Showing papers on "Infrared dark cloud published in 2011"
TL;DR: In this paper, the authors present results of near-infrared (JHKs) polarization observations of the serpens south embedded cluster, which is located in the constricted part of a long, filamentary, infrared dark cloud, is believed to be in a very early stage of cluster formation.
Abstract: The Serpens South embedded cluster, which is located in the constricted part of a long, filamentary, infrared dark cloud, is believed to be in a very early stage of cluster formation. We present results of near-infrared (JHKs) polarization observations of the filamentary cloud. Our polarization measurements of near-infrared point sources indicate a well-ordered global magnetic field that is perpendicular to the main filament, implying that the magnetic field is likely to have controlled the formation of the main filament. On the other hand, the sub-filaments, which converge on the central part of the cluster, tend to run along the magnetic field. The global magnetic field appears to be curved in the southern part of the main filament. Such morphology is consistent with the idea that the global magnetic field is distorted by gravitational contraction along the main filament toward the northern part, which contains larger mass. Applying the Chandrasekhar-Fermi method, the magnetic field strength is roughly estimated to be a few ×100 μG, suggesting that the filamentary cloud is close to magnetically critical.
140 citations
TL;DR: In this paper, the authors measured the annual parallax of the H2O maser source associated with an infrared dark cloud MSXDC G034.43+00.24 from the observations with VERA (VLBI Exploration of Radio Astrometry).
Abstract: We have measured the annual parallax of the H2O maser source associated with an infrared dark cloud MSXDC G034.43+00.24 from the observations with VERA (VLBI Exploration of Radio Astrometry). The parallax is 0.643±0.049 mas, corresponding to the distance of 1.56 −0.11 kpc. This value is less than the half of the previous kinematic distance of 3.7 kpc. We revise the core mass estimates of MSXDC G034.43+00.24, based on virial masses, LTE masses and dust masses and show that the core masses decrease from the previous estimations of ∼ 1000M⊙ to hundreds of M⊙. The spectral type derived from the luminosity also changes from O9.5 to B1 in the case of MM1. This spectral type is still consistent with that of the massive star. The radial velocity derived from the flat rotation model is smaller than the observed velocity, which corresponds to the peculiar motion of ∼ 40 km s in the line-of-sight direction.
108 citations
TL;DR: In this article, the authors analyzed C 18 O J = 1 → 0 and J = 2 → 1 emission line data, taken with the Instituto de Radioastronomia Milimetrica 30 m telescope, of the highly filamentary IRDC G035.
Abstract: Infrared Dark Clouds (IRDCs) are cold, high mass surface density and high density structures, likely to be representative of the initial conditions for massive star and star cluster formation. CO emission from IRDCs has the potential to be useful for tracing their dynamics, but may be affected by depleted gas phase abundances due to freeze out onto dust grains. Here we analyze C 18 O J = 1 → 0 and J = 2 → 1 emission line data, taken with the Instituto de Radioastronomia Milimetrica 30 m telescope, of the highly filamentary IRDC G035.39.-0033. We derive the excitation temperature as a function of position and velocity, with typical values of ∼7 K, and thus derive total mass surface densities, ΣC18O, assuming standard gas phase abundances and accounting for optical depth in the line, which can reach values of ∼1. The mass surface densities reach values of ∼0.07 g cm −2 . We compare these results to the mass surface densities derived from mid-infrared extinction mapping, ΣSMF, by Butler & Tan, which are expected to be insensitive to the dust temperatures in the cloud. With a significance of 10σ, we find ΣC18O/ΣSMF decreases by about a factor of five as Σ increases from ∼0.02 to ∼0. 2gc m −2 , which we interpret as evidence for CO depletion. Several hundred solar masses are being affected, making this one of the most massive clouds in which CO depletion has been observed directly. We present a map of the depletion factor in the filament and discuss implications for the formation of the IRDC.
