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The multi-phase gaseous halos of star forming late-type galaxies. I. XMM-Newton observations of the hot ionized medium
This study presents first results from an X-ray mini-survey carried outwith XMM-Newton to investigate the diffuse Hot Ionized Medium in thehalos of nine nearby star-forming edge-on spiral galaxies. Diffusegaseous X-ray halos are detected in eight of our targets, covering awide range of star formation rates from quiescent to starburst cases.For four edge-on spiral galaxies, namely NGC 3044, NGC 3221, NGC 4634,and NGC 5775, we present the first published high resolution/sensitivitydetections of extended soft X-ray halos. EPIC X-ray contour mapsoverlaid onto Hα imaging data reveals that in all cases thepresence of X-ray halos is correlated with extraplanar Diffuse IonizedGas. Moreover, these halos are also associated with non-thermal cosmicray halos, as evidenced by radio continuum observations. SupplementalUV-data obtained with the OM-telescope at 210 nm show Diffuse IonizedGas to be well associated with UV emission originating in the underlyingdisk. Beside NGC 891, NGC 4634 is the second non-starburst galaxy with adiffuse soft X-ray halo (|z|≤ 4 kpc). In case of NGC 3877, for whichwe also present the first high resolution X-ray imaging data, no haloemission is detectable. EPIC pn spectra (0.3-12 keV) of the diffuseX-ray emission are extracted at different offset positions from thedisk, giving evidence to a significant decrease of gas temperatures,electron densities, and gas masses with increasing distance to theplane. A comparison between dynamical and radiative cooling time scalesimplies that the outflow in all targets is likely to be sustained. Wefind very strong indications that spatially correlated multi-phasegaseous halos are created by star forming activity in the disk plane. Ina forthcoming paper, we will present multi-frequency luminosityrelations and evaluate key parameters which might trigger the formationof multi-phase galaxy halos.
| The XMM-Newton Needles in the Haystack Survey: the local X-ray luminosity function of `normal' galaxies
In this paper we estimate the local (z < 0.22) X-ray luminosityfunction of `normal' galaxies derived from the XMM-Newton Needles in theHaystack Survey. This is an on-going project that aims to identifyX-ray-selected normal galaxies (i.e. non-AGN dominated) in the localUniverse. We are using a total of 70 XMM-Newton fields covering an areaof 11 deg2 which overlap with the Sloan Digital Sky SurveyData Release 2. Normal galaxies are selected on the basis of theirresolved optical light profile, their low X-ray-to-optical flux ratio[log(fx/fo) < - 2] and soft X-ray colours. Wefind a total of 28 candidate normal galaxies to the 0.5-8keV band fluxlimit of ~2 × 10-15ergcm-2s-1.Optical spectra are available for most sources in our sample (82 percent). These provide additional evidence that our sources are bona fidenormal galaxies with X-ray emission coming from diffuse hot gas emissionand/or X-ray binaries rather than a supermassive black hole. 16 of ourgalaxies have narrow emission lines or a late-type spectral energydistribution (SED) while the remaining 12 present only absorption linesor an early-type SED. Combining our XMM-Newton sample with 18 local (z< 0.22) galaxies from the Chandra Deep Field North and South surveys,we construct the local X-ray luminosity function of normal galaxies.This can be represented with a Schechter form with a break atL*~ 3+1.4-1.0×1041ergs-1 and a slope of α~ 1.78 +/- 0.12.Using this luminosity function and assuming pure luminosity evolution ofthe form ~(1 +z)3.3 we estimate a contribution to the X-raybackground from normal galaxies of ~10-20 per cent (0.5-8keV). Finally,we derive, for the first time, the luminosity functions for early- andlate-type systems separately.
