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Improved 3D Fabry-Perot data reduction techniques*
Improved data reduction techniques for three-dimensional (3D) data cubesobtained from Fabry-Perot integral field spectroscopy are presented.They provide accurate sky emission subtraction and adaptive spatialbinning and smoothing. They help avoiding the effect analogous to thebeam smearing, seen in HI radio data, when strong smoothing is appliedto 3D data in order to get the most extended signal coverage. The datareduction techniques presented in this paper allow one to get the bestof both worlds: high spatial resolution in high signal-to-noise regionsand large spatial coverage in low signal-to-noise regions.
| Hαkinematics of the SINGS nearby galaxies survey - I*
This is the first part of an Hαkinematics follow-up survey of theSpitzer Infrared Nearby Galaxies Survey (SINGS) sample. The data for28galaxies are presented. The observations were done on three differenttelescopes with Fabry-Perot of New Technology for the Observatoire dumont Megantic (FaNTOmM), an integral field photon-counting spectrometer,installed in the respective focal reducer of each telescope. The datareduction was done through a newly built pipeline with the aim ofproducing the most homogenous data set possible. Adaptive spatialbinning was applied to the data cubes in order to get a constantsignal-to-noise ratio across the field of view. Radial velocity andmonochromatic maps were generated using a new algorithm, and thekinematical parameters were derived using tilted-ring models.
| Hubble Space Telescope Identification of the Optical Counterparts of Ultraluminous X-Ray Sources in M51
We present the results of a search for optical identifications ofultraluminous X-ray sources (ULXs) in M51 by using mosaic images takenwith the Hubble Space Telescope(HST) Advanced Camera for Surveys (ASC)in filters F435W (B), F555W (V), F814W (I), and F658N (Hα). Oursample, consisting of nine ULXs, is defined by analyzing the threeChandra observations of M51 performed in 2000 June, 2001 June, and 2003August. We found that four ULXs have one or two candidates forcounterparts, while two have multiple stars within their error circles.The other three have no candidate counterparts. Four ULXs are locatednear or in a star cluster, while others have no association with acluster. These results indicate that the companion stars, environments,and origins of ULXs are probably heterogeneous.
| Identification of the Red Supergiant Progenitor of Supernova 2005cs: Do the Progenitors of Type II-P Supernovae Have Low Mass?
The stars that end their lives as supernovae (SNe) have been directlyobserved in only a handful of cases, mainly because of the extremedifficulty of identifying them in images obtained prior to the SNexplosions. Here we report the identification of the progenitor for therecent Type II-plateau (core collapse) SN 2005cs in pre-explosionarchival images of the Whirlpool Galaxy (M51) obtained with the HubbleSpace Telescope (HST) Advanced Camera for Surveys (ACS). Fromhigh-quality ground-based images of the SN obtained with theCanada-France-Hawaii Telescope, we precisely determine the position ofthe SN and are able to isolate the SN progenitor to within 0.04" in theHST ACS optical images. We further pinpoint the SN location to within0.005" from HST ACS ultraviolet images of the SN, confirming ourprogenitor identification. From photometry of the SN progenitor obtainedwith the pre-SN ACS images, and also from limits to its brightness inpre-SN HST NICMOS images, we infer that the progenitor is a redsupergiant star of spectral type K3-M4 with initial mass 10+/-3Msolar. We also discuss the implications of the SN 2005csprogenitor identification and its mass estimate. There is an emergingtrend that the most common Type II-plateau SNe originate from low-masssupergiants (8-20 Msolar).
| The Spatial Distribution of Faint Fuzzy Star Clusters in NGC 5195
We present a study of a faint fuzzy star cluster system in the nearbySB0 galaxy NGC 5195 interacting with the famous spiral galaxy NGC 5194(M51), based on HST ACS BVI mosaic images taken by the Hubble HeritageTeam. We have found about 50 faint fuzzy star clusters around NGC 5195that are larger than typical globular clusters with effective radiireff>7 pc and that are red with (V-I)>1.0. They aremostly fainter than MV~-8.3 mag. From the comparison of BVIphotometry of these clusters with the simple stellar population models,we find that they are as massive as ~105 Msolarand older than 1 Gyr. Strikingly, most of these clusters are found to bescattered in an elongated region almost perpendicular to the northernspiral arm of NGC 5194, and the center of the region is slightly northof the NGC 5195 center, while normal compact red clusters of NGC 5195are located around the bright optical body of the host galaxy. This isin contrast to the cases of NGC 1023 and NGC 3384 where the spatialdistribution of faint fuzzy clusters shows a ring structure around thehost galaxy. We suggest that at least some faint fuzzy clusters areexperiencing tidal interactions with the companion galaxy NGC 5194 andmust be associated with the tidal debris in the western halo of NGC5195.
