Abstract
We report SOFIA/GREAT observations of high-
J
CO lines and C
ii
observations of the super star cluster candidate H72.97-69.39 in the Large Magellanic Cloud (LMC), which is in its very early ...formation stage. We use our observations to determine if shocks are heating the gas or if photon-dominated regions (PDRs) are being heated by local far-UV radiation. We use a PDR model and a shock model to determine whether the CO and C
ii
lines arise from PDRs or shocks. We can reproduce the observed high-
J
CO and C
ii
emission with a clumpy PDR model with the following properties: a density of 10
4.7
cm
−3
, a mass of 10
4
M
⊙
, and UV radiation of 10
3.5
in units of Draine field. Comparison with the ALMA beam-filling factor suggests a higher density within the uncertainty of the fit. We find the lower-limit C
ii
/total infrared (TIR) ratio (
ϵ
) traced by C
ii
/TIR to be 0.026%, lower than other known young star-forming regions in the LMC. Our shock models may explain the CO (16−15) and CO (11−10) emission lines with shock velocity of 8–11 km s
−1
, pre-shock density of 10
4
–10
5
cm
−3
, and
G
UV
= 0 in units of Draine field. However, the C
ii
line emission cannot be explained by a shock model, thus it is originating in a different gas component. Observations of O
i
63
μ
m predicted to be 1.1 × 10
−13
W m
−2
by PDR models and 7.8 × 10
−15
W m
−2
by shock models will help distinguish between the PDR and shock scenarios.
Context. With Herschel, we can for the first time observe a wealth of high-J CO lines in the interstellar medium with a high angular resolution. These lines are specifically useful for tracing the ...warm and dense gas and are therefore very appropriate for a study of strongly irradiated dense photodissocation regions (PDRs). Aims. We characterize the morphology of CO J = 19–18 emission and study the high-J CO excitation in a highly UV-irradiated prototypical PDR, the Orion Bar. Methods. We used fully sampled maps of CO J = 19–18 emission with the Photoconductor Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory over an area of ~110′′ × 110′′ with an angular resolution of 9′′. We studied the morphology of this high-J CO line in the Orion Bar and in the region in front and behind the Bar, and compared it with lower-J lines of CO from J = 5–4 to J = 13–12 and 13CO from J = 5–4 to J = 11–10 emission observed with the Herschel Spectral and Photometric Imaging Receiver (SPIRE). In addition, we compared the high-J CO to polycyclic aromatic hydrocarbon (PAH) emission and vibrationally excited H2. We used the CO and 13CO observations and the RADEX model to derive the physical conditions in the warm molecular gas layers. Results. The CO J = 19–18 line is detected unambiguously everywhere in the observed region, in the Bar, and in front and behind of it. In the Bar, the most striking features are several knots of enhanced emission that probably result from column and/or volume density enhancements. The corresponding structures are most likely even smaller than what PACS is able to resolve. The high-J CO line mostly arises from the warm edge of the Orion Bar PDR, while the lower-J lines arise from a colder region farther inside the molecular cloud. Even if it is slightly shifted farther into the PDR, the high-J CO emission peaks are very close to the H/H2 dissociation front, as traced by the peaks of H2 vibrational emission. Our results also suggest that the high-J CO emitting gas is mainly excited by photoelectric heating. The CO J = 19–18/J = 12–11 line intensity ratio peaks in front of the CO J = 19–18 emission between the dissociation and ionization fronts, where the PAH emission also peak. A warm or hot molecular gas could thus be present in the atomic region where the intense UV radiation is mostly unshielded. In agreement with recent ALMA detections, low column densities of hot molecular gas seem to exist between the ionization and dissociation fronts. As found in other studies, the best fit with RADEX modeling for beam-averaged physical conditions is for a density of 106 cm−3 and a high thermal pressure (P∕k = nH × T) of ~1–2 × 108 K cm−3. Conclusions. The high-J CO emission is concentrated close to the dissociation front in the Orion Bar. Hot CO may also lie in the atomic PDR between the ionization and dissociation fronts, which is consistent with the dynamical and photoevaporation effects.
