내용
사진
사진 업로드
DSS Images Other Images
관련 글
Deviations from passive evolution - star formation and the ultraviolet excess in z~ 1 radio galaxies
Galaxy colours are determined for two samples of 6C and 3CR radiosources at z~ 1, differing by a factor of ~6 in radio power. Correctionsare made for emission-line contamination and the presence of any nuclearpoint source, and the data analysed as a function of both redshift andthe radio source properties. The galaxy colours are remarkably similarfor the two populations, and the ultraviolet excess evolves with radiosource size similarly in both samples, despite the fact that thealignment effect is more extensive for the more powerful 3CR radiogalaxies. These results seem to suggest that the alignment effect atthese redshifts does not scale strongly with radio power, and is insteadmore closely dependent on galaxy mass (which is statistically comparablefor the two samples). However, it is likely that the presence ofrelatively young (<~several times 108-yr-old) stellarpopulations has considerably contaminated the K-band flux of thesesystems, particularly in the case of the more powerful 3CR sources,which are ~0.5mag more luminous than the predictions of passiveevolution models at z~ 1. The higher luminosity of the 3CR alignmenteffect is balanced by emission at longer wavelengths, thereby leading tocomparable colours for the two samples.
| Minkowski's Object: A Starburst Triggered by a Radio Jet, Revisited
We present neutral hydrogen, ultraviolet, optical, and near-infraredimaging, and optical spectroscopy, of Minkowski's Object (MO), astar-forming peculiar galaxy near NGC 541. The observations strengthenevidence that star formation in MO was triggered by the radio jet fromNGC 541. Key new results are the discovery of a 4.9×108Msolar double H I cloud straddling the radio jet downstreamfrom MO, where the jet changes direction and decollimates; strongdetections of MO, also showing double structure, in UV and Hα andnumerous H II regions and associated clusters in MO. In UV, MO resemblesthe radio-aligned, rest-frame UV morphologies in many high-redshiftradio galaxies (HzRGs), also thought to be caused by jet-induced starformation. MO's stellar population is dominated by a 7.5 Myr old,1.9×107 Msolar instantaneous burst, with acurrent star formation rate of 0.52 Msolar yr-1(concentrated upstream from where the H I column density is high). Thisis unlike the jet-induced star formation in Centaurus A, where the jetinteracts with preexisting cold gas; in MO, the H I may have cooled outof a warmer, clumpy intergalactic or interstellar medium as a result ofjet interaction, followed by the collapse of the cooling clouds andsubsequent star formation (consistent with numerical simulations). Sincethe radio source that triggered star formation in MO is much lessluminous, and therefore more common than powerful HzRGs, and because theenvironment around MO is not particularly special in terms of abundantdense, cold gas, jet-induced star formation in the early universe mightbe even more prevalent than previously thought.
| Neutral hydrogen in radio galaxies: Results from nearby, importance for far away
The study of neutral hydrogen emission and absorption in radio galaxiesis giving new and important insights on a variety of phenomena observedin these objects. Such observations are helping to understand the originof the host galaxy, the effects of the interaction between the radio jetand the ISM, the presence of fast gaseous outflows as well asjet-induced star formation. Recent results obtained on these phenomenaare summarized in this review. Although the {H I observationsconcentrate on nearby radio galaxies, the results also have relevancefor the high-z objects as all these phenomena are important, and likelyeven more common, in high-redshift radio sources.
