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The Feedback-regulated Growth of Black Holes and Bulges through Gas Accretion and Starbursts in Cluster Central Dominant Galaxies
We present an analysis of the growth of black holes through accretionand bulges through star formation in 33 galaxies at the centers ofcooling flows. Most of these systems show evidence of cavities in theintracluster medium (ICM) inflated by radio jets emanating from theiractive galactic nuclei (AGNs). We present a new and extensive analysisof X-ray cavities in these systems. We find that AGNs are energeticallyable to balance radiative losses (cooling) from the ICM in more thanhalf of our sample. We examine the relationship between cooling and starformation and find that the star formation rates are approaching or arecomparable to X-ray and far-UV limits on the rates of gas condensationonto the central galaxy. The vast gulf between radiative losses and thesink of cooling material, which has been the primary objection tocooling flows, has narrowed significantly. Using the cavity (jet)powers, we place strong lower limits on the rate of growth of thecentral black holes, and we find that they are growing at an averagerate of ~0.1 Msolar yr-1, with some systemsgrowing as quickly as ~1 Msolar yr-1. We find atrend between bulge growth (star formation) and black hole growth thatis approximately in accordance with the slope of the local (Magorrian)relation between black hole and bulge mass, but the scatter suggeststhat bulges and black holes do not necessarily grow in lockstep. Bondiaccretion can power the low-luminosity sources, provided the nuclear gasdensity rises as ~r-1 to the Bondi radius, but is probablytoo feeble to fuel the most powerful outbursts.
| The galaxy cluster Abell 3581 as seen by Chandra
We present results from an analysis of a Chandra observation of thecluster of galaxies Abell 3581. We discover the presence of apoint-source in the central dominant galaxy that is coincident with thecore of the radio source PKS 1404-267. The emission from theintracluster medium is analysed, both as seen in projection on the sky,and after correcting for projection effects, to determine the spatialdistribution of gas temperature, density and metallicity. We find thatthe cluster, despite hosting a moderately powerful radio source, shows atemperature decline to around 0.4 Tmax within the central 5kpc. The cluster is notable for the low entropy within its core. We testand validate the XSPEC PROJCT model for determining the intrinsiccluster gas properties.
| Particle energies and filling fractions of radio bubbles in cluster cores
Using Chandra images of cluster cores with clear radio bubbles, we havedetermined k, which is the ratio of the total particle energy to that ofthe electrons radiating between 10 MHz and 10 GHz. Radiative anddynamical constraints on the bubbles indicate that the ratio of theenergy factor, k, to the volume filling factor, f, lies within the range1 <~k/f<~ 1000. Assuming pressure equilibrium between theradio-emitting plasma and the surrounding X-ray gas, none of the lobeshas equipartition between relativistic particles and magnetic field.There is no evidence for any dependence of the upper limit of the k/fratio on any physical parameter of the cluster or the radio source. Thedistribution of the upper limit on k/f appears to be bimodal, the valuebeing ~3 for some clusters and ~300 for the others. We show that thismay be due to the composition of the jet which forms the bubbles, thevariation in the volume filling fraction or variation in the amount ofreacceleration occurring in the bubble.
| Thermal conduction and reduced cooling flows in galaxy clusters
Conduction may play an important role in reducing cooling flows ingalaxy clusters. We analyse a sample of 16 objects using Chandra dataand find that a balance between electron conduction and cooling canexist in the hotter clusters (T>~ 5 keV), provided that the plasmaconductivity is close to the unhindered Spitzer value. In the absence ofany additional heat sources, a reduced mass inflow must then develop inthe cooler objects in the sample. We fit cooling flow models todeprojected spectra and compare the spectral mass deposition rates foundto the values required to account for the excess luminosity, assumingSpitzer-rate heat transfer over the observed temperature gradients. Themeasured mass inflow rates are insufficient to maintain energy balancein at least five clusters. However, emission from cooling gas may bepartially absorbed. We also compute the flux supplied by turbulent heattransport and find conductivity profiles that follow a strikinglysimilar temperature dependence to the conductivity values required toprevent cooling. The larger-scale turbulent motions implied by thisprocess are required to have velocities of between 10 and 50 per cent ofthe speed of sound in the local intracluster gas.