| HI in NGC 5433 and its environment: high-latitude emission in a small galaxy group
We present HI synthesis maps of the edge-on starburst NGC 5433 and itsenvironment, obtained with the Very Large Array in its C and Dconfigurations. The observations and spectral model residuals of themain disc emission in NGC 5433 reveal three extraplanar features. Weassociate two of these features with coherent extraplanar extensionsacross multiple spectral channels in our data, including a complete loopin position-velocity space. Interpreting the latter as an expandingshell we derive a corresponding input energy of 2 ×1054 erg, comparable to that for the largest supershellsfound in the Galaxy and those in other edge-on systems. NGC 5433 is in aricher environment than previously thought. We confirm that KUG 1359+326is a physical companion to NGC 5433 and find two new faint companions,both with Minnesota Automated Plate Scanner identifications, which welabel SIS-1 and SIS-2. Including the more distant IC 4357, NGC 5433 isthe dominant member of a group of at least five galaxies, spanning over750 kpc in a filamentary structure. A variety of evidence suggests thatinteractions are occurring in this group. While a number of underlyingmechanisms are consistent with the morphology of the high-latitudefeatures in NGC 5433, we argue that environmental effects may play arole in their generation.
| The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe
The characteristics of the starburst galaxies from the Pico dos Diassurvey (PDS) are compared with those of the nearby ultraviolet (UV)bright Markarian starburst galaxies, having the same limit in redshift(vh < 7500 km s-1) and absolute B magnitude(MB < -18). An important difference is found: theMarkarian galaxies are generally undetected at 12 and 25 μm in IRAS.This is consistent with the UV excess shown by these galaxies andsuggests that the youngest star-forming regions dominating thesegalaxies are relatively free of dust.The far-infrared selection criteria for the PDS are shown to introduce astrong bias towards massive (luminous) and large size late-type spiralgalaxies. This is contrary to the Markarian galaxies, which are found tobe remarkably rich in smaller size early-type galaxies. These resultssuggest that only late-type spirals with a large and massive disc arestrong emitters at 12 and 25 μm in IRAS in the nearby Universe.The Markarian and PDS starburst galaxies are shown to share the sameenvironment. This rules out an explanation of the differences observedin terms of external parameters. These differences may be explained byassuming two different levels of evolution, the Markarian being lessevolved than the PDS galaxies. This interpretation is fully consistentwith the disc formation hypothesis proposed by Coziol et al. to explainthe special properties of the Markarian SBNG.
| The sub-mm/radio correlation in spiral galaxies.
Not Available
| Extraplanar Emission-Line Gas in Edge-On Spiral Galaxies. I. Deep Emission-Line Imaging
The extraplanar diffuse ionized gas (eDIG) in 17 nearby, edge-on diskgalaxies is studied using deep Taurus Tunable Filter Hα and [N II]λ6583 images and conventional interference filter Hα+[N II]λλ6548, 6583 images that reach flux levels generally below~1×10-17 ergs s-1 cm-2arcsec-2. [N II] λ6583/Hα excitation maps areavailable for 10 of these objects. All but one galaxy in the sampleexhibit eDIG. The contribution of the eDIG to the total Hαluminosity is relatively constant, on the order of 12%+/-4%. TheHα scale height of the eDIG derived from a two-exponential fit tothe vertical emission profile ranges from 0.4 to 17.9 kpc, with anaverage of 4.3 kpc. This average value is noticeably larger than theeDIG scale height measured in our Galaxy and other galaxies. Thisdifference in scale height is probably due in part to the lower fluxlimits of our observations. The ionized mass of the extraplanarcomponent inferred by assuming a constant filling factor of 0.2 and aconstant path length through the disk of 5 kpc ranges from1.4×107 to 2.4×108 Msolar,with an average value of 1.2×108 Msolar.Under these same assumptions, the recombination rate required to keepthe eDIG ionized ranges from 0.44×106 to13×106 s-1 cm-2 of the disk, orabout 10%-325% of the Galactic value. A quantitative analysis of thetopology of the eDIG confirms that several galaxies in the sample have ahighly structured eDIG morphology. The distribution of the eDIG emissionis often correlated with the locations of the H II regions in the disk,supporting the hypothesis that the predominant source of ionization ofthe eDIG is photoionization from OB stars located in the H II regions. Astrong correlation is found between the IR (or far-IR) luminosities perunit disk area (basically a measure of the star formation rate per unitdisk area) and the extraplanar ionized mass, further providing supportfor a strong connection between the disk and eDIG components in thesegalaxies. The excitation maps confirm that the [N II]/Hα ratiosare systematically higher in the eDIG than in the disk. Althoughphotoionization by disk OB stars is generally able to explain theseelevated [N II]/Hα ratios, a secondary source of ionizationappears to be needed when one also takes into account other line ratios;more detail is given in a companion paper (our Paper II).
