scholarly journals The nature of molecular cloud boundary layers from SOFIA [O I] observations

2018 ◽  
Vol 617 ◽  
pp. A94 ◽  
Author(s):  
W. D. Langer ◽  
P. F. Goldsmith ◽  
J. L. Pineda ◽  
E. T. Chambers ◽  
K. Jacobs ◽  
...  
Keyword(s):  
Fine Structure ◽  
Boundary Layers ◽  
Molecular Clouds ◽  
High Spectral Resolution ◽  
Thermal Pressure ◽  
Physical Conditions ◽  
Upper Limits ◽  
Structure Line ◽  
Warm Ionized Medium ◽  
Fine Structure Lines

Context. Dense highly ionized boundary layers (IBLs) outside of the neutral Photon Dominated Regions (PDRs) have recently been detected via the 122 and 205 μm transitions of ionized nitrogen. These layers have higher densities than in the Warm Ionized Medium (WIM) but less than typically found in H II regions. Observations of [C II] emission, which is produced in both the PDR and IBL, do not fully define the characteristics of these sources. Observations of additional probes which just trace the PDRs, such as the fine structure lines of atomic oxygen, are needed derive their properties and distinguish among different models for [C II] and [N II] emissison. Aims. We derive the properties of the PDRs adjacent to dense highly ionized boundary layers of molecular clouds. Methods. We combine high-spectral resolution observations of the 63 μm [O I] fine structure line taken with the upGREAT HFA-band instrument on SOFIA with [C II] observations to constrain the physical conditions in the PDRs. The observations consist of samples along four lines of sight (LOS) towards the inner Galaxy containing several dense molecular clouds. We interpret the conditions in the PDRs using radiative transfer models for [C II] and [O I]. Results. We have a 3.5-σ detection of [O I] toward one source but only upper limits towards the others. We use the [O I] to [C II] ratio, or their upper limits, and the column density of C+ to estimate the thermal pressure, Pth, in these PDRs. In two LOS the thermal pressure is likely in the range 2–5 × 105 in units of K cm−3, with kinetic temperatures of order 75–100 K and H2 densities, n(H2) ~ 2–4 × 103 cm−3. For the other two sources, where the upper limits on [O I] to [C II] are larger, Pth ≲105 (K cm−3). We have also used PDR models that predict the [O I] to [C II] ratio, along with our observations of this ratio, to limit the intensity of the Far UV radiation field. Conclusions. The [C II] and [N II] emission with either weak, or without any, evidence of [O I] indicates that the source of dense highly ionized gas traced by [N II] most likely arises from the ionized boundary layers of clouds rather than from H II regions.

Fine Structure Lines in HII Regions Interacting with Molecular Clouds

1982 ◽  
pp. 73-80 ◽  
Author(s):  
D. A. Naylor ◽  
R. Emery ◽  
B. Fitton ◽  
I. Furniss ◽  
R. E. Jennings ◽  
...  
Keyword(s):  
Fine Structure ◽  
Molecular Clouds ◽  
Hii Regions ◽  
Fine Structure Lines

scholarly journals The Orion Nebula in the Far-Infrared: High-J CO and fine-structure lines mapped by FIFI-LS/SOFIA

2015 ◽  
Vol 12 (S316) ◽  
pp. 153-154
Author(s):  
Randolf Klein ◽  
Leslie W. Looney ◽  
Erin Cox ◽  
Christian Fischer ◽  
Christof Iserlohe ◽  
...  
Keyword(s):  
Fine Structure ◽  
Far Infrared ◽  
Molecular Gas ◽  
Orion Nebula ◽  
Star Forming ◽  
Physical Conditions ◽  
Molecular Outflow ◽  
Integral Field ◽  
Fine Structure Lines ◽  
Co Observations

AbstractThe Orion Nebula is the closest massive star forming region allowing us to study the physical conditions in such a region with high spatial resolution. We used the far infrared integral-field spectrometer, FIFI-LS, on-board the airborne observatory SOFIA to study the atomic and molecular gas in the Orion Nebula at medium spectral resolution.The large maps obtained with FIFI-LS cover the nebula from the BN/KL-object to the bar in several fine structure lines. They allow us to study the conditions of the photon-dominated region and the interface to the molecular cloud with unprecedented detail.Another investigation targeted the molecular gas in the BN/KL region of the Orion Nebula, which is stirred up by a violent explosion about 500 years ago. The explosion drives a wide angled molecular outflow. We present maps of several high-J CO observations, allowing us to analyze the heated molecular gas.

