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The stellar dynamics of spiral arms in barred spiral galaxies
A dynamical mechanism is proposed that explains the spiral structureobserved frequently as a continuation of the bars in barred spiralgalaxies. It is argued that the part of the spirals attached to the baris due to chaotic orbits. These are chaotic orbits that exhibit for longtime intervals a 4:1-resonance orbital behaviour. They are of the sametype of orbit as is responsible for the boxiness of the outer isophotesof the bar in cases like NGC 4314, as indicated by Patsis, Athanassoula& Quillen. The spirals formed this way are faint with respect to thebar, open as they wind out, and do not extend over an angle larger thanπ/2. A possible continuation of the spiral structure towards largerangles can be due to orbits trapped around stable periodic orbits at thecorotation region. We present a family of stable, banana-like periodicorbits, precessing as EJ increases, that can play this role.
| An Atlas of Hα and R Images and Radial Profiles of 29 Bright Isolated Spiral Galaxies
Narrowband Hα+[N II] and broadband R images and surface photometryare presented for a sample of 29 bright (MB<-18 mag)isolated S0-Scd galaxies within a distance of 48 Mpc. These galaxies areamong the most isolated nearby spiral galaxies of their Hubbleclassifications as determined from the Nearby Galaxies Catalog.
| Low-Luminosity Active Galaxies and Their Central Black Holes
Central black hole masses for 117 spiral galaxies representingmorphological stages S0/a through Sc and taken from the largespectroscopic survey of Ho et al. are derived using Ks-banddata from the Two Micron All Sky Survey. Black hole masses are foundusing a calibrated black hole-Ks bulge luminosity relation,while bulge luminosities are measured by means of a two-dimensionalbulge-disk decomposition routine. The black hole masses are correlatedagainst a variety of parameters representing properties of the nucleusand host galaxy. Nuclear properties such as line width (FWHM [N II]), aswell as emission-line ratios (e.g., [O III]/Hβ, [O I]/Hα, [NII]/Hα, and [S II]/Hα), show a very high degree ofcorrelation with black hole mass. The excellent correlation with linewidth supports the view that the emission-line gas is in virialequilibrium with either the black hole or bulge potential. The very goodemission-line ratio correlations may indicate a change in ionizingcontinuum shape with black hole mass in the sense that more massiveblack holes generate harder spectra. Apart from theinclination-corrected rotational velocity, no excellent correlations arefound between black hole mass and host galaxy properties. Significantdifferences are found between the distributions of black hole masses inearly-, mid-, and late-type spiral galaxies (subsamples A, B, and C) inthe sense that early-type galaxies have preferentially larger centralblack holes, consistent with observations that Seyfert galaxies arefound preferentially in early-type systems. The line width distributionsshow a marked difference among subsamples A, B, and C in the sense thatearlier type galaxies have larger line widths. There are also cleardifferences in line ratios between subsamples A+B and C that likely arerelated to the level of ionization in the gas. Finally, aKs-band Simien & de Vaucouleurs diagram shows excellentagreement with the original B-band relation, although there is a largedispersion at a given morphological stage.
| A Comparison of Hα and Stellar Scale Lengths in Virgo and Field Spirals
The scale lengths of the old stars and ionized gas distributions arecompared for similar samples of Virgo Cluster members and field spiralgalaxies via Hα and broad R-band surface photometry. While theR-band and Hα scale lengths are, on average, comparable for thecombined sample, we find significant differences between the field andcluster samples. While the Hα scale lengths of the field galaxiesare a factor of 1.14+/-0.07 longer, on average, than their R-band scalelengths, the Hα scale lengths of Virgo Cluster members are, onaverage, 20% smaller than their R-band scale lengths. Furthermore, inVirgo, the scale length ratios are correlated with the size of thestar-forming disk: galaxies with smaller overall Hα extents alsoshow steeper radial falloff of star formation activity. At the sametime, we find no strong trends in scale length ratio as a function ofother galaxy properties, including galaxy luminosity, inclination,morphological type, central R-band light concentration, or bar type. Ourresults for Hα emission are similar to other results for dustemission, suggesting that Hα and dust have similar distributions.The environmental dependence of the Hα scale length placesadditional constraints on the evolutionary process(es) that cause gasdepletion and a suppression of the star formation rate in clusters ofgalaxies.