Context. The methylidyne cation (CH+) and hydroxyl (OH) are key molecules in the warm interstellar chemistry, but their formation and excitation mechanisms are not well understood. Their abundance ...and excitation are predicted to be enhanced by the presence of vibrationally excited H2 or hot gas (~500−1000 K) in photodissociation regions (PDRs) with high incident far-ultraviolet (FUV) radiation field. The excitation may also originate in dense gas (>105 cm-3) followed by nonreactive collisions with H2, H, and electrons. Previous observations of the Orion Bar suggest that the rotationally excited CH+ and OH correlate with the excited CO, which is a tracer of dense and warm gas, and that formation pumping contributes to CH+ excitation. Aims. Our goal is to examine the spatial distribution of the rotationally excited CH+ and OH emission lines in the Orion Bar to establish their physical origin and main formation and excitation mechanisms. Methods. We present spatially sampled maps of the CH+J = 3–2 transition at 119.8 μm and the OH Λ doublet at 84 μm in the Orion Bar over an area of 110″× 110″ with Herschel/PACS. We compare the spatial distribution of these molecules with those of their chemical precursors, C+, O and H2, and tracers of warm and dense gas (high-J CO). We assess the spatial variation of the CH+J = 2–1 velocity-resolved line profile at 1669 GHz with Herschel/HIFI spectrometer observations. Results. The OH and especially CH+ lines correlate well with the high-J CO emission and delineate the warm and dense molecular region at the edge of the Bar. While notably similar, the differences in the CH+ and OH morphologies indicate that CH+ formation and excitation are strongly related to the observed vibrationally excited H2. This, together with the observed broad CH+ line widths, indicates that formation pumping contributes to the excitation of this reactive molecular ion. Interestingly, the peak of the rotationally excited OH 84 μm emission coincides with a bright young object, proplyd 244–440, which shows that OH can be an excellent tracer of UV-irradiated dense gas. Conclusions. The spatial distribution of CH+ and OH revealed in our maps is consistent with previous modeling studies. Both formation pumping and nonreactive collisions in a UV-irradiated dense gas are important CH+J = 3–2 excitation processes. The excitation of the OH Λ doublet at 84 μm is mainly sensitive to the temperature and density.
Context.
The CII 158 μm far-infrared fine-structure line is one of the dominant cooling lines of the star-forming interstellar medium. Hence CII emission originates in and thus can be used to trace a ...range of ISM processes. Velocity-resolved large-scale mapping of CII in star-forming regions provides a unique perspective of the kinematics of these regions and their interactions with the exciting source of radiation.
Aims.
We explore the scientific applications of large-scale mapping of velocity-resolved CII observations. With the CII observations, we investigate the effect of stellar feedback on the ISM. We present the details of observation, calibration, and data reduction using a heterodyne array receiver mounted on an airborne observatory.
Methods.
A 1.15 square degree velocity-resolved map of the Orion molecular cloud centred on the bar region was observed using the German REceiver for Astronomy at Terahertz Frequencies (upGREAT) heterodyne receiver flying on board the Stratospheric Observatory for Infrared Astronomy. The data were acquired using the 14 pixels of the German REceiver for Astronomy at Terahertz Frequencies that were observed in an on-the-fly mapping mode. 2.4 million spectra were taken in total. These spectra were gridded into a three-dimensional cube with a spatial resolution of 14.1 arcseconds and a spectral resolution of 0.3 km s
−1
.
Results.
A square-degree CII map with a spectral resolution of 0.3 km s
−1
is presented. The scientific potential of this data is summarized with discussion of mechanical and radiative stellar feedback, filament tracing using CII, CII opacity effects, CII and carbon recombination lines, and CII interaction with the large molecular cloud. The data quality and calibration is discussed in detail, and new techniques are presented to mitigate the effects of unavoidable instrument deficiencies (e.g. baseline stability) and thus to improve the data quality. A comparison with a smaller CII map taken with the
Herschel
/Heterodyne Instrument for the Far-Infrared spectrometer is presented.
Conclusions.