| Understanding the Nuclear Gas Dispersion in Early-Type Galaxies in the Context of Black Hole Demographics
The majority of nearby early-type galaxies contain detectable amounts ofemission-line gas at their centers. The nuclear gas kinematics form avaluable diagnostic of the central black hole (BH) mass. Here we analyzeand model Hubble Space Telescope STIS observations of a sample of 27galaxies; 16 Fanaroff-Riley Type I radio galaxies and 11 (more) normalearly-type galaxies. We focus here on what can be learned from thenuclear velocity dispersion (line width) of the gas as a complement tothe many studies dealing with gas rotation velocities. We find that thedispersion in a STIS aperture of ~0.1"-0.2" generally exceeds thelarge-scale stellar velocity dispersion of the galaxy. This isqualitatively consistent with the presence of central BHs but raises thequestions of whether the excess gas dispersion is of gravitational ornongravitational origin and whether the implied BH masses are consistentwith our current understanding of BH demography (as predicted by theM-σ relation between BH mass and stellar velocity dispersion). Toaddress this we construct purely gravitational axisymmetric dynamicalmodels for the gas, both thin-disk models and models with more generalaxis ratios and velocity anisotropies. For the normal galaxies thenuclear gas dispersions are adequately reproduced assuming disks aroundthe BHs with masses that follow the M-σ relation. In contrast, thegas dispersions observed for the radio galaxies generally exceed thosepredicted by any of the models. We attribute this to the presence ofnongravitational motions in the gas that are similar to or larger thanthe gravitational motions. The nongravitational motions are presumablydriven by the active galactic nucleus (AGN), but we do not find arelation between the radiative output of the AGN and thenongravitational dispersion. Given the uncertainties about the dynamicalstate of the gas, it is not possible to uniquely determine the BH massfor each galaxy from its nuclear gas dispersion. However, for the sampleas a whole the observed dispersions do not provide evidence forsignificant deviations from the M-σ relation.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| Examining the Seyfert-Starburst Connection with Arcsecond-Resolution Radio Continuum Observations
We compare the arcsecond-scale circumnuclear radio continuum propertiesof five Seyfert and five starburst galaxies, concentrating on the searchfor any structures that could imply a spatial or causal connectionbetween the nuclear activity and a circumnuclear starburst ring. Noevidence is found in the radio emission for a link between thetriggering or feeding of nuclear activity and the properties ofcircumnuclear star formation. Conversely, there is no clear evidence ofnuclear outflows or jets triggering activity in the circumnuclear ringsof star formation. Interestingly, the difference in the angle betweenthe apparent orientation of the most elongated radio emission and theorientation of the major axis of the galaxy is on average larger inSeyfert galaxies than in starburst galaxies, and Seyfert galaxies appearto have a larger physical size scale of the circumnuclear radiocontinuum emission. The concentration, asymmetry, and clumpinessparameters of radio continuum emission in Seyfert galaxies andstarbursts are comparable, as are the radial profiles of radio continuumand near-infrared line emission. The circumnuclear star formation andsupernova rates do not depend on the level of nuclear activity. Theradio emission usually traces the near-infrared Brγ andH2 1-0 S(1) line emission on large spatial scales, butlocally their distributions are different, most likely because of theeffects of varying local magnetic fields and dust absorption andscattering.
| The scaling relation of early-type galaxies in clusters. II. Spectroscopic data for galaxies in eight nearby clusters
Aims.We present low and intermediate resolution spectroscopic datacollected for 152 early type galaxies in 8 nearby clusters with z ≤0.10. Methods: .We use low resolution data to produce the redshiftand the K-correction for each galaxy, as well as to give their overallspectral energy distribution and some spectral indicators, including the4000 Å break, the Mg2 strength and the NaD equivalent width. Wehave also obtained higher resolution data for early type galaxies inthree of the clusters, to determine their central velocity dispersion. Results: .The effect of the resolution on the measured parametersis discussed. Conclusions: .A new accurate systemic redshift andvelocity dispersion is presented for four of the surveyed clusters, A98,A3125, A3330, and DC2103-39. We have found that the K-correction valuesfor E/S0 bright galaxies in the given nearby clusters are very similar.We also find that the distribution of the line indicators significantlydiffers from cluster to cluster.
| Unification in the low radio luminosity regime: evidence from optical line emission
We address the question of whether or not the properties of alllow-luminosity flat spectrum radio sources, not just the obvious BL Lacobjects, are consistent with them being the relativistically beamedcounterparts of the low radio luminosity radio galaxies (theFanaroff-Riley type 1, FR I). We have accumulated data on a well-definedsample of low redshift, core-dominated, radio sources all of which haveone-sided core-jet structures seen with very long baselineinterferometry, just like most BL Lac objects. We first compare theemission-line luminosities of the sample of core-dominated radio sourceswith a matched sample of FR I radio galaxies. The emission lines in thecore-dominated objects are on average significantly more luminous thanthose in the comparison sample, inconsistent with the simplest unifiedmodels in which there is no orientation dependence of the line emission.We then compare the properties of our core-dominated sample with thoseof a sample of radio-emitting UGC galaxies selected without bias to corestrength. The core-dominated objects fit well on the UGC correlationbetween line emission and radio core strength found by Verdoes Kleijn etal. The results are not consistent with all the objects participating ina simple unified model in which the observed line emission isorientation independent, though they could fit a single, unified modelprovided that some FR I radio galaxies have emission line regions thatbecome more visible when viewed along the jet axis. However, they areequally consistent with a scenario in which, for the majority ofobjects, beaming has minimal effect on the observed core luminosities ofa large fraction of the FR I population and that intrinsically strongercores simply give rise to stronger emission lines. We conclude that FR Iunification is much more complex than usually portrayed, and modelscombining beaming with an intrinsic relationship between core andemission line strengths need to be explored.