| The structure of galactic disks. Studying late-type spiral galaxies using SDSS
Using imaging data from the SDSS survey, we present the g' and r' radialstellar light distribution of a complete sample of ~90 face-on tointermediate inclined, nearby, late-type (Sb-Sdm) spiral galaxies. Thesurface brightness profiles are reliable (1 σ uncertainty lessthan 0.2 mag) down to μ27 mag/''. Only ~10% of all galaxies havea normal/standard purely exponential disk down to our noise limit. Thesurface brightness distribution of the rest of the galaxies is betterdescribed as a broken exponential. About 60% of the galaxies have abreak in the exponential profile between 1.5-4.5 times thescalelength followed by a downbending, steeper outer region. Another~30% shows also a clear break between 4.0-6.0 times thescalelength but followed by an upbending, shallower outer region. A fewgalaxies have even a more complex surface brightness distribution. Theshape of the profiles correlates with Hubble type. Downbending breaksare more frequent in later Hubble types while the fraction of upbendingbreaks rises towards earlier types. No clear relation is found betweenthe environment, as characterised by the number of neighbours, and theshape of the profiles of the galaxies.
| The AMIGA sample of isolated galaxies. II. Morphological refinement
We present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies.
| BHαBAR: big Hα kinematical sample of barred spiral galaxies - I. Fabry-Perot observations of 21 galaxies
We present the Hα gas kinematics of 21 representative barredspiral galaxies belonging to the BHαBAR sample. The galaxies wereobserved with FaNTOmM, a Fabry-Perot integral-field spectrometer, onthree different telescopes. The three-dimensional data cubes wereprocessed through a robust pipeline with the aim of providing the mosthomogeneous and accurate data set possible useful for further analysis.The data cubes were spatially binned to a constant signal-to-noiseratio, typically around 7. Maps of the monochromatic Hα emissionline and of the velocity field were generated and the kinematicalparameters were derived for the whole sample using tilted-ring models.The photometrical and kinematical parameters (position angle of themajor axis, inclination, systemic velocity and kinematical centre) arein relative good agreement, except perhaps for the later-type spirals.
| Imprints of spiral arms in the oxygen distribution over the galactic disc
A theory for the oxygen abundance radial distribution formation in thegalactic disc of a spiral galaxy is developed. We take into account thatthe main sources of oxygen are Type II supernovae (SN II), theprogenitors of which are massive short-lived stars strongly concentratedin the spiral arms. Hence oxygen is the most sensitive indicator ofspiral arms' influence on galactic disc enrichment by heavy elements.Various models for the spiral density waves were analysed. We predictthat the imprints in the oxygen radial distribution will enable us todistinguish between different models for spiral patterns. Among otherparameters, the corotation radius happens to be one of the mostimportant.
| On the Relevance of the Tremaine-Weinberg Method Applied to an Hα Velocity Field: Pattern Speed Determination in M100 (NGC 4321)
The relevance of the Tremaine-Weinberg (TW) method is tested formeasuring bar, spiral, and inner structure pattern speeds using agaseous velocity field. The TW method is applied to various simulatedbarred galaxies in order to demonstrate its validity in seven differentconfigurations, including star formation and/or dark matter halo. Thereliability of the different physical processes involved and of thevarious observational parameters is also tested. The simulations showthat the TW method could be applied to gaseous velocity fields to get agood estimate of the bar pattern speed, under the condition that regionsof shocks are avoided and measurements are confined to regions where thegaseous bar is well formed. We successfully apply the TW method to theHα velocity field of the Virgo Cluster galaxy M100 (NGC 4321) andderive pattern speeds of 55+/-5 km s-1 kpc-1 forthe nuclear structure, 30+/-2 km s-1 kpc-1 for thebar, and 20+/-1 km s-1 kpc-1 for the spiralpattern, in full agreement with published determinations using the samemethod or alternative ones.
