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|Magnetic fields in barred galaxies. IV. NGC 1097 and NGC 1365|
We present λ3.5 cm and λ6.2 cm radio continuum maps intotal and polarized intensity of the barred galaxies NGC 1097 (at2´´-15´´ resolution) and NGC 1365 (at9´´-25´´ resolution). A previously unknown radiogalaxy southwest of NGC 1097 is reported. Apart from a smooth faintenvelope and a bright central region, both galaxies exhibit radio ridgesroughly overlapping with the massive dust lanes in the bar region. Thecontrast in total intensity across the radio ridges is compatible withcompression and shear of an isotropic random magnetic field, where thegas density compression ratio is approximately equal to 4 and the cosmicray density is constant across the ridges. The contrast in polarizedintensity is significantly smaller than that expected from compressionand shearing of the regular magnetic field; this could be the result ofdecoupling of the regular field from the dense molecular clouds. Theregular field in the ridge is probably strong enough to reducesignificantly shear in the diffuse gas (to which it is coupled) andhence to reduce magnetic field amplification by shearing. Thiscontributes to the misalignment of the observed field orientation withrespect to the velocity vectors of the dense gas. Our observations, forthe first time, indicate that magnetic forces can control the flow ofthe diffuse interstellar gas at kiloparsec scales. The total radiointensity reaches its maximum in the circumnuclear starburst regions,where the equipartition field strength is about 60 μG, amongst thestrongest fields detected in spiral galaxies so far. The regular fieldin the inner region has a spiral shape with large pitch angle,indicating the action of a dynamo. Magnetic stress leads to mass inflowtowards the centre, sufficient to feed the active nucleus in NGC 1097. -We detected diffuse X-ray emission, possibly forming a halo of hot gasaround NGC 1097.
|Low-luminosity Type II supernovae: spectroscopic and photometric evolution|
In this paper we present spectroscopic and photometric observations forfour core-collapsed supernovae (SNe), namely SNe 1994N, 1999br, 1999euand 2001dc. Together with SN 1997D, we show that they form a group ofexceptionally low-luminosity events. These SNe have narrow spectrallines (indicating low expansion velocities) and low luminosities atevery phase (significantly lower than those of typical core-collapsedsupernovae). The very-low luminosity during the 56Coradioactive decay tail indicates that the mass of 56Niejected during the explosion is much smaller (MNi~ 2-8× 10-3 Msolar) than the average(MNi~ 6-10 × 10-2 Msolar). Twosupernovae of this group (SN 1999br and SN 2001dc) were discovered veryclose to the explosion epoch, allowing us to determine the lengths oftheir plateaux (~100 d) as well as establishing the explosion epochs ofthe other, less completely observed SNe. It is likely that this group ofSNe represent the extreme low-luminosity tail of a single continuousdistribution of Type II plateau supernovae events. Their kinetic energyis also exceptionally low. Although an origin from low-mass progenitorshas also been proposed for low-luminosity core-collapsed SNe, recentwork provides evidence in favour of the high-mass progenitor scenario.The incidence of these low-luminosity SNe could be as high as 4-5 percent of all Type II SNe.
|Supernova 2003B near NGC 1097|
IAUC 8042 available at Central Bureau for Astronomical Telegrams.
|Supernova 2003B near NGC 1097|
IAUC 8042 available at Central Bureau for Astronomical Telegrams.
|A Minor-Merger Interpretation for NGC 1097's ``Jets''|
We have conducted a deep search for neutral hydrogen gas associated withthe faint optical ``jets'' of NGC 1097 using the Very Large Array.Measurable H I would have been expected if the jets were tidal in origingiven their moderately blue optical and near-infrared colors. The jetsare free of H I emission to a limiting surface density(ΣHI) of 0.06 Msolar pc-2 (3σ) over a 1102 km s-1 velocity range. We also rule outextended H I emission down to 0.02 Msolar pc-2 (3σ, ΔV=45 km s-1) within a 4' FWHM aperturecentered on the right-angle turn in jet R1. We have detected an H Isource [MHI=(5.1+/-1.0)×106Msolar] coincident with a small edge-on spiral or irregulargalaxy (NGC 1097B) 12' southwest of NGC 1097, situated between two jets.Two other ~106 Msolar H I point sources in thefield are considered marginal detections. Neither are associated withthe optical jets.The jets' radio-X-ray spectral energy distribution is most consistentwith starlight. However, from their morphology, optical/near-infraredcolors, and lack of H I, we argue that the jets are not tidal tailsdrawn out of NGC 1097's disk or stars stripped from the ellipticalcompanion NGC 1097A. We also reject in situ star formation in ancientradio jets as this requires essentially 100% conversion of gas intostars on large scales. Instead, we conclude that the jets represent thecaptured remains of a disrupted dwarf galaxy that passed through theinner few kiloparsecs of NGC 1097's disk.We present N-body simulations of such an encounter that reproduce theessential features of NGC 1097's jets: A long and narrow ``X''-shapedmorphology centered near the spiral's nucleus, right-angle bends, and nodiscernible dwarf galaxy remnant. A series of jetlike distributions areformed, with the earliest appearing ~1.4 Gyr after impact. Well-definedX shapes form only when the more massive galaxy has a strong diskcomponent. Ram-pressure stripping of the dwarf's interstellar mediumwould be expected to occur while passing through NGC 1097's disk,accounting for the jets' lack of H I and H II. The remnants' (B-V) colorwould still agree with observations even after ~3 Gyr of passiveevolution, provided the cannibalized dwarf was low-metallicity anddominated by young stars at impact.
