Contents
Images
Upload your image
DSS Images Other Images
Related articles
Recent discoveries of bright supernovae at the Bronberg Observatory.
Not Available
| Detection of Diffuse Interstellar Bands in the z=0.5 Damped Lyα System toward AO 0235+164
We report the first detection of the 5705 and 5780 Å diffuseinterstellar bands (DIBs) in a moderate-redshift damped Lyα (DLA)system. We measure a rest-frame equivalent width of 63.2+/-8.7 mÅfor the 5705 Å feature and 216+/-9 mÅ for the 5780 Åfeature in the zabs=0.524 DLA toward AO 0235+164 and derivelimits for the equivalent widths of the bands at 5797, 6284, and 6613Å. The equivalent width of the 5780 Å band is lower thanwould be expected based on the Galactic correlation of DIB strength withN(H I) but is in good agreement with the correlation with E(B-V). Therelative strengths of the 5780 and 6284 Å DIBs are inconsistentwith all Galactic and extragalactic sight lines, except one SmallMagellanic Cloud wing sight line toward Sk 143. However, the relativestrengths of the 5705 and 5780 Å DIBs are consistent with theGalactic relation, indicating that the relative strengths of these bandsmay be less sensitive to environment or that they may be associated witha similar carrier. The detection of DIBs at z~0.5 demonstrates that theorganic compounds usually assumed to be the band carriers were alreadypresent in the universe some 5 Gyr ago.Based on observations made with ESO telescopes at the ParanalObservatory under program ID 075.C-0029.
| Reddening, Absorption, and Decline Rate Corrections for a Complete Sample of Type Ia Supernovae Leading to a Fully Corrected Hubble Diagram to v < 30,000 km s-1
Photometric (BVI) and redshift data corrected for streaming motions arecompiled for 111 ``Branch-normal,'' four 1991T-like, seven 1991bg-like,and two unusual supernovae of Type Ia (SNe Ia). Color excessesE(B-V)host of normal SNe Ia, due to the absorption of thehost galaxy, are derived by three independent methods, giving excellentagreement leading to the intrinsic colors at maximum of(B-V)00=-0.024+/-0.010 and (V-I)00=-0.265+/-0.016if normalized to a common decline rate of Δm15=1.1. Thestrong correlation between redshift absolute magnitudes (based on anarbitrary Hubble constant of H0=60 km s-1Mpc-1), corrected only for the extrinsic Galactic absorption,and the derived E(B-V)host color excesses leads to thewell-determined yet abnormal absorption-to-reddening ratios ofRBVI=3.65+/-0.16, 2.65+/-0.15, and 1.35+/-0.21.Comparison with the canonical Galactic values of 4.1, 3.1, and 1.8forces the conclusion that the law of interstellar absorption in thepath length to the SN in the host galaxy is different from the localGalactic law, a result consistent with earlier conclusions by others.Improved correlations of the fully corrected absolute magnitudes (on thesame arbitrary Hubble constant zero point) with host galaxymorphological type, decline rate, and intrinsic color are derived. Werecover the result that SNe Ia in E/S0 galaxies are ~0.3 mag fainterthan in spiral galaxies for possible reasons discussed in the text. Thenew decline rate corrections to absolute magnitudes are smaller thanthose by some authors for reasons explained in the text. The fourspectroscopically peculiar 1991T-type SNe are significantly overluminousas compared to Branch-normal SNe Ia. The overluminosity of the seven1999aa-like SNe is less pronounced. The seven 1991bg types in the sampleconstitute a separate class of SNe Ia, averaging in B 2 mag fainter thanthe normal Ia. New Hubble diagrams in B, V, and I are derived out to~30,000 km s-1 using the fully corrected magnitudes andvelocities, corrected for streaming motions. Nine solutions for theintercept magnitudes in these diagrams show extreme stability at the0.02 mag level using various subsamples of the data for both low andhigh extinctions in the sample, proving the validity of the correctionsfor host galaxy absorption. We shall use the same precepts for fullycorrecting SN magnitudes for the luminosity recalibration of SNe Ia inthe forthcoming final review of our Hubble Space Telescope Cepheid-SNexperiment for the Hubble constant.