| The Central Region of Barred Galaxies: Molecular Environment, Starbursts, and Secular Evolution
Stellar bars drive gas into the circumnuclear (CN) region of galaxies.To investigate the fate of the CN gas and star formation (SF), we studya sample of barred nonstarbursts and starbursts with high-resolution CO,optical, Hα, radio continuum, Brγ, and HST data, and findthe following. (1) The inner kiloparsec of bars differs markedly fromthe outer disk. It hosts molecular gas surface densitiesΣgas-m of 500-3500 Msolar pc-2,gas mass fractions of 10%-30%, and epicyclic frequencies of several100-1000 km s-1 kpc-1. Consequently, in the CNregion gravitational instabilities can only grow at high gas densitiesand on short timescales, explaining in part why powerful starburstsreside there. (2) Across the sample, we find bar pattern speeds withupper limits of 43-115 km s-1 pc-1 and outer innerLindblad resonance radii of >500 pc. (3) Barred starbursts andnonstarbursts have CN SF rates of 3-11 and 0.1-2 Msolaryr-1, despite similar CN gas masses. TheΣgas-m value in the starbursts is larger (1000-3500Msolar pc-2) and close to the Toomre criticaldensity over a large region. (4) Molecular gas makes up 10%-30% of theCN dynamical mass and fuels large CN SF rates in the starbursts,building young, massive, high-V/σ components. Implications forsecular evolution along the Hubble sequence are discussed.
| The internal dynamical equilibrium of H II regions: A statistical study
We present an analysis of the integrated Hα emission line profilesfor the H SHAPE Ii region population of the spiral galaxies NGC 1530,NGC 6951 and NGC 3359. We show that 70% of the line profiles showtwo or three Gaussian components. The relations between the luminosity(log LHα) and non-thermal line width (logσnt) for the H SHAPE Ii regions of the three galaxiesare studied and compared with the relation found taken all the H SHAPEIi regions of the three galaxies as a single distribution. In all ofthese distributions we find a lower envelope in logσnt. A clearer envelope in σnt isfound when only those H SHAPE Ii regions with σnt>σs(13 km s-1) are considered, whereσs is a canonical estimate of the sound speed in theinterestellar medium. The linear fit for the envelope is logLHα =(36.8±0.7)+(2.0±0.5) logσnt where the Hα luminosity of the region istaken directly from a photometric H SHAPE Ii region catalogue. When theHα luminosity used instead is that fraction of the H SHAPE Iiregion luminosity, corresponding to the principal velocity component,i.e. to the turbulent non-expanding contribution, the linear fit is logLHα=(36.8±0.6)+(2.0±0.5) logσnt, i.e. unchanged but slightly tighter. The masses ofthe H SHAPE Ii regions on the envelope using the virial theorem and themass estimates from the Hα luminosity are comparable, whichoffers evidence that the H SHAPE Ii regions on the envelope arevirialized systems, while the remaining regions, the majority, are notin virial equilibrium.
| Expansive components in H II regions
We study the presence of low intensity high velocity components, whichwe have termed wing features in the integrated Hα emission lineprofiles of the H II region populations of the spiral barred galaxiesNGC 1530, NGC 3359 and NGC 6951. We find that more than a third of the HII region line profiles in each galaxy show these components. Thehighest fraction is obtained in the galaxy whose line profiles show thebest S:N, which suggests that wing features of this type may well existin most, if not all, H II region line profiles. Applying selectioncriteria to the wing features, we obtain a sample of H II regions withclearly defined high velocity components in their profiles.Deconvolution of a representative sample of the line profiles eliminatesany doubt that the wing features could possibly be due to instrumentaleffects. We present an analysis of the high velocity low intensityfeatures fitting them with Gaussian functions; the emission measures,central velocities and velocity dispersions for the red and bluefeatures take similar values. We interpret the features as signatures ofexpanding shells inside the H II regions. Up to a shell radius ofRshell 0.2 Rreg, the stellar winds from thecentral ionizing stars appear to satisfy the energy and momentumrequirements for the formation and driving the shell. Several examplesof the most luminous H II regions show that the shells appear to havelarger radii; in these cases additional mechanisms may well be needed toexplain the kinetic energies and momenta of the shells.
