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Hot ammonia in NGC 6334I & I(N)
Aims.The massive twin cores NGC 6334I and I(N) are in differentevolutionary stages and hence ideal targets to study evolutionaryvariations within the same larger-scale environment. Here, we study thewarm, compact gas components. Methods: We imaged the two regions withthe Australia Telescope Compact Array (ATCA) at high angular resolutionin the NH3(3, 3) to (6, 6) inversion lines. Results: Compact emissionis detected toward both regions in all observed inversion lines withenergy levels up to 407 K above ground. This is particularly surprisingfor NGC 6334I(N) since it lacks bright infrared emission and isconsidered a massive cold core at an early evolutionary stage. Highoptical depth and multiply-peaked line profiles complicate rotationtemperature estimates, and we can only conclude that gas components withtemperatures >100 K are present in both regions. Toward NGC 6334I, weconfirm previous reports of NH3(3, 3) maser emission toward the outflowbow-shocks. Furthermore, we report the first detection of an NH3(6, 6)maser toward the central region of NGC 6334I. This maser is centered onthe second millimeter (mm) peak and elongated along the outflow axis,indicating that this mm continuum core harbors the driving source of themolecular outflow. Toward the main mm peak in NGC 6334I(N), we detect adouble-horn line profile in the NH3(6, 6) transition. The current datado not allow us to differentiate whether this double-horn profile isproduced by multiple gas components along the line of sight, or whetherit may trace a potential underlying massive accretion disk.FITS files of Figs. 3 to 7 are available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/989
| The interaction of young massive stars with their environment. A millimeter and submillimeter line study of NGC 6334 FIR II
Using the 15-m Swedish ESO Sub-millimeter Telescope (SEST), CO, HCN, andHCO+ observations of the galactic star-forming region NGC6334 FIR II are presented, complemented by [C i] ^3P1-^3P{0} and^3P2-^3P{1} data from the Atacama Pathfinder Experiment (APEX 12-mtelescope). Embedded in the extended molecular cloud and associated withthe H ii region NGC 6334-D, there is a molecular "void". [C i]correlates well with 13CO and other molecular lines and showsno rim brightening relative to molecular cloud regions farther off thevoid. While an interpretation in terms of a highly clumped cloudmorphology is possible, with photon dominated regions (PDRs) reachingdeep into the cloud, the data do not provide any direct evidence for aclose association of [C i] with PDRs. Kinetic temperatures are 40-50 Kin the molecular cloud and ⪆200 K toward the void. CO and [C i]excitation temperatures are similar. A comparison of molecular andatomic fine structure line emission with the far infrared and radiocontinuum as well as the distribution of 2.2 μm H2 emission indicatesthat the well-evolved H ii region expands into a medium that ishomogeneous on pc-scales. If the H2 emission is predominantly shockexcited, both the expanding ionization front (classified as subsonic,"D-type") and the associated shock front farther out (traced by H2) canbe identified, observationally confirming for the first time a classicalscenario that is predicted by evolutionary models of Hii regions.Integrated line intensity ratios of the observed molecules aredetermined, implying a mean C18O/C17O abundanceratio of 4.13 ± 0.13 that reflects the18O/17O isotope ratio. This ratio is consistentwith values determined in nearby clouds. Right at the edge of the void,however, the oxygen isotope ratio might be smaller.Based on observations with the Atacama Pathfinder EXperiment telescope(APEX, Chile) and the Swedish-ESO Sub-millimeter Telescope (SEST, ESO/LaSilla, Chile). Figure [see full text] is only available in electronicform at http://www.aanda.org
| Star formation in a clustered environment around the UCH {II} region in IRAS 20293+3952
Aims.We aim at studying the cluster environment surrounding the UCH IIregion in IRAS 20293+3952, a region in the first stages of formation ofa cluster around a high-mass star. Methods: BIMA and VLA were used toobserve the 3 mm continuum, N2H+ (1-0), NH3 (1, 1), NH3 (2,2), and CH3OH (2-1) emission of the surroundings of the UCH II region.We studied the kinematics of the region and computed the rotationaltemperature and column density maps by fitting the hyperfine structureof N2H+ and NH3. Results: The dense gas traced byN2H+ and NH3 shows two different clouds, a main cloud to theeast of the UCH II region, of ~0.5 pc and ~250 Mȯ, and awestern cloud, of ~0.15 pc and ~30 Mȯ. The dust emissionreveals two strong components in the northern side of the main cloud,BIMA 1 and BIMA 2, associated with Young Stellar Objects (YSOs) drivingmolecular outflows, and two fainter components in the southern side,BIMA 3 and BIMA 4, with no signs of star forming activity. Regarding theCH3OH, we found strong emission in a fork-like structure associated withoutflow B, as well as emission associated with outflow A. The YSOsassociated with the dense gas seem to have a diversity of age andproperties. The rotational temperature is higher in the northern side ofthe main cloud, around 22 K, where there are most of the YSOs, than inthe southern side, around 16 K. There is strong chemical differentiationin the region, since we determined low values of the NH3/N2H+ratio, ~50, associated with YSOs in the north of the main cloud, andhigh values, up to 300, associated with cores with no detected YSOs, inthe south of the main cloud. Such a chemical differentiation is likelydue to abundance/depletion effects. Finally, interaction between thedifferent sources in the region is important. First, the UCH II regionis interacting with the main cloud, heating it and enhancing the CN(1-0) emission. Second, outflow A seems to be excavating a cavity andheating its walls. Third, outflow B is interacting with the BIMA 4 core,likely producing the deflection of the outflow and illuminating a clumplocated ~0.2 pc to the northeast of the shock. Conclusions: .The starformation process in IRAS 20293+3952 is not obviously associated withinteractions, but seems to take place where density is highest.
