Context. Star formation at earlier cosmological times took place in an interstellar medium with low metallicity. The Large Magellanic Cloud (LMC) is ideally suited to study star formation in such an ...environment. Aims. The physical and chemical state of the ISM in a star forming environment can be constrained by observations of submm and FIR spectral lines of the main carbon carrying species, CO, C I and C II, which originate in the surface layers of molecular clouds illuminated by the UV radiation of the newly formed, young stars. Methods. We present high-angular resolution sub- millimeter observations in the N159W region in the LMC obtained with the NANTEN2 telescope of the super(12) CO J = 4 \to 3, J = 7 \to 6, and super(13) CO J = 4 \to 3 rotational and C I super(3) P sub(1)- super(3) P sub(0) and super(3) P sub(2)- super(3) P sub(1) fine-structure transitions. The super(13) CO J = 4 \to 3 and C I super(3) P sub(2)- super(3) P sub(1) transitions are detected for the first time in the LMC. We derive the physical and chemical properties of the low-metallicity molecular gas using an escape probability code and a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. Results. The separate excitation analysis of the submm CO lines and the carbon fine structure lines shows that the emitting gas in the N159W region has temperatures of about 80 K and densities of about 10 super(4) cm super(-3). The estimated C to CO abundance ratio close to unity is substantially higher than in dense massive star-forming regions in the Milky Way. The analysis of all observed lines together, including the C II line intensity reported in the literature, in the context of a clumpy cloud PDR model constrains the UV intensity to about \chi \approx 220 and an average density of the clump ensemble of about 10 super(5) cm super(-3), thus confirming the presence of high density material in the LMC N159W region.
We describe the design and performance of waveguide mixers at 1.4 THz and 1.9 THz based on NbTiN phonon-cooled hot electron bolometers (HEBs) fabricated on a 2-mum thick Si 3 N 4 membrane. The ...membrane is bonded to a silicon frame in the mixer block using a flip chip process. Simulated RF coupling is compared with experimental results, showing good agreement. Receiver noise temperature measurements show uncorrected values of 1600 K at 1.4 THz and 2100 K at 1.9 THz, both at 1.5GHz intermediate frequency. Device cooling on the membrane seems not to be problematic. The mixers are used in receivers for the Stratospheric Observatory for Infrared Astronomy (SOFIA) German REceiver At THz frequencies (GREAT) and the Atacama path finder experiment (APEX) CO, N + , deuterium observations receiver (CONDOR)
Context. The Stratospheric Observatory for Infrared Astronomy (SOFIA) with its 2.5 m telescope provides new science opportunities for spectroscopic observations of planetary atmospheres in the ...far-infrared wavelength range. Aims. This paper presents first results from the 14 May, 2014 observing campaign of the Martian atmosphere at 4.7 THz using the German REceiver for Astronomy at Terahertz frequencies (GREAT) instrument. Methods. The atomic oxygen 63 μm transition, OI, was detected in absorption against the Mars continuum, with a high signal-to-noise ratio (~35). A beam-averaged atomic oxygen from a global circulation model was used as input to the radiative transfer simulations of the observed line area and to obtain a new estimate on the column density using a grid-search method. Results. Minimizing differences between the calculated and observed line intensities in the least-square sense yields an atomic oxygen column density of (1.1 ± 0.2) × 1017 cm-2. This value is about twice as low as predicted by a modern photochemical model of Mars. The radiative transfer simulations indicate that the line forms in the upper atmospheric region over a rather extended altitude region of 70–120 km. Conclusions. For the first time, a far-infrared transition of the atomic oxygen line was detected in the atmosphere of Mars. The absorption depth provides an estimate on the column density, and this measurement provides additional means to constrain the photochemical models in global circulation models and airglow studies. The lack of other means for monitoring the atomic oxygen in the Martian upper atmosphere makes future observations with the SOFIA observatory highly desirable.
Superconducting heterodyne mixers have found widespread use throughout the Millimeter- and Sub-millimeter wavelength range in radio astronomy applications that need very high spectral resolution. To ...extend their operating range into the Terahertz region, which is opened up by new high altitude observatories, airborne platforms or satellites, requires further development of superconductor materials as well as progress in radio frequency (RF) design and detector fabrication. This paper summarizes the basic challenges in these areas.
