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3D NIR spectroscopy at subarcsecond resolution
We present a scientific case approached through high quality 3D NIRspectroscopy performed with CIRPASS, attached to the Gemini Southtelescope. A binary mass concentration at the nucleus of the galaxy M 83was suggested by Thatte et al. [A&A 364 (2000) L47] and Mast et al.[BAAA 45 (2002) 98. Astroph#0505264] determined the possible position ofthe hidden secondary mass concentration with 2D H-alpha kinematics. Thepreliminary results of the NIR study presented here are based in almost1500 spectra centered in the wavelength 1.3 μm, with a spectralresolving power of 3200. They allow us to unveil, with 0.36″ (6.4pc) sampling and subarcsecond resolution, the velocity field in a regionof 13″ × 9″ around the optical nucleus. We confirmthat the optical nucleus is not located at the most important center ofsymmetry of the ionized gas velocity field. The largest black hole thatcould fit to the circular motion in this kinematic center should have amass not larger than 3 × 106(sin i)‑1Mȯ solar masses.
| Scale Heights of Non-Edge-on Spiral Galaxies
We present a method of calculating the scale height of non-edge-onspiral galaxies, together with a formula for errors. The method is basedon solving Poisson's equation for a logarithmic disturbance of matterdensity in spiral galaxies. We show that the spiral arms can not extendto inside the ``forbidden radius'' r0, due to the effect ofthe finite thickness of the disk. The method is tested by re-calculatingthe scale heights of 71 northern spiral galaxies previously calculatedby Ma, Peng & Gu. Our results differ from theirs by less than 9%. Wealso present the scale heights of a further 23 non-edge-on spiralgalaxies.
| Optical Counterparts of Ultraluminous X-Ray Sources Identified from Archival HST WFPC2 Images
We present a systematic analysis of archival HST WFPC2 ``Association''data sets that correlate with the Chandra positions of a set of 44ultraluminous X-ray sources (ULXs) of nearby galaxies. The mainmotivation is to address the nature of ULXs by searching for opticalcounterparts. Sixteen of the ULXs are found in early-type galaxies (RC3Hubble type <3). We have improved the Chandra/HST relative astrometrywhenever possible, resulting in errors circles of 0.3"-1.7" in size.Disparate numbers of potential ULX counterparts are found, and in somecases none are found. The lack of or low number of counterparts in somecases may be due to insufficient depth in the WFPC2 images. Particularlyin late-type galaxies, the HST image in the ULX region was often complexor crowded, requiring source detection to be performed manually. Wetherefore address various scenarios for the nature of the ULX since itis not known which, if any, of the sources found are true counterparts.The optical luminosities of the sources are typically in the range104-106 Lsolar, with (effective) Vmagnitudes typically in the range 22-24. In several cases colorinformation is available, with the colors roughly tending to be more redin early-type galaxies. This suggests that, in general, the (potential)counterparts found in early-type galaxies are likely to be older stellarpopulations and are probably globular clusters. Several early-typegalaxy counterparts have blue colors, which may be due to youngerstellar populations in the host galaxies, however, these could also bebackground sources. In spiral galaxies the sources may also be due tolocalized structure in the disks rather than bound stellar systems.Alternatively, some of the counterparts in late-type galaxies may beisolated supergiant stars. The observed X-ray/optical flux ratio isdiluted by the optical emission of the cluster in cases where the systemis an X-ray binary in a cluster, particularly in the case of a low-massX-ray binaries in an old cluster. If any of the counterparts are boundsystems with ~104-106 stars and are the truecounterparts to the ULX sources, then the X-ray luminosities of the ULXare generally well below the Eddington limit for a black hole with mass~0.1% of the cluster mass. Finally, we find that the optical flux of thecounterparts is consistent with being dominated by emission from anaccretion disk around an intermediate-mass black hole if the black holehappens to have a mass >~102 Msolar and isaccreting at close to the Eddington rate, unless the accretion disk isirradiated (which would result in high optical disk luminosities atlower black hole masses).Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. This project isassociated with Archival proposal 9545.
