Contents
Images
Upload your image
DSS Images Other Images
Related articles
Stellar populations and dust extinction in non-active and Seyfert spiral galaxies
Metallicity and age gradients of the stellar populations and dustextinction are studied for a sample of 32 non-active, seven type 1Seyfert (S1) and 17 type 2 Seyfert (S2) spiral galaxies. The samplegalaxies cover the whole range from face-on to edge-on view, and thevariation of the optical and near-infrared colour gradients in the discas a function of the inclination angle is investigated in order toseparate colour changes caused by population gradients from those due todust effects.The measurements show that the observed colour gradients in the discs ofthe non-active galaxies are significantly larger than those found forthe S1 and S2 galaxies. In the near-infrared wavelengths, however, thesedifferences disappear, and the colour gradients are the same for allthree galaxy types. No systematic differences are found between thecolour gradients of the discs of the S1 galaxies and those of the S2galaxies.The data are compared to model images of dusty galaxies with a varietyof age and metallicity gradients in the disc. The radial variations ofthe optical and near-infrared colours of the model galaxies arecalculated from the radial changes of the ages and the metallicities ofthe stars, using broad-band colours of a single stellar population. Thestellar content at a given position in the disc is determined by theaverage age, the metallicity and the star formation history.For the non-active galaxies, the observed colour gradients arerepresented best by a model with a metallicity gradient, with the innerregions of the stellar disc being more metal-rich than the outerregions. However, the presence of an age gradient, with the innerregions of the stellar disc being older than the outer regions, cannotbe ruled out. For the S1 and S2 galaxies, the comparison between dataand models indicates that the age and metallicity gradients in thestellar disc are small. As far as the internal dust extinction isconcerned, the comparison between data and models indicates that boththe non-active and the S2 galaxies show significant dust extinction, butthey are not optically thick.
| COLA. II. Radio and Spectroscopic Diagnostics of Nuclear Activity in Galaxies
We present optical spectroscopic observations of 93 galaxies taken fromthe infrared-selected COLA (compact objects in low-power AGNs) sample.These are all galaxies for which we have previously obtainedlow-resolution radio observations and high-resolution (<0.05")Australian Long Baseline Array snapshots. The sample spans the range offar-IR luminosities from normal galaxies to luminous infrared galaxiesand contains a significant number of galaxies involved in galaxy-galaxyinteractions. Of the galaxies observed, 78 (84%) exhibit emission linesindicating that they are either AGNs or actively forming stars(starburst galaxies). Using a newly developed, theoretically based,optical emission line scheme to classify the spectra, we find that 15%of the emission-line galaxies are Seyfert galaxies, 77% are starbursts,and the rest are either borderline AGN/starburst or show ambiguouscharacteristics. We find little evidence for an increase in the fractionof AGNs in the sample as a function of far-IR (FIR) luminosity, incontrast to previous studies, but our sample covers only a small rangein infrared luminosity(1010.5Lsolar<=LFIR<=1011.7 Lsolar), and thus a weak trend may be masked. Instead,as the infrared luminosity increases, so does the fraction of metal-richstarbursts, objects that on more traditional diagnostic diagrams wouldhave been classified as weak, low-ionization, narrow emission lineregions. As a whole the Seyfert galaxies exhibit a small, butstatistically significant, radio excess on the radio-FIR correlationcompared to the galaxies classified as starbursts. Compact (<0.05")radio cores are detected in 55% of the Seyfert galaxies, and thesegalaxies exhibit a significantly larger radio excess than the Seyfertgalaxies in which compact cores were not detected. Our results indicatethat there may be two distinct populations of Seyfert galaxies,``radio-excess'' Seyfert galaxies, which exhibit extended radiostructures and compact radio cores, and ``radio-quiet'' Seyfertgalaxies, in which the majority of the radio emission can be attributedto star formation in the host galaxy. No significant difference is seenbetween the IR and optical spectroscopic properties of Seyfert galaxieswith and without radio cores.
| Star Formation Rates in Interacting Starburst Galaxies
By narrowband imaging in Hα and in the adjacent red stellarcontinuum we have studied the rate and distribution of star formation in43 systems of luminous and ultraluminous IR galaxies currentlyundergoing interaction and merging. These galaxies are amongst the mostluminous at 60 μm and range in distance from ~50 up to 100 Mpc. Herewe present the Hα and the adjacent red-continuum narrowbandimages, and we compare the star formation rates derived from Hαwith those estimated from the IR luminosity. We find clear evidence forsubstantial extinction and obscuration of star-forming regions in theoptical. Without correction for reddening in the host galaxy orcorrection for [N II] contamination, the star formation rates derivedfor Hα are typically 0.5-1.0 dex lower than those estimated fromthe IR flux, and the scatter in the correlation is very large. However,an unexpected result is that when spectroscopic data are used toeliminate objects dominated by an active nucleus, to determine thegalaxian extinction, and to correct the Hα flux for both reddeningand for the contamination by the [N II] emission, a remarkably goodcorrelation emerges between the star formation rates estimated from theHα flux and those derived from the FIR continuum. In addition, astrong correlation is found between the extinction in the line-emittingregion, AHα, and the rate of star formation. Ourresults invalidate the use of Hα imaging as a reliable indicatorof star formation in starburst galaxies unless spectroscopic data arealso available. This has important implications for the determination ofstar formation rates in high-redshift galaxies. Finally, we find nocorrelation between the measured star formation rates, and theinteraction class, suggesting that the enhanced star formation ratestriggered by the interaction continue throughout the whole of themerging sequence.
