have H I and Hαcounterparts. These velocities correspond to those of galaxies in thegroup, suggesting that this gas is material that has been removed fromtwo galaxies in the group. The CO/H I/Hα ratios for bothcomponents are similar to global values for spiral galaxies.
| Stellar population synthesis for blue compact galaxies.
Not Available
| Neutral Hydrogen and Dark Matter in Spiral Galaxies
The first part presents a brief review of the main HI properties ofisolated, normal spiral galaxies and of the phenomena which seem tocharacterize and dominate their internal metabolism. In the second partattention is drawn to all those processes, such as tidal interactions,accretion and mergers, that depend on the galaxy environment and mayplay a significant role in galaxy formation and evolution. In the thirdpart the observational evidence for the dark matter component of spiralgalaxies is discussed.
| A Near- and Mid-Infrared Study of the Interacting Galaxy Pair UGC 12914/12915: ``Taffy''
We report on an infrared 1 to 17 μm study of the nearby (cz=4600 kms-1) interacting spiral galaxy system UGC 12914/12915, usingthe ground-based Palomar 200 inch (5 m) telescope and PFIRCAMnear-infrared detector and space-based mid-infrared imaging and spectralobservations using ISOCAM and PHT-S on the Infrared Space Observatory.The system consists of two counterrotating spirals having suffered anearly face-on collision only ~2x107 yr ago. In conjunctionwith radio observations we explore the complex gas/dust morphology ofthe postcollision disks, ring structures, current epoch of starformation, and the remnant connecting bridge: It is the unusual radiosynchrotron bridge that this study was largely aimed at understanding.Strong line emission from aromatic band features at 6.2, 7.7, and 11.3μm are seen in both the mid-IR imaging and PHT-S spectrophotometrycentered on the nuclei. Theaverage mid-IR (5-17 μm) flux density is~0.42 Jy, or about 7% of the 60 μm IRAS flux density. Ournear-/mid-IRdata support the hypothesis that the restricted form of galaxy-galaxyinteraction-counterrotating direct head-on collision among comparablymassed spirals-has produced a large-scale dynamically expanding ``ring''of recent star formation and gas ``bar'' structure within the disk ofUGC 12914. The nucleus and northwestern disk of UGC 12915 are undergoingvigorous star formation probably triggered by the interaction. UGC 12914appears to be more quiescent in comparison, although there aresignatures of massive star formation as revealed in direct comparisonbetween the radio, mid-IR, and Hα imaging. Within the connectingbridge region, the mid-IR imaging reveals dust grains intermixed withthe atomic hydrogen gas. The heating mechanism for the hot dust islikely to be UV photons diffusing out from the galactic disks and the HII complex located along the extreme northeastern portion of the bridge:The dust emission, or mid-IR intensity per atomic hydrogen columndensity ratio, is consistent with heating from the local (bridge)interstellar radiation field.
| Population synthesis for the spectra of blue compact dwarf galaxies.
Not Available
| Stellar populations in blue compact galaxies
Blue compact galaxies (BCGs) are compact galaxies that are dominated byintense star formation. Comparing the observational properties with thepredictions of the stellar population synthesis model, we have analyzedthe nuclear stellar population and emission line spectra in a sample of10 BCGs. The results indicate that the continuum flux fractions at 5870Å due to old stellar components and young stellar components areboth important. The contribution from intermediate age components isdifferent in different galaxies. Our results suggest that BCGs are oldgalaxies, in which star formation occurs in short intense burstsseparated by long quiescent phases. We have also derived the internalreddening for the stellar population by the population synthesis method,and the internal reddening for the emitting gas clouds by the Balmerline ratio. The former is significantly smaller than the latter forBCGs. A model of clumpy foreground dust, with different covering factorsfor the gas and stars, can explain the difference. Combining theinternal reddening value and the stellar population, we have decreasedthe effecting from the internal reddening and underlying stellarabsorption, and accurately measured most emission lines for each BCGs.Using these emission lines, we have attempted to identify the ionizingmechanism of BCGs. The ionizing mechanism for these emission lineregions of BCGs is typical of photoionization by stars, characteristicsof a low extinction HII regions.
| Ultraviolet spectral properties of magellanic and non-magellanic irregulars, H BT II and starburst galaxies
This paper presents the results of a stellar population analysisperformed on nearby (V_R<=5 000 km s^{-1}) star-forming galaxies,comprising magellanic and non-magellanic irregulars, H Ii and starburstgalaxies observed with the IUE satellite. Before any comparison ofgalaxy spectra, we have formed subsets according to absolute magnitudeand morphological classification. Subsequently, we have coadded thespectra within each subset into groups of similar spectral properties inthe UV. As a consequence, high signal-to-noise ratio templates have beenobtained, and information on spectral features can now be extracted andanalysed. Seven groups resulted from this procedure: the magellanicirregulars (including H Ii galaxies) produced two different bluespectral groups; the non-magellanic irregulars could be grouped into twospectral groups with rather peculiar properties; and the luminousstarbursts produced one flat and two blue template spectra. Theirstellar populations are analysed by means of a population synthesisalgorithm based on star cluster spectral components. The syntheticspectra reproduce the observed ones successfully (except thenon-magellanic irregular groups) both in terms of continuum distributionand spectral features. The synthesis flux fractions of different agegroups were transformed into mass fractions, allowing inferences on thestar formation histories. Young stellar populations (age <500 Myrs)are the main flux contributors; in a few cases the intermediate agepopulation (age~1 M_B-2 Myrs) is important, while the old bulgepopulation contributes at most with ~2 % of the lambda2646 Angstromsflux in the case of starburst galaxies, and is negligible in themagellanic irregulars. We also study the reddening values and theextinction law: an SMC-like extinction law is appropriate for all cases.Based upon data collected with the International Ultraviolet Explorer(IUE) Satellite, supported by NASA, SERC and ESA.