| 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.
| The luminosity function of young star clusters: implications for the maximum mass and luminosity of clusters
We introduce a method to relate a possible truncation of the starcluster mass function at the high mass end to the shape of the clusterluminosity function (LF). We compare the observed LFs of five galaxiescontaining young star clusters with synthetic cluster population modelswith varying initial conditions. The LF of the SMC, the LMC and NGC 5236are characterized by a power-law behavior N d L ∝L-α d L, with a mean exponent of < α> = 2.0± 0.2. This can be explained by a cluster population formed witha constant cluster formation rate, in which the maximum cluster mass perlogarithmic age bin is determined by the size-of-sample effect andtherefore increases with log (age/yr). The LFs of NGC 6946 and M 51 arebetter described by a double power-law distribution or a Schechterfunction. When a cluster population has a mass function that istruncated below the limit given by the size-of-sample effect, the totalLF shows a bend at the magnitude of the maximum mass, with the age ofthe oldest cluster in the population, typically a few Gyr due todisruption. For NGC 6946 and M 51 this suggests a maximum mass of M_max= 0.5-1×10^6 Mȯ, although the bend is only a 1-2σ detection. Faint-ward of the bend the LF has the same slope asthe underlying initial cluster mass function and bright-ward of the bendit is steeper. This behavior can be well explained by our populationmodel. We compare our results with the only other galaxy for which abend in the LF has been observed, the "Antennae" galaxies (NGC4038/4039). There the bend occurs brighter than in NGC 6946 and M 51,corresponding to a maximum cluster mass of M_max =1.3-2.5×106 Mȯ. Hence, if the maximumcluster mass has a physical limit, then it can vary between differentgalaxies. The fact that we only observe this bend in the LF in the"Antennae" galaxies, NGC 6946 and M 51 is because there are enoughclusters available to reach the limit. In other galaxies there might bea physical limit as well, but the number of clusters formed or observedis so low, that the LF is not sampled up to the luminosity of the bend.The LF can then be approximated with a single power-law distribution,with an index similar to the initial mass function index.
| Observational evidence for a truncation of the star cluster initial mass function at the high mass end
We present the luminosity function (LF) of star clusters in M 51 basedon HST/ACS observations taken as part of the Hubble Heritage project.The clusters are selected based on their size and with the resulting5990 clusters we present one of the largest cluster samples of a singlegalaxy. We find that the LF can be approximated with a double power-lawdistribution with a break around MV = -8.9. On the brightside the index of the power-law distribution is steeper (α = 2.75)than on the faint-side (α = 1.93), similar to what was foundearlier for the "Antennae" galaxies. The location of the bend, however,occurs about 1.6 mag fainter in M 51. We confront the observed LF withthe model for the evolution of integrated properties of clusterpopulations of Gieles et al. (2006, A&A, accepted), which predictsthat a truncated cluster initial mass function would result in a bendin, and a double power-law behaviour of, the integrated LF. Thecombination of the large field-of view and the high star clusterformation rate of M 51 make it possible to detect such a bend in the LF.Hence, we conclude that there exists a fundamental upper limit to themass of star clusters in M 51. Assuming a power-law cluster initial massfunction with exponentional cut-off of the form N d M ∝M-β exp(-M/M_C) d M, we find that MC =105 Mȯ. A direct comparison with the LF ofthe "Antennae" suggests that there MC =4×105 Mȯ.
