Context. In bright photodissociation regions (PDR) associated with massive star formation, the presence of dense “clumps” that are immersed in a less dense interclump medium is often proposed to ...explain the difficulty of models to account for the observed gas emission in high-excitation lines. Aims. We aim to present a comprehensive view of the modelling of the CO rotational ladder in PDRs, including the high-J lines that trace warm molecular gas at PDR interfaces. Methods. We observed the 12CO and 13CO ladders in two prototypical PDRs, the Orion Bar and NGC 7023 NW using the instruments onboard Herschel. We also considered line emission from key species in the gas cooling of PDRs (C+, O, and H2) and other tracers of PDR edges such as OH and CH+. All the intensities are collected from Herschel observations, the literature and the Spitzer archive and were analysed using the Meudon PDR code. Results. A grid of models was run to explore the parameter space of only two parameters: thermal gas pressure and a global scaling factor that corrects for approximations in the assumed geometry. We conclude that the emission in the high-J CO lines, which were observed up to Jup = 23 in the Orion Bar (Jup = 19 in NGC 7023), can only originate from small structures with typical thicknesses of a few 10−3 pc and at high thermal pressures (Pth ~ 108 K cm−3). Conclusions. Compiling data from the literature, we find that the gas thermal pressure increases with the intensity of the UV radiation field given by G0, following a trend in line with recent simulations of the photoevaporation of illuminated edges of molecular clouds. This relation can help to rationalise the analysis of high-J CO emission in massive star formation and provides an observational constraint for models which study stellar feedback on molecular clouds.
FEEDBACK is a SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program dedicated to study the interaction of massive stars with their environment. It performs a survey of 11 galactic ...high mass star-forming regions in the 158 m (1.9 THz) line of C ii and the 63 m (4.7 THz) line of O i. We employ the 14 pixel Low Frequency Array and 7 pixel High Frequency Array upGREAT heterodyne instrument to spectrally resolve (0.24 MHz) these far-infrared fine structure lines. With a total observing time of 96h, we will cover ∼6700 arcmin2 at 14 1) angular resolution for the C ii line and 6 3 for the O i line. The observations started in spring 2019 (Cycle 7). Our aim is to understand the dynamics in regions dominated by different feedback processes from massive stars such as stellar winds, thermal expansion, and radiation pressure, and to quantify the mechanical energy injection and radiative heating efficiency. This is an important science topic because feedback of massive stars on their environment regulates the physical conditions and sets the emission characteristics in the interstellar medium (ISM), influences the star formation activity through molecular cloud dissolution and compression processes, and drives the evolution of the ISM in galaxies. The C ii line provides the kinematics of the gas and is one of the dominant cooling lines of gas for low to moderate densities and UV fields. The O i line traces warm and high-density gas, excited in photodissociations regions with a strong UV field or by shocks. The source sample spans a broad range in stellar characteristics from single OB stars, to small groups of O stars, to rich young stellar clusters, to ministarburst complexes. It contains well-known targets such as Aquila, the Cygnus X region, M16, M17, NGC7538, NGC6334, Vela, and W43 as well as a selection of H ii region bubbles, namely RCW49, RCW79, and RCW120. These C ii maps, together with the less explored O i 63 m line, provide an outstanding database for the community. They will be made publically available and will trigger further studies and follow-up observations.
We upgraded the chemical network from the UMIST Database for Astrochemistry 2006 to include isotopes such as 13C and 18O. This includes all corresponding isotopologues, their chemical reactions and ...the properly scaled reaction rate coefficients. We study the fractionation behavior of astrochemically relevant species over a wide range of model parameters, relevant for modelling of photo-dissociation regions (PDRs). We separately analyze the fractionation of the local abundances, fractionation of the total column densities, and fractionation visible in the emission line ratios. We find that strong C+ fractionation is possible in cool C+ gas. Optical thickness as well as excitation effects produce intensity ratios between 40 and 400. The fractionation of CO in PDRs is significantly different from the diffuse interstellar medium. PDR model results never show a fractionation ratio of the CO column density larger than the elemental ratio. Isotope-selective photo-dissociation is always dominated by the isotope-selective chemistry in dense PDR gas. The fractionation of C, CH, CH+ and HCO+ is studied in detail, showing that the fractionation of C, CH and CH+ is dominated by the fractionation of their parental species. The light hydrides chemically derive from C+, and, consequently, their fractionation state is coupled to that of C+. The fractionation of C is a mixed case depending on whether formation from CO or HCO+ dominates. Ratios of the emission lines of C ii, C i, 13CO, and H13CO+ provide individual diagnostics to the fractionation status of C+, C, and CO.
