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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.
| 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.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| 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.
| 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.
| A multiparametric analysis of the Einstein sample of early-type galaxies. 1: Luminosity and ISM parameters
We have conducted bivariate and multivariate statistical analysis ofdata measuring the luminosity and interstellar medium of the Einsteinsample of early-type galaxies (presented by Fabbiano, Kim, &Trinchieri 1992). We find a strong nonlinear correlation betweenLB and LX, with a power-law slope of 1.8 +/- 0.1,steepening to 2.0 +/- if we do not consider the Local Group dwarfgalaxies M32 and NGC 205. Considering only galaxies with logLX less than or equal to 40.5, we instead find a slope of 1.0+/- 0.2 (with or without the Local Group dwarfs). Although E and S0galaxies have consistent slopes for their LB-LXrelationships, the mean values of the distribution functions of bothLX and LX/LB for the S0 galaxies arelower than those for the E galaxies at the 2.8 sigma and 3.5 sigmalevels, respectively. We find clear evidence for a correlation betweenLX and the X-ray color C21, defined by Kim,Fabbiano, & Trinchieri (1992b), which indicates that X-rayluminosity is correlated with the spectral shape below 1 keV in thesense that low-LX systems have relatively large contributionsfrom a soft component compared with high-LX systems. We findevidence from our analysis of the 12 micron IRAS data for our samplethat our S0 sample has excess 12 micron emission compared with the Esample, scaled by their optical luminosities. This may be due toemission from dust heated in star-forming regions in S0 disks. Thisinterpretation is reinforced by the existence of a strongL12-L100 correlation for our S0 sample that is notfound for the E galaxies, and by an analysis of optical-IR colors. Wefind steep slopes for power-law relationships between radio luminosityand optical, X-ray, and far-IR (FIR) properties. This last point arguesthat the presence of an FIR-emitting interstellar medium (ISM) inearly-type galaxies is coupled to their ability to generate nonthermalradio continuum, as previously argued by, e.g., Walsh et al. (1989). Wealso find that, for a given L100, galaxies with largerLX/LB tend to be stronger nonthermal radiosources, as originally suggested by Kim & Fabbiano (1990). We notethat, while LB is most strongly correlated withL6, the total radio luminosity, both LX andLX/LB are more strongly correlated with L6CO, the core radio luminosity. These points support the argument(proposed by Fabbiano, Gioia, & Trinchieri 1989) that radio cores inearly-type galaxies are fueled by the hot ISM.
| An X-ray catalog and atlas of galaxies
An X-ray catalog and atlas of galaxies observed with the EinsteinObservatory imaging instruments (IPC and HRI) are presented. The catalogcomprises 493 galaxies, including targets of pointed observations, andRSA or RC2 galaxies serendipitously included in Einstein fields. A totalof 450 of these galaxies were imaged well within the instrumentalfields, resulting in 238 detections and 2123 sigma upper limits. Theother galaxies were either at the edge of the visible field of view orconfused with other X-ray sources. For these a rough measure of theirX-ray emission is also given. The atlas shows X-ray contour maps ofdetected galaxies superposed on optical photographs and givesazimuthally averaged surface brightness profiles of galaxies detectedwith a high signal-to-noise ratio.
| The neutral hydrogen content of early type disk galaxies
This paper presents the results of a sensitive 21-cm survey of massiveearly type galaxies made with the Arecibo radio telescope. Of the 81galaxies observed, the detections comprise 48 percent of the S0s, 73percent of the S0a's, and 96 percent of the Sa's. The values of thehybrid, distance-independent H I surface densities of the S0 galaxies inthe sample ranged continuously from amounts comparable to the mostgas-rich Sa galaxies to low estimated upper limts of the H I content.CCD images of most of the gas-rich S0s revealed either faint spiralfeatures or patchy structure in the disks. While no firm correlationbetween H I content and environmental density is apparent for thegalaxies in the sample, two-sample statistics suggest a differencebetween the highest and the lowest density bins. Early-type diskgalaxies within low density environments tend to have higher gas surfacedensities than those within high-density environments.
| UGC galaxies stronger than 25 mJy at 4.85 GHz
UGC galaxies in the declination band +5 to +75 deg were identified byposition coincidence with radio sources stronger than 25 mJy on theGreen Bank 4.85 GHz sky maps. Candidate identifications were confirmedor rejected with the aid of published aperture-synthesis maps and new4.86 GHz VLA maps having 15 or 18 arcsec resolution, resulting in asample of 347 nearby radio galaxies plus five new quasar-galaxy pairs.The radio energy sources in UGC galaxies were classified as 'starbursts'or 'monsters' on the basis of their infrared-radio flux ratios, infraredspectral indices, and radio morphologies. The rms scatter in thelogarithmic infrared-radio ratio q is not more than 0.16 for starburstgalaxies selected at 4.85 GHz. Radio spectral indices were obtained fornearly all of the UGC galaxies, and S0 galaxies account for adisproportionate share of the compact flat-spectrum (alpha less than0.5) radio sources. The extended radio jets and lobes produced bymonsters are preferentially, but not exclusively, aligned within about30 deg of the optical minor axes of their host galaxies. The tendencytoward minor-axis ejection appears to be independent of radio-sourcesize and is strongest for elliptical galaxies.
