Showing papers on "Infrared dark cloud published in 2012"
TL;DR: In this article, the authors developed the mid-infrared extinction (MIREX) mapping technique of Butler & Tan (Paper I), presenting a new method to correct for the Galactic foreground emission based on observed saturation in independent cores.
Abstract: We develop the mid-infrared extinction (MIREX) mapping technique of Butler & Tan (Paper I), presenting a new method to correct for the Galactic foreground emission based on observed saturation in independent cores. Using Spitzer GLIMPSE 8 μm images, this allows us to accurately probe mass surface densities, Σ, up to 0.5 g cm–2 with 2'' resolution and mitigate one of the main sources of uncertainty associated with Galactic MIREX mapping. We then characterize the structure of 42 massive starless and early-stage cores and their surrounding clumps, selected from 10 infrared dark clouds, measuring Σcl(r) from the core/clump centers. We first assess the properties of the core/clump at a scale where the total enclosed mass as projected on the sky is M cl = 60 M ☉. We find that these objects have a mean radius of R cl 0.1 pc, mean and, if fitted by a power-law (PL) density profile , a mean value of k ρ, cl = 1.1. If we assume a core is embedded in each clump and subtract the surrounding clump envelope to derive the core properties, then we find a mean core density PL index of k ρ, c = 1.6. We repeat this analysis as a function of radius and derive the best-fitting PL plus uniform clump envelope model for each of the 42 core/clumps. The cores have typical masses of Mc ~ 100 M ☉ and , and are embedded in clumps with comparable mass surface densities. We also consider Bonnor-Ebert density models, but these do not fit the observed Σ profiles as well as PLs. We conclude that massive starless cores exist and are well described by singular polytropic spheres. Their relatively low values of Σ and the fact that they are IR dark may imply that their fragmentation is inhibited by magnetic fields rather than radiative heating. Comparing to massive star-forming cores and clumps, there is tentative evidence for an evolution toward higher densities and steeper density profiles as star formation proceeds.
207 citations
TL;DR: In this article, the Expanded Very Large Array 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 complex G28.34+0.06 harbors a massive protostellar cluster at its extreme youth. Our previous Submillimeter Array 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 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 features 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.
75 citations
TL;DR: In this paper, the authors derived mass from combined NIR and MIR extinction maps and velocity dispersion from C18O (1-0) and (2-1) line emission for the filamentary IRDC G035.39-00.33.
Abstract: The initial conditions of massive star and star cluster formation are expected to be cold, dense, and high column density regions of the interstellar medium, which can reveal themselves via near-, mid-, and even far-infrared absorption as infrared dark clouds (IRDCs). Elucidating the dynamical state of IRDCs thus constrains theoretical models of these complex processes. In particular, it is important to assess whether IRDCs have reached virial equilibrium, where the internal pressure balances that due to the self-gravitating weight of the cloud plus the pressure of the external environmental. We study this question for the filamentary IRDC G035.39-00.33 by deriving mass from combined NIR and MIR extinction maps and velocity dispersion from C18O (1-0) and (2-1) line emission. In contrast to our previous moderately super-virial results based on 13CO emission and MIR-only extinction mapping, with improved mass measurements we now find that the filament is consistent with being in virial equilibrium, at least in its central parsec-wide region where ~1000 M ☉ snakes along several parsecs. This equilibrium state does not require large-scale net support or confinement by magnetic fields.
46 citations
TL;DR: In this paper, the kinematical and dynamical state of the cloud and clumps within it, and the amount of CO depletion in the clumps were investigated, showing that most of them are gravitationally bound and the external pressure may also play a nonnegligible role in the dynamics.
