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|The Survey for Ionization in Neutral Gas Galaxies. I. Description and Initial Results|
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG),a census of star formation in H I-selected galaxies. The survey consistsof Hα and R-band imaging of a sample of 468 galaxies selected fromthe H I Parkes All Sky Survey (HIPASS). The sample spans three decadesin H I mass and is free of many of the biases that affect otherstar-forming galaxy samples. We present the criteria for sampleselection, list the entire sample, discuss our observational techniques,and describe the data reduction and calibration methods. This paperfocuses on 93 SINGG targets whose observations have been fully reducedand analyzed to date. The majority of these show a single emission linegalaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs ina single field. All of the targets in this sample are detected inHα, indicating that dormant (non-star-forming) galaxies withMHI>~3×107 Msolar are veryrare. A database of the measured global properties of the ELGs ispresented. The ELG sample spans 4 orders of magnitude in luminosity(Hα and R band), and Hα surface brightness, nearly 3 ordersof magnitude in R surface brightness and nearly 2 orders of magnitude inHα equivalent width (EW). The surface brightness distribution ofour sample is broader than that of the Sloan Digital Sky Survey (SDSS)spectroscopic sample, the EW distribution is broader than prism-selectedsamples, and the morphologies found include all common types ofstar-forming galaxies (e.g., irregular, spiral, blue compact dwarf,starbursts, merging and colliding systems, and even residual starformation in S0 and Sa spirals). Thus, SINGG presents a superior censusof star formation in the local universe suitable for further studiesranging from the analysis of H II regions to determination of the localcosmic star formation rate density.
|Accretion and Nuclear Activity of Quiescent Supermassive Black Holes. II. Optical Study and Interpretation|
Our X-ray study of the nuclear activity in a new sample of six quiescentearly-type galaxies, as well as in a larger sample from the literature,confirmed (Paper I) that the Bondi accretion rate of diffuse hot gas isnot a good indicator of the SMBH X-ray luminosity. Here we suggest thata more reliable estimate of the accretion rate must include the gasreleased by the stellar population inside the sphere of influence of theSMBH, in addition to the Bondi inflow of hot gas across that surface. Weuse optical surface brightness profiles to estimate the mass-loss ratefrom stars in the nuclear region: we show that for our sample ofgalaxies it is an order of magnitude higher (~10-4 to10-3 Msolar yr-1) than the Bondi inflowrate of hot gas, as estimated from Chandra (Paper I). Only by takinginto account both sources of fuel can we constrain the true accretionrate, the accretion efficiency, and the power budget. Radiativelyefficient accretion is ruled out, for quiescent SMBHs. For typicalradiatively inefficient flows, the observed X-ray luminosities of theSMBHs imply accretion fractions ~1%-10% (i.e., ~90%-99% of the availablegas does not reach the SMBH) for at least five of our six targetgalaxies and most of the other galaxies with known SMBH masses. Wediscuss the conditions for mass conservation inside the sphere ofinfluence, so that the total gas injection is balanced by accretion plusoutflows. We show that a fraction of the total accretion power(mechanical plus radiative) would be sufficient to sustain aself-regulating, slow outflow that removes from the nuclear region allthe gas that does not sink into the BH (``BH feedback''). The rest ofthe accretion power may be carried out in a jet or advected. We alsodiscuss scenarios that would lead to an intermittent nuclear activity.
|Accretion and Nuclear Activity of Quiescent Supermassive Black Holes. I. X-Ray Study|
We have studied the nuclear activity in a sample of six quiescentearly-type galaxies, with new Chandra data and archival HST opticalimages. Their nuclear sources have X-ray luminosities~1038-1039 ergs s-1(LX/LEdd~10-8 to 10-7) andcolors or spectra consistent with accreting supermassive black holes(SMBHs), except for the nucleus of NGC 4486B, which is softer thantypical AGN spectra. In a few cases, the X-ray morphology of the nuclearsources shows hints of marginally extended structures, in addition tothe surrounding diffuse thermal emission from hot gas, which isdetectable on scales >~1 kpc. In one case (NGC 5845), a dusty diskmay partially obstruct our direct view of the SMBH. We have estimatedthe temperature and density of the hot interstellar medium, which is onemajor source of fuel for the accreting SMBH; typical central densitiesare ne~(0.02+/-0.01) cm-3. Assuming that the hotgas is captured by the SMBH at the Bondi rate, we show that the observedX-ray luminosities are too faint to be consistent with standard diskaccretion, but brighter than predicted by radiatively inefficientsolutions (e.g., advection-dominated accretion flows [ADAFs]). In total,there are ~20 galaxies for which SMBH mass, hot gas density, and nuclearX-ray luminosity are simultaneously known. In some cases, the nuclearsources are brighter than predicted by the ADAF model; in other cases,they are consistent or fainter. We discuss the apparent lack ofcorrelations between Bondi rate and X-ray luminosity and suggest that,in order to understand the observed distribution, we need to know twoadditional parameters: the amount of gas supplied by the stellarpopulation inside the accretion radius, and the fraction (possibly<<1) of the total gas available that is accreted by the SMBH. Weleave a detailed study of these issues to a subsequent paper.