|Companions of Bright Barred Shapley-Ames Galaxies|
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
|Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry|
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
|Near-infrared line imaging of the circumnuclear starburst rings in the active galaxies NGC 1097 and NGC 6574|
We present high spatial resolution near-infrared broad-band JHK andBrgaussmma 2.166 mum and H_2 1-0 S(1) 2.121 mum emission line images ofthe circumnuclear star formation rings in the LINER/Seyfert 1 galaxy NGC1097 and in the Seyfert 2 galaxy NGC 6574. We investigate themorphology, extinction, and the star formation properties and history ofthe rings, by comparing the observed properties with an evolutionarypopulation synthesis model. The clumpy morphology in both galaxiesvaries strongly with wavelength, due to a combination of extinction,emission from hot dust and red supergiants, and the age of the stellarpopulations in the rings. The near-infrared and radio morphologies arein general agreement, although there are differences in the detailedmorphology. From the comparison of Brgaussmma and Hα fluxes, wederive average extinctions toward the hot spots A_V = 1.3 for NGC 1097and A_V = 2.1 for NGC 6574. The observed H_2/Brgaussmma ratios indicatethat in both rings the main excitation mechanism of the molecular gas isUV radiation from hot young stars, while shocks can contribute only in afew regions. The starburst rings in both galaxies exhibit smallBrgaussmma equivalent widths. Assuming a constant star formation ratewith M_u = 100 M_sun results in extremely long ages (up to 1 Gyr), indisagreement with the morphology and the radio spectral index of thegalaxies. This situation is only slightly remedied by a reduced uppermass cutoff (M_u = 30 M_sun). We prefer a model of an instantaneousburst of star formation with M_u = 100 M_sun occurring sim6-7 Myr ago.Gaseous nuclear bars parallel to the stellar nuclear bar were detectedin both galaxies, and we derive M sim100 M_sun for the mass of theexcited nuclear H_2 emission. Finally, we briefly discuss the connectionbetween the rings, bars and the fuelling of nuclear activity.
|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%.
|The Southern Sky Redshift Survey|
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
|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.
|Preliminary radio continuum maps of three spiral galaxies|
The Australia Telescope Compact Array has been used in two 6 kmconfigurations to make 12 hour observations of the radio continuumstructure of three spiral galaxies at 1380 and 2378 MHz. Radio maps ofNGC 1792, 6300 and 1097 are presented here, as part of a survey to findexamples of anomalous radio structures in spiral galaxies.
|H i and the Maffei 2 Starburst: A Merger Scenario|
We present high-resolution H I maps of the nearby starburst galaxyMaffei 2. These VLA maps have maximum resolutions of 20" and showemission extending across 15', well beyond the optical extent of thegalaxy. The radio continuum emission matches the barred asymmetricmorphology seen in the infrared. The asymmetries in the outer disk arealso evident in H I, although the nucleus, which exhibits strong COemission, is deficient in atomic gas. The total H I mass of the galaxyis 1.1 x 10^9^ M_sun_, accounting for ~1.5% of its total inferreddynamical mass. Its velocity field is, to first, order, typical ofsymmetrical barred galaxies, although there is a 10 km s^-1^ differencein systemic velocity between the disk and nucleus. Maffei 2 has amarkedly disturbed appearance with an unusual H I "double arc" to thenorth that is probably a tidal feature indicating a recent or ongoinginteraction. We propose that the asymmetries in the galaxy as well asits nuclear starburst are driven by an ongoing merger with a smallsatellite companion galaxy.