| Extraplanar Emission-Line Gas in Edge-on Spiral Galaxies. II. Optical Spectroscopy
The results from deep long-slit spectroscopy of nine edge-on spiralgalaxies with known extraplanar line emission are reported. Emissionfrom Hα, [N II] λλ6548, 6583, and [S II]λλ6716, 6731 is detected out to heights of a fewkiloparsecs in all of these galaxies. Several other fainter diagnosticlines such as [O I] λ6300, [O III] λλ4959, 5007,and He I λ5876 are also detected over a smaller scale. Therelative strengths, centroids, and widths of the various emission linesprovide constraints on the electron density, temperature, reddening,source(s) of ionization, and kinematics of the extraplanar gas. In allbut one galaxy, photoionization by massive OB stars alone hasdifficulties explaining all of the line ratios in the extraplanar gas.Hybrid models that combine photoionization by OB stars and anothersource of ionization such as photoionization by turbulent mixing layersor shocks provide a better fit to the data. The (upper limits on the)velocity gradients measured in these galaxies are consistent with thepredictions of the galactic fountain model to within the accuracy of themeasurements.
| 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).
| Flat Galaxies of the RFGC Catalog Detected in the HIPASS Survey
Data from the H I Parkes All-Sky Survey (HIPASS) of the southern sky inthe neutral hydrogen line are used to determine the radial velocitiesand widths of the H I line for flat spiral galaxies of the RevisedFlat-Galaxy Catalog (RFGC) seen edge-on. The sample of 103 flat galaxiesdetected in HIPASS is characterized by a median radial velocity of +2037km/sec and a median width of the H I line at the level of 50% of maximumof 242 km/sec. For RFGC galaxies the 50% detection level in HIPASScorresponds to an apparent magnitude B t = 14 m .5 or an angulardiameter a = 2.9. The relative number of detected galaxies increasesfrom 2% for the morphological types Sbc and Sc to 41% for the type Sm.The median value of the ratio of hydrogen mass to total mass for RFGCgalaxies is 0.079. With allowance for the average internal extinctionfor edge-on galaxies, B t m .75, the median ratio of hydrogen mass toluminosity, M H I/L B = 0.74 M ȯ/L ȯ, is typical for late-typespirals. Because of its small depth, HIPASS reveals only a few RFGCgalaxies with previously unknown velocities and line widths.
| 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.
| Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of Hαemission line of a sample of 111 spiral galaxies with recognizable andwell defined spiral morphology and with a well determined environmentalstatus, ranging from isolation to non-disruptive interaction withsatellites or companions. The form and properties of the rotation curvesare considered as a function of the isolation degree, morphological typeand luminosity. The line ratios are used to estimate the metallicity ofall the detected HII regions, thus producing a composite metallicityprofile for different types of spirals. We have found that isolatedgalaxies tend to be of later types and lower luminosity than theinteracting galaxies. The outer parts of the rotation curves of isolatedgalaxies tend to be flatter than in interacting galaxies, but they showsimilar relations between global parameters. The scatter of theTully-Fisher relation defined by isolated galaxies is significantlylower than that of interacting galaxies. The [NII]/Hα ratios, usedas a metallicity indicator, show a clear trend between Z andmorphological type, t, with earlier spirals showing higher ratios; thistrend is tighter when instead of t the gradient of the inner rotationcurve, G, is used; no trend is found with the change in interactionstatus. The Z-gradient of the disks depends on the type, being almostflat for early spirals, and increasing for later types. The[NII]/Hα ratios measured for disk HII regions of interactinggalaxies are higher than for normal/isolated objects, even if all thegalaxy families present similar distributions of Hα EquivalentWidth. Tables 3 and 4 and Figs. 6, 7 and 21 are only available inelectronic form at http://www.edpsciences.org. Table 5 is only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/389 Based on dataobtained Asiago/Ekar Observatory. Also based on observations made withINT operated on the island of La Palma by ING in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias.
