Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Chandra and ROSAT Observations of NGC 5044: Profile of Dark Halos in Galaxy Groups
We combined spatially resolved Chandra data with the ROSAT data toconstrain the dark-matter distribution in the galaxy group NGC 5044.Within 250 h-150kpc, the total mass is found to be 1.6 × 1013 Mȯ, 12% of whichconstitutes baryonic mass. Within the inner central regions, the totalmass profile exhibits a double structure, typical for groups containinga cD galaxy. Following previous studies of mostly rich galaxy clusters,we studied in detail the nature of such a double structure, whereby weinferred likely interface between the cD galaxy and the surroundinggalaxies. For this interesting group, we determined for the first timethe galaxy-group interface, which is around 7.5kpc from the peak of theX-ray emission. The total mass internal to this interface radius isfound to be 7.1 × 1010 Mȯ. Beyondthis radius, the total mass profile becomes DM-dominated and thecorresponding DM profile is reasonably fitted with the NFW model,yielding results consistent with the observed scatter expected for CDMhalos. A power-law fit to the DM mass profile gives α = 1.88± 0.32, a slope that is within the observed range, but issignificantly larger than that of low surface brightness galaxies andself-interacting DM halos.
| Oxygen abundances in the most oxygen-rich spiral galaxies
Oxygen abundances in the spiral galaxies expected to be richest inoxygen are estimated. The new abundance determinations are based on therecently discovered ff relation between auroral and nebular oxygen-linefluxes in high-metallicity HII regions. We find that the maximumgas-phase oxygen abundance in the central regions of spiral galaxies is12+log(O/H) ~ 8.75. This value is significantly lower (by a factor of>~5) than the previously accepted value. The central oxygen abundancein the Milky Way is similar to that in other large spirals.
| Mining for normal galaxies in the first XMM-Newton Serendipitous Source Catalog
This paper uses the first XMM-Newton Serendipitous Source Catalogcompiled by the XMM-Newton Science Centre to identify low-z X-rayselected normal galaxy candidates. Our sample covers a total area of~6deg2 to the 0.5-2keV limit~10-15ergs-1cm-2. A total of 23 sourcesare selected on the basis of low X-ray to optical flux ratiologfX/fopt < -2, soft X-ray spectral propertiesand optical spectra, when available, consistent with stellar formationrather than active galactic nucleus (AGN) processes. This sample iscombined with similarly selected systems from the Needles in theHaystack Survey to provide a total of 46 unique (z<~ 0.2) X-raydetected normal galaxies, the largest low-z sample yet available. Thisis first used to constrain the normal galaxy logN-logS at bright fluxes(10-15-10-13ergs-1cm-2). Weestimate a slope of -1.46 +/- 0.13 for the cumulative number countsconsistent with the Euclidean prediction. We further combine our samplewith 23 local (z<~ 0.2) galaxies from the Chandra Deep Field-Northand -South surveys to construct the local X-ray luminosity function ofnormal galaxies. A Schechter form provides a good fit to the data with abreak at logL*=41.02+0.14-0.12ergs-1 and a slope ofα=-1.76 +/- 0.10. Finally, for the sample of 46 systems, weexplore the association between X-ray luminosity and host galaxyproperties, such as star formation rate (SFR) and stellar mass. We findthat the LX of the emission-line systems correlates withHα luminosity and 1.4-GHz radio power, both providing an estimateof the current SFR. In the case of early-type galaxies withabsorption-line optical spectra, we use the K band as an approximationof stellar mass and find a correlation of the formLX~L1.5K. This is flatter than theLX-LB relation for local ellipticals. This may bedue to either LK providing a better approximation of galaxymass or selection effects biasing our sample against very luminousearly-type galaxies, LX >1042ergs-1.
| 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.
| 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.
| 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.
