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Late-type galaxies observed with SAURON: two-dimensional stellar and emission-line kinematics of 18 spirals
We present the stellar and gas kinematics of a sample of 18 nearbylate-type spiral galaxies (Hubble types ranging from Sb to Sd), observedwith the integral-field spectrograph SAURON at the 4.2-m WilliamHerschel Telescope. SAURON covers the spectral range 4800-5380Å,allowing us to measure the Hβ, Fe, Mgb absorption features and theemission in the Hβ line and the [OIII]λλ4959,5007Å and [NI]λλ5198, 5200Å doublets over a 33× 41-arcsec2 field of view. The maps cover the nuclearregion of these late-type galaxies and in all cases include the entirebulge. In many cases the stellar kinematics suggests the presence of acold inner region, as visible from a central drop in the stellarvelocity dispersion. The ionized gas is almost ubiquitous and behaves ina complicated fashion: the gas velocity fields often display morefeatures than the stellar ones, including wiggles in the zero-velocitylines, irregular distributions, ring-like structures. The line ratio[OIII]/Hβ often takes on low values over most of the field,probably indicating a wide-spread star formation.
| Revisiting the infrared spectra of active galactic nuclei with a new torus emission model
We describe improved modelling of the emission by dust in atoroidal-like structure heated by a central illuminating source withinactive galactic nuclei (AGNs). We have chosen a simple but realistictorus geometry, a flared disc, and a dust grain distribution functionincluding a full range of grain sizes. The optical depth within thetorus is computed in detail taking into account the differentsublimation temperatures of the silicate and graphite grains, whichsolves previously reported inconsistencies in the silicate emissionfeature in type 1 AGNs. We exploit this model to study the spectralenergy distributions (SEDs) of 58 extragalactic (both type 1 and type 2)sources using archival optical and infrared data. We find that both AGNand starburst contributions are often required to reproduce the observedSEDs, although in a few cases they are very well fitted by a pure AGNcomponent. The AGN contribution to the far-infrared luminosity is foundto be higher in type 1 sources, with all the type 2 requiring asubstantial contribution from a circumnuclear starburst. Our resultsappear in agreement with the AGN unified scheme, because thedistributions of key parameters of the torus models turn out to becompatible for type 1 and type 2 AGNs. Further support to theunification concept comes from comparison with medium-resolutioninfrared spectra of type 1 AGNs by the Spitzer observatory, showingevidence for a moderate silicate emission around 10 μm, which ourcode reproduces. From our analysis we infer accretion flows in the innernucleus of local AGNs characterized by high equatorial optical depths(AV~= 100), moderate sizes (Rmax < 100 pc) andvery high covering factors (f~= 80 per cent) on average.
| 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 Hα Galaxy Survey . III. Constraints on supernova progenitors from spatial correlations with Hα emission
Aims.We attempt to constrain progenitors of the different types ofsupernovae from their spatial distributions relative to star formationregions in their host galaxies, as traced by Hα + [Nii] lineemission. Methods: .We analyse 63 supernovae which have occurredwithin galaxies from our Hα survey of the local Universe. Threestatistical tests are used, based on pixel statistics, Hα radialgrowth curves, and total galaxy emission-line fluxes. Results:.Many type II supernovae come from regions of low or zero emission lineflux, and more than would be expected if the latter accurately traceshigh-mass star formation. We interpret this excess as a 40% "Runaway"fraction in the progenitor stars. Supernovae of types Ib and Ic doappear to trace star formation activity, with a much higher fractioncoming from the centres of bright star formation regions than is thecase for the type II supernovae. Type Ia supernovae overall show a weakcorrelation with locations of current star formation, but there isevidence that a significant minority, up to about 40%, may be linked tothe young stellar population. The radial distribution of allcore-collapse supernovae (types Ib, Ic and II) closely follows that ofthe line emission and hence star formation in their host galaxies, apartfrom a central deficiency which is less marked for supernovae of typesIb and Ic than for those of type II. Core-collapse supernova ratesoverall are consistent with being proportional to galaxy totalluminosities and star formation rates; however, within this total thetype Ib and Ic supernovae show a moderate bias towards more luminoushost galaxies, and type II supernovae a slight bias towardslower-luminosity hosts.
