First spectrally-resolved H<sub>2</sub>observations towards HH 54

Santangelo, G.; Antoniucci, S.; Nisini, B.; Codella, C.; Bjerkeli, P.; Giannini, T.; Lorenzani, A.; Lundin, L.; Cabrit, S.; Calzoletti, L.; Liseau, R.; Neufeld, David A.; Tafalla, M.; Dishoeck, E. F. van

doi:10.1051/0004-6361/201424748

Cited by 13 publications

(14 citation statements)

References 28 publications

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“…For example, if 90% of [O I] flux comes from the shock, corresponding to an increase in the observed [C II] / [O I] by a factor of 10, the best fit densities are in the range 10 4 -10 5 cm −3 and UV field of ∼ 10 1 -10 2 G 0 . In fact, the spectrally resolved line profile of [O I] in a single outflow position in NGC1333 I4A, observed with SOFIA-GREAT by Kristensen et al (2017a), resembles the high-velocity H 2 O and CO 16-15 profiles associated with the shocks observed with Herschel by Santangelo et al (2014a). Similarly, [C II] profiles from HIFI obtained for a subsample of WISH sources reveal that the origin of emission may be shocks rather than a PDR Benz et al 2016).…”

Section: Atomic Line Fluxes Vs Models Of Photodissociationmentioning

confidence: 85%

The Herschel-PACS Legacy of Low-mass Protostars: The Properties of Warm and Hot Gas Components and Their Origin in Far-UV Illuminated Shocks

Karska

Kaufman

Kristensen

et al. 2018

ApJS

118

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Recent observations from Herschel allow the identification of important mechanisms responsible for the heating of gas surrounding low-mass protostars and its subsequent cooling in the far-infrared (FIR). Shocks are routinely invoked to reproduce some properties of the far-IR spectra, but standard models fail to reproduce the emission from key molecules, e.g. H 2 O. Here, we present the Herschel-PACS far-IR spectroscopy of 90 embedded low-mass protostars (Class 0/I). The Herschel-PACS spectral maps covering ∼ 55 − 210 µm with a field-of-view of ∼50" are used to quantify the gas excitation conditions and spatial extent using rotational transitions of H 2 O, high-J CO, and OH, as well as [O I] and [C II]. We confirm that a warm (∼300 K) CO reservoir is ubiquitous and that a hotter component (760 ± 170 K) is frequently detected around protostars. The line emission is extended beyond ∼1000 AU spatial scales in 40/90 objects, typically in molecular tracers in Class 0 and atomic tracers in Class I objects. High-velocity emission ( 90 km s −1 ) is detected in only 10 sources in the [O I] line, suggesting that the bulk of [O I] arises from gas that is moving slower than typical jets. Line flux ratios show an excellent agreement with models of C-shocks illuminated by UV photons for pre-shock densities of ∼10 5 cm −3 and UV fields 0.1-10 times the interstellar value. The far-IR molecular and atomic lines are a unique diagnostic of feedback from UV emission and shocks in envelopes of deeply embedded protostars.

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Section: Atomic Line Fluxes Vs Models Of Photodissociationmentioning

confidence: 85%

The Herschel-PACS Legacy of Low-mass Protostars: The Properties of Warm and Hot Gas Components and Their Origin in Far-UV Illuminated Shocks

Karska

Kaufman

Kristensen

et al. 2018

ApJS

118

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“…In addition to the CO ladder, one OH line, the [O i] lines at 63 and 145 μm, and several H 2 O lines are detected. The water emission from HH 54 is further discussed in a forthcoming paper (Santangelo et al 2014a The emission from all lines is confined to the HH 54 region. A bump-like feature (also discussed in Bjerkeli et al 2011) is clearly detected in the CO (3−2) spectrum and likely also in the CO (15−14) spectrum.…”

