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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.
| Does the Milky Way Produce a Nuclear Galactic Wind?
We detect high-velocity absorbing gas using Hubble Space Telescope andFar Ultraviolet Spectroscopic Explorer medium-resolution spectroscopyalong two high-latitude active galactic nucleus (AGN) sight lines (Mrk1383 and PKS 2005-489) above and below the Galactic center (GC). Theseabsorptions are most straightforwardly interpreted as a wind emanatingfrom the GC that does not escape from the Galaxy's gravitationalpotential. Spectra of four comparison B stars are used to identify andremove foreground velocity components from the absorption-line profilesof O VI, N V, C II, C III, C IV, Si II, Si III, and Si IV. Twohigh-velocity (HV) absorption components are detected along each AGNsight line, three redshifted and one blueshifted. Assuming that the fourHV features trace a large-scale Galactic wind emanating from the GC, theblueshifted absorber is falling toward the GC at a velocity of 250+/-20km s-1, which can be explained by ``Galactic fountain''material that originated in a bound Galactic wind. The other threeabsorbers represent outflowing material; the largest derived outflowvelocity is +250+/-20 km s-1, which is only 45% of thevelocity necessary for the absorber to escape from its current positionin the Galactic gravitational potential. All four HV absorbers are foundto reach the same maximum height above the Galactic plane(zmax=12+/-1 kpc), implying that they were all ejected fromthe GC with the same initial velocity. The derived metallicity limits of>~10%-20% solar are lower than expected for material recently ejectedfrom the GC unless these absorbers also contain significant amounts ofhotter gas in unseen ionization stages.
| Absorption-Line Study of Halo Gas in NGC 3067 toward the Background Quasar 3C 232
We present new H I 21 cm absorption data and ultraviolet spectroscopyfrom Hubble Space Telescope/Space Telescope Imaging Spectrograph of theQSO/galaxy pair 3C 232/NGC 3067. The QSO sight line lies near the minoraxis and 1&farcm;8 (11 h-170 kpc) above the planeof NGC 3067, a nearby luminous (cz=1465+/-5 km s-1,L=0.5L*) starburst galaxy with a moderate star formation rateof 1.4 Msolar yr-1. The UV spectra show that theSi IV and C IV doublets have the same three velocity components atcz=1369, 1417, and 1530 km s-1 found in Ca II H and K, Na ID, Mg I, Mg II, and Fe II, implying that the low- and high-ionizationgas are both found in three distinct absorbing clouds (only thestrongest component at 1420 km s-1 is detected in H I 21 cm).The new Lyα observation allows the first measurements of the spinand kinetic temperatures of halo gas: Ts=435+/-140 K andTk/Ts~1. However, while a standard photoionizationmodel can explain the low ions, the C IV and Si IV are explained moreeasily as collisionally ionized boundary layers of the photoionizedclouds. Because of their small inferred space velocity offsets(Δv=-260, -130, and +170 km s-1) relative to thenucleus of NGC 3067 and the spatial coincidence of low- andhigh-ionization gas, we propose that these absorbers are analogous toGalactic high-velocity clouds (HVCs). A comparison of the NGC 3067clouds and Galactic HVCs finds similar H I column densities, kinematics,metallicities, spin temperatures, and inferred sizes. We find nocompelling evidence that any halo gas along this sight line is escapingthe gravitational potential of NGC 3067, despite its modest starburst.