| The Galactic distribution of magnetic fields in molecular clouds and HII regions
Aims.Magnetic fields exist on all scales in our Galaxy. There is acontroversy about whether the magnetic fields in molecular clouds arepreserved from the permeated magnetic fields in the interstellar medium(ISM) during cloud formation. We investigate this controversy usingavailable data in the light of the newly revealed magnetic fieldstructure of the Galactic disk obtained from pulsar rotation measures(RMs). Methods: We collected measurements of the magnetic fields inmolecular clouds, including Zeeman splitting data of OH masers in cloudsand OH or HI absorption or emission lines of clouds themselves. Results: The Zeeman data show structures in the sign distribution of theline-of-sight component of the magnetic field. Compared to thelarge-scale Galactic magnetic fields derived from pulsar RMs, the signdistribution of the Zeeman data shows similar large-scale fieldreversals. Previous such examinations were flawed in the over-simplifiedglobal model used for the large-scale magnetic fields in the Galacticdisk. Conclusions: .We conclude that the magnetic fields in the cloudsmay still "remember" the directions of magnetic fields in the GalacticISM to some extent, and could be used as complementary tracers of thelarge-scale magnetic structure. More Zeeman data of OH masers in widelydistributed clouds are required.Tables 1 and 2 are only available in electronic form athttp://www.aanda.org
| Compact Centimeter and Millimeter Sources in NGC 6334 I(N): OB Stars in the Making?
We present sensitive, high angular resolution 1.3 cm and 7 mmobservations of the massive core NGC 6334 I(N), a region known to beundergoing massive star formation. At 1.3 cm we detect three sources,two of which had previously been detected at centimeter or millimeterwavelengths. At 7 mm we detect four sources. We suggest that three ofthese sources are subcomponents of the millimeter source SMA 1, which atthese wavelengths is the dominant source in the region. The fourth 7 mmsource appears to be associated with the relatively isolated source SMA6. In all four 7 mm sources, the continuum emission is arising fromstructures of dimensions of order 1000 AU for which we estimate massesof order a few solar masses. We interpret these 7 mm sources as massivecircumstellar disks that, however, surround stars or compact smallstellar groups that at present have masses comparable to those of thedisks but that may be accreting on their way to becoming massive stars.
| Hard X-Rays from Ultracompact H II Regions in W49A
We report the Chandra detection of hard X-ray emission from the Welchring in W49A, an organized structure of ultracompact (UC) H II regionscontaining a dozen nascent early-type stars. Two UC H II regions areassociated with hard X-ray emission in a deep Advanced CCD ImagingSpectrometer (ACIS) image exposed for ~96.7 ks. One of the two X-raysources has no near-infrared counterpart and is extended by ~5", or ~0.3pc, at a distance of ~11.4 kpc, which is spatially aligned with thecometary radio continuum emission associated with the UC H II region.The X-ray spectrum of the emission, when fit with a thermal model,indicates a heavily absorbed plasma with extinction of~5×1023 cm-2, temperature ~7 keV, and X-rayluminosity in the 3.0-8.0 keV band of ~3×1033 ergss-1. Both the luminosity and the size of the emissionresemble the extended hard emission found in UC H II regions inSagittarius B2, yet they are smaller by an order of magnitude than theemission found in massive star clusters such as NGC 3603. Threepossibilities are discussed for the cause of the hard extended emissionin the Welch ring: an ensemble of unresolved point sources, shockedinteracting winds of the young O stars, and a wind-blown bubbleinteracting with ambient cold matter.
