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Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| The High-Energy Spectrum of NGC 4151
We present the first INTEGRAL observations of the type 1.5 Seyfertgalaxy NGC 4151. Combining several INTEGRAL observations performedduring 2003, totaling ~400 ks of exposure time, allows us to study thespectrum in the 2-300 keV range. The measurements presented here revealan overall spectrum from X-rays up to soft gamma-rays that can bedescribed by an absorbed (NH=6.9×1022cm-2) model based on a Compton continuum from a hot electronpopulation (kTe=94 keV) from an optically thick (τ=1.3)corona, reflected on cold material (R=0.7), consistent with earlierclaims. The time-resolved analysis shows little variation of thespectral parameters over the duration of the INTEGRAL observations. Thecomparison with CGRO OSSE data shows that the same spectral model can beapplied over a time span of 15 yr, with flux variations of the order ofa factor of 2 and changes in the underlying continuum reflected by thetemperature of the electron population (kTe=50-100 keV). Whenmodeled with an exponential cutoff power law plus Compton reflection,this results in photon indices ranging from Γ=1.5 to 1.9 and acutoff energy in the range 100-500 keV.
| X-ray obscuration and obscured AGN in the local universe
We discuss the X-ray properties of 49 local (z<0.035) Seyfert 2galaxies with HST/WFC2 high-resolution optical coverage. It includes theresults of 26 still unpublished Chandra and XMM-Newton observations,which yield 25 (22) new X-ray detections in the 0.5-2 keV (2-10 keV)energy band. Our sample covers a range in the 2-10 keV observed flux,F2-10, from 3 × 10-11 to 6 ×10-15 erg cm-2 s-1. The percentage ofobjects that are likely obscured by Compton-thick matter (columndensity, NH ≥ σt-1 ≃1.6 × 1024 cm-2) is ≃50%, and reaches≃80% for log (F2-10) < 12.3. Hence, Kαfluorescent iron lines with large Equivalent Width ({EW} > 0.6 keV)are common in our sample (6 new detections at a confidence level≥2σ). They are explained as due to reflection off theilluminated side of optically thick material. We confirm a correlationbetween the presence of a 100-pc scale nuclear dust in the WFC2 imagesand Compton-thin obscuration. We interpret this correlation as due tothe large covering fraction of gas associated with the dust lanes. TheX-ray spectra of highly obscured AGN invariably present a prominent softexcess emission above the extrapolation of the hard X-ray component.This soft component can account for a very large fraction of the overallX-ray energy budget. As this component is generally unobscured - andtherefore likely produced in extended gas structures - it may lead to asevere underestimation of the nuclear obscuration in z 1 absorbedAGN, if standard X-ray colors are used to classify them. As a by-productof our study, we report the discovery of a soft X-ray, luminous(≃7 × 1040 erg s-1) halo embedding theinteracting galaxy pair Mkn 266.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| The Tully-Fisher Relation of Barred Galaxies
We present new data exploring the scaling relations, such as theTully-Fisher relation (TFR), of bright barred and unbarred galaxies. Aprimary motivation for this study is to establish whether barrednesscorrelates with, and is a consequence of, virial properties of galaxies.Various lines of evidence suggest that dark matter is dominant in disksof bright unbarred galaxies at 2.2 disk scale lengths, the point of peakrotation for a pure exponential disk. We test the hypothesis that theTully-Fisher (TF) plane of barred high surface brightness galaxies isoffset from the mean TFR of unbarred galaxies, as might be expected ifbarred galaxies are ``maximal'' in their inner parts. We use existingand new TF data to search for basic structural differences betweenbarred and unbarred galaxies. Our new data consist of two-dimensionalHα velocity fields derived from SparsePak integral fieldspectroscopy and V- and I-band CCD images collected at the WIYNObservatory2 for 14 strongly barredgalaxies. Differences may exist between kinematic and photometricinclination angles of barred versus unbarred galaxies. These findingslead us to restrict our analysis to barred galaxies withi>50deg. We use WIYN/SparsePak (two-dimensional) velocityfields to show that long-slit (one-dimensional) spectra yield reliablecircular speed measurements at or beyond 2.2 disk scale lengths, farfrom any influence of the bar. This enables us to consider line widthmeasurements from extensive TF surveys that include barred and nonbarreddisks and derive detailed scaling relation comparisons. We find that fora given luminosity, barred and unbarred galaxies have comparablestructural and dynamical parameters, such as peak velocities, scalelengths, and colors. In particular, the location of a galaxy in the TFplane is independent of barredness. In a global dynamical sense, barredand unbarred galaxies behave similarly and are likely to have, onaverage, comparable fractions of luminous and dark matter at a givenradius.
