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Публикации по объекту
Late-Time Radio Observations of 68 Type Ibc Supernovae: Strong Constraints on Off-Axis Gamma-Ray Bursts
We present late-time radio observations of 68 local Type Ibc supernovae,including six events with broad optical absorption lines(``hypernovae''). None of these objects exhibit radio emissionattributable to off-axis gamma-ray burst jets spreading into our line ofsight. Comparison with our afterglow models reveals the followingconclusions. (1) Less than ~10% of Type Ibc supernovae are associatedwith typical gamma-ray bursts initially directed away from our line ofsight; this places an empirical constraint on the GRB beaming factor of<~104, corresponding toan average jet opening angle, θj>~0.8d. (2) Thisholds in particular for the broad-lined supernovae (SNe 1997dq, 1997ef,1998ey, 2002ap, 2002bl, and 2003jd), which have been argued to host GRBjets. Our observations reveal no evidence for typical (or evensubenergetic) GRBs and rule out the scenario in which every broad-linedSN harbors a GRB at the 84% confidence level. Their large photosphericvelocities and asymmetric ejecta (inferred from spectropolarimetry andnebular spectroscopy) appear to be characteristic of the nonrelativisticSN explosion and do not necessarily imply the existence of associatedGRB jets.
| 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.
| Spectroscopic study of blue compact galaxies. V. Oxygen abundance and the metallicity-luminosity relation
This is the fifth paper in a series studying the stellar components,star formation histories, star formation rates and metallicities of ablue compact galaxy (BCG) sample. Based on our high-quality ground-basedspectroscopic observations, we have determined the electrontemperatures, electron densities, nitrogen abundances and oxygenabundances for 72 star-forming BCGs in our sample, using differentoxygen abundance indicators. The oxygen abundance covers the range 7.15< 12 + log (O/H)< 9.0, and nitrogen is found to be mostly aproduct of secondary nucleosynthesis for 12 + log (O/H)>8.2 andapparently a product of primary nucleosynthesis for 12 + log (O/H)<8.2. To assess the possible systematic differences among differentoxygen abundance indicators, we have compared oxygen abundances of BCGsobtained with the Te method, R23 method, P method,N2 method and O3N2 method. The oxygen abundances derived from theTe method are systematically lower by 0.1-0.25 dex than thosederived from the strong line empirical abundance indicators, consistentwith previous studies based on region samples. We confirm the existenceof the metallicity-luminosity relation in BCGs over a large range ofabundances and luminosities. Our sample of galaxies shows that the slopeof the metallicity-luminosity relation for the luminous galaxies(~-0.05) is slightly shallower than that for the dwarf galaxies(~-0.17). An offset was found in the metallicity-luminosity relation ofthe local galaxies and that of the intermediate redshift galaxies. Itshows that the metallicity-luminosity relation for the emission linegalaxies at high redshift is displaced to lower abundances, higherluminosities, or both.
