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Extragalactic H_2O masers and X-ray absorbing column densities
Having conducted a search for the λ 1.3 cm (22 GHz) water vaporline towards galaxies with nuclear activity, large nuclear columndensities or high infrared luminosities, we present H2O spectra for NGC2273, UGC 5101, and NGC 3393 with isotropic luminosities of 7, 1500, and400 Lȯ. The H2O maser in UGC 5101 is by far the mostluminous yet found in an ultraluminous infrared galaxy. NGC 3393 revealsthe classic spectrum of a "disk maser", represented by three distinctgroups of Doppler components. As in all other known cases except NGC4258, the rotation velocity of the putative masing disk is well below1000 km s-1. Based on the literature and archive data, X-rayabsorbing column densities are compiled for the 64 galaxies withreported maser sources beyond the Magellanic Clouds. For NGC 2782 andNGC 5728, we present Chandra archive data that indicate the presence ofan active galactic nucleus in both galaxies. Modeling the hard nuclearX-ray emission, NGC 2782 is best fit by a high energy reflectionspectrum with NH 1024 cm-2. ForNGC 5728, partial absorption with a power law spectrum indicatesNH 8 × 1023 cm-2. Thecorrelation between absorbing column and H2O emission is analyzed. Thereis a striking difference between kilo- and megamasers with megamasersbeing associated with higher column densities. All kilomasers (L_H_2O< 10 Lȯ) except NGC 2273 and NGC 5194 areCompton-thin, i.e. their absorbing columns are <1024cm-2. Among the H{2}O megamasers, 50% arise fromCompton-thick and 85% from heavily obscured (>1023cm-2) active galactic nuclei. These values are not larger butconsistent with those from samples of Seyfert 2 galaxies not selected onthe basis of maser emission. The similarity in column densities can beexplained by small deviations in position between maser spots andnuclear X-ray source and a high degree of clumpiness in thecircumnuclear interstellar medium.
| Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black holeresearch, as seen from a purely observational standpoint. Since theearly ‘90s, rapid technological advances, most notably the launchof the Hubble Space Telescope, the commissioning of the VLBA andimprovements in near-infrared speckle imaging techniques, have not onlygiven us incontrovertible proof of the existence of supermassive blackholes, but have unveiled fundamental connections between the mass of thecentral singularity and the global properties of the host galaxy. It isthanks to these observations that we are now, for the first time, in aposition to understand the origin, evolution and cosmic relevance ofthese fascinating objects.
| New H2O masers in Seyfert and FIR bright galaxies
Using the Effelsberg 100-m telescope, detections of four extragalacticwater vapor masers are reported. Isotropic luminosities are ~50, 1000, 1and 230 Lȯ for Mrk 1066 (UGC 2456), Mrk 34, NGC 3556 andArp 299, respectively. Mrk 34 contains by far the most distant and oneof the most luminous water vapor megamasers so far reported in a Seyfertgalaxy. The interacting system Arp 299 appears to show two maserhotspots separated by approximately 20´´. With these newresults and even more recent data from Braatz et al. (2004, ApJ, 617,L29), the detection rate in our sample of Seyferts with known jet-NarrowLine Region interactions becomes 50% (7/14), while in star forminggalaxies with high (S100~μ m>50 Jy) far infrared fluxesthe detection rate is 22% (10/45). The jet-NLR interaction sample maynot only contain “jet-masers” but also a significant numberof accretion “disk-masers” like those seen in NGC 4258. Astatistical analysis of 53 extragalactic H2O sources (excluding theGalaxy and the Magellanic Clouds) indicates (1) that the correlationbetween IRAS Point Source and H2O luminosities, established forindividual star forming regions in the galactic disk, also holds forAGN-dominated megamaser galaxies; (2) that maser luminosities are notcorrelated with 60 μm/100 μm color temperatures; and (3) that onlya small fraction of the luminous megamasers (L_H_2O > 100Lȯ) detectable with 100-m sized telescopes have so farbeen identified. The H2O luminosity function (LF) suggests that thenumber of galaxies with 1 Lȯ < L_H_2O < 10Lȯ, the transition range between“kilomasers” (mostly star formation) and“megamasers” (active galactic nuclei), is small. The overallslope of the LF, ~-1.5, indicates that the number of detectable masersis almost independent of their luminosity. If the LF is not steepeningat very high maser luminosities and if it is possible to find suitablecandidate sources, H2O megamasers at significant redshifts should bedetectable even with present day state-of-the-art facilities.
