Formation of Cold Filamentary Structure From Wind-Blown Superbubbles

Ntormousi, Evangelia; Burkert, Andreas; Fierlinger, Katharina; Heitsch, Fabian

doi:10.1088/0004-637x/731/1/13

Cited by 75 publications

(87 citation statements)

References 55 publications

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“…Molecular clouds that consist of large-scale fiber-like, elongated structures arise naturally in numerical simulations of diffuse, warm HI gas flows that undergo a cooling instability coupled with various hydrodynamical instabilities (Ballesteros-Paredes et al 1999;Heitsch et al 2008a;Ntormousi et al 2011). Another possibility might be gravitational modes, sweeping up material at the edges of collapsing structures (Burkert & Hartmann 2004;Hartmann & Burkert 2007;Vázquez-Semadeni et al 2007;Heitsch et al 2008b).…”

Section: Discussion: Macroscopic Turbulence and Tangled Molecular Cloudsmentioning

confidence: 99%

Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic turbulence and tangled molecular clouds

Hacar

Alves

Burkert

et al. 2016

A&A

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Context. Since their first detection in the interestellar medium, (sub-)millimeter line observations of different CO isotopic variants have routinely been employed to characterize the kinematic properties of the gas in molecular clouds. Many of these lines exhibit broad linewidths that greatly exceed the thermal broadening expected for the low temperatures found within these objects. These observed suprathermal CO linewidths are assumed to originate from unresolved supersonic motions inside clouds. Aims. The lowest rotational J transitions of some of the most abundant CO isotopologues, 12 CO and 13 CO, are found to present large optical depths. In addition to well-known line saturation effects, these large opacities present a non-negligible contribution to their observed linewidths. Typically overlooked in the literature, in this paper we aim to quantify the impact of these opacity broadening effects on the current interpretation of the CO suprathermal line profiles. Methods. Combining large-scale observations and LTE modeling of the ground J = 1−0 transitions of the main 12 CO, 13 CO, C 18 O isotopologues, we have investigated the correlation of the observed linewidths as a function of the line opacity in different regions of the Taurus molecular cloud. Results. Without any additional contributions to the gas velocity field, a large fraction of the apparently supersonic (M ∼ 2-3) linewidths measured in both 12 CO and 13 CO (J = 1−0) lines can be explained by the saturation of their corresponding sonic-like, optically thin C 18 O counterparts assuming standard isotopic fractionation. Combined with the presence of multiple components detected in some of our C 18 O spectra, these opacity effects also seem to be responsible for most of the highly supersonic linewidths (M > 8-10) detected in some of the broadest 12 CO and 13 CO spectra in Taurus.Conclusions. Our results demonstrate that most of the suprathermal 12 CO and 13 CO linewidths reported in nearby clouds like Taurus could be primarily created by a combination of opacity broadening effects and multiple gas velocity components blended in these saturated emission lines. Once corrected by their corresponding optical depth, each of these gas components present transonic intrinsic linewidths consistently traced by the three isotopologues, 12 CO, 13 CO, and C 18 O, with differences within a factor of 2. Highly correlated and velocity-coherent at large scales, the largest and highly supersonic velocity differences inside clouds are generated by the relative motions between individual gas components. In contrast to the classical interpretation within the framework of microscopic turbulence, this highly discretized structure of the molecular gas traced in CO suggest that the gas dynamics inside molecular clouds could be better described by the properties of a fully resolved macroscopic turbulence.

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Section: Discussion: Macroscopic Turbulence and Tangled Molecular Cloudsmentioning

confidence: 99%

Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic turbulence and tangled molecular clouds

Hacar

Alves

Burkert

et al. 2016

A&A

View full text Add to dashboard Cite

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“…In this scenario, molecular gas forms from the converging HI gas through the dynamically-triggered thermal instability. As summarized in Dobbs et al (2012), the sources of the converging flows can be stellar winds or supernovae (Koyama & Inutsuka 2000;Heitsch & Hartmann 2008;Ntormousi & Burkert 2011), turbulence in the interstellar medium (Ballesteros-Paredes et al 1999), spiral shocks (Leisawitz & Bash 1982), and gravitational instability. In our case, the filamentary gas wisp cannot be created by converging stellar winds, supernovae, or turbulence in the interstellar medium, since these mechanisms are local and cannot create structures that are larger than the thickness of the Milky Way disk.…”