| Water-Vapor Maser Survey for Active Galactic Nuclei: A Megamaser in NGC 6926
We made a survey of water-vapor maser emission for 93 AGNs with theNobeyama 45-m and Mopra 22-m telescopes from 1999 to 2002. A megamaserwas detected in a Seyfert 2 galaxy, NGC 6926, at a distance of 80Mpc, in2002 June. [Greenhill et al. (2003a) have also reported a detection ofthe megamaser at the close date.] The peak flux density was 110mJy, andthe total isotropic luminosity was 340 Lȯ. The masershows triply peaked spectrum, suggesting an edge-on disk. A narrow-linefeature of the maser components at VLSR = 6001 kms-1 was strongly variable with a time scale of a few tens ofdays, and the variation should be of intrinsic origin. We also showed apossibility of variability of water-vapor maser emission of a megamaserpreviously detected in a Seyfert/ultraluminous FIR galaxy, NGC 6240.
| The evolution of actively star-forming galaxies in the mid-infrared
In this paper we analyze the evolution of actively star-forming galaxiesin the mid-infrared (MIR). This spectral region, characterized bycontinuum emission by hot dust and by the presence of strong emissionfeatures generally ascribed to polycyclic aromatic hydrocarbon (PAH)molecules, is the most strongly affected by the heating processesassociated with star formation and/or active galactic nuclei (AGNs).Following the detailed observational characterization of galaxies in theMIR by the Infrared Space Observatory (ISO), we have updated themodelling of this spectral region in our spectrophotometric modelGRASIL. In the diffuse component we have updated the treatment of PAHsaccording to the model by Li & Draine. As for the dense phase of theinterstellar medium associated with the star-forming regions, themolecular clouds, we strongly decrease the abundance of PAHs as comparedto that in the cirrus, based on the observational evidence of the lackor weakness of PAH bands close to the newly formed stars, possibly dueto the destruction of the molecules in strong ultraviolet fields. Therobustness of the model is checked by fitting near-infrared to radiobroad-band spectra and the corresponding detailed MIR spectra of a largesample of galaxies, at once. With this model, we have analyzed thelarger sample of actively star-forming galaxies by Dale et al. We showthat the observed trends of galaxies in the ISO-IRAS-radio colour-colourplots can be interpreted in terms of the different evolutionary phasesof star formation activity, and the consequent different dominance inthe spectral energy distribution of the diffuse or dense phase of theISM. We find that the observed colours indicate a surprising homogeneityof the starburst phenomenon, allowing only a limited variation of themost important physical parameters, such as the optical depth of themolecular clouds, the time-scale of the escape of young stars from theirfor mation sites, and the gas consumption time-scale. In this paper wedo not attempt to reproduce the far-infrared coolest region in thecolour-colour plots, as we concentrate on models meant to reproduceactive star-forming galaxies, but we discuss possible requirements of amore complex modelling for the coldest objects.
| How large are the bars in barred galaxies?
I present a study of the sizes (semimajor axes) of bars in discgalaxies, combining a detailed R-band study of 65 S0-Sb galaxies withthe B-band measurements of 70 Sb-Sd galaxies from Martin (1995). As hasbeen noted before with smaller samples, bars in early-type (S0-Sb)galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies;this is true both for relative sizes (bar length as fraction ofisophotal radius R25 or exponential disc scalelength h) andabsolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~ 3.3 kpc),~0.2-0.8R25 (mean ~ 0.38R25) and ~0.5-2.5h (mean ~1.4h). Late-type bars extend to only ~0.5-3.5 kpc,~0.05-0.35R25 and 0.2-1.5h their mean sizes are ~1.5 kpc, ~0.14R25 and ~0.6h. Sb galaxies resemble earlier-type galaxiesin terms of bar size relative to h; their smallerR25-relative sizes may be a side effect of higher starformation, which increases R25 but not h. Sbc galaxies form atransition between the early- and late-type regimes. For S0-Sbcgalaxies, bar size correlates well with disc size (both R25and h); these correlations are stronger than the known correlation withMB. All correlations appear to be weaker or absent forlate-type galaxies; in particular, there seems to be no correlationbetween bar size and either h or MB for Sc-Sd galaxies.Because bar size scales with disc size and galaxy magnitude for mostHubble types, studies of bar evolution with redshift should selectsamples with similar distributions of disc size or magnitude(extrapolated to present-day values); otherwise, bar frequencies andsizes could be mis-estimated. Because early-type galaxies tend to havelarger bars, resolution-limited studies will preferentially find bars inearly-type galaxies (assuming no significant differential evolution inbar sizes). I show that the bars detected in Hubble Space Telescope(HST) near-infrared(IR) images at z~ 1 by Sheth et al. have absolutesizes consistent with those in bright, nearby S0-Sb galaxies. I alsocompare the sizes of real bars with those produced in simulations anddiscuss some possible implications for scenarios of secular evolutionalong the Hubble sequence. Simulations often produce bars as large as(or larger than) those seen in S0-Sb galaxies, but rarely any as smallas those in Sc-Sd galaxies.