| A Comprehensive Search for Gamma-Ray Lines in the First Year of Data from the INTEGRAL Spectrometer
We have carried out an extensive search for gamma-ray lines in the firstyear of public data from the spectrometer (SPI) on the INTEGRAL mission.INTEGRAL has spent a large fraction of its observing time in theGalactic plane with particular concentration in the Galactic center (GC)region (~3 Ms in the first year). Hence the most sensitive searchregions are in the Galactic plane and center. The phase space of thesearch spans the energy range 20-8000 keV and line widths from 0 to 1000keV (FWHM). It includes both diffuse and pointlike emission. We havesearched for variable emission on timescales down to ~1000 s. Diffuseemission has been searched for on a range of different spatial scalesfrom ~20° (the approximate field of view of the spectrometer) up tothe entire Galactic plane. Our search procedures were verified by therecovery of the known gamma-ray lines at 511 and 1809 keV at theappropriate intensities and significances. We find no evidence for anypreviously unknown gamma-ray lines. The upper limits range from afew×10-5 to a few×10-2 cm-2s-1 depending on line width, energy, and exposure; regions ofstrong instrumental background lines were excluded from the search.Comparison is made between our results and various prior predictions ofastrophysical lines.
| Magnetic Fields in Starburst Galaxies and the Origin of the FIR-Radio Correlation
We estimate minimum energy magnetic fields (Bmin) for asample of galaxies with measured gas surface densities, spanning morethan four orders of magnitude in surface density, from normal spirals toluminous starbursts. We show that the ratio of the minimum energymagnetic pressure to the total pressure in the ISM decreasessubstantially with increasing surface density. For the ultraluminousinfrared galaxy Arp 220, this ratio is ~10-4. Therefore, ifthe minimum energy estimate is applicable, magnetic fields in starburstsare dynamically weak compared to gravity, in contrast to normalstar-forming spiral galaxies. We argue, however, that rapid cooling ofrelativistic electrons in starbursts invalidates the minimum energyestimate. We assess a number of independent constraints on the magneticfield strength in starburst galaxies. In particular, we argue that theexistence of the FIR-radio correlation implies that the synchrotroncooling timescale for cosmic-ray electrons is much shorter than theirescape time from the galactic disk; this in turn implies that the truemagnetic field in starbursts is significantly larger thanBmin. The strongest argument against such large fields isthat one might expect starbursts to have steep radio spectra indicativeof strong synchrotron cooling, which is not observed. However, we showthat ionization and bremsstrahlung losses can flatten the nonthermalspectra of starburst galaxies even in the presence of rapid cooling,providing much better agreement with observed spectra. We furtherdemonstrate that ionization and bremsstrahlung losses are likely to beimportant in shaping the radio spectra of most starbursts at GHzfrequencies, thereby preserving the linearity of the FIR-radiocorrelation. We thus conclude that magnetic fields in starbursts aresignificantly larger than Bmin. We highlight severalobservations that can test this conclusion.
| The First INTEGRAL AGN Catalog
We present the first INTEGRAL AGN catalog, based on observationsperformed from launch of the mission in 2002 October until 2004 January.The catalog includes 42 AGNs, of which 10 are Seyfert 1, 17 are Seyfert2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rathersmall, with five detected objects, and only one galaxy cluster and nostarburst galaxies have been detected so far. A complete subset consistsof 32 AGNs with a significance limit of 7 σ in the INTEGRAL ISGRI20-40 keV data. Although the sample is not flux limited, thedistribution of sources shows a ratio of obscured to unobscured AGNs of1.5-2.0, consistent with luminosity-dependent unified models for AGNs.Only four Compton-thick AGNs are found in the sample. Based on theINTEGRAL data presented here, the Seyfert 2 spectra are slightly harder(Γ=1.95+/-0.01) than Seyfert 1.5 (Γ=2.10+/-0.02) and Seyfert1 (Γ=2.11+/-0.05).
