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HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| The association between gas and galaxies - I. CFHT spectroscopy and pair analysis
We investigate the relative distribution of the gaseous contents of theUniverse (as traced by a sample of Lyα absorbers), and theluminous baryonic matter (as traced by a redshift survey of galaxies inthe same volume searched for Lyα absorbers), along 16 lines ofsight (LOS) between redshifts 0 and 1. Our galaxy redshift survey wasmade with the multi-object spectrograph on the Canada-France-HawaiiTelescope and, when combined with galaxies from the literature in thesame LOS, gives us a galaxy sample of 636 objects. By combining thiswith an absorption-line sample of 406 absorbing systems drawn frompublished works, we are able to study the relationship between gas andgalaxies over the latter half of the age of the Universe. A correlationbetween absorbers and galaxies is detected out to separation of 1.5Mpc.This correlation is weaker than the galaxy-galaxy correlation. There isalso some evidence that the absorbing systems seen in CIV are moreclosely related to galaxies, although this correlation could be withcolumn density rather than metallicity. The above results are allconsistent with the absorbing gas and the galaxies coexisting in darkmatter filaments and knots as predicted by current models where thecolumn density of the absorbing gas is correlated with the underlyingmatter density.
| Electric Redshift and Quasars
A new redshift mechanism-the electric redshift-is proposed, in accordwith the five-dimensional Kaluza-Klein theory, which unifies Einsteiniangeneral relativity and Maxwellian electromagnetic theory. It is shownthat a dense, massive, and charged object can significantly shift alight ray that is emitted from the object's surface toward the red ascompared with the gravitational redshift. A compact, electricallycharged object with density and mass comparable to those of a neutronstar can impart a redshift as great as quasars have. Therefore, ifquasars are dense, massive, and electrically charged objects, theirlarge redshifts do not imply that all quasars are extremely distant;thus, the luminosity of quasars and their association with low-redshiftgalaxies can be understood. This interpretation does not conflict withbig bang cosmology, because the electric redshifts are negligible fornormal stars, galaxies, and large-scale matter, which are not dense andelectrically charged.
| Toward a clean sample of ultra-luminous X-ray sources
Context: .Observational follow-up programmes for the characterization ofultra-luminous X-ray sources (ULXs) require the construction of cleansamples of such sources in which the contamination byforeground/background sources is minimum. Aims: .We calculate thedegree of foreground/background contaminants among the ULX samplecandidates in a published catalogue and compare these computations withavailable spectroscopic identifications. Methods: .We usestatistics based on known densities of X-ray sources and AGN/QSOsselected in the optical. The analysis is done individually for eachparent galaxy. The existing identifications of the optical counterpartsare compiled from the literature. Results: .More than a half ofthe ULXs, within twice the distance of the major axis of the 25mag/arcsec2 isophote from RC3 nearby galaxies and with X-rayluminosities L_X[ 2-10 keV] ≥ 1039 erg/s, are expected tobe high redshift background QSOs. A list of 25 objects (clean sample)confirmed to be real ULXs or to have a low probability of beingcontaminant foreground/background objects is provided.
| How large are the bars in barred galaxies?
I present a study of the sizes (semimajor axes) of bars in discgalaxies, combining a detailed R-band study of 65 S0-Sb galaxies withthe B-band measurements of 70 Sb-Sd galaxies from Martin (1995). As hasbeen noted before with smaller samples, bars in early-type (S0-Sb)galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies;this is true both for relative sizes (bar length as fraction ofisophotal radius R25 or exponential disc scalelength h) andabsolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~ 3.3 kpc),~0.2-0.8R25 (mean ~ 0.38R25) and ~0.5-2.5h (mean ~1.4h). Late-type bars extend to only ~0.5-3.5 kpc,~0.05-0.35R25 and 0.2-1.5h their mean sizes are ~1.5 kpc, ~0.14R25 and ~0.6h. Sb galaxies resemble earlier-type galaxiesin terms of bar size relative to h; their smallerR25-relative sizes may be a side effect of higher starformation, which increases R25 but not h. Sbc galaxies form atransition between the early- and late-type regimes. For S0-Sbcgalaxies, bar size correlates well with disc size (both R25and h); these correlations are stronger than the known correlation withMB. All correlations appear to be weaker or absent forlate-type galaxies; in particular, there seems to be no correlationbetween bar size and either h or MB for Sc-Sd galaxies.Because bar size scales with disc size and galaxy magnitude for mostHubble types, studies of bar evolution with redshift should selectsamples with similar distributions of disc size or magnitude(extrapolated to present-day values); otherwise, bar frequencies andsizes could be mis-estimated. Because early-type galaxies tend to havelarger bars, resolution-limited studies will preferentially find bars inearly-type galaxies (assuming no significant differential evolution inbar sizes). I show that the bars detected in Hubble Space Telescope(HST) near-infrared(IR) images at z~ 1 by Sheth et al. have absolutesizes consistent with those in bright, nearby S0-Sb galaxies. I alsocompare the sizes of real bars with those produced in simulations anddiscuss some possible implications for scenarios of secular evolutionalong the Hubble sequence. Simulations often produce bars as large as(or larger than) those seen in S0-Sb galaxies, but rarely any as smallas those in Sc-Sd galaxies.