| 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
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| An Ultraviolet/Optical Atlas of Bright Galaxies
We present wide-field imagery and photometry of 43 selected nearbygalaxies of all morphological types at ultraviolet and opticalwavelengths. The ultraviolet (UV) images, in two broad bands at 1500 and2500 Å, were obtained using the Ultraviolet Imaging Telescope(UIT) during the Astro-1 Spacelab mission. The UV images have ~3"resolution, and the comparison sets of ground-based CCD images (in oneor more of B, V, R, and Hα) have pixel scales and fields of viewclosely matching the UV frames. The atlas consists of multiband imagesand plots of UV/optical surface brightness and color profiles. Otherassociated parameters, such as integrated photometry and half-lightradii, are tabulated. In an appendix, we discuss the sensitivity ofdifferent wavebands to a galaxy's star formation history in the form of``history weighting functions'' and emphasize the importance of UVobservations as probes of evolution during the past 10-1000 Myr. We findthat UV galaxy morphologies are usually significantly different fromvisible band morphologies as a consequence of spatially inhomogeneousstellar populations. Differences are quite pronounced for systems in themiddle range of Hubble types, Sa through Sc, but less so for ellipticalsor late-type disks. Normal ellipticals and large spiral bulges arefainter and more compact in the UV. However, they typically exhibitsmooth UV profiles with far-UV/optical color gradients which are largerthan any at optical/IR wavelengths. The far-UV light in these cases isprobably produced by extreme horizontal branch stars and theirdescendants in the dominant, low-mass, metal-rich population. The coolstars in the large bulges of Sa and Sb spirals fade in the UV while hotOB stars in their disks brighten, such that their Hubble classificationsbecome significantly later. In the far-UV, early-type spirals oftenappear as peculiar, ringlike systems. In some spiral disks, UV-brightstructures closely outline the spiral pattern; in others, the disks canbe much more fragmented and chaotic than at optical wavelengths.Contributions by bright active galactic nuclei (AGNs) to the integratedUV light in our sample range from less than 10% to nearly 100%. A numberof systems have unusual UV-bright structures in their inner disks,including rings, compact knots, and starburst nuclei, which could easilydominate the UV light in high-redshift analogs. A significant butvariable fraction of the far-UV light in spiral disks is diffuse ratherthan closely concentrated to star-forming regions. Dust in normal spiraldisks does not control UV morphologies, even in some highly inclineddisk systems. The heaviest extinction is apparently confined to thinlayers and the immediate vicinity of young H II complexes; the UV lightemerges from thicker star distributions, regions evacuated of dust byphotodestruction or winds, or by virtue of strong dust clumpiness. Onlyin cases where the dust layers are disturbed does dust appear to be amajor factor in UV morphology. The UV-bright plume of M82 indicates thatdust scattering of UV photons can be important in some cases. In acompanion paper, we discuss far-UV data from the Astro-2 mission andoptical comparisons for another 35 galaxies, emphasizing face-onspirals.
| A Possible Relationship between Quasars and Clusters of Galaxies
The distribution on the sky of clusters of galaxies shows significantassociation with relatively nearby, large, active galaxies. The patternis that of clusters paired equidistant across a central galaxy with theapparent magnitudes and redshifts of their constituent galaxies beingclosely matched. The clusters and the galaxies in them tend to be strongX-ray and radio emitters, and their redshifts occur at preferredredshift values. The central, low-redshift galaxies often show evidenceof ejection in the direction of these higher redshift clusters. In allthese respects the clusters resemble closely quasars which have beenincreasingly shown for the last 34 years to be similarly associated withactive parent galaxies. New, especially significant pairings of quasarsare presented here, which are, at the same time, associated with Abellclusters of galaxies. It is argued here that, empirically, the quasarsare ejected from active galaxies. They evolve to lower redshift withtime, forming stars, and fragmenting at the end of their developmentinto clusters of low-luminosity galaxies. The cluster galaxies can be atthe same distance as their lower redshift parents because they stillretain a component of their earlier, quasar intrinsic redshift.