|Scaling Mass Profiles around Elliptical Galaxies Observed with Chandra and XMM-Newton|
We investigated the dynamical structure of 53 elliptical galaxies usingthe Chandra archival X-ray data. In X-ray-luminous galaxies, temperatureincreases with radius and gas density is systematically higher at theoptical outskirts, indicating the presence of a significant amount ofthe group-scale hot gas. In contrast, X-ray-dim galaxies show a flat ordeclining temperature profile against radius and the gas density isrelatively lower at the optical outskirts. Thus, it is found thatX-ray-bright and faint elliptical galaxies are clearly distinguished bythe temperature and gas density profile. The mass profile is well scaledby a virial radius r200 rather than an optical half-radiusre, is quite similar at (0.001-0.03)r200 betweenX-ray-luminous and dim galaxies, and smoothly connects to those profilesof clusters of galaxies. At the inner region of(0.001-0.01)r200 or (0.1-1)re, the mass profilewell traces a stellar mass with a constant mass-to-light ratio ofM/LB=3-10 Msolar/Lsolar. TheM/LB ratio of X-ray-bright galaxies rises up steeply beyond0.01r200 and thus requires a presence of massive dark matterhalo. From the deprojection analysis combined with the XMM-Newton data,we found that X-ray-dim galaxies NGC 3923, NGC 720, and IC 1459 alsohave a high M/LB ratio of 20-30 at 20 kpc, comparable to thatof X-ray-luminous galaxies. Therefore, dark matter is indicated to becommon in elliptical galaxies; their dark matter distribution, as wellas that of galaxy clusters, almost follows the NFW profile.
|XMM-Newton Observation of Diffuse Gas and Low-Mass X-Ray Binaries in the Elliptical Galaxy NGC 4649 (M60)|
We present an XMM-Newton X-ray observation of the X-ray-bright E2elliptical galaxy NGC 4649. In addition to bright diffuse emission, weresolve 158 discrete sources, ~50 of which are likely to be LMXBsassociated with NGC 4649. We find evidence for variability in threesources between this observation and a previous Chandra observation.Additionally, we detect five sources that were not detected with Chandradespite its better detection limit, suggesting that these sources havesince brightened. The total X-ray spectrum of the resolved sources iswell fit by a hard power law, while the diffuse spectrum requires a hardand a soft component, presumably due to the relatively soft diffuse gasand the harder unresolved sources. A deprojection of the diffuseemission revealed a radial temperature gradient that is hot in thecenter, drops to a minimum at about 20"-50" (1.6-4.1 kpc), and risesagain in the outer regions. The diffuse emission appears to require atwo-temperature model with heavy-element abundance ratios that differfrom the solar values. We have verified the existence of faint radialfeatures extending out from the core of NGC 4649 that had previouslybeen seen with Chandra. The fingers are morphologically similar toradial features seen in hydrodynamic simulations of cooling flows inelliptical galaxies, and although their other properties do not matchthe predictions of the particular simulations used, we conclude that theradial fingers might be due to convective motions of hot outflowing gasand cooler inflowing gas. We also find evidence for a longer, previouslyundetected filament that extends to the northeastern edge of NGC 4649.The diffuse gas in the region of the filament appears to have a lowertemperature and may also have a higher abundance as compared to nearbyregions. There also appears to be an excess of X-ray sources along thefilament, although the excess is not statistically significant. Weconclude that the filament may be the result of a tidal interaction,possibly with NGC 4647, although more work is necessary to verify thisconclusion.