| Galactic Winds
Galactic winds are the primary mechanism by which energy and metals arerecycled in galaxies and are deposited into the intergalactic medium.New observations are revealing the ubiquity of this process,particularly at high redshift. We describe the physics behind thesewinds, discuss the observational evidence for them in nearbystar-forming and active galaxies and in the high-redshift universe, andconsider the implications of energetic winds for the formation andevolution of galaxies and the intergalactic medium. To inspire futureresearch, we conclude with a set of observational and theoreticalchallenges.
| Magnetohydrodynamic Simulations of Shock Interactions with Radiative Clouds
We present results from two-dimensional numerical simulations of theinteractions between magnetized shocks and radiative clouds. Our primarygoal is to characterize the dynamical evolution of the shocked clouds.We perform runs in both the strong and weak magnetic field limits andconsider three different field orientations. For the geometriesconsidered, we generally find that magnetic fields external to, butconcentrated near, the surface of the cloud suppress the growth ofdestructive hydrodynamic instabilities. External fields also increasethe compression of the cloud by effectively acting as a confinementmechanism driven by the interstellar flow and local field stretching.This can have a dramatic effect on both the efficiency of radiativecooling, which tends to increase with increasing magnetic fieldstrength, and on the size and distribution of condensed cooledfragments. In contrast, fields acting predominately internally to thecloud tend to resist compression, thereby inhibiting cooling. We observethat, even at modest strengths (β0<~100), internalfields can completely suppress low-temperature (T<100 K) cooling intwo-dimensional clouds.
| The HST view of the nuclear emission line region in low luminosity radio-galaxies
We study the properties of the emission line regions in two samples oflow luminosity radio-galaxies, while focusing on the Compact EmissionLine Region (CELR) revealed to be a characteristic feature of theseobjects by HST narrow-band imaging. We find a strong correlation betweenline and optical continuum nuclear emission, which suggests that theoptical cores (most likely of non-thermal origin) can be directlyassociated to the source of ionizing photons, i.e. that we are seeing ajet-ionized narrow line region. A photon budget argument indicates thatthe optical nuclear sources produce sufficient photon flux provided thatthe covering factor of the circum-nuclear gas is rather large, onaverage 0.3. Analysis of HST images and spectra suggests that the CELRmay take the form of a pc-scale, high filling factor structure, possiblyan optically thin torus. Estimates of the CELR mass lead to values assmall as 10{-}10^3 Mȯ, and photon counting sets a limitto the Broad Line Region mass of M_BLR < 10-2Mȯ. When considered together with the low accretion rateand the tenuous torus structure, a general paucity of gas in theinnermost regions of low luminosity radio-galaxies emerges as the maincharacterizing difference from more powerful Active Galactic Nuclei.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| Jet-Induced Star Formation
Jets from radio galaxies can have dramatic effects on the medium throughwhich they propagate. We review observational evidence for jet-inducedstar formation in low (`FR-I') and high (`FR-II') luminosity radiogalaxies, at low and high redshifts respectively. We then discussnumerical simulations which are aimed to explain a jet-induced starburst(`Minkowski's Object') in the nearby FR-I type radio galaxy NGC 541. Weconclude that jets can induce star formation in moderately dense (10cm-3), warm (104 K) gas; that this may be morecommon in the dense environments of forming, active galaxies; and thatthis may provide a mechanism for `positive' feedback from AGN in thegalaxy formation process.