| A Comparison of Ultraviolet Imaging Telescope Far-Ultraviolet and Hα Star Formation Rates
We have used archival ultraviolet (UV) imaging of 50 nearby star-forminggalaxies obtained with the Ultraviolet Imaging Telescope (UIT) to deriveintegrated near-UV and far-UV magnitudes, and have combined these datawith Hα, far-infrared, and thermal radio continuum measurements toexplore the consistency of UV and Hα star formation rates (SFRs).In agreement with previous studies, we find that the UV and HαSFRs are qualitatively consistent, even before corrections forextinction are applied. The uncorrected UV SFRs are systematically lowerby a factor of 1.5 (with a factor of 2 scatter) among luminous galaxieswith SFR>~1 Msolar yr-1, indicating a highereffective attenuation of the far-UV radiation. Among less luminousgalaxies there is no significant offset between the Hα and far-UVSFR scales. This behavior is consistent with that of higher redshiftsamples observed by Sullivan et al., Glazebrook et al., and Yan et al.for comparable ranges of galaxy luminosities and absolute SFRs.Far-infrared and thermal radio continuum data available for a subset ofour sample allow us to estimate the attenuation in the UV and atHα independently. The UV and Hα attenuations appear to becorrelated, and confirm systematically higher attenuations in the UV.Although the galaxies in our sample show modest levels of attenuation(with median values of 0.9 mag at Hα and 1.4 mag at 1550 Å),the range across the sample is large, ~4 mag for Hα and >~5 magin the far-UV (1550 Å). This indicates that the application of asingle characteristic extinction correction to Hα or UV SFRs isonly realistic for large, well-defined and well-studied galaxy samples,and that extinction bias may be important for UV oremission-line-selected samples of star-forming galaxies.
| Homogenization of the Stellar Population along Late-Type Spiral Galaxies
We present a study of the broadband UBV color profiles for 257 Sbcbarred and nonbarred galaxies, using photoelectric aperture photometrydata from the literature. Using robust statistical methods, we haveestimated the color gradients of the galaxies, as well as the total andbulge mean colors. A comparative photometric study using CCD images wasdone. In our sample, the color gradients are negative (reddish inward)in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. The results do not change, essentially,when we include the edge-on galaxies. As a consequence of this study wehave also found that barred galaxies are overrepresented among theobjects having null or positive gradients, indicating that bars act as amechanism of homogenization of the stellar population. This effect ismore evident in the U-B color index, although it can also be detected inthe B-V color. A correlation between the total and bulge colors wasfound that is a consequence of an underlying correlation between thecolors of bulges and disks found by other authors. Moreover, the meantotal color is the same irrespective of the gradient regime, whilebulges are bluer in galaxies with null or positive gradients, whichindicates an increase of the star formation rate in the central regionsof these objects. We have also made a quantitative evaluation of theamount of extinction in the center of these galaxies. This was doneusing the Wide Field Planetary Camera 2 (WFPC2) and the Near InfraredCamera and Multi-Object Spectrometer (NICMOS) Hubble Space Telescope(HST) archival data, as well as CCD B, V, and I images. We show thatalthough the extinction in the V-band can reach values up to 2 mag inthe central region, it is unlikely that dust plays a fundamental role inglobal color gradients. We found no correlation between color and O/Habundance gradients. This result could suggest that the color gradientsare more sensitive to the age rather than to the metallicity of thestellar population. However, the absence of this correlation may becaused by dust extinction. We discuss this result by considering apicture in which bars are a relatively fast, recurrent phenomenon. Theseresults are not compatible with a pure classical monolithic scenario forbulge and disk formation. On the contrary, they favor a scenario inwhich both these components are evolving in a correlated process inwhich stellar bars play a crucial role. Based partly on observationsmade at the Pico dos Dias Observatory (PDO/LNA-CNPq), Brazil.