| A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei
Seyfert galaxies commonly host compact jets spanning 10-100 pc scales,but larger structures are resolved out in long-baseline aperturesynthesis surveys. Previous, targeted studies showed thatkiloparsec-scale radio structures (KSRs) may be a common feature ofSeyfert and LINER galaxies, and the origin of KSRs may be starbursts oractive galactic nuclei (AGNs). We report a new Very Large Array surveyof a complete sample of Seyfert and LINER galaxies. Out of all of thesurveyed radio-quiet sources, we find that 44% (19 out of 43) showextended radio structures at least 1 kpc in total extent that do notmatch the morphology of the disk or its associated star-forming regions.The detection rate is a lower limit owing to the combined effects ofprojection and resolution. The infrared colors of the KSR host galaxiesare unremarkable compared to other Seyfert galaxies, and the large-scaleoutflows orient randomly with respect to the host galaxy axes. The KSRSeyfert galaxies instead stand out by deviating significantly from thefar-infrared-radio correlation for star-forming galaxies, with tendencytoward radio excess, and they are more likely to have a relativelyluminous, compact radio source in the nucleus; these results argue thatKSRs are powered by the AGNs rather than starbursts. The high detectionrate indicates that Seyfert galaxies generate radio outflows over asignificant fraction of their lifetime, which is much longer than thedynamical timescale of an AGN-powered jet but is comparable instead tothe buoyancy timescale. The likely explanation is that the KSRsoriginate from jet plasma that has been decelerated by interaction withthe nuclear interstellar medium (ISM). Based on a simple ram pressureargument, the kinetic power of the jet on kiloparsec scales is about 3orders of magnitude weaker than the power of the jet on 10-100 pcscales. This result is consistent with the interaction model, in whichcase virtually all of the jet power must be lost to the ISM within theinner kiloparsec.
| 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.
| On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
We investigate the relation between X-ray nuclear emission, opticalemission line luminosities and black hole masses for a sample of 47Seyfert galaxies. The sample, which has been selected from the Palomaroptical spectroscopic survey of nearby galaxies (Ho et al. 1997a, ApJS,112, 315), covers a wide range of nuclear powers, from L2-10keV ~ 1043 erg/s down to very low luminosities(L2-10 keV ~ 1038 erg/s). Best available data fromChandra, XMM-Newton and, in a few cases, ASCA observations have beenconsidered. Thanks to the good spatial resolution available from theseobservations and a proper modeling of the various spectral components,it has been possible to obtain accurate nuclear X-ray luminosities notcontaminated by off-nuclear sources and/or diffuse emission. X-rayluminosities have then been corrected taking into account the likelycandidate Compton thick sources, which are a high fraction (>30%)among type 2 Seyferts in our sample. The main result of this study isthat we confirm strong linear correlations between 2-10 keV,[OIII]λ5007, Hα luminosities which show the same slope asquasars and luminous Seyfert galaxies, independent of the level ofnuclear activity displayed. Moreover, despite the wide range ofEddington ratios (L/L_Edd) tested here (six orders of magnitude, from0.1 down to ~10-7), no correlation is found between the X-rayor optical emission line luminosities and the black hole mass. Ourresults suggest that Seyfert nuclei in our sample are consistent withbeing a scaled-down version of more luminous AGN.
| X-ray spectral survey with XMM-Newton of a complete sample of nearby Seyfert galaxies
Results obtained from an X-ray spectral survey of nearby Seyfertgalaxies using XMM-Newton are reported. The sample was opticallyselected, well defined, complete in B magnitude, and distance limited:it consists of the nearest (D 22 Mpc) 27 Seyfert galaxies (9 oftype 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315)sample. This is one of the largest atlases of hard X-ray spectra oflow-luminosity active galaxies ever assembled. All nuclear sourcesexcept two Seyfert 2s are detected between 2 and 10 keV, half for thefirst time ever, and average spectra are obtained for all of them.Nuclear luminosities reach values down to 1038 ergs-1. The shape of the distribution of X-ray parameters isaffected by the presence of Compton-thick objects (30% among type2s). The latter have been identified either directly from their intenseFeK line and flat X-ray spectra, or indirectly with flux diagnosticdiagrams which use isotropic indicators. After taking into account thesehighly absorbed sources, we find that (i) the intrinsic X-ray spectralproperties (i.e., spectral shapes and luminosities above 2 keV) areconsistent between type 1 and type 2 Seyferts, as expected from "unifiedmodels"; (ii) Seyfert galaxies as a whole are distributed fairlycontinuously over the entire range of N_H, between 1020 and1025 cm-2; and (iii) while Seyfert 1s tend to havelower NH and Seyfert 2s tend to have the highest, we find 30%and 10% exceptions, respectively. Overall the sample is of sufficientquality to well represent the average intrinsic X-ray spectralproperties of nearby active galactic nuclei, including a proper estimateof the distribution of their absorbing columns. Finally, we concludethat, with the exception of a few cases, the present study agrees withpredictions of unified models of Seyfert galaxies, and extends theirvalidity down to very low luminosities.