| Spectral characteristics of water megamaser galaxies. II. ESO 103-G035, TXS 2226-184, and IC 1481
Long-slit optical emission-line spectra of the H2O megamasergalaxies ESO 103-G035, TXS2226-184, and IC 1481 are evaluated inorder to look for characteristics typical for water-megamaser galaxies.We present rotation curves, line ratios, electron densities,temperatures, and Hβ luminosities. The successful line-profiledecompositions rest on d-Lorentzians with an additional parameter d toadjust the wings, rather than Gaussians or Lorentzians as basicfunctions. No significant velocity gradient is found along the majoraxis in the innermost 2 kpc of TXS 2226-184.IC 1481 reveals a spectrum suggestive of a vigorousstarburst in the central kiloparsec 108 years ago. None ofthe three galaxies shows any hints for outflows nor special featureswhich could give clues to the presence of H2O megamaseremission. The galaxies are of normal Seyfert-2 (ESO103-G035) or LINER (TXS 2226-184,IC 1481) type.Based on observations collected at the European Southern Observatory,Chile.
| Spectral Analysis of four Water-megamaser Galaxies: Rotation-curves, Emission-line Profiles and Ratios
Not Available
| A Survey for H2O Megamasers. III. Monitoring Water Vapor Masers in Active Galaxies
We present single-dish monitoring of the spectra of 13 extragalacticwater megamasers taken over a period of 9 years and a single epoch ofsensitive spectra for seven others. The primary motivation is a searchfor drifting line velocities analogous to those of the systemic featuresin NGC 4258, which are known to result from centripetal acceleration ofgas in an edge-on, subparsec molecular disk. We detect a velocity driftanalogous to that in NGC 4258 in only one source, NGC 2639. Another, themaser source in NGC 1052, exhibits erratic changes in its broad maserprofile over time. Narrow maser features in all of the other diskgalaxies discussed here either remain essentially constant in velocityover the monitoring period or are sufficiently weak or variable inintensity that individual features cannot be traced reliably from oneepoch to the next. In the context of a circumnuclear, molecular diskmodel, our results suggest that either (a) the maser lines seen aresystemic features subject to a much smaller acceleration than present inNGC 4258, presumably because the gas is farther from the nuclear blackhole, or (b) we are detecting ``satellite'' lines for which theacceleration is in the plane of the sky.Our data include the first K-band science observations taken with thenew 100 m Green Bank Telescope (GBT). The GBT data were taken duringtesting and commissioning of several new components and so are subjectto some limitations; nevertheless, they are in most cases the mostsensitive H2O spectra ever taken for each source and cover800 MHz (~=10,800 km s-1) of bandwidth. Many new maserfeatures are detected in these observations. Our data also include atentative and a clear detection of the megamaser in NGC 6240 at epochs ayear and a few months, respectively, prior to the detections reported byHagiwara et al. and Nakai et al.We also report a search for water vapor masers toward the nuclei of 58highly inclined (i>80deg), nearby galaxies. These sourceswere selected to investigate the tendency that H2O megamasersfavor inclined galaxies. None were detected, confirming that megamasersare associated exclusively with active galactic nuclei.
