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.

Infrared dark clouds from the ISOGAL survey ? Constraints on the interstellar extinction curve

Abstract: The ISO galactic survey provides images of the inner disk in two broad lters (around 7 and 15m) over some 15 square degrees, away from the brightest star forming regions. A multiresolution analysis of the images leads to a catalogue of infrared dark clouds, most of which are condensed cores of large molecular clouds, several kpc away from the Sun, seen in absorption in front of the diuse galactic emission. The longitude distributions of the background emission and of the dark clouds correlate with known tracers of young population components. We analyse the morphology of the dark clouds and the intensity fluctuations within the cloud boundaries at the two wavelengths. The 7 to 15 m contrast ratio is 0:75 0:15 for the clouds located away from the Galactic Centre (jlj > 1 )a nd 1:05 0:15 for the clouds closest to the Galactic Centre (jlj < 1;jbj < 0:2). Using a simple absorption model, we derive a 7 to 15 m opacity ratio equal to 0:7 0:1 for the clouds located away from the Galactic Centre and estimate the opacity, , of a few objects at 15 m in the range 1 to 4. Several explanations for the variation of the contrast ratio, including absorption along the line of sight and local variations of the extinction curve are discussed.

The Skeleton of the Milky Way

Abstract: Recently, Goodman et al. argued that the very long, very thin infrared dark cloud "Nessie" lies directly in the Galactic midplane and runs along the Scutum–Centaurus Arm in position–position–velocity (p–p–v) space as traced by lower-density and higher-density gas. Nessie was presented as the first "bone" of the Milky Way, an extraordinarily long, thin, high-contrast filament that can be used to map our Galaxy's "skeleton." Here we present evidence for additional bones in the Milky Way, arguing that Nessie is not a curiosity but one of several filaments that could potentially trace Galactic structure. Our 10 bone candidates are all long, filamentary, mid-infrared extinction features that lie parallel to, and no more than 20 pc from, the physical Galactic mid-plane. We use , and radial velocity data to establish the three-dimensional location of the candidates in p–p–v space. Of the 10 candidates, 6 also have a projected aspect ratio of ≥50:1; run along, or extremely close to, the Scutum–Centaurus Arm in p–p–v space; and exhibit no abrupt shifts in velocity. The evidence presented here suggests that these candidates mark the locations of significant spiral features, with the bone called filament 5 ("BC_18.88-0.09") being a close analog to Nessie in the northern sky. As molecular spectral-line and extinction maps cover more of the sky at increasing resolution and sensitivity, it should be possible to find more bones in future studies.

SMA observations of Infrared Dark Clouds: A tale of two cores

Abstract: We present high-angular resolution sub-millimeter continuum images and molecular line spectra obtained with the SMA toward two massive cores that lie within Infrared Dark Clouds; one actively star-forming (G034.43+00.24 MM1) and the other more quiescent (G028.53-00.25 MM1). The high-angular resolution sub-mm continuum image of G034.43+00.24 MM1 reveals a compact (~0.03 pc) and massive (~29 Msun) structure while the molecular line spectrum shows emission from numerous complex molecules. Such a rich molecular line spectrum from a compact region indicates that G034.43+00.24 MM1 contains a hot molecular core, an early stage in the formation of a high-mass protostar. Moreover, the velocity structure of its 13CO(3-2) emission indicates that this B0 protostar may be surrounded by a rotating circumstellar envelope. In contrast, the sub-mm continuum image of G028.53-00.25 MM1 reveals three compact (<0.06 pc), massive (9-21 Msun) condensations but with no lines detected in its spectrum. We suggest that the core G028.53-00.25 MM1 is in a very early stage in the high-mass star-formation process; its size and mass are sufficient to form at least one high-mass star, yet it shows no signs of localized heating. Because the combination of high velocity line wings with a large IR-mm bolometric luminosity (~100 Lsun) indicates that this core has already begun to form accreting protostars, we speculate that the condensations may be in the early phase of accretion and may eventually become high-mass protostars. We, therefore, have found the possible existence of two high-mass star-forming cores; one in a very early phase of star-formation and one in the later hot core phase. Together the properties of these two cores support the idea that the earliest stages of high-mass star-formation occur within IRDCs.

The seeds of star formation in the filamentary infrared-dark cloud G011.11-0.12

Abstract: Infrared-dark clouds (IRDCs) are the precursors to massive stars and stellar clusters. G011.11-0.12 is a well-studied filamentary IRDC, though, to date, the absence of far-infrared data with sufficient spatial resolution has limited the understanding of the structure and star-formation activity. We use Herschel to study the embedded population of young pre- and protostellar cores in this IRDC. We examine the cloud structure, which appears in absorption at short wavelength and in emission at longer wavelength. We derive the properties of the massive cores from the spectral energy distributions of bright far-infrared point sources detected with the PACS instrument aboard Herschel. We report on the detection and characterization of pre- and protostellar cores in a massive filamentary infrared-dark cloud G011.11-0.12 using PACS. We characterize 18 cores directly associated with the filament, two of which have masses over 50 Msun, making them the best candidates to become massive stars in G011.11-0.12. These cores are likely at various stages of protostar formation, showing elevated temperature ( ~ 22 K) with respect to the ambient gas reservoir. The core masses ( ~ 24 Msun) are small compared to that in the cold filament. The mean core separation is 0.9 pc, well in excess of the Jeans length in the filament. We confirm that star formation in IRDCs is underway and diverse, and IRDCs have the capability of forming massive stars and clusters.

An Ordered Bipolar Outflow from a Massive Early-stage Core

Abstract: We present ALMA follow-up observations of two massive, early-stage core candidates, C1-N & C1-S, in Infrared Dark Cloud (IRDC) G028.37+00.07, which were previously identified by their N2D+(3-2) emission and show high levels of deuteration of this species. The cores are also dark at far infrared wavelengths up to ~100 microns. We detect 12CO(2-1) from a narrow, highly-collimated bipolar outflow that is being launched from near the center of the C1-S core, which is also the location of the peak 1.3mm dust continuum emission. This protostar, C1-Sa, has associated dense gas traced by C18O(2-1) and DCN(3-2), from which we estimate it has a radial velocity that is near the center of the range exhibited by the C1-S massive core. A second outflow-driving source is also detected within the projected boundary of C1-S, but appears to be at a different radial velocity. After considering properties of the outflows, we conclude C1-Sa is a promising candidate for an early-stage massive protostar and as such it shows that these early phases of massive star formation can involve highly ordered outflow, and thus accretion, processes, similar to models developed to explain low-mass protostars.