| X-ray observations of the edge-on star-forming galaxy NGC 891 and its supernova SN1986J
We present XMM-Newton observations of NGC 891, a nearby edge-on spiralgalaxy. We analyse the extent of the diffuse emission emitted from thedisc of the galaxy, and find that it has a single-temperature profilewith best-fitting temperature of 0.26 keV, though the fit of adual-temperature plasma with temperatures of 0.08 and 0.30 keV is alsoacceptable. There is a considerable amount of diffuse X-ray emissionprotruding from the disc in the north-west direction out toapproximately 6 kpc. We analyse the point-source population using aChandra observation, using a maximum-likelihood method to find that theslope of the cumulative luminosity function of point sources in thegalaxy is -0.77+0.13-0.1. Using a sample of otherlocal galaxies, we compare the X-ray and infrared properties of NGC 891with those of `normal' and starburst spiral galaxies, and conclude thatNGC 891 is most likely a starburst galaxy in a quiescent state. Weestablish that the diffuse X-ray luminosity of spirals scales with thefar-infrared luminosity asLX~L0.87+/-0.07FIR, except for extremestarbursts, and NGC 891 does not fall in the latter category. We studythe supernova SN1986J in both XMM-Newton and Chandra observations, andfind that the X-ray luminosity has been declining with time more steeplythan expected (LX~t-3).
| A study of the Type II-P supernova 2003gd in M74
We present photometric and spectroscopic data of the Type II-P supernova(SN II-P) 2003gd, which was discovered in M74 close to the end of itsplateau phase. SN 2003gd is the first Type II supernova (SN) to have adirectly confirmed red supergiant (RSG) progenitor. We compare SN 2003gdto SN 1999em, a similar SN II-P, and estimate an explosion date of 2003March 18. We determine a reddening towards the SN of E(B-V) = 0.14 +/-0.06, using three different methods. We also calculate three newdistances to M74 of 9.6 +/- 2.8, 7.7 +/- 1.7 and 9.6 +/- 2.2Mpc. Theformer was estimated using the standard candle method (SCM), for Type IIsupernovae (SNe II), and the latter two using the brightest supergiantsmethod (BSM). When combined with existing kinematic and BSM distanceestimates, we derive a mean value of 9.3 +/- 1.8Mpc. SN 2003gd was foundto have a lower tail luminosity compared with other normal Type II-Psupernovae (SNe II-P) bringing into question the nature of this SN. Wepresent a discussion concluding that this is a normal SN II-P, which isconsistent with the observed progenitor mass of8+4-2 Msolar.
| 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.
| First Results from THINGS: The HI Nearby Galaxy Survey
We describe The HI Nearby Galaxy Survey (THINGS), the largestprogramever undertaken at the Very Large Array to perform 21-cm HIobservations of thehighest quality ( 7'', ≤ 5 km s^{-1}resolution) ofnearby galaxies. The goal of THINGS is to investigatekeycharacteristics related to galaxy morphology, star formation andmassdistribution across the Hubble sequence. A sample of 34 objectswithdistances between 3 and 10 Mpc will be observed, covering a widerangeof evolutionary stages and properties. Data from THINGSwillcomplement SINGS, the Spitzer Infrared Nearby Galaxy Survey. Forthe THINGS sample, high-quality observations at comparable resolutionwillthus be available from the X-ray regime through to the radio partofthe spectrum. THINGS data can be used to investigate issues such asthesmall-scale structure of the ISM, its three-dimensional structure,the(dark) matter distribution and processes leading to starformation. Todemonstrate the quality of the THINGS data products, wepresent someprelimary HI maps here of four galaxies from the THINGSsample.
| A Chandra Survey of Nearby Spiral Galaxies. I. Point Source Catalogs
Emission from discrete point sources dominates the X-ray luminosity inspiral galaxies. We present results from a survey of 11 nearby, nearlyface-on spiral galaxies with the Chandra X-ray Observatory. Thesegalaxies span the Hubble sequence for spirals, allowing insights intothe X-ray source population of many diverse systems. In this paper, wepresent source lists for the 11 galaxies along with fluxes,luminosities, X-ray colors, and variability properties. We brieflydiscuss X-ray luminosity functions and how they relate to star formationof the host galaxies. We also discuss source colors and variability andwhat these can tell us about the composition of the X-ray sourcepopulation.
| Evidence for Spectropolarimetric Diversity in Type Ia Supernovae
We present single-epoch, postmaximum spectropolarimetry of four Type Iasupernovae (SNe Ia) that span a range of spectral and photometricproperties: SN 2002bf and SN 2004dt exhibit unusually high-velocity (HV)absorption lines. SN 1997dt is probably somewhat subluminous, and SN2003du is slightly overluminous. We detect polarization modulationsacross strong lines in all four objects, demonstrating that all areintrinsically polarized. However, the nature and degree of thepolarization varies considerably. Including all SNe Ia studied thus far,the following order emerges in terms of increasing strength ofline-polarization features: ordinary/overluminous
| 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.