104 citations
TL;DR: In this paper, the authors measured the annual parallax of the H2O maser source associated with an infrared dark cloud MSXDC G034.43+00.24 from the observations with VERA (VLBI Exploration of Radio Astrometry).
Abstract: We have measured the annual parallax of the H2O maser source associated with an infrared dark cloud MSXDC G034.43+00.24 from the observations with VERA (VLBI Exploration of Radio Astrometry). The parallax is 0.643 +/- 0.049 mas, corresponding to the distance of 1.56 +0.12/-0.11 kpc. This value is less than the half of the previous kinematic distance of 3.7 kpc. We revise the core mass estimates of MSXDC G034.43+00.24, based on virial masses, LTE masses and dust masses and show that the core masses decrease from the previous estimations of ~1000 Mo to hundreds of Mo. The spectral type derived from the luminosity also changes from O9.5 to B1 in the case of MM1. This spectral type is still consistent with that of the massive star. The radial velocity derived from the flat rotation model is smaller than the observed velocity, which corresponds to the peculiar motion of ~40 km/s in the line-of-sight direction.
61 citations
TL;DR: In this article, the authors used the Large APEX Bolometer Camera LABOCA at the APEX telescope to map a 1.25° × 1.5° region at 870μ m with 18′′ angular resolution and an rms-noise level of ǫ 20mJy/beam.
Abstract: Context. The Great Nebula in Carina is one of the most massive (M ∗ ,total ≳25 000 M ⊙ ) star-forming complexes in our Galaxy and contains several stars with (initial) masses exceeding ≈100 M ⊙ ; it is therefore a superb location in which to study the physics of violent massive star-formation and the resulting feedback effects, including cloud dispersal and triggered star-formation. Aims. We aim to reveal the cold dusty clouds in the Carina Nebula complex, to determine their morphology and masses, and to study the interaction of the luminous massive stars with these clouds. Methods. We used the Large APEX Bolometer Camera LABOCA at the APEX telescope to map a 1.25° × 1.25° (≙ 50 × 50 pc2 ) region at 870 μ m with 18′′ angular resolution (= 0.2 pc at the distance of the Carina Nebula) and an rms noise level of ≈20 mJy/beam.Results. From a comparison to Hα images we infer that about 6% of the 870 μ m flux in the observed area is likely free-free emission from the HII region, while about 94% of the flux is very likely thermal dust emission. The total (dust + gas) mass of all clouds for which our map is sensitive is ~60 000 M ⊙ , in good agreement with the mass of the compact clouds in this region derived from 13 CO line observations. There is a wide range of different cloud morphologies and sizes, from large, massive clouds with several 1000 M ⊙ , to small diffuse clouds containing just a few M ⊙ . We generally find good agreement in the cloud morphology seen at 870 μ m and the Spitzer 8 μ m emission maps, but also identify a prominent infrared dark cloud. Finally, we construct a radiative transfer model for the Carina Nebula complex that reproduces the observed integrated spectral energy distribution reasonably well.Conclusions. Our analysis suggests a total gas + dust mass of about 200 000 M ⊙ in the investigated area; most of this material is in the form of molecular clouds, but a widely distributed component of (partly) atomic gas, containing up to ~50% of the total mass, may also be present. Currently, only some 10% of the gas is in sufficiently dense clouds to be immediately available for future star formation, but this fraction may increase with time owing to the ongoing compression of the strongly irradiated clouds and the expected shockwaves of the imminent supernova explosions.
55 citations
TL;DR: In this article, NH3 (1,1), (2,2), and CCS (2_1-1_0) emission toward the Infrared Dark Cloud (IRDC) G19.30+0.07 at ~22GHz were observed.