| K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
We investigate the near-infrared K-band properties of the brightestcluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters andgroups, using data from the Two Micron All Sky Survey. Our clustersample spans a factor of 70 in mass, making it sensitive to any clustermass-related trends. We derive the cumulative radial distribution forthe BCGs in the ensemble and find that 70% of the BCGs are centered inthe cluster to within 5% of the virial radius r200; thisquantifies earlier findings that BCG position coincides with the clustercenter as defined by the X-ray emission peak. We study the correlationsbetween the luminosity of the BCGs (Lb) and the mass and theluminosity of the host clusters, finding that BCGs in more massiveclusters are more luminous than their counterparts in less massivesystems and that the BCGs become less important in the overall clusterlight (L200) as cluster mass increases. By examining a largesample of optically selected groups, we find that these correlationshold for galactic systems less massive than our clusters(<3×1013 Msolar). From the differencesbetween luminosity functions in high- and low-mass clusters, we arguethat BCGs grow in luminosity mainly by merging with other luminousgalaxies as the host clusters grow hierarchically; the decreasing BCGluminosity fraction (Lb/L200) with cluster massindicates that the rate of luminosity growth in BCGs is slow compared tothe rate at which clusters acquire galaxy light from the field or othermerging clusters. Utilizing the observed correlation between the clusterluminosity and mass and a merger tree model for cluster formation, weestimate that the amount of intracluster light (ICL) increases withcluster mass; our calculations suggest that in 1015Msolar clusters more than 50% of total stellar mass is inICL, making the role of ICL very important in the evolution andthermodynamic history of clusters. The cluster baryon fractionaccounting for the ICL is in good agreement with the value derived fromcosmic microwave background observations. The inclusion of ICL reducesthe discrepancy between the observed cluster cold baryon fraction andthat found in hydrodynamical simulations. Based on the observed ironabundance in the intracluster medium, we find that the ICL predicted byour model, together with the observed galaxy light, match the ironmass-to-light ratio expected from simple stellar population models,provided that the Salpeter initial mass function is adopted. The ICLalso makes it easier to produce the ``iron excess'' found in the centralregions of cool-core clusters.
| Uniformity of foreground Galactic neutral hydrogen over cooling flow clusters
Radio maps at 21 cm of foreground neutral hydrogen over three coolingflow clusters of galaxies show that the foreground gas is uniform onscales from ~1-10 arcmin. Five sigma limits on fluctuations in theforeground column density for Abell 3581, Sersic 159-03 and Abell 2597are 6.2 × 1019, 7.8 × 1019 and 4.3× 1019 cm-2, or 14, 43 and 17 per cent ofthe mean foreground column density in the region of the system,respectively. Fluctuations in the column density of neutral gas in theGalaxy are unlikely to account for any excesses of photoelectricabsorption in these or other cooling flow clusters. Fluctuations in theforeground neutral gas on arcmin scales are also unlikely to be thecause of excess extreme ultraviolet and soft X-ray emission fromclusters.
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| Interferometric Phase Calibration Sources in the Declination Range 0° to -30°
We present a catalog of 321 compact radio sources in the declinationrange 0deg>δ>-30deg. The positions ofthese sources have been measured with a two-dimensional rms accuracy of35 milliarcseconds using the NRAO6 VeryLarge Array. Each source has a peak flux density >50 mJy at 8.4 GHz. Weintend for this catalog to be used mainly for selection of phasecalibration sources for radio interferometers, although compact radiosources have other scientific uses.
| 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.
| The black hole mass of low redshift radiogalaxies
We make use of two empirical relations between the black hole mass andthe global properties (bulge luminosity and stellar velocity dispersion)of nearby elliptical galaxies, to infer the mass of the central blackhole (CM MBH) in low redshift radiogalaxies. Using the mostrecent determinations of black hole masses for inactive early typegalaxies we show that the bulge luminosity and the central velocitydispersion are almost equally correlated (similar scatter) with thecentral black-hole mass. Applying these relations to two large andhomogeneous datasets of radiogalaxies we find that they host black-holeswhose mass ranges from ~ 5*E7 to ~ 6*E9CMMsun (average ~ 8.9). CMMBH is found to be proportional to the mass of the bulge (CMMbulge). The distribution of the ratio CM MBH/CMMbulge has a mean value of 8*E-4 and shows ascatter that is consistent with that expected from the associatederrors. At variance with previous claims no significant correlation isinstead found between CM MBH (or CM Mbulge) andthe radio power at 5 GHz.
