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Multiwavelength Star Formation Indicators: Observations
We present a compilation of multiwavelength data on different starformation indicators for a sample of nearby star forming galaxies. Herewe discuss the observations, reductions and measurements of ultravioletimages obtained with STIS on board the Hubble Space Telescope (HST),ground-based Hα, and VLA 8.46 GHz radio images. These observationsare complemented with infrared fluxes, as well as large-apertureoptical, radio, and ultraviolet data from the literature. This databasewill be used in a forthcoming paper to compare star formation rates atdifferent wave bands. We also present spectral energy distributions(SEDs) for those galaxies with at least one far-infrared measurementsfrom ISO, longward of 100 μm. These SEDs are divided in two groups,those that are dominated by the far-infrared emission, and those forwhich the contribution from the far-infrared and optical emission iscomparable. These SEDs are useful tools to study the properties ofhigh-redshift galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| Ultraviolet-to-Far-Infrared Properties of Local Star-forming Galaxies
We present the results of a multiwavelength study of nearby galaxiesaimed at understanding the relation between the ultraviolet andfar-infrared emission in star-forming galaxies. The data set comprisesnew ultraviolet (from HST STIS), ground-based Hα, and radiocontinuum observations, together with archival infrared data (from IRASand ISO). The local galaxies are used as benchmarks for comparison ofthe infrared-to-ultraviolet properties with two populations ofhigh-redshift galaxies: the submillimeter star-forming galaxies detectedby SCUBA and the ultraviolet-selected Lyman break galaxies (LBGs). Inaddition, the long wavelength baseline covered by the present dataenables us to compare the star formation rates (SFRs) derived from theobserved ultraviolet, Hα, infrared, and radio luminosities and togauge the impact of dust opacity in the local galaxies. We also derive anew calibration for the nonthermal part of the radio SFR estimator,based on the comparison of 1.4 GHz measurements with a new estimator ofthe bolometric luminosity of the star-forming regions. We find that moreactively star-forming galaxies show higher dust opacities, which is inline with previous results. We find that the local star-forming galaxieshave a lower Fλ(205 μm)/Fλ(UV)ratio by 2-3 orders of magnitude than the submillimeter-selectedgalaxies and may have a similar or somewhat higherFλ(205 μm)/Fλ(UV) ratio thanLBGs. The Fλ(205 μm)/Fλ(UV) ratioof the local galaxy population may be influenced by the cool dustemission in the far-infrared heated by nonionizing stellar populations,which may be reduced or absent in the LBGs.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| Structure and kinematics of edge-on galaxy discs - IV. The kinematics of the stellar discs
The stellar disc kinematics in a sample of 15 intermediate- to late-typeedge-on spiral galaxies are studied using a dynamical modellingtechnique. The sample covers a substantial range in maximum rotationvelocity and deprojected face-on surface brightness and contains sevenspirals with either a boxy- or peanut-shaped bulge. Dynamical models ofthe stellar discs are constructed using the disc structure from I-bandsurface photometry and rotation curves observed in the gas. Thedifferences in the line-of-sight stellar kinematics between the modelsand absorption-line spectroscopy are minimized using a least-squaresapproach. The modelling constrains the disc surface density and stellarradial velocity dispersion at a fiducial radius through the freeparameter (σz/σR)-1, whereσz/σR is the ratio of vertical andradial velocity dispersion and M/L is the disc mass-to-light ratio. For13 spirals a transparent model provides a good match to the meanline-of-sight stellar velocity dispersion. Models that include arealistic radiative transfer prescription confirm that the effect ofdust on the observable stellar kinematics is small at the observed slitpositions. We discuss possible sources of systematic error and concludethat most of these are likely to be small. The exception is the neglectof the dark halo gravity, which has probably caused an overestimate ofthe surface density in the case of low surface brightness discs.