Abstract: We present Very Large Array observations of ammonia (NH3) (1,1), (2,2), and CCS (2_1-1_0) emission toward the Infrared Dark Cloud (IRDC) G19.30+0.07 at ~22GHz. The NH3 emission closely follows the 8 micron extinction. The NH3 (1,1) and (2,2) lines provide diagnostics of the temperature and density structure within the IRDC, with typical rotation temperatures of ~10 to 20K and NH3 column densities of ~10^15 cm^-2. The estimated total mass of G19.30+0.07 is ~1130 Msun. The cloud comprises four compact NH3 clumps of mass ~30 to 160 Msun. Two coincide with 24 micron emission, indicating heating by protostars, and show evidence of outflow in the NH3 emission. We report a water maser associated with a third clump; the fourth clump is apparently starless. A non-detection of 8.4GHz emission suggests that the IRDC contains no bright HII regions, and places a limit on the spectral type of an embedded ZAMS star to early-B or later. From the NH3 emission we find G19.30+0.07 is composed of three distinct velocity components, or "subclouds." One velocity component contains the two 24 micron sources and the starless clump, another contains the clump with the water maser, while the third velocity component is diffuse, with no significant high-density peaks. The spatial distribution of NH3 and CCS emission from G19.30+0.07 is highly anti-correlated, with the NH3 predominantly in the high-density clumps, and the CCS tracing lower-density envelopes around those clumps. This spatial distribution is consistent with theories of evolution for chemically young low-mass cores, in which CCS has not yet been processed to other species and/or depleted in high-density regions.
48 citations
TL;DR: In this article, the Expanded Very Large Array (EVLA) spectral line observations toward P1 in the NH3 (J,K) = (1,1), (2,2), (3,3) lines, as well as H2O and class I CH3OH masers are presented.
Abstract: The dense molecular clump P1 in the infrared dark cloud (IRDC) complex G28.34+0.06 harbors a massive protostellar cluster at its extreme youth. Our previous Submillimeter Array (SMA) observations revealed several jet-like CO outflows emanating from the protostars, indicative of intense accretion and potential interaction with ambient natal materials. Here we present the Expanded Very Large Array (EVLA) spectral line observations toward P1 in the NH3 (J,K) = (1,1), (2,2), (3,3) lines, as well as H2O and class I CH3OH masers. Multiple NH3 transitions reveal the heated gas widely spread in the 1 pc clump. The temperature distribution is highly structured; the heated gas is offset from the protostars, and morphologically matches the outflows very well. Hot spots of spatially compact, spectrally broad NH3 (3,3) emission are also found coincident with the outflows. A weak NH3 (3,3) maser is discovered at the interface between an outflow jet and the ambient gas. These findings suggest that protostellar heating may not be effective in suppressing fragmentation during the formation of massive cores.
41 citations
TL;DR: In this article, the Mid-course Space Experiment dark cloud G084.81-01.09 was mapped in the NH(3)(1, 1, 1)-(4, 4) lines and in the J = 1-0 transitions of (12)CO, (13) CO, C(18)O, and HCO(+) in order to study the physical properties of infrared dark clouds and to better understand the initial conditions for massive star formation.
Abstract: We mapped the Mid-course Space Experiment dark cloud G084.81-01.09 in the NH(3)(1,1)-(4,4) lines and in the J = 1-0 transitions of (12)CO, (13)CO, C(18)O, and HCO(+) in order to study the physical properties of infrared dark clouds, and to better understand the initial conditions for massive star formation. Six ammonia cores are identified with masses ranging from 60 to 250 M(circle dot), a kinetic temperature of 12 K, and a molecular hydrogen number density n(H(2)) similar to 10(5) cm(-3). In our high-mass cores, the ammonia line width of 1 km s(-1) is larger than those found in lower mass cores but narrower than the more evolved massive ones. We detected self-reversed profiles in HCO(+) across the northern part of our cloud and velocity gradients in different molecules. These indicate an expanding motion in the outer layer and more complex motions of the clumps more inside our cloud. We also discuss the millimeter wave continuum from the dust. These properties indicate that our cloud is a potential site of massive star formation but is still in a very early evolutionary stage.
30 citations
TL;DR: In this article, the MSX dark cloud G084.81-01.09 was mapped in the NH3 (1) - (4,4) lines and in the J = 1-0 transitions of 12CO, 13CO, C18O and HCO+ to study the physical properties of infrared dark clouds, and to better understand the initial conditions for massive star formation.