| 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.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Spectroscopic study of blue compact galaxies. IV. Star formation rates and gas depletion timescales
This is the fourth paper in a series studying star formation rates,stellar components, metallicities, and star formation histories of ablue compact galaxy (BCG) sample. Using Hα, [O II]λ3727,infrared (IR), radio (1.4 GHz) luminosities and neutral hydrogen (H I)gas masses, we estimated star formation rates and gas depletiontimescales of 72 star-forming BCGs. The star formation rates of the BCGsin our sample span nearly four orders of magnitude, from approximately10-2 to 102 Mȯ yr-1,with a median star formation rate of about 3 Mȯyr-1. The typical gas depletion timescale of BCGs is aboutone billion years. Star formation could be sustained at the currentlevel only on a timescale significantly lower than the age of theuniverse before their neutral gas reservoir is completely depleted. Toassess the possible systematic differences among different starformation rate indicators, we compared the star formation rates derivedfrom Hα, [O II]λ3727, IR, and radio luminosities, andinvestigated the effects from underlying stellar absorption and dustextinction. We found that subtracting underlying stellar absorption isvery important to calculate both dust extinction and star formation rateof galaxies. Otherwise, the intrinsic extinction will be overestimated,the star formation rates derived from [O II]λ3727 and Hαwill be underestimated (if the underlying stellar absorption and theinternal extinction were not corrected from the observed luminosity) oroverestimated (if an overestimated internal extinction were used forextinction correction). After both the underlying stellar absorption andthe dust extinction were corrected, a remarkably good correlationemerges among Hα, [O II]λ3727, IR and radio star formationrate indicators. Finally, we find a good correlation between themeasured star formation rate and the absolute blue magnitude,metallicity, interstellar extinction of BCGs. Our results indicate thatfaint, low-mass BCGs have lower star formation rates.Star formation rates and gas depletion timescales of BCGs are availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/425/417
| Cold dust and molecular gas towards the centers of Magellanic type galaxies and irregulars. I. The data
We present 1300 μm continuum emission measurements and observationsof the 12CO (1-0) and (2-1) transition towards the centers of64 Magellanic type galaxies (Sdm/Sm) and irregulars (Im/I0/Irr). Thesources are selected to have IRAS flux densities S100 μm≥1000 mJy and optical diameters mainly below 180 arcsec. We wereable to detect 12CO towards 41 and the continuum emissiontowards 28 galaxies. In addition, we obtained the corresponding data fora set of 6 complementary galaxies of different morphological type.Based on observations collected at ESO, La Silla, Chile and IRAM, PicoVeleta, Spain.The full version of Figs. \ref{spec1.fig} and \ref{spec2.fig} is onlyavailable in electronic form at http://www.edpsciences.org
| Classifications of the Host Galaxies of Supernovae, Set II
Classifications on the DDO system are given for an additional 231 hostgalaxies of supernovae that have been discovered during the course ofthe Lick Observatory Supernova Search with the Katzman Automatic ImagingTelescope (KAIT). This brings the total number of hosts of supernovae(SNe) discovered (or independently rediscovered) by KAIT, which have sofar been classified on a homogeneous system, to 408. The probabilitythat SNe Ia and SNe II have a different distribution of host-galaxyHubble types is found to be 99.7%. A significant difference is alsofound between the distributions of the host galaxies of SNe Ia and ofSNe Ibc (defined here to include SNe Ib, Ib/c, and Ic). However, nosignificant difference is detected between the frequency distributionsof the host galaxies of SNe II and SNe IIn. This suggests that SNe IInare generally not SNe Ia embedded in circumstellar material that aremasquerading as SNe II. Furthermore, no significant difference is foundbetween the distribution of the Hubble types of the hosts of SNe Ibc andof SNe II. Additionally, SNe II-P and SNe II-L are found to occur amongsimilar stellar populations. The ratio of the number of SNe Ia-pec tonormal SNe Ia appears to be higher in early-type galaxies than it is ingalaxies of later morphological types. This suggests that the ancestorsof SNe Ia-pec may differ systematically in age or composition from theprogenitors of normal SNe Ia. Unexpectedly, five SNe of Types Ib/c, II,and IIn (all of which are thought to have massive progenitors) are foundin host galaxies that are nominally classified as types E and S0.However, in each case the galaxy classification is uncertain, or newlyinspected images show evidence suggesting a later classification. Amongthese five objects, NGC 3720, the host galaxy of SN 2002at, wasapparently misidentified in the Carnegie Atlas of Galaxies.