|Nuclear Rings in Active Galaxies|
We investigate two current problems in active galactic nuclei-the modeof fueling the putative black hole, and the question of whether thecircumnuclear regions have experienced unusual chemical processing-bystudying the kinematics and chemical abundance of the gas in the innerregions of active galaxies with circumnuclear star formation. We discussresults for three galaxies with nuclear rings: NGC 1097 and NGC 1672,both of which contain a LINER nucleus, and NGC 5248, a galaxy with aring but no nuclear activity. Narrowband images have been obtained inHα + [NII], to map out the ionized gas. Medium-dispersionlong-slit spectroscopy at several positions over the nuclear region hasbeen used to obtain the gaseous velocity field and the distribution ofexcitation. The gaseous kinematics indicate large central massconcentrations in the three galaxies. The two galaxies with LINER nucleiappear to have two inner Lindblad resonances, with the star-formingrings located between them. The high sensitivity of the data has allowedus to detect faint ionized gas with high [N II]/Hα ratios-a warmionized medium-up to several kiloparsecs from the nuclei. We find acorrelation between the [NII]/Hα and [S II]/Hα ratios andthe FWHM of the [NII] λ6584 emission line. This correlation isstrongest for the circumnuclear gas but is also present in the warmionized medium of the two galaxies with LINER nuclei, suggesting thatshocks contribute to the ionization of the gas. From long-slitspectroscopy at low dispersion, we have obtained the chemicalcomposition of the H II regions in the ring and far beyond. The highestcentral metallicities (O/H ~ 2 times solar and N/O ~ 3 times solar) werefound around the two LINER nuclei, confirming previous results based onspectroscopy of the narrow-line region that LINER nuclei have abundancesconsiderably in excess of solar. Nevertheless, these abundances aresimilar to those of the nuclei of non- active galaxies with the samemorphological type and absolute magnitude.
|Multiband Images of the Barred Galaxy NGC 1097|
We present B, V, R, J, H, and K broadband images of the barred galaxyNGC 1097. The optical and infrared colors maps trace the location of themajor dust features. The dust lanes are relatively free of starformation and have low opacity. The depth of the dust lanes decreases asa function of wavelength so that they are deepest at B and shallower atH and K where they are difficult to detect. We find that the dust laneon the Northwest side of the galaxy has colors consistent with those ofa dust screen with opacity derived from the galactic extinction law.Thus, it must be located on the near side of the galaxy. The colors inthe dust lane on the Southeast side of the galaxy, on the other hand,suggest that there are stars both in front of and behind the dust,consistent with this dust lane being located on the far side of thegalaxy. From the K images, we estimate that the total stellar mass ofthe star forming spiral ring at a radius of - 1 kpc from the nucleus isof the same order as the molecular gas mass in the ring. The infraredimages show a short bar inside the inner spiral ring. In the principalplane of the galaxy, the short bar is not perpendicular to the prominentouter bar. This suggests that there are torques between the inner barand the spiral ring and that this inner bar may have a pattern speeddifferent from the outer bar. Near the inner spiral ring (at ~17" = 1.4kpc from the nucleus), the dust lane becomes double peaked with a peakto valley extinction ratio similar to that observed in radio continuumby Ondrechen & van der Hulst (1983). This suggests that if the colddiffuse component of the interstellar medium (traced by the dust) moveswith the cosmic ray electron component then the magnetic field pressureis not a significant force in the shocks. Alternatively if the twophases do not move together a more detailed comparison may showdifferences in the shock shapes.
|General study of group membership. II - Determination of nearby groups|
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
|A Weak Interaction Model for Shell Galaxies|
We describe numerical simulations which show the formation of shellstructures in spherical galaxy systems. The model simulates theinteraction of a primary galaxy of test particles with another galaxy.The test-particle orbits are initially near-circular (but not coplanar)and the effect of changing the perigalactic distance of the encounter,the secondary mass, and heating the particles (by adding random motions)is described. Our results show that shell structures, similar to thoseobserved in many elliptical galaxies, can be formed by this process, andremain visible for about 10^10^ yr. If this model is correct, then itimplies that (at least some) elliptical galaxies have thick discs andthat the underlying galaxies are predominantly oblate spheroids.