| Background Consistency in Overlapping Images
We present an algorithm for achieving background consistency inoverlapping images. The algorithm consists of two main steps. First, theimages are interpolated to a common grid. Second, the cumulativepixel-by-pixel difference between the overlapping areas of all pairs ofimages is minimized with respect to the unknown constant offsets of theinput images. The images are corrected by adding the computed offsets.Optionally, detection and masking of bright objects in the images can beperformed prior to minimization. This option is especially useful forimages with a high density of cosmic-ray hits. We use simulated data tooptimize the algorithm in order to achieve a trade-off between the speedof execution and the quality of the background matching. We also showseveral examples of the application of this algorithm to real Spitzerdata. The algorithm has been implemented and successfully used by theSpitzer image processing package MOPEX (Makovoz & Khan) and deployedby the Spitzer automated pipeline.
| The progenitor of SN 2005cs in the Whirlpool Galaxy
The progenitor of SN 2005cs, in the galaxy M51, is identified inpre-explosion Hubble Space Telescope (HST) Advanced Camera for Surveys(ACS) Wide Field Channel (WFC) imaging. Differential astrometry, withpost-explosion ACS High Resolution Channel (HRC) F555W images, permittedthe identification of the progenitor with an accuracy of 0.006 arcsec.The progenitor was detected in the F814W pre-explosion image with I=23.3 +/- 0.2, but was below the detection thresholds of the F435W andF555W images, with B < 24.8 and V < 25 at 5σ. Limits werealso placed on the U- and R-band fluxes of the progenitor frompre-explosion HST Wide Field Planetary Camera 2 (WFPC2) F336W and F675Wimages. Deep images in the infrared from the Near Infra-red Imager(NIRI) on the Gemini North Telescope were taken 2 months prior toexplosion, but the progenitor is not clearly detected on these. Theupper limits for the JHK magnitudes of the progenitor were J < 21.9,H < 21.1 and K < 20.7. Despite having a detection in only oneband, a restrictive spectral energy distribution of the progenitor starcan be constructed and a robust case is made that the progenitor was ared supergiant with spectral type between mid-K and late-M. The spectralenergy distribution allows a region in the theoreticalHertzsprung-Russell diagram to be determined that must contain theprogenitor star. The initial mass of the star is constrained to beMZAMS= 9+3-2Msolar, which isvery similar to the identified progenitor of the Type II-P SN 2003gd,and also consistent with upper mass limits placed on five other similarsupernovae. The upper limit in the deep K-band image is significant inthat it allows us to rule out the possibility that the progenitor was asignificantly higher mass object enshrouded in a dust cocoon before corecollapse. This is further evidence that the trend for Type II-Psupernovae to arise in low- to moderate-mass red supergiants is real.
| XMM-Newton observations of the interacting galaxy pairs NGC 7771/0 and NGC 2342/1
We present XMM-Newton X-ray observations of the interacting galaxy pairsNGC 7771/7770 and NGC 2342/2341. In NGC 7771, for the first time we areable to resolve the X-ray emission into a bright central source plus twobright (LX > 1040 erg s-1)ultraluminous X-ray sources (ULXs) located either end of the bar. In thebright central source (LX~ 1041 ergs-1), the soft emission is well-modelled by a two-temperaturethermal plasma with kT= 0.4/0.7 keV. The hard emission is modelled witha flat absorbed power-law (Γ~ 1.7, NH~ 1022cm-2), and this together with a low-significance (1.7σ)~ 300 eV equivalent width emission line at ~6 keV are the firstindications that NGC 7771 may host a low-luminosity AGN. For the barULXs, a power-law fit to X-1 is improved at the 2.5σ level withthe addition of a thermal plasma component (kT~ 0.3 keV), while X-2 isimproved only at the 1.3σ level with the addition of a discblackbody component with Tin~ 0.2 keV. Both sources arevariable on short time-scales implying that their emission is dominatedby single accreting X-ray binaries (XRBs). The three remaining galaxies,NGC 7770, NGC 2342 and NGC 2341, have observed X-ray luminosities of0.2, 1.8 and 0.9 × 1041 erg s-1,respectively (0.3-10 keV). Their integrated spectra are alsowell-modelled by multi-temperature thermal plasma components with kT=0.2-0.7 keV, plus power-law continua with slopes of Γ= 1.8-2.3that are likely to represent the integrated emission of populations ofXRBs as observed in other nearby merger systems. A comparison with otherisolated, interacting and merging systems shows that all four galaxiesfollow the established correlations for starburst galaxies betweenX-ray, far-infrared and radio luminosities, demonstrating that theirX-ray outputs are dominated by their starburst components.