| A Search for Core-Collapse Supernova Progenitors in Hubble Space Telescope Images
Identifying the massive progenitor stars that give rise to core-collapsesupernovae (SNe) is one of the main pursuits of supernova and stellarevolution studies. Using ground-based images of recent, nearby SNeobtained primarily with the Katzman Automatic Imaging Telescope,astrometry from the Two Micron All Sky Survey, and archival images fromthe Hubble Space Telescope, we have attempted the direct identificationof the progenitors of 16 Type II and Type Ib/c SNe. We may haveidentified the progenitors of the Type II SNe 1999br in NGC 4900, 1999evin NGC 4274, and 2001du in NGC 1365 as supergiant stars withM0V~-6 mag in all three cases. We may have alsoidentified the progenitors of the Type Ib SNe 2001B in IC 391 and 2001isin NGC 1961 as very luminous supergiants withM0V~-8 to -9 mag, and possibly the progenitor ofthe Type Ic SN 1999bu in NGC 3786 as a supergiant withM0V~-7.5 mag. Additionally, we have recovered atlate times SNe 1999dn in NGC 7714, 2000C in NGC 2415, and 2000ew in NGC3810, although none of these had detectable progenitors on pre-supernovaimages. In fact, for the remaining SNe only limits can be placed on theabsolute magnitude and color (when available) of the progenitor. Thedetected Type II progenitors and limits are consistent with redsupergiants as progenitor stars, although possibly not as red as we hadexpected. Our results for the Type Ib/c SNe do not strongly constraineither Wolf-Rayet stars or massive interacting binary systems asprogenitors. Based on observations made with the NASA/ESA Hubble SpaceTelescope, obtained from the data archive of the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
| 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.
| Spectroscopic study of blue compact galaxies. III. Empirical population synthesis
This is the third paper of a series dedicated to the study of the starformation rates, star formation histories, metallicities and dustcontents of a sample of blue compact galaxies (BCGs). We constrain thestellar contents of 73 blue compact galaxies by analyzing theircontinuum spectra and the equivalent widths of strong stellar absorptionfeatures using a technique of empirical population synthesis based on alibrary of observed star-cluster spectra. Our results indicate that bluecompact galaxies are typically age-composite stellar systems; inaddition to young stars, intermediate-age and old stars contributesignificantly to the 5870 Å continuum emission of most galaxies inour sample. The stellar populations of blue compact galaxies also span avariety of metallicities. The ongoing episodes of star formation startedtypically less than a billion years ago. Some galaxies may be undergoingtheir first global episode of star formation, while for most galaxies inour sample, older stars are found to contribute up to half the opticalemission. Our results suggest that BCGs are primarily old galaxies withdiscontinuous star formation histories. These results are consistentwith the results from deep imaging observations of the color-magnitudediagrams of a few nearby BCGs using HST and large ground-basedtelescopes. The good quality of our population synthesis fits of BCGspectra allow us to estimate the contamination of the Hβox{Hα }, Hβ , Hγ and Hdelta Balmer emission lines bystellar absorption. The absorption equivalent widths measured in thesynthetic spectra range from typically 1.5 Å for Hβox{Hα }, to 2-5 Å for Hβ , Hγ , and Hdelta . Theimplied accurate measurements of emission-line intensities will be usedin a later study to constrain the star formation rates and gas-phasechemical element abundances of blue compact galaxies.
| 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.