| 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.
| Simulating the Spitzer Mid-Infrared Color-Color Diagrams
We use a simple parameterization of the mid-IR spectra of a wide rangeof galaxy types in order to predict their distribution in the InfraredArray Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 μm and MultibandPhotometer for Spitzer 24 μm color-color diagrams. We distinguishthree basic spectral types by the energetically dominant component inthe 3-12 μm regime: stellar-dominated, polycyclic aromatichydrocarbon (PAH)-dominated, and continuum-dominated. We use a Markovchain Monte Carlo approach to arrive at a more systematic and robustrepresentation of the mid-IR spectra of galaxies than do moretraditional approaches. We find that IRAC color-color plots are wellsuited to distinguishing the above spectral types, while the addition of24 μm data allows us to suggest practical three-color cuts thatpreferentially select higher redshift sources of a specific type. Wecompare our simulations with the color-color plot obtained by theSpitzer First Look Survey and find reasonable agreement. Lastly, wediscuss other applications as well as future directions for this work.
| A Chandra Snapshot Survey of Infrared-bright LINERs: A Possible Link Between Star Formation, Active Galactic Nucleus Fueling, and Mass Accretion
We present results from a high-resolution X-ray imaging study of nearbyLINERs observed by ACIS on board Chandra. This study complements andextends previous X-ray studies of LINERs, focusing on the underexploredpopulation of nearby dust-enshrouded infrared-bright LINERs. The sampleconsists of 15 IR-bright LINERs (LFIR/LB>3),with distances that range from 11 to 26 Mpc. Combining our sample withprevious Chandra studies, we find that ~51% (28/55) of the LINERsdisplay compact hard X-ray cores. The nuclear 2-10 keV luminosities ofthe galaxies in this expanded sample range from ~2×1038to ~2×1044 ergs s-1. We find that the mostextreme IR-faint LINERs are exclusively active galactic nuclei (AGNs).The fraction of LINERs containing AGNs appears to decrease with IRbrightness and increase again at the highest values ofLFIR/LB. We find that of the 24 LINERs showingcompact nuclear hard X-ray cores in the expanded sample that wereobserved at Hα wavelengths, only eight actually show evidence of abroad line. Similarly, of the 14 LINERs showing compact nuclear hardX-ray cores with corresponding radio observations, only eight display acompact flat spectrum radio core. These findings emphasize the need forhigh-resolution X-ray imaging observations in the study of IR-brightLINERs. Finally, we find an intriguing trend in the Eddington ratioversus LFIR and LFIR/LB for theAGN-LINERs in the expanded sample that extends over 7 orders ofmagnitude in L/LEdd. This correlation may imply a linkbetween black hole growth, as measured by the Eddington ratio, and thestar formation rate, as measured by the far-IR luminosity andIR-brightness ratio. If the far-IR luminosity is an indicator of themolecular gas content in our sample of LINERs, our results may furtherindicate that the mass accretion rate scales with the host galaxy's fuelsupply. We discuss the potential implications of our results in theframework of black hole growth and AGN fueling in low-luminosity AGNs.