| High-Latitude H I in NGC 2613: Structure and Dynamics
Studies of edge-on spiral galaxies have revealed a number of cases inwhich kiloparsec-scale H I features extend from the disk into the haloregion. We have obtained VLA CnB array 21 cm H I observations of NGC2613, an edge-on spiral galaxy 26 Mpc away. We report that NGC 2613 isan extremely massive galaxy with a nearby companion galaxy (ESO495-G017). We present the first H I maps and masses for this companion.We have found three high-latitude features above the plane, symmetric inprojection with three below the plane in NGC 2613. All six features showa multiple velocity structure, with several ``spurs,'' as well as atrend to lag behind the disk gas with increasing distance from theplane. The radio continuum emission shows two large extensionsassociated with a strong continuum source in the disk. These are thehighest latitude discrete features clearly connected to a spiral galaxyyet detected in radio continuum. Moreover, two of the H I features showa strong correlation with these large continuum extensions, with thecontinuum arranged on the perimeter of the H I. We postulate that thesefeatures were formed by some mechanism internal to the galaxy, possiblyby spatially correlated supernovae or by the action of a preexistingrelativistic jet flowing through the plane of the galaxy.
| Properties of tidally-triggered vertical disk perturbations
We present a detailed analysis of the properties of warps andtidally-triggered perturbations perpendicular to the plane of 47interacting/merging edge-on spiral galaxies. The derived parameters arecompared with those obtained for a sample of 61 non-interacting edge-onspirals. The entire optical (R-band) sample used for this study waspresented in two previous papers. We find that the scale height of disksin the interacting/merging sample is characterized by perturbations onboth large ( =~ disk cut-off radius) and short ( =~ z0)scales, with amplitudes of the order of 280 pc and 130 pc on average,respectively. The size of these large (short) -scale instabilitiescorresponds to 14% (6%) of the mean disk scale height. This is a factorof 2 (1.5) larger than the value found for non-interacting galaxies. Ahallmark of nearly all tidally distorted disks is a scale height thatincreases systematically with radial distance. The frequent occurrenceand the significantly larger size of these gradients indicate that diskasymmetries on large scales are a common and persistent phenomenon,while local disturbances and bending instabilities decline on shortertimescales. Nearly all (93%) of the interacting/merging and 45% of thenon-interacting galaxies studied are noticeably warped. Warps ofinteracting/merging galaxies are ~ 2.5 times larger on average thanthose observed in the non-interacting sample, with sizes of the order of340 pc and 140 pc, respectively. This indicates that tidal distortionsdo considerably contribute to the formation and size of warps. However,they cannot entirely explain the frequent occurrence of warped disks.Based on observations obtained at the European Southern Observatory(ESO, La Silla, Chile), Calar Alto Observatory operated by the MPIA(DSAZ, Spain), Lowell Observatory (Flagstaff,AZ, USA), and Hoher ListObservatory (Germany).
| A list of peculiar velocities of RFGC galaxies
A list of radial velocities, HI line widths and peculiar velocities of1327 galaxies from the RFGC catalogue has been compiled using actualobservations and literature data. The list can be used for studying bulkmotions of galaxies, construction of the field of peculiar velocitiesand other tasks.
| Diffuse Ionized Gas in a Sample of Edge-on Galaxies and Comparisons with H I and Radio Continuum Emission
We present Hα images of four edge-on galaxies: NGC 5775, NGC 3044,NGC 4183, and NGC 3556. Our goals are twofold: first, to continue thestudy of the occurrence and physical properties of extraplanar diffuseionized gas (DIG), and second, to compare extraplanar Hα, H I, andradio continuum emission. The DIG of NGC 5775 is found to beconcentrated in numerous bright filaments extending as high as 6 kpc offthe midplane. NGC 3044, on the other hand, has a bright, smooth regionof DIG above the central part of the disk with some faint filaments athigher galactocentric radius. Vertical profile fits to the extraplanaremission show that both NGC 5775 and NGC 3044 have DIG layers moreextended than the Reynolds layer. In contrast, NGC 4183 shows verylittle extraplanar DIG. Profile fits suggest that it is very unlikelythat the DIG layer of NGC 4183 is as extended as the Reynolds layer. Thecorrelation between levels of star formation and prominence of DIGlayers for these galaxies is consistent with previous observations. Aprediction of the ``chimney model'' of the ISM is that extraplanarHα features should have H I and radio continuum counterparts.Comparisons among these three tracers have revealed, for the first time,correlations on the scale of individual extraplanar filaments in agalactic disk. NGC 5775 shows correlations between Hα filaments, HI shells, and radio continuum spurs that are consistent with a chimneymodel. However, features identified as possible chimneys in NGC 5775show radio spectral indices steeper than would be expected if cosmicrays were swept into the halo via galactic winds. Calculations ofcosmic-ray propagation scale lengths within the DIG filamentsdemonstrate that diffusion may indeed be responsible for transportingcosmic rays through chimneys marked by DIG filaments. Correlatedemission in these three tracers is also seen in NGC 3044, whereextraplanar H I and radio continuum features appear to be associatedwith the galaxy's central region of extraplanar DIG, as well asfilaments above the disk. Such correlations are not as prominent in NGC3556, where extraplanar DIG detection is hampered by the galaxy'srelatively low inclination.
