Measuring H2 spin temperature in molecular cloud by near-infrared absorption spectroscopy

• Applicant: Miwa Goto, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 323730877

We propose to measure the nuclear spin temperature of the molecular hydrogen for the first time in a quiescent cloud. The formation of H2 is the archetype of the surface chemistry in the interstellar medium, and yet our understanding is plagued with weak links and unknowns. The nuclear spin of H2 cools down only very slowly in a molecular cloud. The spin temperature of H2 therefore retains the pristine relic of its formation on a dust grain surface. The high spin temperature of newly formed H2 in a quiescent cloud will be one of the pillars of our understanding how the molecules come to fill the interstellar medium. We will quantitatively constrain the H2 spin temperature by the observation of vibrational transitions of H2 v=1-0 S(0) and S(1) at 2.223 and 2.122 um in absorption against the stars behind the dense and translucent clouds in the Pipe Nebula. Such attempts were beyond the scope of astronomical observations until now, for the lack of decent continuum sources toward quiescent clouds, and for the lack of high-resolution spectrographs at large aperture telescopes with a high observing efficiency. The latter hurdle will be lifted by CRIRES+, which will come to the VLT in 2017 after its major upgrade. To overcome the former, we will make use of the populous late type stars, and apply our newly developed technique to remove the stellar absorption lines to the finest precision. The observing scheme, which we will refine in the program, will also be an important asset to chart the mass of a molecular cloud for the first time with its principal constituent, the molecular hydrogen.

• DFG Programme: Research Grants