| First Results from the COLA Project: The Radio-Far-Infrared Correlation and Compact Radio Cores in Southern COLA Galaxies
We present the first results from the COLA (compact objects in low-powerAGNs) project, which aims to determine the relationship between onefacet of AGN activity, the compact radio core, and star formation in thecircumnuclear region of the host galaxy. This will be accomplished bythe comparison of the multiwavelength properties of a sample of AGNswith compact radio cores to those of a sample of AGNs without compactcores and a matched sample of galaxies without AGNs. In this paper wediscuss the selection criteria for our galaxy samples and present theinitial radio observations of the 107 southern(δ<0deg) galaxies in our sample. Low-resolution ATCAobservations at 4.8, 2.5, and 1.4 GHz and high-resolution,single-baseline snapshots at 2.3 GHz with the Australian Long BaselineArray (LBA) are presented. We find that for the majority of the galaxiesin our sample, the radio luminosity is correlated with the far-infrared(FIR) luminosity. However, a small number of galaxies exhibit a radioexcess causing them to depart from the FIR-radio correlation. Compactradio cores are detected at fluxes greater than 1.5 mJy in nine of the105 galaxies observed with the LBA. The majority (8/9) of these galaxiesexhibit a radio excess, and 50% (7/14) of the galaxies that lie abovethe radio-FIR correlation by more than 1 σ have compact radiocores. The emission from the compact cores is too weak to account forthis radio excess, implying that there are radio structures associatedwith the compact cores that extend farther than the 0.05" resolution(corresponding to a linear scale 11-22 pc) of the LBA. There is noevidence that the radio luminosity of the compact cores is correlatedwith the FIR galaxy luminosity, indicating that the core contributeslittle to the overall FIR emission of the galaxy. The galaxies withcompact cores tend to be classified optically as AGNs, with two-thirds(6/9) exhibiting Seyfert-like optical emission line ratios, and theremaining galaxies classified either as composite objects (2/9) orstarburst (1/9). The galaxies classified optically as AGNs also exhibitthe largest radio excesses, and we therefore conclude that a large radioexcess on the radio-FIR correlation is a strong indication of an AGNwith a compact radio core.
| Disc scalelengths of non-active and active spiral galaxies
Disc scalelengths rD are determined for a sample of 32non-active and 28 active spiral galaxies from optical CCD images. For 21of the 32 non-active galaxies and 20 of the 28 active galaxies B, V, Rand I data have been obtained, while for the remaining galaxies only Band I images have been taken. For 18 of the 21 non-active galaxies,which are measured in all four passbands, rD decreasessystematically from B to I, whereas such a decrease is found for onlyfour of the 20 active galaxies with BVRI data. For the non-activegalaxies, the ratios rD(B)/rD(I),rD(V)/rD(I) and rD(R)/rD(I)increase systematically with increasing apparent ellipticity ɛof the galaxies. For the active galaxies, no systematic variation of anyof the ratios with increasing ɛ is found. The variation ofrD(B)/rD(I) with ɛ is compared with modelcalculations. For the non-active galaxies, the data are represented bestby a model with a stellar disc that has an intrinsic colour gradient andwith a central optical depth in the B band for face-on view ofτ0B=3. For the active galaxies, the best agreement between data andmodels is found for models with a stellar disc with no intrinsic colourgradient and no dust. The best-fitting model for the non-active galaxiesdoes not reproduce the data of the active galaxies. The main conclusionof this work is that structural differences seem to exist between thediscs of non-active and active galaxies. The non-active galaxies showsignificant colour gradients within their discs, whereas the activegalaxies do not. These gradients are probably caused by a combination ofan intrinsic colour gradient within the stellar disc, and dustextinction. Furthermore, the measurements indicate that the non-activegalaxies show significant dust extinction in the centre, but they areoptically thin in the outer regions. The active galaxies do not seem tohave intrinsic colour gradients within the stellar disc and they areoptically thin throughout the disc.