Large-scale CII mapping provides new insight into the kinematics of the ISM. The interaction between massive stars and the ISM is probed through CII observations. Spectrally resolving the CII emission is necessary to probe the microphysics induced by the feedback of massive stars. We show that certain heterodyne instrument data quality issues can be resolved using a spline-based technique, and better data correction routines allow for more efficient observing strategies.
We present the performance of the upGREAT heterodyne array receivers on the SOFIA telescope after several years of operations. This instrument is a multi-pixel high resolution (
R
≳
1
0
7
) ...spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel subarrays configured in a hexagonal layout around a central pixel. The low frequency array receiver (LFA) has
2
×
7
pixels (dual polarization), and presently covers the 1.83–2.07
THz frequency range, which allows to observe the CII and OI lines at 158
μ
m and 145
μ
m wavelengths. The high frequency array (HFA) covers the OI line at 63
μ
m and is equipped with one polarization at the moment (7 pixels, which can be upgraded in the near future with a second polarization array). The 4.7
THz array has successfully flown using two separate quantum-cascade laser local oscillators from two different groups. NASA completed the development, integration and testing of a dual-channel closed-cycle cryocooler system, with two independently operable He compressors, aboard SOFIA in early 2017 and since then, both arrays can be operated in parallel using a frequency separating dichroic mirror. This configuration is now the prime GREAT configuration and has been added to SOFIA’s instrument suite since observing cycle 6.
The methylidyne cation (CH
) and hydroxyl (OH) are key molecules in the warm interstellar chemistry, but their formation and excitation mechanisms are not well understood. Their abundance and ...excitation are predicted to be enhanced by the presence of vibrationally excited H
or hot gas (~500-1000 K) in photodissociation regions with high incident FUV radiation field. The excitation may also originate in dense gas (> 10
cm
) followed by nonreactive collisions with H
, H, and electrons. Previous observations of the Orion Bar suggest that the rotationally excited CH
and OH correlate with the excited CO, a tracer of dense and warm gas, and formation pumping contributes to CH
excitation.
Our goal is to examine the spatial distribution of the rotationally excited CH
and OH emission lines in the Orion Bar in order to establish their physical origin and main formation and excitation mechanisms.
We present spatially sampled maps of the CH
J=3-2 transition at 119.8 µm and the OH Λ-doublet at 84 µm in the Orion Bar over an area of 110″×110″ with
(PACS). We compare the spatial distribution of these molecules with those of their chemical precursors, C
, O and H
, and tracers of warm and dense gas (high-J CO). We assess the spatial variation of CH
J=2-1 velocity-resolved line profile at 1669 GHz with
HIFI spectrometer observations.
The OH and especially CH
lines correlate well with the high-J CO emission and delineate the warm and dense molecular region at the edge of the Bar. While notably similar, the differences in the CH
and OH morphologies indicate that CH
formation and excitation are strongly related to the observed vibrationally excited H
. This, together with the observed broad CH
line widths, indicates that formation pumping contributes to the excitation of this reactive molecular ion. Interestingly, the peak of the rotationally excited OH 84 µm emission coincides with a bright young object, proplyd 244-440, which shows that OH can be an excellent tracer of UV-irradiated dense gas.
The spatial distribution of CH
and OH revealed in our maps is consistent with previous modeling studies. Both formation pumping and nonreactive collisions in a UV-irradiated dense gas are important CH
J=3-2 excitation processes. The excitation of the OH Λ-doublet at 84 µm is mainly sensitive to the temperature and density.
Media Archaeology Huhtamo, Erkki; Parikka, Jussi
2011, 2011-06-16, 20110101
eBook
This book introduces an archaeological approach to the study of media - one that sifts through the evidence to learn how media were written about, used, designed, preserved, and sometimes discarded. ...Edited by Erkki Huhtamo and Jussi Parikka, with contributions from internationally prominent scholars from Europe, North America, and Japan, the essays help us understand how the media that predate today's interactive, digital forms were in their time contested, adopted and embedded in the everyday. Providing a broad overview of the many historical and theoretical facets of Media Archaeology as an emerging field, the book encourages discussion by presenting a full range of different voices. By revisiting 'old' or even 'dead' media, it provides a richer horizon for understanding 'new' media in their complex and often contradictory roles in contemporary society and culture.
