Abstract-Unveiling the chemistry of interstellar CH: Spectroscopy of the 2 THz N=2←1 ground state line

Helmut Wiesemeyer, Rolf Güsten, Karl M. Menten, Carlos A. Durán, Timea Csengeri, Arshia M. Jacob, Robert Simon, Jürgen Stutzki, Friedrich Wyrowski

https://arxiv.org/abs/1804.04707

The methylidyne radical CH is commonly used as a proxy for H2 in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a "canonical" CH abundance needs to be addressed. The N=2←1 ground state transition of CH at λ149μm has become accessible to high-resolution spectroscopy thanks to GREAT aboard SOFIA. Its unsaturated absorption and the absence of emission makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant, far-infrared bright Galactic star forming regions. If combined with the sub-millimeter line of CH at λ560μm, environments forming massive stars can be analyzed. For this we present a case study on the "proto-Trapezium" cluster W3 IRS5, and demonstrate that the sub-millimeter/far-infrared lines of CH reliably trace not only diffuse but also dense, molecular gas. While we confirm the global correlation between the column densities of HF and those of CH, clear signposts of an over-abundance of CH are observed towards lower densities. A quiescent ion-neutral chemistry alone cannot account for this over-abundance. Vortices forming in turbulent, diffuse gas may be the setting for an enhanced production path.

Abstract-Detection of interstellar ortho-D2H+ with SOFIA

Jorma Harju (1,2), Olli Sipilä (1), Sandra Brünken (3), Stephan Schlemmer (3), Paola Caselli (1), Mika Juvela (2), Karl M. Menten (4), Jürgen Stutzki (3), Oskar Asvany (3), Tomasz Kaminski (5), Yoko Okada (3), Ronan Higgins (3) ((1) Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, (2) Department of Physics, University of Helsinki, Finland, (3) I. Physikalisches Institut, Universität zu Köln, Germany, (4) Max-Planck-Institut für Radioastronomie, Bonn, Germany, (5) Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA)

(Submitted on 8 Apr 2017)

https://arxiv.org/abs/1704.02526

We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 micron) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) onboard the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T<18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of ~500 000 yr for the core, with an uncertainty of ~200 000 yr. The core material has probably been pre-processed for another 500 000 years in conditions corresponding to those in the ambient molecular cloud. The inferred time scale is more than ten times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+para) fractional abundances of ~10−9 in the outer envelope. This confirms the central role of H3+ in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D3+ should be abundant in these conditions.

Abstract-Terahertz Heterodyne Array Receivers for Astronomy

Urs U. Graf, 

Cornelia E. Honingh, 

Karl Jacobs, 

Jürgen Stutzki

http://link.springer.com/article/10.1007%2Fs10762-015-0171-7
We review the development of multi-pixel heterodyne receivers for astronomical research in the submillimeter and terahertz spectral domains. We shortly address the historical development, highlighting a few pioneering instruments. A discussion of the design concepts is followed by a presentation of the technologies employed in the various receiver subsystems and of the approaches taken to optimize these for current and future instruments.