| Seeing Galaxies through Thick and Thin. IV. The Superposed Spiral Galaxies of NGC 3314
The superposed pair of spiral galaxies making up NGC 3314 offers aunique opportunity to trace the dust properties in a spiral galaxy. Weanalyze multicolor Hubble Space Telescope imaging, supported byground-based near-IR imaging and fiber-array spectroscopy, to measuredust extinction in the foreground Sc galaxy NGC 3314A, which is backlitby the Sb system NGC 3314B. The superposition allows us to measureextinctions over a wide range of galactocentric radii in the foregroundgalaxy from 0.4-4.5 kpc. In the outer half of the disk, the extinctionis strongly localized in discrete dust lanes, including some patcheswhose galactic setting is clear only because of associated Hαemission at the foreground velocity. These dust features show anextinction curve with a slope close to the Galactic mean (R=3.5+/-0.3)over a range in galactocentric radius from 1.6 to 3.8 kpc, with noradial trend. Using the I-K color of the background nucleus, we derivean extinction of AI=3.3 through the disk at a projecteddistance of 400 pc from the nucleus of NGC 3314A. The extinction in eventhe inner disk of NGC 3314A is quite patchy, since background Hαemission is detected from all parts of the system. Localanticorrelations between foreground and background line emissiondemonstrate that the dust is concentrated in star-forming regions, ashas been found for the blue light in several systems. The colors of thedust lanes in NGC 3314A that are projected only partially against thebackground disk indicate that the dust scale height in the foregrounddisk is substantially smaller than that of the stars. Thecolor-intensity behavior of the net light in these regions tracks thepredictions of a thin-layer model closely. Based on observations withthe NASA/ESA Hubble Space Telescope obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555.
| 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.
| BVRI surface photometry for a sample of 14 SB galaxies
Profiles of surface brightness, ellipticity and position angle obtainedfrom CCD-BVRI images are presented for a sample of 14 spiral galaxieswith 13 < B_T < 16.1. For these galaxies, exponential disccomponents were fitted to the profiles. A decrease of disc scalelengthsfrom B to I is found for 13 galaxies, while for one galaxy scalelengthsincrease from B to I. The scalelength ratios r_D(B)/r_D(I),r_D(V)/r_D(I) and r_D(R)/r_D(I) show a systematic increase withincreasing apparent ellipticity. The maximum variation is found forr_D(B)/r_D(I) which is 80 % larger for edge-on galaxies than for face-ongalaxies. Based on observations collected at the South AfricanAstronomical Observatory, Sutherland, Republic of South Africa.
| 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.
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| A Preliminary Classification Scheme for the Central Regions of Late-Type Galaxies
The large-scale prints in The Carnegie Atlas of Galaxies have been usedto formulate a classification scheme for the central regions oflate-type galaxies. Systems that exhibit small bright central bulges ordisks (type CB) are found to be of earlier Hubble type and of higherluminosity than galaxies that do not contain nuclei (type NN). Galaxiescontaining nuclear bars, or exhibiting central regions that are resolvedinto individual stars and knots, and galaxies with semistellar nuclei,are seen to have characteristics that are intermediate between those oftypes CB and NN. The presence or absence of a nucleus appears to be auseful criterion for distinguishing between spiral galaxies andmagellanic irregulars.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| Photometrically distinct nuclei in elliptical and early-type disks galaxies.
Not Available
| The extended 12 micron galaxy sample
We have selected an all-sky (absolute value of b greater than or equalto 25 deg) 12 micron flux-limited sample of 893 galaxies from the IRASFaint Source Catalog, Version 2 (FSC-2). We have obtained accurate totalfluxes in the IRAS wavebands by using the ADDSCAN procedure for allobjects with FSC-2 12 micron fluxes greater than 0.15 Jy and increasingflux densities from 12 to 60 microns, and defined the sample by imposinga survey limit of 0.22 Jy on the total 12 micron flux. Its completenessis verified, by means of the classical log N - log S andV/Vmax tests, down to 0.30 Jy, below which we have measuredthe incompleteness down to the survey limit, using the log N - log Splot, for our statistical analysis. We have obtained redshifts (mostlyfrom catalogs) for virtually all (98.4%) the galaxies in the sample.Using existing catalogs of active galaxies, we defined a subsample of118 objects consisting of 53 Seyfert 1s and quasars, 63 Seyfert 2s, andtwo blazars (approximately 13% of the full sample), which is the largestunbiased sample of Seyfert galaxies ever assembled. Since the 12 micronflux has been shown to be about one-fifth of the bolometric flux forSeyfert galaxies and quasars, the subsample of Seyferts (includingquasars and blazars) is complete not only to 0.30 Jy at 12 microns butalso with respect to a bolometric flux limit of approximately 2.0 x10-10 ergs/s/sq cm. The average value of V/Vmaxfor the full sample, corrected for incompleteness at low fluxes, is 0.51+/- 0.04, expected for a complete sample of uniformly distributedgalaxies, while the value for the Seyfert galaxy subsample is 0.46 +/-0.10. We have derived 12 microns and far-infrared luminosity functionsfor the AGNs, as well as for the entire sample. We extracted from oursample a complete subsample of 235 galaxies flux-limited (8.3 Jy) at 60microns. The 60 micron luminosity function computed for this subsampleis in satisfactory agreement with the ones derived from the brightgalaxy sample (BGS) and the deep high-galactic latitude sample, bothselected at 60 microns.