| Obtaining Galaxy Masses Using Stellar Absorption and [O II] Emission-Line Diagnostics in Late-Type Galaxies
The [O II] λ3727 emission lines and absorption features fromstellar Balmer and Ca H and K lines are the most accessible kinematicdiagnostics in galaxies at z~1. We investigate the kinematics of 22local late-type galaxies using these spectral features, and we comparethe results with 21 cm neutral hydrogen spectra in order to assess theutility of each diagnostic for measuring galaxy masses. In order tosimulate data at high redshift, where only one-dimensional velocityprofiles are normally available, we study spatially integrated, as wellas spatially resolved, spectra. Although the studied galaxies span awide range of morphological types, inclinations, and star formationrates, we find that the gaseous and stellar kinematic tracers yieldcomparable kinematic line widths and systemic velocities. The [O II] andH I line widths correlate most strongly, showing an intrinsic dispersionof ~20 km s-1, or ~10% for a typical galaxy with a kinematicwidth of 200 km s-1. In a few extreme cases, the [O II] linewidths underestimate the neutral hydrogen width by 50%. Reliablevelocity widths can also be obtained from the stellar Balmer and Ca Hand K absorption lines, even for some of the very late type galaxiesthat have strong emission lines. The intrinsic dispersion is <=10%between the stellar absorption and H I line widths. We provide aprescription for using these strong stellar absorption and [O II]emission features to measure the kinematics, and thus masses, ofgalaxies in the distant universe.
| High-Resolution Radio Continuum Observations of Edge-on Spiral Galaxies
Radio continuum emission at 20 cm has been observed in a sample of 16edge-on galaxies, using the VLA in its A configuration. These galaxieswere observed recently at lower resolution by Irwin et al., who foundevidence for extraplanar disk-halo features in 15 of the 16 galaxies.Twelve of the galaxies are detected in the new high-resolutionobservations. Of these, only two, which were previously known Seyferts,show convincing evidence for AGNs. For six of the galaxies, we provideimproved positions for the galaxy nuclei. In four galaxies, radiocontinuum loops extending perpendicular to the major axis have beendiscovered, confirming previous conclusions from lower resolutionobservations that extraplanar emission is present, as well as providingfurther evidence that radio ``halos'' consist, at least in part, ofunderlying discrete features. For several galaxies, the resolution issufficient to reveal individual star-forming regions in the disk. Weexamine NGC 3556 in detail since this galaxy has been shown by King& Irwin to display extremely large H I supershells. The estimatedinput energy from supernovae in the brightest radio component of thisgalaxy is insufficient to drive the observed H I supershells. We explorepossible resolutions to this energy deficit.