| Spectroscopic identification of ten faint hard X-ray sources discovered by Chandra
We report optical spectroscopic identifications of 10 hard (2-10 keV)X-ray selected sources discovered by Chandra. The X-ray flux of thesources ranges between 1.5 and 25 x 10^ - 14 erg cm^ - 2 s^ - 1, thelower value being 3 times fainter than in previous BeppoSAX and ASCAsurveys. Their R band magnitudes are in the range 12.8-22. Six of theChandra sources are broad line quasars with redshifts between 0.42 and1.19, while the optical identification of the remaining four is quitevaried: two are X-ray obscured, emission line AGN at z = 0.272 and z =0.683, one is a starburst galaxy at z = 0.016 and one, most unusually,is an apparently normal galaxy at z = 0.158. These findings confirm andextend down to fainter X-ray fluxes the BeppoSAX results, in providingsamples with a wide range of X-ray and optical properties. The ratiobetween the soft X-ray and the optical luminosity of the z = 0.158galaxy is a factor at least 30 higher than that of normal galaxies, andsimilar to those of AGN. The high X-ray luminosity and the lack ofoptical emission lines suggest an AGN in which either continuum beamingdominates, or emission lines are obscured or not efficiently produced.
| The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the Very Large Array (VLA) FIRST survey and the AutomatedPlate Measuring Facility (APM) catalog of the Palomar Observatory SkySurvey I (POSS-I) plates as the basis for constructing a newradio-selected sample of optically bright quasars. This is the firstradio-selected sample that is competitive in size with current opticallyselected quasar surveys. Using only two basic criteria, radio-opticalpositional coincidence and optical morphology, quasars and BL Lacobjects can be identified with 60% selection efficiency; the efficiencyincreases to 70% for objects fainter than 17 mag. We show that a moresophisticated selection scheme can predict with better than 85%reliability which candidates will turn out to be quasars. This paperpresents the second installment of the FIRST Bright Quasar Survey(FBQS), with a catalog of 636 quasars distributed over 2682deg2. The quasar sample is characterized and all spectra aredisplayed. The FBQS detects both radio-loud and radio-quiet quasars outto redshift z>3. We find a large population of objects ofintermediate radio loudness; there is no evidence in our sample for abimodal distribution of radio characteristics. The sample includes ~29broad absorption line quasars, both high and low ionization, and anumber of new objects with remarkable optical spectra.
| The active galaxy NGC 4151: Archetype or exception?
The Seyfert galaxy NGC 4151 harbors in its nucleus the most intensivelystudied AGN (Active Galactic Nucleus). Among the brightest AGN (inapparent luminosity) it is the most widely variable and the variationsof its ultraviolet and X-ray spectrum have been studied on time scalesranging from hours to decades. These observations have formed the basisof methods and models which have been found to generally apply to broademission line AGN: the rich and complex relation between the X-ray andUV variations, the comptonization model of the X-ray spectrum frommedium X-ray to γ-rays, the reverberation mapping, thestratification in velocity and physical conditions of the gas in thebroad line region, and a method to estimate the black hole mass fromemission line variability. The large barred spiral which hosts thisnucleus has been extensively studied especially in the central region.Inflow of gas along the x1 and possibly also thex2 orbits have been detected, but since the accretion disk isnot in the galactic plane (as evidenced by the significant angleseparating the radio axis and the rotation axis of the galaxy) theincoming gas seen on kpcs scale must, as it flows further inward, moveout of the galactic plane, along trajectories which are entirelyunknown.