| The VLBA Calibrator Survey-VCS1
A catalog containing milliarcsecond-accurate positions of 1332extragalactic radio sources distributed over the northern sky ispresented-the Very Long Baseline Array Calibrator Survey (VCS1). Thepositions have been derived from astrometric analysis of dual-frequency2.3 and 8.4 GHz VLBA snapshot observations; in a majority of cases,images of the sources are also available. These radio sources aresuitable for use in geodetic and astrometric experiments, and asphase-reference calibrators in high-sensitivity astronomical imaging.The VCS1 is the largest high-resolution radio survey ever undertaken andtriples the number of sources available to the radio astronomy communityfor VLBI applications. In addition to the astrometric role, this surveycan be used in active galactic nuclei, Galactic, gravitational lens, andcosmological studies.
| Active Galactic Nucleus Black Hole Masses and Bolometric Luminosities
Black hole mass, along with mass accretion rate, is a fundamentalproperty of active galactic nuclei (AGNs). Black hole mass sets anapproximate upper limit to AGN energetics via the Eddington limit. Wecollect and compare all AGN black hole mass estimates from theliterature; these 177 masses are mostly based on the virial assumptionfor the broad emission lines, with the broad-line region size determinedfrom either reverberation mapping or optical luminosity. We introduce200 additional black hole mass estimates based on properties of the hostgalaxy bulges, using either the observed stellar velocity dispersion orthe fundamental plane relation to infer σ these methods assumethat AGN hosts are normal galaxies. We compare 36 cases for which blackhole mass has been generated by different methods and find, forindividual objects, a scatter as high as a couple of orders ofmagnitude. The less direct the method, the larger the discrepancy withother estimates, probably due to the large scatter in the underlyingcorrelations assumed. Using published fluxes, we calculate bolometricluminosities for 234 AGNs and investigate the relation between blackhole mass and luminosity. In contrast to other studies, we find nosignificant correlation of black hole mass with luminosity, other thanthose induced by circular reasoning in the estimation of black holemass. The Eddington limit defines an approximate upper envelope to thedistribution of luminosities, but the lower envelope depends entirely onthe sample of AGNs included. For any given black hole mass, there is arange in Eddington ratio of up to 3 orders of magnitude.
| The Parkes quarter-Jansky flat-spectrum sample. I. Sample selection and source identifications
We present a new sample of quarter-Jansky flat-spectrum radio sourcesselected to search for high-redshift quasars and to study the evolutionof the flat-spectrum quasar population. The sample comprises 878 radiosources selected from the Parkes catalogues with spectral indices alpha5 GHz_2.7 GHz >=-0.4 where Snu ~ nu alpha. The sample covers all right ascensions and the declination rangefrom -80fdg0 to +2fdg5 , excluding low galactic latitudes (mid b mid< 10deg) and the Magellanic Cloud regions. We haveobtained improved radio source positions, firstly to reconfirm themajority of the existing identifications, and secondly, using digitizedsky-survey data and deep B, Gunn-i and Gunn-z CCD-imaging, to findoptical identifications for 223 previously-unidentified sources. Wepresent the final catalogue of 878 flat-spectrum sources: 827 arecompact radio sources identified with galaxies, quasars and BL Lacobjects, 38 have either extended radio structure or are identified withGalactic objects (PN, HII or non-compact radio source), 4 are obscuredby Galactic stars, and 9 (1 per cent of the total sample) remainunidentified. Full Appendices A-D are only available in electronic format http://www.edpsciences.org
| The Infrared Surface Brightness Fluctuation Hubble Constant
We measured infrared surface brightness fluctuation (SBF) distances toan isotropically distributed sample of 16 distant galaxies withredshifts reaching 10,000 km s-1 using the near-IR camera andmultiobject spectrometer (NICMOS) on the Hubble Space Telescope (HST).The excellent spatial resolution, very low background, and brightness ofthe IR fluctuations yielded the most distant SBF measurements to date.Twelve nearby galaxies were also observed and used to calibrate theF160W (1.6 μm) SBF distance scale. Of these, three have Cepheidvariable star distances measured with HST and eleven have optical I-bandSBF distance measurements. A distance modulus of 18.5 mag to the LargeMagellanic Cloud was adopted for this calibration. We present the F160WSBF Hubble diagram and find a Hubble constant H0=76+/-1.3 (1σ statistical) +/-6 (systematic) km s-1Mpc-1. This result is insensitive to the velocity model usedto correct for local bulk motions. Restricting the fit to the six mostdistant galaxies yields the smallest value of H0=72+/-2.3 kms-1 Mpc-1 that is consistent with the data. This6% decrease in the Hubble constant is consistent with the hypothesisthat the Local Group inhabits an underdense region of the universe, butis also consistent with the best-fit value of H0=76 kms-1 Mpc-1 at the 1.5 σ level. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by AURA, Inc.,under NASA contract NAS 5-26555.