| High-energy sources before INTEGRAL. INTEGRAL reference catalog
We describe the INTEGRAL reference catalog which classifies previouslyknown bright X-ray and gamma-ray sources before the launch of INTEGRAL.These sources are, or have been at least once, brighter than ~ 1 mCrababove 3 keV, and are expected to be detected by INTEGRAL. This catalogis being used in the INTEGRAL Quick Look Analysis to discover newsources or significantly variable sources. We compiled several publishedX-ray and gamma-ray catalogs, and surveyed recent publications for newsources. Consequently, there are 1122 sources in our INTEGRAL referencecatalog. In addition to the source positions, we show an approximatespectral model and expected flux for each source, based on which wederive expected INTEGRAL counting rates. Assuming the default instrumentperformances and at least ~ 105 s exposure time for anypart of the sky, we expect that INTEGRAL will detect at least ~ 700sources below 10 keV and ~ 400 sources above 20 keV over the missionlife.The Catalog is available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/411/L59
| Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177supernovae (SNe) that have been discovered since 1997 during the courseof the Lick Observatory Supernova Search with the Katzman AutomaticImaging Telescope. Whereas SNe Ia occur in all galaxy types, it isfound, at a high level of statistical confidence, that SNe Ib, Ic, andII are strongly concentrated in late-type galaxies. However, attentionis drawn to a possible exception provided by SN 2001I. This SN IInoccurred in the E2 galaxy UGC 2836, which was not expected to harbor amassive young supernova progenitor.
| Observational study on extragalactic H2O megamaser sources and associated molecular emission lines
Since the first extragalactic H2O megamaser source toward theactive galactic nuclei NGC 4945 was discovered, 19 sources have beenfound. The observational study of extragalactic H2O megamasersources and molecular emission lines associated with AGNs is a veryefficient tool to investigate characteristics of central sources in AGNsand circumnuclear tori of gas and dust. Current researches of searching,observation and theory on extragalactic H2O megamaser sourcesand associated molecular emission lines are mainly reviewed in thispaper.
| H I Absorption in the Gigamaser Galaxy TXS 2226-184 and the Relation between H I Absorption and Water Emission
We report on the discovery of H I in absorption toward the gigamasergalaxy TXS 2226-184 using the Very Large Array. The absorption appearsto consist of two components-one with a width of 125 km s-1and one broader (420 km s-1)-both toward the compact radiosource in the nucleus of the galaxy. Based on these large velocitywidths, we suggest that the H I absorption is produced in the centralparsecs of the galaxy, on a scale similar to that which gives rise tothe water maser emission. This brings to eight the number of galaxiesknown to exhibit both water masers and H I absorption. We explore therelationship between these two phenomena and present a physicallymotivated (but unfruitful) search for water maser emission in five radiogalaxies known to exhibit strong H I absorption.
| A Search for H2O Maser Emission in Southern Active Galactic Nuclei and Star-forming Galaxies: Discovery of a Maser in the Edge-on Galaxy IRAS F01063-8034
We report the cumulative results of five surveys for H2Omaser emission at 1.35 cm wavelength in 131 active galactic nuclei(AGNs) and star-forming galaxies, conducted at the Parkes Observatorybetween 1993 and 1998. We detected one new maser, in the edge-on galaxyIRAS F01063-8034, which exhibits a single ~0.1 Jy spectral feature at4282+/-6 km s-1 (heliocentric) with an unusually large54+/-16 km s-1 half-power full width. The centroid velocityof the emission increased to 4319.6+/-0.6 km s-1 (38+/-2 kms-1 width) over the 13 days between discovery andconfirmation of the detection. A similarly broad-line width and largechange in velocity has been noted for the maser in NGC 1052, wherein jetactivity excites the emission. Neither optical spectroscopy,radio-infrared correlations, nor infrared colors provide compellingevidence of unusual activity in the nucleus of IRAS F01063-8034. Sincethe galaxy appears to be outwardly normal at optical and infraredwavelengths, detection of an H2O maser therein is unique. Themaser emission is evidence that the galaxy harbors an AGN that isprobably obscured by the edge-on galactic disk. The detection highlightsthe possibility that undetected AGNs could be hidden in other relativelynearby galaxies. No other maser emission features have been identifiedat velocities between 3084 and 6181 km s-1.
| Spectral analysis of four water-megamaser galaxies: rotation-curves, emission-line profiles and ratios.
