Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Serendipitous detection of galaxies behind the Milky Way from the DENIS survey
A search has been undertaken at Lyon Observatory to identify, by eye,galaxy candidates at galactic latitudes lower than +/-15 degrees on theDENIS J and K-band images. This paper presents a list of 2028 objectsthat were serendipitously detected throughout the DENIS survey.Cross-identification with galaxy entries in the LEDA Database has beenperformed. Comparison with the second release of the 2MASS survey led toa satisfactory agreement of J band magnitudes (std. dev. = 0.3 mag). Thedistribution of galaxy candidates along the Galactic Plane shows aconcentration near the galactic longitude l=305 deg . As a by product ofthis inspection of J and K images some interesting galactic objects werefound (star clusters and nebulae). Based on observations collected atthe European Southern Observatory, La Silla, Chile. The catalog (Table1) is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.188.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/387/1
| Homogenization of the Stellar Population along Late-Type Spiral Galaxies
We present a study of the broadband UBV color profiles for 257 Sbcbarred and nonbarred galaxies, using photoelectric aperture photometrydata from the literature. Using robust statistical methods, we haveestimated the color gradients of the galaxies, as well as the total andbulge mean colors. A comparative photometric study using CCD images wasdone. In our sample, the color gradients are negative (reddish inward)in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. The results do not change, essentially,when we include the edge-on galaxies. As a consequence of this study wehave also found that barred galaxies are overrepresented among theobjects having null or positive gradients, indicating that bars act as amechanism of homogenization of the stellar population. This effect ismore evident in the U-B color index, although it can also be detected inthe B-V color. A correlation between the total and bulge colors wasfound that is a consequence of an underlying correlation between thecolors of bulges and disks found by other authors. Moreover, the meantotal color is the same irrespective of the gradient regime, whilebulges are bluer in galaxies with null or positive gradients, whichindicates an increase of the star formation rate in the central regionsof these objects. We have also made a quantitative evaluation of theamount of extinction in the center of these galaxies. This was doneusing the Wide Field Planetary Camera 2 (WFPC2) and the Near InfraredCamera and Multi-Object Spectrometer (NICMOS) Hubble Space Telescope(HST) archival data, as well as CCD B, V, and I images. We show thatalthough the extinction in the V-band can reach values up to 2 mag inthe central region, it is unlikely that dust plays a fundamental role inglobal color gradients. We found no correlation between color and O/Habundance gradients. This result could suggest that the color gradientsare more sensitive to the age rather than to the metallicity of thestellar population. However, the absence of this correlation may becaused by dust extinction. We discuss this result by considering apicture in which bars are a relatively fast, recurrent phenomenon. Theseresults are not compatible with a pure classical monolithic scenario forbulge and disk formation. On the contrary, they favor a scenario inwhich both these components are evolving in a correlated process inwhich stellar bars play a crucial role. Based partly on observationsmade at the Pico dos Dias Observatory (PDO/LNA-CNPq), Brazil.
| H I-bright Galaxies in the Southern Zone of Avoidance
A blind survey for H I-bright galaxies in the southern zone of avoidance(212deg<=l<=36deg, |b|<=5deg)has been made with the 21 cm multibeam receiver on the Parkes 64 m radiotelescope. The survey, sensitive to normal spiral galaxies to a distanceof ~40 Mpc and more nearby dwarfs, detected 110 galaxies. Of these, 67have no counterparts cataloged in the NASA/IPAC Extragalactic Database.In general, the uncataloged galaxies lie behind thicker obscuration thando the cataloged objects. All the newly discovered galaxies have H Iflux integrals that are more than an order of magnitude lower than thoseof the Circinus galaxy. The survey recovers the Puppis Cluster andforeground group, and the Local Void remains empty. The H I massfunction derived for the sample is satisfactorily fitted by a Schechterfunction with parameters α=1.51+/-0.12,Φ*=0.006+/-0.003, and logM*=9.7+/-0.10.
