Interactions between young stars and their parent molecular clouds are poorly understood. High-resolution observations of the Orion nebula now reveal these interactions, which have implications for ...star formation. See Letter (https://www.nature.com/articles/nature18957)
Aims. The aim of our study is to investigate the physical properties of the star-forming interstellar medium (ISM) in the Large Magellanic Cloud (LMC) by separating the origin of the emission lines ...spatially and spectrally. The LMC provides a unique local template to bridge studies in the Galaxy and high redshift galaxies because of its low metallicity and proximity, enabling us to study the detailed physics of the ISM in spatially resolved individual star-forming regions. Following Okada et al. (Okada, Y., Requena-Torres, M. A., Güsten, R., et al. 2015, A&A, 580, A54), we investigate different phases of the ISM traced by carbon-bearing species in four star-forming regions in the LMC, and model the physical properties using the KOSMA-τ PDR model. Methods. We mapped 3–13 arcmin2 areas in 30 Dor, N158, N160, and N159 along the molecular ridge of the LMC in C II 158 μm with GREAT on board SOFIA. We also observed the same area with CO(2-1) to (6-5), 13CO(2-1) and (3-2), C I 3P1–3P0 and 3P2–3P1 with APEX. For selected positions in N159 and 30 Dor, we observed O I 145 μm and O I 63 μm with upGREAT. All spectra are velocity resolved. Results. In all four star-forming regions, the line profiles of CO, 13CO, and C I emission are similar, being reproduced by a combination of Gaussian profiles defined by CO(3-2), whereas C II typically shows wider line profiles or an additional velocity component. At several positions in N159 and 30 Dor, we observed the velocity-resolved O I 145 and 63 μm lines for the first time. At some positions, the O I line profiles match those of CO, at other positions they are more similar to the C II profiles. We interpret the different line profiles of CO, C II and O I as contributions from spatially separated clouds and/or clouds in different physical phases, which give different line ratios depending on their physical properties. We modeled the emission from the CO, C I, C II, and O I lines and the far-infrared continuum emission using the latest KOSMA-τ PDR model, which treats the dust-related physics consistently and computes the dust continuum SED together with the line emission of the chemical species. We find that the line and continuum emissions are not well-reproduced by a single clump ensemble. Toward the CO peak at N159 W, we propose a scenario that the CO, C II, and O I 63 μm emission are weaker than expected because of mutual shielding among clumps.
Context. M 33 is a gas rich spiral galaxy of the Local Group. Its vicinity allows us to study its interstellar medium (ISM) on linear scales corresponding to the sizes of individual giant molecular ...clouds. Aims. We investigate the relationship between the two major gas cooling lines and the total infrared (TIR) dust continuum. Methods. We mapped the emission of gas and dust in M 33 using the far-infrared lines of C II and O I(63 μm) and the total infrared continuum. The line maps were observed with the PACS spectrometer on board the Herschel Space Observatory. These maps have 50 pc resolution and form a ∼370 pc wide stripe along its major axis covering the sites of bright H II regions, but also more quiescent arm and inter-arm regions from the southern arm at 2 kpc galacto-centric distance to the south out to 5.7 kpc distance to the north. Full-galaxy maps of the continuum emission at 24 μm from Spitzer/MIPS, and at 70 μm, 100 μm, and 160 μm from Herschel/PACS were combined to obtain a map of the TIR. Results. TIR and C II intensities are correlated over more than two orders of magnitude. The range of TIR translates to a range of far ultraviolet (FUV) emission of G0, obs ∼ 2 to 200 in units of the average Galactic radiation field. The binned C II/TIR ratio drops with rising TIR, with large, but decreasing scatter. The contribution of the cold neutral medium to the C II emission, as estimated from VLA H I data, is on average only 10%. Fits of modified black bodies to the continuum emission were used to estimate dust mass surface densities and total gas column densities. A correction for possible foreground absorption by cold gas was applied to the O I data before comparing it with models of photon dominated regions. Most of the ratios of C II/O I and (C II+O I)/TIR are consistent with two model solutions. The median ratios are consistent with one solution at n ∼ 2 × 102 cm−3, G0 ∼ 60, and a second low-FUV solution at n ∼ 104 cm−3, G0 ∼ 1.5. Conclusions. The bulk of the gas along the lines-of-sight is represented by a low-density, high-FUV phase with low beam filling factors ∼1. A fraction of the gas may, however, be represented by the second solution.
We investigate the physical conditions of the gas, atomic and molecular, in the filaments in the context of Photo-Dissociation Regions (PDRs) using the KOSMA-PDR mode of clumpy clouds. We also ...compare the CII vs. NII integrated intensity predictions in Abel et al. 2005 for HII regions and adjacent PDRs in the Galactic disk, and check for their applicability under the extreme physical conditions present in the GC. Our preliminary results show that observed integrated intensities are well reproduced by the PDR model. The gas is exposed to a relatively low Far-UV field between 102 – 103 Draine fields. The total volume hydrogen density is well constrained between 104 – 105 cm−3. The hydrogen ionization rate due to cosmic-rays varies between 10−15 and 4× 10−15 s−1, with the highest value ~ 10−14 s−1 found towards G0.07+0.04. Our results show that the line-of-sight contribution to the total distance of the filaments to the Arches Cluster is not negligible. The spatial distribution of the CII/NII ratio shows that the integrated intensity ratios are fairly homogeneously distributed for values below 10 in energy units. Calculations including variation on the C/N abundance ratio show that tight constraints on this ratio are needed to reproduce the observations.