| BUDDA: A New Two-dimensional Bulge/Disk Decomposition Code for Detailed Structural Analysis of Galaxies
We present BUDDA (Bulge/Disk Decomposition Analysis), a new code devotedto perform a two-dimensional bulge/disk decomposition directly from theimages of galaxies. The bulge component is fitted with a generalizedSérsic profile, whereas disks have an exponential profile. Noother components are included. Bars and other substructures, likelenses, rings, inner bars, and inner disks, are studied with theresidual images obtained through the subtraction of bulges and disksfrom the original images. This means that a detailed structural analysisof galaxies may be performed with a small number of parameters, andsubstructures may be directly studied with no a priori assumptions. Ashas been already shown by several studies, two-dimensional fitting ismuch more reliable than one-dimensional profile fitting. Moreover, ourcode has been thoroughly tested with artificial data, and we demonstrateit to be an accurate tool for determining structural parameters ofgalaxies. We also show that our code is useful in various kinds ofstudies, including galaxies of, e.g., different morphological types, andinclinations, which also may be observed at different spatialresolutions. Thus, the code has a broader range of potentialapplications than most of the previous codes, which are developed totackle specific problems. To illustrate its usefulness, we present theresults obtained with a sample of 51 mostly early-type galaxies (butcovering the whole Hubble sequence). These results show some of theapplications in which the code may be used: the determination ofparameters for fundamental plane and structural studies, quantitativemorphological classification of galaxies, and the identification andstudy of hidden substructures. We have determined the structuralparameters of the galaxies in our sample and found many examples ofhidden inner disks in ellipticals, secondary bars, nuclear rings anddust lanes in lenticulars and spirals, and also wrong morphologicalclassification cases. We now make BUDDA generally available to theastronomical community.Based on observations made at the Pico dos Dias Observatory(PDO/LNA-CNPq), Brazil.
| Radiative Shock-induced Collapse of Intergalactic Clouds
Accumulating observational evidence for a number of radio galaxiessuggests an association between their jets and regions of active starformation. The standard picture is that shocks generated by the jetpropagate through an inhomogeneous medium and trigger the collapse ofoverdense clouds, which then become active star-forming regions. In thiscontribution, we report on recent hydrodynamic simulations of radiativeshock-cloud interactions using two different cooling models: anequilibrium cooling-curve model assuming solar metallicities and anonequilibrium chemistry model appropriate for primordial gas clouds. Weconsider a range of initial cloud densities and shock speeds in order toquantify the role of cooling in the evolution. Our results indicate thatfor moderate cloud densities (>~1 cm-3) and shock Machnumbers (<~20), cooling processes can be highly efficient and resultin more than 50% of the initial cloud mass cooling to below 100 K. Wealso use our results to estimate the final H2 mass fractionfor the simulations that use the nonequilibrium chemistry package. Thisis an important measurement, since H2 is the dominant coolantfor a primordial gas cloud. We find peak H2 mass fractions of>~10-2 and total H2 mass fractions of>~10-5 for the cloud gas, consistent with cosmologicalsimulations of first star formation. Finally, we compare our resultswith the observations of jet-induced star formation in ``Minkowski'sObject,'' a small irregular starburst system associated with a radio jetin the nearby cluster of galaxies Abell 194. We conclude that itsmorphology, star formation rate (~0.3 Msolar yr-1)and stellar mass (~1.2×107 Msolar) can beexplained by the interaction of a ~9×104 kms-1 jet with an ensemble of moderately dense (~10cm-3), warm (104 K) intergalactic clouds in thevicinity of its associated radio galaxy at the center of the galaxycluster.
| Hubble Space Telescope Observations of cD Galaxies and Their Globular Cluster Systems
We have used WFPC2 on the Hubble Space Telescope (HST) to obtain F450Wand F814W images of four cD galaxies (NGC 541 in Abell 194, NGC 2832 inAbell 779, NGC 4839 in Abell 1656, and NGC 7768 in Abell 2666) in therange 5400 km s-1<~cz<~8100 km s-1. For NGC541, the HST data are supplemented by ground-based B and I imagesobtained with FORS1 on the Very Large Telescope. We present surfacebrightness and color profiles for each of the four galaxies, confirmingtheir classification as cD galaxies. Isophotal analyses reveal thepresence of subarcsecond-scale dust disks in the nuclei of NGC 541 andNGC 7768. Despite the extreme nature of these galaxies in terms ofspatial extent and luminosity, our analysis of their globular cluster(GC) systems reveals no anomalies in terms of specific frequencies,metallicity gradients, average metallicities, or the metallicity offsetbetween the globular clusters and the host galaxy. We show that thelatter offset appears roughly constant at Δ[Fe/H]~0.8 dex forearly-type galaxies spanning a luminosity range of roughly 4 orders ofmagnitude. We combine the globular cluster metallicity distributionswith an empirical technique described in a series of earlier papers toinvestigate the form of the protogalactic mass spectrum in these cDgalaxies. We find that the observed GC metallicity distributions areconsistent with those expected if cD galaxies form through thecannibalism of numerous galaxies and protogalactic fragments that formedtheir stars and globular clusters before capture and disruption.However, the properties of their GC systems suggest that dynamicalfriction is not the primary mechanism by which these galaxies areassembled. We argue that cD's instead form rapidly, via hierarchicalmerging, prior to cluster virialization.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555Based in part on observations obtained at the European SouthernObservatory, for VLT program 68.D-0130(A).