| Hα Imaging of Early-Type Sa-Sab Spiral Galaxies. II. Global Properties
New results, based on one of the most comprehensive Hα imagingsurveys of nearby Sa-Sab spirals completed to date, reveals early-typespirals to be a diverse group of galaxies that span a wide range inmassive star formation rates. While the majority of Sa-Sab galaxies inour sample are forming stars at a modest rate, a significant fraction(~29%) exhibit star formation rates greater than 1 Msolaryr-1, rivaling the most prolifically star-forming late-typespirals. A similar diversity is apparent in the star formation historyof Sa-Sab spirals as measured by their Hα equivalent widths.Consistent with our preliminary results presented in the first paper inthis series, we find giant H II regions [L(Hα)>=1039ergs s-1] in the disks of ~37% of early-type spirals. Wesuspect that recent minor mergers or past interactions are responsiblefor the elevated levels of Hα emission and, perhaps, for thepresence of giant H II regions in these galaxies. Our results, however,are not in total agreement with the Hα study of Kennicutt &Kent, who did not find any early-type spirals with Hα equivalentwidths >14 Å. A close examination of the morphologicalclassification of galaxies, however, suggests that systematicdifferences between the Revised Shapley-Ames Catalog and the SecondReference Catalogue may be responsible for the contrasting results.Based on observations obtained with the 3.5 m telescope at Apache PointObservatory (APO) and the 0.9 m telescope at Kitt Peak NationalObservatory (KPNO). The APO 3.5 m telescope is owned and operated by theAstrophysical Research Consortium.
| 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.
| Minor-axis velocity gradients in disk galaxies
We present the ionized-gas kinematics and photometry of a sample of 4spiral galaxies which are characterized by a zero-velocity plateau alongthe major axis and a velocity gradient along the minor axis,respectively. By combining these new kinematical data with thoseavailable in the literature for the ionized-gas component of the S0s andspirals listed in the Revised Shapley-Ames Catalog of Bright Galaxies werealized that about 50% of unbarred galaxies show a remarkable gasvelocity gradient along the optical minor axis. This fraction rises toabout 60% if we include unbarred galaxies with an irregular velocityprofile along the minor axis. This phenomenon is observed all along theHubble sequence of disk galaxies, and it is particularly frequent inearly-type spirals. Since minor-axis velocity gradients are unexpectedif the gas is moving onto circular orbits in a disk coplanar to thestellar one, we conclude that non-circular and off-plane gas motions arenot rare in the inner regions of disk galaxies.Based on observations carried out at the European Southern Observatoryin La Silla (Chile) (ESO 69.B-0706 and 70.B-0338), with the MultipleMirror Telescope which is a joint facility of the SmithsonianInstitution and the University of Arizona, and with the ItalianTelescopio Nazionale Galileo (AOT-5, 3-18) at the Observatorio del Roquede los Muchachos in La Palma (Spain).Table 1 is only available in electronic form athttp://www.edpsciences.org. Table 5 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/507
| A Survey for H2O Megamasers. III. Monitoring Water Vapor Masers in Active Galaxies
We present single-dish monitoring of the spectra of 13 extragalacticwater megamasers taken over a period of 9 years and a single epoch ofsensitive spectra for seven others. The primary motivation is a searchfor drifting line velocities analogous to those of the systemic featuresin NGC 4258, which are known to result from centripetal acceleration ofgas in an edge-on, subparsec molecular disk. We detect a velocity driftanalogous to that in NGC 4258 in only one source, NGC 2639. Another, themaser source in NGC 1052, exhibits erratic changes in its broad maserprofile over time. Narrow maser features in all of the other diskgalaxies discussed here either remain essentially constant in velocityover the monitoring period or are sufficiently weak or variable inintensity that individual features cannot be traced reliably from oneepoch to the next. In the context of a circumnuclear, molecular diskmodel, our results suggest that either (a) the maser lines seen aresystemic features subject to a much smaller acceleration than present inNGC 4258, presumably because the gas is farther from the nuclear blackhole, or (b) we are detecting ``satellite'' lines for which theacceleration is in the plane of the sky.Our data include the first K-band science observations taken with thenew 100 m Green Bank Telescope (GBT). The GBT data were taken duringtesting and commissioning of several new components and so are subjectto some limitations; nevertheless, they are in most cases the mostsensitive H2O spectra ever taken for each source and cover800 MHz (~=10,800 km s-1) of bandwidth. Many new maserfeatures are detected in these observations. Our data also include atentative and a clear detection of the megamaser in NGC 6240 at epochs ayear and a few months, respectively, prior to the detections reported byHagiwara et al. and Nakai et al.We also report a search for water vapor masers toward the nuclei of 58highly inclined (i>80deg), nearby galaxies. These sourceswere selected to investigate the tendency that H2O megamasersfavor inclined galaxies. None were detected, confirming that megamasersare associated exclusively with active galactic nuclei.