| Digital Image Reconstruction: Deblurring and Denoising
Digital image reconstruction is a robust means by which the underlyingimages hidden in blurry and noisy data can be revealed. The mainchallenge is sensitivity to measurement noise in the input data, whichcan be magnified strongly, resulting in large artifacts in thereconstructed image. The cure is to restrict the permitted images. Thisreview summarizes image reconstruction methods in current use.Progressively more sophisticated image restrictions have been developed,including (a) filtering the input data, (b) regularization by globalpenalty functions, and (c) spatially adaptive methods that impose avariable degree of restriction across the image. The most reliablereconstruction is the most conservative one, which seeks the simplestunderlying image consistent with the input data. Simplicity iscontext-dependent, but for most imaging applications, the simplestreconstructed image is the smoothest one. Imposing the maximum,spatially adaptive smoothing permitted by the data results in the bestimage reconstruction.
| 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.
| XMM-Newton View of the Ultraluminous X-Ray Sources in M51
We present results based on XMM-Newton observations of the nearby spiralgalaxy M51 (NGC 5194 and NGC 5195). We confirm the presence of the sevenknown ultraluminous X-ray sources (ULXs) with luminosities exceeding theEddington luminosity for a 10 Msolar black hole, alow-luminosity active galactic nucleus (LLAGN) with 2-10 keV luminosityof 1.6×1039 ergs s-1, and soft thermalextended emission from NGC 5194 detected with Chandra. In addition, wealso detected a new ULX with luminosity of ~1039 ergss-1. We have studied the spectral and temporal properties ofthe LLAGN and eight ULXs in NGC 5194 and an ULX in NGC 5195. Two ULXs inNGC 5194 show evidence for short-term variability, and all but two ULXsvary on long timescales (over a baseline of ~2.5 yr), providing strongevidence that these are accreting sources. One ULX in NGC 5194, source69, shows possible periodic behavior in its X-ray flux. We derive aperiod of 5925+/-200 s at a confidence level of 95% on the basis ofthree cycles. This period is lower than the period of 7620+/-500 sderived from a Chandra observation in 2000. The higher effective area ofXMM-Newton enables us to identify multiple components in the spectra ofULXs. Most ULXs require at least two components, a power law and a softX-ray excess component that is modeled by an optically thin plasma or amulticolor disk blackbody (MCD). However, the soft excess emissionsinferred from all ULXs except source 69 are unlikely to be physicallyassociated with the ULXs, as their strengths are comparable to that ofthe surrounding diffuse emission. The soft excess emission of source 69is well described either by a two-temperature MEKAL plasma or asingle-temperature MEKAL plasma (kT~690 eV) and an MCD (kT~170 eV). TheMCD component suggests a cooler accretion disk compared to those inGalactic X-ray binaries, consistent with those expected forintermediate-mass black holes (IMBHs). An iron Kα line (EW~700 eV)or K absorption edge at ~7.1 keV is present in the EPIC pn spectrum ofsource 26. The spectrum of the ULX in NGC 5195, source 12, is consistentwith a simple power law. The LLAGN in NGC 5194 shows an extremely flathard X-ray power law (Γ~0.7), a narrow iron Kα line at 6.4keV (EW~3 keV), and strong soft X-ray excess emission. The full-bandspectrum is well described by a two-component MEKAL plasma andreflection from cold material such as a putative torus.
