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A new method for determining mass-to-light ratios of nearly face-on spiral galaxies
Context: . Aims: .This letter gives a new method for determiningmass-to-light ratios of nearly face-on spiral galaxies. Methods:.The method is based on the effective thickness of the galactic disk,the distribution of the vertical velocity dispersion, and the surfacebrightness of a spiral galaxy. Results: .As examples, the resultsof the determination of NGC 1566 and NGC 5247 in B-band are presented,and their mass-to-light ratios are 4.86 8.99 {M_ȯ L_ȯ-1} and 5.02 6.90 {M_ȯ L_ȯ -1}respective. Conclusions: .
| The future is BLISS sensitive far-IR spectroscopy on SPICA and SAFIR
Half the energy produced since decoupling emerges in the far-IR, hence acomplete understanding of the history of stellar nucleosynthesis andgalaxy evolution requires a systematic study of dust-enshrouded energyrelease at all epochs. Sensitive far-IR spectroscopy is the natural toolfor this, and we present the first opportunity for cosmological far-IRspectroscopy with new cryogenic telescopes and instruments. We arestudying a US-built spectrograph BLISS for the Japanese SPICA mission tolaunch in 2013, and NASA’s SAFIR mission, envisioned for 2025.With sensitive detectors and the very low backgrounds provided by thecold telescope, we anticipate 5 8 orders of magnitude speed improvementrelative to preceeding platforms, enabling measurements throughout theepoch of peak activity in galaxies, to z 5.
| The near-infrared spectrum of Mrk 1239: direct evidence of the dusty torus?
We report 0.8-4.5 μm SpeX spectroscopy of the narrow-line Seyfert 1galaxy Mrk 1239. The spectrum is outstanding because the nuclearcontinuum emission in the near-infrared (NIR) is dominated by a strongbump of emission peaking at 2.2 μm, with a strength not reportedbefore in an active galactic nucleus. A comparison of the Mrk 1239spectrum to that of Ark 564 allowed us to conclude that the continuum isstrongly reddened by E(B-V) = 0.54. The excess of emission, confirmed byaperture photometry and additional NIR spectroscopy, follows a simpleblackbody curve at T~ 1200 K. This suggests that we may be observingdirect evidence of dust heated to near to the sublimation temperature,likely produced by the putative torus of the unification model. Althoughother alternatives are also plausible, the lack of star formation, thestrong polarization and low extinction derived for the emission linessupport the scenario where the hot dust is located between the narrowline region and the broad line region.
| Discovery of counter-rotating gas in the galaxies NGC 1596 and 3203 and the incidence of gas counter-rotation in S0 galaxies
We have identified two new galaxies with gas counter-rotation (NGC 1596and 3203) and have confirmed similar behaviour in another one (NGC 128),this using results from separate studies of the ionized-gas and stellarkinematics of a well-defined sample of 30 edge-on disc galaxies. Gascounter-rotators thus represent 10 +/- 5 per cent of our sample, but thefraction climbs to 21 +/- 11 per cent when only lenticular (S0) galaxiesare considered and to 27 +/- 13 per cent for S0 galaxies with detectedionized gas only. Those fractions are consistent with but slightlyhigher than previous studies. A compilation from well-defined studies ofS0 galaxies in the literature yields fractions of 15 +/- 4 and 23 +/- 5per cent, respectively. Although mainly based on circumstantialevidence, we argue that the counter-rotating gas originates primarilyfrom minor mergers and tidally induced transfer of material from nearbyobjects. Assuming isotropic accretion, twice those fractions of objectsmust have undergone similar processes, underlining the importance of(minor) accretion for galaxy evolution. Applications of gascounter-rotators to barred galaxy dynamics are also discussed.
