Home     Getting Started     To Survive in the Universe    
Inhabited Sky
    News@Sky     Astro Photo     The Collection     Forum     Blog New!     FAQ     Press     Login  

NGC 6215



Upload your image

DSS Images   Other Images

Related articles

Constraining Dark Matter Halo Profiles and Galaxy Formation Models Using Spiral Arm Morphology. I. Method Outline
We investigate the use of spiral arm pitch angles as a probe of diskgalaxy mass profiles. We confirm our previous result that spiral armpitch angles (P) are well correlated with the rate of shear (S) in diskgalaxy rotation curves by using a much larger sample (51 galaxies) thanused previously (17 galaxies). We use this correlation to argue thatimaging data alone can provide a powerful probe of galactic massdistributions out to large look-back times. In contrast to previouswork, we show that observed spiral arm pitch angles are similar whenmeasured in the optical (at 0.4 μm) and the near-infrared (at 2.1μm) with a mean difference of 2.3d+/-2.7d. This is then used tostrengthen the known correlation between P and S using B-band images. Wethen use two example galaxies to demonstrate how an inferred shear ratecoupled with a bulge-disk decomposition model and a Tully-Fisher-derivedvelocity normalization can be used to place constraints on a galaxy'sbaryon fraction and dark matter halo profile. We show that ESO 582-G12,a galaxy with a high shear rate (slightly declining rotation curve) at~10 kpc, favors an adiabatically contracted halo, with high initial NFWconcentration (cvir>16) and a high fraction of halobaryons in the form of stars (~15%-40%). In contrast, IC 2522 has a lowshear rate (rising rotation curve) at ~10 kpc and favorsnonadiabatically contracted models with low NFW concentrations(cvir~=2-8) and a low stellar baryon fraction <10%.

Stellar abundance gradients in galactic discs - I. Method and spectral line gradients
We describe the technique of absorption-line imaging of galaxy discsusing the Taurus Tunable Filter on the Anglo-Australian Telescope anddemonstrate its sensitivity to the behaviour of spectral featuresassociated with Mg and Fe. Radial profiles of Mg2 and Fe5270line strengths are presented for a sample of eight face-on spiralgalaxies spanning a range of Hubble types. Signatures of phenomenaincluding merger-induced star formation, HII rings and galactic bars arealso reported. This study demonstrates the capacity of tunable filtersto measure Mg and Fe line strengths across the face of spiral galaxies,which can ultimately reveal clues about the star formation history andchemical evolution.

A wide-field HI study of the NGC 1566 group
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.

The Distribution of Bar and Spiral Arm Strengths in Disk Galaxies
The distribution of bar strengths in disk galaxies is a fundamentalproperty of the galaxy population that has only begun to be explored. Wehave applied the bar-spiral separation method of Buta and coworkers toderive the distribution of maximum relative gravitational bar torques,Qb, for 147 spiral galaxies in the statistically well-definedOhio State University Bright Galaxy Survey (OSUBGS) sample. Our goal isto examine the properties of bars as independently as possible of theirassociated spirals. We find that the distribution of bar strengthdeclines smoothly with increasing Qb, with more than 40% ofthe sample having Qb<=0.1. In the context of recurrent barformation, this suggests that strongly barred states are relativelyshort-lived compared to weakly barred or nonbarred states. We do notfind compelling evidence for a bimodal distribution of bar strengths.Instead, the distribution is fairly smooth in the range0.0<=Qb<0.8. Our analysis also provides a first look atspiral strengths Qs in the OSUBGS sample, based on the sametorque indicator. We are able to verify a possible weak correlationbetween Qs and Qb, in the sense that galaxies withthe strongest bars tend to also have strong spirals.

Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.