| The fundamental plane of radio galaxies
We collected photometrical and dynamical data for 73 low red-shift(z<0.2) Radio Galaxies (LzRG) in order to study their FundamentalPlane (FP). For 22 sources we also present new velocity dispersion datathat complement the photometric data given in our previous study of LzRG(Govoni et al. \cite{Govoni00}a). It is found that the FP of LzRG issimilar to the one defined by non-active elliptical galaxies, with LzRGrepresenting the brightest end of the population of early type galaxies.Since the FP mainly reflects the virial equilibrium condition, ourresult implies that the global properties of early-type galaxies(defining the FP) are not influenced by the presence of gas accretion inthe central black hole. This is fully in agreement with the recentresults in black hole demography, showing that virtually all luminousspheroidal galaxies host a massive black hole and therefore maypotentially become active. We confirm and extend to giant ellipticalsthe systematic increase of the mass-to-light ratio with galaxyluminosity. Based on observations collected at European SouthernObservatory, La Silla, Chile.
| Optical integral field spectroscopy of the extended line emission around six radio-loud quasars
We present integral field spectroscopy of a small sample of radio-loudquasars at intermediate redshift (0.26
| Optical surface photometry of radio galaxies. II. Observations and data analysis
Optical imaging observations for 50 radio galaxies are presented. Foreach object isophotal contours, photometric profiles, structuralparameters (position angle, ellipticity, Fourier coefficients), andtotal magnitudes are given. These observations, obtained in the CousinsR band, complement the data presented in a previous paper and are partof a larger project aimed at studying the optical properties of lowredshift (z<= 0.12) radio galaxies (Govoni et al. 1999). Comments foreach individual source are reported.
| The optical properties of low redshift radio galaxies
We present morphological and photometric properties of 79 low redshift(z<=0.12) radio galaxies extracted from two radio flux limitedsamples of radio sources. All objects are imaged in the R band and for asubsample we have also obtained B band images. The sample includessources of both FRI and FRII radio morphological type. Through thedecomposition of the luminosity profiles and the analysis of thestructural profiles (ellipticity, PA, c4) of the galaxies we are able tocharacterize in detail the optical properties of the radio galaxies. Itis found that most of host galaxies are luminous bulge dominated systemssimilar to normal giant ellipticals. Some cases of additional diskcomponents are found whose spheroid-to-disk luminosity ratio is similarto that found in S0 galaxies. The average absolute magnitude is =-24.0 with a clear trend for FRI sources tobe ~ 0.5 mag brighter than FRII galaxies. In about 40% of the objectsobserved we find an excess of light in the nucleus that is attributed tothe presence of a nuclear point source whose luminosity is on average ~1-2% of the total flux of the host galaxy. The luminosity of thesenuclear point sources appears correlated with the core radio power ofthe galaxies. Radio galaxies follow the same mu_e - R_e relationship asnormal elliptical galaxies. The distribution of ellipticity, the amountof twisting and shape of isophotes (boxy, disky) do not differsignificantly from other ellipticals. The evidence for recentinteractions is therefore rather modest. Finally on average radiogalaxies are bluer and have a color dispersion larger than normalelliptical galaxies, and the average color gradient in radio galaxiesappears slightly steeper than in normal ellipticals. These resultssupport a scenario where radio emission is weakly related with theoverall properties and/or the activity have negligible effects on theglobal characteristics of the host galaxy. Based on observationscollected at the European Southern Observatory, La Silla, Chile. Basedon observations collected at the Nordic Optical Telescope, La Palma.
| X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?