| 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.
| Antitruncation of Disks in Early-Type Barred Galaxies
The disks of spiral galaxies are commonly thought to be truncated: theradial surface brightness profile steepens sharply beyond a certainradius (3-5 inner disk scale lengths). Here we present the radialbrightness profiles of a number of barred S0-Sb galaxies with theopposite behavior: their outer profiles are distinctly shallower inslope than the main disk profile. We term these ``antitruncations'' theyare found in at least 25% of a larger sample of barred S0-Sb galaxies.There are two distinct types of antitruncations. About one-third show afairly gradual transition and outer isophotes that are progressivelyrounder than the main disk isophotes, suggestive of a disk embeddedwithin a more spheroidal outer zone-either the outer extent of the bulgeor a separate stellar halo. But the majority of the profiles have rathersharp surface brightness transitions to the shallower, outer exponentialprofile and, crucially, outer isophotes that are not significantlyrounder than the main disk; in the Sab-Sb galaxies, the outer isophotesinclude visible spiral arms. This suggests that the outer light is stillpart of the disk. A subset of these profiles are in galaxies withasymmetric outer isophotes (lopsided or one-armed spirals), suggestingthat interactions may be responsible for at least some of the disklikeantitruncations.
| The Discovery of a High-Redshift X-Ray-Emitting QSO Very Close to the Nucleus of NGC 7319
A strong X-ray source only 8" from the nucleus of the Seyfert 2 galaxyNGC 7319 in Stephan's Quintet has been discovered by Chandra. We haveidentified the optical counterpart and show that it is a QSO withze=2.114. It is also an ultraluminous X-ray source withLX=1.5×1040 ergs s-1. From theoptical spectra of the QSO and the interstellar gas of NGC 7319together, we show that it is very likely that the QSO is interactingwith the interstellar gas.
| The opacity of spiral galaxy disks. VII. The accuracy of galaxy counts as an extinction probe
The "Synthetic Field Method" (SFM) was introduced by González etal. (1998, ApJ, 506, 152) to calibrate numbers of distant galaxies as aprobe of extinction in a foreground spiral disk. González et al.(2003, AJ, 125, 1182) studied the effect of the foreground disk on thesenumbers using simulations of current and future instruments for fieldsin the LMC, M 31 and NGC 4536, a galaxy in Virgo. They concludedthat: (1) the brighter centers of disks were unsuitable; (2) thegranularity of the disk at a fixed surface brightness is the limitingfactor in the detection of distant galaxies; and (3) the optimumdistance for measurements would be that of the Virgo cluster for thecurrent instruments on board HST. At this distance the foreground diskis smoothed with distance, improving detection of distant backgroundgalaxies. Holwerda et al. (2005a, AJ, 129, 1381) automated the SFM andHolwerda et al. (2005b, AJ, 129, 1396) applied it to a large set ofWFPC2 fields. In this paper, the quality of the extinction measurementin these fields is compared to their distance, granularity, surfacebrightness and structure.