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| H2O megamasers in extragalaxies
Main observational results and theoretical studies for H2Omegamasers are briefly reviewed. The H2O megamaser emissionoften originates in thin circumnuclear disks near the centers of activegalactic nuclei (AGN) and has been detected in 20 galaxies withisotropic luminosities of about 10 - 6000 Lsolar. All ofmegamaser galaxies show evidence for nuclear activity, being classifiedas either Seyfert 2 or LINER, so there appears to be a link between themegamaser phenomenon and AGN. There was a trend for megamasers to occurpreferentially in highly inclined host galaxies. The AGN apparentlyproduces the seed radio photons and the X-ray photons or shock wavesneed to pump the maser material. The observed spectral charateristicssupport a model with inverted molecular gas located in front of thenuclear source that in part amplifies the background continuum.
| Supernova 2000ey in IC 1481
IAUC 7531 available at Central Bureau for Astronomical Telegrams.
| X-ray Emission Mechanisms of LINERs
We present here an analysis of the X-ray properties of a sample of LINERgalaxies observed with the ROSAT PSPC and HRI instruments. A spatialanalysis shows that the bulk of the X-ray emission is consistent witharising from a point source; some extended emission appears at weakemission levels. The X-ray spectra are formally best described by apowerlaw with photon index Γ_x ~ -2 or thermal emission from aRaymond-Smith plasma with highly subsolar abundances (Z <= 0.1).Several emission mechanisms that might contribute to the observed X-rayspectra are discussed. In particular, we take the very subsolarabundances derived from Raymond-Smith fits as an indication of a morecomplex emission mechanism, like the presence of a second hard componentor plasma out of equilibrium.
| An Imaging and Spectroscopic Survey of Galaxies within Prominent Nearby Voids. II. Morphologies, Star Formation, and Faint Companions
We analyze the optical properties of ~300 galaxies within and aroundthree prominent voids of the Center for Astrophysics Redshift Survey. Wedetermine CCD morphologies and Hα equivalent widths from ourimaging and spectroscopic survey. We also describe a redshift survey of250 neighboring galaxies in the imaging survey fields. We assess themorphology-density relation, EW(Hα)-density relation, and theeffects of nearby companions for galaxies in low-density environmentsselected with a smoothed large-scale (5 h-1 Mpc) galaxynumber density n. Both the morphological mix and the Hα line widthdistribution of galaxies at modest underdensities, 0.5R=16.13, demonstrates that the incidence ofa close companion in redshift space is insensitive to global densityover the range we investigate (0.163 σ) fromΔcz>~200 km s-1 at 0.5-1 at n<=0.5n. In the lowest densityenvironments, galaxies with companions clearly (~4 σ) havestronger star formation than comparable galaxies at larger globaldensity (0.5-1 kpc and 1000 km s-1) varies little over theentire density range. These results, combined with the luminosity- andcolor-density relations of this sample (Paper I), suggest that theformation and evolution of field galaxies are insensitive to large-scaleunderdensity down to a threshold of roughly half the mean density. Thedifferences in galaxy properties at the lowest global densities we canexplore (n<=0.5n) may be explained by (1) a relative scarcity of thesmall-scale primordial density enhancements needed to form massiveearly-type/absorption-line galaxies and (2) present-day galaxyencounters that are relatively more effective because of the lowervelocity dispersion on small scales (<~200 h-1 kpc) weobserve in these regions. In the voids, where the luminous galaxiespresumably formed more recently, there should be more gas and dustpresent for active star formation triggered by nearby companions.
| The FIR-radio correlation of Wolf-Rayet galaxies and the role of star formation in LINERs
We find that a preliminary classification of LINERs' energetics may bemade in terms of the FIR-radio correlation of Wolf-Rayet galaxies. TheAGN- or starburst-supported LINERs can be distinguished by theirFIR-to-radio ratio, Qequiv L(1.4GHz)/ L(60mum )> or <0.01. It isinteresting to note that almost all the LINERs with inner rings might bestarburst-supported, indicating reduced AGN activities compared withthose of the AGN-supported ones. We also find that a shock-heating phasefor the warm dust component might be important for some starbursts atthe burst age of >= 107 yr, with Q<0.001.
| The role of star formation in liners.