We investigate the X-ray properties of the Parkes sample offlat-spectrum radio sources using data from the ROSAT All-Sky Survey andarchival pointed PSPC observations. In total, 163 of the 323 sources aredetected. For the remaining 160 sources, 2sigma upper limits to theX-ray flux are derived. We present power-law photon indices in the0.1-2.4 keV energy band for 115 sources, which were determined eitherwith a hardness ratio technique or from direct fits to pointed PSPC dataif a sufficient number of photons were available. The average photonindex is =1.95^+0.13_-0.12 for flat-spectrum radio-loudquasars, =1.70^+0.23_-0.24 for galaxies, and=2.40^+0.12_-0.31 for BL Lac objects. The soft X-ray photonindex is correlated with redshift and with radio spectral index in thesense that sources at high redshift and/or with flat (or inverted) radiospectra have flatter X-ray spectra on average. The results are in accordwith orientation-dependent unification schemes for radio-loud activegalactic nuclei. Webster et al. discovered many sources with unusuallyred optical continua among the quasars of this sample, and interpretedthis result in terms of extinction by dust. Although the X-ray spectrain general do not show excess absorption, we find that low-redshiftoptically red quasars have significantly lower soft X-ray luminositieson average than objects with blue optical continua. The differencedisappears for higher redshifts, as is expected for intrinsic absorptionby cold gas associated with the dust. In addition, the scatter in log(f_x/f_o) is consistent with the observed optical extinction, contraryto previous claims based on optically or X-ray selected samples.Although alternative explanations for the red optical continua cannot beexcluded with the present X-ray data, we note that the observed X-rayproperties are consistent with the idea that dust plays an importantrole in some of the radio-loud quasars with red optical continua.
| X-ray and radio observations of the poor cluster A3581 which hosts the radio galaxy PKS 1404-267
We present new X-ray and HI 21-cm data on the poor cluster of galaxiesAbell 3581. The ASCA spectrum requires a low temperature, has a strongrequirement for excess absorption and shows evidence formulti-temperature components. The ROSAT HRI image shows the stronglypeaked emission indicative of a cooling flow. Despite the lowtemperature (~1.5-2.0 keV) and low luminosity(~2×1042ergs-1 in the 2-10keV band), Abell3581 has a mass deposition rate ~80 Msolar yr-1 which islarger than found for other nearby low-luminosity objects. VLAobservations in the 21-cm band set velocity width and spin temperaturedependent limits on the column density of atomic hydrogen.
| A Medium Survey of the Hard X-Ray Sky with the ASCA Gas Imaging Spectrometer: The (2--10 keV) Number Counts Relationship
In this paper, we report the first results of a medium survey programconducted in the 2-10 keV energy band using data from the GIS2instrument onboard the ASCA satellite. We have selected from the ASCApublic archive (as of 1996 February 14) 87 images suitable for thisproject. Sixty serendipitous X-ray sources with a signal-to-noise ratiogreater than 3.5 were found. The 2-10 keV flux of the detected sourcesranges from ~1.1 x 10-13 ergs cm-2 s-1 to ~4.1 x 10-12 ergs cm-2 s-1.Using this sample, we have extended the description of the 2-10 keV logN(>S)-log S to a flux limit of ~6.3 x 10-14 ergs cm-2 s-1 (thefaintest detectable flux), i.e., about 2.7 orders of magnitude fainterthan the Piccinotti et al. determination. The derived number-fluxrelationship is well described by a power-law model, N(>S) = K x S-alpha , with best-fit values alpha = 1.67 +/- 0.18 and K = 2.85 x 10-21deg-2. At the flux limit of the survey, about 27% of the cosmic X-raybackground in the 2-10 keV energy band is resolved in discrete sources.A flattening of the number-flux relationship, within a factor of 10 fromthe flux limit of the present survey, is expected in order to avoidsaturation. The implications of these results for models of the originof the hard X-ray background are briefly discussed.