The Orion Molecular Clouds OMC‐1 and OMC‐2 Mapped in the Far‐Infrared Fine‐Structure Line Emission of C+and O0

1997 ◽  
Vol 481 (1) ◽  
pp. 343-354 ◽  
Author(s):  
F. Herrmann ◽  
S. C. Madden ◽  
T. Nikola ◽  
A. Poglitsch ◽  
R. Timmermann ◽  
...  
Keyword(s):  
Fine Structure ◽  
Molecular Clouds ◽  
Line Emission ◽  
Far Infrared ◽  
Structure Line

scholarly journals Molecular Hydrogen in the High Redshift Damped Ly-α Systems:

2005 ◽  
Vol 13 ◽  
pp. 833-838
Author(s):  
R. Srianand ◽  
P. Petitjean ◽  
C. Ledoux ◽  
G. Ferland
Keyword(s):  
Fine Structure ◽  
Star Formation ◽  
Molecular Hydrogen ◽  
High Redshift ◽  
Simple Consequence ◽  
Preliminary Results ◽  
Physical Conditions ◽  
Lower Temperature ◽  
Fine Structure Lines ◽  
High Dust

AbstractThis review talk summarizes the main results obtained from the just completed survey of molecular hydrogen in damped Lyman-a systems (DLAs). Preliminary results based on modeling ionization conditions and chemical network is also presented. The presence of H2 and fine-structure lines of C 1 in 13-20% of DLAs allow one to investigate the physical conditions using the techniques that are commonly used in the studies of the Galactic ISM. It is shown that the DLAs with H2 trace regions with higher density, lower temperature, moderate to high dust depletion, and local star-formation. Absence of H2 in DLAs with moderate dust depletion could just be a simple consequence of lower densities in the systems.

scholarly journals Nature of the DLA towards Q 0528−250: High pressure and strong UV field revealed by excitation of C i, H2, and Si ii

2020 ◽  
Vol 497 (2) ◽  
pp. 1946-1956 ◽  
Author(s):  
S A Balashev ◽  
C Ledoux ◽  
P Noterdaeme ◽  
R Srianand ◽  
P Petitjean ◽  
...  
Keyword(s):  
Fine Structure ◽  
Relative Velocity ◽  
Energy Levels ◽  
Line Of Sight ◽  
Host Galaxy ◽  
Neutral Medium ◽  
Kinetic Temperature ◽  
Thermal Pressure ◽  
Physical Conditions ◽  
Companion Galaxy

ABSTRACT We present the detection of excited fine-structure energy levels of singly ionized silicon and neutral carbon associated with the proximate damped Lyman-α system at zabs = 2.811 towards Q 0528−250. This absorber has an apparent relative velocity that is inconsistent with the Hubble flow indicating motion along the line-of-sight towards the quasar, i.e. zabs > zem. We measure the metallicity of the system to be [Zn/H] = −0.68 ± 0.02. Using the relative populations of the fine-structure levels of Si ii and C i, as well as the populations of H2 rotational levels, we constrain the physical conditions of the gas. We derive hydrogen number densities of $n_{\rm H}=190^{+70}_{-50}$ cm−3 and $260^{+30}_{-20}$ cm−3 in two velocity components where both C i and H2 are detected. Taking into account the kinetic temperature in each component, ∼150 K, we infer high values of thermal pressure in the cold neutral medium probed by the observations. The strengths of the UV field in Draine’s unit are $I_{\rm UV} = 10^{+5}_{-3}$ and $14^{+3}_{-3}$ in each of these two components, respectively. Such enhanced UV fluxes and thermal pressure compared to intervening DLAs are likely due to the proximity of the quasar. The typical size of the absorber is ∼104 au. Assuming the UV flux is dominated by the quasar, we constrain the distance between the quasar and the absorber to be ∼150−200 kpc. This favours a scenario where the absorption occurs in a companion galaxy located in the group where the quasar-host galaxy resides. This is in line with studies in emission that revealed the presence of several galaxies around the quasar.

scholarly journals Observations of Infrared Fine-Structure Lines: [S III]

1978 ◽  
Vol 76 ◽  
pp. 126-126
Author(s):  
Lawrence T. Greenberg
Keyword(s):  
Fine Structure ◽  
Electron Density ◽  
Experimental Error ◽  
Column Density ◽  
Surface Brightness ◽  
Ngc 7027 ◽  
Structure Line ◽  
Electron Density And Temperature ◽  
Fine Structure Lines