| Spectroscopic study of blue compact galaxies. II. Spectral analysis and correlations
This is the second paper in a series studying the star formation rates,stellar components, metallicities, and star formation histories andevolution of a sample of blue compact galaxies. We analyzed spectralproperties of 97 blue compact galaxies, obtained with the BeijingAstronomical Observatory (China) 2.16 m telescope, with spectral range3580 Å-7400 Å. We classify the spectra according to theiremission lines: 13 of the total 97 BCG sample are non-emission linegalaxies (non-ELGs); 10 have AGN-like emission (AGNs), and 74 of themare star-forming galaxies (SFGs). Emission line fluxes and equivalentwidths, continuum fluxes, the 4000 Å Balmer break index andequivalent widths of absorption lines are measured from the spectra. Weinvestigate the emission line trends in the integrated spectra of thestar-forming galaxies in our sample, and find that: 1) The equivalentwidths of emission lines are correlated with the galaxy absolute bluemagnitude MB; lower luminosity systems tend to have largerequivalent widths. 2) The equivalent width ratio [N II]6583/Hα isanti-correlated with equivalent width Hα; a relationship is giventhat can be used to remove the [N II] contribution from blendedHα+ [N II]6548, 6583. 3) The [O II], Hβ , Hγ andHα fluxes are correlated; those can be used as star formationtracers in the blue. 4) The metallicity indices show trends with galaxyabsolute magnitude and attenuation by dust, faint, low-mass BCGs havelower metallicity and color excess. Tables 1-4, and 6 are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/396/503
| Spectroscopic study of blue compact galaxies. I. The spectra
Blue compact galaxies are compact objects that are dominated by intensestar formation. Most of them have dramatically different propertiescompared to the Milky Way and many other nearby galaxies. Using theIRAS, H I data, and optical spectra, we wanted to measure the currentstar formation rates, stellar components, metallicities, and starformation histories and evolution of a large blue compact galaxy sample.We anticipate that our study will be useful as a benchmark for studiesof emission line galaxies at high redshift. In the first paper of thisseries, we describe the selection, spectroscopic observation, datareduction and calibration, and spectrophotometric accuracy of a sampleof 97 luminous blue compact galaxies. We present a spectrophotometricatlas of rest-frame spectra, as well as tables of the recessionvelocities and the signal-to-noise ratios. The recession velocities ofthese galaxies are measured with an accuracy of delta V< 67 kms-1. The average signal-to-noise ratio of sample spectra is ~51. The spectral line strengths, equivalent widths and continuum fluxesare also measured for the same galaxies and will be analyzed in the nextpaper of this series. The atlas and tables of measurements will be madeavailable electronically. Table 3 and Fig. 4 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/389/845
| Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies. II. Spatially Resolved and Integrated Photometry
This is the second in a series of papers devoted to the study of asample of 28 blue compact dwarf galaxies (BCDs). In the first paper, wepresented the broadband observations in B, V, R, and I. Deep contourmaps, surface-brightness profiles, and color profiles were used toanalyze and discuss their morphology and structure. Here, we present newU-band and Hα observations. We compute isophotal and asymptoticmagnitudes of the sample galaxies and total Hα fluxes. Comparisonwith previous works is done to assess the quality of the data availablefor BCDs. Finally, we produce an atlas of detailed color and Hαmaps, the first systematic atlas of this kind published so far. The highquality of the data allows us to identify the different star-formingknots in the maps and to discriminate between them and the regions wherestar formation activity has already ceased. We supplement the atlas witha morphological description of each galaxy and group the galaxies infour classes according to the distribution of their star-formingregions.
| Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies. I. Surface Brightness Distribution, Morphology, and Structural Parameters
Broadband observations in B, V, R, and I have been performed for asample of 28 galaxies cataloged as blue compact dwarf galaxies (BCDs).Our deep imaging, reaching surface brightness levels of a few percent ofthe sky brightness, has allowed the detection of underlying emission orlow surface brightness features for a substantial fraction of thesample. In this paper we present the first results of the program: deepcontour maps in the B band, surface brightness profiles, and colorprofiles for all the galaxies. The information derived for this sampleof galaxies has allowed us to analyze the morphology and the structuralcomponents of BCDs. Over 70% of the galaxies show complex profiles thatpreclude fitting by a single standard law, with extra structure at highto intermediate intensity levels. In 21 galaxies of the sample, anunderlying low surface brightness component has been detected.
| Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies
We present preliminary results of the surface photometry of a sample ofblue compact dwarf galaxies (BCDGs). A total of 28 galaxies have beenobserved in the BVRI bands. From these data the contour maps and surfacebrightness distributions in each band have been built. Contour maps andsurface profiles of the 22 galaxies already analysed are presented,together with preliminary conclusions regarding their morphology andstructural components.