The average surface brightness of theof a field is shown to directly influence the accuracy of the SFM. Thisrestricts meaningful measurements to the disks of spiral galaxies. Largestructures such as spiral arms have a similar effect. The granularity orsmall scale structure in a field influences the detection of distantgalaxies, limiting the SFM measurements in nearby disks. From the trendsin the accuracy and maximum practical field-of-view considerations, theminimum and maximum distance for SFM application, approximately 5 and 35Mpc respectively. Using the same instrument and detection method, therelations with SFM parameters and field characteristics can be used toforgo the synthetic fields altogether. For the wealth of ACS fieldsbecoming available in the archive, these relations can be used to selectthose fields based on expected SFM accuracy.
| A Search for Short-Timescale Microvariability in Active Galactic Nuclei in the Ultraviolet
We observed four active galactic nuclei (AGNs) (the type 1 Seyfertsystems 3C 249.1, NGC 6814, and Mrk 205, and the BL Lac object 3C 371)using the High Speed Photometer on the Hubble Space Telescope (HST) tosearch for short-timescale microvariability in the UV. Continuousobservations of ~3000 s duration were obtained for each system onseveral consecutive HST orbits using a 1 s sample time in a 1400-3000Å bandpass. No photometric variability greater than 0.3% (0.003mag) was detected in any AGN on timescales shorter than 1500 s. Thedistribution of photon arrival times observed from each source wasconsistent with Poisson statistics. Because of HST optical problems, thelimit on photometric variability at longer timescales is less precise.These results restrict the masses of black holes as the central enginesof AGNs and the diskoseismic oscillations of any accretion disk aroundsuch a black hole.
| The field surrounding NGC 7603: Cosmological or non-cosmological redshifts?
We present new observations of the field surrounding the Seyfert galaxyNGC 7603, where four galaxies with different redshifts - NGC 7603(z=0.029), NGC 7603B (z=0.057) and two fainter emission line galaxies(z=0.245 and z=0.394) - are apparently connected by a narrow filament,leading to a possible case of anomalous redshift. The observationscomprise broad and narrow band imaging and intermediate resolutionspectroscopy of some of the objects in the field. The new data confirmthe redshift of the two emission-line objects found within the filamentconnecting NGC 7603 and NGC 7603B, and settles their type with betteraccuracy. Although both objects are point-like in ground based images,using HST archive images we show that the objects have structure with aFWHM = 0.3-0.4 arcsec. The photometry in the R-band obtained duringthree different campaigns spread over two years does not show any signsof variability in these objects above 0.3-0.4 mag. All the aboveinformation and the relative strength and width of the main spectrallines allow us to classify these as HII galaxies with very vigorous starformation, while the rest of the filament and NGC 7603B lack starformation. We delineate the halo of NGC 7603 out to 26.2mag/arcsec2 in the Sloan r band filter and find evidence forstrong internal distortions. New narrow emission line galaxies atz=0.246, 0.117 and 0.401 are also found at respectively 0.8, 1.5 and 1.7arcmin to the West of the filament within the fainter contour of thishalo. We have studied the spatial distribution of objects in the fieldwithin 1.5 arcmin of NGC 7603. We conclude that the density of QSOs isroughly within the expected value of the limiting magnitude of ourobservations. However, the configuration of the four galaxies apparentlyconnected by the filament appears highly unusual. The probability ofthree background galaxies of any type with apparent B-magnitudes up to16.6, 21.1 and 22.1 (the observed magnitudes, extinction correctionincluded) being randomly projected on the filament of the fourth galaxy(NGC 7603) is ≈ 3× 10-9. Furthermore, the possibledetection of very vigorous star formation observed in the HII galaxiesof the filament would have a low probability if they were backgroundnormal-giant galaxies; instead, the intensity of the lines is typical ofdwarf HII galaxies. Hence, a set of coincidences with a very lowprobability would be necessary to explain this as a fortuitousprojection of background sources. Several explanations in terms ofcosmological or non-cosmological redshifts are discussed.
| BeppoSAX observations of the quasar Markarian 205
We present the first BeppoSAX observation (0.1 to 220 keV) of the quasarMrk 205. We have searched for the unusual Fe lineprofile observed in the XMM-Newton spectrum which has been widelydiscussed in the recent literature. We find no evidence for a broad,ionized Fe line component in our data. We detect for the first time aCompton hump in this object. When this component is included in the fit,the line strength diminishes, in agreement with a recent re-analysis ofthe XMM-Newton data, but with better constraints on the reflectioncomponent thanks to the PDS instrument (15-220 keV). We interpret thisfact as another indication for illumination of distant, cold materialrather than reprocessing in the highly ionized inner part of anaccretion disk. We cannot constrain the presence of a high energy cutoffbut we confirm the existence of a variable soft excess (one year timescale).