Abstract: Context Infrared dark clouds (IRDCs) are promising sites to study the earliest formation stages of stellar clusters and high-mass stars, and the physics of molecular-cloud formation and fragmentation Aims We attempt to improve our understanding of the physical and chemical properties of the filamentary IRDC G30474+0132 (hereafter, G30474) In particular, we investigate the kinematical and dynamical state of the cloud and clumps within it, and the amount of CO depletion Methods All of the submillimetre peak positions in the cloud identified from our previous LABOCA 870-μm map were observed in C 17 O(2−1) with APEX These are the first line observations along the whole filament that have been made so far Selected positions were also observed in the 13 CO(2−1), SiO(5−4), and CH3OH(5k−4k) transitions at ∼1 mm Results The C 17 O lines were detected towards all target positions at similar radial velocities CO does not appear to be significantly depleted in the clumps, the largest depletion factors being only about 2 Two to three methanol 5k−4k lines near ∼2418 GHz were detected towards all selected positions, whereas SiO(5−4) was seen in only one of these positions, namely SMM 3 In the band covering SiO(5−4), we also detected the DCN(3−2) line towards SMM 3 The 13 CO(2−1) lines display blue asymmetric profiles, which are indicative of large-scale infall motions The clumps show transonic to supersonic non-thermal motions, and a virial-parameter analysis suggests that most of them are gravitationally bound The external pressure may also play a non-negligible role in the dynamics Our analysis suggests that the fragmentation of the filament into clumps is caused by a “sausage”-type instability, in agreement with results from other IRDCs Conclusions The uniform C 17 O radial velocities along the G30474 cloud shows that it is a coherent filamentary structure Although the clumps appear to be gravitationally bound, the ambient turbulent ram pressure may be an important factor in the cloud dynamics This is qualitatively consistent with our earlier suggestion that the filament was formed by converging supersonic turbulent flows The poloidal magnetic field could resist the radial cloud collapse, which conforms to the low infall velocites that we derived The cloud may be unable to form high-mass stars based on the mass-size threshold The star-formation activity in the cloud, such as outflows, is likely responsible for the release of CO from the icy grain mantles back into the gas phase Shocks related to outflows may also have injected CH3OH, SiO, and DCN into the gas-phase in SMM 3
44 citations
TL;DR: In this paper, the authors used data taken as part of the Herschel infrared Galactic Plane survey (Hi-GAL) to study 3171 infrared dark cloud (IRDC) candidates that were identified in the mid-IR (8 μm) by Spitzer (we refer to these as ‘Spitzer-dark’ regions).
Abstract: We have used data taken as part of the Herschel infrared Galactic Plane survey (Hi-GAL) to study 3171 infrared dark cloud (IRDC) candidates that were identified in the mid-IR (8 μm) by Spitzer (we refer to these as ‘Spitzer-dark’ regions). They all lie in the range l= 300–330° and |b|≤ 1°. Of these, only 1205 were seen in emission in the far-IR (250–500 μm) by Herschel (we call these ‘Herschel-bright’ clouds). It is predicted that a dense cloud will not only be seen in absorption in the mid-IR, but will also be seen in emission in the far-IR at the longest Herschel wavebands (250–500 μm). If a region is dark at all wavelengths throughout the mid-IR and far-IR, then it is most likely to be simply a region of lower background IR emission (a ‘hole in the sky’). Hence, it appears that previous surveys, based on Spitzer and other mid-IR data alone, may have overestimated the total IRDC population by a factor of ∼2. This has implications for estimates of the star formation rate in IRDCs in the Galaxy. We studied the 1205 Herschel-bright IRDCs at 250 μm and found that 972 of them had at least one clearly defined 250-μm peak, indicating that they contained one or more dense cores. Of these, 653 (67 per cent) contained an 8-μm point source somewhere within the cloud, 149 (15 per cent) contained a 24-μm point source but no 8-μm source and 170 (18 per cent) contained no 24- or 8-μm point sources. We use these statistics to make inferences about the lifetimes of the various evolutionary stages of IRDCs.
40 citations
TL;DR: In this article, the authors search for genuine infrared-dark clouds (IRDCs) and precursors to massive stars and stellar clusters in the Galactic plane, and to determine their basic physical properties.
