Shocks in dense clouds

Anderl, S.; Guillet, V.; Forêts, G. Pineau des; Flower, D. R.

doi:10.1051/0004-6361/201321399

Cited by 45 publications

(64 citation statements)

References 46 publications

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“…To compare with the observed CO SLEDs, we then employ a post-processing treatment based on the LVG approximation, following the method used in Gusdorf et al (2012), Anderl et al (2014), and Gusdorf et al (2015). In our modelling, the effects of grain-grain interactions (e.g., Guillet et al 2011;Anderl et al 2013) are not considered, since these effects play an important role only for high density and shock velocity (n pre > 10 4 cm −3 and v s > 20 km s −1 ) cases. Finally, we note that reducing the input metallicity by a factor of 2 to match the LMC value (∼0.5 Z ⊙ ; e.g., Pagel 2003) would not change our main results.…”

Section: Paris-durham Shock Modellingmentioning

confidence: 99%

Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud

Lee

Madden

Lebouteiller

et al. 2016

A&A

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We present Herschel SPIRE Fourier Transform Spectrometer (FTS) observations of N159W, an active star-forming region in the Large Magellanic Cloud (LMC). In our observations, a number of far-infrared cooling lines including CO J = 4 → 3 to J = 12 → 11, [CI] 609 µm and 370 µm, and [NII] 205 µm are clearly detected. With an aim of investigating the physical conditions and excitation processes of molecular gas, we first construct CO spectral line energy distributions (SLEDs) on ∼10 pc scales by combining the FTS CO transitions with ground-based low-J CO data and analyze the observed CO SLEDs using non-LTE radiative transfer models. We find that the CO-traced molecular gas in N159W is warm (kinetic temperature of 153-754 K) and moderately dense (H 2 number density of (1.1-4.5) × 10 3 cm −3 ). To assess the impact of the energetic processes in the interstellar medium on the physical conditions of the CO-emitting gas, we then compare the observed CO line intensities with the models of photodissociation regions (PDRs) and shocks. We first constrain the properties of PDRs by modelling Herschel observations of [OI] 145 µm, [CII] 158 µm, and [CI] 370 µm fine-structure lines and find that the constrained PDR components emit very weak CO emission. X-rays and cosmic-rays are also found to provide a negligible contribution to the CO emission, essentially ruling out ionizing sources (ultraviolet photons, X-rays, and cosmic-rays) as the dominant heating source for CO in N159W. On the other hand, mechanical heating by low-velocity C-type shocks with ∼10 km s −1 appears sufficient enough to reproduce the observed warm CO.

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Section: Paris-durham Shock Modellingmentioning

confidence: 99%

Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud

Lee

Madden

Lebouteiller

et al. 2016

A&A

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“…The final considered ages range from a few tens to around fifteen thousand years. Our grid also includes a few stationary models including the effects of grain-grain interactions, as presented in Guillet et al (2011); Anderl et al (2013), and already used in Anderl et al (2014); Leurini et al (2014a).…”

Section: Constraining Shock Modelsmentioning

confidence: 99%

“…Interestingly, the transfer of Si from the core to the mantles in the form of SiO was also considered by Anderl et al (2013) in the context of denser shock models. Indeed, for pre-shock densities above 10 5 cm −3 , the effect of grain-grain interactions cannot be neglected in shock models, as shown by Guillet et al (2011).…”