| Early and late time VLT spectroscopy of SN 2001el - progenitor constraints for a type Ia supernova
We present early time high-resolution (VLT/UVES) and late timelow-resolution (VLT/FORS) optical spectra of the normal type Iasupernova, SN 2001el. The high-resolution spectra were obtained 9 and 2days before (B-band) maximum light. This was in order to allow thedetection of narrow hydrogen and/or helium emission lines from thecircumstellar medium of the supernova. No such lines were detected inour data. We therefore use these spectra together with photoionisationmodels to derive upper limits of 9×10-6 {M}_ȯyr-1 and 5×10-5 {M}_ȯ yr-1for the mass loss rate from the progenitor system of SN 2001el assumingvelocities of 10 km s-1 and 50 km s-1,respectively, for a wind extending to outside at least a few ×1015 cm away from the supernova explosion site. So far, theseare the best Hα based upper limits obtained for a type Iasupernova, and exclude a symbiotic star in the upper mass loss rateregime (so called Mira type stars) from being the progenitor of SN2001el. The low-resolution spectrum was obtained in the nebular phase ofthe supernova, 400 days after the maximum light, to search for anyhydrogen rich gas originating from the supernova progenitor system.However, we see no signs of Balmer lines in our spectrum. Therefore, wemodel the late time spectra to derive an upper limit of 0.03Mȯ for solar abundance material present at velocitieslower than 1000 km s-1 within the supernova explosion site.According to numerical simulations of Marietta et al. (2000) this isless than the expected mass lost by a subgiant, red giant or amain-sequence secondary star at a small binary separation as a result ofthe SN explosion. Our data therefore exclude these scenarios as theprogenitor of SN 2001el. Finally, we discuss the origin of high velocityCa II lines previously observed in a few type Ia supernovae before themaximum light. We see both the Ca II IR triplet and the H&K lines inour earliest (-9 days) spectrum at a very high velocity of up to 34 000km s-1. The spectrum also shows a flat-bottomed Si II "6150Å" feature similar to the one previously observed in SN 1990N(Leibundgut et al. 1991, ApJ, 371, L23) at 14 days before maximum light.We compare these spectral features in SN 2001el to those observed in SN1984A and SN 1990N at even higher velocities.
| Nonlinear particle acceleration at reverse shocks in supernova remnants
Without amplification, magnetic fields in expanding ejecta of youngsupernova remnants (SNRs) will be orders of magnitude below thoserequired to shock accelerate thermal electrons, or ions, to relativisticenergies or to produce radio synchrotron emission at the reverse shock.The reported observations of such emission give support to the idea thatdiffusive shock acceleration (DSA) can amplify magnetic fields by largefactors. Furthermore, the uncertain character of the amplificationprocess leaves open the possibility that ejecta fields, while largeenough to support radio emission and DSA, may be much lower than typicalinterstellar medium values. We show that DSA in such low reverse shockfields is extremely nonlinear and efficient in the production ofcosmic-ray (CR) ions, although CRs greatly in excess of mc2are not produced. These nonlinear effects, which occur at the forwardshock as well, are manifested most importantly in shock compressionratios ≫ 4 and cause the interaction region between the forward andreverse shocks to become narrower, denser, and cooler than would be thecase if efficient cosmic-ray production did not occur. The changes inthe SNR structure and evolution should be clearly observable, ifpresent, and they convey important information on the nature of DSA andmagnetic field amplification with broad astrophysical implications.
| Diffuse Interstellar Bands in NGC 1448
We present spectroscopic VLT/UVES observations of two emergingsupernovae, the Type Ia SN 2001el and the Type IISN 2003hn, in the spiral galaxy NGC1448. Our high resolution and high signal-to-noise spectradisplay atomic lines of Ca II, Na I, Ti II and K I in the host galaxy.In the line of sight towards SN 2001el, we alsodetect over a dozen diffuse interstellar bands (DIBs) withinNGC 1448. These DIBs have strengths comparable to lowreddening galactic lines of sight, albeit with some variations. Inparticular, a good match is found with the line of sight towards theσ type diffuse cloud (HD 144217). The DIBstowards SN 2003hn are significantly weaker, and thisline of sight has also lower sodium column density. The DIB centralvelocities show that the DIBs towards SN 2001el areclosely related to the strongest interstellar Ca II and Na I components,indicating that the DIBs are preferentially produced in the same cloud.The ratio of the λ 5797 and λ 5780 DIB strengths (r 0.14) suggests a rather strong UV field in the DIB environment towardsSN 2001el. We also note that the extinction estimatesobtained from the sodium lines using multiple line fitting agree withreddening estimates based on the colors of the Type Ia SN2001el.Based on observations collected at the European Southern Observatory,Paranal, Chile (ESO Programmes 67.D-0227 and 71.D-0033).Table \ref{tb:ISfit} and Figs. \ref{fig:IS_MW} and \ref{fig:6284} areonly available in electronic form at http://www.edpsciences.org
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Amateur observations - Successes and opportunities.