| Radio-loud and Radio-quiet Active Galactic Nuclei
We have generated a sample of 409 active galactic nuclei (AGNs) forwhich both the radio luminosity at 5 GHz and the line luminosity in [OIII] lambda5007 have been measured. The radio luminosity spans a rangeof 10 orders of magnitude, and the [O III] line luminosity spans a rangeof 8 orders of magnitude-both considerably larger than the ranges inprevious studies. We show that these two quantities are correlated in asimilar way for both radio-loud and radio-quiet AGNs. We demonstratethat the observed correlation can be explained in terms of a model inwhich jets are accelerated and collimated by a vertical magnetic field.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Linear polarization measurements of extragalactic radio sources at lambda 6.3 CM
We present linear polarization measurements of 154 extragalactic radiosources at lambda6 .3 cm, as part of a continuing effort to expand andimprove our Faraday rotation determinations of radio galaxies andquasars. The excellent telescope optics of the Effelsberg 100 mtelescope at this wavelength, combined with a matrix method we appliedfor calibrating out all components of the instrumental polarizationenables us to achieve better than average accuracy in the determinationsof linear polarization degree and position angle. In the absence ofthermal noise errors, these are repeatable to better than 0.2% and 0fdg1 respectively, for the prime calibrator, 3C 286. A very brief overviewof the results is also included.
| A Hubble Space Telescope Imaging Survey of Nearby Active Galactic Nuclei
We have obtained WFPC2 images of 256 of the nearest (z <= 0.035)Seyfert 1, Seyfert 2, and starburst galaxies. Our 500 s broadband(F606W) exposures reveal much fine-scale structure in the centers ofthese galaxies, including dust lanes and patches, bars, rings, wisps,and filaments, and tidal features such as warps and tails. Most of thisfine structure cannot be detected in ground-based images. We haveassigned qualitative classifications for these morphological featuresand a Hubble type for the inner region of each galaxy, and we have alsomeasured quantitative information such as 0."18 and 0."92 aperturemagnitudes, position angles, and ellipticities, where possible. There islittle direct evidence for unusually high rates of interaction in theSeyfert galaxies. Slightly less than 10% of all the galaxies show tidalfeatures or multiple nuclei. The incidence of inner starburst rings isabout 10% in both classes of Seyfert galaxies. In contrast, galaxieswith H II region emission-line spectra appear substantially moreirregular and clumpy because of their much higher rates of current starformation per unit of galactic mass. The presence of an unresolvedcentral continuum source in our Hubble Space Telescope images is avirtually perfect indicator of a Seyfert 1 nucleus as seen byground-based spectroscopy. Fifty-two percent of these Seyfert 1 pointsources are saturated in our images; we use their wings to estimatemagnitudes ranging from 15.8 to 18.5. The converse is not universallytrue, however, as over one-third of Seyferts with direct spectroscopicevidence for broad Balmer wings show no nuclear point source. These 34resolved Seyfert 1's have fainter nonstellar nuclei, which appear to bemore extinguished by dust absorption. Like the Seyfert 2's, they havecentral surface brightnesses consistent with those expected for thebulges of normal galaxies. The rates for the occurrences of bars inSeyfert 1's and 2's and non-Seyferts are the same. We found onesignificant morphological difference between the host galaxies ofSeyfert 1 and Seyfert 2 nuclei. The Seyfert 2 galaxies are significantlymore likely to show nuclear dust absorption, especially in lanes andpatches that are irregular or reach close to the nucleus. A few simpletests show that the difference cannot be explained by different averageredshifts or selection techniques. It is confirmed by our galaxymorphology classifications, which show that Seyfert 1 nuclei reside inearlier type galaxies than Seyfert 2 nuclei. If, as we believe, this isan intrinsic difference in host galaxy properties, it undermines one ofthe postulates of the strong unification hypothesis for Seyfertgalaxies, that they merely appear different because of the orientationof their central engine. The excess galactic dust we see in Seyfert 2'smay cause substantial absorption that obscures their hypothesized broademission line regions and central nonstellar continua. This galacticdust could produce much of the absorption in Seyfert 2 nuclei that hadinstead been attributed to a thick dusty accretion torus forming theouter part of the central engine.