| Star Formation in NGC 5194 (M51a): The Panchromatic View from GALEX to Spitzer
Far-ultraviolet to far-infrared images of the nearby galaxy NGC 5194(M51a), from a combination of space-based (Spitzer, GALEX, and HubbleSpace Telescope) and ground-based data, are used to investigate localand global star formation and the impact of dust extinction. The Spitzerdata provide unprecedented spatial detail in the infrared, down to sizes~500 pc at the distance of NGC 5194. The multiwavelength set is used totrace the relatively young stellar populations, the ionized gas, and thedust absorption and emission in H II-emitting knots, over 3 orders ofmagnitude in wavelength range. As is common in spiral galaxies, dustextinction is high in the center of the galaxy (AV~3.5 mag),but its mean value decreases steadily as a function of galactocentricdistance, as derived from both gas emission and stellar continuumproperties. In the IR/UV-UV color plane, the NGC 5194 H II knots showthe same trend observed for normal star-forming galaxies, having a muchlarger dispersion (~1 dex peak to peak) than starburst galaxies. Weidentify the dispersion as due to the UV emission predominantly tracingthe evolved, nonionizing stellar population, up to ages ~50-100 Myr.While in starbursts the UV light traces the current star formation rate(SFR), in NGC 5194 it traces a combination of current and recent pastSFRs. Possibly, mechanical feedback from supernovae is less effective atremoving dust and gas from the star formation volume in normalstar-forming galaxies than in starbursts because of the typically lowerSFR densities in the former. The application of the starburst opacitycurve for recovering the intrinsic UV emission (and deriving SFRs) inlocal and distant galaxies appears therefore appropriate only for SFRdensities >~1 Msolar yr-1 kpc-2.Unlike the UV emission, the monochromatic 24 μm luminosity is anaccurate local SFR tracer for the H II knots in NGC 5194, with apeak-to-peak dispersion of less than a factor of 3 relative to hydrogenemission line tracers; this suggests that the 24 μm emission carriersare mainly heated by the young, ionizing stars. However, preliminaryresults show that the ratio of the 24 μm emission to the SFR variesby a factor of a few from galaxy to galaxy; this variation needs to beunderstood and carefully quantified before the 24 μm luminosity canbe used as an SFR tracer for galaxy populations. While also correlatedwith star formation, the 8 μm emission is not directly proportionalto the number of ionizing photons; it is overluminous, by up to a factorof ~2, relative to the galaxy's average in weakly ionized regions and isunderluminous, by up to a factor of ~3, in strongly ionized regions.This confirms earlier suggestions that the carriers of the 8 μmemission are heated by more than one mechanism.Based on observations obtained with the Spitzer Space Telescope and withGALEX.
| 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.
| Light and Motion in the Local Volume
Using high-quality data on 149 galaxies within 10 Mpc, I find nocorrelation between luminosity and peculiar velocity at all. There is nounequivocal sign on scales of 1-2 Mpc of the expected gravitationaleffect of the brightest galaxies, in particular infall toward groups, orof infall toward the supergalactic plane on any scale. Either darkmatter is not distributed in the same way as luminous matter in thisregion, or peculiar velocities are not due to fluctuations in mass. Thesensitivity of peculiar velocity studies to the background model ishighlighted.
| A Chandra Snapshot Survey of Infrared-bright LINERs: A Possible Link Between Star Formation, Active Galactic Nucleus Fueling, and Mass Accretion
We present results from a high-resolution X-ray imaging study of nearbyLINERs observed by ACIS on board Chandra. This study complements andextends previous X-ray studies of LINERs, focusing on the underexploredpopulation of nearby dust-enshrouded infrared-bright LINERs. The sampleconsists of 15 IR-bright LINERs (LFIR/LB>3),with distances that range from 11 to 26 Mpc. Combining our sample withprevious Chandra studies, we find that ~51% (28/55) of the LINERsdisplay compact hard X-ray cores. The nuclear 2-10 keV luminosities ofthe galaxies in this expanded sample range from ~2×1038to ~2×1044 ergs s-1. We find that the mostextreme IR-faint LINERs are exclusively active galactic nuclei (AGNs).The fraction of LINERs containing AGNs appears to decrease with IRbrightness and increase again at the highest values ofLFIR/LB. We find that of the 24 LINERs showingcompact nuclear hard X-ray cores in the expanded sample that wereobserved at Hα wavelengths, only eight actually show evidence of abroad line. Similarly, of the 14 LINERs showing compact nuclear hardX-ray cores with corresponding radio observations, only eight display acompact flat spectrum radio core. These findings emphasize the need forhigh-resolution X-ray imaging observations in the study of IR-brightLINERs. Finally, we find an intriguing trend in the Eddington ratioversus LFIR and LFIR/LB for theAGN-LINERs in the expanded sample that extends over 7 orders ofmagnitude in L/LEdd. This correlation may imply a linkbetween black hole growth, as measured by the Eddington ratio, and thestar formation rate, as measured by the far-IR luminosity andIR-brightness ratio. If the far-IR luminosity is an indicator of themolecular gas content in our sample of LINERs, our results may furtherindicate that the mass accretion rate scales with the host galaxy's fuelsupply. We discuss the potential implications of our results in theframework of black hole growth and AGN fueling in low-luminosity AGNs.