| An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Mid-Infrared Spectral Diagnostics of Nuclear and Extranuclear Regions in Nearby Galaxies
Mid-infrared diagnostics are presented for a large portion of theSpitzer Infrared Nearby Galaxies Survey (SINGS) sample plus archivaldata from ISO and Spitzer. The SINGS data set includes low- andhigh-resolution spectral maps and broadband imaging in the infrared forover 160 nuclear and extranuclear regions within 75 nearby galaxiesspanning a wide range of morphologies, metallicities, luminosities, andstar formation rates. Our main result is that these mid-infrareddiagnostics effectively constrain a target's dominant power source. Thecombination of a high-ionization line index and PAH strength serves asan efficient discriminant between AGNs and star-forming nuclei,confirming progress made with ISO spectroscopy on starbursting andultraluminous infrared galaxies. The sensitivity of Spitzer allows us toprobe fainter nuclear and star-forming regions within galaxy disks. Wefind that both star-forming nuclei and extranuclear regions stand apartfrom nuclei that are powered by Seyfert or LINER activity. In fact, weidentify areas within four diagnostic diagrams containing >90%Seyfert/LINER nuclei or >90% H II regions/H II nuclei. We also findthat, compared to starbursting nuclei, extranuclear regions typicallyseparate even further from AGNs, especially for low-metallicityextranuclear environments. In addition, instead of the traditionalmid-infrared approach to differentiating between AGNs and star-formingsources that utilizes relatively weak high-ionization lines, we showthat strong low-ionization cooling lines of X-ray-dominated regions like[Si II] 34.82 μm can alternatively be used as excellentdiscriminants. Finally, the typical target in this sample showsrelatively modest interstellar electron density (~400 cm-3)and obscuration (AV~1.0 mag for a foreground screen),consistent with a lack of dense clumps of highly obscured gas and dustresiding in the emitting regions.
| Constraining Dark Matter Halo Profiles and Galaxy Formation Models Using Spiral Arm Morphology. I. Method Outline
We investigate the use of spiral arm pitch angles as a probe of diskgalaxy mass profiles. We confirm our previous result that spiral armpitch angles (P) are well correlated with the rate of shear (S) in diskgalaxy rotation curves by using a much larger sample (51 galaxies) thanused previously (17 galaxies). We use this correlation to argue thatimaging data alone can provide a powerful probe of galactic massdistributions out to large look-back times. In contrast to previouswork, we show that observed spiral arm pitch angles are similar whenmeasured in the optical (at 0.4 μm) and the near-infrared (at 2.1μm) with a mean difference of 2.3d+/-2.7d. This is then used tostrengthen the known correlation between P and S using B-band images. Wethen use two example galaxies to demonstrate how an inferred shear ratecoupled with a bulge-disk decomposition model and a Tully-Fisher-derivedvelocity normalization can be used to place constraints on a galaxy'sbaryon fraction and dark matter halo profile. We show that ESO 582-G12,a galaxy with a high shear rate (slightly declining rotation curve) at~10 kpc, favors an adiabatically contracted halo, with high initial NFWconcentration (cvir>16) and a high fraction of halobaryons in the form of stars (~15%-40%). In contrast, IC 2522 has a lowshear rate (rising rotation curve) at ~10 kpc and favorsnonadiabatically contracted models with low NFW concentrations(cvir~=2-8) and a low stellar baryon fraction <10%.
| Spitzer Space Telescope IRAC and MIPS Observations of the Interacting Galaxies IC 2163 and NGC 2207: Clumpy Emission
IC 2163 and NGC 2207 are interacting galaxies that have been wellstudied at optical and radio wavelengths and simulated in numericalmodels to reproduce the observed kinematics and morphological features.Spitzer IRAC and MIPS observations reported here show over 200 brightclumps from young star complexes. The brightest IR clump is amorphologically peculiar region of star formation in the western arm ofNGC 2207. This clump, which dominates the Hα and radio continuumemission from both galaxies, accounts for ~12% of the total 24 μmflux. Nearly half of the clumps are regularly spaced along somefilamentary structure, whether in the starburst oval of IC 2163 or inthe thin spiral arms of NGC 2207. This regularity appears to influencethe clump luminosity function, making it peaked at a value nearly afactor of 10 above the completeness limit, particularly in the starburstoval. This is unlike the optical clusters inside the clumps, which havea luminosity function consistent with the usual power-law form. Thegiant IR clumps presumably formed by gravitational instabilities in thecompressed gas of the oval and the spiral arms, whereas the individualclusters formed by more chaotic processes, such as turbulencecompression, inside these larger scale structures.
| The Extended H I Rotation Curve and Mass Distribution of M31
New H I observations of Messier 31 (M31) obtained with the Effelsbergand Green Bank 100 m telescopes make it possible to measure the rotationcurve of that galaxy out to ~35 kpc. Between 20 and 35 kpc, the rotationcurve is nearly flat at a velocity of ~226 km s-1. A model ofthe mass distribution shows that at the last observed velocity point,the minimum dark-to-luminous mass ratio is ~0.5 for a total mass of3.4×1011 Msolar at R<35 kpc. This can becompared to the estimated Milky Way mass of 4.9×1011Msolar for R<50 kpc.