| The Unified Model and Evolution of Active Galaxies: Implications from a Spectropolarimetric Study
We extend the analysis presented in Paper I of a spectropolarimetricsurvey of the CfA and 12 μm samples of Seyfert 2 galaxies (S2s). Weconfirm that polarized (hidden) broad-line region (HBLR) S2s tend tohave hotter circumnuclear dust temperatures, show mid-IR spectra morecharacteristic of Seyfert 1 galaxies (S1s), and are intrinsically moreluminous than non-HBLR S2s. The levels of obscuration and circumnuclearstar formation, however, appear to be similar between HBLR and non-HBLRS2 galaxies, based on an examination of various observationalindicators. HBLR S2s, on average, share many similar large-scale,presumably isotropic, characteristics with S1s, as would be expected ifthe unified model is correct, while non-HBLR S2s generally do not. Theactive nuclear engines of non-HBLR S2s, then, appear to be truly weakerthan HBLR S2s, which in turn are fully consistent with being S1s viewedfrom another direction. There is also evidence that the fraction ofdetected HBLRs increases with the radio power of the active galacticnucleus. Thus, all S2 galaxies may not be intrinsically similar innature, and we speculate that evolutionary processes may be at work.
| 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 Far-Infrared Energy Distributions of Seyfert and Starburst Galaxies in the Local Universe: Infrared Space Observatory Photometry of the 12 Micron Active Galaxy Sample
New far-infrared photometry with ISOPHOT aboard the Infrared SpaceObservatory (ISO) is presented for 58 galaxies with homogeneouspublished data for another 32 galaxies, all belonging to the 12 μmgalaxy sample-in total, 29 Seyfert 1 galaxies, 35 Seyfert 2 galaxies,and 12 starburst galaxies, or about half of the 12 μm active galaxysample, plus 14 normal galaxies for comparison. ISO and InfraredAstronomical Satellite (IRAS) data are used to define color-colordiagrams and spectral energy distributions (SEDs). Thermal dust emissionat two temperatures (one cold at 15-30 K and one warm at 50-70 K) canfit the 60-200 μm SED, with a dust emissivity law proportional to theinverse square of the wavelength. Seyfert 1 galaxies and Seyfert 2galaxies are indistinguishable longward of 100 μm, while, as alreadyseen by IRAS, the former have flatter SEDs shortward of 60 μm. A mildanticorrelation is found between the [200-100] color and the ``60 μmexcess.'' We infer that this is due to the fact that galaxies with astrong starburst component and thus a strong 60 μm flux have asteeper far-infrared turnover. In non-Seyfert galaxies, increasing theluminosity corresponds to increasing the star formation rate, whichenhances the 25 and 60 μm emission. This shifts the peak emissionfrom around 150 μm in the most quiescent spirals to shorter than 60μm in the strongest starburst galaxies. To quantify these trendsfurther, we identified with the IRAS colors three idealized infraredSEDs: pure quiescent disk emission, pure starburst emission, and pureSeyfert nucleus emission. Even between 100 and 200 μm, the quiescentdisk emission remains much cooler than the starburst component. Seyfertgalaxies have 100-200 μm SEDs ranging from pure disks to purestarbursts, with no apparent contribution from their active nuclei atthose wavelengths. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, the Netherlands, and the United Kingdom) with theparticipation of ISAS and NASA.