| Structure and star formation in disk galaxies. III. Nuclear and circumnuclear Hα emission
From Hα images of a carefully selected sample of 57 relativelylarge, Northern spiral galaxies with low inclination, we study thedistribution of the Hα emission in the circumnuclear and nuclearregions. At a resolution of around 100 parsec, we find that the nuclearHα emission in the sample galaxies is often peaked, andsignificantly more often so among AGN host galaxies. The circumnuclearHα emission, within a radius of two kpc, is often patchy inlate-type, and absent or in the form of a nuclear ring in early-typegalaxies. There is no clear correlation of nuclear or circumnuclearHα morphology with the presence or absence of a bar in the hostgalaxy, except for the nuclear rings which occur in barred hosts. Thepresence or absence of close bright companion galaxies does not affectthe circumnuclear Hα morphology, but their presence does correlatewith a higher fraction of nuclear Hα peaks. Nuclear rings occur inat least 21% (±5%) of spiral galaxies, and occur predominantly ingalaxies also hosting an AGN. Only two of our 12 nuclear rings occur ina galaxy which is neither an AGN nor a starburst host. We confirm thatweaker bars host larger nuclear rings. The implications of these resultson our understanding of the occurrence and morphology of massive starformation, as well as non-stellar activity, in the central regions ofgalaxies are discussed.
| Distribution of the oxygen abundance over the discs of eight spiral galaxies
Oxygen abundances in H II regions of eight spiral galaxies are derivedthrough the p-method using published spectrophotometric data (314spectra of H II regions in eight spiral galaxies). The values of theradial oxygen abundance gradients were determined. The search for aglobal asymmetry in oxygen abundance distributions over the disks ofgalaxies was carried out. We do not find a significant signs of globalasymmetry with one exception. In the galaxy NGC 2903, a compact areawith several H II regions is revealed in which the oxygen abundance isconsiderably less than the average oxygen abundance for the samedistance from the galaxy centre.
| Astrophysics in 2003
Five coherent sections appear this year, addressing solar physics,cosmology (with WMAP highlights), gamma-ray bursters (and theirassociation with Type Ia supernovae), extra-solar-system planets, andthe formation and evolution of galaxies (from reionization to assemblageof Local Group galaxies). There are also eight incoherent sections thatdeal with other topics in stellar, galactic, and planetary astronomy andthe people who study them.
| Chandra and XMM-Newton observations of NGC 4214: the hot interstellar medium and the luminosity function of dwarf starbursts
We present results from Chandra and XMM-Newton X-ray observations of NGC4214, a nearby dwarf starburst galaxy containing several young regionsof very active star-formation. Starburst regions are known to beassociated with diffuse X-ray emission, and in this case the X-rayemission from the galaxy shows an interesting morphological structurewithin the galaxy, clearly associated with the central regions of activestar formation. Of the two main regions of star formation in thisgalaxy, X-ray emission associated with the older is identified whereaslittle is detected from the younger, providing an insight into theevolutionary process of the formation of superbubbles around youngstellar clusters. The spectra of the diffuse emission from the galaxycan be fitted with a two-temperature-component thermal model with kT=0.14 keV and 0.52 keV, and analysis of this emission suggests that NGC4214 will suffer a blow-out in the future.The point source population of the galaxy has an X-ray luminosityfunction with a slope of -0.76. This result, together with those forother dwarf starburst galaxies (NGC 4449 and NGC 5253), was added to asample of luminosity functions for spiral and starburst galaxies. Theslope of the luminosity function of dwarf starbursts is seen to besimilar to that of their larger counterparts and clearly flatter thanthose seen in spirals. Further comparisons between the luminosityfunctions of starbursts and spiral galaxies are also made.