| Properties of Resolved Star Clusters in M51
We present a study of compact star clusters in the nearby pair ofinteracting galaxies NGC 5194/5195 (M51), based on multifilter HubbleSpace Telescope (HST) WFPC2 archival images. We have detected ~400isolated, resolved clusters in five HST WFPC2 fields of the two-galaxysystem. Due to our requirement that the clusters be detected based onlyon their morphology, which results in the selection of relativelyisolated objects, we estimate that we are missing the majority (by afactor of 4-6) of clusters younger than ~10 Myr due to the extremecrowding in the spiral arms and star-forming regions. Hence, we focus onthe cluster population older than 10 Myr. An age distribution of thedetected clusters shows a broad peak between 100 and 500 Myr, which isconsistent with the crossing times of the companion galaxy NGC 5195through the NGC 5194 disk estimated in both single- and multiple-passagedynamical models. We estimate that the peak contains ~2.2-2.5 times moreclusters than expected from a constant rate of cluster formation overthis time interval. While there is also evidence for individual peaksnear 100 and 500 Myr in the cluster age distribution (consistent withthe predictions of multiple-passage models), this result requiresverification. We estimate the effective radii of our sample clusters andfind a median value of ~3-4 pc. In addition, we see correlations of(increasing) cluster size with cluster mass (with a best-fit slope of0.14+/-0.03) at the ~4 σ level, and with cluster age (0.06+/-0.02)at the 3 σ level. Finally, we report for the first time thediscovery of faint, extended star clusters in the companion, NGC 5195,an SB0 galaxy. These have red [(V-I)>1.0] colors and effective radii>7 pc, and are scattered over the disk of NGC 5195. Our resultstherefore indicate that NGC 5195 is currently the third known barredlenticular galaxy to have formed so-called faint fuzzy star clusters.
| The star cluster population of M 51. III. Cluster disruption and formation history
In this work we concentrate on the evolution of the cluster populationof the interacting galaxy M 51 (NGC 5194), more precisely the timescaleof cluster disruption and possible variations in the cluster formationrate. We present a method to compare observed age vs. mass numberdensity diagrams with predicted populations including various physicalinput parameters like the cluster initial mass function, clusterdisruption, cluster formation rate and star bursts. If we assume thatthe cluster formation rate increases at the moments of the encounterswith NGC 5195, we find an increase in the cluster formation rate of afactor of 3.0+4.6-1.2, combined with a disruptiontimescale which is slightly higher than when assuming a constantformation rate (t4 =2.0+2.3-1.1×108 yr vs.1.0+0.6-0.5×108 yr). The measuredcluster disruption time is a factor of 5 shorter than expected ontheoretical grounds. This implies that the disk of M 51 is not apreferred location for survival of young globular clusters, since evenclusters with masses on the order of 106 Mȯwill be destroyed within a few Gyr.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| The star cluster population of M 51. II. Age distribution and relations among the derived parameters
We use archival Hubble Space Telescope observations of broad-band imagesfrom the ultraviolet (F255W-filter) through the near infrared (NICMOSF160W-filter) to study the star cluster population of the interactingspiral galaxy M 51. We obtain age, mass, extinction, and effectiveradius estimates for 1152 star clusters in a region of ~7.3 × 8.1kpc centered on the nucleus and extending into the outer spiral arms. Inthis paper we present the data set and exploit it to determine the agedistribution and relationships among the fundamental parameters (i.e.age, mass, effective radius). We show the critical dependence of the agedistribution on the sample selection, and confirm that using a constantmass cut-off, above which the sample is complete for the entire agerange of interest, is essential. In particular, in this sample we arecomplete only for masses above 5×104~Mȯ for the last 1 Gyr. Using this datasetwe find: i) that the cluster formation rate seems to have had a largeincrease ~50-70 Myr ago, which is coincident with the suggested secondpassage of its companion, NGC 5195; ii) a large number of extremelyyoung (<10 Myr) star clusters, which we interpret as a population ofunbound clusters of which a large majority will disrupt within the next~10 Myr; and iii) that the distribution of cluster sizes can be wellapproximated by a power-law with exponent, -η = -2.2 ± 0.2,which is very similar to that of Galactic globular clusters, indicatingthat cluster disruption is largely independent of cluster radius. Inaddition, we have used this dataset to search for correlations among thederived parameters. In particular, we do not find any strong trendsbetween the age and mass, mass and effective radius, nor between thegalactocentric distance and effective radius. There is, however, astrong correlation between the age of a cluster and its extinction, withyounger clusters being more heavily reddened than older clusters.