Recent observations of the 18.7 ym fine-structure line of S++ in NGC 7027 and BD+30°3639 (Greenberg, Dyal and Geballe, 1977 Ap.J.(Letters), 213, L74) allow the first determination of an ionic column density in ionized nebulae. The line ratios 18.7 μm/A9532 and λ6312/λ9532, besides yielding both electron density and temperature in the S++ region, have been used to indicate that the fine-structure levels of S++ are collisionally saturated. In this case the 18.7 ym surface brightness directly measures the column density of S++ ions with little dependence upon nebular structure, the major uncertainty being the experimental error. This research has been partially supported by NASA Grants NGR 05-003-511 and NGL 05-003-272.

scholarly journals Unveiling the remarkable photodissociation region of Messier 8

2018 ◽  
Vol 615 ◽  
pp. A158 ◽  
Author(s):  
M. Tiwari ◽  
K. M. Menten ◽  
F. Wyrowski ◽  
J. P. Pérez-Beaupuits ◽  
H. Wiesemeyer ◽  
...  
Keyword(s):  
Fine Structure ◽  
Quantitative Analysis ◽  
Spectral Lines ◽  
Hii Region ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Structure Line ◽  
Velocity Information ◽  
Photodissociation Region

Aims. Messier 8 (M8) is one of the brightest HII regions in the sky. We collected an extensive dataset comprising multiple sub- millimeter spectral lines from neutral and ionized carbon and from CO. Based on this dataset, we aim to understand the morphology of M8 and that of its associated photodissociation region (PDR) and to carry out a quantitative analysis of the physical conditions of these regions such as kinetic temperatures and volume densities. Methods. We used the Stratospheric Observatory For Infrared Astronomy (SOFIA), the Atacama Pathfinder Experiment (APEX) 12 m, and the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescopes to perform a comprehensive imaging survey of the emission from the fine structure lines of [C II] and [C I] and multiple rotational transitions of carbon monoxide (CO) isotopologs within 1.3 × 1.3 pc around the dominant Herschel 36 (Her 36) system, which is composed of at least three massive stars. To further explore the morphology of the region, we compared archival infrared, optical, and radio images of the nebula with our newly obtained fine structure line and CO data, and in particular with the velocity information these data provide. We performed a quantitative analysis, using both LTE and non-LTE methods to determine the abundances of some of the observed species, kinetic temperatures, and volume densities. Results. Bright CO, [C II] and [C I] emission have been found toward the HII region and the PDR in M8. Our analysis places the bulk of the molecular material in the background of the nebulosity illuminated by the bright stellar systems Her 36 and 9 Sagitarii. Since the emission from all observed atomic and molecular tracers peaks at or close to the position of Her 36, we conclude that the star is still physically close to its natal dense cloud core and heats it. A veil of warm gas moves away from Her 36 toward the Sun and its associated dust contributes to the foreground extinction in the region. One of the most prominent star forming regions in M8, the Hourglass Nebula, is particularly bright due to cracks in this veil close to Her 36. We obtain H2 densities ranging from ~104–106 cm–3 and kinetic temperatures of 100–150 K in the bright PDR caused by Her 36 using radiative transfer modeling of various transitions of CO isotopologs.

scholarly journals A dense, solar metallicity ISM in the z = 4.2 dusty star-forming galaxy SPT 0418−47

2019 ◽  
Vol 631 ◽  
pp. A167 ◽  
Author(s):  
Carlos De Breuck ◽  
Axel Weiß ◽  
Matthieu Béthermin ◽  
Daniel Cunningham ◽  
Yordanka Apostolovski ◽  
...  
Keyword(s):  
Fine Structure ◽  
Interstellar Medium ◽  
Far Infrared ◽  
Line Ratio ◽  
Star Forming ◽  
Physical Conditions ◽  
Solar Metallicity ◽  
Fine Structure Lines ◽  
Compact Array

We present a study of six far-infrared fine structure lines in the z = 4.225 lensed dusty star-forming galaxy SPT 0418−47 to probe the physical conditions of its interstellar medium (ISM). In particular, we report Atacama Pathfinder EXperiment (APEX) detections of the [OI] 145 μm and [OIII] 88 μm lines and Atacama Compact Array (ACA) detections of the [NII] 122 and 205 μm lines. The [OI] 145 μm/[CII] 158 μm line ratio is ∼5× higher compared to the average of local galaxies. We interpret this as evidence that the ISM is dominated by photo-dissociation regions with high gas densities. The line ratios, and in particular those of [OIII] 88 μm and [NII] 122 μm imply that the ISM in SPT 0418−47 is already chemically enriched to nearly solar metallicity. While the strong gravitational amplification was required to detect these lines with APEX, larger samples can be observed with the Atacama Large Millimeter/submillimeter Array (ALMA), and should allow observers to determine if the dense, solar metallicity ISM is common among these highly star-forming galaxies.

Sign in / Sign up

Export Citation Format

Share Document