| Galaxies, Clusters of Galaxies, and the Magnetic Field Interchange
Not Available
| High-resolution observations of SN 2001gd in NGC 5033
We report on 8.4-GHz very-long-baseline interferometry (VLBI)observations of SN 2001gd in the spiral galaxy NGC 5033 made on 2002June 26 (2002.48) and 2003 April 8 (2003.27). We used theinterferometric visibility data to estimate angular diameter sizes forthe supernova by model fitting. Our data nominally suggest a relativelystrong deceleration for the expansion of SN 2001gd, but we cannotdismiss the possibility of a free supernova expansion. From our VLBIobservations on 2003 April 8, we inferred a minimum total energy inrelativistic particles and magnetic fields in the supernova shell ofEmin= (0.3-14) × 1047 erg, and acorresponding equipartition average magnetic field of Bmin=50-350 mG. We also present multiwavelength Very Large Array (VLA)measurements of SN 2001gd made at our second VLBI epoch at frequenciesof 1.4, 4.9, 8.4, 15.0, 22.5 and 43.3 GHz. The VLA data are well fittedby an optically thin, synchrotron spectrum (α=-1.0 +/- 0.1;Sν~να), partially absorbed by thermalplasma. We obtain a supernova flux density of 1.02 +/- 0.05 mJy at theobserving frequency of 8.4 GHz for the second epoch, which results in anisotropic radio luminosity of (6.0 +/- 0.3) × 1036 ergs-1 between 1.4 and 43.3 GHz, at an adopted distance of 13.1Mpc. Finally, we report on an XMM-Newton X-ray detection of SN 2001gd on2002 December 18. The supernova X-ray spectrum is consistent withoptically thin emission from a soft component (associated with emissionfrom the reverse shock) at a temperature of around 1 keV. The observedflux corresponds to an isotropic X-ray luminosity of LX= (1.4+/- 0.4) × 1039 erg s-1 in the 0.3-5 keVband. We suggest that both radio and X-ray observations of SN 2001gdindicate that a circumstellar interaction similar to that displayed bySN 1993J in M 81 is taking place.
| Imprints of spiral arms in the oxygen distribution over the galactic disc
A theory for the oxygen abundance radial distribution formation in thegalactic disc of a spiral galaxy is developed. We take into account thatthe main sources of oxygen are Type II supernovae (SN II), theprogenitors of which are massive short-lived stars strongly concentratedin the spiral arms. Hence oxygen is the most sensitive indicator ofspiral arms' influence on galactic disc enrichment by heavy elements.Various models for the spiral density waves were analysed. We predictthat the imprints in the oxygen radial distribution will enable us todistinguish between different models for spiral patterns. Among otherparameters, the corotation radius happens to be one of the mostimportant.
| VLBI Imaging of Young Radio Supernovae .
