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The gas content of peculiar galaxies: Strongly interacting systems
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
| 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.
| Unabsorbed Seyfert 2 galaxies
We present a sample of 17 type 2 Seyfert galaxies which have an X-raycolumn density lower than 1022 cm-2. The Comptonthin nature of these sources is strongly suggested by isotropicindicators. We estimate the fraction of these sources to be in the rangeof 10%-30% of the population of type 2 Seyfert galaxies. Furthermore,this fraction appears to increase progressively at lower luminosities.The simple formulation of the Unified Model for Seyfert galaxies is notapplicable in such sources since the pc-scale molecular torus is notlikely to be responsible for the low column density observed; insteadthe absorption observed is likely to originate at larger scales.According to this hypothesis, in these objects the broad line regionsare covered by some dusty obscuring material. In particular, this couldoccur in objects with dust lanes, patches or HII regions. However, wecannot rule out that in the lowest luminosity sources the BLR is weak,absent or has faded away. This last scenario is consistent with thepredictions of some recent theoretical models for low luminosity AGNs.
| A Three-dimensional Diagnostic Diagram for Seyfert 2 Galaxies: Probing X-Ray Absorption and Compton Thickness
We present and discuss a three-dimensional diagnostic diagram forSeyfert 2 galaxies obtained using X-ray and [O III] data on a largesample of objects (reported in the Appendix). The diagram shows theKalpha iron line equivalent width as a function of both the columndensity derived from the photoelectric cutoff and the 2-10 keV fluxnormalized to the [O III] optical-line flux (the latter corrected forextinction and assumed to be a true indicator of the source intrinsicluminosity). We find that the hard X-ray properties of type 2 objectsdepend on a single parameter, the absorbing column density along theline of sight, in accordance with the unified model. The diagram can beused to identify Compton-thick sources and to isolate and study peculiarobjects. From this analysis we have obtained a column densitydistribution of Seyfert 2 galaxies that is thought to be a goodapproximation of the real distribution. A large population of heavilyabsorbed objects is discovered, including many Compton-thick candidates.Our results indicate that the mean log N_H cm^-2 in type 2 Seyfertgalaxies is 23.5 and that as many as 23%-30% of sources haveN_H>=10^24 cm^-2.
| High-Energy Spectra of Active Galactic Nuclei. II. Absorption in Seyfert Galaxies
Absorption by cold material in a large sample of active galaxies hasbeen analyzed in order to study statistically the behavior of absorbedsources. The analysis indicates that on the basis of the column densityalone, sources can be divided into low-absorption([N_{{H}}/N_{{H}_{{Gal}}}]<=50) and high-absorption([N_{{H}}/{N}_{{H}_{{Gal}}}]>=50) objects. While the second groupconsists mostly of narrow emission line galaxies (Seyfert galaxies oftype 1.9-2), the first group is less homogenous, being formed by amixture of broad and narrow emission line objects (Seyfert 1-2galaxies). A study of the distribution of the column density values bymeans of bootstrap analysis confirms the reality of this effect. Onegroup consisting of optically selected objects is well explained withinthe unified theory as nuclei obscured by a molecular torus. The secondgroup made up of X-ray- and IRAS-selected objects is more difficult todefine: in these sources the absorption is underestimated owing todifficulties (1) in fitting complex absorption spectra or (2) inmeasuring NH values in Compton-thick sources or the absorption has adifferent origin than in the torus. Possible correlations of absorptionwith X-ray luminosity, axial ratio, and Balmer decrement have also beeninvestigated. Previous suggestions that lower luminosity AGNs tend to bemore highly absorbed than those with higher luminosity are not confirmedby the present data; neither is any evidence for a correlation of NHwith axial ratio (b/a) found except for a preference of Seyfert 1-1.5galaxies to be in face-on galaxies. While some sources (Seyfert 1-1.5galaxies and low-absorption objects) have X-ray absorption compatiblewith Balmer decrement, high-absorption objects have column densitiesmuch higher than predicted from optical observations. These results arein agreement with the unified theory since the torus parameters areexpected to be independent of luminosity, its orientation should berandom with respect to the host galaxy, and its location should be inbetween the broad- and narrow-line regions. A study of the NHvariability indicates that in a large fraction (70%) of the sources forwhich the analysis could be done, NH varies on timescales from months toyears. In Seyfert 1-1.5 galaxies, the variability is associated with aregion in or near the broad-line region and is explained in terms ofpartial covering and/or warm absorption models. In Seyfert 2 galaxies,the only variability observed is that associated with narrow emissionline galaxies. The study of the column density distributions indicatesthat Seyfert 1-1.5 galaxies are characterized byN_{{H}}=18^{+9}_{-7}x1021 atoms cm-2. Seyfert 1.9-2 galaxieshave instead N_{{H}}=96^{+54}_{-35}x1021 atoms cm-2 and alarger dispersion; if this group is divided into low- andhigh-absorption objects, N_{{H}}=14.5^{+7.2}_{-5.3}x1021atoms cm-2 and N_{{H}}=132.8^{+80.1}_{-52.6} x 1021 atoms cm-2,respectively, are obtained. The observed dispersion in each group isconsistent with being entirely due to column density variability.
