The prospects of HD as a tracer for H2 in interstellar clouds

Ploeg, Geart van der (2023) The prospects of HD as a tracer for H2 in interstellar clouds. Bachelor's Thesis, Astronomy.

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Abstract

To study interstellar clouds we need to determine their properties. Their temperatures, particles, densities, sizes, mass, etc. Most of the mass is contained in atomic and molecular hydrogen (H2). Because H2 is invisible in the cold interstellar medium, carbon monoxide (CO) is used to trace H2. In tenuous clouds this is not possible due to the photodissociation of CO. Hydrogen Deuteride (HD) abundances are above 1e-6 compared to the total hydrogen number density nH, at lower cloud densities than CO. We investigate if HD can be observed in interstellar clouds at nH = 1e2 − 1e5. We use a radiative transfer code, RADEX, and data files from LAMDA, to calculate the line flux of HD and CO. Furthermore, we compare the HD line flux to the sensitivity of FIRSST, SPICA, and HERSCHEL, similarly for CO to ALMA. We have found that HD 1-0, 2-1, and 3-2 are observable by the next generation of far infrared space telescopes such as FIRSST. The limits of observing line fluxes above the sensitivity of FIRSST are at n(H2) ≈ 10cm−3 for HD 1-0 at 10K, n(H2) ≈ 150cm−3 for HD 2-1 at 15K, for T = 30K below n(H2) ≈ 550cm−3, n(H2) ≈ 18cm−3 for HD 3-2 at 50K. HD 2-1 at 10K and HD 3-2 at 10, 15 K are below the sensitivity of FIRSST. The HD 1-0/2-1 ratio could be used for temperature estimation in diffuse clouds, and in sufficiently warm translucent and dense clouds. The HD 1-0/3-2 and 2-1/3-2 may be used to infer temperature in warm dense molecular clouds.

Item Type:	Thesis (Bachelor's Thesis)
Supervisor name:	Tak, F.F.S. van der
Degree programme:	Astronomy
Thesis type:	Bachelor's Thesis
Language:	English
Date Deposited:	24 Jul 2023 10:15
Last Modified:	24 Jul 2023 10:15
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/30878

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