Infrared dark cloud

About: Infrared dark cloud is a research topic. Over the lifetime, 232 publications have been published within this topic receiving 13800 citations.

The protostar in the massive infrared dark cloud irdc 18223-3

Abstract: At the onset of high-mass star formation, accreting protostars are deeply embedded in massive cores made of gas and dust. Their spectral energy distribution is still dominated by the cold dust and rises steeply from near- to far-infrared wavelengths. The young massive star-forming region IRDC 18223-3 is a prototypical infrared dark cloud with a compact millimeter continuum core that shows no protostellar emission below 8 μm. However, based on outflow tracers, early star formation activity was previously inferred for this region. Here we present recent Spitzer observations from the MIPSGAL survey that identify the central protostellar object for the first time at 24 and 70 μm. Combining the mid- to far-infrared data with previous millimeter continuum observations and the upper limits below 8 μm, one can infer the physical properties of the central source. At least two components with constant gas mass M and dust temperature T are necessary: one cold component (~15 K and ~576 M☉) that contains most of the mass and luminosity, and one warmer component (≥51 K and ≥0.01 M☉) to explain the 24 μm data. The integrated luminosity of ~177 L☉ can be used to constrain additional parameters of the embedded protostar from the turbulent core accretion model for massive star formation. The data of IRDC 18223-3 are consistent with a massive gas core harboring a low-mass protostellar seed of still less than half a solar mass with high accretion rates of the order 10-4 M☉ yr-1. In the framework of this model, the embedded protostar is destined to become a massive star at the end of its formation processes.

The dynamics and star-forming potential of the massive Galactic centre cloud G0.253+0.016

Abstract: Context. The massive infrared dark cloud G0.253+0.016 projected ∼45 pc from the Galactic centre contains ∼10 5 Mof dense gas whilst being mostly devoid of observed star-formation tracers. Aims. Our goals are therefore to scrutinise the physical properties, dynamics and structure of this cloud with reference to its star- forming potential. Methods. We have carried out a concerted SMA and IRAM 30 m study of this enigmatic cloud in dust continuum, CO isotopologues, several shock tracing molecules, as well as H2CO to trace the gas temperature. In addition, we include ancillary far-IR and sub-mm Herschel and SCUBA data in our analysis. Results. We detect and characterise a total of 36 dust cores within G0.253+0.016 at 1.3 mm and 1.37 mm, with masses between 25 and approximately 250 M� , and find that the kinetic temperature of the gas traced by H2CO ratios is >320 K on size-scales of ∼0.15 pc. Analysis of the position-velocity diagrams of our observed lines shows broad linewidths and strong shock emission in the south of the cloud, indicating that G0.253+0.016 is colliding with another cloud at vLSR ∼ 70 km s −1 . We confirm via an analysis of the observed dynamics in the Central Molecular Zone that it is an elongated structure, orientated with Sgr B2 closer to the Sun than Sgr A*, however our results suggest that the actual geometry may be more complex than an elliptical ring. We find that the column density probability distribution function of G0.253+0.016 derived from SMA and SCUBA dust continuum emission is log-normal with no discernible power-law tail, consistent with little star formation, and that its width can be explained in the framework of theory predicting the density structure of clouds created by supersonic, magnetised turbulence. We also present the Δ-variance spectrum of this region, a proxy for the density power spectrum of the cloud, and show it is consistent with that expected for clouds with no current star formation. Finally, we show that even after determining a scaled column density threshold for star formation by incorporating the effects of the increased turbulence in the cloud, we would still expect ten stars with masses >15 Mto form in G0.253+0.016. If these cannot be accounted for by new radio continuum observations, then further physical aspects may be important, such as the background column density level, which would turn an absolute column density threshold for star formation into a critical over-density. Conclusions. We conclude that G0.253+0.016 contains high-temperatures and wide-spread shocks, displaying evidence of interaction with a nearby cloud which we identify at v LSR ∼ 70 km s −1 . Our analysis of the structure of the cloud can be well-explained by theory of magnetised turbulence, and is consistent with little or no current star formation. Using G0.253+0.016 as a test-bed of the conditions required for star formation in a different physical environment to that of nearby clouds, we also conclude that there is not one column density threshold for star formation, but instead this value is dependant on the local physical conditions.

Protostellar outflow heating in a growing massive protocluster

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.

The Bones of the Milky Way

Abstract: The very long and thin infrared dark cloud "Nessie" is even longer than had been previously claimed, and an analysis of its Galactic location suggests that it lies directly in the Milky Way's mid-plane, tracing out a highly elongated bone-like feature within the prominent Scutum-Centaurus spiral arm. Re-analysis of mid-infrared imagery from the Spitzer Space Telescope shows that this IRDC is at least 2, and possibly as many as 5 times longer than had originally been claimed by Nessie's discoverers (Jackson et al. 2010); its aspect ratio is therefore at least 300:1, and possibly as large as 800:1. A careful accounting for both the Sun's offset from the Galactic plane ($\sim 25$ pc) and the Galactic center's offset from the $(l^{II},b^{II})=(0,0)$ position shows that the latitude of the true Galactic mid-plane at the 3.1 kpc distance to the Scutum-Centaurus Arm is not $b=0$, but instead closer to $b=-0.4$, which is the latitude of Nessie to within a few pc. An analysis of the radial velocities of low-density (CO) and high-density (${\rm NH}_3$) gas associated with the Nessie dust feature suggests that Nessie runs along the Scutum-Centaurus Arm in position-position-velocity space, which means it likely forms a dense `spine' of the arm in real space as well. The Scutum-Centaurus arm is the closest major spiral arm to the Sun toward the inner Galaxy, and, at the longitude of Nessie, it is almost perpendicular to our line of sight, making Nessie the easiest feature to see as a shadow elongated along the Galactic Plane from our location. Future high-resolution dust mapping and molecular line observations of the harder-to-find Galactic "bones" should allow us to exploit the Sun's position above the plane to gain a (very foreshortened) view "from above" of the Milky Way's structure.

The TOP-SCOPE Survey of Planck Galactic Cold Clumps: Survey Overview and Results of an Exemplar Source, PGCC G26.53+0.17

Abstract: The low dust temperatures (<14 K) of Planck Galactic cold clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. "TOP-SCOPE" is a joint survey program targeting ~2000 PGCCs in J = 1–0 transitions of CO isotopologues and ~1000 PGCCs in 850 μm continuum emission. The objective of the "TOP-SCOPE" survey and the joint surveys (SMT 10 m, KVN 21 m, and NRO 45 m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis, and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, length, and mean line mass (M/L) of the G26 filament are ~6200 M ☉, ~12 pc, and ~500 M ☉ pc−1, respectively. Ten massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (β) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.