Neutral hydrogen gas in interacting galaxies: the NGC 6221/6215 galaxy group
Neutral hydrogen observations of the spiral galaxies NGC 6221 and 6215with the Australia Telescope Compact Array (ATCA) reveal a wide,two-stranded bridge of at least 3 × 108Msolar which can be traced between the two galaxies over aprojected distance of 100 kpc. The velocity gradient of the HI bridgeprovides a rough estimate for the time since the encounter of 500 Myr.For NGC 6221, the brightest and most massive galaxy of the group, wederive a dynamical mass of Mtot= 8 × 1010Msolar, while its companion NGC 6215 has a mass of onlyMtot~ 2 × 109 Msolar. Further, wefind three low-surface-brightness dwarf galaxies (Dwarfs 1, 2 and 3) inthe neighbourhood of NGC 6221/15 with HI masses of 3.3, 0.6 and 0.3× 108 Msolar, respectively. The smallest,previously uncatalogued galaxy, Dwarf 3, lies between NGC 6221 and 6215,and may have formed out of bridge material.The brightest part of the HI bridge lies roughly halfway between theinteracting galaxies, indicating that bridge gas close to NGC 6221 and6215 may have fallen back to the galaxies. The asymmetric extensions tothe HI envelope of NGC 6221 are likely to be reaccreted gas, stillsettling in. Also, the peculiar velocity field of NGC 6215 may beexplained by accreted bridge material settling into a plane offset fromthe old disc.

HI Tidal Tails, Bridges and Clouds
There is plenty of intergalactic H I gas without any obvious stellarcontent ranging from (1) extended gas envelopes around some normal andpeculiar galaxies, (2) tidal tails/bridges in interacting or merginggalaxy systems, (3) large-scale rings around early type galaxies, and(4) detached clouds at varying distances from associated galaxies, butthere are few or no isolated H I clouds.The HIPASS Bright Galaxy Catalog, which covers the whole southern sky,contains only one definite extragalactic H I cloud which is locatedclose to the galaxy NGC 2442 whereas it is sensitive to isolated H Iclouds with MHI > 106 × D2Mȯ. The space density of H I clouds is therefore about1/1000th that of galaxies with the same MHI.

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).

Deprojecting spiral galaxies using Fourier analysis. Application to the Ohio sample
We use two new methods developed recently (Barberàet al.\cite{bar03}, A&A, 415, 849), as well as information obtained fromthe literature, to calculate the orientation parameters of the spiralgalaxies in the Ohio State University Bright Galaxy Survey. We comparethe results of these methods with data from the literature, and find ingeneral good agreement. We provide a homogeneous set of mean orientationparameters which can be used to approximately deproject the disks of thegalaxies and facilitate a number of statistical studies of galaxyproperties.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/421/595

Extragalactic large-scale structures behind the southern Milky Way. IV. Redshifts obtained with MEFOS
As part of our efforts to unveil extragalactic large-scale structuresbehind the southern Milky Way, we here present redshifts for 764galaxies in the Hydra/Antlia, Crux and Great Attractor region(266o ≤ℓ ≤338o, | b | 10o), obtained with the Meudon-ESO Fibre Object Spectrograph(MEFOS) at the 3.6-m telescope of ESO. The observations are part of aredshift survey of partially obscured galaxies recorded in the course ofa deep optical galaxy search behind the southern Milky Way(Kraan-Korteweg \cite{Kra00a}; Woudt & Kraan-Korteweg \cite{Wou01}).A total of 947 galaxies have been observed, a small percentage of thespectra (N = 109, 11.5%) were contaminated by foreground stars, and 74galaxies (7.8%) were too faint to allow a reliable redshiftdetermination. With MEFOS we obtained spectra down to the faintestgalaxies of our optical galaxy survey, and hence probe large-scalestructures out to larger distances (v  30 000 km s-1)than our other redshift follow-ups using the 1.9-m telescope at theSouth African Astronomical Observatory (Kraan-Korteweg et al.\cite{Kra95}; Fairall et al. \cite{Fai98}; Woudt et al. \cite{Wou99})and the 64-m Parkes radio telescope (Kraan-Korteweg et al.\cite{Kra02}). The most distinct large-scale structures revealed in thesouthern Zone of Avoidance are discussed in context to known structuresadjacent to the Milky Way.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/9 Based onobservations taken at the European Southern Observatory, La Silla,Chile.

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.

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.