| Star formation in distant starburst galaxies
This paper discusses the stellar population content of distant (5 000 kms^{-1} <== V_R<=16 000 km s^{-1}) galaxies with enhancedstar-formation activity. Distinction is made between isolated galaxiesand galaxies morphologically disturbed, with clear signs of interactionsuch as mergers. In these galaxies the International UltravioletExplorer (M_BoxIUE) large aperture samples most of the galaxy's body.Consequently, the resulting integrated spectra arise primarily from bluestellar populations of different ages together with significantcontributions from intermediate and old age components, subject tovarying reddening amounts. Instead of analysing individual, usually lowSignal-to-Noise ratio (S/N) spectra, our approach is to coadd thespectra of objects with similar spectral properties in the UV,considering as well their properties in the visible/near-infraredranges. Consequently, the resulting high (S/N) template spectra containthe average properties of a rather uniform class of objects, andinformation on spectral features can now be analysed with moreprecision. Three groups have been found for the interacting galaxies,corresponding to a red, blue and very blue continuum. Isolated galaxieshave been separated into two groups, one with a flat/red continuum andthe other with a blue continuum. For comparison, we also include in thepresent analysis two groups of nearby disturbed galaxies. Stellarpopulations are analysed by means of a synthesis algorithm based on starcluster spectral components of different ages which fit the observedspectra both in terms of continuum distribution and spectral features.Flux fractions of the different age groups found in the synthesis havebeen transformed into mass fractions, allowing inferences on the starformation histories. Young stellar populations (age <500 Myr) are themain flux contributors, except for the groups with a red spectrum notdue to extinction, arising from the intermediate (age ~1 - 2 Gyr) andold age populations. We also study the reddening values and theextinction law: a Small Magellanic Cloud-like extinction law isappropriate for all cases. As compared to nearby galaxies with enhancedstar-formation, the distant starburst galaxy spectral groups exhibitlarger contributions from the intermediate and old age populations. Thiseffect is mainly accounted for by the larger spatial area sampled by theM_BoxIUE slit in the distant galaxies, including not only the entirebulge but also evolved disk populations. The present results provide aquantitative measure of the star-forming activity in interactinggalaxies, compared to isolated galaxies. Based upon data collected withthe International Ultraviolet Explorer (IUE) Satellite, supported byNASA, SERC and ESA.
| Gas dynamics in the barred Seyfert galaxy NGC 4151 - II. High-resolution HI study
We present sensitive, high angular resolution (6x 5 arcsec^2) lambda21-cm observations of the neutral hydrogen in the nearby barred Seyfertgalaxy, NGC 4151. These HI observations, obtained using the VLA in Bconfiguration, are the highest resolution of this galaxy to date, andreveal hitherto unprecedented detail in the distribution and kinematicsof the HI on sub-kiloparsec scales. A complete analysis and discussionof the HI data are presented and the global properties of the galaxy arerelated to the bar dynamics presented in Paper I. HI absorption,consistent with previous studies, is detected against the radiocontinuum nucleus and shows two components - a deep absorptioncomponent, centred at 987 +/- 1 km s^-1 and width 87 +/- 3 km s^-1, anda weaker component, redshifted to 1096 +/- 6 km s^-1 with a width of 35+/- 15 km s^-1. An alternative fit is also presented. In addition to theabsorption, a high velocity cloud is detected in emission, coincidentwith the nucleus. This cloud is redshifted by 260 km s^-1 from systemic,has an HI mass of 2.3 x 10^7 M_solar, and corresponds to outflow on thefar side of the nucleus. Contrary to previous studies, no HI bridge isdetected reaching from the shocks directly across the nucleus. Instead,the gas streams from the shocks on to smaller orbits and forms fingersof HI that wind around the nucleus, consistent with predictions fromgeneral numerical simulations of bars. These fingers correspond closelywith dust arcs seen in optical studies and resemble nuclear featuresseen by others in weak barred galaxies such as M100. A new rotationcurve is presented, extending to within 8 arcsec of the nucleus andshowing a turnover at a radius of ~35 arcsec, which was previouslyundetected in lower resolution studies. The corresponding resonancecurve and the properties of the shocks (Paper I) yield a bar patternspeed of 24.5 +/- 3.7 km s^-1 and one inner Lindblad resonance (ILR) ata radius of 2.8 +/- 0.6 kpc. Our observations, however, do not rule outthe possibility of an inner ILR.