|The origin of the hot metal-poor gas in NGC 1291. Testing the hypothesis of gas dynamics as the cause of the gas heating|
In this paper we test the idea that the low-metallicity hot gas in thecentre of NGC 1291 is heated via a dynamical process. In this scenario,the gas from the outer gas-rich ring loses energy through bar-drivenshocks and falls to the centre. Heating of the gas to X-ray temperaturescomes from the high velocity that it reaches (≈700 km s-1)as it falls to the bottom of the potential well. This would explain whythe stellar metallicity in the bulge region is around solar while thehot gas metallicity is around 0.1 solar. We carried out an observationaltest to check this hypothesis by measuring the metallicity of HIIregions in the outer ring to check whether they matched the hot gasmetallicity. For this purpose we obtained medium resolution long slitspectroscopy with FORS1 on the ESO VLT at Paranal and obtained themetallicities using emission line ratio diagnostics. The obtainedmetallicities are compatible with the bulge stellar metallicities butvery different from the hot-gas metallicity. However, when comparing thedifferent time-scales, the gas in the ring had time enough to getenriched through stellar processes, therefore we cannot rule out thedynamical mechanism as the heating process of the gas. However, the bluecolours of the outer ring and the dust structures in the bar regioncould suggest that the origin of the X-ray hot gas is due to the infallof material from further out.
|Toward a clean sample of ultra-luminous X-ray sources|
Context: .Observational follow-up programmes for the characterization ofultra-luminous X-ray sources (ULXs) require the construction of cleansamples of such sources in which the contamination byforeground/background sources is minimum. Aims: .We calculate thedegree of foreground/background contaminants among the ULX samplecandidates in a published catalogue and compare these computations withavailable spectroscopic identifications. Methods: .We usestatistics based on known densities of X-ray sources and AGN/QSOsselected in the optical. The analysis is done individually for eachparent galaxy. The existing identifications of the optical counterpartsare compiled from the literature. Results: .More than a half ofthe ULXs, within twice the distance of the major axis of the 25mag/arcsec2 isophote from RC3 nearby galaxies and with X-rayluminosities L_X[ 2-10 keV] ≥ 1039 erg/s, are expected tobe high redshift background QSOs. A list of 25 objects (clean sample)confirmed to be real ULXs or to have a low probability of beingcontaminant foreground/background objects is provided.
|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).
|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.
|The Classification of Galaxies: Early History and Ongoing Developments|
"You ask what is the use of classification, arrangement,systematization. I answer you; order and simplification are the firststeps toward the mastery of a subject the actual enemy is the unknown."
|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.
|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.
|A Possible Detection of M31* with Chandra|
Two independent sets of Chandra and HST images of the nuclear region ofM31 allow registration of X-ray and optical images to ~0.1". Thisregistration shows that none of the bright (~1037 ergss-1) X-ray sources near the nucleus is coincident with thecentral supermassive black hole, M31*. A 50 ks Chandra HRC image shows2.5 σ evidence for a faint (~1036 ergs s-1)discrete source that is consistent with the position of M31*. The Bondiradius of M31* is 0.9", making it one of the few supermassive blackholes with a resolvable accretion flow. This large radius and theprevious detections of diffuse X-ray-emitting gas in the nuclear regionmake M31* one of the most secure cases for a radiatively inefficientaccretion flow and place some of the most severe constraints on theradiative processes in such a flow.
|Nuclear Accretion in Galaxies of the Local Universe: Clues from Chandra Observations|
In order to find an explanation for the radiative quiescence ofsupermassive black holes in the local universe, the most accurateestimates for a sample of nearby galaxies are collected for the mass ofa central black hole (MBH), the nuclear X-ray luminosityLX,nuc, and the circumnuclear hot gas density andtemperature, by using Chandra data. The nuclear X-ray luminosityLX,nuc varies by ~3 orders of magnitude and does not show arelationship with MBH or with the Bondi mass accretion rateM˙B LX,nuc is always much lower than expectedif M˙B ends in a standard accretion disk with highradiative efficiency (this instead can be the case of the active nucleusof Cen A). Radiatively inefficient accretion as in the standardadvection-dominated accretion flow (ADAF) modeling may explain the lowluminosities of a few cases; for others, the predicted luminosity isstill too high, and, in terms of Eddington-scaled quantities, it isincreasingly higher than that observed for increasingM˙B. Variants of the simple radiatively inefficientscenario including outflow and convection may reproduce the low emissionlevels observed, since the amount of matter actually accreted is reducedconsiderably. However, the most promising scenario includes feedbackfrom accretion on the surrounding gas; this has the important advantagesof naturally explaining the observed lack of relationship amongLX,nuc, MBH, and M˙B, and evadingthe problem of the fate of the material accumulating in the centralgalactic regions over cosmological times.
|XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups|
We study the distribution of gas pressure and entropy in eight groups ofgalaxies belonging to the ROSAT All-Sky Survey/Center for AstrophysicsLoose Systems (RASSCALS). We use archival and proprietary XMM-Newtonobservations, supplementing the X-ray data with redshifts derived fromthe literature; we also list 127 new redshifts measured with the GeminiNorth telescope. The groups are morphologically heterogeneous in boththe optical and the X-ray, and several suffer from superpositions withbackground galaxies or clusters of galaxies. Nevertheless, they showremarkable self-similarity in their azimuthally averaged entropy andtemperature profiles. The entropy increases with radius; the behavior ofthe entropy profiles is consistent with an increasing broken power lawwith inner and outer slope 0.92+0.04-0.05 and0.42+0.05-0.04 (68% confidence), respectively.There is no evidence of a central, isentropic core, and the entropydistribution in most of the groups is flatter at large radii than in theinner region, challenging earlier reports, as well as theoretical modelspredicting large isentropic cores or asymptotic slopes of 1.1 asr-->&infy;. The pressure profiles are consistent with a self-similardecreasing broken power law in radius; the inner and outer slopes are-0.78+0.04-0.03 and-1.7+0.1-0.3, respectively. The results suggestthat the larger scatter in the entropy distribution reflects the variedgasdynamical histories of the groups; the regularity and self-similarityof the pressure profiles is a sign of a similarity in the underlyingdark matter distributions.Based on observations obtained with XMM-Newton, an ESA science missionwith instruments and contributions directly funded by ESA Member Statesand the US (NASA). The XMM-Newton project is supported by theBundesministerium für Bildung und Forschung/Deutsches Zentrumfür Luft- und Raumfahrt (BMFT/DLR), the Max-Planck Society, and theHeidenhain-Stiftung, and also by PPARC, CEA, CNES, and ASI. Also basedon observations obtained at the Gemini Observatory, which is operated bythe Association of Universities for Research in Astronomy, Inc., under acooperative agreement with the NSF on behalf of the Gemini partnership:the National Science Foundation (US), the Particle Physics and AstronomyResearch Council (UK), the National Research Council (Canada), CONICYT(Chile), the Australian Research Council (Australia), CNPq (Brazil), andCONICET (Argentina).
|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 (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/1125
|Statistical properties of the combined emission of a population of discrete sources: astrophysical implications|
We study the statistical properties of the combined emission of apopulation of discrete sources (for example, the X-ray emission of agalaxy due to its population of X-ray binaries). Namely, we consider thedependence of their total luminosity and of the fractionalrmstot of their variability on the number of sources n or,equivalently, on the normalization of the luminosity function. We showthat, as a result of small number statistics, a regime exists in whichLtot grows non-linearly with n, in apparent contradictionwith the seemingly obvious prediction . In this non-linear regime,rmstot decreases with n significantly more slowly thanexpected from the averaging law. For example, for a power-law luminosityfunction with a slope of α= 3/2, in the non-linear regime,Ltot~n2 and rmstot does not depend atall on the number of sources n. Only in the limit of n->&infy; dothese quantities behave as intuitively expected, Ltot~n and .We give exact solutions and derive convenient analytical approximationsfor Ltot and rmstot.Using the total X-ray luminosity of a galaxy due to its X-ray binarypopulation as an example, we show that the LX-star formationrate and LX-M* relations predicted from therespective `universal' luminosity functions of high- and low-mass X-raybinaries are in good agreement with observations. Although caused bysmall number statistics, the non-linear regime in these examples extendsas far as SFR <~ 4-5Msolaryr-1 andlog(M*/Msolar) <~ 10.0-10.5, respectively.