| The Ultraluminous X-Ray Source Population from the Chandra Archive of Galaxies
One hundred fifty-four discrete non-nuclear ultraluminous X-ray (ULX)sources, with spectroscopically determined intrinsic X-ray luminositiesgreater than 1039 ergs s-1, are identified in 82galaxies observed with Chandra's Advanced CCD Imaging Spectrometer.Source positions, X-ray luminosities, and spectral and timingcharacteristics are tabulated. Statistical comparisons between theseX-ray properties and those of the weaker discrete sources in the samefields (mainly neutron star and stellar-mass black hole binaries) aremade. Sources above ~1038 ergs s-1 display similarspatial, spectral, color, and variability distributions. In particular,there is no compelling evidence in the sample for a new and distinctclass of X-ray object such as the intermediate-mass black holes.Eighty-three percent of ULX candidates have spectra that can bedescribed as absorbed power laws with index <Γ>=1.74 andcolumn density =2.24×1021cm-2, or ~5 times the average Galactic column. About 20% ofthe ULXs have much steeper indices indicative of a soft, and likelythermal, spectrum. The locations of ULXs in their host galaxies arestrongly peaked toward their galaxy centers. The deprojected radialdistribution of the ULX candidates is somewhat steeper than anexponential disk, indistinguishable from that of the weaker sources.About 5%-15% of ULX candidates are variable during the Chandraobservations (which average 39.5 ks). Comparison of the cumulative X-rayluminosity functions of the ULXs to Chandra Deep Field results suggests~25% of the sources may be background objects, including 14% of the ULXcandidates in the sample of spiral galaxies and 44% of those inelliptical galaxies, implying the elliptical galaxy ULX population isseverely compromised by background active galactic nuclei. Correlationswith host galaxy properties confirm the number and total X-rayluminosity of the ULXs are associated with recent star formation andwith galaxy merging and interactions. The preponderance of ULXs instar-forming galaxies as well as their similarities to less-luminoussources suggest they originate in a young but short-lived populationsuch as the high-mass X-ray binaries with a smaller contribution (basedon spectral slope) from recent supernovae. The number of ULXs inelliptical galaxies scales with host galaxy mass and can be explainedmost simply as the high-luminosity end of the low-mass X-ray binarypopulation.
| Circumnuclear Structure and Black Hole Fueling: Hubble Space Telescope NICMOS Imaging of 250 Active and Normal Galaxies
Why are the nuclei of some galaxies more active than others? If mostgalaxies harbor a central massive black hole, the main difference isprobably in how well it is fueled by its surroundings. We investigatethe hypothesis that such a difference can be seen in the detailedcircumnuclear morphologies of galaxies using several quantitativelydefined features, including bars, isophotal twists, boxy and diskyisophotes, and strong nonaxisymmetric features in unsharp-masked images.These diagnostics are applied to 250 high-resolution images of galaxycenters obtained in the near-infrared with NICMOS on the Hubble SpaceTelescope. To guard against the influence of possible biases andselection effects, we have carefully matched samples of Seyfert 1,Seyfert 2, LINER, starburst, and normal galaxies in their basicproperties, taking particular care to ensure that each was observed witha similar average scale (10-15 pc pixel-1). Severalmorphological differences among our five different spectroscopicclassifications emerge from the analysis. The H II/starburst galaxiesshow the strongest deviations from smooth elliptical isophotes, whilethe normal galaxies and LINERs have the least disturbed morphology. TheSeyfert 2s have significantly more twisted isophotes than any othercategory, and the early-type Seyfert 2s are significantly more disturbedthan the early-type Seyfert 1s. The morphological differences betweenSeyfert 1s and Seyfert 2s suggest that more is at work than simply theviewing angle of the central engine. They may correspond to differentevolutionary stages.
| The Role of Pressure in Giant Molecular Cloud Formation
We examine the hypothesis that hydrostatic pressure alone determines theratio of atomic to molecular gas averaged over a particular radius indisk galaxies. The hypothesis implies that the transition radius, thelocation where the ratio is unity, should always occur at the same valueof stellar surface density in all galaxies. We examine data for 28galaxies and find that the stellar surface density at the transitionradius is indeed constant to within 40% at a value of 120Msolar pc-2. If the hypothesis can be confirmed atall radii within a large range of galaxy types and metallicities,combining it with the observed relation between the star formation rateand H2 surface density may enable us to derive a physicallymotivated star formation prescription with wide applicability.