Section: Implications For the Formation Of Molecular Cloudsmentioning

confidence: 99%

A 500 pc filamentary gas wisp in the disk of the Milky Way

Wyrowski

Menten

et al. 2013

A&A

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Star formation occurs in molecular gas. In previous studies, the structure of the molecular gas has been studied in terms of molecular clouds, but has been overlooked beyond the cloud scale. We present an observational study of the molecular gas at 49.5 • < l < 52.5 • and −5.0 km s −1 < v lsr < 17.4 km s −1 . The molecular gas is found in the form of a huge ( 500 pc) filamentary gas wisp. This has a large physical extent and a velocity dispersion of ∼5 km s −1 . The eastern part of the filamentary gas wisp is located ∼130 pc above the Galactic disk (which corresponds to 1.5-4 e-folding scale-heights), and the total mass of the gas wisp is 1 × 10 5 M . It is composed of two molecular clouds and an expanding bubble. The velocity structure of the gas wisp can be explained as a smooth quiescent component disturbed by the expansion of a bubble. That the length of the gas wisp exceeds by much the thickness of the molecular disk of the Milky Way is consistent with the cloud-formation scenario in which the gas is cold prior to the formation of molecular clouds. Star formation in the filamentary gas wisp occurs at the edge of a bubble (G52L nebula), which is consistent with some models of triggered star formation.

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“…its morphology with imprinted bubbles and superbubbles (Gruendl et al 2000;Arthur 2007;Chu 2008;Sasaki et al 2011), its molecularcloud fragments in formation or in dispersal, and its level of turbulence -are strongly affected by the physics and dynamics of stellar feedback (e.g. de Avillez & Breitschwerdt 2004Dobbs et al 2011b,a;Ntormousi et al 2011). The actual agents of stellar feedback are massive stars, which are born in the denser parts of the ISM (for recent reviews see McKee & Ostriker 2007;Zinnecker & Yorke 2007).…”

Section: Introductionmentioning

confidence: 99%

“…3. Ntormousi et al (2011) have simulated the merging of two superbubbles in 2D with identical stellar content. One of the most interesting findings in the simulations of Ntormousi et al (2011) and is the occurrence of the Vishniac thin shell instability (Vishniac 1983).…”

Section: Introductionmentioning

confidence: 99%

Feedback by massive stars and the emergence of superbubbles

Krause

Fierlinger

Diehl

et al. 2013

A&A

113

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Context. Massive stars influence their environment through stellar winds, ionising radiation, and supernova explosions. This is signified by observed interstellar bubbles. Such feedback is an important factor for galaxy evolution theory and galactic wind models. The efficiency of the energy injection into the interstellar medium (ISM) via bubbles and superbubbles is uncertain, and is usually treated as a free parameter for galaxy scale effects. In particular, since many stars are born in groups, it is interesting to study the dependence of the effective energy injection on the concentration of the stars. Aims. We aim to reproduce observations of superbubbles, their relation to the energy injection of the parent stars, and to understand their effective energy input into the ISM, as a function of the spatial configuration of the group of parent stars. Methods. We study the evolution of isolated and merging interstellar bubbles of three stars (25, 32, and 60 M ) in a homogeneous background medium with a density of 10m p cm −3 via 3D-hydrodynamic simulations with standard ISM thermodynamics (optically thin radiative cooling and photo-electric heating) and time-dependent energy and mass input according to stellar evolutionary tracks. We vary the position of the three stars relative to each other to compare the energy response for cases of isolated, merging and initially cospatial bubbles. Results. Mainly due to the Vishniac instability, our simulated bubbles develop thick shells and filamentary internal structures in column density. The shell widths reach tens of per cent of the outer bubble radius, which compares favourably to observations. More energy is retained in the ISM for more closely packed groups, by up to a factor of three and typically a factor of two for intermediate times after the first supernova. Once the superbubble is established, different positions of the contained stars make only a minor difference to the energy tracks. For our case of three massive stars, the energy deposition varies only very little for distances up to about 30 pc between the stars. Energy injected by supernovae is entirely dissipated in a superbubble on a timescale of about 1 Myr, which increases slightly with the superbubble size at the time of the explosion. Conclusions. The Vishniac instability may be responsible for the broadening of the shells of interstellar bubbles. Massive star winds are significant energetically due to their -in the long run -more efficient, steady energy injection and because they evacuate the space around the massive stars. For larger scale simulations, the feedback effect of close groups of stars or clusters may be subsumed into one effective energy input with insignificant loss of energy accuracy.

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Formation of Cold Filamentary Structure From Wind-Blown Superbubbles

Cited by 75 publications

References 55 publications

Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic turbulence and tangled molecular clouds

Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic turbulence and tangled molecular clouds

A 500 pc filamentary gas wisp in the disk of the Milky Way

Feedback by massive stars and the emergence of superbubbles

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