| The Hot Intergalactic Medium-Galaxy Connection: Two Strong O VI Absorbers in the Sight Line toward PG 1211+143
We present Hubble Space Telescope (HST) Space Telescope ImagingSpectrograph (STIS) and Far Ultraviolet Spectroscopic Explorer (FUSE)spectra of the QSO PG 1211+143 (zem=0.081) and a galaxysurvey of the surrounding field. This sight line shows two strongintergalactic absorption systems at cz~=15,300 and 19,300 kms-1. This sight line addresses the nature and origin of the OVI absorbers and their connection to galaxies. We explore therelationship of these absorbers to the nearby galaxies and compare themto other O VI-bearing absorbers in diverse environments. At 15,300 kms-1, we find four distinct H I components and associated CII, C III, C IV, Si II, Si III, Si IV, N V, and O VI, lying near aspiral-dominated galaxy group with a bright member galaxy 137h-170 kpc from the sight line. The observed ionsof C, Si, and N are likely to be photoionized, but the O VI is moreconsistent with collisional ionization. The ion ratios in this absorberresemble the highly ionized Galactic high-velocity clouds (HVCs); it mayalso trace the hot intragroup medium gas or the unbound wind of anundiscovered dwarf galaxy. At 19,300 km s-1, we find five H Icomponents and associated C III, Si III, and collisionally ionized O VIlying 146 h-170 kpc from an isolated galaxy. Theproperties of the O VI-bearing gas are consistent with an origin instrong shocks between low-metallicity gas (>=2%-6% solar) and one ormore of the warm photoionized components. It is likely that theseabsorbers are related to the nearby galaxies, perhaps by outflows or gasstripped from unseen satellite galaxies by interactions. However, wecannot reject completely the hypothesis that they reside in the samelarge-scale structure in which the galaxies are embedded but areotherwise not directly related.
| The Westerbork HI survey of spiral and irregular galaxies. III. HI observations of early-type disk galaxies
We present Hi observations of 68 early-type disk galaxies from the WHISPsurvey. They have morphological types between S0 and Sab and absoluteB-band magnitudes between -14 and -22. These galaxies form the massive,high surface-brightness extreme of the disk galaxy population, few ofwhich have been imaged in Hi before. The Hi properties of the galaxiesin our sample span a large range; the average values of MHI/LB and DH I/D25 are comparableto the ones found in later-type spirals, but the dispersions around themean are larger. No significant differences are found between the S0/S0aand the Sa/Sab galaxies. Our early-type disk galaxies follow the same Himass-diameter relation as later-type spiral galaxies, but theireffective Hi surface densities are slightly lower than those found inlater-type systems. In some galaxies, distinct rings of Hi emissioncoincide with regions of enhanced star formation, even though theaverage gas densities are far below the threshold of star formationderived by Kennicutt (1989, ApJ, 344, 685). Apparently, additionalmechanisms, as yet unknown, regulate star formation at low surfacedensities. Many of the galaxies in our sample have lopsided gasmorphologies; in most cases this can be linked to recent or ongoinginteractions or merger events. Asymmetries are rare in quiescentgalaxies. Kinematic lopsidedness is rare, both in interacting andisolated systems. In the appendix, we present an atlas of the Hiobservations: for all galaxies we show Hi surface density maps, globalprofiles, velocity fields and radial surface density profiles.
| Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies
Why are the nuclei of some galaxies more active than others? If mostgalaxies harbor a central massive black hole, the main difference isprobably in how well it is fueled by its surroundings. We investigatethe hypothesis that such a difference can be seen in the detailedcircumnuclear morphologies of galaxies using several quantitativelydefined features, including bars, isophotal twists, boxy and diskyisophotes, and strong nonaxisymmetric features in unsharp-masked images.These diagnostics are applied to 250 high-resolution images of galaxycenters obtained in the near-infrared with NICMOS on the Hubble SpaceTelescope. To guard against the influence of possible biases andselection effects, we have carefully matched samples of Seyfert 1,Seyfert 2, LINER, starburst, and normal galaxies in their basicproperties, taking particular care to ensure that each was observed witha similar average scale (10-15 pc pixel-1). Severalmorphological differences among our five different spectroscopicclassifications emerge from the analysis. The H II/starburst galaxiesshow the strongest deviations from smooth elliptical isophotes, whilethe normal galaxies and LINERs have the least disturbed morphology. TheSeyfert 2s have significantly more twisted isophotes than any othercategory, and the early-type Seyfert 2s are significantly more disturbedthan the early-type Seyfert 1s. The morphological differences betweenSeyfert 1s and Seyfert 2s suggest that more is at work than simply theviewing angle of the central engine. They may correspond to differentevolutionary stages.