We present the first ~7.5'×11.5' velocity-resolved (~0.2 km s
) map of the C ii 158
m line toward the Orion molecular cloud 1 (OMC 1) taken with the
/HIFI instrument. In combination with far-infrared ...(FIR) photometric images and velocity-resolved maps of the H41
hydrogen recombination and CO
=2-1 lines, this data set provides an unprecedented view of the intricate small-scale kinematics of the ionized/PDR/molecular gas interfaces and of the radiative feedback from massive stars. The main contribution to the C ii luminosity (~85 %) is from the extended, FUV-illuminated face of the cloud (
>500,
>5×10
cm
) and from dense PDRs (
≳10
,
≳10
cm
) at the interface between OMC 1 and the H ii region surrounding the Trapezium cluster. Around ~15 % of the C ii emission arises from a different gas component without CO counterpart. The C ii excitation, PDR gas turbulence, line opacity (from
C ii) and role of the geometry of the illuminating stars with respect to the cloud are investigated. We construct maps of the
C ii/
and
/
ratios and show that
C ii/
decreases from the extended cloud component (~10
-10
) to the more opaque star-forming cores (~10
-10
). The lowest values are reminiscent of the "C ii deficit" seen in local ultra-luminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing
C ii/
ratio correlates better with the column density of dust through the molecular cloud than with
/
. We conclude that the C ii emitting column relative to the total dust column along each line of sight is responsible for the observed
C ii/
variations through the cloud.
FEEDBACK from the NGC 7538 H II region Beuther, H.; Schneider, N.; Simon, R. ...
Astronomy and astrophysics (Berlin),
3/2022, Letnik:
659
Journal Article
Recenzirano
Odprti dostop
Context.
The interaction of expanding H
II
regions with their environmental clouds is one of the central questions driving the Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program ...FEEDBACK.
Aims.
We want to understand the interaction of the prototypical NGC 7538 H
II
region with the neighboring molecular cloud hosting several active star-forming regions.
Methods.
Using the SOFIA, we mapped an area of ~210′
2
(~125 pc
2
) around NGC 7538 in the velocity-resolved ionized carbon fine-structure line CII at 1.9 THz (158 μm). Complementary observed atomic carbon CI at 492 GHz and high-J CO(8–7) data, as well as archival near- and far-infrared, cm continuum, CO(3–2), and HI data are folded into the analysis.
Results.
The ionized carbon CII data reveal rich morphological and kinematic structures. While the overall morphology follows the general ionized gas that is also visible in the radio continuum emission, the channel maps show multiple bubble-like structures with sizes on the order of ~80–100″ (~1.0–1.28 pc). While at least one of them may be an individual feedback bubble driven by the main exciting sources of the NGC 7538 H
II
region (the O3 and O9 stars IRS6 and IRS5), the other bubble-like morphologies may also be due to the intrinsically porous structure of the H
II
region. An analysis of the expansion velocities around 10 km s
−1
indicates that thermal expansion is not sufficient but that wind-driving from the central O-stars is required. The region exhibits a general velocity gradient across, but we also identify several individual velocity components. The most blue-shifted CII component has barely any molecular or atomic counterparts. At the interface to the molecular cloud, we find a typical photon-dominated region (PDR) with a bar-shape. Ionized C
+
, atomic C
0
and molecular carbon CO show a layered structure in this PDR. The carbon in the PDR is dominated by its ionized C
+
form with atomic C
0
and molecular CO masses of ~0.45 ± 0.1
M
⊙
and ~1.2 ± 0.1
M
⊙
, respectively, compared to the ionized carbon C
+
in the range of 3.6−9.7
M
⊙
. This bar-shaped PDR exhibits a velocity-gradient across, indicating motions along the line of sight toward the observer.
Conclusions.
Even if it is shown to be dominated by two nearby exciting sources (IRS6 and IRS5), the NGC 7538 H
II
region exhibits a diverse set of substructures that interact with each other as well as with the adjacent cloud. Compared to other recent CII observations of H
II
regions (e.g., Orion Veil, RCW120, RCW49), the bubble-shape morphologies revealed in CII emission that are indicative of expanding shells are recurring structures of PDRs.