| 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 Hubble Space Telescope Imaging Survey of Nearby Active Galactic Nuclei
We have obtained WFPC2 images of 256 of the nearest (z <= 0.035)Seyfert 1, Seyfert 2, and starburst galaxies. Our 500 s broadband(F606W) exposures reveal much fine-scale structure in the centers ofthese galaxies, including dust lanes and patches, bars, rings, wisps,and filaments, and tidal features such as warps and tails. Most of thisfine structure cannot be detected in ground-based images. We haveassigned qualitative classifications for these morphological featuresand a Hubble type for the inner region of each galaxy, and we have alsomeasured quantitative information such as 0."18 and 0."92 aperturemagnitudes, position angles, and ellipticities, where possible. There islittle direct evidence for unusually high rates of interaction in theSeyfert galaxies. Slightly less than 10% of all the galaxies show tidalfeatures or multiple nuclei. The incidence of inner starburst rings isabout 10% in both classes of Seyfert galaxies. In contrast, galaxieswith H II region emission-line spectra appear substantially moreirregular and clumpy because of their much higher rates of current starformation per unit of galactic mass. The presence of an unresolvedcentral continuum source in our Hubble Space Telescope images is avirtually perfect indicator of a Seyfert 1 nucleus as seen byground-based spectroscopy. Fifty-two percent of these Seyfert 1 pointsources are saturated in our images; we use their wings to estimatemagnitudes ranging from 15.8 to 18.5. The converse is not universallytrue, however, as over one-third of Seyferts with direct spectroscopicevidence for broad Balmer wings show no nuclear point source. These 34resolved Seyfert 1's have fainter nonstellar nuclei, which appear to bemore extinguished by dust absorption. Like the Seyfert 2's, they havecentral surface brightnesses consistent with those expected for thebulges of normal galaxies. The rates for the occurrences of bars inSeyfert 1's and 2's and non-Seyferts are the same. We found onesignificant morphological difference between the host galaxies ofSeyfert 1 and Seyfert 2 nuclei. The Seyfert 2 galaxies are significantlymore likely to show nuclear dust absorption, especially in lanes andpatches that are irregular or reach close to the nucleus. A few simpletests show that the difference cannot be explained by different averageredshifts or selection techniques. It is confirmed by our galaxymorphology classifications, which show that Seyfert 1 nuclei reside inearlier type galaxies than Seyfert 2 nuclei. If, as we believe, this isan intrinsic difference in host galaxy properties, it undermines one ofthe postulates of the strong unification hypothesis for Seyfertgalaxies, that they merely appear different because of the orientationof their central engine. The excess galactic dust we see in Seyfert 2'smay cause substantial absorption that obscures their hypothesized broademission line regions and central nonstellar continua. This galacticdust could produce much of the absorption in Seyfert 2 nuclei that hadinstead been attributed to a thick dusty accretion torus forming theouter part of the central engine.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.
| A Deep ROSAT Survey - X. X-ray-luminous narrow-emission-line galaxies
X-ray luminous narrow-emission-line galaxies (NELGs) have beenpreviously identified and proposed as an important class ofextragalactic X-ray source, with a potentially significant contributionto the total extragalactic X-ray flux at energies below ~10 keV. Inorder to investigate and clarify this possibility, we have used a sampleof NELGs found in five deep ROSAT fields, and similar samples belongingto the Cambridge-Cambridge ROSAT Serendipity Survey and to the EinsteinObservatory Extended Medium Sensitivity Survey sample. We have been ableto study their X-ray properties, derive their number-flux relationship,investigate their cosmological evolution and derive a preliminaryX-ray-luminosity function (XLF) for this class of objects. We havecompared the above-mentioned properties to those exhibited bysoft-X-ray-selected broad-line active galactic nuclei (BLAGN) and/ornormal galaxies. The principal results of this investigation are asfollows: (a) for a given optical luminosity, the typical X-rayluminosity of NELGs is about one or two orders of magnitude higher thanthat of normal galaxies; (b) the ratio of the surface density of NELGscompared with BLAGN increases from ~0.04 at f_X>~6x10^-13 erg cm^-2s^-1 to ~0.1 at f_X>~10^-14 erg cm^-2 s^-1, suggesting that thesurface density of NL galaxies might be very close to that of BLAGN atf_X~10^-15 erg cm^-2 s^-1 (c) we find that these objects are describedby a cosmological evolution rate similar to that of soft-X-ray-selectedBLAGN; and (d) the de-evolved (z=0) XLF of NELGs in the luminosity range10^41 to 5x10^43 erg s^-1 is steeper than the BLAGN (z=0) XLF in thesame luminosity interval. The spatial density of NELGs is significantlylower than that of X-ray-selected BLAGN at L_X (z=0)~5x10^43lo} erg s-1,but this difference decreases at lower luminosities such that atL_X(z=0)<=10^42 erg s^-1 the spatial density of NELGs is very closeto that of BLAGN. The implications of these results for the contributionof this class of objects to the cosmic X-ray background are discussed.