| Good News from Big Bad Black Holes: Jet-Induced Star Formation in ``Minkowski's Object"
We present VLA neutral hydrogen (HI) observations which show that``Minkowski's Object", a peculiar starburst system, is due to theinteraction of a low luminosity (FR-I type) radio jet with theintergalactic medium (IGM) in the cluster of galaxies A194. Thetransverse size and bimodal structure of the HI cloud, straddling thejet; its location downstream from the star forming region; and kinematicevidence for gas entrainment all are in agreement with previousnumerical simulations (Fragile et al 2004) which concluded that FR-Itype jets can trigger star formation by driving radiative shocks intothe moderately dense, warm gas that is typical of central galaxy clusterregions. We compare the timescales for HI formation with the age of thestarburst derived from recent Keck, Lick and HST spectroscopic andimaging data (see poster by Croft et al), which allows us to putconstraints on the physical conditions in the radio jet (speed) and itsambient medium (density).
| Space Telescope Imaging Spectrograph Spectroscopy of the Emission-Line Gas in the Nuclei of Nearby FR-I Galaxies
We present the results of the analysis of a set of medium-resolutionspectra, obtained by the Space Telescope Imaging Spectrograph on boardthe Hubble Space Telescope, of the emission-line gas present in thenuclei of a complete sample of 21 nearby, early-type galaxies with radiojets (the UGC FR-I Sample). For each galaxy nucleus we presentspectroscopic data in the region of Hα and the derived kinematics.We find that in 67% of the nuclei the gas appears to be rotating and,with one exception, the cases where rotation is not seen are eitherface-on or have complex central morphologies. We find that in 62% of thenuclei the fit to the central spectrum is improved by the inclusion of abroad component. The broad components have a mean velocity dispersion of1349+/-345 km s-1 and are redshifted from the narrow linecomponents (assuming an origin in Hα) by 486+/-443 kms-1.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| Core Radio and Optical Emission in the Nuclei of nearby FR I Radio Galaxies
In this paper we analyze the relation between radio, optical continuumand Hα+[N II] emission from the cores of a sample of 21 nearbyFanaroff and Riley type I galaxies as observed with the VLBA and HST.The emission arises inside the inner tens of parsecs of the galaxies.Core radio emission is observed in 19/20 galaxies, optical corecontinuum emission is detected in 12/21 galaxies and Hα+[N II]core emission is detected in 20/21 galaxies. We confirm the recentlydetected linear correlation between radio and optical core emission inFR I galaxies and show that both core emissions also correlate withcentral Hα+[N II] emission. The tight correlations between radio,optical, and Hα+[N II] core emission constrain the bulk Lorentzfactor to γ~2-5 and γ<~2 for a continuous jet and a jetconsisting of discrete blobs, respectively, assuming jet-viewing anglesin the range 30°-90°. Radio and optical core emissions arelikely to be synchrotron radiation from the inner jet, possibly with asignificant contribution from emission by an accretion disk and/or flow.Elliptical galaxies with LINER nuclei without large-scale radio jetsseem to follow the core emission correlations found in FR I galaxies.This suggests that the central engines could be very similar for the twoclasses of active galactic nuclei. Based on observations with theNASA/ESA Hubble Space Telescope obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| Optical emission-line spectra from jet-cloud collisions?