| Radio emission and the hot interstellar medium of early-type galaxies
The results of an analysis of a sample of 84 elliptical and S0 galaxies,observed in X-rays with the Einstein Observatory and in radio continuumat 5 GHz, are reported. Radio flux densities result in some of thelowest radio powers yet reported for early-type galaxies. Radiostructures extending beyond the optical radius are found only ingalaxies with 5 GHz radio power greater than about 10 exp 29.5ergs/s/Hz. Radio and X-ray luminosities are correlated, although withlarge intrinsic scatter, suggesting that more than one mechanism may beinvolved. A correlation between core radio power and theX-ray-to-optical ratio suggests a connection between the hot ISM andnuclear radio sources and points to accreting cooling flows as the fuelfor the radio sources. For the same radio core power, extended radiolobes tend to be associated with galaxies with relatively smallerX-ray-to-optical ratios, pointing to the importance of the hot ISM indisrupting the radio jets and confining extended radio structures.
| Properties of the X-ray emitting gas in early-type galaxies
The properties of the X-ray emitting gas in a sample of 81 E and S0galaxies observed with the Einstein Observatory are studied. Measuredfluxes for 55 of the galaxies and upper limits for 26 of them arereported. An attempt is made to use consistent optical parameters forthe galaxies, including a correction to the velocities for theVirgocentric flow. The sample is then used to explore the contributionfrom discrete sources, the global physical properties of the hot gas,and the implications for heating by supernovae and gravity. Finally, thequestion of the presence of heavy halos is addressed.
| X-ray emission from E and S0 galaxies with compact nuclear radio sources
The imaging proportional counter on the Einstein Observatory has beenused to search for X-ray emission from 13 nearby E and S0 galaxies withcompact nuclear radio sources. Five galaxies with X-ray luminosity ofabout 10 to the 41st ergs/s were detected, and one of them was resolved.These galaxies and a few similar ones observed by others are compared toa sample of radio-quiet E and S0 galaxies. The radio-emitting galaxieshave consistently greater X-ray luminosities per unit of opticalluminosity than most radio-quiet galaxies. Possible emission mechanismsand models for the resolved source, for the most powerful source, andfor the class of E/S0 galaxies with active nuclei are discussed.
| A radio continuum survey of nearby galaxies. I - Observations at 0.4, 0.8, 4.8, and 10.7 GHz
Observations have been conducted of a total of 136 galaxies at one ormore of four frequencies: 430, 834, 4750, and 10,700 MHz. For a subsetof these, spectral indices could be determined. A mean value alpha =-0.68 + or - 0.04 is found over the whole frequency range covered. Themean high frequency spectral index (4.9-10.7 GHz) for Sc galaxies isalpha = -0.55 + or - 0.07, which indicates the presence of significantamounts of thermal emission in a considerable fraction of the sample. At10.7 GHz the mean thermal contribution to the radio emission of thesample Sc galaxies is 35 + or - 15 percent; for the sample Sb galaxiesthis is 20 + or - 15 percent.
| Radial velocities of galaxies detected in the Arecibo 2380 MHz survey
The Loiano telescope's image tube spectrograph was used to obtain thepreviously unknown radial velocities of 50 galaxies detected during theArecibo 2380 MHz survey of bright galaxies, leading to the determinationof 224 radio-detected galaxy redshifts north of 15 deg. Both a 100km/sec typical standard error and minus 60 plus or minus 20 km/secsystematic zero error are derived for the velocities presented, on thebasis of comparisons with other redshift sources made on a furthersample of 35 galaxies.
| VLBI observations of galactic nuclei
A three telescope VLBI survey has been carried out of optically brightgalaxies with nuclear radio sources which are unresolved at a fewseconds of arc. Twenty out of 58 galaxies were detected at 18 cm,indicating the presence of radio structure on a scale of about 10milli-arcsec. Most of these were normal galaxies, although emissionlines were present in many cases. Fifteen of the galaxies detected inthe survey (as well as M51, M81, and M82) were then observed in a sixtelescope VLBI network experiment to determine the general structure ofthe compact nuclear sources. Models of the milli-arcsec radio structurewere developed for 17 of these 18 galaxies. Except for the unusuallycomplex source in M87, the models are all composed of a small number ofcomponents in a region no larger than a few parsecs. They resemblemodels and hybrid maps of the compact sources in quasars and activegalaxies, indicating that a common physical mechanism is probablyresponsible for the compact radio sources in a wide range of opticalobjects.
| Very-long-baseline interferometry of compact sources in bright galaxies
Thirty-one optically bright galaxies with compact radio nuclei have beenobserved with a 20-million-wavelength baseline at 2380 MHz. Thirteennuclei have been detected, with angular sizes smaller than 0.01 arcsec.Twelve of the detected nuclei have flat spectra and are about 1 pc, orsmaller, in size. This confirms the continuity of properties from theradio nuclei of strong radio galaxies to the less-luminous nuclei ofnearby bright galaxies.
| Compact radio sources in and near bright galaxies
Compact radio sources in galaxies stronger than 35 mJy at 2380 MHz fromthe Arecibo survey of galaxies brighter than a photographic magnitude of+14.5 have been detected and observed at 2695 and 8085 MHz with the NRAOthree-element interferometer. Accurate radio and optical positions showthat all compact radio sources identifiable with these galaxies arelocated in their nuclei. Five new BSO (blue stellar object)/galaxy pairswere discovered, and the BSO 0241 +011 lies in a spiral arm of thegalaxy U02210 = N1073. The number of BSO/galaxy pairs is compatible withrandom projection of cosmological QSOs onto bright galaxy fields. Mostof the nuclear compact sources, and nearly all of those with flatspectra, are found in E or S0 galaxies. Early Hubble subtypes arefavored in spiral galaxies with compact radio sources, and there is astrong tendency for them to occur in paired galaxies. These observationsare interpreted in terms of accretion by massive black holes in galacticnuclei.
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