| From gas to galaxies
The unsurpassed sensitivity and resolution of the Square Kilometer Array(SKA) will make it possible for the first time to probe the continuumemission of normal star forming galaxies out to the edges of theuniverse. This opens the possibility for routinely using the radiocontinuum emission from galaxies for cosmological research as it offersan independent probe of the evolution of the star formation density inthe universe. In addition it offers the possibility to detect the firststar forming objects and massive black holes. In deep surveys SKA willbe able to detect HI in emission out to redshifts of z ≈ 2.5 andhence be able to trace the conversion of gas into stars over an erawhere considerable evolution is taking place. Such surveys will be ableto uniquely determine the respective importance of merging and accretinggas flows for galaxy formation over this redshift range (i.e. out towhen the universe was only one third its present age). It is obviousthat only SKA will able to see literally where and how gas is turnedinto stars. These and other aspects of SKA imaging of galaxies will bediscussed.
| Evidence for Gas Accretion in Galactic Disks
Studies of the H I in galaxies have clearly shown that subtle details ofthe H I distribution and kinematics often harbour key information forunderstanding the structure and evolution of galaxies. Evidence for theaccretion of material has grown over the past many years and clearsignatures can be found in H I observations of galaxies. We haveobtained new detailed and sensitive H I synthesis observations of threenearby galaxies which are suspected of capturing small amounts of H Iand show that indeed accretion of small amounts of gas is taking placein these galaxies. This could be the same kind of phenomenon ofmaterial infall as observed in the stellar streams in the halo and outerparts of our galaxy and M 31.
| The Nuclear Gasdynamics and Star Formation of NGC 7469
We report interferometric radio CO 2-1 and HCN 1-0 observations atresolutions of 0.7" and 2.0", respectively, and 0.085" resolutionadaptive optics K-band spectroscopy, including H2 1-0 S(1)line emission and CO 2-0 stellar absorption, of the inner few arcsecondsof NGC 7469. The CO 2-1 map shows a ring of molecular clouds (which ingeneral lie outside the compact knots seen in K-band images) and abright extended nucleus, with a bar or pair of spiral arms between them.The dynamical structure of both the radio CO 2-1 and the K-bandH2 1-0 S(1) lines at their different resolutions can bereproduced using a single axisymmetric mass model comprising threecomponents: a broad disk, a ring 4"-5" across, and an extended nucleus,which we interpret as an inner nuclear ring about 0.5" across. Thevelocity residuals between the model and the data have a standarddeviation of 25 km s-1, and no noncircular motions fasterthan this are seen, although this may be because in some cases asecondary bar is not expected to cause gas inflow. From the dynamicalmass and estimates of the stellar mass we find that theCO-to-H2 conversion is 0.4-0.8 times that for the Milky Way,following the trend to small factors that has been reported for intensestar-forming environments. The central H2 1-0 S(1) morphologyhas a strong peak at the nucleus, but this does not trace the massdistribution; the rotation curves indicate that there is no strongnuclear mass concentration. The origins of the 1-0 S(1) emission areinstead likely to lie in X-ray and UV irradiation of gas by the activegalactic nucleus rather than via processes associated with starformation. Using the 2.3 μm stellar CO 2-0 band head absorption andthe slope of the continuum, we have directly resolved the nuclear starcluster to be 0.15"-0.20" across and find that it is asymmetric. Thiscluster has an age of less than about 60 Myr and contributes 20%-30% ofthe nuclear K-band light and about 10% of the nuclear bolometricluminosity. Within a radius of ~4" gas contributes more than half thetotal mass, but in the nucleus, within a radius of 0.1", it is likelythat most of the mass is due instead to stars.The near-infrared data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation. The radio data are based on observations carried out withthe IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS(France), MPG (Germany), and IGN (Spain).