Section: Employing Shock Models: Sio Chemistrymentioning

confidence: 99%

Impacts of pure shocks in the BHR71 bipolar outflow

Gusdorf

Riquelme

Anderl

et al. 2015

A&A

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Context. During the formation of a star, material is ejected along powerful jets that impact the ambient material. This outflow regulates star formation by e.g. inducing turbulence and heating the surrounding gas. Understanding the associated shocks is therefore essential to the study of star formation. Aims. We present comparisons of shock models with CO, H 2 , and SiO observations in a "pure" shock position in the BHR71 bipolar outflow. These comparisons provide an insight into the shock and pre-shock characteristics, and allow us to understand the energetic and chemical feedback of star formation on Galactic scales. Methods. New CO (J up = 16, 11, 7, 6, 4, 3) observations from the shocked regions with the SOFIA and APEX telescopes are presented and combined with earlier H 2 and SiO data (from the Spitzer and APEX telescopes). The integrated intensities are compared to a grid of models that were obtained from a magneto-hydrodynamical shock code, which calculates the dynamical and chemical structure of these regions combined with a radiative transfer module based on the "large velocity gradient" approximation. Results. The CO emission leads us to update the conclusions of our previous shock analysis: pre-shock densities of 10 4 cm −3 and shock velocities around 20−25 km s −1 are still constrained, but older ages are inferred (∼4000 years). Conclusions. We evaluate the contribution of shocks to the excitation of CO around forming stars. The SiO observations are compatible with a scenario where less than 4% of the pre-shock SiO belongs to the grain mantles. We infer outflow parameters: a mass of 1.8 × 10 −2 M was measured in our beam, in which a momentum of 0.4 M km s −1 is dissipated, corresponding to an energy of 4.2 × 10 43 erg. We analyse the energetics of the outflow species by species. Comparing our results with previous studies highlights their dependence on the method: H 2 observations only are not sufficient to evaluate the mass of outflows.

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“…SiO: Gusdorf et al 2008;Anderl et al 2013), the double-Gaussian decomposition of the OH line profiles (Sect. 4.1) fails to account for the complexity of the observed emission.…”

Section: Scenario 1: One Outflow Two Shock Layersmentioning

confidence: 99%

“…Guillet et al 2009Guillet et al , 2011. Anderl et al (2013) have shown that including them does not significantly alter the predicted OH emission of C-type models with n H of the order of 10 5 cm −3 (see their Fig. B.4), but that it does affect the shape of the predicted energy distribution of the CO spectral line (see their Fig.…”

Section: Scenario 1: One Outflow Two Shock Layersmentioning

confidence: 99%

Challenging shock models with SOFIA OH observations in the high-mass star-forming region Cepheus A

Güsten

Menten

Flower

et al. 2015

A&A

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Context. OH is a key molecule in H 2 O chemistry, a valuable tool for probing physical conditions, and an important contributor to the cooling of shock regions around high-mass protostars. OH participates in the re-distribution of energy from the protostar towards the surrounding Interstellar Medium. Aims. Our aim is to assess the origin of the OH emission from the Cepheus A massive star-forming region and to constrain the physical conditions prevailing in the emitting gas. We thus want to probe the processes at work during the formation of massive stars. Methods. We present spectrally resolved observations of OH towards the protostellar outflows region of Cepheus A with the GREAT spectrometer onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) telescope. Three triplets were observed at 1834.7 GHz, 1837.8 GHz, and 2514.3 GHz (163.4 µm, 163.1 µm between the 2 Π 1/2 J = 3/2 and J = 1/2 states, and 119.2 µm, a ground transition between the 2 Π 3/2 J = 5/2 and J = 3/2 states), at angular resolutions of 16. 3, 16. 3, and 11. 9, respectively. We also present the CO (16-15) spectrum at the same position. We compared the integrated intensities in the redshifted wings to the results of shock models. Results. The two OH triplets near 163 µm are detected in emission, but with blending hyperfine structure unresolved. Their profiles and that of can be fitted by a combination of two or three Gaussians. The observed 119.2 µm triplet is seen in absorption, since its blending hyperfine structure is unresolved, but with three line-of-sight components and a blueshifted emission wing consistent with that of the other lines. The OH line wings are similar to those of CO, suggesting that they emanate from the same shocked structure. Conclusions. Under this common origin assumption, the observations fall within the model predictions and within the range of use of our model only if we consider that four shock structures are caught in our beam. Overall, our comparisons suggest that all the observations might be consistently fitted by a J-type shock model with a high pre-shock density (n H > 10 5 cm −3 ), a high shock velocity ( s 25 km s −1 ), and with a filling factor of the order of unity. Such a high pre-shock density is generally found in shocks associated to high-mass protostars, contrary to low-mass ones.

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Shocks in dense clouds

Cited by 45 publications

References 46 publications

Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud

Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud

Impacts of pure shocks in the BHR71 bipolar outflow

Challenging shock models with SOFIA OH observations in the high-mass star-forming region Cepheus A

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