We present a new multi-pixel high resolution (R ≳ 107) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receiver uses 2 × 7-pixel subarrays in orthogonal ...polarization, each in an hexagonal array around a central pixel. We present the first results for this new instrument after commissioning campaigns in May and December 2015 and after science observations performed in May 2016. The receiver is designed to ultimately cover the full 1.8−2.5 THz frequency range but in its first implementation, the observing range was limited to observations of the CII line at 1.9 THz in 2015 and extended to 1.83−2.07 THz in 2016. The instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. An example of large scale mapping around the Horsehead Nebula is presented here illustrating this improvement. The array has been added to SOFIA’s instrument suite already for ongoing observing cycle 4.
Globules and pillars in Cygnus X Schneider, N.; Röllig, M.; Polehampton, E. T. ...
Astronomy and astrophysics (Berlin),
09/2021, Letnik:
653
Journal Article
Recenzirano
Odprti dostop
IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240
M
⊙
, length ~1.5 pc) with an internal H
II
region created by the stellar feedback of embedded ...intermediate-mass stars, in particular, one Herbig Be star. In Schneider et al. 2012, (A&A, 542, L18) and Djupvik et al. 2017, (A&A, 599, A37), we proposed that the emission of the far-infrared (FIR) lines of C
II
at 158 μm and O
I
at 145 μm in the globule head are mostly due to an internal photodissociation region (PDR). Here, we present a
Herschel
/HIFI C
II
158 μm map of the whole globule and a large set of other FIR lines (mid-to high-
J
CO lines observed with
Herschel
/PACS and SPIRE, the O
I
63 μm line and the
12
CO 16→15 line observed with upGREAT on SOFIA), covering the globule head and partly a position in the tail. The C
II
map revealed that the whole globule is probably rotating. Highly collimated, high-velocity C
II
emission is detected close to the Herbig Be star. We performed a PDR analysis using the KOSMA-
τ
PDR code for one position in the head and one in the tail. The observed FIR lines in the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy, dense, and thin inner PDR layer, representing the interface between the H
II
region cavity and the external PDR. The modelled internal UV field of ~2500
G
°
is similar to what we obtained from the
Herschel
FIR fluxes, but lower than what we estimated from the census of the embedded stars. External illumination from the ~30 pc distant Cyg OB2 cluster, producing an UV field of ~150–600
G
°
as an upper limit, is responsible for most of the C
II
emission. For the tail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140
G
°
.
Globules and pillars in Cygnus X Schneider, N; Röllig, M; Polehampton, E T ...
Astronomy and astrophysics (Berlin),
09/2021, Letnik:
653
Journal Article
Recenzirano
Odprti dostop
IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240 M⊙, length ~1.5 pc) with an internal H II region created by the stellar feedback of embedded ...intermediate-mass stars, in particular, one Herbig Be star. In Schneider et al. 2012, (A&A, 542, L18) and Djupvik et al. 2017, (A&A, 599, A37), we proposed that the emission of the far-infrared (FIR) lines of C II at 158 μm and O I at 145 μm in the globule head are mostly due to an internal photodissociation region (PDR). Here, we present a Herschel/HIFI C II 158 μm map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observed with Herschel/PACS and SPIRE, the O I 63 μm line and the 12CO 16→15 line observed with upGREAT on SOFIA), covering the globule head and partly a position in the tail. The C II map revealed that the whole globule is probably rotating. Highly collimated, high-velocity C II emission is detected close to the Herbig Be star. We performed a PDR analysis using the KOSMA-τ PDR code for one position in the head and one in the tail. The observed FIR lines in the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy, dense, and thin inner PDR layer, representing the interface between the H II region cavity and the external PDR. The modelled internal UV field of ~2500 G° is similar to what we obtained from the Herschel FIR fluxes, but lower than what we estimated from the census of the embedded stars. External illumination from the ~30 pc distant Cyg OB2 cluster, producing an UV field of ~150–600 G° as an upper limit, is responsible for most of the C II emission. For the tail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140 G°.
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