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Nuclear Dust Morphology and Starburst Rings
We present a study of the nuclear morphology of a sample of narrow- andbroad-line Seyfert 1 galaxies (NLS1s and BLS1s, respectively) based onbroadband images in the Hubble Space Telescope archives. In our previousstudy we found that large-scale stellar bars at >1 kpc from thenucleus are more common in NLS1s than BLS1s. In this paper we find thatNLS1s preferentially have grand-design dust spirals within ~1 kpc oftheir centers. We also find that NLS1s have a higher fraction of nuclearstar-forming rings than BLS1s. We find that many of the morphologicaldifferences are due to the presence or absence of a large-scale stellarbar within the spiral host galaxy. In general, barred Seyfert 1 galaxiestend to have grand-design dust spirals at their centers, confirming theresults of other researchers. The high fraction of grand-design nucleardust spirals and stellar nuclear rings observed in NLS1s' host galaxiessuggests a means for efficient fueling of their nuclei to support theirhigh Eddington ratios.
| Objective Classification of Spiral Galaxies Having Extended Rotation Curves Beyond the Optical Radius
We carry out an objective classification of four samples of spiralgalaxies having extended rotation curves beyond the optical radius. Amultivariate statistical analysis (viz., principal component analysis[PCA]) shows that about 96% of the total variation is due to twocomponents, one being the combination of absolute blue magnitude andmaximum rotational velocity beyond the optical region and the otherbeing the central density of the halo. On the basis of PCA a fundamentalplane has been constructed that reduces the scatter in the Tully-Fisherrelation up to a maximum of 16%. A multiple stepwise regression analysisof the variation of the overall shape of the rotation curves shows thatit is mainly determined by the central surface brightness, while theshape purely in the outer part of the galaxy (beyond the optical radius)is mainly determined by the size of the galactic disk.
| Double Nucleus in M83
M83 is one of the nearest galaxies with enhanced nuclear star formation,and it presents one of the best opportunities to study the kinematicsand physical properties of a circumnuclear starburst. Ourthree-dimensional spectroscopy data in the R band confirm the presenceof a secondary nucleus or mass concentration (previously suggested byThatte and coworkers). We determine the position of this hidden nucleus,which would be more massive than the visible one and was not detected inthe optical Hubble Space Telescope images due, probably, to the strongdust extinction. Using a Keplerian approximation, we estimated for theoptical nucleus a mass of (5.0+/-0.8)×106Msolar/sini (r<1.5"), and for the hidden nucleus, located4''+/-1'' to the northwest (position angle of271deg+/-15deg) of the optical nucleus, a mass of(1.00+/-0.08)×107 Msolar/sini (r<1.5").The emission-line ratio map also unveils the presence of a secondcircumnuclear ring structure, previously discovered by IR imaging(Elmegreen and coworkers). The data allow us to resolve the behavior ofthe interstellar medium inside the circumnuclear ring and around thebinary mass concentration.
| Toward a clean sample of ultra-luminous X-ray sources
Context: .Observational follow-up programmes for the characterization ofultra-luminous X-ray sources (ULXs) require the construction of cleansamples of such sources in which the contamination byforeground/background sources is minimum. Aims: .We calculate thedegree of foreground/background contaminants among the ULX samplecandidates in a published catalogue and compare these computations withavailable spectroscopic identifications. Methods: .We usestatistics based on known densities of X-ray sources and AGN/QSOsselected in the optical. The analysis is done individually for eachparent galaxy. The existing identifications of the optical counterpartsare compiled from the literature. Results: .More than a half ofthe ULXs, within twice the distance of the major axis of the 25mag/arcsec2 isophote from RC3 nearby galaxies and with X-rayluminosities L_X[ 2-10 keV] ≥ 1039 erg/s, are expected tobe high redshift background QSOs. A list of 25 objects (clean sample)confirmed to be real ULXs or to have a low probability of beingcontaminant foreground/background objects is provided.