| Discovery of a Dwarf Poststarburst Galaxy near a High Column Density Local Lyα Absorber
We report the discovery of a dwarf (MB=-13.9) poststarburstgalaxy coincident in recession velocity (within uncertainties) with thehighest column density absorber (NHI=1015.85cm-2 at cz=1586 km s- 1) in the 3C 273 sight line.This galaxy is by far the closest galaxy to this absorber, projectedjust 71h-170 kpc on the sky from the sight line.The mean properties of the stellar populations in this galaxy areconsistent with a massive starburst ~3.5 Gyr ago, whose attendantsupernovae, we argue, could have driven sufficient gas from this galaxyto explain the nearby absorber. Beyond its proximity on the sky and inrecession velocity, the further evidence in favor of this conclusionincludes both a match in the metallicities of absorber and galaxy andthe fact that the absorber has an overabundance of Si/C, suggestingrecent Type II supernova enrichment. Thus, this galaxy and its ejectaare in the expected intermediate stage in the fading dwarf evolutionarysequence envisioned by Babul & Rees to explain the abundance offaint blue galaxies at intermediate redshifts. While this one instanceof a QSO metal-line absorber and a nearby dwarf galaxy is not proof of atrend, a similar dwarf galaxy would be too faint to be observed bygalaxy surveys around more distant metal-line absorbers. Thus, we cannotexclude the possibility that dwarf galaxies are primarily responsiblefor weak (NHI=1014-1017cm-2) metal-line absorption systems in general. If a largefraction of the dwarf galaxies expected to exist at high redshift had asimilar history (i.e., they had a massive starburst that removed all ormost of their gas), these galaxies could account for at least severalhundred high-z metal-line absorbers along the line of sight to a high-zQSO. The volume-filling factor for this gas, however, would be less than1%.ID="FN1"> 1Based on observations made with the Apache Point 3.5 mtelescope, operated by the Astronomical Research Consortium, and the 2.6m du Pont telescope of the Las Campanas Observatory, operated by theCarnegie Institution of Washington, DC, and Pasadena, CA.
| 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.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies. I. How common are gaseous halos among non-starburst galaxies?
In a series of two papers we present results of a new Hα imagingsurvey, aiming at the detection of extraplanar diffuse ionized gas inhalos of late-type spiral galaxies. We have investigated a sample of 74nearby edge-on spirals, covering the northern and southern hemisphere.In 30 galaxies we detected extraplanar diffuse emission at meandistances of |z| ~ 1-2 kpc. Individual filaments can be traced out to|z|<=6 kpc in a few cases. We find a good correlation between the FIRflux ratio (S60/S100) and the SFR per unit area(LFIR/D225), based on thedetections/non-detections. This is actually valid for starburst, normaland for quiescent galaxies. A minimal SFR per unit area for the lowestS60/S100 values, at which extended emission hasbeen detected, was derived, which amounts to dotEA25thres = (3.2+/-0.5)*E40ergs-1 kpc-2. There are galaxies where extraplanaremission was detected at smaller values ofLFIR/D225, however, only in combinationwith a significantly enhanced dust temperature. The results corroboratethe general view that the gaseous halos are a direct consequence of SFactivity in the underlying galactic disk.Based on observations collected at the European Southern Observatory,Chile (ESO No. 63.N-0070, ESO No. 64.N-0034, ESO No. 65.N.-0002).
| 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
| Ejection of quasars from galaxies and the variable mass hypothesis.