| Supernova 1998bm in IC 2458
IAUC 6882 available at Central Bureau for Astronomical Telegrams.
| A Hubble Space Telescope Imaging Survey of Nearby Active Galactic Nuclei
We have obtained WFPC2 images of 256 of the nearest (z <= 0.035)Seyfert 1, Seyfert 2, and starburst galaxies. Our 500 s broadband(F606W) exposures reveal much fine-scale structure in the centers ofthese galaxies, including dust lanes and patches, bars, rings, wisps,and filaments, and tidal features such as warps and tails. Most of thisfine structure cannot be detected in ground-based images. We haveassigned qualitative classifications for these morphological featuresand a Hubble type for the inner region of each galaxy, and we have alsomeasured quantitative information such as 0."18 and 0."92 aperturemagnitudes, position angles, and ellipticities, where possible. There islittle direct evidence for unusually high rates of interaction in theSeyfert galaxies. Slightly less than 10% of all the galaxies show tidalfeatures or multiple nuclei. The incidence of inner starburst rings isabout 10% in both classes of Seyfert galaxies. In contrast, galaxieswith H II region emission-line spectra appear substantially moreirregular and clumpy because of their much higher rates of current starformation per unit of galactic mass. The presence of an unresolvedcentral continuum source in our Hubble Space Telescope images is avirtually perfect indicator of a Seyfert 1 nucleus as seen byground-based spectroscopy. Fifty-two percent of these Seyfert 1 pointsources are saturated in our images; we use their wings to estimatemagnitudes ranging from 15.8 to 18.5. The converse is not universallytrue, however, as over one-third of Seyferts with direct spectroscopicevidence for broad Balmer wings show no nuclear point source. These 34resolved Seyfert 1's have fainter nonstellar nuclei, which appear to bemore extinguished by dust absorption. Like the Seyfert 2's, they havecentral surface brightnesses consistent with those expected for thebulges of normal galaxies. The rates for the occurrences of bars inSeyfert 1's and 2's and non-Seyferts are the same. We found onesignificant morphological difference between the host galaxies ofSeyfert 1 and Seyfert 2 nuclei. The Seyfert 2 galaxies are significantlymore likely to show nuclear dust absorption, especially in lanes andpatches that are irregular or reach close to the nucleus. A few simpletests show that the difference cannot be explained by different averageredshifts or selection techniques. It is confirmed by our galaxymorphology classifications, which show that Seyfert 1 nuclei reside inearlier type galaxies than Seyfert 2 nuclei. If, as we believe, this isan intrinsic difference in host galaxy properties, it undermines one ofthe postulates of the strong unification hypothesis for Seyfertgalaxies, that they merely appear different because of the orientationof their central engine. The excess galactic dust we see in Seyfert 2'smay cause substantial absorption that obscures their hypothesized broademission line regions and central nonstellar continua. This galacticdust could produce much of the absorption in Seyfert 2 nuclei that hadinstead been attributed to a thick dusty accretion torus forming theouter part of the central engine.
| Abundances in Spiral Galaxies: Evidence for Primary Nitrogen Production
We present the results of nitrogen and oxygen abundance measurements for185 H II regions spanning a range of radii in 13 spiral galaxies. Asexpected, the nitrogen-to-oxygen ratio increases linearly with theoxygen abundance for high-metallicity H II regions, indicating thatnitrogen is predominantly a secondary element. However, thenitrogen-to-oxygen ratio plateaus for oxygen abundances less than \frac{1}{3} solar [12 + log (O/H) < 8.45], as is also seen inlow-metallicity dwarf galaxies. This result suggests that the observedtrend in dwarf galaxies is not due to the outflow of enriched materialin a shallow gravitational potential. While the effects of the infall ofpristine material and delayed nitrogen delivery are still unconstrained,nitrogen does appear to have both a primary and a secondary component atlow metallicities in all types of galaxies.
| Spectroscopy of Outlying H II Regions in Spiral Galaxies: Abundances and Radial Gradients
We present the results of low-dispersion optical spectroscopy of 186 HII regions spanning a range of radius in 13 spiral galaxies. Abundancesfor several elements (oxygen, nitrogen, neon, sulfur, and argon) weredetermined for 185 of the H II regions. As expected, low metallicitieswere found for the outlying H II regions of these spiral galaxies.Radial abundance gradients were derived for the 11 primary galaxies;similar to results for other spiral galaxies, the derived abundancegradients are typically -0.04 to -0.07 dex kpc^-1.
| 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
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Sweeping the Supergalactic Plane.
Not Available
| The heating of dust in starburst galaxies: The contribution of the nonionizing radiation
The IUE UV and optical spectra and the far-infrared (FIR) IRAS fluxdensities of a sample of starburst and blue compact galaxies are used toinvestigate the relationship between dust obscuration and dust emission.The amount of dust obscuration at UV wavelengths correlates with theFIR-to-blue ratio; and an analysis of the correlation indicates that notonly the ionizing but also the nonionizing radiation contribute to theFIR emission. The amount of UV and optical energy lost to dustobscuration accounts for most of the cool dust FIUR emission and forabout 70% of the warm dust FIR emission. The remaining 30% of the warmdust FIR flux is probably due to dust emission from regions of starformation which are embedded in opaque giant molecular clouds and do notcontribute to the integrated UV and optical spectrum. The use of the FIRemission as an indicator of high-mass star formation rate instar-forming galaxies can be problematic, since the contribution to theFIR flux from cool dust emission heated by relatively old stars isnonnegligible.
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