| A new method to determine the thickness of non-edge-on disk galaxies
Aims.We present a new method to determine the thickness of non-edge-ondisk galaxies. This method allows us to investigate the mass-to-lightratio of the disk. Methods: .Our method is based on the comparisonof observations and theory of the distribution of the vertical velocitydispersion, which is obtained from the solution of three dimensionalPoisson equations and the galactic dynamical equation. Results:.As examples, the thickness and mass-to-light ratio of two diskgalaxies, NGC 1566 and NGC 5247, which have been extensively studied byspectroscopy, have been calculated. The calculated results areconsistent with observations and support the use of this method.However, due to the small sample size available, the results should beconfirmed on other samples of galaxies.
| Adaptive Optics Observations of Active Galactic Nuclei: Zooming into the Central Parsec Region
First results from the AGN-Heidelberg program aimed at resolving thecentral pc region of the closest Active Galactic Nuclei in the IR arepresented. The core region of prototype active nuclei are clearlyunveiled at IR waves and at distances from the nucleus - few pc- wherecircumnuclear starforming regions appear not to be present. Within thatperspective, classical active nuclei as Circinus and NGC 1097, revealwith unprecedented detail clear channels of material being driven to thecore whereas others as Centaurus A and NGC 1566, show a `clean' coreenvironment. At the very center, a central compact region of about 2 pcscale is resolved in Circinus but not in the other cases challengingthus the universal presence of the putative obscuring torus.
| Secular Evolution in Disk Galaxies: The Growth of Pseudobulges and Problems for Cold Dark Matter Galaxy Formation
We review internal secular evolution in galaxy disks - the fundamentalprocess by which isolated disks evolve. We concentrate on the buildup ofdense central features that look like classical, merger-built bulges butthat were made slowly out of disk gas. We call these pseudobulges. As anexistence proof, we review how bars rearrange disk gas into outer rings,inner rings, and gas dumped into the center. In simulations, this gasreaches high densities, and in the observations, many SB and ovalgalaxies show central concentrations of gas. Associated star formationrates imply plausible pseudobulge growth times of a few billion years.If secular processes built dense centers that masquerade as bulges, canwe distinguish them from merger-built bulges? Observations show thatpseudobulges retain a memory of their disky origin. They have one ormore characteristics of disks: (1) flatter shapes than those ofclassical bulges, (2) larger ratios of ordered to random velocities, (3)smaller velocity dispersions, (4) nuclear bars or spiral structure, (5)boxy structure when seen edge-on, (6) nearly exponential brightnessprofiles, and (7) starbursts. These features occur preferentially inbarred and oval galaxies in which secular evolution should be rapid. Sothe cleanest examples of pseudobulges are recognizable. Thusobservations and theory contribute to a new picture of galaxy evolutionthat complements hierarchical clustering and merging.However, an important problem with cold dark matter galaxy formationgets more acute. How can hierarchical clustering produce so many puredisk galaxies with no evidence for merger-built bulges?
| Astrophysical magnetic fields and nonlinear dynamo theory
Electronic Article Available from Elsevier Science.
| Structure and kinematics of edge-on galaxy discs - V. The dynamics of stellar discs
In earlier papers in this series we determined the intrinsic stellardisc kinematics of 15 intermediate- to late-type edge-on spiral galaxiesusing a dynamical modelling technique. The sample covers a substantialrange in maximum rotation velocity and deprojected face-on surfacebrightness, and contains seven spirals with either a boxy orpeanut-shaped bulge. Here we discuss the structural, kinematical anddynamical properties. From the photometry we find that intrinsicallymore flattened discs tend to have a lower face-on central surfacebrightness and a larger dynamical mass-to-light ratio. This observationsuggests that, at a constant maximum rotational velocity, lower surfacebrightness discs have smaller vertical stellar velocity dispersions.Although the individual uncertainties are large, we find from thedynamical modelling that at least 12 discs are submaximal. The averagedisc contributes 53 +/- 4 per cent to the observed rotation at 2.2 discscalelengths (hR), with a 1σ scatter of 15 per cent.This percentage becomes somewhat lower when effects of finite discflattening and gravity by the dark halo and the gas are taken intoaccount. Since boxy and peanut-shaped bulges are probably associatedwith bars, the result suggests that at 2.2hR the submaximalnature of discs is independent of barredness. The possibility remainsthat very high surface brightness discs are maximal, as these discs areunderrepresented in our sample. We confirm that the radial stellar discvelocity dispersion is related to the galaxy maximum rotationalvelocity. The scatter in this σ versus vmax relationappears to correlate with the disc flattening, face-on central surfacebrightness and dynamical mass-to-light ratio. Low surface brightnessdiscs tend to be more flattened and have smaller stellar velocitydispersions. The findings are consistent with the observed correlationbetween disc flattening and dynamical mass-to-light ratio and cangenerally be reproduced by the simple collapse theory for disc galaxyformation. Finally, the disc mass Tully-Fisher relation is offset fromthe maximum-disc scaled stellar mass Tully-Fisher relation of the UrsaMajor cluster. This offset, -0.3 dex in mass, is naturally explained ifthe discs of the Ursa Major cluster spirals are submaximal.