| Star Formation Properties of a Large Sample of Irregular Galaxies
We present the results of Hα imaging of a large sample ofirregular galaxies. Our sample includes 94 galaxies with morphologicalclassifications of Im, 26 blue compact dwarfs (BCDs), and 20 Sm systems.The sample spans a large range in galactic parameters, includingintegrated absolute magnitude (MV of -9 to -19), averagesurface brightness (20-27 mag arcsec-2), current starformation activity (0-1.3 Msolar yr-1kpc-2), and relative gas content(0.02-5Msolar/LB). The Hα images were usedto measure the integrated star formation rates, determine the extents ofstar formation in the disks, and compare azimuthally averaged radialprofiles of current star formation to older starlight. The integratedstar formation rates of Im galaxies normalized to the physical size ofthe galaxy span a range of a factor of 104 with 10% Imgalaxies and one Sm system having no measurable star formation at thepresent time. The BCDs fall, on average, at the high star formation rateend of the range. We find no correlation between star formation activityand proximity to other cataloged galaxies. Two galaxies located in voidsare similar in properties to the Sm group in our sample. The H IIregions in these galaxies are most often found within the Holmbergradius RH, although in a few systems H II regions are tracedas far as 1.7RH. Similarly, most of the star formation isfound within three disk scale lengths RD, but in somegalaxies H II regions are traced as far as 6RD. A comparisonof Hα surface photometry with V-band surface photometry shows thatthe two approximately follow each other with radius in Sm galaxies, butin most BCDs there is an excess of Hα emission in the centers thatdrops with radius. In approximately half of the Im galaxies Hα andV correspond well, and in the rest there are small to large differencesin the relative rate of falloff with radius. The cases with stronggradients in the LHα/LV ratios and with highcentral star formation rate densities, which include most of the BCDs,require a significant fraction of their gas to migrate to the center inthe last gigayear. We discuss possible torques that could have causedthis without leaving an obvious signature, including dark matter barsand past interactions or mergers with small galaxies or H I clouds.There is now a substantial amount of evidence for these processes amongmany surveys of BCDs. We note that such gas migration will also increasethe local pressure and possibly enhance the formation of massive denseclusters but conclude that the star formation process itself does notappear to differ much among BCD, Im, and Sm types. In particular, thereis evidence in the distribution function for Hα surface brightnessthat the turbulent Mach numbers are all about the same in these systems.This follows from the Hα distribution functions corrected forexponential disk gradients, which are log-normal with a nearly constantdispersion. Thus, the influence of shock-triggered star formation isapparently no greater in BCDs than in Im and Sm types.
| 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
| The Galactic abundance gradient from Cepheids. V. Transition zone between 10 and 11 kpc
This paper reports on the spectroscopic investigation of 12 Cepheidswhich are situated in the crucial region of galactocentric distancesfrom 9 kpc to 12 kpc, where according to our previous results(Andrievsky et al. \cite{andret02c}; Luck et al. \cite{lucket03}) theradial metallicity distribution experiences an obvious change. Inparticular, the wriggle in the iron abundance distribution is found tofall approximately at galactocentric distances 10-11 kpc (assuminggalactocentric distance of the Sun RG, ȯ = 7.9 kpc).Within the transition zone from 10 to 11 kpc the relative-to-solar ironabundance decreases approximately to -0.2 dex. The new sample of stars,analyzed in present paper, gives results supporting the previousconclusion about the multimodal character of the metallicitydistribution in galactic disc. Using a quite simple consideration ofgalactic chemical evolution we show that the observed distribution canbe explained in the framework of a model which includes the spiral arms.In particular, the wriggle feature associated with RG ≈ 11kpc can be interpreted as a change of metallicity level in the vicinityof the galactic corotation resonance.Based on spectra collected at the 3.6-m Canada-France-Hawaii Telescope.Table A1 (Appendix) is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/159
| Physical Scenarios for Supersonic Gas Flows Observed in H II Regions
Line profiles in ensuremath {{H}alpha } emission from H II regionpopulations in spiral galaxies show emission features at +/-50 km/sfrom the main emission peaks of a significant fraction of regions, whichare characteristic of expanding shells. We interpret these in twopossible scenarios: mass-loaded wind outflows from the central OB stars,or dust-coupled, radiation-driven outflows, caused by the same objects.
| Observations of Massive Supersonic Outflows in Highly Luminous H II Regions
Using H alpha emission line profiles we detect outflowing ionized gasat velocities of order 50 km/s from representative luminous H II regionsin two sample disk galaxies, NGC 3359 and NGC 1530, and calculate thephysical parameters of the outflowing material.