| An Unusual Radio Galaxy in Abell 428: A Large, Powerful FR I Source in a Disk-dominated Host
We report the discovery of a powerful (~1024 h^{-2}75{WHz}^{-1} at 20 cm) FR I radio source in a highly flatteneddisk-dominated galaxy. Half the radio flux from this source isconcentrated within the host galaxy, with the remainder in a pair ofnearly symmetrical lobes of total extent ~200 kpc nearly perpendicularto the disk. Traditional wisdom maintains that powerful, extended radiosources are found only in ellipticals or recent merger events. We reportB, R, J, and K imaging, optical spectroscopy, a rotation curve, an IRASdetection, and a VLA 20 cm image for this galaxy, 0313-192. The opticaland near-infrared images clearly show a disk. We detect apparent spiralarms in a deep B-band exposure, and a dust lane from a higher resolutionB-band image. The reddened nucleus is consistent with extinction by asimilar dust lane. The optical spectrum suggests a central AGN and showssome evidence of a starburst, with both the AGN and central starlightappearing substantially reddened (perhaps by the optical dust lane).From analysis of the extended line emission in [O III] and H alpha , wederive a rotation curve consistent with an early-type, dusty spiral seenedge-on. From the IRAS detection at 60 and 100 mu m, we find that theratio of far-infrared to radio flux places this object firmly as a radiogalaxy (i.e., the radio emission is not powered by star formation). Theradio structure suggests that the radio source in this galaxy is relatedto the same physical mechanisms that are present in jet-fed powerfulradio sources, and that such powerful, extended sources can (albeitextremely rarely) occur in a disk-dominated host.
| Kinematical models of double radio sources and the unified scheme. II. The database
A large database of 1038 edge-brightened double radio sources has beencollected from the literature with special emphasis on finding the bestradio map for each source and on obtaining flux information of theextended radio lobes and the core component. The data are collected withtwo goals in mind. The first goal is to provide the data for ourstatistical study of double radio source symmetry and the unified schemein the theoretical framework of \cite[Baryshev & Teerikorpi (1995,Paper I)]{bar:tee}. It is also believed that the data are useful to theresearch community and thus extensive data are given in tabular form.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| HI searches in the Zone of Avoidance: Past and present (and future)
In the regions of highest optical obscuration and infrared confusion,only 21-cm emission can be used to find galaxies in the Zone ofAvoidance. A feasibility study conducted with the 300-ft telescopesuccessfully uncovered galaxies which seem to be consistent withpopulations of optically-selected low surface brightness galaxies. Acomplete survey is currently being conducted in the north with theDwingeloo telescope. The big breakthrough should come in the south,however, with the advent of the Parkes telescope multibeam system.