| New H2O masers in Seyfert and FIR bright galaxies
Using the Effelsberg 100-m telescope, detections of four extragalacticwater vapor masers are reported. Isotropic luminosities are ~50, 1000, 1and 230 Lȯ for Mrk 1066 (UGC 2456), Mrk 34, NGC 3556 andArp 299, respectively. Mrk 34 contains by far the most distant and oneof the most luminous water vapor megamasers so far reported in a Seyfertgalaxy. The interacting system Arp 299 appears to show two maserhotspots separated by approximately 20´´. With these newresults and even more recent data from Braatz et al. (2004, ApJ, 617,L29), the detection rate in our sample of Seyferts with known jet-NarrowLine Region interactions becomes 50% (7/14), while in star forminggalaxies with high (S100~μ m>50 Jy) far infrared fluxesthe detection rate is 22% (10/45). The jet-NLR interaction sample maynot only contain “jet-masers” but also a significant numberof accretion “disk-masers” like those seen in NGC 4258. Astatistical analysis of 53 extragalactic H2O sources (excluding theGalaxy and the Magellanic Clouds) indicates (1) that the correlationbetween IRAS Point Source and H2O luminosities, established forindividual star forming regions in the galactic disk, also holds forAGN-dominated megamaser galaxies; (2) that maser luminosities are notcorrelated with 60 μm/100 μm color temperatures; and (3) that onlya small fraction of the luminous megamasers (L_H_2O > 100Lȯ) detectable with 100-m sized telescopes have so farbeen identified. The H2O luminosity function (LF) suggests that thenumber of galaxies with 1 Lȯ < L_H_2O < 10Lȯ, the transition range between“kilomasers” (mostly star formation) and“megamasers” (active galactic nuclei), is small. The overallslope of the LF, ~-1.5, indicates that the number of detectable masersis almost independent of their luminosity. If the LF is not steepeningat very high maser luminosities and if it is possible to find suitablecandidate sources, H2O megamasers at significant redshifts should bedetectable even with present day state-of-the-art facilities.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| 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.
| Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation?
Infrared (IR) emission features at 3.3, 6.2, 7.7, 8.6, and 11.3 μmare generally attributed to IR fluorescence from (mainly)far-ultraviolet (FUV) pumped large polycyclic aromatic hydrocarbon (PAH)molecules. As such, these features trace the FUV stellar flux and arethus a measure of star formation. We examined the IR spectralcharacteristics of Galactic massive star-forming regions and of normaland starburst galaxies, as well as active galactic nuclei (AGNs) andultraluminous infrared galaxies (ULIRGs). The goal of this study is toanalyze whether PAH features are a good qualitative and/or quantitativetracer of star formation, and hence to evaluate the application of PAHemission as a diagnostic tool in order to identify the dominantprocesses contributing to the infrared emission from Seyfert galaxiesand ULIRGs. We develop a new mid-infrared (MIR)/far-infrared (FIR)diagnostic diagram based on our Galactic sample and compare it to thediagnostic tools of Genzel and coworkers and Laurent and coworkers, withthese diagnostic tools also applied to our Galactic sample. This MIR/FIRdiagnostic is derived from the FIR normalized 6.2 μm PAH flux and theFIR normalized 6.2 μm continuum flux. Within this diagram, theGalactic sources form a sequence spanning a range of 3 orders ofmagnitude in these ratios, ranging from embedded compact H II regions toexposed photodissociation regions (PDRs) and the (diffuse) interstellarmedium (ISM). However, the variation in the 6.2 μm PAHfeature-to-continuum ratio is relative small. Comparison of ourextragalactic sample with our Galactic sources revealed an excellentresemblance of normal and starburst galaxies to exposed PDRs. WhileSeyfert 2 galaxies coincide with the starburst trend, Seyfert 1 galaxiesare displaced by at least a factor of 10 in 6.2 μm continuum flux, inaccordance with general orientation-dependent unification schemes forAGNs. ULIRGs show a diverse spectral appearance. Some show a typical AGNhot dust continuum. More, however, either are starburst-like or showsigns of strong dust obscuration in the nucleus. One characteristic ofthe ULIRGs also seems to be the presence of more prominent FIR emissionthan either starburst galaxies or AGNs. We discuss the observedvariation in the Galactic sample in view of the evolutionary state andthe PAH/dust abundance and discuss the use of PAHs as quantitativetracers of star formation activity. Based on these investigations, wefind that PAHs may be better suited as a tracer of B stars, whichdominate the Galactic stellar energy budget, than as a tracer of massivestar formation (O stars).