| SiO and CH_3CCH abundances and dust emission in high-mass star-forming cores
Aims.We determine the fractional SiO abundance in high-mass star-formingcores, and investigate its dependence on physical conditions, to provideconstraints on the chemistry models of the formation of SiO in the gasphase or via grain mantle evaporation. The work addresses also CH3CCHchemistry, as the kinetic temperature is determined using thismolecule. Methods: .We estimate the physical conditions of 15high-mass star-forming cores and derive the fractional SiO and CH3CCHabundances using spectral line and dust continuum observations with theSEST. Results: .The kinetic temperatures as derived from CH3CCHrange from 25 to 39 K, the average being 33 K. The average gas densityin the cores is 4.5 × 106 cm-3. The SiOemission regions are extended and typically half of the integrated lineemission comes from the velocity range traced out by CH3CCH emission.The upper limit of SiO abundance in this "quiescent" gas component is~10-10. The average CH3CCH abundance is about 7 ×10-9. It shows a shallow, positive correlation with thetemperature, whereas SiO shows the opposite tendency. Conclusions:.We suggest that the high CH3CCH abundance and its possible increasewhen the clouds become warmer is related to the intensified desorptionof the chemical precursors of the molecule from grain surfaces. Incontrast, the observed tendency of SiO does not support the idea thatthe evaporation of Si-containing species from the grain mantles would beimportant, and it contradicts models where neutral reactions withactivation barriers dominate SiO production. A possible explanation forthe decrease is that warmer cores represent more evolved stages of coreevolution with fewer high-velocity shocks and thus less efficient SiOreplenishment.
| Evolution of HII regions in hierarchically structured molecular clouds
We present observations of the H91α recombination line emissiontowards a sample of nine HII regions associated with 6.7-GHz methanolmasers, and report arcsecond-scale emission around compact cores. Wederive physical parameters for our sources, and find that althoughsimple hydrostatic models of region evolution reproduce the observedregion sizes, they significantly underestimate emission measures. Weargue that these findings are consistent with young source ages in oursample, and can be explained by existence of density gradients in theionized gas.
| The Discovery of Diffuse X-Ray Emission in NGC 2024, One of the Nearest Massive Star-forming Regions
We analyzed deep 75 ks Chandra ACIS-I data of NGC 2024 with the aim ofsearching for diffuse X-ray emission in this most nearby (415 pc) ofmassive star-forming regions. After removing point sources, extendedemission was detected in the central circular region with a radius of0.5 pc, and it is spatially associated with this young massive stellarcluster. Its X-ray spectrum exhibits a very hard continuum (kT>8 keV)and shows signs of having a He-like Fe Kα line with a 0.5-7 keVabsorption-corrected luminosity of 2 × 1031 ergss-1. Undetected faint point sources, estimated from theluminosity function of the detected sources, contribute less than 10% tothis emission. Hence, the emission is truly diffuse in nature. Becauseof the proximity of NGC 2024 and the long exposure, this discovery isone of the strongest pieces of evidence in support of the existence ofdiffuse X-ray emission in massive star-forming regions.
| On the Nature of the Hard X-Ray Source IGR J2018+4043
We found a very likely counterpart to the recently discovered hard X-raysource IGR J2018+4043 in the multiwavelength observations of the sourcefield. The source, originally discovered in the 20-40 keV band, is nowconfidently detected also in the 40-80 keV band, with a flux of(1.4+/-0.4)×10-11 ergs cm-2 s-1.A 5 ks Swift observation of the IGR J2018+4043 field revealed a hardpointlike source with an observed 0.5-10 keV flux of3.4+0.7-0.8×10-12 ergscm-2 s-1 (90% confidence level) atα=20h18m38.55 s,δ=+40deg41'00.4" (with a 4.2" uncertainty).The combined Swift-INTEGRAL spectrum can be described by an absorbedpower-law model with photon index Γ=1.3+/-0.2 andNH=6.1+3.2-2.2×1022cm-2. In archival optical and infrared data we found aslightly extended and highly absorbed object at the Swift sourceposition. There is also an extended VLA 1.4 GHz source peaked at abeamwidth distance from the optical and X-ray positions. The observedmorphology and multiwavelength spectra of IGR J2018+4043 are consistentwith those expected for an obscured accreting object, i.e., an AGN or aGalactic X-ray binary. The identification suggests possible connectionof IGR J2018+4043 to the bright γ-ray source GEV J2020+4023detected by COS B and CGRO EGRET.