Power spectra of deprojected images of late-type galaxies in gas or dust emission are very useful diagnostics of the dynamics and stability of their interstellar medium. Previous studies have shown ...that the power spectra can be approximated as two power laws, a shallow one on large scales (larger than 500 pc) and a steeper one on small scales, with the break between the two corresponding to the line-of-sight thickness of the galaxy disk. The break separates the 3D behavior of the interstellar medium on small scales, controlled by star formation and feedback, from the 2D behavior on large scales, driven by density waves in the disk. The break between these two regimes depends on the thickness of the plane, which is determined by the natural self-gravitating scale of the interstellar medium. We present a thorough analysis of the power spectra of the dust and gas emission at several wavelengths in the nearby galaxy M 33. In particular, we use the recently obtained images at five wavelengths by PACS and SPIRE onboard Herschel. The wide dynamical range (2–3 dex in scale) of most images allows us to clearly determine the change in slopes from −1.5 to −4, with some variations with wavelength. The break scale increases with wavelength from 100 pc at 24 and 100 μm to 350 pc at 500 μm, suggesting that the cool dust lies in a thicker disk than the warm dust, perhaps because of star formation that is more confined to the plane. The slope on small scales tends to be steeper at longer wavelength, meaning that the warmer dust is more concentrated in clumps. Numerical simulations of an isolated late-type galaxy, rich in gas and with no bulge, such as M 33, are carried out to better interpret these observed results. Varying the star formation and feedback parameters, it is possible to obtain a range of power spectra, with two power-law slopes and breaks, that nicelybracket the data. The small-scale power-law does indeed reflect the 3D behavior of the gas layer, steepening strongly while the feedback smoothes the structures by increasing the gas turbulence. M 33 appears to correspond to a fiducial model with an SFR of ~ 0.7 M⊙/yr, with 10% supernovae energy coupled to the gas kinematics.
The KArlsruhe TRItium Neutrino (KATRIN) experiment will measure the absolute mass scale of neutrinos with a sensitivity of mν = 200 meV c2 by high-precision spectroscopy close to the tritium β-decay ...endpoint at 18.6 keV. Its Windowless Gaseous Tritium Source (WGTS) is a β-decay source of high intensity (1011 s−1) and stability, where high-purity molecular tritium at 30 K is circulated in a closed loop with a yearly throughput of 10 kg. To limit systematic effects the column density of the source has to be stabilized at the 10−3 level. This requires extensive sensor instrumentation and dedicated control and monitoring systems for parameters such as the beam tube temperature, injection pressure, gas composition and so on. In this paper, we give an overview of these systems including a dedicated laser-Raman system as well as several β-decay activity monitors. We also report on the results of the WGTS demonstrator and other large-scale test experiments giving proof-of-principle that all parameters relevant to the systematics can be controlled and monitored on the 10−3 level or better. As a result of these works, the WGTS systematics can be controlled within stringent margins, enabling the KATRIN experiment to explore the neutrino mass scale with the design sensitivity.
We study the effects of a metallicity variation on the thermal balance and CII fine-structure line strengths in interstellar photon dominated regions (PDRs). We find that a reduction in the ...dust-to-gas ratio and the abundance of heavy elements in the gas phase changes the heat balance of the gas in PDRs. The surface temperature of PDRs decreases as the metallicity decreases except for high density ($n>10^6$ cm-3) clouds exposed to weak ($\chi< 100$) FUV fields where vibrational H2-deexcitation heating dominates over photoelectric heating of the gas. We incorporate the metallicity dependence in our KOSMA-τ PDR model to study the metallicity dependence of CII/CO line ratios in low metallicity galaxies. We find that the main trend in the variation of the observed CII/CO ratio with metallicity is well reproduced by a single spherical clump, and does not necessarily require an ensemble of clumps as in the semi-analytical model presented by Bolatto et al. (1999).
Pulse thermography (PT) has proven to be a valuable non-destructive testing method to identify and quantify defects in fiber-reinforced polymers. To perform a quantitative defect characterization, ...the heat diffusion within the material as well as the material parameters must be known. The heterogeneous material structure of glass fiber-reinforced polymers (GFRP) as well as the semitransparency of the material for optical excitation sources of PT is still challenging. For homogeneous semitransparent materials, 1D analytical models describing the temperature distribution are available. Here, we present an analytical approach to model PT for laterally inhomogeneous semitransparent materials. We show the validity of the model by considering different configurations of the optical heating source, the IR camera, and the differently coated GFRP sample. The model considers the lateral inhomogeneity of the semitransparency by an additional absorption coefficient. It includes additional effects such as thermal losses at the samples surfaces, multilayer systems with thermal contact resistance, and a finite duration of the heating pulse. By using a sufficient complexity of the analytical model, similar values of the material parameters were found for all six investigated configurations by numerical fitting.
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