| Unified theories of active galactic nuclei: a hard X-ray sample of Seyfert 2 galaxies
We have re-analysed the Ginga 2-18 keV X-ray observations of Seyfert 2galaxies, and find that their mean spectrum can be described by a powerlaw of index alpha~1, reflection from an optically thick accretion discand/or molecular torus, and absorption from cold material. These objectsthen have a mean intrinsic spectrum similar to that of Seyfert 1s, andso support the predictions of orientation-dependent Seyfert unificationschemes. There is also an intrinsic dispersion about this mean spectrumwhich is similar to that seen in the Seyfert 1s. We demonstrate thisdispersion explicitly in several objects with data of highsignal-to-noise ratio, where the intrinsic spectra are much flatter orsteeper than alpha~1 despite the inclusion of neutral reflection,ionized reflection, unobscured reflection and/or ionized absorption.This is important, as a currently popular explanation for the Seyfert 1spectra (and hence the Seyfert 2 spectra presented here) is that ofHaardt & Maraschi, in which the UV seed photons for Compton coolingof the energetic electrons are produced from reprocessing of the hardX-ray spectrum in an accretion disc. This feedback model correctlypredicts the observed mean spectral index of alpha~1 for a wide range ofoptical depths. Steeper spectra than this can be produced naturally inthese models if the thermal plasma optical depth approaches unity or ifthere is intrinsic emission from the disc itself. However, such modelsare unable easily to explain intrinsic spectra much flatter thanalpha~1. Thus the flat-spectrum sources presented here, which are mostreminiscent of the atypical Seyfert galaxy NGC 4151, pose seriousproblems for the Haardt & Maraschi model if there are no otherexternal processes modifying the hard X-ray spectra in Seyfert galaxies.
| A Multiwavelength Catalog of Seyfert 2 Galaxies Observed in the 2--10 keV Energy Band
This paper is a catalog of Seyfert 2 galaxies observed in the 2-10 keVband (339 flux entries). In total, it contains data on 150 objects; for76 objects, a positive detection is reported, while for the remainingsources, 2 σ upper limits to the X-ray emission are given. Most ofthe data have been collected from the literature over a period startingfrom 1974 up to the middle of 1995. Accurate searches of literature anddatabases were performed for all objects, and frequently spectral fitswere reevaluated in order to make the data in the catalog uniform andcomplete. Some unpublished data are also included. For six objects,EXOSAT/ME date have been extracted from the satellite database andanalyzed; the 13 fluxes obtained have been added to the present catalog.The compilation of hard X-ray data has been complemented with data inthe soft (0.1-3 keV) X-ray band, as well as in ultraviolet (1450 A),optical (5500 A), infrared (3.5, 12, 25, 60, 100 micron), and radio (6cm) bands. Fluxes of the [O II] λ5007 and Hβ emission linesas well as the Balmer decrement Hα/Hβ, and axial ratio a/bare also given. The present database is meant to be a useful tool forthe study of the Seyfert 2 phenomenon in its various aspects.
| The Montreal Blue Galaxy survey. 2: Second list of UV-bright candidates
We present and discuss the second list of the Montreal Blue Galaxysurvey. Following the inspection of 71 plates, we found 237 newcandidates with B less than 15.5. 73 percent of them are also detectedby Infrared Astronomy Satellite (IRAS). Spectrophotometry was carriedout, at medium resolution, for a subset of 40 objects leading to theidentification of three new AGNs and producing 13 new radial velocities.Spectral classification of our candidates confirms our previous findingthat the majority of our candidates are starburst nucleus galaxiessimilar to the objects studied by Balzano in 1983. Our survey is biasedagainst the high excitation starburst H II galaxies and the LINERgalaxies. Metallicities of our galaxies are found to be from log(O/H)=8.4 to 9.0, which suggests galaxies in advanced stages of chemicalevolution.
| X-ray and infrared selected AGN. II - Optical spectroscopy
In a search for obscured active galactic nuclei, 144 X-ray/IR emittinggalaxies were selected. Optical spectroscopy of this sample ispresented. A classification according to the nuclear activity shows that28 are AGN, 39 are transition-type objects, and 44 are H II region-likegalaxies. Three of the 28 AGN are Seyfert 1 galaxies and the others areof Type 2. It is suggested that the objects identified as narrow lineAGN are obscured Seyfert 1. Most of the observed galaxies are seenedge-on, indicating that dust may have a flattened distribution coplanarto the disk of the parent galaxy. With the inclusion of the newlyidentified AGN, the sample of the X-ray emitting Seyfert 2 galaxies isfairly complete above a flux limit of log F(Hx) = -10.8.
| Southern Galaxy Catalogue.
Not Available
| A catalog of morphological types in 55 rich clusters of galaxies
Data are presented from a study of 55 rich clusters of galaxies. Thedata include positions, morphological types, estimated total magnitudes,bulge sizes, and ellipticities for about 6000 galaxies, as determinedfrom high scale photographic plates. Data reduction procedures aredescribed, and a brief analysis of cluster richness, which indicatesthat Abell richness classes are only rough indicators of total clustermembership, is included.
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