| Results of SPARO 2003: Mapping Magnetic Fields in Giant Molecular Clouds
We present results from the Austral Winter 2003 observing campaign ofSPARO, a 450 μm polarimeter used with a 2 m telescope at the SouthPole. We mapped large-scale magnetic fields in four GMCs in the Galacticdisk: NGC 6334, the Carina Nebula, G333.6-0.2, and G331.5-0.1. We find astatistically significant correlation of the inferred field directionswith the orientation of the Galactic plane. Specifically, three of thefour GMCs (NGC 6334 is the exception) have mean field directions thatare within 15° of the plane. The simplest interpretation is that thefield direction tends to be preserved during the process of GMCformation. We have also carried out an analysis of published opticalpolarimetry data. For the closest of the SPARO GMCs, NGC 6334, we cancompare the field direction in the cloud as measured by SPARO with thefield direction in a larger region surrounding the cloud, as determinedfrom optical polarimetry. For purposes of comparison, we also useoptical polarimetry to determine field directions for 9-10 other regionsof similar size. We find that the region surrounding NGC 6334 is anoutlier in the distribution of field directions determined from opticalpolarimetry, just as the NGC 6334 cloud is an outlier in thedistribution of cloud field directions determined by SPARO. In bothcases the field direction corresponding to NGC 6334 is rotated away fromthe direction of the plane by a large angle. This finding is consistentwith our suggestion that field direction tends to be preserved duringGMC formation. Finally, by comparing the disorder in our magnetic fieldmaps with the disorder seen in magnetic field maps derived from MHDturbulence simulations, we conclude that the magnetic energy density inour clouds is comparable to the turbulent energy density.
| [C I] 809 GHz Imaging of the NGC 6334 Complex
We present Antarctic Submillimeter Telescope and Remote Observatory(AST/RO) observations of submillimeter emissions from the NGC 6334complex for both the 12[CI]3P2 ->3P1 fine-structure line of atomic carbon and the12CO J = 4->3 rotational transition of CO. We detectedstrong 12[CI]3P2 ->3P1 emission from the entire star-forming NGC 6334complex, and present maps of 12[CI]3P2-> 3P1 emission and 12CO J = 4->3emission. Comparing these maps with archival ASCA data, we show that, tothe south of NGC 6334, the [CI] emissions are likely to be associatedwith strong X-ray emissions from the FIR sources. However, thecalculation using the X-ray dissociation region model shows that themajority of the [CI] emission can not arise from X-ray dissociation ofthe cloud. Alternatively, far-ultraviolet radiation produced in thephotodissociation regions is expected to contribute to dissociate thecarbon monoxide in the NGC 6334 complex.
| Determining the H+ Region / PDR Equation of State in Star-forming Regions
The emission-line regions of starburst galaxies and active nuclei reveala wealth of spectroscopic information. A unified picture of therelationship among ionized, atomic, and molecular gas makes it possibleto better understand these observations. We performed a series ofcalculations designed to determine the equation of state-therelationship among density, temperature, and pressure-throughemission-line diagnostic ratios that form in the H+ regionand the photodissociation region (PDR). We consider a wide range ofphysical conditions in the H+ region. We connect theH+ region to the PDR by considering two constant pressurecases: one with no magnetic field and one in which the magnetic fieldoverwhelms the thermal pressure. We show that diagnostic ratios canyield the equation of state for single H+ regions adjacent tosingle PDRs, with the results being more ambiguous when consideringobservations of entire galaxies. As a test, we apply our calculations tothe Orion H+/PDR region behind the Trapezium. We find theratio of thermal to magnetic pressure in the PDR to be ~1.2. If magneticand turbulent energy are in equipartition, our results mean that themagnetic field is not the cause of the unexplained broadening in M42,but may significantly affect line broadening in the PDR. Since Orion isoften used to understand physical processes in extragalacticenvironments, our calculations suggest that magnetic pressure should beconsidered in modeling such regions.
| The high velocity outflow in NGC 6334 I
Aims.We observed the high velocity outflow originating from NGC 6334 Iin several CO transitions with the APEX telescope, with the goal ofderiving the physical parameters of the gas. Methods: .Using anLVG analysis, we studied line ratios between the CO(3-2), CO(4-3), andCO(7-6) data as a function of the density and of the kinetic temperatureof the gas. An upper limit on the CO column density is derived bycomparison with 13CO data. Results: .We constrained thetemperature to be higher than 50 K and the H2 density to values higherthan n˜ 104 cm-3 towards the peak positionin the red lobe, while T>15 K and n>103 cm-3are derived towards the peak position in the blue lobe. The physicalparameters of the outflow, its mass and its energetics, have beencomputed using the temperatures derived from this analysis.Conclusions: .We conclude that high kinetic temperatures are present inthe outflow and traced by high excitation CO lines. Observations ofhigh-J CO lines are thus needed to infer reliable values of the kinetictemperatures and of the other physical parameters in outflows.