| The Parkes Half-Jansky Flat-Spectrum Sample
We present a new sample of Parkes half-jansky flat-spectrum radiosources, having made a particular effort to find any previouslyunidentified sources. The sample contains 323 sources selected accordingto a flux limit of 0.5Jy at 2.7GHz, a spectral index measured between2.7 and 5.0GHz of alpha_2.7/5.0>-0.5, where S(nu)~nu ^alpha, Galacticlatitude |b|>20 deg and -45 deg< declination (B1950) <+10 deg.The sample was selected from a region 3.90 steradians in area. We haveobtained accurate radio positions for all the unresolved sources in thissample, and combined these with accurate optical positions fromdigitized photographic sky survey data to check all the opticalidentifications. We report new identifications based on R- and Kn-bandimaging and new spectroscopic measurements of many of the sources. Wepresent a catalogue of the 323 sources, of which 321 now have identifiedoptical counterparts and 277 have measured spectral redshifts.
| 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 of clusters and galaxies towards the Shapley Concentration
We report velocity measurements of galaxies in this, the densest massconcentration within $z=0.1$, obtained with the multifiber spectrographMEFOS at ESO, La Silla. We derive redshifts of a number of Abellclusters and draw implications for the supercluster structure. Theclusters A3554, A3566, A3577 and AS718 are confirmed as members, whilethe clusters A3524, A3531, A3542, A3545 and A3549 are shown to bebackground systems and A3581 a foreground one. Based on observationsmade at ESO, La Silla, Chile.
| CA depletion and the presence of dust in large scale nebulosities in radiogalaxies. II.
We investigate here the origin of the gas observed in extended emissionline regions surrounding AGNs. We use the technique of calcium depletionas a test to prove or disprove the existence of dust in such a gas inorder to discriminate between two main theories: (1) a cooling processfrom a hotter X-ray emitting phase surrounding the galaxy, (2) mergingor tidal interaction between two or more components. We have obtainedlong slit spectroscopy of a sample of objects representative ofdifferent galaxy types although our main interest focusses on radiogalaxies. The spectral range was set to always include the[CaII]λλ7291,7324 doublet. The faintness or absence ofsuch lines is interpreted as due to the depletion of calcium onto thedust grains and, therefore, is a proof of the existence of dust mixedwith the gas in the EELRs.
| 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.
| Brightest cluster galaxies as standard candles
We investigate the use of brightest cluster galaxies (BCGs) as standardcandles for measuring galaxy peculiar velocities on large scales. Wehave obtained precise large-format CCD surface photometry and redshiftsfor an all-sky, volume-limited (z less than or = 0.05) sample of 199BCG. We reinvestigate the Hoessel (1980) relationship between the metricluminosity, Lm, within the central 10 kpc/h of the BCGs andthe logarithmic slope of the surface brightness profile, alpha. TheLm-alpha relationship reduces the cosmic scatter inLm from 0.327 mag to 0.244 mag, yielding a typical distanceaccuracy of 17% per BCG. Residuals about the Lm-alpharelationship are independent of BCG luminosity, BCG B - Rccolor, BCG location within the host cluster, and richness of the hostcluster. The metric luminosity is independent of cluster richness evenbefore correcting for its dependence on alpha, which provides furtherevidence for the unique nature of the BCG luminosity function. Indeed,the BCG luminosity function, both before and after application of thealpha-correction, is consistent with a single Gaussian distribution.Half the BCGs in the sample show some evidence of small color gradientsas a function of radius within their central 50 kpc/h regions but withalmost equal numbers becoming redder as becoming bluer. However, withthe central 10 kpc/h the colors are remarkably constant -- the mean B -Rc color is 1.51 with a dispersion of only 0.06 mag. Thenarrow photometric and color distributions of the BCGs, the lack of'second-parameter' effects, as well as the unique rich clusterenvironment of BCGs, argue that BCGs are the most homogeneous distanceindicators presently available for large-scale structure research.
| Parsecscale Radio Cores in Early Type Galaxies
We find compact (<0.03 arcsec) radio-continuum cores in about 70 percent of radio-emitting elliptical and S0 galaxies over a wide range intotal radio power (10^21^-,10^26^ W Hz^-1^ at 5 GHz). The cores usuallyhave a flat or rising spectrum between 2.3 and 8.4 GHz, with a medianspectral index of + 0.3. Even at low luminosities, the radio emissionfrom most elliptical galaxies appears to be powered by a parsec-scale`engine' like those in classical radio galaxies and quasars. The coreand total radio power are related (P_core_ is proportional toP_total_^0.7^ on average), and the parsec-scale cores of radio galaxiesare typically one hundred times more powerful than those in `normal'giant elliptical galaxies.
| 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.
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