| Principal components in active galactic nuclei variability data and the estimation of the flux contributions from different components
It has been found that the near-infrared flux variations of Seyfertgalaxies satisfy relations of the formFi~αij+βijFj,where Fi, Fj are the fluxes in filters i and j;and αi,j, βi,j are constants. Theserelations have been used to estimate the constant contributions of thenon-variable underlying galaxies. The paper attempts a formal treatmentof the estimation procedure, allowing for the possible presence of athird component, namely non-variable hot dust. In an analysis of asample of 38 Seyfert galaxies, inclusion of the hot dust componentimproves the model fit in approximately half the cases. All derived dusttemperatures are below 300 K, in the range 540-860 K or above 1300 K. Anoteworthy feature is the estimation of confidence intervals for thecomponent contributions: this is achieved by bootstrapping. It is alsopointed out that the model implies that such data could be fruitfullyanalysed in terms of principal components.
| The continuum and narrow-line region of the narrow-line Seyfert 1 galaxy Mrk 766
We present the first spectroscopic observations in the interval 0.8-4.0μm, complemented with existing Hubble Space Telescope ultraviolet(UV) and optical spectroscopy, of the narrow-line Seyfert 1 galaxy Mrk766. The near-infrared spectrum is characterized by numerous permittedlines of HI, HeI, HeII and FeII, and forbidden lines of [SII], [SIII]and [FeII] among others. Highly ionized species such as [SiIX], [SiX],[SIX] and [MgVII] are also observed. The continuum emission has acomplex shape, with contributions from the central engine, circumnuclearstellar population and dust. This last component is demonstrated by thepresence of an excess of emission peaking at 2.25 μm, well fitted bya blackbody function with Tbb= 1200 K. That temperature isclose to the evaporation temperature of graphite grains. As such, itprovides strong evidence of hot dust, probably very close to thenucleus. Consistent modelling of the line spectrum and the broad-bandcontinuum by composite models, which account for the photoionizing fluxof the central engine and shocks, shows that shock velocities rangebetween 100 and 500 km s-1, the pre-shock densities between100 and 1000 cm-3 and the radiation fluxes from the activecentre between 109 and 5 × 1012 photoncm-2 s-1 eV-1 at 1 Ryd with spectralindices αUV=-1.5 and αX=-0.4. Adoptingsilicate grains, dust-to-gas ratios are between 10-6 and 4× 10-4 by mass. The emitting clouds are at an averagedistance of 160 pc from the centre, with high-velocity clouds closer andlow-velocity clouds further from the centre. The N/H relative abundancededuced from the fit of the [NII] 6548+/[OIII] 5007+ line ratio could betwice the solar value. On the other hand, Fe is depleted from thegaseous phase by a factor >2, most probably trapped into grains.Ratios of calculated to observed line ratios to Hβ indicate anaverage contribution of the broad-line region to the observed Hβ ofapproximately 40 per cent.
| A wide-field HI study of the NGC 1566 group
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| The Relationship of Hard X-Ray and Optical Line Emission in Low-Redshift Active Galactic Nuclei
In this paper we assess the relationship of the population of activegalactic nuclei (AGNs) selected by hard X-rays to the traditionalpopulation of AGNs with strong optical emission lines. First, we studythe emission-line properties of a new hard-X-ray-selected sample of 47local AGNs (classified optically as Type 1 and 2 AGNs). We find that thehard X-ray (3-20 keV) and [O III] λ5007 optical emission-lineluminosities are well-correlated over a range of about 4 orders ofmagnitude in luminosity (mean luminosity ratio 2.15 dex with a standarddeviation of σ=0.51 dex). Second, we study the hard X-rayproperties of a sample of 55 local AGNs selected from the literature onthe basis of the flux in the [O III] line. The correlation between thehard X-ray (2-10 keV) and [O III] luminosity for the Type 1 AGNs isconsistent with what is seen in the hard-X-ray-selected sample. However,the Type 2 AGNs have a much larger range in the luminosity ratio, andmany are very weak in hard X-rays (as expected for heavily absorbedAGNs). We then compare the hard X-ray (3-20 keV) and [O III] luminosityfunctions of AGNs in the local universe. These have similar faint-endslopes, with a luminosity ratio of 1.60 dex (0.55 dex smaller than themean value for individual hard-X-ray-selected AGNs). We conclude that atlow redshift, selection by narrow optical emission lines will recovermost AGNs selected by hard X-rays (with the exception of BL Lacobjects). However, selection by hard X-rays misses a significantfraction of the local AGN population with strong emission lines.