Abstract: We mapped the MSX dark cloud G084.81-01.09 in the NH3 (1,1) - (4,4) lines and in the J = 1-0 transitions of 12CO, 13CO, C18O and HCO+ in order to study the physical properties of infrared dark clouds, and to better understand the initial conditions for massive star formation. Six ammonia cores are identified with masses ranging from 60 to 250 M_sun, a kinetic temperature of 12 K, and a molecular hydrogen number density n(H2) ~ 10^5 cm^-3. In our high mass cores, the ammonia line width of 1 km/s is larger than those found in lower mass cores but narrower than the more evolved massive ones. We detected self-reversed profiles in HCO+ across the northern part of our cloud and velocity gradients in different molecules. These indicate an expanding motion in the outer layer and more complex motions of the clumps more inside our cloud. We also discuss the millimeter wave continuum from the dust. These properties indicate that our cloud is a potential site of massive star formation but is still in a very early evolutionary stage.
25 citations
TL;DR: In this article, the physical properties of IRDCs in very early evolutionary phases were studied. But the authors focused on the early stages of the IRDC evolution and only selected the filamentary IRDC G351.77−0.51, which is remarkably IR quiet at 8 μm.
Abstract: Context. Infrared dark clouds are massive, dense clouds seen in extinction against the IR Galactic background. Many of these objects appear to be on the verge of star and star cluster formation.
Aims. Our aim is to understand the physical properties of IRDCs in very early evolutionary phases. We selected the filamentary IRDC G351.77−0.51, which is remarkably IR quiet at 8 μm.
Methods. As a first step, we observed mm dust continuum emission and rotational lines of moderate and dense gas tracers to characterise different condensations along the IRDC and study the velocity field of the filament.
Results. Our initial study confirms coherent velocity distribution along the infrared dark cloud ruling out any coincidental projection effects. Excellent correlation between MIR extinction, mm continumm emission and gas distribution is found. Large-scale turbulence and line profiles throughout the filament is indicative of a shock in this cloud. Excellent correlation between line width and MIR brightness indicates turbulence driven by local star formation.
23 citations
TL;DR: In this article, a core in the archetypal filamentary IRDC G11.11-0.12 at few arcsecond resolution was analyzed with the Plateau de Bure Interferometer.
Abstract: Recent studies suggest that infrared dark clouds (IRDCs) have the potential of harboring the earliest stages of massive star formation and indeed evidence for this is found toward distinct regions within them. We present a study with the Plateau de Bure Interferometer of a core in the archetypal filamentary IRDC G11.11-0.12 at few arcsecond resolution to determine its physical and chemical structure. The data consist of continuum and line observations covering the C34S 2-1 line and the methanol 2_k-1_k v_t=0 lines at 3mm and the methanol 5_k-4_k v_t =0 lines at 1mm. Our observations show extended emission in the continuum at 1 and 3 mm. The methanol 2_k-1_k v_t=0 emission presents three maxima extending over 1 pc scale (when merged with single-dish short-spacing observations); one of the maxima is spatially coincident with the continuum emission. The fitting results show enhanced methanol fractional abundance (~3x10^-8) at the central peak with respect to the other two peaks, where it decreases by about an order of magnitude (~4-6x10^-9). Evidence of extended 4.5 microns emission, "wings" in the CH3OH 2_k-1_k spectra, and CH3OH abundance enhancement point to the presence of an outflow in the East-West direction. In addition, we find a gradient of ~4 km/s in the same direction, which we interpret as being produced by an outflow(s)-cloud interaction.
01 May 2011
TL;DR: In this article, the behavior of different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission was investigated.