| 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
| The influence of interactions and minor mergers on the structure of galactic disks I. Observations and disk models
This paper is the first part in our series on the influence of tidalinteractions and minor mergers on the radial and vertical disk structureof spiral galaxies. We report on the sample selection, our observations,and data reduction. Surface photometry of the optical and near infrareddata of a sample of 110 highly-inclined/edge-on disk galaxies arepresented. This sample consists of two subsamples of 61 non-interactinggalaxies (control sample) and of 49 interacting galaxies/minor mergingcandidates. Additionally, 41 of these galaxies were observed in the nearinfrared. We show that the distribution of morphological types of bothsubsamples is almost indistinguishable, covering the range between 0<= T <= 9. An improved, 3-dimensional disk modelling- and fittingprocedure is described in order to analyze and to compare the diskstructure of our sample galaxies by using characteristic parameters. Wefind that the vertical brightness profiles of galactic disks respondvery sensitive even to small deviations from the perfect edge-onorientation. Hence, projection effects of slightly inclined disks maycause substantial changes in the value of the disk scale height and musttherefore be considered in the subsequent study. Based on observationsobtained at the European Southern Observatory (ESO, La Silla, Chile),Calar Alto Observatory operated by the MPIA (DSAZ, Spain), LowellObservatory (Flagstaff/AZ, USA), and Hoher List Observatory (Germany).
| Spectroscopy of diffuse ionized gas in halos of selected edge-on galaxies
In order to examine the excitation and ionization mechanism ofextraplanar diffuse ionized gas (DIG) we have obtained optical longslitspectra of seven edge-on spiral galaxies. In four objects the brightestemission lines can be traced out to distances of typically 1.5 kpc abovethe disk. For NGC 1963 and NGC 3044 line ratios such as [N Ii]lambda6583 /Hα or [S Ii] lambda6717 /Hα as well as [ion{O{iii}] lambda5007 }/Hβ could be measured for the halo DIG. Thisallows us to discuss the DIG in the halo of these objects in theframework of diagnostic diagrams. For these two objects, the line ratiosof [ion {O{iii}] lambda5007 }/Hβ decrease with increasing |z|,different from the recently reported trend in NGC 891 (Rand\cite{rand}). We find that emission lines from the DIG in the disks arein good agreement with photoionization models using a dilute radiationfield. However, with increasing |z| these models fail to predict themeasured [ion {Oi] lambda 6300}/Hα \ and ion {Hei lambda5876}/Hα line ratios for NGC 1963. Diagnostic diagrams reveal forNGC 1963 the need for a second ionization mechanism of the halo DIG(besides photoionization). This additional source could be shockionization. The same diagrams demonstrate an intermediate classificationfor NGC 3044. Plots of [ion {S}{ii}]/[ion {N}{ii}] vs. emission measurereveal significant changes towards the halo and seem to trace localsmall scale density fluctuations of the extraplanar DIG. Based onobservations obtained at ESO/La Silla (Chile)
| Radio jet-blown neutral hydrogen supershells in spiral galaxies?
Taking a clue from the pair of HI supershells found in the Scd galaxyNGC 3556 (M 108), we propose a new mechanism for the origin of HIsupershells in gas-rich massive galaxies. In this scenario, the twosupershells were inflated out of the neutral hydrogen disk due to thelocalised flaring of a pair of radio lobes formed by the jets ejectedfrom the nucleus during an active phase about ~ 107 yearsago, but have faded away by now. It is shown that the salient featuresof this supershell pair, such as their symmetrical locations about thegalactic centre, the anomalously large energy requirements, the largegalacto-centric distances, as well as the Z-symmetric hemisphericalshapes, find a more natural explanation in terms of this scenario, ascompared to the standard models which postulate either a massivestarburst, or the infall of external gas clouds. Other possibleimplications of this hypothesis are briefly discussed.
| The influence of interactions and minor mergers on the structure of galactic disks. II. Results and interpretations
We present the second part of a detailed statistical study focussed onthe effects of tidal interactions and minor mergers on the radial andvertical disk structure of spiral galaxies. In the first part wereported on the sample selection, observations, and applied disk models.In this paper the results are presented, based on disk parametersderived from a sample of 110 highly-inclined/edge-on galaxies. Thissample consists of two subsamples of 49 interacting/merging and 61non-interacting galaxies. Additionally, 41 of these galaxies wereobserved in the NIR. We find significant changes of the disk structurein vertical direction, resulting in ~ 1.5 times larger scale heights andthus vertical velocity dispersions. The radial disk structure,characterized by the cut-off radius and the scale length, shows nostatistically significant changes. Thus, the ratio of radial to verticalscale parameters, h/z0, is ~ 1.7 times smaller for the sampleof interacting/merging galaxies. The total lack of typical flat diskratios h/z0 > 7 in the latter sample implies that verticaldisk heating is most efficient for (extremely) thin disks. Statisticallynearly all galactic disks in the sample (93%) possess non-isothermalvertical luminosity profiles like the sech (60%) and exp (33%)distribution, independent of the sample and passband investigated. Thisindicates that, in spite of tidal perturbations and disk thickening, theinitial vertical distribution of disk stars is not destroyed byinteractions or minor mergers. Based on observations obtained at theEuropean Southern Observatory (ESO, La Silla, Chile), Calar AltoObservatory operated by the MPIA (DSAZ, Spain), Lowell Observatory(Flagstaff/AZ, USA), and Hoher List Observatory (Germany).