| Diffuse X-Ray Emission in Spiral Galaxies
We compare the soft diffuse X-ray emission from Chandra images of 12nearby intermediate-inclination spiral galaxies to the morphology seenin Hα, molecular gas, and mid-infrared emission. We find thatdiffuse X-ray emission is often located along spiral arms in the outerparts of spiral galaxies but tends to be distributed in a more nearlyradially symmetric morphology in the center. The X-ray morphology in thespiral arms matches that seen in the mid-infrared or Hα and thusimplies that the X-ray emission is associated with recent active starformation. In the spiral arms there is a good correlation between thelevel of diffuse X-ray emission and that in the mid-infrared indifferent regions. The correlation between X-ray and mid-IR flux in thegalaxy centers is less strong. We also find that the central X-rayemission tends to be more luminous in galaxies with brighter bulges,suggesting that more than one process is contributing to the level ofcentral diffuse X-ray emission. We see no strong evidence for X-rayemission trailing the location of high-mass star formation in spiralarms. However, population synthesis models predict a high mechanicalenergy output rate from supernovae for a time period that is about 10times longer than the lifetime of massive ionizing stars, conflictingwith the narrow appearance of the arms in X-rays. The fraction ofsupernova energy that goes into heating the interstellar medium mustdepend on environment and is probably higher near sites of active starformation. The X-ray estimated emission measures suggest that the volumefilling factors and scale heights are low in the outer parts of thesegalaxies but higher in the galaxy centers. The differences between theX-ray properties and morphology in the centers and outer parts of thesegalaxies suggest that galactic fountains operate in outer galaxy disksbut that winds are primarily driven from galaxy centers.
| Old and Young X-Ray Point Source Populations in Nearby Galaxies
We have analyzed Chandra ACIS observations of 32 nearby spiral andelliptical galaxies and present the results of 1441 X-ray point sourcesthat were detected in these galaxies. The total point-source X-ray(0.3-8.0 keV) luminosity LXP is well correlated with theB-band, K-band, and FIR+UV luminosities of spiral host galaxies and iswell correlated with the B-band and K-band luminosities of ellipticalgalaxies. This suggests an intimate connection between LXPand both the old and young stellar populations, for which K and FIR+UVluminosities are reasonable proxies for the galaxy mass M and starformation rate SFR. We derive proportionality constantsα=1.3×1029 ergs s-1M-1solar and β=0.7×1039 ergss-1 (Msolar yr-1)-1, whichcan be used to estimate the old and young components from M and SFR,respectively. The cumulative X-ray luminosity functions for the pointsources have significantly different slopes. For the spiral andstarburst galaxies, γ~0.6-0.8, and for the elliptical galaxies,γ~1.4. This implies that the most luminous point sources-thosewith LX>~1038 ergss-1-dominate LXP for the spiral andstarburst galaxies. Most of the point sources have X-ray colors that areconsistent with soft-spectrum (photon index Γ~1-2) low-mass X-raybinaries, accretion-powered black hole high-mass X-ray binaries (BHHMXBs), or ultraluminous X-ray sources (ULXs, also known as IXOs). Werule out hard-spectrum neutron star HMXBs (e.g., accretion-powered X-raypulsars) as contributing much to LXP. Thus, for spirals,LXP is dominated by ULXs and BH HMXBs. We find no discernibledifference between the X-ray colors of ULXs(LX>=1039 ergs s-1) in spiralgalaxies and point sources withLX~1038-1039 ergs s-1. Weestimate that >~20% of all ULXs found in spirals originate from theolder (Population II) stellar populations, indicating that many of theULXs that have been found in spiral galaxies are in fact Population IIULXs, like those in elliptical galaxies. We find that LXPdepends linearly (within uncertainties) on both M and SFR for our samplegalaxies (M<~1011 Msolar and SFR<~10Msolar yr-1).
| The Origin and Distribution of Diffuse Hot Gas in the Spiral Galaxy NGC 3184
Deep Chandra exposures reveal the presence of diffuse X-ray emissionwith a luminosity of 1.3×1039 ergs s-1 fromthe spiral galaxy NGC 3184. This appears to be truly diffuse thermalemission distinct from the low-luminosity emission from low-mass X-raybinaries (LMXBs). While the unresolved emission from older LMXBs is moreuniformly distributed across the galaxy, the diffuse X-ray emission isconcentrated in areas of younger stellar populations and star-formingregions. The surface brightness of the diffuse emission over the spiralarms is 5 times greater than in off-arm regions, and 8 times brighter inH II regions than in non-H II regions. Spectral fits to the diffusethermal emission are consistent with a low-temperature component,T~1.5×106 K, plus a higher temperature component,T~5×106 K.