| Missing Massive Stars in Starbursts: Stellar Temperature Diagnostics and the Initial Mass Function
Determining the properties of starbursts requires spectral diagnosticsof their ultraviolet radiation fields, to test whether very massivestars are present. We test several such diagnostics, using new models ofline ratio behavior combining CLOUDY, Starburst99, and up-to-datespectral atlases. For six galaxies we obtain new measurements of He I1.7 μm/Br10, a difficult to measure but physically simple (andtherefore reliable) diagnostic. We obtain new measurements of He I 2.06μm/Brγ in five galaxies. We find that He I 2.06 μm/Brγand [O III]/Hβ are generally unreliable diagnostics in starbursts.The heteronuclear and homonuclear mid-infrared line ratios (notably [NeIII] 15.6 μm/[Ne II] 12.8 μm) consistently agree with each otherand with He I 1.7 μm/Br10 this argues that the mid-infrared lineratios are reliable diagnostics of spectral hardness. In a sample of 27starbursts, [Ne III]/[Ne II] is significantly lower than modelpredictions for a Salpeter initial mass function (IMF) extending to 100Msolar. Plausible model alterations strengthen thisconclusion. By contrast, the low-mass and low-metallicity galaxies II Zw40 and NGC 5253 show relatively high neon line ratios, compatible with aSalpeter slope extending to at least ~40-60 Msolar. Onesolution for the low neon line ratios in the high-metallicity starburstswould be that they are deficient in >~40 Msolar starscompared to a Salpeter IMF. An alternative explanation, which we prefer,is that massive stars in high-metallicity starbursts spend much of theirlives embedded within ultracompact H II regions that prevent the near-and mid-infrared nebular lines from forming and escaping. Thishypothesis has important consequences for starburst modeling andinterpretation.
| Star Formation History and Extinction in the Central Kiloparsec of M82-like Starbursts
We report on the star formation histories and extinction in the centralkiloparsec region of a sample of starburst galaxies that have similarfar-infrared (FIR), 10 μm, and K-band luminosities as those of thearchetype starburst M82. Our study is based on new optical spectra andpreviously published K-band photometric data, both sampling the samearea around the nucleus. Model starburst spectra were synthesized as acombination of stellar populations of distinct ages formed over theHubble time and were fitted to the observed optical spectra and K-bandflux. The model is able to reproduce simultaneously the equivalentwidths of emission and absorption lines, the continuum fluxes between3500 and 7000 Å, and the K-band and FIR flux. A good fit requiresa minimum of three populations: (1) a young population of age <=8Myr, with its corresponding nebular emission, (2) an intermediate-agepopulation (age <500 Myr), and (3) an old population that forms partof the underlying disk or/and bulge population. The birthrate parameter,which is defined as the ratio of the current star formation rate to theaverage past rate, is found to be in the range 1-12. The contribution ofthe old population to the K-band luminosity depends on the birthrateparameter and remains above 60% in the majority of the sample galaxies.Even in the blue band, the intermediate-age and old populationscontribute more than 40% of the total flux in all the cases. Arelatively high contribution from the old stars to the K-band nuclearflux is also apparent from the strength of the 4000 Å break andthe Ca II K line. The extinction of the old population is found to bearound half that of the young population. The contribution to thecontinuum from the relatively old stars has the effect of diluting theemission equivalent widths below the values expected for young bursts.The mean dilution factors are found to be 5 and 3 for the Hα andHβ lines, respectively.