| Infrared Spectral Energy Distributions of Nearby Galaxies
The Spitzer Infrared Nearby Galaxies Survey (SINGS) is carrying out acomprehensive multiwavelength survey on a sample of 75 nearby galaxies.The 1-850 μm spectral energy distributions (SEDs) are presented usingbroadband imaging data from Spitzer, 2MASS, ISO, IRAS, and SCUBA. Theinfrared colors derived from the globally integrated Spitzer data aregenerally consistent with the previous generation of models that weredeveloped using global data for normal star-forming galaxies, althoughsignificant deviations are observed. Spitzer's excellent sensitivity andresolution also allow a detailed investigation of the infrared SEDs forvarious locations within the three large, nearby galaxies NGC 3031(M81), NGC 5194 (M51), and NGC 7331. A wide variety of spectral shapesis found within each galaxy, especially for NGC 3031, the closest of thethree targets and thus the galaxy for which the smallest spatial scalescan be explored. Strong correlations exist between the local starformation rate and the infrared colors fν(70μm)/fν(160 μm) and fν(24μm)/fν(160 μm), suggesting that the 24 and 70 μmemission are useful tracers of the local star formation activity level.Preliminary evidence indicates that variations in the 24 μm emission,and not variations in the emission from polycyclic aromatic hydrocarbonsat 8 μm, drive the variations in the fν(8.0μm)/fν(24 μm) colors within NGC 3031, NGC 5194, andNGC 7331. If the galaxy-to-galaxy variations in SEDs seen in our sampleare representative of the range present at high redshift, thenextrapolations of total infrared luminosities and star formation ratesfrom the observed 24 μm flux will be uncertain at the factor of 5level (total range). The corresponding uncertainties using theredshifted 8.0 μm flux (e.g., observed 24 μm flux for a z=2source) are factors of 10-20. Considerable caution should be used wheninterpreting such extrapolated infrared luminosities.
| The Link between Star Formation and Accretion in LINERs: A Comparison with Other Active Galactic Nucleus Subclasses
We present archival high-resolution X-ray imaging observations of 25nearby LINERs observed by ACIS on board Chandra. This sample builds onour previously published proprietary and archival X-ray observations andincludes the complete set of LINERs with published black hole masses andFIR luminosities that have been observed by Chandra. Of the 82 LINERsobserved by Chandra, 41 (50%) display hard nuclear cores consistent withan AGN. The nuclear 2-10 keV luminosities of these AGN-LINERs range from~2×1038 to ~1×1044 ergss-1. Reinforcing our previous work, we find a significantcorrelation between the Eddington ratio,Lbol/LEdd, and the FIR luminosity,LFIR, as well as the IR brightness ratio,LFIR/LB, in the host galaxy of AGN-LINERs thatextends over 7 orders of magnitude in Lbol/LEdd.Combining our AGN-LINER sample with galaxies from other AGN subclasses,we find that this correlation is reinforced in a sample of 129 AGNs,extending over almost 9 orders of magnitude inLbol/LEdd. Using archival and previously publishedobservations of the 6.2 μm PAH feature from ISO, we find that it isunlikely that dust heating by the AGN dominates the FIR luminosity inour sample of AGNs. Our results may therefore imply a fundamental linkbetween the mass accretion rate (M˙), as measured by the Eddingtonratio, and the star formation rate (SFR), as measured by the FIRluminosity. Apart from the overall correlation, we find that thedifferent AGN subclasses occupy distinct regions in the LFIRand Lbol/LEdd plane. Assuming a constant radiativeefficiency for accretion, our results may imply a variation in theSFR/M˙ ratio as a function of AGN activity level, a result that mayhave significant consequences for our understanding of galaxy formationand black hole growth.