| A Survey for H 2O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies
A survey for H2O megamaser emission from 354 active galaxies hasresulted in the detection of 10 new sources, making 16 known altogether.The galaxies surveyed include a distance-limited sample (coveringSeyferts and LINERs with recession velocities less than 7000 km s-1) anda magnitude-limited sample (covering Seyferts and LINERs with mB <=14.5). In order to determine whether the H2O-detected galaxies are"typical" active galactic nuclei (AGNs) or have special properties thatfacilitate the production of powerful masers, we have accumulated adatabase of physical, morphological, and spectroscopic properties of theobserved galaxies. The most significant finding is that H2O megamasersare detected only in Seyfert 2 and LINER galaxies, not Seyfert 1's. Thislack of detection in Seyfert 1's indicates either that they do not havemolecular gas in their nuclei with physical conditions appropriate toproduce 1.3 cm H2O masers or that the masers are beamed away from Earth,presumably in the plane of the putative molecular torus that hides theSeyfert 1 nucleus in Seyfert 2's. LINERs are detected at a similar rateto Seyfert 2's, which constitutes a strong argument that at least somenuclear LINERs are AGNs rather than starbursts, since starbursts havenot been detected as H2O megamasers. We preferentially detect H2Oemission from the nearer galaxies and from those that are apparentlybrighter at mid- and far-infrared and centimeter radio wavelengths.There is also a possible trend for the H2O-detected galaxies to be moreintrinsically luminous in nuclear 6 cm radio emission than theundetected ones, though these data are incomplete. We find evidence thatSeyfert 2's with very high (NH > 1024 cm-2) X-ray--absorbing columnsof gas are more often detected as H2O maser emitters than Seyfert 2'swith lower columns. It may be that the probability of detecting H2Omaser emission in Seyfert galaxies increases with increasing column ofcool gas to the nucleus, from Seyfert 1's through narrow-line X-raygalaxies to Seyfert 2's.
| 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
| A Survey for H 2O Megamasers in Active Galactic Nuclei. I. Observations
We report an extensive search for 22 GHz H_2_O maser emission fromnearby active galaxies. Our sample includes all Seyfert and LINERgalaxies listed in the Huchra catalog or the Veron-Cetty & Veroncatalog with recessional velocities less than 7000 km s^-1^, and allSeyfert galaxies and LINERs in Huchra's catalog with m_b_ <= 14. Inaddition to these distance- and magnitude-limited samples, we have alsoobserved a number of active galaxies, including radio galaxies, athigher redshift; In all, some 354 galaxies have been surveyed. Ten newH_2_O megamaser sources have been detected, resulting in 16 galaxiesthat are currently known to contain H_2_O masers with isotropicluminosities greater than 20 L_sun_. Of the observed active galaxieswith cz < 7000 km s^-1^, 5.4% have detectable H_2_O megamaseremission. This fraction increases to 11% for those sources with cz <2000 km s^-1^. The newly discovered megamaser sources were monitored onsubsequent observing runs. The strength of the maser features varies forthese sources, as they do for Galactic masers. Three of the galaxieshave sufficient data to test for velocity changes of narrow masercomponents comparable in magnitude to those of the well-studied systemicfeatures in NGC 4258. The maser line in one of these galaxies-NGC2639-is found to have a systematic redward velocity drift of 6.6 +/- 0.4km s^-1^ yr^-1^. No systematic velocity drifts are found for the othertwo sources. We also report large apparent velocity changes in theunusual broad H_2_O emission feature in NGC 1052.
| Evidence for Acceleration and Nonradial Motion of Parsec-Scale Jet Components in the Lobe-dominated Superluminal Quasar 3C 263
We report evidence for accelerated and nonradial motion of parsec- scalejet components in the nucleus of the lobe-dominated quasar 3C 263. NewVLBI maps at 10.7 GHz confirm that the jet component J1 moves withsuperluminal speed. While the initial apparent transverse velocity of J1was v_app_ ~ 1.2 h^-1^ c (H_0_ = 100h kms^-1^ Mpc^-1^, q_0_ = 0.5), thenew maps indicate an average v_app_ ~ 2.2 h^-1^ c over a span of ~8 yr.This suggests the possibility of component acceleration, which couldmost simply be accounted for in a relativistic jet model that allowstime variations in the Lorentz factor. The new maps also reveal a secondjet component J2 that has moved along a significantly different radialdirection than J1 with respect to the core component C. Component J2shows a marginal change in direction that may be bringing it intoalignment with the path of J1. We estimate v_app_ ~ 0.7 h^-1^c for J2.We also present a new 8.4 GHz VLBI map that will enable us to continuemonitoring 3C 263 with the VLBA. We relate our results to otherproperties of 3C 263 and discuss their implications for relativistic jetmodels and "unified schemes." We conclude that the low superluminalspeeds in many lobe-dominated quasars, together with the suggestedmildly accelerated and nonradial motion exhibited by 3C 263, areconsistent with unification of core- and lobe-dominated quasars.
| A CO survey of galaxies with the SEST and the 20-m Onsala telescope.