| 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.
| The velocity field of clusters of galaxies within 100 megaparsecs. I - Southern clusters
Distances from the Tully-Fisher relation have been measured with theParkes radio telescope for eight additional southern clusters ofgalaxies in the redshift range 2500-5000 km/s. Most of them have large(average 1000 km/s) positive peculiar velocities in a comoving frame inwhich the microwave background radiation shows no dipole anisotropy. Infive out of eight cases these measurements have a significance at orabove the 2-sigma level. Outflow is seen on both sides of the Galacticplane. The source of this large-scale flow, if gravitational in orgin,lies at or beyond the limit of the present sample.
| Planetary nebula with a neutral envelope?
The IUE ultraviolet spectral recording for a low excitating planetarynebula NGC 6369 is obtained. The very strong doublet 2800 Mg II inemission as well as not less strong absorption line 2852 Mg I arediscovered in the spectrum of this nebula. It is shown that theresonance line 2852 Mg I may originate only in a neutral envelope,around the nebula, consisting of neutral hydrogen, neutral magnesium,and dust particles (H I + Mg I). The possibility of the existence of onemore envelope, transition zone immediately contacting with the brightthat is ionized part of nebula (H II + Mg II), is also shown. Thetransition zone consists of neutral hydrogen, ionized magnesium and dustparticles (H I + Mg II). The main parameters of this zone are alsoobtained. The temperature of the central star of this nebula is 48,000K. Continuous background in the interval 2600-3000 A is identified withBalmer continuum, with electron temperature T(c) = 12,500 K.
| The surface brightness test for the expansion of the universe. II - Radii, surface brightness, and absolute magnitude correlations for nearby E galaxies
Data for elliptical galaxies in the Virgo, Fornax, and Coma clusters andin the general field are analyzed in order to determine the dispersionin average surface brightness. The data are discussed using measures ofboth the effective radius and the Petrosian r(eta) radii. The dispersionis found to be about 0.5 mag after reducing the data to absolutemagnitude M(B) = -22. This value is smaller than the 1.8 mag Tolman (1 +z) exp 4 factor, even at the modest redshift of z = 0.5, showing thatthe Tolman test is feasible in practice as well as in principle.
| The Hubble relation - Differences between galaxy types SB and SC
It is shown that the Sb galaxies have apparent magnitudes which varyalmost exactly as if their redshifts were a measure of the distance atwhich they are observed, while the Sc do not exhibit a linear Hubblerelation. An attempt is made to determine whether the Sc discordancefrom the Hubble law is caused by Malmquist bias operating in thisfainter luminosity class of galaxies or there are inherent fundamentalpeculiarities. To this purpose the search is undertaken for other kindsof galaxies physically associated which these deviating Sc's. It isshown that luminosity criterion (Tully-Fisher) gives much smallerdistances for these galaxies than their redshifts do. The interaction ofspecific high redshift ScI's with nearby galaxies is presented as anindependent proof that ScI's are generally small, low luminositygalaxies.
| Southern Galaxy Catalogue.
Not Available
| Inner ring structures in galaxies as distance indicators. III - Distances to 453 spiral and lenticular galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983ApJS...51..149B&db_key=AST
| UBV photometry of 262 southern galaxies
Multiaperture photometry of 262 bright southern galaxies in the JohnsonUBV system is given. Most of these are south of -30 deg declination,although some northward to -10 deg are included. A total of 169 objectshave published radial-velocity determinations. These provide distancesand enable construction of color-magnitude diagrams for this subset ofobjects through a physical diameter of 2.0 kpc (with H = 100). Thetwo-color diagrams for the inner regions of the galaxies differ fromthose of integrated galaxies due to the color changes towards theircenters. Comparison with theoretical models of Larson and Tinsley (1978)suggest that the colors of the inner portions of most ellipticals andlenticulars are consistent with their having all stars formed at nearlyone epoch with little subsequent star formation, while for spiralslarger amounts of star formation, either in bursts or continuously, aresuggested. This simple picture is complicated by the presence of certainobjects having peculiar colors indicative of large amounts of recentstar formation.
| Radial Velocities of Southern Galaxies. II
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
INHABITED SKY