Not Available
| Beyond the Bulge: A Fundamental Relation between Supermassive Black Holes and Dark Matter Halos
The possibility that the masses MBH of supermassive blackholes (SBHs) correlate with the total gravitational mass of their hostgalaxy, or the mass MDM of the dark matter halo in which theypresumably formed, is investigated using a sample of 16 spiral and 20elliptical galaxies. The bulge velocity dispersion σc,typically defined within an aperture of size R<~0.5 kpc, is found tocorrelate tightly with the galaxy's circular velocity vc, thelatter measured at distances from the Galactic center at which therotation curve is flat, R~20-80 kpc. By using the well-knownMBH-σc relation for SBHs and a prescriptionto relate vc to the mass of the dark matter haloMDM in a standard ΛCDM cosmology, the correlationbetween σc and vc is equivalent to onebetween MBH and MDM. Such a correlation is foundto be nonlinear, with the ratio MBH/MDM decreasingfrom 2×10-4 for MDM~1014Msolar to 10-5 for MDM~1012Msolar. Preliminary evidence suggests that halos of masssmaller than ~5×1011 Msolar are increasinglyless efficient at forming SBHs-perhaps even unable to form them.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| 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.
| Spiral Galaxies with HST/NICMOS. II. Isophotal Fits and Nuclear Cusp Slopes
We present surface brightness profiles for 56 of the 78 spiral galaxiesobserved in the HST/NICMOS2 F160W snapshot survey introduced in Paper Iof this series, as well as surface brightness profiles for 23 objectsout of the 41 that were also observed in the F110W filter. We fit thesesurface brightness profiles with the Nuker law of Lauer et al. and usethe smooth analytical descriptions of the data to compute the averagenuclear stellar cusp slopes <γ> in the 0.1"-0.5" radialrange. Our main result is the startling similarity between the nuclearstellar cusp slopes <γ> in the near-infrared compared withthose derived in the visual passband. This similarity has severalimplications: (1) Despite the significant local color variations thatare found in the nuclear regions of spirals and that are documented inPaper I, there are typically little or no optical-NIR global colorgradients, and thus no global stellar population variations, inside~50-100 pc from the nucleus in nearby spirals. (2) The large observedrange of the strength of the nuclear stellar cusps seen in the HSToptical study of spiral galaxies reflects a physical difference betweengalaxies and is not an artifact caused by nuclear dust and/or recentstar formation. (3) The dichotomy between R1/4 bulges, withsteep nuclear stellar cusps <γ>~1, and exponential bulges,with shallow nuclear stellar cusps <γ><0.3, is also notan artifact of the effects of dust or recent star formation. (4) Thepresence of a surrounding massive disk appears to have no effect on therise of the stellar density distribution within the innermost hundredparsecs of the R1/4 spheroids. These results imply abreakdown within the family of exponential bulges of the nuclear versusglobal relationships that have been found for the R1/4spheroids. Such a breakdown is likely to have significant implicationsconcerning the formation of exponential bulges and their connection withthe R1/4 spheroids. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| Spiral Galaxies with HST/NICMOS. I. Nuclear Morphologies, Color Maps, and Distinct Nuclei
This is the first of two papers where we present the analysis of anHST/NICMOS2 near-infrared (NIR) snapshot survey in the F160W (H) filterfor a sample of 78 spiral galaxies selected from the UGC and ESOLVcatalogs. For 69 of these objects we provide nuclear color informationderived by combining the H data either with additional NICMOS F110W (J)images or with V WFPC2/HST data. Here we present the NIR images and theoptical-NIR color maps. We focus our attention on the properties of thephotometrically distinct ``nuclei'' which are found embedded in most ofthe galaxies and provide measurements of their half-light radii andmagnitudes in the H (and when available in the J) band. We find that (1)in the NIR the nuclei embedded in the bright early- to intermediate-typegalaxies span a much larger range in brightness than the nuclei whichare typically found embedded in bulgeless late-type disks: the nucleiembedded in the early- to intermediate-type galaxies reach, on thebright end, values up to HAB~-17.7 mag; (2) nuclei are foundin both