| A Search for H2O Maser Emission in Southern Active Galactic Nuclei and Star-forming Galaxies: Discovery of a Maser in the Edge-on Galaxy IRAS F01063-8034
We report the cumulative results of five surveys for H2Omaser emission at 1.35 cm wavelength in 131 active galactic nuclei(AGNs) and star-forming galaxies, conducted at the Parkes Observatorybetween 1993 and 1998. We detected one new maser, in the edge-on galaxyIRAS F01063-8034, which exhibits a single ~0.1 Jy spectral feature at4282+/-6 km s-1 (heliocentric) with an unusually large54+/-16 km s-1 half-power full width. The centroid velocityof the emission increased to 4319.6+/-0.6 km s-1 (38+/-2 kms-1 width) over the 13 days between discovery andconfirmation of the detection. A similarly broad-line width and largechange in velocity has been noted for the maser in NGC 1052, wherein jetactivity excites the emission. Neither optical spectroscopy,radio-infrared correlations, nor infrared colors provide compellingevidence of unusual activity in the nucleus of IRAS F01063-8034. Sincethe galaxy appears to be outwardly normal at optical and infraredwavelengths, detection of an H2O maser therein is unique. Themaser emission is evidence that the galaxy harbors an AGN that isprobably obscured by the edge-on galactic disk. The detection highlightsthe possibility that undetected AGNs could be hidden in other relativelynearby galaxies. No other maser emission features have been identifiedat velocities between 3084 and 6181 km s-1.
| Spiral Galaxies with HST/NICMOS. I. Nuclear Morphologies, Color Maps, and Distinct Nuclei
This is the first of two papers where we present the analysis of anHST/NICMOS2 near-infrared (NIR) snapshot survey in the F160W (H) filterfor a sample of 78 spiral galaxies selected from the UGC and ESOLVcatalogs. For 69 of these objects we provide nuclear color informationderived by combining the H data either with additional NICMOS F110W (J)images or with V WFPC2/HST data. Here we present the NIR images and theoptical-NIR color maps. We focus our attention on the properties of thephotometrically distinct ``nuclei'' which are found embedded in most ofthe galaxies and provide measurements of their half-light radii andmagnitudes in the H (and when available in the J) band. We find that (1)in the NIR the nuclei embedded in the bright early- to intermediate-typegalaxies span a much larger range in brightness than the nuclei whichare typically found embedded in bulgeless late-type disks: the nucleiembedded in the early- to intermediate-type galaxies reach, on thebright end, values up to HAB~-17.7 mag; (2) nuclei are foundin both nonbarred and barred hosts, in large-scale (>~1 kpc) as wellas in nuclear (up to a few 100 pc) bars; (3) there is a significantincrease in half-light radius with increasing luminosity of the nucleusin the early/intermediate types (a decade in radius for ~8 magbrightening), a correlation which was found in the V band and which isalso seen in the NIR data; (4) the nuclei of early/intermediate-typespirals cover a large range of optical-NIR colors, from V-H~-0.5 to 3.Some nuclei are bluer and others redder than the surroundinggalaxy,indicating the presence of activity or reddening by dust in many ofthese systems; (5) someearly/intermediate nuclei are elongated and/orslightly offset from the isophotal center of the host galaxy. Onaverage, however, these nuclei appear as centered, star-cluster-likestructures similar to those whichare found in the late-type disks. Basedon observations with the NASA/ESA Hubble Space Telescope, obtained atthe Space Telescope Science Institute, which is operated by Associationof Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
| Seyfert Galaxies with Circumnuclear/Nuclear Starbursts
In this paper, we present our preliminary results on Seyfert galaxieswith circumnuclear/nuclear starburst (SB) activity. We have searched therecent available literature and found 76 active galaxies with clearevidence of nuclear SB activity, among which 16 are Seyfert 1s, 51Seyfert 2s, and 9 LINERs. After studying the 51 Seyfert 2s, we find thatthose Seyfert 2s with hidden Seyfert 1 nuclei, have similarInfrared-Radio properties as Seyfert 1 galaxies, and are different from``real'' Seyfert 2s without a hidden Seyfert 1 nucleus. The later aresimilar to starburst galaxies.