Abstract: We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in high-density molecular tracers at 3 mm using the 22 m ATNF Mopra Telescope located in Australia. After determining kinematic distances, we eliminated clumps that are not located in IRDCs and clumps with a separation between them of less than one Mopra beam. Our final sample consists of 92 IRDC clumps. The most commonly detected molecular lines are (detection rates higher than 8%) N2H+, HNC, HN13C, HCO+, H13CO+, HCN, C2H, HC3N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. The presence of HNC and N2H+ lines does not depend on the star formation activity. On the other hand, HC3N, HNCO, and SiO are predominantly detected in later stages of evolution. Optical depth calculations show that in IRDC clumps the N2H+ line is optically thin, the C2H line is moderately optically thick, and HNC and HCO+ are optically thick. The HCN hyperfine transitions are blended, and, in addition, show self-absorbed line profiles and extended wing emission. These factors combined prevent the use of HCN hyperfine transitions for the calculation of physical parameters. Total column densities of the different molecules, except C2H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for N2H+ and HCO+. The N2H+/HCO+ and N2H+/HNC abundance ratios act as chemical clocks, increasing with the evolution of the clumps.
TL;DR: In this article, the first spectroscopic mapping of an atomic carbon line in an infrared dark cloud (IRDC) was performed using the 2 x 4 pixel SMART receiver of the KOSMA observatory on Gornergrat.
Abstract: Aims. We report the first spectroscopic mapping of an atomic carbon line in an infrared dark cloud (IRDC). By observing the spatial distribution of the [Ci] emission in an IRDC, comparing it with the (13)CO emission and the known distribution of internal heating sources, we can quantify the role of internal and external UV irradiation in the production of atomic carbon. Methods. We used the 2 x 4 pixel SMART receiver of the KOSMA observatory on Gornergrat to map the [Ci] (3)P(1) - (3)P(0) line in the IRDC G48.65-0.29 and compared the resulting spectra with data from the BU-FCRAO (13)CO 1-0 Galactic Ring Survey. Results. The [CI]/(13)CO effective beam temperature ratio falls at about 0.3 with local deviations by less than a factor two. All velocity components seen in (13)CO are also detected in [CI]. We find, however, significant differences in the morphology of the brightest regions seen in the two tracers. While (13)CO basically follows the column density distribution derived from the near-infrared (NIR) extinction and the submm continuum, the [CI] emission peaks at the locations of the two known NIR point sources. We find Ci/CO abundance ratios between 0.07 and 0.13 matching the lower end of the range previously measured in star-forming regions. Conclusions. Evaluating the relative importance of the irradiation by embedded sources and by the Galactic interstellar UV field, we find that in G48.65-0.29 most [CI] emission can be attributed to externally illuminated surfaces. Embedded sources have a significant impact on the overall abundance distribution of atomic carbon as soon as they are found in an evolved state with noticeable NIR flux.
TL;DR: In this paper, the polarization measurements of near-infrared point sources indicate a well-ordered global magnetic field that is perpendicular to the main filament, implying that the magnetic field is likely to have controlled the formation of the filament.
Abstract: The Serpens South embedded cluster, which is located at the constricted part in a long filamentary infrared dark cloud, is believed to be in very early stage of cluster formation. We present results of near-infrared (JHKs) polarization observations toward the filamentary cloud. Our polarization measurements of near-infrared point sources indicate a well-ordered global magnetic field that is perpendicular to the main filament, implying that the magnetic field is likely to have controlled the formation of the main filament. On the other hand, the sub-filaments, which converge on the central part of the cluster, tend to run along the magnetic field. The global magnetic field appears to be curved in the southern part of the main filament. Such morphology is consistent with the idea that the global magnetic field is distorted by gravitational contraction along the main filament toward the northern part that contains larger mass. Applying the Chandrasekhar-Fermi method, the magnetic field strength is roughly estimated to be a few x 100 microgauss, suggesting that the filamentary cloud is close to magnetically critical as a whole.
TL;DR: In this article, the authors obtained 350 and 850 μm continuum maps of the infrared dark cloud G049.40-00.01 and reported physical properties of the clumps.