nonbarred and barred hosts, in large-scale (>~1 kpc) as wellas in nuclear (up to a few 100 pc) bars; (3) there is a significantincrease in half-light radius with increasing luminosity of the nucleusin the early/intermediate types (a decade in radius for ~8 magbrightening), a correlation which was found in the V band and which isalso seen in the NIR data; (4) the nuclei of early/intermediate-typespirals cover a large range of optical-NIR colors, from V-H~-0.5 to 3.Some nuclei are bluer and others redder than the surroundinggalaxy,indicating the presence of activity or reddening by dust in many ofthese systems; (5) someearly/intermediate nuclei are elongated and/orslightly offset from the isophotal center of the host galaxy. Onaverage, however, these nuclei appear as centered, star-cluster-likestructures similar to those whichare found in the late-type disks. Basedon observations with the NASA/ESA Hubble Space Telescope, obtained atthe Space Telescope Science Institute, which is operated by Associationof Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
| The Statistical and Physical Properties of the Low-Redshift LYα Forest Observed with the Hubble Space Telescope/STIS
We examine the Lyα absorber population at z<0.3 detected inspectra of the quasars PG 0953+415 and H1821+643 taken with the SpaceTelescope Imaging Spectrograph on board the Hubble Space Telescope. Wecompare their statistical properties to those in carefully constructedmock quasar spectra drawn from a cosmological hydrodynamic simulation ofa Λ-dominated cold dark matter universe. We find very goodagreement in the column density and b-parameter distributions, down tothe smallest observable absorbers with NHI~1012.3cm- 2. The observed absorber population is complete forNHI>~1013 cm- 2, with a columndensity distribution slope of β=2.04+/-0.23 and a medianb-parameter of 21 km s-1 above this limit. The intergalacticgas giving rise to these weak absorbers is analogous to that at highredshift, located in diffuse large-scale structures that are highlyphotoionized by the metagalactic UV flux, though a greater number arisewithin shock-heated warm gas. The density, temperature, and columndensity of these absorbers follow similar relationships of those at highredshift, though with substantially larger scatter due to theshock-heated gas. The b-parameters typically have a significantcontribution from thermal broadening, which facilitates a measurement ofthe low-z intergalactic medium temperature as traced by Lyαabsorbers. From our simulation we estimate TIGM~5000 K, withan upper limit of 104 K, at the mean density. The agreementin predicted and observed amplitude of the column density distributionsallows us to measure the H I photoionization rate at z=0.17 to beΓHI=10-13.3+/-0.7 s-1 (estimatedmodeling uncertainty), close to predictions based on quasar properties.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| Constraints on the Lyman continuum radiation from galaxies: First results with FUSE on Mrk 54
We present Far Ultraviolet Spectroscopic Explorer observations of thestar-forming galaxy Mrk 54 at z = 0.0448. The Lyman continuum radiationis not detected above the H I absorption edge in our Galaxy. An upperlimit is evaluated by comparison with the background measured in regionsof the detector adjacent to the observed spectrum. A spectral window of16 Å, reasonably free of additional H I Lyman series lineabsorption, is used. No correction is needed for molecular hydrogenabsorption in our Galaxy but a foreground extinction of 0.29 mag isaccounted for. An upper limit of 6.15 x 10-16 ergcm-2 s-1 A-1 is obtained for the fluxat ~900 Å in the rest frame of Mrk 54. By comparison with thenumber of ionizing photons derived from the Hα flux, this limittranslates into an upper limit of fmathrm {esc}< 0.062 forthe fraction of Lyman continuum photons that escape the galaxy withoutbeing absorbed by interstellar material. This limit compares with thelimits obtained in three other nearby galaxies and is compatible withthe escape fractions predicted by models. The upper limits obtained innearby galaxies contrasts with the detection of Lyman continuum flux inthe composite spectrum of Lyman-break galaxies at z ~ 3.4. Thedifficulties and implications of a comparison are discussed. Based onobservations made with the NASA-CNES-CSA Far Ultraviolet SpectroscopicExplorer. FUSE is operated for NASA by the Johns Hopkins Universityunder NASA contract NAS5-32985.