| First results from the HI Jodrell All Sky Survey: inclination-dependent selection effects in a 21-cm blind survey
Details are presented of the HI Jodrell All Sky Survey (HIJASS). HIJASSis a blind neutral hydrogen (HI) survey of the northern sky (δ> 22°), being conducted using the multibeam receiver on theLovell Telescope (full width at half-maximum beamwidth 12 arcmin) atJodrell Bank. HIJASS covers the velocity range -3500 to 10 000 kms-1, with a velocity resolution of 18.1 km s-1 andspatial positional accuracy of ~2.5 arcmin. Thus far about 1115deg2 of sky have been surveyed. The average rms noise duringthe early part of the survey was around 16 mJy beam-1.Following the first phase of the Lovell Telescope upgrade (in 2001), therms noise is now around 13 mJy beam-1. We describe themethods of detecting galaxies within the HIJASS data and of measuringtheir HI parameters. The properties of the resulting HI-selected sampleof galaxies are described. Of the 222 sources so far confirmed, 170 (77per cent) are clearly associated with a previously catalogued galaxy. Afurther 23 sources (10 per cent) lie close (within 6 arcmin) to apreviously catalogued galaxy for which no previous redshift exists. Afurther 29 sources (13 per cent) do not appear to be associated with anypreviously catalogued galaxy. The distributions of peak flux, integratedflux, HI mass and cz are discussed. We show, using the HIJASS data, thatHI self-absorption is a significant, but often overlooked, effect ingalaxies with large inclination angles to the line of sight. Properlyaccounting for it could increase the derived HI mass density of thelocal Universe by at least 25 per cent. The effect that this will haveon the shape of the HI mass function will depend on how self-absorptionaffects galaxies of different morphological types and HI masses. We alsoshow that galaxies with small inclinations to the line of sight may alsobe excluded from HI-selected samples, since many such galaxies will haveobserved velocity widths that are too narrow for them to bedistinguished from narrow-band radio-frequency interference. This effectwill become progressively more serious for galaxies with smallerintrinsic velocity widths. If, as we might expect, galaxies with smallerintrinsic velocity widths have smaller HI masses, then compensating forthis effect could significantly steepen the faint-end slope of thederived HI mass function.
| Interaction between OB stars and the interstellar medium.
Not Available
| Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
| 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.
| Revised positions for CIG galaxies
We present revised positions for the 1051 galaxies belonging to theKarachentseva Catalog of Isolated Galaxies (CIG). New positions werecalculated by applying SExtractor to the Digitized Sky Survey CIG fieldswith a spatial resolution of 1 arcsper 2. We visually checked theresults and for 118 galaxies had to recompute the assigned positions dueto complex morphologies (e.g. distorted isophotes, undefined nuclei,knotty galaxies) or the presence of bright stars. We found differencesbetween older and newer positions of up to 38 arcsec with a mean valueof 2 arcsper 96 relative to SIMBAD and up to 38 arcsec and 2 arcsper 42respectively relative to UZC. Based on star positions from the APMcatalog we determined that the DSS astrometry of five CIG fields has amean offset in (alpha , delta ) of (-0 arcsper 90, 0 arcsper 93) with adispersion of 0 arcsper 4. These results have been confirmed using the2MASS All-Sky Catalog of Point Sources. The intrinsic errors of ourmethod combined with the astrometric ones are of the order of 0 arcsper5.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/391
| 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
| High-Velocity Gas in the Luminous H II Regions of NGC 1530
We are carrying out a systematic study of the ensuremath {{H}alpha }emission line profiles from the H II regions in NGC 1530 (Knapen et al.2001) based on a data cube from the TAURUS Fabry-Perot scanner, on the4.2m WHT, La Palma. The data are of high S:N ratio, high spatialresolution (seeing ~ 0.6 arcsec ) and velocity resolution, FWHM, of 18kms ensuremath {^{-1}} . The observations reveal, from the luminousregions, high velocity components forming low intensity wings to theintense emission peak. We cannot tell whether they are absent in theless luminous regions, or below the noise level. We detected similarhigh velocity features from M100, NGC 3359, and NGC 6951 (see e.g.,Rozas et al. 1998).