| 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
| Warm dust and aromatic bands as quantitative probes of star-formation activity
We combine samples of spiral galaxies and starburst systems observedwith ISOCAM on board ISO to investigate the reliability of mid-infrareddust emission as a quantitative tracer of star formation activity. Thetotal sample covers very diverse galactic environments and probes a muchwider dynamic range in star formation rate density than previous similarstudies. We find that both the monochromatic 15 μm continuum and the5-8.5 μm emission constitute excellent indicators of the starformation rate as quantified by the Lyman continuum luminosityLLyc, within specified validity limits which are differentfor the two tracers. Normalized to projected surface area, the 15 μmcontinuum luminosity Σ15 μm,ct is directlyproportional to ΣLyc over several orders of magnitude.Two regimes are distinguished from the relative offsets in the observedrelationship: the proportionality factor increases by a factor of ≈5between quiescent disks in spiral galaxies, and moderate to extremestar-forming environments in circumnuclear regions of spirals and instarburst systems. The transition occurs near ΣLyc 102 Lȯ pc-2 and isinterpreted as due to very small dust grains starting to dominate theemission at 15 μm over aromatic species above this threshold. The5-8.5 μm luminosity per unit projected area is also directlyproportional to the Lyman continuum luminosity, with a single conversionfactor from the most quiescent objects included in the sample up toΣLyc 104 Lȯpc-2, where the relationship then flattens. The turnover isattributed to depletion of aromatic band carriers in the harsherconditions prevailing in extreme starburst environments. The observedrelationships provide empirical calibrations useful for estimating starformation rates from mid-infrared observations, much less affected byextinction than optical and near-infrared tracers in deeply embedded HII regions and obscured starbursts, as well as for theoreticalpredictions from evolutionary synthesis models.Based on observations with ISO, an ESA project with instruments fundedby ESA member states (especially the PI countries: France, Germany, TheNetherlands, and the UK), and with participation of ISAS and NASA.
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| The Hα galaxy survey. I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies
We discuss the selection and observations of a large sample of nearbygalaxies, which we are using to quantify the star formation activity inthe local Universe. The sample consists of 334 galaxies across allHubble types from S0/a to Im and with recession velocities of between 0and 3000 km s-1. The basic data for each galaxy are narrowband H\alpha +[NII] and R-band imaging, from which we derive starformation rates, H\alpha +[NII] equivalent widths and surfacebrightnesses, and R-band total magnitudes. A strong correlation is foundbetween total star formation rate and Hubble type, with the strongeststar formation in isolated galaxies occurring in Sc and Sbc types. Moresurprisingly, no significant trend is found between H\alpha +[NII]equivalent width and galaxy R-band luminosity. More detailed analyses ofthe data set presented here will be described in subsequent papers.Based on observations made with the Jacobus Kapteyn Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.The full version of Table \ref{tab3} is available in electronic form atthe 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/414/23 Reduced image datafor this survey can be downloaded fromhttp://www.astro.livjm.ac.uk/HaGS/
| 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.
| Infrared Observations of Galaxies in the Local Universe. II. 391 Calibrated Images with Photometric and Structural Measurements
This paper presents empirical results from a deep imaging survey ofgalaxies in the local universe at the J and Ks wavelengths.Three hundred ninety-one images have been obtained and calibrated usingthe same camera and filter set with the Steward Observatory 1.6 m KuiperTelescope on Mount Bigelow and the 2.3 m Bok Telescope on Kitt Peak. Thelimiting magnitude is typically 22 mag arcsec-1 at J and 21mag arcsec-1 at Ks. The central surfacebrightness, apparent magnitudes, sizes, scale lengths, and inclinationsare tabulated from measurements made using these data. The purpose ofthis paper is to provide basic near-infrared data on a variety of galaxytypes.
| Nascent Starbursts in Synchrotron-deficient Galaxies with Hot Dust
Three nearby galaxies that have abnormally high infrared-to-radiocontinuum ratios, NGC 1377, IC 1953, and NGC 4491, are investigated witha view to understanding the physical origin of their peculiarity. Wereview the existing data and present new radio continuum measurementsalong with near-infrared integral-field spectroscopy and molecular gasobservations. The three galaxies have low luminosities butstarburst-like infrared colors; in NGC 1377, no synchrotron emission isdetected at any wavelength; in IC 1953, the observed synchrotroncomponent is attributable to the spiral disk alone and is lacking in thecentral regions; and the radio spectrum of NGC 4491 is unusually flat.We also compare and contrast them with NGC 4418, a heavily extinguishedgalaxy that shares some attributes with them. After examining variousscenarios, we conclude that these galaxies are most likely observedwithin a few megayears of the onset of an intense star formation episodeafter being quiescent for at least ~100 Myr. This starburst, whileheating the dust, has not produced optical signatures or a normal amountof cosmic rays yet. We briefly discuss the statistics of such galaxiesand what they imply for star formation surveys.Based on observations with the 100 m telescope of theMax-Planck-Institut für Radioastronomie at Effelsberg.