We have examined the relative emission line strengths of [NII], [OI],and [SII] for selected regions in three nearby objects, all of whichhave published radio images showing detailed correspondence between thedisrupted morphology of the ionized gas clouds and the radio features atspatial resolutions of <=1h-1 kpc. In all of these casesthe clouds have measured velocities which differ from those of theambient medium and are directed away from the impinging radio plasma. Intwo of these objects the values for [NII]:H/α are significantlylower than those usually found for active galaxy nuclei (and EELG) withsimilar values of [OI] and [SII]. None of the published models whichcalculate emission line ratios for shock heating and/or UV continuumexcitation and ionization reproduce the extreme values of the [NII]:H/α ratios which we find here. We postulate that the extremely lowemissivity for [NII] which we see in these two objects may arise fromthe way in which the radio jet energized the interstellar gas in thegalaxy.
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Star Formation in the radio galaxy NGC 4410A
The NGC 4410 group of galaxies provides us with a rare opportunity tostudy a nearby (97 h-175 Mpc) example of a radiogalaxy (NGC 4410A) embedded in an extended X-ray source, with evidencefor star formation that can be readily spatially distinguished fromregions dominated by the active galactic nucleus and shocks. We presentbroadband and narrowband optical images, along with optical and IUEultraviolet spectroscopy, for the radio galaxy NGC 4410A and itscompanion, NGC 4410B. Our Hα+[N II] images reveal six luminous HII regions (LHα~1040 ergs s-1)distributed in an arc near NGC 4410A. Partially completing the ring is aprominent stellar loop containing diffuse ionized gas. This filamentarygas, in contrast to the H II regions, shows spectroscopic signatures ofshock ionization. The star formation in this system may have beentriggered by a collision or interaction between the two galaxies,perhaps by an expanding density wave, as in classical models of ringgalaxies. Alternatively, the star formation may have been induced by theimpact of a radio jet on the interstellar matter. Extended Lyα isdetected in the ultraviolet IUE spectrum. The ultraviolet continuum,which is presumably radiated by the nucleus of NGC 4410A, is notextended. NGC 4410A appears to be interacting with its neighbors in theNGC 4410 group and could be an example of a spiral galaxy transforminginto an elliptical.
| A new list of extra-galactic radio jets
A catalogue of extra-galactic jets is very useful both in observationaland theoretical studies of active galaxies. With the use of new powerfulradio instruments, the detailed structures of very compact or weak radiosources are investigated observationally and many new radio jets aredetected. In this paper, we give a list of 661 radio sources withdetected radio jets known to us prior to the end of December 2000. Allreferences are collected for the observations of jets in radio, IR,optical, UV and X-ray wave-bands. Table 1 and references to Table 1 areonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/757
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| 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.
| VLBA Observations of a Sample of Nearby FR I Radio Galaxies
We observed 17 nearby low-luminosity FR I radio galaxies using the NRAOVery Long Baseline Array (VLBA) at 1.67 GHz, as part of amultiwavelength study of a complete sample of 21 sources selected byradio flux density from the Uppsala General Catalogue of Galaxies. Wedetected radio emission from all 17 galaxies. At a FWHM resolution of~10×4 mas, five galaxies show only an unresolved radio core, 10galaxies show core-jet structures, and two galaxies show twin-jetstructures. Comparing these VLBA images with images previously obtainedwith the NRAO VLA, we find that all detected VLBA jets are well alignedon parsec scales with the VLA jets on kiloparsec scales and that thejet-to-counterjet surface brightness ratios, or the sidedness, decreasessystematically with increasing distance along the jet. We attribute thesidedness to the Doppler boosting effect and its decline to thedeceleration of the jets. We show that a distribution of Lorentz factorcentered near Γ=5 can reproduce our VLBA detection statistics forcore, core-jet, and twin-jet sources. We also note that the luminosityper unit length, Lj, of the VLBA jets drops quickly withdistance, r, along the jet, approximately asLj~r-2.0. We discuss three different mechanisms toexplain this jet fading: (1) the decrease of Doppler boosting due to jetdeceleration, (2) synchrotron losses, and (3) expansion losses inconstant velocity but adiabatically spreading jets. Mechanisms (1) and(2) are inconsistent with the observations, while mechanism (3) isconsistent with the observations provided the magnetic field lines inthe jets are aligned perpendicular to the jet axis. This implies thatthe deceleration of the jets required by the unified scheme does notoccur on the tens of parsec scales but must occur on larger scales.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