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| Observational Evidence for Massive Black Holes in the Centers of Active Galaxies
Naturally occurring water vapor maser emission at 1.35 cm wavelengthprovides an accurate probe for the study of accretion disks aroundhighly compact objects, thought to be black holes, in the centers ofactive galaxies. Because of the exceptionally fine angular resolution,200 microarcseconds, obtainable with very long baseline interferometry,accompanied by high spectral resolution, < 0.1 km/s, the dynamics andstructures of these disks can be probed with exceptional clarity. Thedata on the galaxy NGC4258 are discussed here in detail. The mass of theblack hole binding the accretion disk is 3.9 times 10^7 solar masses.Although the accretion disk has a rotational period of about 800 years,the physical motions of the masers have been directly measured with VLBIover a period of a few years. These measurements also allow the distancefrom the earth to the black hole to be estimated to an accuracy of 4percent. The status of the search for other maser/black hole candidatesis also discussed.
| 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.
| Soft X-ray properties of LINERs
Not Available
| An Imaging and Spectroscopic Survey of Galaxies within Prominent Nearby Voids. I. The Sample and Luminosity Distribution
We study the optical properties of a large sample of galaxies inlow-density regions of the nearby universe. We make a 5 h-1Mpc smoothed map of the galaxy density throughout the Center forAstrophysics Redshift Survey (CfA2) to identify galaxies within threeprominent nearby ``voids'' with diameter >~30 h-1 Mpc. Weaugment the CfA2 void galaxy sample with fainter galaxies found in thesame regions from the more recent and deeper Century and Redshiftsurveys . We obtain B and R CCD images and high signal-to-noiselong-slit spectra for the resulting sample of 149 void galaxies, as wellas for an additional 131 galaxies on the periphery of these voids. Herewe describe the photometry for the sample, including B isophotalmagnitudes and B-R colors. For the 149 galaxies that lie in regionsbelow the mean survey density, the luminosity functions in B and R arewell fit by Schechter functions with respective parameters(αB=-0.5+/-0.3, B*=-18.9+/-0.2) and(αR=-0.9+/-0.3, R*=-20.4+/-0.3). The Bluminosity function (LF) is consistent with typical survey LFs (e.g.,the Southern Sky Redshift Survey), and the R LF is consistent with theCentury Survey. The B and R LFs of 131 galaxies in the ``voidperiphery''-regions between the mean density and twice the mean-havesimilar Schechter parameters. The CfA2 LF is inconsistent with bothsamples at the 3.5 σ level. When we narrow our analysis to the 46galaxies in regions below half the mean density, the LF is significantlysteeper: α~-1.4+/-0.5. The typical survey LFs are inconsistentwith this subsample at the ~2 σ level. The B-R color distributionof galaxies in the lowest density regions is also shifted significantly(~3 σ) blueward of the higher density samples. The most luminousred galaxies (R<~-21) are absent from the lowest density regions at the2.5 σ level.
| X-ray properties of LINERs
We present an investigation of the X-ray properties of 13 LINERs basedon {ROSAT} all-sky survey and pointed PSPC and HRI observations. Severalsources are studied for the first time in X-rays. The X-ray spectra arebest described by a powerlaw with photon index {Gamma_x } ~ -2.0 orthermal emission from gas with very subsolar abundances. Theluminosities range between log L_x = 37.7 (NGC 404) and 40.8 (NGC 4450).No X-ray variability on the timescale of hours/days is detected. This isin line with the suggestion that LINERs may accrete in theadvection-dominated mode. On a longer term, one of the objects, NGC2768, turns out to be slightly variable. Some sources appear to beextended at weak emission levels whereas the bulk of the X-ray emissionis consistent with arising from a point source within the PSPCinstrumental resolution. L_x/L_B ratios are derived and emissionmechanisms that potentially contribute to the observed X-rayluminosities are discussed. We also examine the presence of second X-raysources near the target sources both in terms of instrumental effectsand in terms of `real' sources within the LINER galaxies.