| Radio Recombination Lines in Galactic H II Regions
We report radio recombination line (RRL) and continuum observations of asample of 106 Galactic H II regions made with the NRAO 140 Foot (43 m)radio telescope in Green Bank, West Virginia. We believe this to be themost sensitive RRL survey ever made for a sample this large. Most of oursource integration times range between 6 and 90 hr, yielding typical rmsnoise levels of ~1.0-3.5 mK. Our data result from two differentexperiments performed, calibrated, and analyzed in similar ways. A C IIsurvey was made at the 3.5 cm wavelength to obtain accurate measurementsof carbon radio recombination lines. When combined with atomic (C I) andmolecular (CO) data, these measurements will constrain the composition,structure, kinematics, and physical properties of the photodissociationregions that lie on the edges of H II regions. A second survey was madeat the 3.5 cm wavelength to determine the abundance of 3He inthe interstellar medium of the Milky Way. Together with measurements ofthe 3He+ hyperfine line, we get high-precision RRLparameters for H, 4He, and C. Here we discuss significantimprovements in these data with both longer integrations and newlyobserved sources.
| Core Mass Function of Molecular Clouds and its Dependence on Temperature
We report observations of dust continuum emission towards the starforming regions NGC 6334 and NGC 6357 made with the SIMBA bolometerarray at the SEST (La Silla). The observations cover an area ˜1°×3° with approximately uniform noise. On a preliminaryanalysis of the map using the clumpfind algorithm (clfind2d, Williams,de Geus, & Blitz, 1994) we find 347 clumps spanning almost threeorders of magnitude in mass. Masses were estimated as being proportionalto optically thin dust emission at 250 GHz. We derive an overall clumpmass function of the form dN/d logM ∝ M^{-0.6}. In this poster weconcentrate on the mass spectrum of NGC 6334 and on the possible effectsof having a distribution of clump temperatures in this mass spectrum.MSX three color images were used to correlate dust clumps with infraredsources searching for embedded protostars. Also, the clumps consideredto have embedded sources correlated well with ATCA free-free emissionmaps, verifying their higher temperatures. We find that having up to 10endtex2html[d]eferred% of the clumps with hotter temperatures does notaffect significantly the mass spectrum even though it tends to decreasesignificantly the higher clump masses.
| Spectra and Sizes of Hypercompact H II Regions
We present the analysis of the spectra and sizes of the hypercompact HII regions G34.26+0.15 A and B. We compare their radio continuum spectraand angular sizes with simple models of spherical ionized regionsbounded by an inner and an outer radius, with a power-law electrondensity profile, ne(r)~r-α. The radiocontinuum spectra and sizes can be reasonably reproduced by both uniformsphere models and shell models with large inner radii of the order of500 AU. High spatial resolution observations at ν>15 GHz, wherethe regions are optically thin, could distinguish between the twomodels. The optically thin radio emission implies, after accounting fordust absorption of ionizing photons, that the ionizing stars of sourcesA and B have spectral types earlier than main-sequence B1 type.
| INTEGRAL detection of hard X-rays from NGC 6334: nonthermal emission from colliding winds or an AGN?
Aims.We report the detection of hard X-ray emission from the field ofthe star-forming region NGC 6334 with the International Gamma-RayAstrophysics Laboratory INTEGRAL .Methods.The JEM-X monitor and ISGRIimager aboard INTEGRAL and Chandra ACIS imager were used to construct3-80 keV images and spectra of NGC 6334.Results.The 3-10 keV and 10-35keV images made with JEM-X show a complex structure of extended emissionfrom NGC 6334. The ISGRI source detected in the energy ranges 20-40 keV,40-80 keV, and 20-60 keV coincides with the NGC 6334 ridge. The 20-60keV flux from the source is (1.8±0.37)×10-11 erg cm-2 s-1. Spectral analysis of the sourcerevealed a hard power-law component with a photon index about 1. Theobserved X-ray fluxes are in agreement with extrapolations of X-rayimaging observations of NGC 6334 by Chandra ACIS and ASCAGIS.Conclusions.The X-ray data are consistent with two very differentphysical models. A probable scenario is emission from a heavilyabsorbed, compact and hard Chandra source that is associated with theAGN candidate radio source NGC 6334B. Another possible model is theextended Chandra source of nonthermal emission from NGC 6334 that canalso account for the hard X-ray emission observed by INTEGRAL. Theorigin of the emission in this scenario is due to electron accelerationin energetic outflows from massive early type stars. The possibility ofemission from a young supernova remnant, as suggested by earlierinfrared observations of NGC 6334, is constrained by the non-detectionof 44Ti lines.