Not Available
| Supernova 2003hn in NGC 1448
IAUC 8187 available at Central Bureau for Astronomical Telegrams.
| Supernova 2003hn in NGC 1448
IAUC 8186 available at Central Bureau for Astronomical Telegrams.
| A Survey for H2O Megamasers. III. Monitoring Water Vapor Masers in Active Galaxies
We present single-dish monitoring of the spectra of 13 extragalacticwater megamasers taken over a period of 9 years and a single epoch ofsensitive spectra for seven others. The primary motivation is a searchfor drifting line velocities analogous to those of the systemic featuresin NGC 4258, which are known to result from centripetal acceleration ofgas in an edge-on, subparsec molecular disk. We detect a velocity driftanalogous to that in NGC 4258 in only one source, NGC 2639. Another, themaser source in NGC 1052, exhibits erratic changes in its broad maserprofile over time. Narrow maser features in all of the other diskgalaxies discussed here either remain essentially constant in velocityover the monitoring period or are sufficiently weak or variable inintensity that individual features cannot be traced reliably from oneepoch to the next. In the context of a circumnuclear, molecular diskmodel, our results suggest that either (a) the maser lines seen aresystemic features subject to a much smaller acceleration than present inNGC 4258, presumably because the gas is farther from the nuclear blackhole, or (b) we are detecting ``satellite'' lines for which theacceleration is in the plane of the sky.Our data include the first K-band science observations taken with thenew 100 m Green Bank Telescope (GBT). The GBT data were taken duringtesting and commissioning of several new components and so are subjectto some limitations; nevertheless, they are in most cases the mostsensitive H2O spectra ever taken for each source and cover800 MHz (~=10,800 km s-1) of bandwidth. Many new maserfeatures are detected in these observations. Our data also include atentative and a clear detection of the megamaser in NGC 6240 at epochs ayear and a few months, respectively, prior to the detections reported byHagiwara et al. and Nakai et al.We also report a search for water vapor masers toward the nuclei of 58highly inclined (i>80deg), nearby galaxies. These sourceswere selected to investigate the tendency that H2O megamasersfavor inclined galaxies. None were detected, confirming that megamasersare associated exclusively with active galactic nuclei.
| Spectropolarimetry of SN 2001el in NGC 1448: Asphericity of a Normal Type Ia Supernova
High-quality spectropolarimetry (range 417-860 nm; spectral resolution1.27 nm and 0.265 nm pixel-1) of the Type Ia supernova (SNIa) 2001el was obtained with the ESO Very Large Telescope Melipal(+FORS1) at five epochs. The spectra a week before maximum and aroundmaximum indicate photospheric expansion velocities of about 10,000 kms-1. Prior to optical maximum, the linear polarization of thecontinuum was ~0.2%-0.3% with a constant position angle, showing that SN2001el has a well-defined axis of symmetry. The polarization was nearlyundetectable a week after optical maximum. The spectra are similar tothose of the normally bright SN 1994D, with the exception of a strongdouble-troughed absorption feature seen around 800 nm (FWHM about 22nm). The 800 nm feature is probably due to the Ca II IR triplet at veryhigh velocities (20,000-26,000 km s-1) involving ~0.004Msolar of calcium and perhaps 0.1 Msolar totalmass. The 800 nm feature is distinct in velocity space from thephotospheric Ca II IR triplet and has a significantly higher degree ofpolarization (~0.7%) and different polarization angle than thecontinuum. Taken together, these aspects suggest that this high-velocitycalcium is a kinematically distinct feature with the matter distributedin a filament, torus, or array of ``blobs'' almost edge-on to the lineof sight. This feature could thus be an important clue to the binarynature of SNe Ia, perhaps associated with an accretion disk, or to thenature of the thermonuclear burning, perhaps representing a stream ofmaterial ballistically ejected from the site of the deflagration todetonation transition. If modeled in terms of an oblate spheroid, thecontinuum polarization implies a minor to major axis ratio of around 0.9if seen equator-on this level of asymmetry would produce an absoluteluminosity dispersion of about 0.1 mag when viewed at different viewingangles. If typical for SNe Ia, this would create an rms scatter ofseveral hundredths of a magnitude around the mean brightness-declinerelation. We discuss the possible implications of this scatter for thehigh-precision measurements required to determine the cosmologicalequation of state.Based on observations collected at the European Southern Observatory,Chile (ESO Programme 68.D-0571(A).