| High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample - II. The properties of compact radio components
We discuss the properties of compact nuclear radio components in Seyfertgalaxies from the extended 12-μm AGN sample of Rush et al. Our mainresults can be summarized as follows. Type 1 and type 2 Seyferts producecompact radio components which are indistinguishable in strength andaspect, indicating that their central engines are alike, as proposed bythe unification model. Infrared IRAS fluxes are more closely correlatedwith low-resolution radio fluxes than high-resolution radio fluxes,suggesting that they are dominated by kiloparsec-scale, extranuclearemission regions; extranuclear emission may be stronger in type 2Seyferts. Early-type Seyfert galaxies tend to have stronger nuclearradio emission than late-type Seyfert galaxies. V-shaped extendedemission-line regions, indicative of `ionization cones', are usuallyfound in sources with large, collimated radio outflows. Hidden broadlines are most likely to be found in sources with powerful nuclear radiosources. Type 1 and type 2 Seyferts selected by their IRAS 12-μm fluxdensities have well-matched properties.
| Global physical conditions of the interstellar medium in nearby galaxies
Far-infrared spectra (43-197 mu m) of 34 nearby galaxies obtained by theLong Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory(ISO) were analyzed to investigate the general properties ofinterstellar matter in galaxies. The present sample includes not onlynormal galaxies but also starbursts and active galactic nuclei (AGNs).Far-infrared forbidden lines, such as [C Ii]158 mu m, [O I]63 mu m, [NIi]122 mu m, and [O Iii]88 mu m, were detected in most of the samplegalaxies. [O I]145 mu m line was detected in 13 galaxies. The linefluxes of [C Ii]158 mu m and [N Ii]122 mu m relative to the totalfar-infrared flux (FIR) decrease as the far-infrared color becomesbluer, while the ratio of the [O I]63 mu m flux to FIR does not show asystematic trend with the color. The [O Iii]88 mu m to FIR ratio shows alarge scatter with a weak trend of increase with the color. AGNs do notshow any distinguishable trend from normal and starburst galaxies in thefar-infrared spectra, suggesting that the far-infrared emission ismainly driven by star-formation activities even in AGNs. We estimate thephysical conditions of photodissociation regions (PDRs) in the samplegalaxies, such as the far-ultraviolet radiation field intensityG0 and the gas density n by assuming that all the observed [OI]63 mu m and far-infrared continuum emissions come from PDRs.Comparison with PDR models indicates that G0 ranges from102-104 and n ~ 102-104cm-3. The present results also suggest that n variesproportionally with G0. The ratio of [C Ii] 158 mu m to CO(J=1-0) line emission supports the linear increase in n withG0. We estimate that about a half of [C Ii]158 mu m emissionoriginates from PDRs and attribute the rest to the emission as comingfrom low-density diffuse ionized gas. The estimated intensity of [CIi]158 mu m from the ionized gas is compatible with the observedintensity of [N Ii]122 mu m if both lines come from the same diffuseionized gas. The present analysis suggests that the decrease in [CIi]158 mu m/FIR with the far-infrared color may not be accounted for bythe decrease in the photoelectric heating efficiency owing to theincrease in positive charges of dust grains because a measure of theefficiency, G0/n, is found to stay constant with thefar-infrared color. Instead the decrease can be interpreted in terms ofeither the increase in the collisional de-excitation of the [C Ii]transition due to the increase in the gas density or the decrease in theionized component relative to the far-infrared intensity suggested bythe decrease in [N Ii]122 mu m/FIR. Based on the present analysis, wederive average relations of the far-infrared color with G0and n in galaxies, which can be applied to the investigation ofinterstellar matter in distant galaxies. Based on observations with ISO,an ESA project with instruments funded by ESA Member States (especiallythe PI countries: France, Germany, The Netherlands and the UK) and withthe participation of ISAS and NASA.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Compact Radio Emission from Warm Infrared Galaxies
In this paper, we present a comparison between the optical spectroscopicdata and the incidence of compact radio emission for a sample of 60 warminfrared galaxies. We find that 80% of optically classified activegalactic nucleus (AGN)-type galaxies contain compact radio sources,while 37% of optically classified starburst galaxies contain compactradio sources. The compact radio luminosity shows a bimodaldistribution, indicating two populations in our sample. The majority ofthe higher radio luminosity class (L>104Lsolar) are AGNs, while the majority of the lower radioluminosity class (L<104 Lsolar) are starbursts.The compact radio emission in the starburst galaxies may be due toeither obscured AGNs or complexes of extremely luminous supernovae suchas that seen in Arp 220. The incidence of optically classified AGNsincreases with increasing far-infrared (FIR) luminosity. Using FIRcolor-color diagrams, we find that globally the energetics of 92% of thegalaxies in our sample are dominated by starburst activity, including60% of galaxies that we find to contain AGNs on the basis of theiroptical classification. The remainder are energetically dominated bytheir AGNs in the infrared. For starburst galaxies, electron densityincreases with dust temperature, consistent with the merger model forinfrared galaxies.