In this contribution, we present an overview of several young radiosupernovae studied with the VLBI technique. Imaging radio supernovae haspermitted, among other things, to characterize the structure of theemitting region, and to estimate the deceleration of supernovaeexpansion and to probe the circumstellar interaction, thus yieldingrelevant information on the ejecta and circumstellar density profiles.We review results on high resolution observations of the nearby radiosupernovae: SN 1979C, SN 1986J, SN 1993J and SN 2001gd. Finally, wereview recent results on the detection of radio supernovae in starburstgalaxies, the so-called "Supernova Factories".
| A further argument for the iron lines in active galactic nuclei arising from cerenkov line-like radiation - Calculation for an optically thin case
Not Available
| Supermassive Black Holes: Relation to Dark Halos
Estimates of the masses of supermassive black holes (M bh ) in thenuclei of disk galaxies with known rotation curves are compared withestimates of the rotational velocities V m and the“indicative” masses of the galaxies M i . Although there isa correlation between M bh and V m or M i , it is appreciably weakerthan the correlation with the central velocity dispersion. The values ofM bh for early-type galaxies (S0-Sab), which have more massive bulges,are, on average, higher than the values for late-type galaxies with thesame rotational velocities. We conclude that the black-hole masses aredetermined primarily by the properties of the bulge and not therotational velocity or the mass of the galaxy.
| 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.
| 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 Baryonic Tully-Fisher Relation of Galaxies with Extended Rotation Curves and the Stellar Mass of Rotating Galaxies
I investigate the baryonic Tully-Fisher relation for a sample ofgalaxies with extended 21 cm rotation curves spanning the range 20 kms-1<~Vf<=300 km s-1. A variety ofscalings of the stellar mass-to-light ratio Υ* areconsidered. For each prescription for Υ*, I give fitsof the form Md=AVxf.Presumably, the prescription that comes closest to the correct valuewill minimize the scatter in the relation. The fit with minimum scatterhas A=50 Msolar km-4 s4 andx=4. This relation holds over five decades in mass. Galaxy color,stellar fraction, and Υ* are correlated with eachother and with Md, in the sense that more massivegalaxies tend to be more evolved. There is a systematic dependence ofthe degree of maximality of disks on surface brightness. High surfacebrightness galaxies typically have Υ*~3/4 of themaximum disk value, while low surface brightness galaxies typicallyattain ~1/4 of this amount.
| Secular Evolution via Bar-driven Gas Inflow: Results from BIMA SONG
We present an analysis of the molecular gas distributions in the 29barred and 15 unbarred spirals in the BIMA CO (J=1-0) Survey of NearbyGalaxies (SONG). For galaxies that are bright in CO, we confirm theconclusion by Sakamoto et al. that barred spirals have higher moleculargas concentrations in the central kiloparsec. The SONG sample alsoincludes 27 galaxies below the CO brightness limit used by Sakamoto etal. Even in these less CO-bright galaxies we show that high central gasconcentrations are more common in barred galaxies, consistent withradial inflow driven by the bar. However, there is a significantpopulation of early-type (Sa-Sbc) barred spirals (6 of 19) that have nomolecular gas detected in the nuclear region and have very little out tothe bar corotation radius. This suggests that in barred galaxies withgas-deficient nuclear regions, the bar has already driven most of thegas within the bar corotation radius to the nuclear region, where it hasbeen consumed by star formation. The median mass of nuclear moleculargas is over 4 times higher in early-type bars than in late-type (Sc-Sdm)bars. Since previous work has shown that the gas consumption rate is anorder of magnitude higher in early-type bars, this implies that theearly types have significantly higher bar-driven inflows. The loweraccretion rates in late-type bars can probably be attributed to theknown differences in bar structure between early and late types. Despitethe evidence for bar-driven inflows in both early and late Hubble-typespirals, the data indicate that it is highly unlikely for a late-typegalaxy to evolve into an early type via bar-induced gas inflow.Nonetheless, secular evolutionary processes are undoubtedly present, andpseudobulges are inevitable; evidence for pseudobulges is likely to beclearest in early-type galaxies because of their high gas inflow ratesand higher star formation activity.
| The Hubble Space Telescope View of LINER Nuclei: Evidence for a Dual Population?