| Starbursting nuclear CO disks of early-type spiral galaxies
We have initiated the first CO interferometer survey of early-typespiral galaxies (S0-Sab). We observed five early-type spiral galaxieswith HII nuclei (indicating circumnuclear starburst activities). Theseobservations indicate gas masses for the central kiloparsec of 1{-}5%of the dynamical masses. Such low gas mass fractions suggest thatlarge-scale gravitational instability in the gas is unlikely to be thedriving cause for the starburst activities. We estimated Toomre Q valuesand found that these galaxies have Q>1 (mostly >3) within thecentral kiloparsec, indicating that the gas disks are globallygravitationally stable. From the brightness temperatures of the COemission we estimated the area filling factor of the gas disks withinthe central kiloparsec to be about 0.05. This small value indicates theexistence of lumpy structure, i.e. molecular clouds, in theglobally-gravitationally stable disks. The typical surface density ofthe molecular clouds is as high as 3000 {Mȯ} {pc}-2. In the light of these new observations, we reconsiderthe nature of the Toomre Q criterion, and conclude that the Toomre Qparameter from CO observations indicates neither star formation normolecular cloud formation. This argument should be valid not only forthe circumnuclear disks but also for any region in galactic disks. Wetentatively explore an alternative model as an initiating mechanism ofstar formation. Cloud-cloud collisions might account for the active starformation.
| 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
| Structural parameters of nearby emission-line galaxies
We present the results of an investigation on the main structuralproperties derived from VRI and Hα surface photometry of galaxieshosting nuclear emission-line regions [including Seyfert 1, Seyfert 2,low-ionization nuclear emission region (LINER) and starburst galaxies]as compared with normal galaxies. Our original sample comprises 22active galaxies, four starbursts and one normal galaxy and has beenextended with several samples obtained from the literature. Bulge anddisc parameters, along with the bulge-to-disc luminosity ratio, havebeen derived applying an iterative procedure. The resulting parametershave been combined with additional data in order to reach astatistically significant sample. We find some differences in the bulgedistribution across the different nuclear types that could implyfamilies of bulges with different physical properties. Bulge and disccharacteristic colours have been defined and derived for our sample andcompared with a control sample of early-type objects. The resultssuggest that bulge and disc stellar populations are comparable in normaland active galaxies.
| Visual performance in astronomy near the scotopic threshold. Part 2: vision versus CCD.
Not Available
| HI and Hot Gas in the Outskirts of the M81 Group
Results are presented from a wide area, high resolution HI synthesissurvey of the outer regions of the nearby M81 group, where internal(galactic) and external (group-related) evolution processes can bestudied simultaneously in great detail. The survey encompasses the starforming dwarf galaxies M81dwA, UGC4483, and HoII, where evidence of rampressure stripping was recently discovered. The data do not reveal anyintergalactic HI, but the outer parts of HoII are reminiscent of tidaltails. We argue however that those structures are equally consistentwith the latest ram pressure models including cooling. The case for ahot intergalactic medium in this poor, spiral-only group is thus stillopen. The survey also puts tight constraints on possible counterparts tothe local high velocity cloud population in an external group, reachinga 3σ column density of 1019 atom cm-2 and a6σ limiting mass of 1.5×105 Msun.