| 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.
| Optical and Infrared Photometry of the Nearby Type Ia Supernova 2001el
We present well-sampled optical (UBVRI) and infrared (JHK) light curvesof the nearby (~18.0 Mpc) Type Ia supernova SN 2001el, from 11 daysbefore to 142 days after the time of B-band maximum. The data representone of the best sets of optical and infrared photometry ever obtainedfor a Type Ia supernova (SN). Based on synthetic photometry usingoptical spectra of SN 2001el and optical and infrared spectra of SN1999ee, we were able to devise filter corrections for the BVJHKphotometry of SN 2001el, which to some extent resolve systematicdifferences between SN 2001el data sets obtained with differenttelescope/filter/instrument combinations. We also calculatedV-minus-infrared color curves on the basis of a delayed detonation modeland show that the theoretical color curves match the unreddened loci forType Ia SNe with midrange decline rates to within 0.2 mag. Given thecompleteness of the light curves and the elimination of filter-orientedsystematic errors to some degree, the data presented here will be usefulfor the construction of photometric templates, especially in theinfrared. On the whole the photometric behavior of SN 2001el was quitenormal. The second H-band maximum being brighter than the first H-bandmaximum is in accord with the prediction of Krisciunas et al. for TypeIa SNe with midrange decline rates. The photometry exhibits nonzero hostextinction, with total AV=0.57+/-0.05 mag along the line ofsight. NGC 1448, the host of SN 2001el, would be an excellent target fora distance determination using Cepheids.
| A catalog of warps in spiral and lenticular galaxies in the Southern hemisphere
A catalog of optical warps of galaxies is presented. This can beconsidered complementary to that reported by Sánchez-Saavedra etal. (\cite{sanchez-saavedra}), with 42 galaxies in the northernhemisphere, and to that by Reshetnikov & Combes(\cite{reshetnikov99}), with 60 optical warps. The limits of the presentcatalog are: logr 25 > 0.60, B_t< 14.5, delta (2000) <0deg, -2.5 < t < 7. Therefore, lenticular galaxies havealso been considered. This catalog lists 150 warped galaxies out of asample of 276 edge-on galaxies and covers the whole southern hemisphere,except the Avoidance Zone. It is therefore very suitable for statisticalstudies of warps. It also provides a source guide for detailedparticular observations. We confirm the large frequency of warpedspirals: nearly all galaxies are warped. The frequency and warp angle donot present important differences for the different types of spirals.However, no lenticular warped galaxy has been found within the specifiedlimits. This finding constitutes an important restriction fortheoretical models.
| A Search for H2O Maser Emission in Southern Active Galactic Nuclei and Star-forming Galaxies: Discovery of a Maser in the Edge-on Galaxy IRAS F01063-8034
We report the cumulative results of five surveys for H2Omaser emission at 1.35 cm wavelength in 131 active galactic nuclei(AGNs) and star-forming galaxies, conducted at the Parkes Observatorybetween 1993 and 1998. We detected one new maser, in the edge-on galaxyIRAS F01063-8034, which exhibits a single ~0.1 Jy spectral feature at4282+/-6 km s-1 (heliocentric) with an unusually large54+/-16 km s-1 half-power full width. The centroid velocityof the emission increased to 4319.6+/-0.6 km s-1 (38+/-2 kms-1 width) over the 13 days between discovery andconfirmation of the detection. A similarly broad-line width and largechange in velocity has been noted for the maser in NGC 1052, wherein jetactivity excites the emission. Neither optical spectroscopy,radio-infrared correlations, nor infrared colors provide compellingevidence of unusual activity in the nucleus of IRAS F01063-8034. Sincethe galaxy appears to be outwardly normal at optical and infraredwavelengths, detection of an H2O maser therein is unique. Themaser emission is evidence that the galaxy harbors an AGN that isprobably obscured by the edge-on galactic disk. The detection highlightsthe possibility that undetected AGNs could be hidden in other relativelynearby galaxies. No other maser emission features have been identifiedat velocities between 3084 and 6181 km s-1.