A large survey of galaxies in the J=1-0 CO line, performed during1985-1988 using the 15-m SEST and the 20-m millimetre wave telescope ofOnsala Space Observatory, is presented. The HPBW of the telescopes are44" and 33" at 115GHz, respectively. The central positions of 168galaxies were observed and 101 of these were detected in the CO line.More than 20% of these are new detections. Maps of some of the galaxiesare also presented.
| Radio sources observed with the Culgoora circular array
Presented is a final updated and recalibrated list of sources that wereobserved with the Culgoora circular array in the interval 1970-1984. Thepresent list contains all the sources that were contained in theCulgoora-1, 2, 3 Lists plus additional sources resulting from a surveyof 353 Abell clusters of galaxies. The electronic version of theCulgoora List, with appropriate documentation, is available from theEinstein On-Line Service.
| Total and effective colors of 501 galaxies in the Cousins VRI photometric system
Total color indices (V-R)T, (V-I)T and effectivecolor indices (V-R)e, (V-I)e in the Cousins VRIphotometric system are presented for 501 mostly normal galaxies. Thecolors are computed using a procedure outlined in the Third ReferenceCatalogue of Bright Galaxies (RC3) whereby standard color curvesapproximated by Laplace-Gauss integrals are fitted to observedphotoelectric multiaperture photometry. 11 sources of such photometrywere used for our analysis, each source being assigned an appropriateweight according to a rigorous analysis of residuals of the data fromthe best-fitting standard color curves. Together with the integrated B-Vand U-B colors provided in RC3, our analysis widens the range ofwavelength of homogeneously defined colors of normal galaxies of allHubble types. We present color-color and color-type relations that canbe modeled to understand the star formation history of galaxies.
| 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.
| Penetrating the "zone of avoidance". I. A compilation of optically identified extragalactic objects within |b|<=5deg.
As an introduction to a series of papers on galaxies identified in the"zone of avoidance" (ZOA) of the Milky Way we present a compilation ofhopefully all published galaxies and quasars that were ever opticallyidentified within |b|<=5deg. We present 2304 objects and list (anddiscuss), in addition to their (often considerably improved)coordinates, the best available morphological type, optical maximumdiameters in the red, up-to-date heliocentric radial velocities,reference to the papers where a specific object was first opticallyidentified, and results of cross-checks with the IRAS point sourcecatalogue. This compilation may serve as a presentation of the "state ofaffairs" in optical identifications of extragalactic objects behind theplane of the Galaxy, up to end 1993.
| The Parkes-MIT-NRAO (PMN) surveys. 3: Source catalog for the tropical survey (-29 deg less than delta less than -9 deg .5)
We present a catalog of radio sources discovered at a frequency of 4850MHz in the tropical zone (-29 deg less than delta less than -9 deg.5) ofParkes-MIT-NRAO (PMN) Surveys. The tropical survey covers 2.01 sr andcontains 13,363 sources to a flux limit that is, typically, about 42 mJybut varies as a function of declination. The survey was made using theParkes 64 m radio telescope with the National Radio AstronomyObservatory (NRAO) multibeam receiver during 1990. This survey increasesthe number of known sources in the region surveyed by approximately afactor of 5. The data-taking and principal reduction methods used forthe PMN surveys have been extensively described in a previous paper(Griffith & Wright 1993). In this paper, we describe the specificdetails of the tropical survey, and we list the sources for the tropicalsurvey. Later papers in the series will list objects for other surveyzones, describe images made from the data, and provide analysis of thedata.