We study a complete, distance-limited sample of 25 LINERs, 21 of whichhave been imaged with the Hubble Space Telescope. In nine objects wedetect an unresolved nucleus. To study their physical properties, wecompare the radio and optical properties of the nuclei of LINERs withthose of other samples of local active galactic nuclei (AGNs), namely,Seyfert galaxies and low-luminosity radio galaxies (LLRGs). Our resultsshow that the LINER population is not homogeneous, as there are twosubclasses: (1) the first class is similar to the LLRG class, as itextends the population of radio-loud nuclei to lower luminosities; (2)the second is similar to Seyfert galaxies and extends the properties ofradio-quiet nuclei toward the lowest luminosities. The objects areoptimally discriminated in the plane formed by the black hole massversus nuclear radio loudness: all radio-loud LINERs haveMBH>~108Msolar, while Seyfertgalaxies and radio-quiet LINERs haveMBH<~108Msolar. The different natureof the various classes of local AGNs are best understood when thefraction of the Eddington luminosity they irradiate,Lo/LEdd, is plotted against the nuclearradio-loudness parameter: Seyfert galaxies are associated withrelatively high radiative efficienciesLo/LEdd>~10-4 (and high accretionrates onto low-mass black holes); LLRGs are associated with lowradiative efficiencies (and low accretion rates onto high-mass blackholes); all LINERs have low radiative efficiency (and accretion rates)and can be radio-loud or radio-quiet, depending on their black holemass.Based on observations obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| Extragalactic Source Counts in the 20-50 keV Energy Band from the Deep Observation of the Coma Region by INTEGRAL IBIS
We present the analysis of serendipitous sources in a deep, 500 ks, hardX-ray observation of the Coma Cluster region with the IBIS instrument onboard INTEGRAL. In addition to the Coma Cluster, the final 20-50 keVimage contains 12 serendipitous sources with statistical significance>4 σ. We use these data (after correcting for expected numberof false detections) to extend the extragalactic source counts in the20-50 keV energy band down to a limiting flux of1.0×10-11 ergs s-1 cm-2 (~=1mcrab). This is a more than a factor of 10 improvement in sensitivitycompared to the previous results in this energy band obtained with theHEAO 1 A-4 instrument. The derived source counts are consistent with theEuclidean relation N(>f)~f-3/2. A large fraction ofidentified serendipitous sources are low-redshift, z<0.02, activegalactic nuclei (AGNs), mostly of Seyfert 1 type. The surface density ofhard X-ray sources is (1.4+/-0.5)×10-2 deg-2above a flux threshold of 10-11 ergs s-1cm-2. These sources directly account for ~3% of the cosmicX-ray background in the 20-50 keV energy band. Given the low redshiftdepth of our sample, we expect that similar sources at higher redshiftsaccount for a significant fraction of the hard X-ray background. Ourfield covers only 3% of the sky; a systematic analysis of otherextragalactic INTEGRAL observations can produce much larger sourcesamples and is, therefore, critically important.
| Probing Halos of Galaxies at Very Large Radii Using Background QSOs
Gaseous halos of nine nearby galaxies (with redshifts cz<6000 kms-1) were probed at large galactocentric radii usingbackground quasars observed with the Hubble Space Telescope Goddard HighResolution Spectrograph and the Space Telescope Imaging Spectrograph.The projected quasar-galaxy separations range from 55 to 387h-175 kpc. Lyα absorption lines weresuccessfully detected in the spectra of five quasars, at impactparameters of up to ~170 h-175 kpc from the centerof the nearby galaxy, and in each case at wavelengths consistent withthe galaxy's redshift. Our observations include the lowest redshiftLyα lines detected to date. H I velocity fields were obtained atthe Very Large Array for three of the galaxies in our sample (in onecase the velocity field was available from the literature) to derivetheir rotation curves. When comparing the inner rotation curves of thegalaxies with the velocity at large radius provided by the Lyαline, it is apparent that it is very difficult to explain the observedLyα velocity as due to gas in an extended rotating disk. In mostcases, one would need to invoke large warps in the outer gas disks andalso thick gas disks to reconcile the observed velocities with thepredicted ones. Indeed, in one case, the Lyα line velocityindicates, in fact, counterrotation with respect to the inner diskrotation. In light of these results, we conclude that in a typicalgalaxy there is no longer detectable atomic gas corotating in anextended disk at radii greater than 35α-1, whereα-1 is the stellar disk exponential scale length. Thecosmic web is the most likely origin for the detected Lyα lines.Our observations confirm the recent Bowen et al. correlation ofequivalent widths with the local volume density of galaxies around thesight line, and the observed equivalent widths of the lines areconsistent with expectations of the cosmic web.Based on observations with the NASA ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by AURA,Inc., under NASA contract NAS5-26555.