An Infrared Space Observatory Atlas of Bright Spiral Galaxies
In this first paper in a series we present an atlas of infrared imagesand photometry from 1.2 to 180 μm for a sample of bright spiralgalaxies. The atlas galaxies are an optically selected,magnitude-limited sample of 77 spiral and S0 galaxies chosen from theRevised Shapley-Ames Catalog (RSA). The sample is a representativesample of spiral galaxies and includes Seyfert galaxies, LINERs,interacting galaxies, and peculiar galaxies. Using the Infrared SpaceObservatory (ISO), we have obtained 12 μm images and photometry at60, 100, and 180 μm for the galaxies. In addition to its imagingcapabilities, ISO provides substantially better angular resolution thanis available in the IRAS survey, and this permits discrimination betweeninfrared activity in the central regions and global infrared emission inthe disks of these galaxies. These ISO data have been supplemented withJHK imaging using ground-based telescopes. The atlas includes 2 and 12μm images. Following an analysis of the properties of the galaxies,we have compared the mid-infrared and far-infrared ISO photometry withIRAS photometry. The systematic differences we find between the IRASFaint Source Catalog and ISO measurements are directly related to thespatial extent of the ISO fluxes, and we discuss the reliability of IRASFaint Source Catalog total flux densities and flux ratios for nearbygalaxies. In our analysis of the 12 μm morphological features we findthat most but not all galaxies have bright nuclear emission. We find 12μm structures such as rings, spiral arm fragments, knotted spiralarms, and bright sources in the disks that are sometimes brighter thanthe nuclei at mid-infrared wavelengths. These features, which arepresumably associated with extranuclear star formation, are common inthe disks of Sb and later galaxies but are relatively unimportant inS0-Sab galaxies. Based on observations with the Infrared SpaceObservatory (ISO), an ESA project with instruments funded by ESA MemberStates (especially the PI countries: France, Germany, Netherlands, andUnited Kingdom) and with the participation of ISAS and NASA.

The Obscuring Starburst of NGC 6221 and Implications for the Hard X-Ray Background
We present NGC 6221 as a case study of ``X-ray-loud compositegalaxies,'' which appear similar to starbursts at optical wavelengthsand resemble traditional active galactic nuclei in X-rays. The netoptical spectrum of NGC 6221 is properly characterized as a starburstgalaxy, but in X-rays, NGC 6221 is similar to Seyfert 1 galaxies,exhibiting a power-law continuum spectrum, a broad Fe Kα line, andcontinuum variability on timescales of days and years. High-resolutionimages reveal that the detected active nucleus is relatively weak, notonly at optical, but also at near-infrared wavelengths. An obscuringstarburst, in which the interstellar gas and dust associated with thestarburst conceal the active nucleus, accounts for these peculiarfeatures. We demonstrate quantitatively that obscuration by columndensity NH=1022 cm-2 combined withrelatively weak intrinsic nuclear activity can produce an opticalspectrum that is characteristic of the surrounding starburst alone.While optical surveys would not identify the active nuclei that makethese galaxies significant X-ray sources, such galaxies may, in fact, beimportant contributors to the X-ray background.

A catalogue of galaxies behind the southern Milky Way. II. The Crux and Great Attractor regions (l~ 289o to 338o)
In this second paper of the catalogue series of galaxies behind thesouthern Milky Way, we report on the deep optical galaxy search in theCrux region (289o <= l <= 318o and-10o <= b <= 10o) and the Great Attractorregion (316o <= l <= 338o and-10o <= b <= 10o}). The galaxy cataloguesare presented, a brief description of the galaxy search given, as wellas a discussion on the distribution and characteristics of the uncoveredgalaxies. A total of 8182 galaxies with major diameters D >~ 0.2arcmin were identified in this ~ 850 square degree area: 3759 galaxiesin the Crux region and 4423 galaxies in the Great Attractor region. Ofthe 8182 galaxies, 229 (2.8%) were catalogued before in the optical (3in radio) and 251 galaxies have a reliable (159), or likely (92)cross-identification in the IRAS Point Source Catalogue (3.1%). A numberof prominent overdensities and filaments of galaxies are identified.They are not correlated with the Galactic foreground extinction andhence indicative of extragalactic large-scale structures. Redshiftsobtained at the South African Astronomical Observatory (SAAO) for 518 ofthe newly catalogued galaxies in the Crux and Great Attractor regions(Fairall et al. \cite{Fairall98}; Woudt et al. \cite{Woudt99}) confirmdistinct voids and clusters in the area here surveyed. With this opticalgalaxy search, we have reduced the width of the optical ``Zone ofAvoidance'' for galaxies with extinction-corrected diameters larger than1.3 arcmin from extinction levels AB >= 1.0m toAB >= 3.0m: the remaining optical Zone of Avoidance is nowlimited by | b | <~ 3o (see Fig. \ref{cruxf1new}). The twooptical catalogues and their respective listings of IRAScross-identifications are available in electronic format at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/380/441