|H I in barred spiral galaxies. II - NGC 1097|
H I observations of the southern barred spiral galaxy NGC 1097 have beenmade with about 25 arcsec resolution. The H I is found in the prominentspiral arms and in the bar. Noncircular motions are clearly present inand around the bar and can be understood in terms of existing gas flowmodels. The spiral arms exhibit large streaming motions as found ingalaxies with strong density waves. The outer regions, in particular tothe northwest, are somewhat disturbed, most likely due to gravitationalinteraction with the small companion galaxy.
|Surface photometry of southern elliptical galaxies|
The results of a surface photometry survey for 131 elliptical galaxiesin the southern hemisphere are presented. In this paper isophotal mapsand major-axis profiles are shown, deriving for each galaxy in thesample structural parameters using the de Vaucouleurs law as usefulparametric descriptor of the light distribution of elliptical galaxies.
|A collisional model for the formation of ripples in early-type disk galaxies|
Restricted three-body calculations of high-inclinationlow-impact-parameter encounters between a disk galaxy and its companionare used to demonstrate that the shell-like ripples noted in a number ofdisk galaxies are also collisional artifacts. It is suggested that someof the ripples may be the results of internal oscillations followingsuch encounters. It is assumed that the target is an early-type diskwith a sufficiently low gas fraction that recent star formation does notdominate the appearance of the disturbed disk.
|Radio emission from shell elliptical galaxies|
A subset of the Malin & Carter catalogue of 'shell ellipticalgalaxies' has been surveyed at 20 and 6 cm with the VLA. Forty-two percent of the galaxies were detected, down to a 6-cm flux density limit ofabout 0.6 mJy. This detection rate does not differ significantly from anormal population of mixed elliptical and S0 galaxies. Most of the radiodetections, which are sources coincident with the galaxy nuclei, areunresolved by the C-array and so have angular sizes of less than 3arcsec. The sample contains objects with a wide variety of opticalappearances, suggesting that shell galaxies are not a homogenoeus classwith uniform physical characteristics.
|Spectroscopy and photometry of elliptical galaxies. III - UBV aperture photometry, CCD photometry, and magnitude-related parameters|
Photoelectric aperture photometry of nearly 2000 individual observationsof 449 elliptical galaxies combined with published measurements usingthe self-consistent UVB color catalog developed by Burstein et al.(1987) are presented. The data are placed on a standard magnitude andcolor system, and 'total' magnitudes and effective diameters are derivedby comparison with the standard elliptical magnitude growth curve. Agraphical representation of the standard growth curve and the residualsfrom it for each galaxy are given, and a new diameter measurement Dn ispresented which can be measured reliably for elliptical galaxies andserves as an accurate distance indicator when combined with centralvelocity dispersion. Individual magnitudes, surface brightnesses,effective diameters, and values of Dn are summarized for each galaxy incatalog form.
|Mass-to-Light Ratios of Binary Galaxies. III. Analysis|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987ApJS...64..427S&db_key=AST
|A catalogue of early-type galaxies with emission lines|
Spectroscopic and photometric data on 289 early-type galaxies (E and S0)with optical emission lines are presented and possible correlationsamong properties of the galaxies in the sample are investigated. Theoccurrence of phenomena as radio emission, presence of neutral hydrogenand dust shows an increase in comparison with the occurrence of the samephenomena in these morphological classes as a whole. There is noevidence of a relationship between apparent shape and presence ofionized gas in the central regions.
|Southern Galaxy Catalogue.|
|Redshifts for 228 southern galaxies|
In this paper, new redshifts are presented for 228 galaxies locatedsouth of declination -30 deg. The observations were made with aphoton-counting Reticon detector on the Observatorio Nacional (ON)60-in. telescope. The detector is identical to the one used at MountHopkins for the CfA Redshift Survey, and the redshifts were derivedusing the same data-analysis system. A preliminary comparison withpublished 21-cm redshifts indicates that the velocities have azero-point offset of about -4 km/s, with a typical uncertainty of 40km/s. The observations reported here are the initial results of theON-CfA Redshift Survey currently being undertaken in the southernhemisphere.
|A 5-GHz survey of bright Southern elliptical and S0 galaxies|
The Parkes 64-m telescope has been used in a 5.0-GHz survey of 181Southern E and S0 galaxies from the Reference catalogue of brightgalaxies. Of the 39 detections above the nominal limit of 12 mJy, 15 arenew, several have radio spectra indicating membership in the activeclass, and two have shown intensity variations at centimeterwavelengths. The results of this survey combined with results fromearlier surveys of lower sensitivity suggest that only about 40 per centof the E/S0 galaxies in the Reference catalogue have a flux density at 5GHz exceeding 1 mJy.
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