Context. Studying molecular gas in the central regions of the star burst galaxies NGC 4945 and Circinus enables us to characterize the physical conditions and compare them to previous local and ...high-z studies. Aims.We estimate temperature, molecular density and column densities of CO and atomic carbon. Using model predictions we give a range of estimated CO/C abundance ratios. Methods.Using the new NANTEN2 4 m sub-millimeter telescope in Pampa La Bola, Chile, we observed for the first time CO 4–3 and $\ion{C}{i}$ $\rm ^3P_1{-}^3P_0$ at the centers of both galaxies at linear scale of 682 pc and 732 pc respectively. We compute the cooling curves of 12CO and 13CO using radiative transfer models and estimate the physical conditions of CO and CI. Results.The centers of NGC 4945 and Circinus are very $\ion{C}{i}$ bright objects, exhibiting $\ion{C}{i}$ $\rm ^3P_1{-}^3P_0$ luminosities of 91 and 67 K km s-1 kpc2, respectively. The $\ion{C}{i}$ $\rm ^3P_1{-}^3P_0$/CO 4–3 ratio of integrated intensities are large at 1.2 in NGC 4945 and 2.8 in Circinus. Combining previous CO $J= 1{-}0$, 2–1 and 3–2 and 13CO $J= 1{-}0$, 2–1 studies with our new observations, the radiative transfer calculations give a range of densities, $n(\rm H_{2})=10^{3}{-}3 \times 10^{4}$ cm-3, and a wide range of kinetic temperatures, $T_{\rm kin}= 20{-}100$ K, depending on the density. To discuss the degeneracy in density and temperature, we study two representative solutions. In both galaxies the estimated total CI cooling intensity is stronger by factors of ~$1{-}3$ compared to the total CO cooling intensity. The CO/C abundance ratios are 0.2-2, similar to values found in Galactic translucent clouds. Conclusions.Our new observations enable us to further constrain the excitation conditions and estimate the line emission of higher-J CO- and the upper CI-lines. For the first time we give estimates for the CO/C abundance ratio in the center regions of these galaxies. Future CO $J= 7{-}6$ and CI 2–1 observations will be important to resolve the ambiguity in the physical conditions and confirm the model predictions.
Context. The Stratospheric Observatory for Infrared Astronomy (SOFIA) with its 2.5 m telescope provides new science opportunities for spectroscopic observations of planetary atmospheres in the ...far-infrared wavelength range. Aims. This paper presents first results from the 14 May, 2014 observing campaign of the Martian atmosphere at 4.7 THz using the German REceiver for Astronomy at Terahertz frequencies (GREAT) instrument. Methods. The atomic oxygen 63 mum transition, OI, was detected in absorption against the Mars continuum, with a high signal-to-noise ratio (~35). A beam-averaged atomic oxygen from a global circulation model was used as input to the radiative transfer simulations of the observed line area and to obtain a new estimate on the column density using a grid-search method. Results. Minimizing differences between the calculated and observed line intensities in the least-square sense yields an atomic oxygen column density of (1.1 + or - 0.2) x 10 super(17) cm super(-2). This value is about twice as low as predicted by a modern photochemical model of Mars. The radiative transfer simulations indicate that the line forms in the upper atmospheric region over a rather extended altitude region of 70-120 km. Conclusions. For the first time, a far-infrared transition of the atomic oxygen line was detected in the atmosphere of Mars. The absorption depth provides an estimate on the column density, and this measurement provides additional means to constrain the photochemical models in global circulation models and airglow studies. The lack of other means for monitoring the atomic oxygen in the Martian upper atmosphere makes future observations with the SOFIA observatory highly desirable.
We report the detection of the ground state N,J = 1,3/2 $\rightarrow$ 1,1/2 doublet of the methylidyne radical CH at ~532 GHz and ~536 GHz with the Herschel/HIFI instrument along the sight-line to ...the massive star-forming regions G10.6–0.4 (W31C), W49N, and W51. While the molecular cores associated with these massive star-forming regions show emission lines, clouds in the diffuse interstellar medium are detected in absorption against the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles, with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH, CN, and HCO+ in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO+ deviate from the mean trends, giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better tracers, with CCH/ H2 ~ 3.2±1.1×10-8. The observed CN/CH, CCH/CH abundance ratios suggest that the bulk of the diffuse matter along the lines of sight has gas densities nH = n(H) + 2n(H2) ranging between 100 and 1000 cm-3.
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