| The formation of galaxy bulges: Spectrophotometric constraints
We have measured Mg2, Fe 5270 and Fe 5335 spectrophotometricindices (LICK system) in the bulge of 89 galaxies, mostly spirals fromthe Héraudeau (\cite{her96}) sample. The indices are reduced to anull velocity dispersion and normalized to an aperture of 0.2h-1 kpc. The mean errors are 0.009 mag on Mg2, and0.3 Å on the iron indices. These measurements almost double theamount of similar data already available on spiral galaxies. Our dataconfirm the existence of the relation between Mg2, andsigma0, the central stellar velocity dispersion; we find aneven tighter relation between Mg2, andVmrot, the maximum rotational velocity of thegalaxy, deduced from HI observations. For the most massive bulges, thesecorrelations may be interpreted as a mass-metallicity relation. However,the presence of young stellar populations, traced by the detection of[OIII] lambda 5007 Å, emission, provides clear evidence that ageeffects do play a role. Since the contribution of the young populationis anti-correlated to the mass of the galaxy, it continues theMg2, vs. sigma0 , relation toward thelow-sigma0, region and globally increases its slope. We alsopresent evidence for a new positive correlation between Fe indices andsigma0, and for a significant correlation between theline-strength indices and the total or disk luminosity. We propose tomodel the whole sequence of bulges within the folowing framework: bulgesare composed of a primary population formed prior to the disk, duringthe initial collapse, and of a secondary population formed during itsevolution. The whole family of bulges can be classified into threeclasses: (A) the bulges dominated by young populations are generallysmall, have ionized gas, low velocity dispersion and low line strengths;(B) the bulges dominated by the primary population lie along themass-metallicity sequence defined for elliptical galaxies; and (C) thebulges where the secondary population is significant are lessMg-over-abundant than (B)-type bulges and deviate from theMg2, vs. sigma0, relation of elliptical galaxies.Based on observations collected at the Observatoire de Haute-Provence.Table 3 is presented in electronic form only at the CDS. Tables 1 and 2are also available form at the CDS, Strasbourg, via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/366/68
| The second Kiso Survey for ultraviolet-excess galaxies. II.
Not Available
| 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.
| A Dynamical Study of Galaxies in the Hickson Compact Groups
To investigate dynamical properties of spiral galaxies in the Hicksoncompact groups (HCGs), we present rotation curves of 30 galaxies in 20HCGs. We found as follows: (1) There is no significant relation betweendynamical peculiarity and morphological peculiarity in HCG spiralgalaxies. (2) There is no significant relation between the dynamicalproperties and the frequency distribution of nuclear activities in HCGspiral galaxies. (3) There are no significant correlations between thedynamical properties of HCG spiral galaxies and any group properties(i.e., size, velocity dispersion, galaxy number density, and crossingtime). (4) Asymmetric and peculiar rotation curves are more frequentlyseen in the HCG spiral galaxies than in field spiral galaxies or incluster ones. However, this tendency is more obviously seen in late-typeHCG spiral galaxies. These results suggest that the dynamical propertiesof HCG spiral galaxies do not strongly correlate with the morphology,the nuclear activity, and the group properties. Our results also suggestthat more frequent galaxy collisions occur in the HCGs than in the fieldand in the clusters.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Galaxy Interactions: The HI Signature
Invited review in Session 3: Tidal Interactions.
| 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.