^13CO (J=1-0) Depression in Luminous Starburst Mergers, Revisited
It is known that merging galaxies with luminous starbursts and highfar-infrared luminosities tend to have higher R_1-0=^12CO (J=1-0)/^13CO(J=1-0) integrated line intensity ratios (R_1-0~=20-50) than normalspiral galaxies (R_1-0~=5-15). Comparing far-infrared luminosities[L(FIR)] with those of ^12CO (J=1-0) and ^13CO (J=1-0) for a sample ofnormal and starburst galaxies, Taniguchi & Ohyama found that theobserved high R_1-0 values for the luminous starburst mergers areattributed to their lower (by a factor of 3 on average) ^13CO lineintensities. They suggested the following two possibilities: in theluminous starburst mergers (1) ^13CO is underabundant with respect to^12CO, or (2) exitation and/or optical depth effects are responsible forthe change in R_1-0. In this paper, we investigate the secondpossibility, using higher transition data of both ^12CO and ^13COemission lines. Applying the same method proposed by Taniguchi &Ohyama to both ^12CO (J=2-1) and ^13CO (J=2-1), we find that ^13CO(J=2-1) is also depressed with respect to ^12CO (J=2-1). This suggeststhat the ^13CO gas may be underabundant in the high-R_1-0 starburstmergers, although we cannot rule out the possibility that excitation andoptical depth effects are still affecting R_2-1, for example, as aresult of the large velocity widths in the CO emission lines. Additionalobservations of both ^12CO and ^13CO lines at J>=3 are required tobetter constrain the conditions of the molecular gas in luminousstarburst galaxies.

Cosmic Masks Still Dance
The Hubble classification scheme of galaxies is based on their opticalappearance or `masks'. As one goes from early to late type spirals, bothbarred and unbarred, the optical appearance will be dominated more andmore by the young Population I, i.e., blue stars and dust. Atlasesreveal the rich variety of responses of the Population I component ofgas and dust (the mask) to the underlying, older, stellar population.However, the gaseous Population I component, may only constitute 5percent of the dynamical mass of the galaxy. Masks of negligible massmay conceal the human face - and that of galaxy. In the near-infrared,the morphology of older star-dominated disk indicates a simpleclassification scheme: the dominant Fourier m-mode in the dustpenetrated regime, and the associated pitch angle. A ubiquity of low m=1and m=2 modes is confirmed. On the basis of deprojected H (1.65 μm)and K' (2.1μm) images, we propose that the evolved stellar disks maybe grouped into three principal dust penetrated archetypes: those withtightly wound stellar arms characterised by pitch angles at K' of ~10^° (the α class), an intermediate group with pitch angles of~ 25^° (the β class) and thirdly, those with open spiralsdemarcated by pitch angles at K' of ~ 40^° (the γ bin). Flator falling rotation curves give rise to the tightly wound α class;rising rotation curves are associated with the open γ class. Theobserved dust penetrated classes are inextricably related to the rate ofshear in the stellar disk, as determined by A/ω. Here A is thefirst Oort constant andω denotes the angular velocity. There is nocorrelation between our dust penetrated classes and optical Hubblebinning; the Hubble tuning fork does not constrain the morphology of theold stellar Population II disks. NGC 3223 and NGC 7083 (both SbI-II andalmost the same absolute blue magnitude) have identical Hubble types andidentical luminosity classes; the dust penetrated disk of NGC 3223 hastightly wrapped arms of class α, whereas the near-infrared disk ofNGC 7083 has open arms of class γ. This is in turn associated withtheir very different rotation curve shapes yielding different rates ofshear A/ω in their stellar disks. Any specific dust penetratedarchetype may be the resident disk of both an early or late type galaxy.The number of arms and the pitch angle of the arms at K' of theearly-type `a' spiral NGC 718 are almost identical to those for thelate-type `c' spiral NGC 309. We demonstrate that galaxies on oppositeends of the tuning fork can display remarkably similar evolved diskmorphologies and belong to the same dust penetrated class. In thissense, there is no differentiation between an early and late typegalaxy: the Hubble tuning fork becomes a circle. Furthermore, aprototypically flocculent galaxy such as NGC 5055 (Elmegreen arm class3) can have an evolved disk morphology almost identical to that of NGC5861, characterised in the optical as having one of the most regularspiral patterns known and of Elmegreen class 12. Both opticallyflocculent or grand design galaxies can reside within the same dustpenetrated morphological bin. As was suggested by Block et al. (1994a),it is the gas dominated Population I component which determines theoptical types (a, b, c). This may be partially or even fully decoupledfrom the Population II disk. Those L=lopsided galaxies (where m=1 is adominant mode) are designated Lα, Lβ and Lγ accordingto the dust penetrated pitch angle; E=evensided galaxies (where m=2 isthe dominant Fourier mode) are classified into classes Eα, Eβand Eγ, according to our three principal dust penetratedarchetypes. The L and E modes are the most common morphologies in oursample, which spans a range of Hubble types from early (a) to late(irregular).