| Warps and correlations with intrinsic parameters of galaxies in the visible and radio
From a comparison of the different parameters of warped galaxies in theradio, and especially in the visible, we find that: a) No large galaxy(large mass or radius) has been found to have high amplitude in thewarp, and there is no correlation of size/mass with the degree ofasymmetry of the warp. b) The disc density and the ratio of dark toluminous mass show an opposing trend: smaller values give moreasymmetric warps in the inner radii (optical warps) but show nocorrelation with the amplitude of the warp; however, in the externalradii is there no correlation with asymmetry. c) A third anticorrelationappears in a comparison of the amplitude and degree of asymmetry in thewarped galaxies. Hence, it seems that very massive dark matter haloeshave nothing to do with the formation of warps but only with the degreeof symmetry in the inner radii, and are unrelated to the warp shape forthe outermost radii. Denser discs show the same dependence.
| Supernovae in isolated galaxies, in pairs and in groups of galaxies
In order to investigate the influence of environment on supernova (SN)production, we have performed a statistical investigation of the SNediscovered in isolated galaxies, in pairs and in groups of galaxies. 22SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and211 SNe in 170 galaxy members of 116 groups have been selected andstudied. We found that the radial distributions of core-collapse SNe ingalaxies located in different environments are similar, and consistentwith those reported by Bartunov, Makarova & Tsvetkov. SNe discoveredin pairs do not favour a particular direction with respect to thecompanion galaxy. Also, the azimuthal distributions inside the hostmembers of galaxy groups are consistent with being isotropics. The factthat SNe are more frequent in the brighter components of the pairs andgroups is expected from the dependence of the SN rates on the galaxyluminosity. There is an indication that the SN rate is higher in galaxypairs compared with that in groups. This can be related to the enhancedstar formation rate in strongly interacting systems. It is concludedthat, with the possible exception of strongly interacting systems, theparent galaxy environment has no direct influence on SN production.
| Supernova 2001el in NGC 1448
IAUC 7724 available at Central Bureau for Astronomical Telegrams.
| Supernova 2001el in NGC 1448
IAUC 7723 available at Central Bureau for Astronomical Telegrams.
| Supernova 2001el in NGC 1448
IAUC 7723 available at Central Bureau for Astronomical Telegrams.
| Supernova 2001el in NGC 1448
IAUC 7721 available at Central Bureau for Astronomical Telegrams.
| Supernova 2001el in NGC 1448
IAUC 7720 available at Central Bureau for Astronomical Telegrams.
| Deep submillimeter images of NGC 7331; dust at the periphery of spiral disks
We present deep 450 and 850 mu m SCUBA images of the nearby spiralgalaxy NGC 7331. Using the submillimeter emissivity inferred from COBEobservations of Milky Way dust, we convert our SCUBA images into maps ofoptical depth. The opacity derived in this way is quite low at thevisible limit of NGC 7331 (tau B<= 0.22 at theR25 radius for the disk seen face-on). In a similar fashion,we exploit SCUBA and ISOPHOT images of a further 10 galaxies and,collectively, these data indicate tau B=0.1-0.2 at theR25 radius. Our constraints on disk opacity are fed into asimulation of how light emanating from high redshifts is attenuated byforeground spirals. In making this calculation, we consider thepossibility that galactic disks may have also contained different dustmasses in the past. We estimate that less than 10% of the light emittedby Hubble Deep Field galaxies fails to reach the B-band observer due tointervening spirals.
| The mass distribution in the innermost regions of spiral galaxies
We use high-spatial resolution ( ~ 100 pc) rotation curves of 83 spiralgalaxies to investigate the mass distribution of their innermost kpc. Weshow that in this region the luminous matter completely accounts for thegravitational potential and no dark component is required. The derivedI-band disk mass-to-light ratios Y_I agree well with those obtained frompopulation synthesis models and correlate with color in a similar way.We find strict upper limits of ~ 10^7 M_Sun for the masses of compactbodies at the center of spirals ruling out that these systems host theremnants of the quasar activity.