Abstract: We obtained 350 and 850 μm continuum maps of the infrared dark cloud G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01 based on the 350 μm continuum map with an angular resolution of about 9".6. We present submillimeter continuum maps and report physical properties of the clumps. The masses of clumps range from 50 to 600 M_☉. About 70% of the clumps are associated with bright 24 μm emission sources, and they may contain protostars. The two most massive clumps show extended, enhanced 4.5 μm emission indicating vigorous star-forming activity. The clump-size-mass distribution suggests that many of them are forming high-mass stars. G049.40-00.01 contains numerous objects in various evolutionary stages of star formation, from pre-protostellar clumps to H II regions.
TL;DR: The infrared dark cloud G359.94+0.17 is a conspicuous, opaque cloud, which is seen in silhouette against the Galactic center as discussed by the authors, and it is associated with the 15 km/s cloud, suggesting that it is located at the Norma spiral arm.
Abstract: The infrared dark cloud G359.94+0.17 is a conspicuous, opaque cloud, which is seen in silhouette against the Galactic center. We found unexpectedly strong (~50 Jy) maser emission of CH3OH at 44 GHz with additional weak 22 GHz H2O maser and 43 GHz SiO thermal emissions toward this cloud. Detections of these molecular lines indicate that strong star forming activities are proceeding in this cloud, which were not reported previously despite of numerous works toward the Galactic center. The line profiles of the NH3 inversion lines at 23 GHz indicate that G359.94+0.17 is composed of mainly two clouds with V(lsr)= 0, and 15 km/s overlapped on the line of sight. The maser emission is associated with the 15 km/s cloud, suggesting that it is located at the Norma spiral arm.
TL;DR: In this paper, the authors analyzed C18O J=1-0 and J=2-1 emission line data, taken with the IRAM 30m telescope, of the highly filamentary IRDC G035.
Abstract: Infrared Dark Clouds (IRDCs) are cold, high mass surface density and high density structures, likely to be representative of the initial conditions for massive star and star cluster formation. CO emission from IRDCs has the potential to be useful for tracing their dynamics, but may be affected by depleted gas phase abundances due to freeze-out onto dust grains. Here we analyze C18O J=1-0 and J=2-1 emission line data, taken with the IRAM 30m telescope, of the highly filamentary IRDC G035.39.-0033. We derive the excitation temperature as a function of position and velocity, with typical values of ~7K, and thus derive total mass surface densities, Sigma_C18O, assuming standard gas phase abundances and accounting for optical depth in the line, which can reach values of ~1. The mass surface densities reach values of ~0.07 g/cm^2. We compare these results to the mass surface densities derived from mid-infrared (MIR) extinction mapping, Sigma_SMF, by Butler & Tan, which are expected to be insensitive to the dust temperatures in the cloud. With a significance of >10sigma, we find Sigma_C18O/Sigma_SMF decreases by about a factor of 5 as Sigma increases from ~0.02 to ~0.2 g/cm^2, which we interpret as evidence for CO depletion. Several hundred solar masses are being affected, making this one of the most massive clouds in which CO depletion has been observed directly. We present a map of the depletion factor in the filament and discuss implications for the formation of the IRDC.
TL;DR: In this paper, the authors obtained 350 and 850 micron continuum maps of the infrared dark cloud G049.40-00.01 and reported physical properties of the clumps.
Abstract: We obtained 350 and 850 micron continuum maps of the infrared dark cloud G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01 based on the 350 micron continuum map with an angular resolution of about 9.6". We present submillimeter continuum maps and report physical properties of the clumps. The masses of clumps range from 50 to 600 M_sun. About 70% of the clumps are associated with bright 24 micron emission sources, and they may contain protostars. The most massive two clumps show extended, enhanced 4.5 micron emission indicating vigorous star-forming activity. The clump size-mass distribution suggests that many of them are forming high mass stars. G049.40-00.01 contains numerous objects in various evolutionary stages of star formation, from pre-protostellar clumps to HII regions.