| Properties of isolated disk galaxies
We present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org
| New optical spectra and general discussion on the nature of ULXs
We present optical spectroscopic observations of three Ultra LuminousX-ray sources (ULXs). Two of them are very close to the active galaxyNGC 720 and the other is near NGC 1073. The two around NGC 720 turn outto be quasars at z= 2.216 and z= 0.959, the one near NGC 1073 seems tobe associated to an HII region at the redshift of NGC 1073. Weconcentrate our analysis on the two quasars and analyze them inconjunction with a set of 22 additional X-ray sources close to nearbygalaxies which also fit the criteria of ULXs and which also have beenidentified as quasars of medium to high redshift. This sample shows anunusually large fraction of rare BL Lac type objects. The high redshiftsof these ULXs and their close proximity to their low redshift,supposedly parent galaxies is a surprising result in the light ofstandard models. We describe the main properties of each of theseobjects and their parent galaxy, and briefly discuss possibleinterpretations.
| Kinematics of 10 Early-Type Galaxies from Hubble Space Telescope and Ground-based Spectroscopy
We present stellar kinematics for a sample of 10 early-type galaxiesobserved using the Space Telescope Imaging Spectrograph (STIS) aboardthe Hubble Space Telescope and the Modular Spectrograph on the MDMObservatory 2.4 m telescope. These observations are a part of an ongoingprogram to understand the coevolution of supermassive black holes andtheir host galaxies. Our spectral ranges include either the calciumtriplet absorption lines at 8498, 8542, and 8662 Å or the Mg babsorption at 5175 Å. The lines are used to derive line-of-sightvelocity distributions (LOSVDs) of the stars using a maximum penalizedlikelihood method. We use Gauss-Hermite polynomials to parameterize theLOSVDs and find predominantly negative h4 values (boxy distributions) inthe central regions of our galaxies. One galaxy, NGC 4697, hassignificantly positive central h4 (high tail weight). The majority ofgalaxies have a central velocity dispersion excess in the STISkinematics over ground-based velocity dispersions. The galaxies with thestrongest rotational support, as quantified withvmax/σSTIS, have the smallest dispersionexcess at STIS resolution. The best-fitting, general, axisymmetricdynamical models (described in a companion paper) require black holes inall cases, with masses ranging from 106.5 to 109.3Msolar. We replot these updated masses on theMBH-σ relation and show that the fit to only these 10galaxies has a slope consistent with the fits to larger samples. Thegreatest outlier is NGC 2778, a dwarf elliptical with relatively poorlyconstrained black hole mass. The two best candidates for pseudobulges,NGC 3384 and NGC 7457, do not deviate significantly from the establishedrelation between MBH and σ. Neither do the threegalaxies that show the most evidence of a recent merger, NGC 3608, NGC4473, and NGC 4697.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555. These observations are associatedwith proposal GO-7388.
| NGC 6212, 3C 345, and Other Quasi-stellar Objects Associated with Them
It is pointed out that the Seyfert 1 galaxy NGC 6212 is surrounded by alarge number of quasi-stellar objects (QSOs), including the very activeand rapidly varying radio QSO 3C 345, which lies only 4.7′ awayfrom the center of the galaxy. There are two pairs of QSOs with the sameredshifts, including 3C 345, very close to the nucleus of NGC 6212, andthe very high density of the QSOs falls off rapidly with distance fromthat galaxy. If 3C 345 lies at the distance of NGC 6212, the propermotions in the radio jet in 3C 345, which have been studied in detail,correspond to only mildly relativistic speeds, of about 0.33c.