| The Centers of Early- to Intermediate-Type Spiral Galaxies: A Structural Analysis
A recent Hubble Space Telescope (HST)/WFPC2 visual survey of early- andintermediate-type spiral galaxies has unveiled a great complexity in theinner regions of these systems, which include a high fraction ofphotometrically distinct compact sources sitting at the galactic centers(``nuclei''). The faint nuclei (M_V>~-12) are typically hosted byrather amorphous, quiescent, bulgelike structures with an exponential(rather than the classical R^1/4) light profile. These ``exponentialbulges'' are commonly found inside the intermediate-type disks,consistent with previous studies. Brighter nuclei (M_V<~-12) aretypically found instead in the centers of galaxies with circumnuclearrings/arms of star formation or dust and an active, i.e., H II- orAGN-type, central spectrum at ground-based resolution. On the structuralplane of half-light radius (R_e) versus mean surface brightness withinthe half-light radius (mu_e), faint and bright nuclei overlap with, andfill the region of parameter space between, the old Milky Way globularclusters and the young star clusters, respectively, with typical R_e ofabout a few up to ~20 pc. On the same plane, the exponential bulges havesignificantly fainter mu_e than R^1/4 bulges for any given radius andfollow a mu_e-R_e relation typical of disks, which strengthens thesuggestion that the exponential bulges grow inside the disks as a resultof the secular evolution of the latter. Under the likely assumption thatthe visual light from the faint nuclei embedded in the quiescentexponential bulges is of stellar origin and of a similar (>~1 Gyr)age for the central star clusters and their host bulges, the massesinferred for the former agree with those required to disrupt barscomparable in size to the latter. This offers support to scenarios inwhich the exponential bulges grow inside the disks owing to the orbitaldisruption of progenitor bars caused by the growth of a centralconcentration of mass and suggests that this specific mode of bulgeformation is (still) active in the present-day universe. On the otherhand, the presence of the massive clusters at the very center of thelow-density exponential bulges should prevent any other ``nuclear'' barfrom forming, thereby preventing further infall of dissipative fuel tothe nuclear regions. This may argue against the possibility of evolvingthe exponential bulges into denser, R^1/4 bulges by a simple looping forseveral cycles of the bar formation/disruption mechanism.
| Neutral Hydrogen and Dark Matter in Spiral Galaxies
The first part presents a brief review of the main HI properties ofisolated, normal spiral galaxies and of the phenomena which seem tocharacterize and dominate their internal metabolism. In the second partattention is drawn to all those processes, such as tidal interactions,accretion and mergers, that depend on the galaxy environment and mayplay a significant role in galaxy formation and evolution. In the thirdpart the observational evidence for the dark matter component of spiralgalaxies is discussed.
| New HST Observations of the Halo Gas of NGC 3067: Limits on the Extragalactic Ionizing Background at Low Redshift and the Lyman Continuum Escape Fraction
We present ultraviolet spectroscopy from HST/GHRS and reanalyze existingHα images of the quasar/galaxy pair 3C 232/NGC 3067 and of thehalo gas associated with NGC 3067. The spectra permit measurement of, orlimits on, the column densities of Fe I, Fe II, Mg I, and Mg II in theabsorbing cloud. Two distinct models of the extragalactic radiationfield are considered: (1) the ionizing spectrum is dominated by apower-law extragalactic continuum, and (2) the power-law spectrumcontains a Lyman break, implying enhanced flux longward of 912 Årelative to the hydrogen-ionizing flux. Models of the second type arerequired to fully explore the ionization balance of the Fe and Mg in themodel cloud. The Hα images constrain the escape fraction of Lymancontinuum photons from the galaxy to fesc<=0.02. With theassumption that the cloud is shielded from all galactic contributions,we can constrain the intensity and shape of the extragalactic continuum.For an AGN-dominated power-law extragalactic spectrum, we derive a limiton the extragalactic ionizing flux Φion>=2600 photonscm-2 s-1, or I0>=10-23ergs cm-2 s-1 Hz-1 sr-1 fora ν-1.8 ionizing spectrum and a cloud of constant density.When combined with previous upper limits from the absence of Hαrecombination emission from intergalactic clouds, our observationsrequire 2600<=Φion<=10,000 photons cm-2s-1. We show that if galactic contributions to the incidentradiation are important, it is difficult to constrainΦion. These results demonstrate that galactic haloopacities and their wavelength dependence are crucial to understandingthe abundance of low-ionization metals in the IGM.
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