| Bar strengths in spiral galaxies estimated from 2MASS images
Non-axisymmetric forces are presented for a sample of 107 spiralgalaxies, of which 31 are barred (SB) and 53 show nuclear activity. As adata base we use JHK images from the 2 Micron All-sky Survey, and thenon-axisymmetries are characterized by the ratio of the tangential forceto the mean axisymmetric radial force field, following Buta & Block.Bar strengths have an important role in many extragalactic problems andtherefore it is important to verify that the different numerical methodsapplied for calculating the forces give mutually consistent results. Weapply both direct Cartesian integration and a polar grid integrationutilizing a limited number of azimuthal Fourier components of density.We find that the bar strength is independent of the method used toevaluate the gravitational potential. However, because of thedistance-dependent smoothing by Fourier decomposition, the polar methodis more suitable for weak and noisy images. The largest source ofuncertainty in the derived bar strength appears to be the uncertainty inthe vertical scaleheight, which is difficult to measure directly formost galaxies. On the other hand, the derived bar strength is ratherinsensitive to the possible gradient in the vertical scaleheight of thedisc or to the exact model of the vertical density distribution,provided that the same effective vertical dispersion is assumed in allmodels. In comparison with the pioneering study by Buta & Block, thebar strength estimate is improved here by taking into account thedependence of the vertical scaleheight on the Hubble type: we find thatfor thin discs bar strengths are stronger than for thick discs by anamount that may correspond to as much as one bar strength class. Weconfirm the previous result by Buta and co-workers showing that thedispersion in bar strength is large among all the de Vaucouleurs opticalbar classes. In the near-infrared 40 per cent of the galaxies in oursample have bars (showing constant phases in the m= 2 Fourier amplitudesin the bar region), while in the optical band one-third of these barsare obscured by dust. Significant non-axisymmetric forces can also beinduced by the spiral arms, generally in the outer parts of the galacticdiscs, which may have important implications on galaxy evolution.Possible biases of the selected sample are also studied: we find thatthe number of bars identified drops rapidly when the inclination of thegalactic disc is larger than 50°. A similar bias is found in theThird Reference Catalogue of Bright Galaxies, which might be of interestwhen comparing bar frequencies at high and low redshifts.
| How the most highly luminous H II regions in galaxies ionize the interstellar and intergalactic media.
Not Available
| A Search for Active Galactic Nuclei in Sc Galaxies with H II Spectra
We have searched for nuclear radio emission from a statisticallycomplete sample of 40 Sc galaxies within 30 Mpc that are opticallyclassified as star-forming objects, in order to determine whether weakactive galactic nuclei might be present. Only three nuclear radiosources were detected, in NGC 864, NGC 4123, and NGC 4535. Thesegalaxies have peak 6 cm radio powers of ~1020 WHz-1 at arcsecond resolution, while upper limits of thenondetected galaxies typically range from 1018.4 to1020 W Hz-1. The three nuclear radio sources areall resolved and appear to have diffuse morphologies, with linear sizesof ~300 pc. This strongly indicates that circumnuclear star formationhas been detected in these three H II galaxies. Comparisons withprevious 20 cm Very Large Array (VLA) results for the detected galaxiesshow that the extended nuclear radio emission has a flat spectrum in twoobjects and is almost certainly generated by thermal emission from gasionized by young stars in the centers of those galaxies. The 6 cm radiopowers are comparable to predictions for thermal emission that are basedon the nuclear Hα luminosities and imply nuclear star formationrates of 0.08-0.8 Msolar yr-1, while thelow-resolution NRAO VLA Sky Survey implies galaxy-wide star formationrates of 0.3-1.0 Msolar yr-1 in stars above 5Msolar. In a few of the undetected galaxies, the upper limitsto the radio power are lower than predicted from the Hαluminosity, possibly because of overresolution of central star-formingregions. Although the presence of active nuclei powered by massive blackholes cannot be definitively ruled out, the present results suggest thatthey are likely to be rare in these late-type galaxies with H IIspectra.
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