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| 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
| Noncosmological Redshifts
This Essay is one of a series of invited contributions appearing in thePASP throughout the years 2000 and 2001 to mark the new millennium.(Eds.)
| The Frequency of Active and Quiescent Galaxies with Companions: Implications for the Feeding of the Nucleus
We analyze the idea that nuclear activity, either active galactic nuclei(AGNs) or star formation, can be triggered by interactions by studyingthe percentage of active, H II, and quiescent galaxies with companions.Our sample was selected from the Palomar survey and avoids selectionbiases faced by previous studies. This sample was split into fivedifferent groups, Seyfert galaxies, LINERs, transition galaxies, H IIgalaxies, and absorption-line galaxies. The comparison between the localgalaxy density distributions of the different groups showed that in mostcases there is no statistically significant difference among galaxies ofdifferent activity types, with the exception that absorption-linegalaxies are seen in higher density environments, since most of them arein the Virgo Cluster. The comparison of the percentage of galaxies withnearby companions showed that there is a higher percentage of LINERs,transition galaxies, and absorption-line galaxies with companions thanSeyfert and H II galaxies. However, we find that when we consider onlygalaxies of similar morphological types (elliptical or spiral), there isno difference in the percentage of galaxies with companions amongdifferent activity types, indicating that the former result was due tothe morphology-density effect. In addition, only small differences arefound when we consider galaxies with similar Hα luminosities. Thecomparison between H II galaxies of different Hα luminositiesshows that there is a significantly higher percentage of galaxies withcompanions among H II galaxies with L(Hα)>1039 ergss-1 than among those with L(Hα)<=1039ergs s-1, indicating that interactions increase the amount ofcircumnuclear star formation, in agreement with previous results. Thefact that we find that galaxies of different activity types have thesame percentage of companions suggests that interactions betweengalaxies is not a necessary condition to trigger the nuclear activity inAGNs. We compare our results with previous ones and discuss theirimplications.
| Petit compte rendu du congres de l'UAI en aout a Manchester.
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| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| NGC 4319/Markarian 205 Association As a Template for Discordant Redshifts Explainable by the Transverse Doppler Effect
Probably, the most intriguing case of closely associated objects havingdiscordand redshifts is represented by the galaxy NGC 4319 (z=0.006) anda peculiar object Mrk 205 (z=0.07) just 40'' away[1]. The luminous connection extending from Mrk 205 into thegalaxian nucleus as well as a corresponding feature on the opposite sideof the disk linking the nucleus with a bright UV knot may indicate anexplosive ejection of both the objects from the nucleus [2].Below, I propose to explain the essentially discordant redshifts of Mrk205 and the UV knot by ejecting them with a relativistic velocity,similar to the two redshifted peculiar objects aligned across NGC 4258[3]. In my interpretation, the redshift of Mrk 205 includes(i) a receding component, zr=0.065, due to the transverseDoppler effect and (ii) a cosmological component, zc=0.006.The velocity of ejection and the angle between the direction of ejectionand the line of sight are found to bevej/c=(zr+z_a))1/2≈ 0.261 and \vartheta= arccos(zr-z_a) (z_r+z_a) -1/2≈ 76o.3, correspondingly, assuming the UV knot to approach with redshift za≈ 0.003 [2]. The proposed interpretation has a number of testable consequences, including the decisive test: Mrk 205 is expected to have an annual proper motion of >= 0.8 (D/20 Mpc))-1 milliarcsec, which could be measured at radio wavelengthsfor the unresolved radio counterpart [4] to Mrk 205. Ifconfirmed, this model would indicate that some pairs of quasar-likesources aligned with galaxies represent relativistic ejecta from thegalactic nuclei, and the redshifts of those sources include asubstantial component produced by the transverse Doppler effect.References: [1] Arp, H. 1995, IAU Symp. 168, p. 369 and refs. therein [2] Sulentic, J.W. & Arp, H. 1987, ApJ 319, 687 and 693 [3] Ozernoy, L.M. 1996, Bull. Amer. Astr. Soc. 28, 846 [4] Sulentic, J.W. 1986, ApJ 304, 617
| Determining the reality of X-ray filaments
A number of authors have reported filaments connecting bright structuresin high-resolution X-ray images, and in some cases these have been takenas evidence for a physical connection between the structures, whichmight be thought to provide support for a model with non-cosmologicalredshifts. In this paper I point out two problems which are inherent inthe interpretation of smoothed photon-limited data of this kind, anddevelop some simple techniques for the assessment of the reality ofX-ray filaments, which can be applied to either simply smoothed oradaptively smoothed data. To illustrate the usefulness of thesetechniques, I apply them to archival ROSAT observations of galaxies andquasars previously analysed by others. I show that several reportedfilamentary structures connecting X-ray sources are not in factsignificantly detected.