|XMM-Newton and Chandra observations of three X-ray-faint early-type galaxies|
We present XMM-Newton observations of three X-ray-underluminouselliptical galaxies, NGC 3585, 4494 and 5322. All three galaxies haverelatively large optical luminosities (logLB= 10.35-10.67Lsolar) but have X-ray luminosities consistent with emissionfrom discrete sources only. In conjunction with a Chandra observation ofNGC 3585, we analyse the XMM-Newton data and show that the threegalaxies are dominated by discrete source emission, but do possess someX-ray-emitting gas. The gas is at relatively low temperatures, kT~=0.25-0.44 keV. All three galaxies show evidence of recent dynamicaldisturbance and formation through mergers, including kinematicallydistinct cores, young stellar ages and embedded stellar discs. Thisleads us to conclude that the galaxies formed relatively recently andhave yet to build up large X-ray haloes. They are likely to be in adevelopmental phase where the X-ray gas has a very low density, makingit undetectable outside the galaxy core. However, if the gas is aproduct of stellar mass loss, as seems most probable, we would expect toobserve supersolar metal abundances. While abundance is not wellconstrained by the data, we find best-fitting abundances <0.1Zsolar for single-temperature models, and it seems unlikelythat we could underestimate the metallicity by such a large factor.
|Low-mass X-ray binaries as a stellar mass indicator for the host galaxy|
Using results of Chandra observations of old stellar systems in 11nearby galaxies of various morphological types and the census oflow-mass X-ray binaries (LMXBs) in the Milky Way, we study thepopulation of LMXBs and their relation to the mass of the host galaxy.We show that the azimuthally averaged spatial distributions of thenumber of LMXBs and, in the majority of cases, of their collectiveluminosity closely follow that of the near-infrared light. Consideringgalaxies as a whole, we find that, in a broad stellar mass range,log(M*) ~ 9-11.5, the total number of LMXBs and theircombined luminosity are proportional to the stellar mass of the hostgalaxy. Within the accuracy of the light-to-mass conversion, we cannotrule out the possibility of a weak dependence of the X/M*ratio on morphological type. However, the effect of such a dependence,if any, does not exceed a factor of ~1.5-2.The luminosity distributions of LMXBs observed in different galaxies aresimilar to each other and, with the possible exception of NGC 1553, areconsistent with the average luminosity function derived from all data.The average X-ray luminosity function of LMXBs in nearby galaxies has acomplex shape and is significantly different from that of high-massX-ray binaries (HMXBs). It follows a power law with a differential slopeof ~1 at low luminosities, gradually steepens at log(LX)>~ 37.0-37.5 and has a rather abrupt cut-off at log(LX) ~39.0-39.5. This value of the cut-off luminosity is significantly, by anorder of magnitude, lower than found for HMXBs.
|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.
|Secular Evolution and the Formation of Pseudobulges in Disk Galaxies|
The Universe is in transition. At early times, galactic evolution wasdominated by hierarchical clustering and merging, processes that areviolent and rapid. In the far future, evolution will mostly be secularthe slow rearrangement of energy and mass that results from interactionsinvolving collective phenomena such as bars, oval disks, spiralstructure, and triaxial dark halos. Both processes are important now.This review discusses internal secular evolution, concentrating on oneimportant consequence, the buildup of dense central components in diskgalaxies that look like classical, merger-built bulges but that weremade slowly out of disk gas. We call these pseudobulges.
|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.
|BUDDA: A New Two-dimensional Bulge/Disk Decomposition Code for Detailed Structural Analysis of Galaxies|
We present BUDDA (Bulge/Disk Decomposition Analysis), a new code devotedto perform a two-dimensional bulge/disk decomposition directly from theimages of galaxies. The bulge component is fitted with a generalizedSérsic profile, whereas disks have an exponential profile. Noother components are included. Bars and other substructures, likelenses, rings, inner bars, and inner disks, are studied with theresidual images obtained through the subtraction of bulges and disksfrom the original images. This means that a detailed structural analysisof galaxies may be performed with a small number of parameters, andsubstructures may be directly studied with no a priori assumptions. Ashas been already shown by several studies, two-dimensional fitting ismuch more reliable than one-dimensional profile fitting. Moreover, ourcode has been thoroughly tested with artificial data, and we demonstrateit to be an accurate tool for determining structural parameters ofgalaxies. We also show that our code is useful in various kinds ofstudies, including galaxies of, e.g., different morphological types, andinclinations, which also may be observed at different spatialresolutions. Thus, the code has a broader range of potentialapplications than most of the previous codes, which are developed totackle specific problems. To illustrate its usefulness, we present theresults obtained with a sample of 51 mostly early-type galaxies (butcovering the whole Hubble sequence). These results show some of theapplications in which the code may be used: the determination ofparameters for fundamental plane and structural studies, quantitativemorphological classification of galaxies, and the identification andstudy of hidden substructures. We have determined the structuralparameters of the galaxies in our sample and found many examples ofhidden inner disks in ellipticals, secondary bars, nuclear rings anddust lanes in lenticulars and spirals, and also wrong morphologicalclassification cases. We now make BUDDA generally available to theastronomical community.Based on observations made at the Pico dos Dias Observatory(PDO/LNA-CNPq), Brazil.