| Relations between the Optical Fe II Emission and Ultraviolet Spectra in Active Galactic Nuclei
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...457..111W&db_key=AST
| Seyfert Galaxies With Companions: Orbital and Kinematic Clues to AGN Triggering
This paper presents imaging and optical spectroscopy of paired Seyfertgalaxies and their companions. The aim is to seek common properties ofSeyfert galaxies in interacting systems, which might provide evidence ofAGN triggering in a way independent of the usual two-sample statisticswhich have proven ambiguous on this issue. Three kinds of comparisonhave been made-the kinds of interactions involving Seyfert galaxies, therelative luminosities of the Seyferts and their companions, and thelevel of kinematic disturbance as measured from rotation curves. (1)Dynamics and tidal features have been used to determine (or at leastlimit) the sense of orbital motion (direct/retrograde/polar with respectto the Seyfert galaxy's disk) for many of these pairs. There is noobviously preferred kind of interaction-direct, polar, and retrogradeencounters are all well represented, despite the gross differences indynamical response of a disk to these various kinds of encounter. To theextent that triggering of Seyfert nuclei occurs due to tidal encounters,the existence of a perturbation seems more important than its exactduration or detailed effects on the disk. However, the ratio of mergingto paired Seyferts is higher than for disk galaxies in general,consistent with more effective triggering of AGN in this specific phase;the implied time scale for enhanced occurrence during mergers is thesame as the timescape for merger remnants to appear as such, a fewdisk-edge crossing times (typically several times 10^8^ yr). (2) Seyfertnuclei occur preferentially in the brighter members of galaxy pairs, bya median of 0.93 mag after making the maximal correction forcontaminating nonstellar light in the nuclei. Only about 1/3 of thiseffect can be accounted for by the known tendency of Seyfert nuclei tooccur in more luminous galaxies. Enhancement of AGN by interactions isevidently more effective for more luminous galaxies (though this willalso be the case if both star formation and AGN occurrence are enhancedin the same galaxies). (3) The rotation curves of the paired Seyfertsshow systematically small regions of rising or solid-body rotationcompared to the disk radius, as a group comparable to Sa but verydifferent from Sb or Sc galaxies (even for Seyfert galaxies with Hubbletype later than Sa). There is weak evidence that this difference is alsopresent with respect to more isolated Seyfert galaxies. Despite theobvious utility of a dynamically disturbed disk for transport of angularmomentum and "feeding the monster," Seyfert galaxies in pairs actuallyhave smaller kinematic disturbances (measured by the maximum departurefrom a symmetric rotation curve, normalized to the full rotationamplitude) than found in a complete sample of non-Seyfert spirals inpairs.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| No X-Ray--luminous Starbursts in the Einstein Medium Sensitivity Survey, Either
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...453..611H&db_key=AST
| New Constraints on the Unified Model of Seyfert Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446..561M&db_key=AST
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| Ultraviolet Imaging Telescope Observations of NGC 4151
The Seyfert 1 galaxy NGC 4151 was observed with the Ultraviolet ImagingTelescope (UIT) during the Astro-1 mission in December 1990. Images wereobtained in one Near UV band (2500 Angstroms) and two Far UV (1500Angstroms, 1620 Angstroms) bands. The active nucleus is prominent in allframes, while the NUV image and the deepest FUV image both show spiralarm structure. The FUV--NUV color index is very blue, indicating thatmassive stars are present in the outer arms. Surface photometry andmulticolor analysis of the UIT and ground based data are presented in ananalysis of the star formation history of the disk of the galaxy. Threeother galaxies in the field of view (NGC 4156, UGC 7173, and UGC 7188)also have FUV-NUV color indices of --1.0 or bluer, possibly indicatingenhanced star formation from tidal interactions.
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