| Anomalous absorption in H2CO molecule
Snyder et al. (1969) detected H2 CO through its transition110 - 111 at 4.829 GHz in absorption in theinterstellar medium in a number of galactic and extragalactic sources(M17, W3, W3(OH position), W49, NGC 2024, DR 21, W43, W44, W51, Sgr A,Sgr B2, W33, NGC 6334, Cas A, and 3C 123). This transition ofH2 CO was found in anomalous absorption by Palmer et al.(1969) in the direction of four dark nebulae. In some objects, thistransition has however been detected in emission and even as a maserline (Forster et al. 1980; Whiteoak et al. 1983). Evans et al. (1970)reported detection of H2 CO molecule through its transition211 - 212 at 14.488 GHz in absorption in somecosmic objects. This transition was also found in anomalous absorptionby Evans et al. (1975). Since the transition 110 - 111 is considered asa unique probe of high density gas at low temperature, the study ofH2 CO in cosmic objects is of great importance. Garrison etal. (1975) investigated the problem of anomalous absorption of110 - 111 and 211 -212transitions of H2 CO where they accounted for 8 energy levelsconnected by 10 radiative transitions and considered a kinetictemperature of 5 - 20 K. They found weak anomalous absorption of110 - 111 and 211 - 212transitions of H2 CO.
| Investigation of Diffuse Hard X-Ray Emission from the Massive Star-forming Region NGC 6334
Chandra ACIS-I data of the molecular cloud and H II region complex NGC6334 were analyzed. The hard X-ray clumps detected with ASCA (Sekimotoand coworkers) were resolved into 792 point sources. After removing thepoint sources, an extended X-ray emission component was detected over a5×9 pc2 region, with the 0.5-8 keV absorption-correctedluminosity of 2×1033 ergs s-1. Thecontribution from faint point sources to this extended emission wasestimated as at most ~20%, suggesting that most of the emission isdiffuse in nature. The X-ray spectrum of the diffuse emission wasobserved to vary from place to place. In tenuous molecular cloud regionswith hydrogen column density of (0.5-1)×1022cm-2, the spectrum can be represented by a thermal plasmamodel with temperatures of several keV. The spectrum in dense cloudcores exhibits harder continuum, together with higher absorption of morethan ~3×1022 cm-2. In some of such highlyobscured regions, the spectra show extremely hard continua equivalent toa photon index of ~1, and favor a nonthermal interpretation. Theseresults are discussed in the context of thermal and nonthermal emission,both powered by fast stellar winds from embedded young early-type starsthrough shock transitions.
| A Millimeter Continuum Survey for Massive Protoclusters in the Outer Galaxy
Our search for the earliest stages of massive star formation turned up12 massive pre-protocluster candidates plus a few protoclusters. Forthis search, we selected 47 FIR-bright IRAS sources in the outer Galaxy.We mapped regions of several square arcminutes around the IRAS source inthe millimeter continuum in order to find massive cold cloud corespossibly being in a very early stage of massive star formation. Massesand densities are derived for the 128 molecular cloud cores found in theobtained maps. We present these maps together with near-infrared,mid-infrared, and radio data collected from the 2MASS, MSX, and NVSScatalogs. Further data from the literature on detections of high-densitytracers, outflows, and masers are added. The multiwavelength data setsare used to characterize each observed region. The massive cloud cores(M>100 Msolar) are placed in a tentative evolutionarysequence depending on their emission at the investigated wavelengths.Candidates for the youngest stages of massive star formation areidentified by the lack of detections in the above-mentionednear-infrared, mid-infrared, and radio surveys. Twelve massive coresprominent in the millimeter continuum fulfill this requirement. Sinceneither FIR nor radio emission have been detected from these cloudcores, massive protostars must be very deeply embedded in these cores.Some of these objects may actually be pre-protocluster cores: an up tonow rare object class, where the initial conditions of massive starformation can be studied.
| Is the INTEGRAL IBIS Source IGR J17204-3554 a Gamma-Ray-emitting Galaxy Hidden behind the Molecular Cloud NGC 6334?