| The Westerbork HI survey of spiral and irregular galaxies. III. HI observations of early-type disk galaxies
We present Hi observations of 68 early-type disk galaxies from the WHISPsurvey. They have morphological types between S0 and Sab and absoluteB-band magnitudes between -14 and -22. These galaxies form the massive,high surface-brightness extreme of the disk galaxy population, few ofwhich have been imaged in Hi before. The Hi properties of the galaxiesin our sample span a large range; the average values of MHI/LB and DH I/D25 are comparableto the ones found in later-type spirals, but the dispersions around themean are larger. No significant differences are found between the S0/S0aand the Sa/Sab galaxies. Our early-type disk galaxies follow the same Himass-diameter relation as later-type spiral galaxies, but theireffective Hi surface densities are slightly lower than those found inlater-type systems. In some galaxies, distinct rings of Hi emissioncoincide with regions of enhanced star formation, even though theaverage gas densities are far below the threshold of star formationderived by Kennicutt (1989, ApJ, 344, 685). Apparently, additionalmechanisms, as yet unknown, regulate star formation at low surfacedensities. Many of the galaxies in our sample have lopsided gasmorphologies; in most cases this can be linked to recent or ongoinginteractions or merger events. Asymmetries are rare in quiescentgalaxies. Kinematic lopsidedness is rare, both in interacting andisolated systems. In the appendix, we present an atlas of the Hiobservations: for all galaxies we show Hi surface density maps, globalprofiles, velocity fields and radial surface density profiles.
| The molecular connection to the FIR-radio continuum correlation in galaxies
We have studied the relationships between the radio continuum (RC) andCO emission for a set of galaxies selected from the BIMA Survey ofNearby Galaxies. We find that the global CO-RC correlation is as tightas the global FIR-RC correlation for the 24 galaxies studied. Within 9galaxies with ~6´´ CO and RC data available, the CO and RCemission is as tightly correlated as its global value; the radiallyaveraged correlation is nearly linear, extends over four order ofmagnitude and holds down to the smallest linear resolution of theobservations, which is ~100 pc. We define q_CO/RC as the log of theratio of the CO to RC flux as a way to characterize the CO-RCcorrelation. Combining 6´´ pixel-by-pixel comparisons acrossall sources yields an average small-scale correlation of q_CO/RC = 1.1± 0.28; that is, the spatially resolved correlation has adispersion that is less than a factor of 2. There are however systematicvariations in the CO/RC ratio; the strongest organized structures inq_CO/RC tend to be found along spiral arms and on size scales muchlarger than the resolution of the observations. We do not measure anysystematic trend in CO/RC ratio as a function of radius in galaxies. Theconstancy of the CO/RC ratio stands in contrast to the previouslymeasured decrease in the FIR/RC ratio as a function of radius ingalaxies. We suggest that the excellent correlation between the CO, RCand FIR emission in galaxies is a consequence of regulation byhydrostatic pressure; this model links all three emissions withoutinvoking an explicit dependence on a star formation scenario.