| A New Nonparametric Approach to Galaxy Morphological Classification
We present two new nonparametric methods for quantifying galaxymorphology: the relative distribution of the galaxy pixel flux values(the Gini coefficient or G) and the second-order moment of the brightest20% of the galaxy's flux (M20). We test the robustness of Gand M20 to decreasing signal-to-noise ratio (S/N) and spatialresolution and find that both measures are reliable to within 10% forimages with average S/N per pixel greater than 2 and resolutions betterthan 1000 and 500 pc, respectively. We have measured G andM20, as well as concentration (C), asymmetry (A), andclumpiness (S) in the rest-frame near-ultraviolet/optical wavelengthsfor 148 bright local ``normal'' Hubble-type galaxies (E-Sd) galaxies, 22dwarf irregulars, and 73 0.05
| Inner-truncated Disks in Galaxies
We present an analysis of the disk brightness profiles of 218 spiral andlenticular galaxies. At least 28% of disk galaxies exhibit innertruncations in these profiles. There are no significant trends oftruncation incidence with Hubble type, but the incidence among barredsystems is 49%, more than 4 times that for nonbarred galaxies. However,not all barred systems have inner truncations, and not allinner-truncated systems are currently barred. Truncations represent areal dearth of disk stars in the inner regions and are not an artifactof our selection or fitting procedures nor the result of obscuration bydust. Disk surface brightness profiles in the outer regions are wellrepresented by simple exponentials for both truncated and nontruncateddisks. However, truncated and nontruncated systems have systematicallydifferent slopes and central surface brightness parameters for theirdisk brightness distributions. Truncation radii do not appear tocorrelate well with the sizes or brightnesses of the bulges. Thissuggests that the low angular momentum material apparently missing fromthe inner disk was not simply consumed in forming the bulge population.Disk parameters and the statistics of bar orientations in our sampleindicate that the missing stars of the inner disk have not simply beenredistributed azimuthally into bar structures. The sharpness of thebrightness truncations and their locations with respect to othergalactic structures suggest that resonances associated with diskkinematics, or tidal interactions with the mass of bulge stars, might beresponsible for this phenomenon.
| Oxygen and nitrogen abundances in nearby galaxies. Correlations between oxygen abundance and macroscopic properties
We performed a compilation of more than 1000 published spectra of H IIregions in spiral galaxies. The oxygen and nitrogen abundances in each HII region were recomputed in a homogeneous way, using the P-method. Theradial distributions of oxygen and nitrogen abundances were derived. Thecorrelations between oxygen abundance and macroscopic properties areexamined. We found that the oxygen abundance in spiral galaxiescorrelates with its luminosity, rotation velocity, and morphologicaltype: the correlation with the rotation velocity may be slightlytighter. There is a significant difference between theluminosity-metallicity relationship obtained here and that based on theoxygen abundances determined through the R23-calibrations.The oxygen abundance of NGC 5457 recently determined using directmeasurements of Te (Kennicutt et al. \cite{Kennicutt2003})agrees with the luminosity-metallicity relationship derived in thispaper, but is in conflict with the luminosity-metallicity relationshipderived with the R23-based oxygen abundances. The obtainedluminosity-metallicity relation for spiral galaxies is compared to thatfor irregular galaxies. Our sample of galaxies shows evidence that theslope of the O/H - MB relationship for spirals (-0.079± 0.018) is slightly more shallow than that for irregulargalaxies (-0.139 ± 0.011). The effective oxygen yields wereestimated for spiral and irregular galaxies. The effective oxygen yieldincreases with increasing luminosity from MB -11 toMB -18 (or with increasing rotation velocity fromVrot 10 km s-1 to Vrot 100km s-1) and then remains approximately constant. Irregulargalaxies from our sample have effective oxygen yields lowered by afactor of 3 at maximum, i.e. irregular galaxies usually keep at least1/3 of the oxygen they manufactured during their evolution.Appendix, Tables \ref{table:refero}, \ref{table:referV}, and Figs.\ref{figure:sample2}-\ref{figure:sample5} are only available inelectronic form at http://www.edpsciences.org}
| The structure and environment of young stellar clusters in spiral galaxies