| Statistical Properties of Ultraluminous IRAS Galaxies from an HST Imaging Survey
We perform photometric measurements on a large HST snapshot imagingsurvey sample of 97 ultraluminous infrared galaxies (ULIRGs). We selectputative nuclei from bright clumps in all the sample targets, mainlybased on a quantitative criterion of I-band luminosity as well as theglobal and local morphological information. All the sources are thenclassified into three categories with multiple, double, and singlenucleus/nuclei. The resultant fractions of multiple, double, and singlenucleus/nuclei ULIRGs are 18%, 39%, and 43%, respectively. This supportsthe multiple merger scenario as a possible origin of ULIRGs, in additionto the commonly accepted pair merger model. Further statistical studiesindicate that the AGN fraction increases from multiple (36%) to double(65%) and then to single (80%) nucleus/nuclei ULIRGs. For the singlenucleus category, there is a high-luminosity tail in the luminositydistribution, which corresponds to a Seyfert 1/QSO excess. Thisindicates that active galactic nuclei tend to appear at final mergingstage. For multiple/double nuclei galaxies, we also find a high fractionof very close nucleus pairs (e.g., 3/4 for those separated by less than5 kpc). This strengthens the conclusion that systems at late mergingphase preferentially host ULIRGs.
| Supernova 2000C in NGC 2415
IAUC 7356 available at Central Bureau for Astronomical Telegrams.
| Supernova 2000C in NGC 2415
IAUC 7352 available at Central Bureau for Astronomical Telegrams.
| Supernova 2000C in NGC 2415
IAUC 7348 available at Central Bureau for Astronomical Telegrams.
| The UK Nova/Supernova Patrol-The First 25 Years
The history, accomplishments, and activities of the UK Nova/SupernovaPatrol are described.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Stellar population synthesis for blue compact galaxies.
Not Available
| 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.
| Dust Absorption and the Ultraviolet Luminosity Density at Z~3 as Calibrated by Local Starburst Galaxies
We refine a technique to measure the absorption-corrected ultraviolet(UV) luminosity of starburst galaxies using rest-frame UV quantitiesalone and apply it to Lyman-limit U dropouts at z~3 found in the HubbleDeep Field (HDF). The method is based on an observed correlation betweenthe ratio of far-infrared (FIR) to UV fluxes with spectral slope beta (aUV color). A simple fit to this relation allows the UV flux absorbed bydust and reprocessed to the FIR to be calculated, and hence thedust-free UV luminosity to be determined. International UltravioletExplorer spectra and Infrared Astronomical Satellite fluxes of localstarbursts are used to calibrate the F_FIR/F_1600 versus beta relationin terms of A_1600 (the dust absorption at 1600 Å) and thetransformation from broadband photometric color to beta. Bothcalibrations are almost completely independent of theoreticalstellar-population models. We show that the recent marginal andnondetections of HDF U dropouts at radio and submillimeter wavelengthsare consistent with their assumed starburst nature and our calculatedA_1600. This is also true of recent observations of the ratio of opticalemission-line flux to UV flux density in the brightest U dropouts. Thislatter ratio turns out not to be a good indicator of dust extinction. InU dropouts, absolute magnitude M_1600,0 correlates with beta: brightergalaxies are redder, as is observed to be the case for local starburstgalaxies. This suggests that a mass-metallicity relationship is alreadyin place at z~3. The absorption-corrected UV luminosity function of Udropouts extends up to M_1600,0~-24 AB mag, corresponding to a starformation rate ~200 M_solar yr^-1 (H_0=50 km s^-1 Mpc^-3 and q_0=0.5 areassumed throughout). The absorption-corrected UV luminosity density atz~3 is rho_1600,0>=1.4x10^27 ergs^-1 Hz^-1 Mpc^-1. It is still alower limit since completeness corrections have not been done andbecause only galaxies with A_1600<~3.6 mag are blue enough in the UVto be selected as U dropouts. The luminosity-weighted meandust-absorption factor of our sample is 5.4+/-0.9 at 1600 Å.
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