Section: Observationsmentioning

confidence: 99%

Resolving the shocked gas in HH 54 withHerschel

Bjerkeli¹,

Liseau²,

Brinch³

et al. 2014

A&A

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Context. The HH 54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II cloud. Observed CO line profiles are due to a complex distribution in density, temperature, velocity, and geometry. Aims. Resolving the HH 54 shock wave in the far-infrared (FIR) cooling lines of CO constrain the kinematics, morphology, and physical conditions of the shocked region. Methods. We used the PACS and SPIRE instruments on board the Herschel space observatory to map the full FIR spectrum in a region covering the HH 54 shock wave. Complementary Herschel-HIFI, APEX, and Spitzer data are used in the analysis as well. The observed features in the line profiles are reproduced using a 3D radiative transfer model of a bow-shock, constructed with the Line Modeling Engine code (LIME). Results. The FIR emission is confined to the HH 54 region and a coherent displacement of the location of the emission maximum of CO with increasing J is observed. The peak positions of the high-J CO lines are shifted upstream from the lower J CO lines and coincide with the position of the spectral feature identified previously in CO (10−9) profiles with HIFI. This indicates a hotter molecular component in the upstream gas with distinct dynamics. The coherent displacement with increasing J for CO is consistent with a scenario where IRAS12500 -7658 is the exciting source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K) molecular component located upstream from the apex of the shock and blueshifted by −7 km s −1 . The spatial proximity of this knot to the peaks of the atomic fine-structure emission lines observed with Spitzer and PACS ([O i]63, 145 μm) suggests that it may be associated with the dissociative shock as the jet impacts slower moving gas in the HH 54 bow-shock.

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“…Moreover, excitation energies are very high and require very high temperatures or strong ultraviolet (UV) fields to excite its rotational levels (Kennicutt & Evans 2012). H 2 can be observed in emission by infrared (IR) rovibrational transitions (Burton et al 1992;Santangelo et al 2014;Habart et al 2011), or in absorption at far-ultraviolet (far-UV) wavelengths from the Lyman and Werner bands. These bands were first observed by Spitzer & Jenkins (1975) using the Copernicus satellite.…”

Section: Introductionmentioning

confidence: 99%

H₂distribution during the formation of multiphase molecular clouds

Valdivia

Hennebelle

Gérin

et al. 2016

A&A

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Context. H 2 is the simplest and the most abundant molecule in the interstellar medium (ISM), and its formation precedes the formation of other molecules. Aims. Understanding the dynamical influence of the environment and the interplay between the thermal processes related to the formation and destruction of H 2 and the structure of the cloud is mandatory to understand correctly the observations of H 2 . Methods. We performed high-resolution magnetohydrodynamical colliding-flow simulations with the adaptive mesh refinement code RAMSES in which the physics of H 2 has been included. We compared the simulation results with various observations of the H 2 molecule, including the column densities of excited rotational levels. Results. As a result of a combination of thermal pressure, ram pressure, and gravity, the clouds produced at the converging point of HI streams are highly inhomogeneous. H 2 molecules quickly form in relatively dense clumps and spread into the diffuse interclump gas. This in particular leads to the existence of significant abundances of H 2 in the diffuse and warm gas that lies in between clumps. Simulations and observations show similar trends, especially for the HI-to-H 2 transition (H 2 fraction vs. total hydrogen column density). Moreover, the abundances of excited rotational levels, calculated at equilibrium in the simulations, turn out to be very similar to the observed abundances inferred from FUSE results. This is a direct consequence of the presence of the H 2 enriched diffuse and warm gas. Conclusions. Our simulations, which self-consistently form molecular clouds out of the diffuse atomic gas, show that H 2 rapidly forms in the dense clumps and, due to the complex structure of molecular clouds, quickly spreads at lower densities. Consequently, a significant fraction of warm H 2 exists in the low-density gas. This warm H 2 leads to column densities of excited rotational levels close to the observed ones and probably reveals the complex intermix between the warm and cold gas in molecular clouds. This suggests that the two-phase structure of molecular clouds is an essential ingredient for fully understanding molecular hydrogen in these objects.

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First spectrally-resolved H₂observations towards HH 54

Cited by 13 publications

References 28 publications

The Herschel-PACS Legacy of Low-mass Protostars: The Properties of Warm and Hot Gas Components and Their Origin in Far-UV Illuminated Shocks

The Herschel-PACS Legacy of Low-mass Protostars: The Properties of Warm and Hot Gas Components and Their Origin in Far-UV Illuminated Shocks

Resolving the shocked gas in HH 54 withHerschel

H₂distribution during the formation of multiphase molecular clouds

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First spectrally-resolved H2observations towards HH 54

Cited by 13 publications

References 28 publications

The Herschel-PACS Legacy of Low-mass Protostars: The Properties of Warm and Hot Gas Components and Their Origin in Far-UV Illuminated Shocks

The Herschel-PACS Legacy of Low-mass Protostars: The Properties of Warm and Hot Gas Components and Their Origin in Far-UV Illuminated Shocks

Resolving the shocked gas in HH 54 withHerschel

H2distribution during the formation of multiphase molecular clouds

Contact Info

Product

Resources

About

First spectrally-resolved H₂observations towards HH 54

H₂distribution during the formation of multiphase molecular clouds