| Search and redshift survey for IRAS galaxies behind the Northern Milky Way
We made a search for IRAS galaxies behind the Northern Milky Way byinfrared selection using IRAS Point Source Catalog and visual inspectionon POSS (Palomar Observatory Sky Survey) paper prints, and carried out aredshift survey of the identified objects. This paper presents a catalogof 649 IRAS galaxies with f_60_>=0.6 Jy between l=150deg and 240degat |b|<=15deg , which contains 254 newly identified galaxies and 188newly measured radial velocities. Due to galactic extinction, our sampleis a lower limit sample of the flux limited sample of IRAS galaxies, butit can give some information on the distribution of galaxies in theregion perpendicular to the Supergalactic Plane. We confirm two regionswith enhanced density at l=~160deg , cz=~5000 km/s and l=~190deg ,cz=~5000 km/s and at least two possible voids.
| A new supercluster behind the Milky Way in Monoceros
The presence of three clusters of galaxies at a region between l = 217and 230 deg and b = 2 and 7 deg was proposed by Saito et al. (1990)based on their search for galaxies on the UK Schmidt Infrared Atlas. Wehave confirmed the existence of the clusters by an analysis of thedistribution of the cataloged galaxies on the sky as well as a redshiftsurvey of galaxies in this region. We have found that the three clustersform a supercluster (named Monoceros supercluster) at a distance ofabout 100/h Mpc, and that it is one of the richest superclusters in theLocal Universe. The supercluster seems to be associated with neighboringclustering features of galaxies recently detected by others and form alarge-scale density peak at around SGZ about 100/h Mpc.
| A search for IRAS galaxies behind the southern Milky Way
We systematically searched for IRAS galaxies with 60 micrometer fluxdensity larger than 0.6 Jy by using the UK Schmidt Infrared and IIIa-JAtlases in the Milky Way region (absolute value of b less than 15 deg)between l = 210 deg and 360 deg. We first selected about 4000 IRAS pointsources by using our far-infrared criteria, which are optimized for thesearch of IRAS galaxies behind the Milky Way region, and then inspectedvisually the optical counterparts of them on the Schmidt Atlas filmcopies. We found 966 IRAS sources associated with galaxy-like objects.The list of the objects is presented here with the IRAS source name,Galactic coordinates, IRAS flux densities, field number and emulsion ofthe Atlas, type and size of galaxy (-like) image, redshift,multiplicity, and cross-identification. Of these, 423 galaxies arealready cataloged in the Catalog of Galaxies and Quasars Observed in theIRAS Survey, and most of the remaining 543 galaxy candidates are newlyidentified in this search. Although the radial velocities are known foronly 387 galaxies, of which 60 were newly measured by us so far, weinferred the contamination by Galactic objects to be small from the goodcorrelation between the sky distributions of the newly identified galaxycandidates and the previously cataloged galaxies. In the regions wherethe Galactic molecular clouds dominate, almost all the sources were notidentified as galaxies. The detected galaxies are clustered in the threeregions around l = 240 deg, 280 deg, and 315 deg, where the projectednumber densities are higher than the whole-sky average of IRAS galaxiesof the same flux limit.
| The excitation mechanism of forbidden Fe II 1.644 micron emission in Seyfert and starburst galaxies revisited
The observational properties of forbidden Fe II are studied in galaxieswith starburst nuclei (SBN) and in AGNs. The forbidden Fe II/Br-gammavalue is controlled by the volume ratio of partly ionized to fullyionized regions, since forbidden Fe II emission is excited in partlyionized gas. The depletion effect is less important to the observedforbidden Fe II/Br-gamma ratio, although iron is one of the refractoryelements which are easily depleted into dust grains. In SBNs, forbiddenFe II emission arises mainly from partly ionized regions associated withSNRs. Photodissociation regions situated near OB stars do not contributesignificantly to the observed forbidden Fe II flux. In AGNs, X-rays fromSeyfert nuclei create extended partly ionized zones ion narrow-lineregions from which forbidden Fe II emission arises. This naturallyexplains the properties of AGNs that forbidden Fe II/Br-gamma is largeand forbidden Fe II emission is broad with respect to SBNs.