We report on the identification of a soft gamma-ray source, IGRJ17204-3554, detected with IBIS, the Imager on Board the INTEGRALSatellite. The source has a 20-100 keV flux of ~3×10-11ergs cm-2 s-1 and is spatially coincident with NGC6334, a molecular cloud located in the Sagittarius arm of the Milky Way.Diffuse X-ray emission has been reported from this region by ASCA andinterpreted as coming from five far-infrared cores located in the cloud.However, the combined ASCA spectrum with a 9 keV temperature wasdifficult to explain in terms of emission from young pre-main-sequencestars known to be embedded in the star-forming regions. Detection ofgamma rays makes this interpretation even more unrealistic and suggeststhe presence of a high-energy source in or behind the cloud. Follow-upobservations with Swift and archival Chandra data allow us todisentangle the NGC 6334 enigma by locating an extragalactic object withthe proper spectral characteristics to explain the gamma-ray emission.The combined Chandra-IBIS spectrum is well fitted by an absorbed powerlaw with Γ=1.2+/-0.1,NH=(1.4+/-0.1)×1023 cm-2, and anunabsorbed 2-10 keV flux of 0.5×10-11 ergscm-2 s-1. This column density is in excess of theGalactic value, implying that we are detecting a background galaxyconcealed by the molecular cloud and further hidden by material locatedeither in the galaxy itself or between IGR J17204-3554 and the cloud.Based on observations obtained with INTEGRAL, an ESA project withinstruments and science data center funded by ESA member states(especially the PI countries: Denmark, France, Germany, Italy,Switzerland, Spain), the Czech Republic, and Poland and with theparticipation of Russia and the US.
| The AAO/UKST SuperCOSMOS Hα survey
The UK Schmidt Telescope (UKST) of the Anglo-Australian Observatorycompleted a narrow-band Hα plus [NII] 6548, 6584-Åsurvey ofthe Southern Galactic Plane and Magellanic Clouds in late 2003. Thesurvey, which was the last UKST wide-field photographic survey and theonly one undertaken in a narrow-band, is now an online digital dataproduct of the Wide-Field Astronomy Unit of the Royal ObservatoryEdinburgh (ROE). The survey utilized a high specification, monolithicHα interference bandpass filter of exceptional quality. Inconjunction with the fine-grained Tech-Pan film as a detector it hasproduced a survey with a powerful combination of area coverage (4000square degrees), resolution (~1 arcsec) and sensitivity (<=5Rayleighs), reaching a depth for continuum point sources of R~= 20.5.The main survey consists of 233 individual fields on a grid of centresseparated by 4° at declinations below +2° and covers a swatheapproximately 20° wide about the Southern Galactic Plane. Theoriginal survey films were scanned by the SuperCOSMOS measuring machineat the Royal Observatory, Edinburgh, to provide the online digital atlascalled the SuperCOSMOS Hα Survey (SHS). We present the backgroundof the survey, the key survey characteristics, details and examples ofthe data product, calibration process, comparison with other surveys anda brief description of its potential for scientific exploitation.
| Radio and infrared study of the region associated with the molecular cloud complex NGC 6334.
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| A Survey of N IV and O IV Features near 3400 Å in O2-O5 Spectra
We have conducted a survey of little-known N IV and O IV multiplets near3400 Å in an extensive sample of well-classified, very earlyO-type spectra. The initial motivation was to search for additionaluseful classification criteria for these types, but an unexpected resultis the high sensitivity of these features to evolutionary CNOprocessing. We have found a useful discriminant between O2 and latertypes in the relative strengths of the O IV multiplets, one of which issubject to selective emission in the hottest spectra; the overallstrengths of these lines also decrease between spectral types O4 and O5.More remarkable, however, are the variations in the N/O ratios amongboth individual stars and clusters. For instance, several O4 If+ spectrahave very large ratios, while main-sequence stars in the Carina Nebulagenerally have smaller values than others of the same spectral types inother regions. These effects correspond to different degrees of mixingof processed material as a function of evolutionary age and initialrotational velocities; the second effect provides significant furtherevidence that very massive stars mix while still on the main sequence.Thus, further analysis of these features will likely provide valuablediagnostics of important evolutionary parameters.
| High Spatial Resolution Observations of NH3 and CH3OH toward the Massive Twin Cores NGC 6334I and NGC 6334I(N)
Molecular line observations of NH3 (J,K)=(1,1) and (2, 2) andCH3OH at 24.93 GHz taken with the Australian TelescopeCompact Array (ATCA) toward the massive twin cores NGC 6334I and NGC6334I(N) reveal significant variations in the line emission between thetwo massive cores. The UC H II region/hot core NGC 6334I exhibits strongthermal NH3 and CH3OH emission adjacent to the UCH II region and coincident with two millimeter continuum peaks observedby T. R. Hunter et al. In contrast, we find neither compactNH3 nor thermal CH3OH line emission toward NGC6334I(N). There the NH3 emission is distributed over a broadregion (>1') without a clear peak, and we find Class ICH3OH maser emission with peak brightness temperatures up to7000 K. The maser emission peaks appear to be spatially associated withthe interfaces between the molecular outflows and the ambient dense gas.Peak NH3 (1, 1) line brightness temperatures >=70 K inboth regions indicate gas temperatures on the same order. NH3emission is also detected toward the outflow in NGC 6334I, resulting inan estimated rotational temperature of Trot~19 K.Furthermore, we observe CH3OH and NH3 absorptiontoward the UC H II region; the velocity structure is consistent withexpanding molecular gas around the UC H II region. Thermal and kinematiceffects possibly imposed from the UC H II region on the molecular coreare also discussed.