| Extraplanar diffuse ionized gas in a small sample of nearby edge-on galaxies
We present narrowband Hα imaging data of a small survey of nearbyedge-on spiral galaxies, aiming at the detection of `extraplanar'diffuse ionized gas (DIG). A few of our studied edge-on spirals showsigns of disk-halo interaction (DHI), where extended line emission farabove the galactic plane of these galaxies is detected. In some cases anextraplanar diffuse ionized gas (eDIG) layer is discovered, e.g.,NGC4634, NGC 3044, while othergalaxies show only filamentary features reaching into the halo (e.g.,IC 2531) and some galaxies show no sign of eDIG atall. The extraplanar distances of the DIG layer in our narrowbandHα images reach values of z<= 2 kpc above the galactic plane.The derived star formation rates (SFRs) from the Hα flux of thestudied galaxies range from 0.05-0.7 Msun yr-1,neglecting a correction for internal absorption. The variation of theSFR values among our sample galaxies reflects the diversity of starformation within this sample. A diagnostic diagram is introduced, whichallows to predict the existence of gas halos in `quiescent' galaxiesbased on the ratio S60 /S100 versusLFIR / D225 in this diagram. We comparethe positions of the non-starburst galaxies with starburst galaxies,since these galaxies populate distinct positions in these diagrams.Based on observations collected at the European Southern Observatory, LaSilla, Chile
| The Revised Flat Galaxy Catalogue.
We present a new improved and completed version of the Flat GalaxyCatalogue (FGC) named the Revised Flat Galaxy Catalogue (RFGC)containing 4236 thin edge-on spiral galaxies and covering the whole sky.The Catalogue is intended to study large-scale cosmic streamings as wellas other problems of observational cosmology. The dipole moment ofdistribution of the RFGC galaxies (l = 273 degr; b =+19 degr) lieswithin statistical errors (+/-10 degr) in the direction of the LocalGroup motion towards the Microwave Background Radiation (MBR).
| The dynamics of a Galactic fountain
In the "galactic fountain" model, hot, buoyant gaseous cavities providean important mechanism for the transfer of mass and energy in theGalactic halo. The influence of thermal conductivity and radiativelosses on the evolution of such cavities is examined. The joint actionof heat conduction and radiative cooling leads to the development of acooling wave propagating in the direction of the hot (thermallyunstable) gas. At temperatures typical for hot interstellar gas, thecavities are subject to erosion by the intrusion of such cooling waves.This effect substantially decreases the efficiency of the galacticfountain: the rate of ejection of hot gas from the disk (M_*<<< 0.3 M_solar/yr) is not sufficient to support the halo in asteady state.
| 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.