|A Chandra View of the Normal S0 Galaxy NGC 1332. II. Solar Abundances in the Hot Gas and Implications for Supernova Enrichment|
Using a new Chandra ACIS-S3 observation of the normal, isolated,moderate-LX lenticular galaxy NGC 1332, we resolve theemission into ~75 point sources and a significant diffuse component. Wepresent a detailed analysis of the spectral properties of the diffuseemission, constraining both the temperature profile and the metalabundances in the hot gas. The characteristics of the point-sourcepopulation and the spatial properties of the diffuse emission arediscussed in two companion papers. The diffuse component comprises hotgas with an ~isothermal temperature profile (~0.5 keV) and emission fromunresolved point sources. In contrast with the cool cores of many groupsand clusters, we find a small central temperature peak. We obtainemission-weighted abundance constraints within 20 kpc for several keyelements: Fe, O, Ne, Mg, and Si. The measured iron abundance(ZFe=1.1 in solar units; >0.53 at 99% confidence) stronglyexcludes the very subsolar values often historically reported forearly-type galaxies. This continues, in a lower LX system, atrend in recent observations of bright galaxies and groups. Theabundance ratios, with respect to Fe, of the other elements were alsofound to be ~solar, with the exception of ZO/ZFe,which was significantly lower (<0.4), as seen in several brightgalaxies, groups, and clusters. Such a low O abundance is not predictedby simple models of ISM enrichment by Type Ia and Type II supernovae(SNe) and may indicate a significant contribution from primordialhypernovae. Revisiting Chandra observations of themoderate-LX, isolated elliptical galaxy NGC 720, we obtainsimilar abundance constraints(ZFe=0.71+0.40-0.21, 90% confidence;ZO/ZFe=0.23+/-0.21). Adopting standard SNe Ia andSNe II metal yield models, our abundance ratio constraints imply that73%+/-5% and 85%+/-6% of the Fe enrichment in NGC 1332 and NGC 720,respectively, arises from SNe Ia. Although these results are sensitiveto the considerable systematic uncertainty in the SNe yields, they arein good agreement with observations of more massive systems. These twocases of moderate-LX early-type galaxies reveal a consistentpattern of metal enrichment from cluster scales to moderateLX/LB galaxies.
|Chandra Observations of Diffuse Gas and Luminous X-Ray Sources around the X-Ray-bright Elliptical Galaxy NGC 1600|
We observed the X-ray-bright E3 galaxy NGC 1600 and nearby members ofthe NGC 1600 group with the Chandra X-Ray Observatory ACIS-S3 to studytheir X-ray properties. Unresolved emission dominates the observation;however, we resolved some of the emission into 71 sources, most of whichare low-mass X-ray binaries associated with NGC 1600. Twenty-one of thesources have LX>2×1039 ergss-1 (0.3-10.0 keV; assuming they are at the distance of NGC1600), marking them as ultraluminous X-ray point source (ULX)candidates; we expect that only 11+/-2 are unrelatedforeground/background sources. NGC 1600 may have the largest number ofULX candidates in an early-type galaxy to date; however, cosmic variancein the number of background active galactic nuclei cannot be ruled out.The spectrum and luminosity function (LF) of the resolved sources aremore consistent with sources found in other early-type galaxies thanwith sources found in star-forming regions of galaxies. The source LFand the spectrum of the unresolved emission both indicate that there area large number of unresolved point sources. We propose that thesesources are associated with globular clusters (GCs) and that NGC 1600has a large GC specific frequency. Observations of the GC population inNGC 1600 would be very useful for testing this prediction. Approximately50%-75% of the unresolved flux comes from diffuse gaseous emission. Thespectral fits, hardness ratios, and X-ray surface brightness profile allpoint to two gas components. We interpret the soft inner component(a<~25'', kT~0.85 keV) as the interstellar medium of NGC1600 and the hotter outer component (a>~25'', kT~1.5 keV)as the intragroup medium of the NGC 1600 group. The X-ray image showsseveral interesting structures. First, there is a central region ofexcess emission that is roughly cospatial with Hα and dustfilaments immediately west of the center of NGC 1600. There appear to beholes in the X-ray emission to the north and south of the galaxy centerthat are roughly coincident with the lobes of the NGC 1600 radio source.On larger scales, there is excess emission to the northeast, which wesuggest may indicate the center of the group potential. The group galaxyNGC 1603 shows a tail of X-ray emission to its west that is probably dueto ram pressure stripping.