A search for stellar clusters has been carried out in 18 nearby spiralgalaxies, using archive images from the Wide Field Planetary Camera 2 onboard the Hubble Space Telescope. All of the galaxies have previouslybeen imaged from the ground in UBVI. A catalogue of structuralparameters, photometry and comments based on visual inspection of theclusters is compiled and used to investigate correlations betweencluster structure, environment, age and mass. Least-squares fits to thedata suggest correlations between both the full-width at half-maximum(FWHM) and half-light radius (Reff) of the clusters and theirmasses (M) at about the 3σ level. Although both relations show alarge scatter, the fits have substantially shallower slopes than for aconstant-density relation (size ∝ M1/3). However, manyof the youngest clusters have extended halos which make theReff determinations uncertain. There is no evidence forgalaxy-to-galaxy variations in the mean cluster sizes. In particular,the mean sizes do not appear to depend on the host galaxy star formationrate surface density. Many of the youngest objects (age <107 years) are located in strongly crowded regions, and about1/3-1/2 of them are double or multiple sources. The HST images are alsoused to check the nature of cluster candidates identified in a previousground-based survey. The contamination rate in the ground-based sampleis generally less than about 20%, but some cluster identificationsremain ambiguous because of crowding even with HST imaging, especiallyfor the youngest objects.Full Tables \ref{tab:all}-\ref{tab:hstphot}, and \ref{tab:gb} are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/537Based on observations obtained with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Deprojecting spiral galaxies using Fourier analysis. Application to the Frei sample
We present two methods that can be used to deproject spirals, based onFourier analysis of their images, and discuss their potential andrestrictions. Our methods perform particularly well for galaxies moreinclined than 50° or for non-barred galaxies moreinclined than 35°. They are fast and straightforward touse, and thus ideal for large samples of galaxies. Moreover, they arevery robust for low resolutions and thus are appropriate for samples ofcosmological interest. The relevant software is available from us uponrequest. We use these methods to determine the values of the positionand inclination angles for a sample of 79 spiral galaxies contained inthe Frei et al. (\cite{frei96}) sample. We compare our results with thevalues found in the literature, based on other methods. We findstatistically very good agreementTable 7 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/415/849
| Classifications of the Host Galaxies of Supernovae, Set II
Classifications on the DDO system are given for an additional 231 hostgalaxies of supernovae that have been discovered during the course ofthe Lick Observatory Supernova Search with the Katzman Automatic ImagingTelescope (KAIT). This brings the total number of hosts of supernovae(SNe) discovered (or independently rediscovered) by KAIT, which have sofar been classified on a homogeneous system, to 408. The probabilitythat SNe Ia and SNe II have a different distribution of host-galaxyHubble types is found to be 99.7%. A significant difference is alsofound between the distributions of the host galaxies of SNe Ia and ofSNe Ibc (defined here to include SNe Ib, Ib/c, and Ic). However, nosignificant difference is detected between the frequency distributionsof the host galaxies of SNe II and SNe IIn. This suggests that SNe IInare generally not SNe Ia embedded in circumstellar material that aremasquerading as SNe II. Furthermore, no significant difference is foundbetween the distribution of the Hubble types of the hosts of SNe Ibc andof SNe II. Additionally, SNe II-P and SNe II-L are found to occur amongsimilar stellar populations. The ratio of the number of SNe Ia-pec tonormal SNe Ia appears to be higher in early-type galaxies than it is ingalaxies of later morphological types. This suggests that the ancestorsof SNe Ia-pec may differ systematically in age or composition from theprogenitors of normal SNe Ia. Unexpectedly, five SNe of Types Ib/c, II,and IIn (all of which are thought to have massive progenitors) are foundin host galaxies that are nominally classified as types E and S0.However, in each case the galaxy classification is uncertain, or newlyinspected images show evidence suggesting a later classification. Amongthese five objects, NGC 3720, the host galaxy of SN 2002at, wasapparently misidentified in the Carnegie Atlas of Galaxies.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
Katalógusok és elnevezések:
|