Abstract: Context. Imaging surveys of dust emission at (sub)millimetre wavelengths provide a powerful tool for studying molecular clouds and the early stages of star formation. Aims. Through submm dust continuum mapping, we attempt to search for genuine infrared-dark clouds (IRDCs) and precursors to massive stars and stellar clusters in the Galactic plane, and to determine their basic physical properties. Methods. We have mapped four selected fields of about 0. 5 × 0. ◦ 5 that contain Spitzer 8-μm dark regions with LABOCA at 870 μm. Selected positions in the fields were observed in C 17 O(2−1) to obtain kinematic information. The obtained LABOCA maps are used in conjunction with the Spitzer IR images. Results. The total number of clumps identified in this survey is 91, out of which 40 (44%) appear dark at 8 and 24 μm. The remaining clumps are associated with mid-IR emission. Seven clumps associated with extended 4.5 μm emission are candidate extended green objects (EGOs). Filamentary dust “ridges” were found towards the Spitzer bubbles N10/11 in one of our fields. The relative number of IR-dark and IR-bright clumps suggests that the duration of the former stage is about 1.6 × 10 5 yr. The mass distribution of the total sample of clumps, and that separately constructed for the IR-dark and IR-bright clumps, could be fitted at the high-mass end with the power-law function dN/dlog M ∝ M −Γ ,w hereΓ � 0.7 ... 0.8. The C 17 O observation positions appear to be dominated by non-thermal motions, and the data also revealed some potential sites of strong CO depletion. In G11.36+0.80, which is the best example of a filamentary IRDC in our sample, the clumps appear to be gravitationally bound. The fragmentation of the filament can be understood in terms of a sausage-type fluid instability, in agreement with the results for other IRDCs. The fragmentation and the CO depletion timescales in G11.36 appear to be very similar to each other. Conclusions. Many of the identified clumps are massive enough to allow high-mass star formation, and some of them already show clear signposts of that. In the N10/11 bubble environment, the morphology of the detected dust emission conforms to the triggered high-mass star formation in the system. The clump mass distributions are similar to those found for diffuse CO clumps, and can be explained by the action of supersonic turbulence. The formation of filamentary IRDCs might be caused by converging turbulent flows, and the same process may play a role in exciting the fluid perturbations responsible for the fragmentation of the clouds into clumps.
31 citations
TL;DR: In this paper, the authors derived mass from combined NIR and MIR extinction maps and velocity dispersion from C18O (1-0) & (2-1) line emission to assess whether IRDCs have reached virial equilibrium.
Abstract: The initial conditions of massive star and star cluster formation are expected to be cold, dense and high column density regions of the interstellar medium, which can reveal themselves via near, mid and even far-infrared absorption as Infrared Dark Clouds (IRDCs). Elucidating the dynamical state of IRDCs thus constrains theoretical models of these complex processes. In particular, it is important to assess whether IRDCs have reached virial equilibrium, where the internal pressure balances that due to the self-gravitating weight of the cloud plus the pressure of the external environmental. We study this question for the filamentary IRDC G035.39-00.33 by deriving mass from combined NIR & MIR extinction maps and velocity dispersion from C18O (1-0) & (2-1) line emission. In contrast to our previous moderately super-virial results based on 13CO emission and MIR-only extinction mapping, with improved mass measurements we now find that the filament is consistent with being in virial equilibrium, at least in its central parsec-wide region where ~1000 M_Sun snakes along several parsecs. This equilibrium state does not require large-scale net support or confinement by magnetic fields.
29 citations
TL;DR: In this paper, the authors have mapped four selected about 0.5 deg x 0. 5 deg-sized fields containing Spitzer 8-micron dark regions with APEX/LABOCA at 870 micron.