| 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.
| ISO Long Wavelength Spectrograph Observations of Cold Dust in Galaxies
We describe observations of five nearby galaxies obtained using the LongWavelength Spectrograph (LWS) on the Infrared Space Observatory (ISO).We observed five galaxies, using spectrograph apertures positioned atthe galactic center and in the outskirts of the disk, to compare thespectral energy distribution of the emitting dust at differentpositions. The central spectra are typical of those inferred previouslyfrom IRAS data; peaking at about 100 μm with estimated dusttemperatures of Td=30-35 K. However, there is a rapid changein the spectral energy distribution with increasing galactocentricdistance. In the outer regions the spectra are flat, or still rising,out to 197μm, indicating a predominantly cold dust component withTd<20 K. In the central regions, the inferred cold dustcomponent is 2-10 times more massive than the warm dust, and itincreasingly dominates the mass and spectral energy distribution in theouter regions. We discuss reasons for believing that emission beyond~150 μm in disk galaxies is associated with a separate component ofdust with an extended distribution that may be associated with apossible molecular halo. Based on observations with ISO, an ESA projectwith instruments funded by ESA Member States (especially the PIcountries: France, Germany, Netherlands, and the United Kingdom) withthe participation of ISAS and NASA.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The distribution of far-infrared emission from edge-on galaxies
We use resolution-enhanced IRAS images (HiRes) to study the distributionof far-infrared (FIR) emission in 20 edge-on, disc galaxies. Half of oursample are selected as infrared-bright galaxies which emit most of theirenergy at wavelengths longer than a few mum. The remaining 10 objectsare `normal' (quiescent) galaxies. The distribution of FIR emissionalong the major axis of the infrared-bright galaxies tends to be farmore centrally concentrated than that detected in quiescent discs.Indeed, many of the infrared-bright objects are dominated by a luminous,compact or unresolved source (<3 kpc) located in the nuclear region.It is known from emission-line studies carried out in the past (Hαimaging and long-slit spectroscopy) that most of the galaxies that wehave selected as infrared-bright possess an energetic outflow or`superwind', which is powered by enhanced, circumnuclear star formation.We believe, therefore, that the compact FIR emission that we havedetected arises from dust enclosing the central starburst.Low-resolution radio continuum maps for the same galaxies show astriking morphological similarity to the IRAS images, confirming thepresence of enhanced, recent star formation at the centre of theinfrared-bright galaxies. The wider availability of higher resolutionFIR images, such as HiRes, also invites an investigation into whetheredge-on discs are resolved along the minor axis. In particular, weexplore the possibility that the starburst-driven superwinds, presentwithin many of our infrared-bright galaxies, are transporting dustgrains out of the disc. None of the objects that we have examined(infrared-bright or quiescent) exhibits structure that can be reliablyinterpreted as dust outflow. Various artefacts of the HiRes data,specifically those which produce faint, spurious structure in thevicinity of bright FIR sources, ultimately constrain the sensitivity ofour images to about 1 MJy sr^-1 at 60 mum. Thus, if the grains entrainedin the outflow are too cold (<=15 K), we cannot expect to detect themwith the present study.
| A Study of External Galaxies Detected by the COBE Diffuse Infrared Background Experiment
A comparison of the COBE 1 Diffuse Infrared Background Experiment(DIRBE) all-sky survey with the locations of known galaxies in the IRASCatalog of Extragalactic Objects and the Center for Astrophysics Catalogof Galaxies led to the detection of as many as 57 galaxies. In thispaper, we present the photometric data for these galaxies and ananalysis of the seven galaxies that were detected at lambda > 100 mum. Estimates of the ratio of the mass of the cold dust (CD) componentdetected at Td = 20-30 K to a very cold dust (VCD) component with Td ~10-15 K suggest that between 2%-100% of the cirrus-like CD mass can alsoexist in many of these galaxies as VCD. In one galaxy, M33, the DIRBEphotometry at 240 mu m suggests as much as 26 times as much VCD may bepresent as compared to the cirrus-like component. Further submillimetermeasurements of this galaxy are required to verify such a largepopulation of VCD. We also present 10 galaxies that were detected in thesky region not previously surveyed by IRAS and that can be used toconstruct a flux-limited all-sky catalog of galaxies brighter than 1000Jy with a modest completeness limit of about 65%.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