| On the Relevance of the Tremaine-Weinberg Method Applied to an Hα Velocity Field: Pattern Speed Determination in M100 (NGC 4321)
The relevance of the Tremaine-Weinberg (TW) method is tested formeasuring bar, spiral, and inner structure pattern speeds using agaseous velocity field. The TW method is applied to various simulatedbarred galaxies in order to demonstrate its validity in seven differentconfigurations, including star formation and/or dark matter halo. Thereliability of the different physical processes involved and of thevarious observational parameters is also tested. The simulations showthat the TW method could be applied to gaseous velocity fields to get agood estimate of the bar pattern speed, under the condition that regionsof shocks are avoided and measurements are confined to regions where thegaseous bar is well formed. We successfully apply the TW method to theHα velocity field of the Virgo Cluster galaxy M100 (NGC 4321) andderive pattern speeds of 55+/-5 km s-1 kpc-1 forthe nuclear structure, 30+/-2 km s-1 kpc-1 for thebar, and 20+/-1 km s-1 kpc-1 for the spiralpattern, in full agreement with published determinations using the samemethod or alternative ones.
| BeppoSAX/PDS serendipitous detections at high galactic latitudes
At a flux limit of 10-11 erg cm-2 s-1in the 20-100 keV band, the PDS instrument on-board BeppoSAX offers theopportunity to study the extragalactic sky with an unprecedentedsensitivity. In this work we report on the results of a search in theBeppoSAX archive for serendipitous high energy sources at high galacticlatitudes (\vert b \vert≥13°). We have defined a set of twelveregions in which the PDS/MECS cross-calibration constant is higher thanthe nominal value. We attribute this mismatch to the presence of aserendipitous source in the PDS field of view. In four cases the likelyhigh energy emitter is also present in the MECS field of view. In thesecases, we have performed a broad band spectral analysis (1.5-100 keV) tounderstand the source spectral behaviour and compare it with previousBeppoSAX observations when available. In eight cases the identificationof the source likely to provide the PDS spectrum is based on indirectevidence (extrapolation to lower energies and/or comparison withprevious observations). This approach led to the discovery of six newhard X-ray emitting objects (PKS 2356-611, 2MASX J14585116-1652223, NGC1566, NGC 7319, PKS 0101-649 and ESO 025-G002) and to the presentationthe PDS spectrum of NGC 3227 for the first time. In the remaining fivecases we provide extra BeppoSAX observations that can be compared withmeasurements already published and/or in the archive.
| A catalogue of ultraluminous X-ray sources in external galaxies
We present a catalogue of ultraluminous X-ray sources (ULXs) in externalgalaxies. The aim of this catalogue is to provide easy access to theproperties of ULXs, their possible counterparts at other wavelengths(optical, IR, and radio), and their host galaxies. The cataloguecontains 229 ULXs reported in the literature until April 2004. Most ULXsare stellar-mass-black hole X-ray binaries, but it is not excluded thatsome ULXs could be intermediate-mass black holes. A small fraction ofthe candidate ULXs may be background Active Galactic Nuclei (AGN) andSupernova Remnants (SNRs). ULXs with luminosity above 1040ergs s-1 are found in both starburst galaxies and in thehalos of early-type galaxies.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/1125
| The Group Evolution Multiwavelength Study (GEMS): bimodal luminosity functions in galaxy groups
We present B- and R-band luminosity functions (LFs) for a sample of 25nearby groups of galaxies. We find that the LFs of the groups with lowX-ray luminosity (LX < 1041.7 ergs-1) are significantly different from those of the X-raybrighter groups, showing a prominent dip around MB=-18. Whileboth categories show lack of late-type galaxies in their centralregions, X-ray dim groups also show a more marked concentration ofoptical luminosity towards the centre. A toy simulation shows that inthe low velocity dispersion environment, as in the X-ray dim group,dynamical friction would facilitate more rapid merging, thus depletingintermediate-luminosity galaxies to form a few giant central galaxies,resulting in the prominent dip seen in our LFs. We suggest that X-raydim (or low velocity dispersion) groups are the present sites of rapiddynamical evolution rather than their X-ray bright counterparts, and maybe the modern precursors of fossil groups. We predict that these groupsof low velocity dispersion would harbour younger stellar populationsthan groups or clusters with higher velocity dispersion.
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