Abstract: We have mapped four selected about 0.5 deg x 0.5 deg-sized fields containing Spitzer 8-micron dark regions with APEX/LABOCA at 870 micron. Selected positions in the fields were observed in C17O(2-1) to obtain kinematic information. The obtained LABOCA maps are used in conjunction with the Spitzer IR images. The total number of clumps identified in this survey is 91, out of which 40 (44%) appear dark at 8 and 24 micron. The remaining clumps are associated with mid-IR emission. Many of the identified clumps are massive enough to allow high-mass star formation, and some of them already show clear signposts of that. Seven clumps associated with extended-like 4.5 micron emission are candidate extended green objects (EGOs). Filamentary dust "ridges" were found towards the Spitzer bubbles N10/11 in one of our fields, which conforms to the triggered high-mass star formation in the system. The relative number of IR-dark and IR-bright clumps suggest that the duration of the former stage is about 1.6x10^5 yr. The mass distribution of the total sample of clumps, and that separately constructed for the IR-dark and IR-bright clumps, could be fitted at the high-mass end with the power-law function dN/dlogM ~ M^(-0.8...-0.7). The C17O observation positions appear to be dominated by non-thermal motions, and the data also revealed some potential sites of strong CO depletion. In G11.36+0.80, which is the best example of a filamentary IRDC in our sample, the clumps appear to be gravitationally bound. The fragmentation of the filament can be understood in terms of a "sausage"-type fluid instability, in agreement with the results for other IRDCs. The formation of filamentary IRDCs might be caused by converging turbulent flows, and the same process may play a role in exciting the fluid perturbations responsible for the fragmentation of the clouds into clumps.
24 citations
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 mentioned in this paper, and it is associated with the 15 km s � 1 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 was not reported previously despite of numerous studies 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 Vlsr = 0, and 15 km s � 1 overlapped on the line of sight. The maser emission is associated with the 15 km s � 1 cloud, suggesting that it is located at the Norma spiral arm.
4 citations
TL;DR: In this article, temperature probability density distributions within a model protostellar core for four dust components were calculated and compared with observations of a representative infrared dark cloud core, and it was shown that stochastic heating induced by the standard interstellar radiation field, cannot explain high mid-IR emission toward the centre of the core.
Abstract: Stochastic heating of small grains is often mentioned as a primary cause of large infrared (IR) fluxes from star-forming galaxies, e.g. at 24\mu m. If the mechanism does work at a galaxy-wide scale, it should show up at smaller scales as well. We calculate temperature probability density distributions within a model protostellar core for four dust components: large silicate and graphite grains, small graphite grains, and polycyclic aromatic hydrocarbon particles. The corresponding spectral energy distributions are calculated and compared with observations of a representative infrared dark cloud core. We show that stochastic heating, induced by the standard interstellar radiation field, cannot explain high mid-IR emission toward the centre of the core. In order to reproduce the observed emission from the core projected centre, in particular, at 24\mu m, we need to increase the ambient radiation field by a factor of about 70. However, the model with enhanced radiation field predicts even higher intensities at the core periphery, giving it a ring-like appearance, that is not observed. We discuss possible implications of this finding and also discuss a role of other non-radiative dust heating processes.
4 citations
01 Jan 2012
TL;DR: In this paper, the authors measured the annual parallax of the H 2 O maser associated with an infrared dark cloud, MSXDC G034.43+00.24, with VERA.
Abstract: We have measured the annual parallax of the H 2 O maser associated with an infrared dark cloud, MSXDC G034.43+00.24, with VERA. The parallax is 0.643 ± 0.049 mas, corresponding to a distance of 1.56 +0.12 −0.11 kpc. This value is less than half of the previous kinematic distance of 3.7 kpc. We revised the core-mass estimates of MSXDC G034.43+00.24 from the previous estimations of 1000 M ⊙ to hundreds of M ⊙ . The spectral type is still consistent with that of the massive star.
TL;DR: In this paper, the physical and chemical properties of the filamentary IRDC G304.74+01.32 have been investigated, including the kinematics and dynamical state of the cloud and clumps within it and the amount of CO depletion.