| Infrared Emission of Normal Galaxies from 2.5 to 12 Micron: Infrared Space Observatory Spectra, Near-Infrared Continuum, and Mid-Infrared Emission Features
We present ISOPHOT spectra of the regions 2.5-4.9 μm and 5.8-11.6μm for a sample of 45 disk galaxies from the US Infrared SpaceObservatory Key Project on Normal Galaxies. The galaxies were selectedto span the range in global properties of normal, star-forming diskgalaxies in the local universe. The spectra can be decomposed into threespectral components: (1) continuum emission from stellar photospheres,which dominates the near-infrared (NIR; 2.5-4.9 μm) spectral region;(2) a weak NIR excess continuum, which has a color temperature of~103 K, carries a luminosity of a few percent of the totalfar-infrared (FIR) dust luminosity LFIR and most likelyarises from the interstellar medium (ISM); and (3) the well-known broademission features at 6.2, 7.7, 8.6, and 11.3 μm, which are generallyattributed to aromatic carbon particles. These aromatic features inemission (AFEs) dominate the mid-infrared (MIR; 5.8-11.6 μm) part ofthe spectrum and resemble the so-called type A spectra observed in manynonstellar sources and the diffuse ISM in our own Galaxy. The fewnotable exceptions include NGC 4418, where a dust continuum replaces theAFEs in MIR, and NGC 1569, where the AFEs are weak and the strongestemission feature is [S IV] 10.51 μm. The relative strengths of theAFEs vary by 15%-25% among the galaxies. However, little correlation isseen between these variations and either IRAS 60 μm/100 μm fluxdensity ratio R(60/100) or the FIR/blue luminosity ratioLFIR/LB, two widely used indicators of the currentstar formation activity, suggesting that the observed variations are nota consequence of the radiation field differences among the galaxies. Wedemonstrate that the NIR excess continuum and AFE emission arecorrelated, suggesting that they are produced by similar mechanisms andsimilar (or the same) material. On the other hand, as the current starformation activity increases, the overall strengths of the AFEs and theNIR excess continuum drop significantly with respect to that of the FIRemission from large dust grains. In particular, the summed luminosity ofthe AFEs falls from ~0.2 LFIR for the most ``IR-quiescent''galaxies to ~0.1 LFIR for the most ``IR-active'' galaxies.This is likely a consequence of the preferential destruction in intenseradiation fields of the small carriers responsible for the NIR/AFEemission.Based on observations with ISO, an ESA project with instruments fundedby ESA member states (especially the PI countries, France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA.
| 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.