| The CA II triplet lines in starburst and AGN
In the frame of the Starburst Model for AGN, we show that the evolutionof a massive stellar cluster in a high metallicity environment canreproduce the observed equivalent widths of Ca II triplet lines inabsorption in Starburst and AGN. In the case of Starburst galaxies, thisstrength, together with the emission-line ratio (O II)/(O III), can beused to determine the age of the cluster. The strength of the Ca IIlines is mainly governed by the age of the stellar cluster through thepresence of red supergiant stars.
| The photoionization mechanism of LINERs - Stellar and nonstellar
We present high quality spectroscopic observations of a sample of 14LINERs. Starlight removal is achieved by the subtraction of a suitableabsorption-line 'template' galaxy, allowing accurate measurements ofemission lines. We use these line fluxes to examine the possibleexcitation mechanisms of LINERs. We suggest that LINERs with weakforbidden O I 6300-A emission may be H II regions photoionized byunusually hot O-type stars. LINERs with forbidden O I/H-alphaapproximately greater than 1/6 may be powered by photoionization from anonstellar continuum. This is supported by the detection of broadH-alpha emission, a correlation between line width and critical density,and pointlike X-ray emission in several of these objects.
| IRAS CPC Observations of Galaxies - Part One - Catalog and Atlas
. - We present the results of far-infrared imaging observations of 258regions of 12' x9' each centered on a selected individual galaxy, aclose pair, or a compact group of galaxies mapped at 50 and 100 micronwavelength with the CPC instrument of the IRAS satellite. The CPCinstrument has a significantly better resolution than the IRAS Surveyinstrument at these wavelengths, i.e. a round beam with a FWHM of about80" at 50 microns and 95" at 100 microns, respectively, intended to bematched to the diffraction limit of the telescope at 100 microns. Themaps were made using a new algorithm to correct for gain variations,which gives better results than the one used previously for the imagesmade available on tape in 1985. Of 262 objects observed, 167 and 188were detected at 50 and 100 microns, respectively, about 85% of thegalaxies from the same sample listed as detected by the Surveyinstrument in the IRAS Point Source Catalog. For all 55 galaxiesresolved (i.e. with a FWHM major axis diameter exceeding 1.6 times thebeam FWHM and/or extended lower-level emission) by the CPC we alsopresent the averaged maps at 50 and 100 microns. These 55 objectsinclude 35 for which there are no published maps obtained with the IRASSurvey instrument. We rescaled the flux densities of the published CPCmaps using the more accurate IRAS Survey instrument data, since theabsolute flux density calibration of the CPC is only accurate to about+/-60%. We also present images of a triplet of galaxies associated witha single Survey point source, which were resolved into separate sourcesby the CPC.
| A study of a 21 centimeter-selected sample of galaxies. I - The survey
This study presents a pilot survey for galaxies at 21 cm conducted withthe NRAO 300-ft telescope, which was performed to test the feasibilityof finding unseen galaxies through the detection of the radiationemitted by neutral hydrogen. The 21-cm galaxies were investigated todetermine whether these galaxies differ from optically collectedsamples. H I mapping of all the uncataloged galaxies, and a few of thecataloged sources, was done at the VLA to determine accurately thegalaxies' H I line widths and masses. A region of galactic underdensity,or cosmic void, was evident in the data. It is inferred that voids arenot filled by low surface brightness, dwarf galaxies, but rather aretruly lacking in bright and faint galaxies. Results of the single-dishand the VLA studies are presented, and the appearance of large-scalestructures in the data is discussed.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
Cataloghi e designazioni:
|