| Shift of spectral lines due to dynamic multiple scattering and screening effect: implications for discordant redshifts
The frequency shift of spectral lines from astronomical objects is mostoften explained by the Doppler Effect arising in relative motion and thebroadening of a particular line is supposed to depend on the absolutetemperature, pressure or the different line of sight velocities. TheWolf effect on the other hand deals with correlation induced spectralchanges and explains both the broadening and shift of the spectrallines. In this framework a sufficient condition for redshift has beenderived and when applicable the shift is shown to be larger thanbroadening. Under this condition of larger shift than broadening we finda critical source frequency below which no spectrum is analyzable for aparticular medium. This gives rise to new type of screening effect whichmay play a significant role both at laboratory scale as well as in theastronomical domain. We apply a simple interpretation of the discordantredshifts in galaxy-quasar associations.
| 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 Subarcsecond-Resolution Near-Infrared Study of Seyfert and ``Normal'' Galaxies. I. Imaging Data
We present new high-resolution near-infrared observations in the J, H,and K bands, obtained to study the properties of Seyfert host galaxies.The data set consists of images in the three bands of practically theentire CfA sample of Seyfert galaxies, and K-band images of a controlsample of nonactive, ``normal,'' galaxies, matched to the Seyfert samplein the distribution of type and inclination. The spatial resolution andsampling of the new images is a factor of 2 better than previouslypublished K-band data. In this paper, we present the data in the form ofprofiles of surface brightness and color, ellipticity and major axisposition angle, as well as gray-scale maps of surface brightness in H orK and both J-H and H-K colors. We compare our surface brightness andcolor profiles with the literature and find good agreement. Our data arediscussed in detail in three subsequent publications, where we analyzethe morphologies of Seyfert and normal hosts, quantify the strength ofnonaxisymmetric features in disks and their relationship to nuclearactivity, address the question of bar fraction in Seyferts and normalgalaxies, and analyze the color information in the framework of emissionmechanisms in Seyfert 1's and 2's and in nonactive galaxies.
| Investigation of Barred Galaxies. V. Surroundings of SB and SA Galaxies
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| The Asymmetric Wind in M82
We have obtained detailed Fabry-Perot imaging observations of the nearbygalaxy M82 in order to understand the physical association between thehigh-velocity outflow and the starburst nucleus. The high spatial andkinematic resolution of our observations has allowed us to performphotometric analyses of H alpha , [N II], and [O III] spectral lines atroughly 100,000 positions across the extent of the galaxy. The observedvelocities of the emitting gas in M82 reveal a bipolar outflow ofmaterial, originating from the bright starburst regions in the galaxy'sinner disk but misaligned with respect to the galaxy spin axis. Thedeprojected outflow velocity indicated by the optical filamentsincreases with radius from 525 to 655 km s-1. All three spectral linesshow double components in the centers of the outflowing lobes, with theH alpha line split by ~300 km s-1 over a region almost 1 kpc in size.The filamentary lobes lie along an axis tilted by 15 deg with respect tothe spin axis, a finding confirmed by the regions of line splitting andby the ionization pattern over the outflow. The filaments are not simplesurfaces of revolution, nor is the emission distributed evenly over thesurfaces. We model these lobes as a composite of cylindrical and conicalstructures, collimated in the inner ~500 pc but expanding at a largeropening angle of ~25 deg beyond that radius. We compare our kinematicmodel with simulations of starburst-driven winds in which disk materialsurrounding the source is entrained by the wind. There is some evidencefor rotation of the wind filaments about the outflow axis in support ofentrainment, and we find strong similarities between the observed andpredicted structures. The data reveal a remarkably low [N II]/H alpharatio in the region of the outflow, indicating that photoionization bythe nuclear starburst may play a significant role in the excitation ofthe optical filament gas, particularly near the nucleus. An increase inthe [O III]/H alpha ratio along the outflow is observed. At largerradii, the line diagnostics and a strong spatial correlation between Halpha and soft X-ray filaments are consistent with shock ionization. Asmooth spherical halo around M82, extending to at least 2 kpc, isobserved in emission lines. We propose that the dusty halo is theprimary source of the linearly polarized optical emission. A diffuseionized medium with enhanced [N II]/H alpha emission pervades thestellar disk. We discuss likely sources of ionization and heating.
| Groups of galaxies. III. Some empirical characteristics.
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