| Asymmetrical structure of ionization and kinematics in the Seyfert galaxy NGC 5033
We present integral field spectroscopy of NGC 5033, a low luminositySeyfert galaxy. The observations were made with INTEGRAL, a fiber basedsystem operating at the WHT. The intensity map of the Hβ emissionline represents a spiral or ring-like pattern of HII regions. On thecontrary, the [OIII] intensity map morphology is markedly anisotropic.The strong morphological differences imply that the [OIII] emittersrepresent highly ionized gas illuminated by the central source. The[OIII] map morphology is compatible with a biconical structure ofionization induced by strong extinction in the galaxy disc that alsoobscures half of the spheroidal stellar bulge. We identify the spectrumcorresponding to the Seyfert 1 nucleus from the presence of Hβbroad emission lines. This spectrum is located in a region where strongextinction is expected but exhibits the bluest spectral energydistribution. The Seyfert 1 nucleus seems to be offcenter with respectto the stellar rotation center. This result has been also found in otherSeyfert galaxies and interpreted in terms of a past merger. Theoffcentering could indicate the presence of nonsymmetric departures inthe gravitational potential which could be fueling the active nucleus.The kinematics of the [OIII] emitters show important deviations at a kpcscale with respect to the stellar velocity field and show featuresrelated to the asymmetrical morphology of the high ionization region.
| 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
| On the alignment between binary spiral galaxies
We show some significance against the null hypothesis of randominteractions of binary spiral galaxies, and in favour of the alternativethat more interactions than expected occur for axes either nearlyparallel (spins being parallel or anti-parallel) or nearly orthogonal.We discuss this in the context of similar prior studies, using adifferent statistical focus in such a way that we are able toincorporate additional data.
| Modulations in the radio light curve of the Type IIb supernova 2001ig: evidence for a Wolf-Rayet binary progenitor?
We describe the radio evolution of supernova (SN) 2001ig in NGC 7424,from 700 d of multifrequency monitoring with the Australia TelescopeCompact Array (ATCA) and the Very Large Array (VLA). We find thatdeviations of the radio light curves at each frequency from the standard`minishell' model are consistent with density modulations in thecircumstellar medium (CSM), which seem to recur with a period near 150d. One possibility is that these are due to enhanced mass loss fromthermal pulses in an asymptotic giant branch star progenitor. A morelikely scenario, however, is that the progenitor was a Wolf-Rayet (WR)star, whose stellar wind collided with that from a massive hot companionon an eccentric 100-d orbit, leading to a regular build-up of CSMmaterial on the required time and spatial scales. Recent observations of`dusty pinwheels' in WR binary systems lend credibility to this model.Since such binary systems are also thought to provide the necessaryconditions for envelope stripping which would cause the WR star toappear as a Type Ib/c SN event rather than a Type II, these radioobservations of SN 2001ig may provide the key to linking Type Ib/c SNeto Type IIb events, and even to some types of gamma-ray bursts.
| The infrared continuum of active galactic nuclei
We discuss the different physical processes contributing to the infraredcontinuum of active galactic nuclei (AGNs), assuming that bothphotoionization from the active centre and shocks ionize and heat thegas and dust contained in an ensemble of clouds surrounding the nucleus.In our model, radiation transfer of primary and secondary radiationthroughout a cloud is calculated consistently with collisional processesdue to the shock. We consider that the observed continuum corresponds toreprocessed radiation from both dust and gas in the clouds. Collisionalprocesses are important in the presence of shocks. The grains aresputtered crossing the shock front. The models are constrained bysputtering as well as by the far-infrared data. The model is applied tothe continuum of Seyfert galaxies from which the best estimate of thenuclear, stellar subtracted, emission is available. The results showthat radiation-dominated high-velocity clouds are more numerous inSeyfert 1-1.5 whereas shock-dominated low-velocity clouds are dominantin Seyfert type 2. This result is in full agreement with the unifiedmodel for AGNs, by which high-velocity clouds, placed deeper into thecentral region and therefore reached by a more intense radiation, shouldplay a more significant role in the spectra of broad-line objects. Wecould therefore conclude that in type 2 objects, radiation is partlysuppressed by a central dusty medium with a high dust-to-gas ratio. Oncethe model approach is tested, a grid of models is used to provide aphenomenological analysis of the observed infrared spectral energydistribution. This empirical method is a useful tool to rapidly accessthe physical conditions of the AGN emitting clouds. For this, analyticalforms are derived for the two processes contributing to the infraredemission: dust emission and thermal bremsstrahlung produced by thenarrow-line region clouds. Their relative contribution provides ameasurement of the dust-to-gas ratio.
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