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Absorption Against the Cosmic 2.7 K Background

  • Suresh Chandra (a1) and W.H. Kegel (a2)

Extract

Observation of an interstellar line in absorption against the cosmic 2.7 K background is an unusual phenomenon. The intensity, I v , of a line generated in an interstellar cloud, with homogeneous excitation conditions, is given by where I v,bg is the intensity of the continuum against which the line is observed, τ v the optical depth of the line, and S v the source function, which is the Planck's function at the excitation temperature T ex , i.e., S v = B v (T ex ). Observation of an interstellar line in absorption against the cosmic 2.7 K background, obviously, implies 0 K < T ex < 2.7 K, which requires rather peculiar physical conditions in the molecule, generating the line.

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References

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Cox, P., Güsten, R. & Henkel, C. 1987, A&A, 181, L19
Forster, J.R., Goss, W.M., Wilson, T.L., Downes, D. & Dickel, H.R. 1980, A&A, 84, L1
Madden, S.C., Irvine, W.M., Matthews, H.E., Friberg, P. & Swade, D.A. 1989 AJ, 97, 1403
Palmer, P., Zuckerman, B., Buhl, D. & Snyder, L.E. 1969, ApJ, 156, L147
Whiteoak, J.B. & Gardner, F.F. 1983. MNRAS, 205, 27p

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