Abstract: The aim of this study is to better understand the physical and chemical properties of the filamentary IRDC G304.74+01.32. In particular, we aim to investigate the kinematics and dynamical state of the cloud and clumps within it, and the amount of CO depletion. All the submillimetre peak positions in the cloud identified from our previous LABOCA 870-micron map were observed in C17O(2-1) with APEX. Selected positions were also observed in the 13CO(2-1), SiO(5-4), and CH3OH(5_k-4_k) transitions at ~1 mm wavelength. The C17O lines were detected towards all target positions at similar radial velocities, indicating that G304.74 is a coherent filamentary structure. CO does not appear to be significantly depleted in the clumps. Two- to three methanol 5_k-4_k lines near ~241.8 GHz were detected towards all selected target positions, whereas SiO(5-4) was seen in only one of these positions. The 13CO(2-1) lines show blue asymmetric profiles, indicating large-scale infall motions. The clumps show trans- to supersonic non-thermal motions, and virial-parameter analysis suggests that most of them are gravitationally bound. The external pressure may also play a non-negligible role in the dynamics. This is qualitatively consistent with our earlier suggestion that the filament was formed by converging supersonic turbulent flows. The analysis suggests that the fragmentation of the filament into clumps is caused by "sausage"-type instability, in agreement with results from other IRDCs. The star-formation activity in the cloud, such as outflows, is likely responsible in releasing CO from the icy grain mantles back into the gas phase. Shocks related to outflows may have also injected CH3OH, SiO, and DCN into the gas-phase in SMM 3.
01 Aug 2012
TL;DR: In this article, the authors performed the PRF photometry of Spitzer MIPSGAL 24 μm data using MOPEX and built a catalog of YSOs by matching the detected 24 µm sources with published catalogs.
Abstract: Abstract Massive stars govern the evolution of galaxies by providing ionizing photons and energy as well as enriching heavy elements into interstellar medium; however, their formation is still poorly understood. Infrared dark clouds (IRDCs) are cold (< 25 K) and very dense (> 105 cm−3) interstellar clouds which are seen silhouette against the bright Galactic background in mid-IR. With very high column densities (∼ 1023–1025cm−2), IRDCs are believed to be the precursors to massive stars and star clusters (Simon et al. 2006). We report a remarkable IRDC at (l, b) ∼ (53°.2, 0°.0) which shows a number of bright mid-IR stellar sources along the cloud that are likely young stellar objects (YSOs). There are also several H2 (at 2.122 μm) outflow features in the cloud revealed by UWISH2 (Ukirt Widefield Infrared Survey for H2, Froebrich et al. 2011), in particular where earlier evolutionary stage of YSOs are located. The IRDC was previously partly identified as three separate IRDCs in the MSXDC catalog (Simon et al. 2006), whereas we have found that a long, filamentary cloud extending ∼ 30 pc including these three IRDCs is very well coincident with a CO cloud at v ∼ 23.5 km/s (or at d ∼ 2 kpc) which is clearly distinct from the other velocity components. Therefore, in this study, we investigate the overall star formation activity in this IRDC (IRDC G53.2, hereafter). We perform the PRF photometry of Spitzer MIPSGAL 24 μm data using MOPEX and build a catalog of YSOs by matching the detected 24 μm sources with published catalogs. The limiting magnitude in 24 μm is ∼ 7.8 mag, and YSO candidates which have counterparts in GLIMPSE I catalog are 354. The YSO candidates are classified using spectral index derived between 2 and 24 μm, following Greene et al. (1994). We also remove the field-star contamination using reference fields where there is no CO cloud; the fraction of each class after reference field analysis is 18, 22, 45, 10, and 5% for Class I, Flat, Class II, Class III, and sources which cannot be classified due to the lack of data. The spatial distribution that earlier classes (i.e., Class I and Flat) are concentrated where far-IR or millimeter emission is strong and larger fraction of Flat objects compared to other low-mass star forming regions (e.g., Evans et al. 2009 and Billot et al. 2010) may imply that the IRDC G53.2 is indeed an active star-forming region in rather early evolutionary stage. Further investigation of each YSO such as SED modeling will reveal detailed information on star formation activity in this intriguing IRDC.