Context.
M 33 is a gas rich spiral galaxy of the Local Group. Its vicinity allows us to study its interstellar medium (ISM) on linear scales corresponding to the sizes of individual giant molecular ...clouds.
Aims.
We investigate the relationship between the two major gas cooling lines and the total infrared (TIR) dust continuum.
Methods.
We mapped the emission of gas and dust in M 33 using the far-infrared lines of C
II
and O
I
(63
μ
m) and the total infrared continuum. The line maps were observed with the PACS spectrometer on board the
Herschel
Space Observatory. These maps have 50 pc resolution and form a ∼370 pc wide stripe along its major axis covering the sites of bright H
II
regions, but also more quiescent arm and inter-arm regions from the southern arm at 2 kpc galacto-centric distance to the south out to 5.7 kpc distance to the north. Full-galaxy maps of the continuum emission at 24
μ
m from
Spitzer
/MIPS, and at 70
μ
m, 100
μ
m, and 160
μ
m from
Herschel
/PACS were combined to obtain a map of the TIR.
Results.
TIR and C
II
intensities are correlated over more than two orders of magnitude. The range of TIR translates to a range of far ultraviolet (FUV) emission of
G
0, obs
∼ 2 to 200 in units of the average Galactic radiation field. The binned C
II
/TIR ratio drops with rising TIR, with large, but decreasing scatter. The contribution of the cold neutral medium to the C
II
emission, as estimated from VLA H
I
data, is on average only 10%. Fits of modified black bodies to the continuum emission were used to estimate dust mass surface densities and total gas column densities. A correction for possible foreground absorption by cold gas was applied to the O
I
data before comparing it with models of photon dominated regions. Most of the ratios of C
II
/O
I
and (C
II
+O
I
)/TIR are consistent with two model solutions. The median ratios are consistent with one solution at
n
∼ 2 × 10
2
cm
−3
,
G
0
∼ 60, and a second low-FUV solution at
n
∼ 10
4
cm
−3
,
G
0
∼ 1.5.
Conclusions.
The bulk of the gas along the lines-of-sight is represented by a low-density, high-FUV phase with low beam filling factors ∼1. A fraction of the gas may, however, be represented by the second solution.
Radiative and mechanical feedback of massive stars regulates star formation and galaxy evolution. Positive feedback triggers the creation of new stars by collecting dense shells of gas, while ...negative feedback disrupts star formation by shredding molecular clouds. Although key to understanding star formation, their relative importance is unknown. Here, we report velocity-resolved observations from the SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program FEEDBACK of the massive star-forming region RCW 120 in the CII 1.9-THz fine-structure line, revealing a gas shell expanding at 15 km/s. Complementary APEX (Atacama Pathfinder Experiment) CO J = 3-2 345-GHz observations exhibit a ring structure of molecular gas, fragmented into clumps that are actively forming stars. Our observations demonstrate that triggered star formation can occur on much shorter time scales than hitherto thought (<0.15 million years), suggesting that positive feedback operates on short time periods.
High-latitude intermediate-velocity clouds (IVCs) are part of the Milky Way’s H I halo and originate from either a galactic fountain process or extragalactic gas infall. They are partly molecular and ...can most of the time be identified in CO. Some of these regions also exhibit high-velocity cloud gas, which is mostly atomic, and gas at local velocities (LVCs), which is partly atomic and partly molecular. We conducted a study on the IVCs Draco and Spider, both were exposed to a very weak UV field, using the spectroscopic receiver upGREAT on the Stratospheric Observatory for Infrared Astronomy (SOFIA). The 158 µm fine-structure line of ionized carbon (C II ) was observed, and the results are as follows: In Draco, the C II line was detected at intermediate velocities (but not at local or high velocities) in four out of five positions. No C II emission was found at any velocity in the two observed positions in Spider. To understand the excitation conditions of the gas in Draco, we analyzed complementary CO and H I data as well as dust column density and temperature maps from Herschel . The observed C II intensities suggest the presence of shocks in Draco that heat the gas and subsequently emit in the C II cooling line. These shocks are likely caused by the fast cloud’s motion toward the Galactic plane that is accompanied by collisions between H I clouds. The nondetection of C II in the Spider IVC and LVC as well as in other low-density clouds at local velocities that we present in this paper (Polaris and Musca) supports the idea that highly dynamic processes are necessary for C II excitation in UV-faint low-density regions.
Abstract
Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter ...in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1–3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter- and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.
![Velocity profiles of [CII],...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361/small "Velocity profiles of [CII], [CI], CO, and [OI] and physical conditions in four star-forming regions in the Large Magellanic Cloud")
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