| Excitation Mechanism of Near-Infrared [Fe II] Emission in Seyfert and Starburst Galaxies
The excitation mechanism of near-infrared [Fe II] emission in Seyfertand starburst galaxies is studied. We carry out numerical calculationsfor photoionization and shock heating, and compare the results with theobservational data. The gas-phase abundance of iron is found to bealways low. This means that destruction of iron-bearing grains isinsufficient to affect the [Fe II] strength. We propose that the [Fe II]strength depends primarily on the ionization structure. The [Fe II]emission is excited by electron collisions in a zone of partiallyionized hydrogen, which is extensive when the gas is heated by X-rays orby a shock. These two processes are discriminated by the electrontemperature of the [Fe II] region: 8000 K in heating by X-rays, and 6000K in shock heating. The [Fe II] emission of a Seyfert galaxy originatesin the narrow-line region, which is heated by X-rays from the nucleusand by shocks due to the nuclear outflow. From the [Fe II] temperature,we propose that the heating by X-rays is more important. On the otherhand, the [Fe II] emission of a starburst galaxy originates in thesupernova-driven shocks. We find that 0.2% of the shock energy istransferred into the [Fe II]a6D9/2-a4D7/2 line at 1.257μm.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Morphology of the 12 Micron Seyfert Galaxies. II. Optical and Near-Infrared Image Atlas
We present 263 optical and near-infrared (NIR) images for 42 1s and 48Seyfert 2s, selected from the Extended 12 μm Galaxy Sample.Elliptically averaged profiles are derived from the images, andisophotal radii and magnitudes are calculated from these. We also reportvirtual aperture photometry that, judging from comparison with previouswork, is accurate to roughly 0.05 mag in the optical, and 0.07 mag inthe NIR. Our B-band isophotal magnitude and radii, obtained from ellipsefitting, are in good agreement with those of Third Reference Catalogueof Bright Galaxies. When compared with the B band, V, I, J, and Kisophotal diameters show that the colors in the outer regions of Seyfertgalaxies are consistent with the colors of normal spirals. Differencesin the integrated isophotal colors and comparison with a simple modelshow that the active nucleus+bulge are stronger and redder in the NIRthan in the optical. Finally, roughly estimated Seyfert disk surfacebrightnesses are significantly brighter in B and K than those in normalspirals of similar morphological type.
| The Centers of Early- to Intermediate-Type Spiral Galaxies: A Structural Analysis
A recent Hubble Space Telescope (HST)/WFPC2 visual survey of early- andintermediate-type spiral galaxies has unveiled a great complexity in theinner regions of these systems, which include a high fraction ofphotometrically distinct compact sources sitting at the galactic centers(``nuclei''). The faint nuclei (M_V>~-12) are typically hosted byrather amorphous, quiescent, bulgelike structures with an exponential(rather than the classical R^1/4) light profile. These ``exponentialbulges'' are commonly found inside the intermediate-type disks,consistent with previous studies. Brighter nuclei (M_V<~-12) aretypically found instead in the centers of galaxies with circumnuclearrings/arms of star formation or dust and an active, i.e., H II- orAGN-type, central spectrum at ground-based resolution. On the structuralplane of half-light radius (R_e) versus mean surface brightness withinthe half-light radius (mu_e), faint and bright nuclei overlap with, andfill the region of parameter space between, the old Milky Way globularclusters and the young star clusters, respectively, with typical R_e ofabout a few up to ~20 pc. On the same plane, the exponential bulges havesignificantly fainter mu_e than R^1/4 bulges for any given radius andfollow a mu_e-R_e relation typical of disks, which strengthens thesuggestion that the exponential bulges grow inside the disks as a resultof the secular evolution of the latter. Under the likely assumption thatthe visual light from the faint nuclei embedded in the quiescentexponential bulges is of stellar origin and of a similar (>~1 Gyr)age for the central star clusters and their host bulges, the massesinferred for the former agree with those required to disrupt barscomparable in size to the latter. This offers support to scenarios inwhich the exponential bulges grow inside the disks owing to the orbitaldisruption of progenitor bars caused by the growth of a centralconcentration of mass and suggests that this specific mode of bulgeformation is (still) active in the present-day universe. On the otherhand, the presence of the massive clusters at the very center of thelow-density exponential bulges should prevent any other ``nuclear'' barfrom forming, thereby preventing further infall of dissipative fuel tothe nuclear regions. This may argue against the possibility of evolvingthe exponential bulges into denser, R^1/4 bulges by a simple looping forseveral cycles of the bar formation/disruption mechanism.