|Evidence of a Misaligned Secondary Bar in the Large Magellanic Cloud|
Evidence of a misaligned secondary bar, within the primary bar of theLarge Magellanic Cloud (LMC), is presented. The density distribution andthe dereddened mean magnitudes (I0) of the red clump stars inthe bar obtained from the Optical Gravitational Lensing Experiment IIdata are used for this study. The bar region that predominantly showed awavy pattern in the line of sight in a recent paper by Subramaniam waslocated. These points in the X-Z plane delineate an S-shaped pattern,clearly indicating a misaligned bar. This feature is statisticallysignificant and does not depend on the considered value of I0for the LMC center. The rest of the bar region was not found to show thewarp or the wavy pattern. The secondary bar is found to be considerablyelongated in the Z-direction, with an inclination of 66.5d+/-0.9d,whereas the undisturbed part of the primary bar is found to have aninclination of 15.1d+/-2.7d, such that the eastern sides are closer tous with respect to the western sides of both the bars. TheP.A.maj of the secondary bar is found to be 108.4d+/-7.3d.The streaming motions found in the H I velocity map close to the LMCcenter could be caused by the secondary bar. The recent star formationand the gas distribution in LMC could be driven by the misalignedsecondary bar.
|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).
|Chandra Observation of Diffuse Gas and Low-Mass X-Ray Binaries in the Elliptical Galaxy NGC 4649 (M60)|
We present a Chandra X-ray observation of the X-ray bright E2 ellipticalgalaxy NGC 4649. In addition to bright diffuse emission, we resolve 165discrete sources, most of which are presumably low-mass X-ray binaries.As found in previous studies, the luminosity function of the resolvedsources is well-fitted by a broken power law. In NGC 4697 and NGC 1553,the break luminosity was comparable to the Eddington luminosity of a 1.4Msolar neutron star. One possible interpretation of thisresult is that those sources with luminosities above the break areaccreting black holes and those below are mainly accreting neutronstars. The total X-ray spectrum of the resolved sources is well fittedby a hard power law, while the diffuse spectrum requires a hard and asoft component, presumably due to the relatively soft diffuse gas andthe harder unresolved sources. We also find evidence for structure inthe diffuse emission near the center of NGC 4649. Specifically, thereappear to be bright ``fingers'' of emission extending from the center ofthe galaxy and a 5" long bar at the center of the galaxy. The fingersare morphologically similar to radial features seen in two-dimensionalhydrodynamic simulations of cooling flows in elliptical galaxies, andalthough their other properties do not match the predictions of theparticular simulations used, we conclude that the radial fingers mightbe due to convective motions of hot outflowing gas and cooler inflowinggas. The bar is coincident with the central extended radio source; weconclude that the bar may be caused by weak shocks in the diffuse gasfrom an undetected low-luminosity active galactic nucleus.
|Spitzer Observations of Two Early-Type Spiral Galaxies with Dust Rings|
We present Spitzer images of the SB0/a galaxy NGC 1291 and the SAagalaxy NGC 4594. Both galaxies contain dust rings that can be used forstudying the relation between dust emission and star formation activity.At 24 microns, the nuclei of both galaxies are the brightest sources inthe galaxies, and dust emission from the rings is relatively weak. At160 microns, however, the dust rings are more prominent sources; in NGC4594, the dust ring is the source of virtually all of the 160 micronemission. We discuss whether the 160 micron emission from the rings isrelated to star formation activity or to heating by older stellarpopulations, and we examine the relation between dust and PAH emission.For NGC 4594, we also present submillimeter data that show that thenucleus dominates the 850 micron emission. These results demonstate thatthe 850 micron emission cannot come from the same dust that dominatesthe 160 micron emission. We examine the possible mechanisms that couldbe generating the 850 micron emission as well as the implications fordust models and galaxy spectral energy distribution templates.
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