| An Infrared Search for Extinguished Supernovae in Starburst Galaxies
IR and radio-band observations of heavily extinguished regions instarburst galaxies suggest a high supernova (SN) rate associated withsuch regions. Optically measured SN rates may therefore underestimatethe total SN rate by factors of up to 10, as a result of the very highextinction (A_B~10-20 mag) to core-collapse SNe in starburst regions.The IR/radio SN rates come from a variety of indirect means, however,which suffer from model dependence and other problems. We describe adirect measurement of the SN rate from a regular patrol of starburstgalaxies done with K'-band imaging to minimize the effects ofextinction. A collection of K'-band measurements of core-collapse SNenear maximum light is presented. Such measurements (excluding 1987A) arenot well reported in the literature. Results of a preliminary K'-bandsearch, using the MIRC camera at the Wyoming Infrared Observatory and animproved search strategy using the new ORCA optics, are described. Amonthly patrol of a sample of IRAS bright (mostly starburst) galaxieswithin 25 Mpc should yield 1-6 SNe yr^-1, corresponding to the range ofestimated SN rates. Our initial MIRC search with low resolution (2.2"pixels) failed to find extinguished SNe in the IRAS galaxies, limitingthe SN rate outside the nucleus (at greater than 15" radius) to lessthan 3.8 far-IR SN rate units (SNe per century per 10^10 L_solarmeasured at 60 and 100 mum, or FIRSRU) at 90% confidence. The MIRCcamera had insufficient resolution to search nuclear starburst regions,where starburst and SN activity is concentrated; therefore, we wereunable to rigorously test the hypothesis of high SN rates in heavilyobscured star-forming regions. We conclude that high-resolution nuclearSN searches in starburst galaxies with small fields are more productivethan low-resolution, large-field searches, even for our sample of large(often several arcminutes) galaxies. With our ORCA high-resolutionoptics, we could limit the total SN rate to less than 1.3 FIRSRU at 90%confidence in 3 years of observations, lower than most estimates.
| High-Latitude Radio Emission in a Sample of Edge-on Spiral Galaxies
We have mapped 16 edge-on galaxies at 20 cm using the Very Large Arrayin its C configuration, and a subset of these galaxies in the Dconfiguration at 6 and/or 20 cm, in a search for extended (>~1 kpc)radio continuum emission above and below the plane. For five galaxies,we could form spectral index, energy, and magnetic field maps (assumingminimum energy). While the galaxies were partly chosen by radio fluxdensity, they span a variety of star formation rates (SFRs), and onlysix might be considered ``starburst'' galaxies. A range of Hubble typeand degree of isolation are also represented. The galaxies largely fallon the FIR-radio continuum correlation. They also display a correlationbetween IR surface brightness and warmth, extending the previouslyobserved relation of Lehnert & Heckman to galaxies with lower starformation rates. We find that all but one galaxy show evidence fornonthermal high-latitude radio continuum emission, suggesting thatcosmic-ray (CR) halos are common in star-forming galaxies. Of these,eight galaxies are new detections. The high-latitude emission is seenover a variety of spatial scales and in discrete and/or smooth features.In some cases, discrete features are seen on large scales, suggestingthat smooth radio halos may consist, in part, of discrete featurescombined with low spatial resolution. In general, the discrete featuresemanate from the disk, but estimates of CR diffusion lengths suggestthat diffusion alone is insufficient to transport the particles to thehigh latitudes seen (>15 kpc in one case). Thus CRs likely diffusethrough low-density regions and/or are assisted by other mechanisms(e.g., winds). We searched for correlations between the prevalence ofhigh-latitude radio emission and a number of other properties, includingthe global SFR, supernova input rate per unit star-forming area, E_A,and environment, and do not find clear correlations with any of theseproperties. A subset of the data allows, at best, for only a weakcorrelation with E_A. Our one nondetection (NGC 4517), however, occursat a threshold level consistent with that found by Dahlem, Lisenfeld,& Golla. The lack of a good correlation with star formationindicators could be the result of the different timescales for starformation processes compared with the duration of the radio emission.Correlations with other properties, such as environment, are moredifficult to assess. However, a few isolated galaxies display strongradio halos, indicating that an interaction is not necessary to producethe extraplanar emission.
| Gamma ray bursts versus OB associations: do they trigger star formation?
We discuss differences in shapes, expansion velocities and fragmentationtimes of structures created by an energy deposition from a singleGamma-Ray Burst (GRB) and an OB association to the ISM. After theinitial inflation, supershells produced by GRBs are almost static orslowly expanding, contrary to more rapidly expanding supershells createdby OB associations. We discuss the position of the energy sourcerelative to the symmetry plane of the galaxy: observed arc-likestructures can be the most dense part of structures formed by anexpansion from a source above or below the galactic plane. Arcs may alsoform if the expansion takes place inside a giant HI cloud. We try toreproduce the size, the age, and the average distance between OBassociations in the Sextant region at the edge of LMC 4.
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