| Enhanced star formation in Seyfert 2 galaxies.
Not Available
| Hα Imaging of Early-Type (SA-SAB) Spiral Galaxies. I.
Hα and continuum images are presented for 27 nearby early-type(Sa-Sab) spiral galaxies. Contrary to popular perception, the imagesreveal copious massive star formation in some of these galaxies. Adetermination of the Hα morphology and a measure of the Hαluminosity suggest that early-type spirals can be classified into twobroad categories based on the luminosity of the largest H II region inthe disk. The first category includes galaxies for which the individualH II regions have L_Hα<10^39 ergs s^-1. Most of the category 1galaxies appear to be morphologically undisturbed but show a widediversity in nuclear Hα properties. The second category includesgalaxies that have at least one H II region in the disk withL_Hα>=10^39 ergs s^-1. All category 2 galaxies show eitherprominent dust lanes or other morphological peculiarities such as tidaltails, which suggests that the anomalously luminous H II regions incategory 2 galaxies may have formed as a result of a recent interaction.The observations, which are part of an ongoing Hα survey, revealearly-type spirals to be a heterogeneous class of galaxies that areevolving in the current epoch. We have also identified some systematicdifferences between the classifications of spiral galaxies in the SecondGeneral Catalog and the Revised Shapley-Ames Catalog that may be tracedto subtle variations in the application of the criteria used forclassifying spiral galaxies. An examination of earlier studies suggeststhat perceptions concerning the Hubble-type dependence of star formationrates among spiral galaxies depends on the choice of catalog.
| Star formation in southern Seyfert galaxies
We have produced radio maps, using the Australia Telescope CompactArray, of the central regions of six southern type 2 Seyfert galaxies(NGC 1365, 4945, 6221, 6810, 7582 and Circinus) with circumnuclear starformation, to estimate the relative contribution of star formationactivity compared to activity from the active galactic nucleus (AGN).The radio morphologies range from extended diffuse structures to compactnuclear emission, with no evidence, even in the relatively compactsources, for synchrotron self-absorption. In each case the radio tofar-infrared (FIR) ratio has a value consistent with star formation, andin all but one case the radio to [FeII] ratio is also consistent withstar formation. We derive supernova rates and conclude that, despite thepresence of a Seyfert nucleus in these galaxies, the radio, FIR and[FeII] line emissions are dominated by processes associated with thecircumnuclear star formation (i.e. supernova remnants and HII regions)rather than with the AGN.
| A comprehensive search for extragalactic 6.7-GHz methanol masers
We have used the Australia Telescope Compact Array (ATCA) to search for6.7-GHz methanol maser emission towards 87 galaxies. We chose the targetsources using several criteria, including far-IR luminosities and thepresence of known OH megamasers. In addition, we searched for methanolmasers in the nearby starburst galaxy NGC 253, making a fullspectral-line synthesis image. No emission was detected in any of thegalaxies, with detection limits ranging from 25 to 75 mJy. This issurprising, given the close association of OH and methanol masers inGalactic star formation regions, and significantly constrains models ofOH megamaser emission. This absence of maser emission may be a result oflow methanol abundances in molecular clouds in starburst galaxies.