| Fire and Ice: Spitzer Infrared Spectrograph (IRS) Mid-Infrared Spectroscopy of IRAS F00183-7111
We report the detection of strong absorption and weak emission featuresin the 4-27 μm Spitzer Infrared Spectrograph (IRS) spectrum of thedistant ultraluminous infrared galaxy IRAS F00183-7111 (z=0.327). Theabsorption features of CO2 and CO gas, water ice,hydrocarbons, and silicates are indicative of a strongly obscured(A9.6>=5.4 AV>=90) and complex line of sightthrough both the hot diffuse interstellar medium and shielded coldmolecular clouds toward the nuclear power source. From the profile ofthe 4.67 μm CO fundamental vibration mode, we deduce that theabsorbing gas is dense (n~106 cm-3) and warm (720K) and has a CO column density of ~1019.5 cm-2,equivalent to NH~1023.5 cm-2. The hightemperature and density, as well as the small inferred size (<0.03pc), locates this absorbing gas close to the power source of thisregion. Weak emission features of molecular hydrogen, polycyclicaromatic hydrocarbons (PAHs), and Ne+, likely associated withstar formation, are detected against the 9.7 μm silicate feature,indicating an origin away from the absorbing region. Based on the 11.2μm PAH flux, we estimate the star formation component to beresponsible for up to 30% of the IR luminosity of the system. While ourmid-infrared spectrum shows no telltale signs of active galactic nucleus(AGN) activity, the similarities to the mid-infrared spectra of deeplyobscured sources (e.g., NGC 4418) and AGN hot dust (e.g., NGC 1068), aswell as evidence from other wavelength regions, suggest that the powersource hiding behind the optically thick dust screen may well be aburied AGN.
| A Uniform Database of 2.2-16.5 μm Spectra from the ISOCAM CVF Spectrometer
We present all ISOCAM circular variable filter (CVF) spectra that covermore than one-third of the 2.2-16.5 μm spectral range of theinstrument. The 364 spectra have been classified according to theclassification system of Kraemer et al., as modified by Hodge et al. toaccount for the shorter wavelength range. Prior to classification, thespectra were processed and recalibrated to create a uniform database.Aperture photometry was performed at each wavelength centered on thebrightest position in each image field and the various spectral segmentsmerged into a single spectrum. The aperture was the same for all scalesizes of the images. Since this procedure differs fundamentally fromthat used in the initial ISOCAM calibration, a recalibration of thespectral response of the instrument was required for the aperturephotometry. The recalibrated spectra and the software used to createthem are available to the community on-line via the ISO Data Archive.Several new groups were added to the KSPW system to describe spectrawith no counterparts in either the SWS or PHT-S databases: CA, E/SA,UE/SA, and SSA. The zodiacal dust cloud provides the most commonbackground continuum to the spectral features, visible in almost 40% ofthe processed sources. The most characteristic and ubiquitous spectralfeatures observed in the CVF spectral atlas are those of theunidentified infrared bands (UIR), which are typically attributed toultraviolet-excited fluorescence of large molecules containing aromatichydrocarbons. The UIR features commonly occur superimposed on thezodiacal background (18%) but can also appear in conjunction with otherspectral features, such as fine-structure emission lines or silicateabsorption. In at least 13 of the galaxies observed, the pattern of UIRemission features has been noticeably shifted to longer wavelengths.Based on observations with the Infrared Space Observatory, a EuropeanSpace Agency (ESA) project with instruments funded by ESA Member States(especially the Principal Investigator countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of theInstitute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei
Using the Green Bank Telescope, we have conducted a survey for 1.3 cmwater maser emission toward the nuclei of nearby active galaxies, themost sensitive large survey for H2O masers to date. Among 145galaxies observed, maser emission was newly detected in 11 sources andconfirmed in one other. Our survey targeted nearby (v<12,000 kms-1), mainly type 2 active galactic nuclei (AGNs) north ofδ=-20deg and includes a few additional sources as well.We find that more than one-third of Seyfert 2 galaxies have strong maseremission, although the detection rate declines beyond v~5000 kms-1 because of sensitivity limits. Two of the masersdiscovered during this survey are found in unexpected hosts: NGC 4151(Seyfert 1.5) and NGC 2782 (starburst). We discuss the possiblerelations between the large X-ray column to NGC 4151 and a possiblehidden AGN in NGC 2782 to the detected masers. Four of the masersdiscovered here, NGC 591, NGC 4388, NGC 5728, and NGC 6323, havehigh-velocity lines symmetrically spaced about the systemic velocity, alikely signature of molecular gas in a nuclear accretion disk. The masersource in NGC 6323, in particular, reveals the classic spectrum of a``disk maser'' represented by three distinct groups of Dopplercomponents. Future single-dish and VLBI observations of these fourgalaxies could provide a measurement of the distance to each galaxy andof the Hubble constant, independent of standard candle calibrations.
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