Extragalactic large-scale structures behind the southern Milky Way. III. Redshifts obtained at the SAAO in the Great Attractor region
In the third of a series of papers on large-scale structures behind thesouthern Milky Way, we report here on redshifts obtained at the SouthAfrican Astronomical Observatory (SAAO) in the Great Attractor region(318deg <~ l <~ 340deg , |b| <= 10deg , Woudt 1998). Thisregion encompasses the peak in the reconstructed mass density field,associated with the Great Attractor (Kolatt et al. 1995, Dekel et al.1998) and covers the crossing of the Supergalactic Plane with theGalactic Plane. Our deep optical galaxy search in the Zone of Avoidance(ZOA) in this region (Woudt 1998) has resulted in the detection of 4423galaxies with observed diameters larger than 0.2 arcmin. We haveobtained reliable redshifts for 309 galaxies of the 4423 galaxies withthe ``Unit'' spectrograph (first with a Reticon, then with a CCDdetector) at the 1.9-m telescope of the SAAO. An additional 13 tentativeredshifts are presented. Before our survey, 127 galaxies had apreviously recorded redshift (NED and SRC96). Given a small overlap withthe literature (44 galaxies), we present here redshifts for 265 galaxiesthat had no previous recorded velocity. In addition, we present centralvelocity dispersion (sigma_o ) measurements for 34 galaxies in ACO 3627.It is known that the Great Attractor (GA) region is overdense ingalaxies at a redshift-distance of v ~ 5000 {km s-1 }(Fairall 1988, Dressler 1991, Visvanathan & Yamada 1996, di Nella etal. 1997). We realise here, however, that the Great Attractor region isdominated by ACO 3627 (hereafter referred to as the Norma cluster), ahighly obscured, nearby and massive cluster of galaxies close to theplane of the Milky Way (l, b, v) = (325.3deg , -7.2deg , 4844 {kms-1 }) (Kraan-Korteweg et al. 1996, Woudt 1998). Previousredshift surveys in the GA region have failed to gauge the significanceof the Norma cluster, primarily due to the diminishing effects of theGalactic foreground extinction on the partially obscured galaxies. Inthe absence of the obscuring effects of the Milky Way, the Norma clusterwould have appeared as prominent as the well-known Coma cluster, butnearer in redshift-space. This cluster most likely marks the bottom ofthe potential well of the Great Attractor (Woudt 1998). All the tablesare only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html

^13CO (J = 1-0) Depression in Luminous Starburst Mergers
It is known that the class of luminous starburst galaxies tends to havehigher R=^12CO (J=1-0)/^13CO (J=1-0) integrated line intensity ratios(R>20) than normal spiral galaxies (R~10). Since most previousstudies investigated only R, it remains uncertain whether the luminousstarburst galaxies are overabundant in ^12CO or underabundant in ^13CO.Here we propose a new observational test to examine this problem. Ournew test is to compare far-infrared luminosities [L(FIR)] with those of^12CO and ^13CO [L(^12CO) and L(^13CO), respectively]. It is shown thatthere is a very tight correlation between L(^12CO) and L(FIR), as foundin many previous studies. However, we find that the ^13CO luminositiesof the high-R galaxies are lower by a factor of 3 on average than thoseexpected from the correlation for the remaining galaxies with ordinary Rvalues. Therefore, we conclude that the observed high R values for theluminous starburst galaxies are attributed to their lower ^13CO lineintensities.