| Doppler Shift Asymmetry in High-Velocity Maser Emission from Shocks in Circumnuclear Disks
The rapidly rotating, masing circumnuclear disk in the central subparsecregion of the galaxy NGC 4258 is remarkably circular and Keplerian, yeta striking asymmetry appears in the maser spectrum: the redshifted,high-velocity sources are much more numerous and significantly moreintense than the blueshifted ones. A similar strong asymmetry alsoappears in the recently discovered, masing, circumnuclear disks in NGC1068 and NGC 4945, thus suggesting it may be a general phenomenon. Weshow that the observed Doppler shift asymmetry can naturally arise dueto spiral shocks in circumnuclear disks. We argue that populationinversion can largely be quenched in these systems because of IR photontrapping, and that the high-velocity maser emission originates withinthin slabs of postshock gas, where the physical conditions are conduciveto maser action. The high-velocity masers with the longest gain pathsappear where the line of sight is tangent to shock fronts. Since thespirals have a trailing geometry due to the action of differentialrotation, the locations of the masers make the blueshifted radiationtravel through a column of non-inverted gas that maintains closevelocity coherence with the maser source, where absorption occurs. Theresulting asymmetry in the high-velocity maser spectrum, where theredshifted emission appears systematically stronger, is independent ofthe existence of a warp in the disk or the azimuthal direction to theobserver, and is insensitive to small distortions in the velocity fieldin the disk. The high velocities of these features reflect therotational velocities in the disk and have nothing to do with the shockspeed. The low-velocity emission arises within a narrow annulus near theinner edge of the disk, where direct irradiation by a central source mayprovide the energy that ultimately powers these masers. In NGC4258--currently the most well-defined masing disk--the proposed scenariocan also account for the intriguing clustering of the high-velocitymaser spots in distinct clumps, the restricted radial distribution ofthe low-velocity sources, and the dip in the maser spectrum at thesystemic velocity of the disk. In this case, we infer a moleculardensity of ~109 cm-3, a disk mass of ~104 Mȯ, and a mass accretionrate of order ~7 x 10-3 Mȯ yr-1, which is consistent with anadvection-dominated accretion flow. These results differ significantlyfrom those of the Neufeld and Maloney model (~=107.5 cm-3, ~100 Mȯ,and ~7 x 10-5 alpha Mȯ yr-1, respectively). The predicted maserluminosities of the blueshifted and redshifted, high-velocity featuresin NGC 4258 are consistent with the observations, both in the case ofC-type (MHD) shocks and dissociative J-type shocks, where the shockspeed is about 20 km s-1. The high-velocity features arise nearly alonga diameter through the disk that makes an angle of about 2 deg with themidline. It does not introduce any noticeable deviation from a Keplerianrotation curve (the velocity gradient across the shock is alwaysperpendicular to the line of sight at a maser location). The correctionsto the previously derived black hole mass and galaxy distance arenegligible. Predictions include slow systematic drifts in the velocityand position of all the high-velocity features, a systematicdisplacement in the locations of the high-velocity maser sources fromthe disk midline, and the existence of circumnuclear disks that aredelineated only by high-velocity maser emission.
| 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.
| 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.
| The spatial distribution of active galactic nuclei. I - The density of Seyfert galaxies and liners
A sample of 26 Seyfert 1 and 23 Seyfert 2 galaxies, 33 low-ionizationnuclear emission regions (LINERs), one QSO and three other objects fromthe CfA Redshift Survey is used to calculate the spatial density ofbright active galactic nuclei (AGNs). Classical Seyfert galaxiescomprise 1.3 percent of all galaxies at integrated absolute magnitude-20.0, which agrees with previous estimates based on more incompletesamples. The fraction of galaxies that are AGNs rises steeply withabsolute magnitude. Three of the five galaxies in the CfA survey moreluminous than M(B) = -21.5 are AGNs; the two most luminous galaxies inthe CfA survey are both Seyfert 1 galaxies. The integrated space densityof Seyfert 2 galaxies is found to be approximately twice as large as thespace density of Seyfert 1 galaxies. Measurement of the spatial densityof LINERs and other types of AGNs is subject to severe optical selectioneffects.
| The far-infrared properties of the CfA galaxy sample. I - The catalog
IRAS flux densities are presented for all galaxies in the Center forAstrophysics magnitude-limited sample (mB not greater than 14.5)detected in the IRAS Faint Source Survey (FSS), a total of 1544galaxies. The detection rate in the FSS is slightly larger than in thePSC for the long-wavelength 60- and 100-micron bands, but improves by afactor of about 3 or more for the short wavelength 12- and 25-micronbands. This optically selected sample consists of galaxies which are, onaverage, much less IR-active than galaxies in IR-selected samples. Itpossesses accurate and complete redshift, morphological, and magnitudeinformation, along with observations at other wavelengths.
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