| An Extended Search for Circularly Polarized Infrared Radiation from the OMC-1 Region of Orion
We present new observations of circular polarization (CP) at 2.2 μmin the Orion (OMC-1) molecular cloud. Our results extend a previouslypublished study of the region. We show that the degree of CP correlatesspatially with the molecular cloud and appears to be generally very lowin regions dominated by H II. We detect a feature with 3%-5% CP thatextends approximately 60" to the southwest of the BN/IRc2 region.Although the morphology of the observed CP is broadly consistent with amodel in which radiation from a central source (probably IRc2) isscattered by aligned spheroidal grains, we conclude that dichroicextinction in the foreground molecular cloud also plays a major role inits production. Implications of our results for the hypothesis that CPradiation imposes chiral asymmetry upon prebiotic organic molecules inprotoplanetary disks are discussed. Mechanisms invoked to explain theobserved CP in the near infrared can also produce CP in the range ofultraviolet wavelengths capable of chiral selection by photolysis;however, the polarized flux is likely to be of limited spatial extentand to have lower percentage CP compared with the infrared.
| Extended emission associated with young HII regions
We have used the Australia Telescope Compact Array (ATCA) to makeobservations of a sample of eight young ultra-compact HII regions,selected on the basis that they have associated class II methanol maseremission. We have made observations sensitive to both compact andextended structures and find both to be present in most sources. Thescale of the extended emission in our sample is in general less thanthat observed towards samples based on IRAS properties, or largesingle-dish flux densities. Our observations are consistent with ascenario where extended and compact radio continuum emission co-existswithin HII regions for a significant period of time.We suggest that these observations are consistent with a model where HIIevolution takes place within hierarchically structured molecular clouds.This model, which is the subject of an upcoming companion paper byShabala et al., addresses both the association between compact andextended emission and the ultra-compact HII region lifetime problem.
| Long-term monitoring of 6.7-GHz methanol masers
A sample of 54 6.7-GHz methanol masers was monitored using theHartebeesthoek 26-m telescope during the period 1999 January - 2003March. The observations were taken at 1-2 week intervals, with dailyobservations when possible if a source was seen to be varying rapidly.It was found that the majority of the sources display a significantlevel of variability. The time-range of variations range from a few daysup to several years. The types of behaviour observed includednon-varying, monotonic increases or decreases, as well as aperiodic,quasi-periodic and periodic variations. Seven sources show clearevidence of periodicity, with periods ranging from 132 d up to 520 d.
| A study of high velocity molecular outflows with an up-to-date sample
A statistical study of the properties of molecular outflows is performedbased on an up-to-date sample. 391 outflows were identified in publishedarticles or preprints before February 28, 2003. The parameters ofposition, morphology, mass, energy, outflow dynamics and central sourceluminosity are presented for each outflow source. Outflow lobe polarityis known for all the sources, and 84% are found to be bipolar. Thesources are divided into low mass and high mass groups according toeither the available bolometric luminosity of the central source or theoutflow mass. The pace of discovery of outflows over the past sevenyears has increased much more rapidly than in previous periods. Surveysfor outflows are still continuing. The number of high-mass outflowsdetected (139) has considerably increased, showing that they arecommonly associated with massive as well as low mass stars. Energeticmass ejection may be a common aspect of the formation of high mass aswell as low mass stars. Outflow masses are correlated strongly withbolometric luminosity of the center sources, which was obtained for thefirst time. There are also correlations between the central sourceluminosity and the parameters of mechanical luminosity and the thrust orforce necessary to drive the outflow. The results show that flow mass,momentum and energy depend on the nature of the central source. Despitetheir similarity, there are differences between the high mass and lowmass outflows. Low mass outflows are more collimated than high massoutflows. On average, the mass of high mass sources can be more than twoorders of magnitude larger than those of low mass outflows. The relationbetween flow mass and dynamical time appears to differ for the two typesof outflows. Low mass sources make up 90% of outflows associated with HHobjects while high mass outflows make up 61% of the sources associatedwith H_2O masers. Sources with characteristics of collapse or infallcomprise 12% of the entire outflow sample. The spatial distribution ofthe outflow sources in the Galaxy is presented and the local occurrencerate is compared with the stellar birth rate.Tables 1a and 1b are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/503
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