Mixed early and late-type properties in the bar of NGC 6221: Evidence for evolution along the Hubble sequence?
Rotation curves and velocity dispersion profiles are presented for boththe stellar and gaseous components along five different position angles(PA =5(deg) , 50(deg) , 95(deg) , 125(deg) , and 155(deg) ) of thenearby barred spiral NGC 6221. The observed kinematics extends out toabout 80'' from the nucleus. Narrow and broad-band imaging is alsopresented. The radial profiles of the fluxes ratio [N II] (lambda 6583.4Angstroms )/Hα reveal the presence of a ring-like structure ofionized gas, with a radius of about 9'' and a deprojected circularvelocity of about 280 km;s(-1) . The analysis of the dynamics of the barindicates this ring is related to the presence of an inner Lindbladresonance (ILR) at 1.3 kpc. NGC 6221 is found to exhibit intermediateproperties between those of the early-type barred galaxies: the presenceof a gaseous ring at an ILR, the bar edge located between the ILR's andthe corotation radius beyond the steep rising portion of the rotationcurve, the dust-lane pattern, and those of the late-type galaxies: analmost exponential surface brightness profile, the presence of Hαregions along all the bar, the spiral-arm pattern. It is consistent withscenarios of bar-induced evolution from later to earlier-type galaxies.Tables 3, 4, 5, 6, 7 and 8 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html Based on observations collectedat the European Southern Observatory, La Silla (Chile).

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.

H i in Starburst Galaxies
Not Available

Unveiling a connection between large-scale structures behind the southern Milky Way
A redshift survey of galaxies located in the direction of the southernMilky Way has been carried out using the FLAIR multi-objects system onthe 1.2-m UK Schmidt Telescope (UKST) at the Anglo-AustralianObservatory in Australia. The galaxy sample was extracted from the LEDAand COSMOS data bases, but essentially by scanning by eye four plates ofthe UKST/SERC Survey in the region between the Centaurus complex and thePavo-Indus (PI) wall. The galaxies selected have high central surfacebrightnesses and are distributed evenly over the whole search area. Themajority of the galaxies have apparent magnitudes in the range11.5

Scaleheights of 486 southern spiral galaxies and some statistical correlation
Based on Peng's method (1988), we obtain scaleheights of 486 southernspiral galaxies, the images of which are taken from the Digitized SkySurvey at Xinglong Station of Beijing Astronomical Observatory. Thefitted spiral arms of 70 galaxies are compared with their images to gettheir optimum inclinations. The scaleheights of other 416 ones arelisted in Table A1 in Appendix. After compiling and analyzing the data,we find some statistical correlations. The most interesting results arethat a flatter galaxy is bluer and looks brighter, and galaxies becomeflatter along the Hubble sequence Sab -- Scd. Based on photographic dataof the National Geographic Society -- Palomar Observatory Sky Survey(NGS-POSS) obtained using the Oschin Telescope Palomar Mountain. TheNGS-POSS was funded by a grant from the National Geographic Society tothe California Institute of Technology. The plates were processed intothe present compressed digital form with their permission. The DigitizedSky Survey was produced at the Space Telescope Science Institute underUS Government grant NAG W-2166. Table A1 is available in electronic fromonly, via anonymous ftp orhttp://cdsweb.u-strasbg.fr/Abstract.html

CA depletion and the presence of dust in large scale nebulosities in radiogalaxies. II.
We investigate here the origin of the gas observed in extended emissionline regions surrounding AGNs. We use the technique of calcium depletionas a test to prove or disprove the existence of dust in such a gas inorder to discriminate between two main theories: (1) a cooling processfrom a hotter X-ray emitting phase surrounding the galaxy, (2) mergingor tidal interaction between two or more components. We have obtainedlong slit spectroscopy of a sample of objects representative ofdifferent galaxy types although our main interest focusses on radiogalaxies. The spectral range was set to always include the[CaII]λλ7291,7324 doublet. The faintness or absence ofsuch lines is interpreted as due to the depletion of calcium onto thedust grains and, therefore, is a proof of the existence of dust mixedwith the gas in the EELRs.