| ^13CO (J = 1-0) Depression in Luminous Starburst Mergers
It is known that the class of luminous starburst galaxies tends to havehigher R=^12CO (J=1-0)/^13CO (J=1-0) integrated line intensity ratios(R>20) than normal spiral galaxies (R~10). Since most previousstudies investigated only R, it remains uncertain whether the luminousstarburst galaxies are overabundant in ^12CO or underabundant in ^13CO.Here we propose a new observational test to examine this problem. Ournew test is to compare far-infrared luminosities [L(FIR)] with those of^12CO and ^13CO [L(^12CO) and L(^13CO), respectively]. It is shown thatthere is a very tight correlation between L(^12CO) and L(FIR), as foundin many previous studies. However, we find that the ^13CO luminositiesof the high-R galaxies are lower by a factor of 3 on average than thoseexpected from the correlation for the remaining galaxies with ordinary Rvalues. Therefore, we conclude that the observed high R values for theluminous starburst galaxies are attributed to their lower ^13CO lineintensities.
| Dust Spirals and Acoustic Noise in the Nucleus of the Galaxy NGC 2207
Observations with the Hubble Space Telescope reveal an irregular networkof dust spiral arms in the nuclear region of the interacting disk galaxyNGC 2207. The spirals extend from ~50 to ~300 pc in galactocentricradius, with a projected width of ~20 pc. Radiative transfercalculations determine the gas properties of the spirals and the innerdisk and imply a factor of ~4 local gas compression in the spirals. Thegas is not strongly self-gravitating, nor is there a nuclear bar, so thespirals could not have formed by the usual mechanisms applied to maingalaxy disks. Instead, they may result from acoustic instabilities thatamplify at small galactic radii. Such instabilities may promote gasaccretion into the nucleus.
| Probing the Dusty Accretion Torus of Seyfert Galaxies
We show that the IRAS colors of Seyfert galaxies can be understood interms of a model in which we see emission by hot dust near itssublimation temperature emitting a spectrum that varies little fromobject to object. For objects observed through the dusty accretiontorus, which is optically thick at 12 mu m, this dust emission isabsorbed to various degrees. In addition, in many objects, this spectrumis veiled by a component produced by a circumnuclear starburst. Thehidden broad-line objects all lie along the reddening line in IRAScolor-color plots, and the dust extinction at 12 mu m lies in the range0.5-2.5, which implies an H I column density of ~5 x 1022 cm-2 for thehot circumnuclear dust located at about 3 pc from the central engine.For these objects we can also estimate the true luminosities of thecentral active nuclei from the dereddened IR fluxes. If the simpleaccretion flow model is correct, then typical accretion rates are on theorder of 10 Mȯ yr-1. The radiation pressure of the central activegalactic nucleus acting on the inner portions of the dust torus islikely to play a critical role in controlling the accretion flow towardthe nucleus and in forming the "ionization" cones seen in thenarrow-line regions of Seyfert galaxies.
| Large-Scale Outflows in Edge-on Seyfert Galaxies. III. Kiloparsec-Scale Soft X-Ray Emission
We present ROSAT PSPC and HRI images of eight galaxies selected from adistance-limited sample of 22 edge-on Seyfert galaxies. Kiloparsec-scalesoft X-ray nebulae extend along the galaxy minor axes in three galaxies(NGC 2992, NGC 4388, and NGC 5506). The extended X-ray emission has0.2-2.4 keV X-ray luminosities of 0.4-3.5 x 1040 ergs s-1. The X-raynebulae are roughly cospatial with the large-scale radio emission,suggesting that both are produced by large-scale galactic outflows.Assuming pressure balance between the radio and X-ray plasmas, the X-rayfilling factor is >~104 times larger than the radio plasma fillingfactor, suggesting that large-scale outflows in Seyfert galaxies arepredominantly winds of thermal X-ray-emitting gas. We favor aninterpretation in which large-scale outflows originate as activegalactic nucleus-driven jets that entrain and heat gas on kiloparsecscales as they make their way out of the galaxy. Active galacticnucleus- and starburst-driven winds are also possible explanations incases where the winds are oriented along the rotation axis of the galaxydisk.
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