| The luminous and dark matter content of disk galaxies
We have compiled a sample of disk galaxies with available photometry inthe B and K bands, velocity line-widths and HI integral fluxes. Severalparameters that trace the luminous, baryonic and dark matter contentswere inferred. We investigated how these parameters vary with differentgalaxy properties, and compared the results with predictions of galaxyevolutionary models in the context of the Λ Cold Dark Matter(ΛCDM) cosmogony. The ratio of disk-to-total maximum circularvelocity, (Vd,m/Vt,m), depends mainly on thecentral disk surface density Σd,0 (or surfacebrightness, SB), increasing roughly asΣd,00.15. While a fraction of high SBgalaxies have a (Vd,m/Vt,m) ratio corresponding tothe maximum disk solution, the low SB are completely dark matterdominated. The trend is similar for the models, although they haveslightly smaller (Vd,m/Vt,m) ratios thanobservations, in particular at the highest SBs and when small baryonfractions are used. The scatter in the(Vd,m/Vt,m)- Σd,0 plot is large.An analysis of residuals shows that (Vd,m/Vt,m)tends to decrease as the galaxy is redder, more luminous (massive), andof earlier type. The models allow us to explain the physics of theseresults, which imply a connexion between halo structure and luminousproperties. The dynamical-to-baryon mass and dynamical mass-to-light (Band K) ratios at a given radius were also estimated. All these ratios,for observations and models, decrease with Σd,0; (orSB) and do not correlate significantly with the galaxy scale, contraryto what has been reported in previous works, based on the analysis ofrotation curve shapes. We discuss this difference and state theimportance of solving the controversy of whether the dark and luminouscontents in disk galaxies depend on SB or luminosity. The broadagreement between the models and observations presented here regardingthe trends of the dynamical-to-baryon matter and mass-to-light ratioswith several galaxy properties favors the ΛCDM scenario. However,the excess of dark matter inside the optical region of disk galaxiesremains the main difficulty.Appendices A and B are only available in electronic form athttp://www.edpsciences.org. Table 1 is only available 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/412/633
| 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
| Gasdynamics in NGC 5248: Fueling a Circumnuclear Starburst Ring of Super-Star Clusters
Through observations and modeling, we demonstrate how the recentlydiscovered large-scale bar in NGC 5248 generates spiral structure thatextends from 10 kpc down to 100 pc, fuels star formation onprogressively smaller scales, and drives disk evolution. Deep inside thebar, two massive molecular spirals cover nearly 180° in azimuth,show streaming motions of 20-40 km s-1, and feed a starburstring of super-star clusters at 375 pc. They also connect to two narrowK-band spirals that delineate the UV bright star clusters in the ring.The data suggest that the K-band spirals are young, and the starbursthas been triggered by a bar-driven spiral density wave (SDW). The lattermay even have propagated closer to the center where a second Hαring and a dust spiral are found. The molecular and Hubble SpaceTelescope data support a scenario where stellar winds and supernovaeefficiently clear out gas from dense star-forming regions on timescalesless than a few Myr. We have investigated the properties of massive COspirals within the framework of bar-driven SDWs, incorporating theeffect of gas self-gravity. We find good agreement between the modelpredictions and the observed morphology, kinematics, and pitch angle ofthe spirals. This combination of observations and modeling provides thebest evidence to date for a strong dynamical coupling between thenuclear region and the surrounding disk. It also confirms that a lowcentral mass concentration, which may be common in late-type galaxies,is particularly favorable to the propagation of a bar-driven gaseous SDWdeep into the central region of the galaxy, whereas a large central massconcentration favors other processes, such as the formation anddecoupling of nuclear bars.
| The H I Line Width/Linear Diameter Relationship as an Independent Test of the Hubble Constant
The relationship between corrected H I line widths and linear diameters(LW/LD) for spiral galaxies is used as an independent check on the valueof the Hubble constant. After calibrating the Tully-Fisher (TF) relationin both the B and I bands, the B-band relation is used for galaxies ofmorphological/luminosity types Sc I, Sc I.2, Sc I.3, Sab, Sb, Sb I-II,and Sb II to derive the LW/LD relation. We find that for this sample thescatter in the LW/LD is smallest with a Hubble constant of 90-95 kms-1 Mpc-1. Lower values of the Hubble constantproduce a separation in the LW/LD relation that is a function ofmorphological type. Since a Hubble constant of 90-95 is significantlylarger than the final Key Project value of 72 km s-1Mpc-1, a comparison of TF, surface brightness fluctuation(SBF), and fundamental plane (FP) is made. This comparison indicatesthat the Key Project TF distances to 21 clusters may be too large. For asample of 11 clusters, the Key Project TF distances provide anunweighted mean Hubble constant of 77 km s-1Mpc-1, while a combination of the FP, SBF, and our TFdistances for the same 11 clusters gives H0=91 kms-1 Mpc-1. A more subtle result in our data is amorphological dichotomy in the Hubble constant. The data suggest that ScI galaxies follow a Hubble constant of 90-95 while Sb galaxies follow aHubble constant closer to 75 km s-1 Mpc-1.Possible explanations for this result are considered, but it is shownthat this Sb/Sc I Hubble flow discrepancy is also present in the VirgoCluster and is consistent with previous investigations that indicatethat some galaxies carry a component of age-related intrinsic redshift.
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