Molecular hydrogen in the central regions of southern infrared galaxies
An extensive set of molecular hydrogen observations of centers ofsouthern infrared galaxies is presented. Our data are combined withpublished infrared and radio observations to investigate therelationship between nuclear and circumnuclear activity. We convert theobservational data to absolute luminosities, by applying the knowndistances. The resulting dataset covers several decades in luminosityfor the various parameters, which observe fairly tight correlations. Theparameters of our (power law) fits are, at the level of accuracyachieved, not dependent on the type of nuclear activity: while thedataset comprises a mixture of alleged Seyfert, Liner & starburstgalaxies, single fits match the complete sample well enough. Inparticular, non-thermal nuclei (AGN) present in some of the galaxies inthe current sample, do not stand out in the parameters we investigated.The absence of a significant dependence on the nuclear type isconsistent with the idea that the ever present starbursts energeticallydominate a possible `AGN in a dusty environment'-component in mostgalaxy nuclei with infrared excesses. The size of the H_2 emittingregion is found to be proportional to the square root of the 21 cm radiocontinuum luminosity. The excitation of the circumnuclear H_2 isdominated by shocks. If the H_2 extent marks the size of an inner cavityin the dense molecular material surrounding a galaxy nucleus and theradio luminosity is proportional to the mechanical luminosity of(circum)nuclear winds. This result then indicates that the cavity sizeoccurs at constant pressure in the sample galaxies, in accordance withthe superwind model by Heckman et al. (1990) [ApJS, 74, 833]. Ourresults, together with those obtained by others, thus suggest thatluminosities and size scales of excited gas associated with activenuclei are dominated by the mechanical energy input. Given thedifficulties of uniquely establishing the presence of an AGN, we cannotexclude that (a large fraction of the) infrared luminous galaxiesprocure part of their radiated energy through accretion onto a massivedark object.

Redshift Distribution of Galaxies in the Southern Milky Way Region 210 degrees < L < 360 degrees and B < 15 degrees
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..521V&db_key=AST

Dust and CO emission in normal spirals. I. The data.
We present 1300μm continuum observations and measurements of the CO(1-0) and (2-1) emission from the inner regions of 98 normal galaxies.The spatial resolution ranges from 11" to 45". The sources come from acomplete FIR selected sample of 138 inactive spirals with an opticaldiameter D_25_<=180".

Parsec-scale radio cores in spiral galaxies
We have used the Parkes-Tidbinbilla Interferometer to search for compact(<0.03 arcsec) radio continuum cores in 54 nearby spiral galaxies, 22of which have Seyfert nuclei. In contrast to the radio cores ofelliptical galaxies, the few parsec-scale cores seen in spirals usuallyhave steep radio spectra, with an apparent median spectral index of-1.0. At present, it is not clear whether this is because the radiocores of spiral galaxies are larger than those in ellipticals (and soare partly resolved by the interferometer), or whether the core spectraof ellipticals and spirals are intrinsically different.

Anisotropic emission, stellar population and X-ray sources in the Seyfert 2 galaxy ESO 138-G01
We present narrow-band CCD images of the high-excitation Seyfert 2galaxy ESO138-G01, centred on the emission lines [OIII] lambda5007,Hα+[NII] lambdalambda6548, 6584 and adjacent continua. Thecontinuum-subtracted [OIII] image presents an elongated jet-likestructure to the west of the nucleus which is only weakly visible in theHα image, and which we conclude is ionized by the nuclear source.The ionization map shows high excitation at the nucleus and at the`jet'. The continuum ratio map shows that this galaxy is very blue forits morphological type, consistent with the large contribution of ayoung stellar population up to 3kpc from the nucleus. We also proposethat ESO138-G01 is the hard X-ray source previously identified with thenearby galaxy NGC 6621.

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:16h51m07.30s
Aparent dimensions:2.399′ × 2.042′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 6215

→ Request more catalogs and designations from VizieR