Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977mnras.178..489n&link_type=abstract
Monthly Notices of the Royal Astronomical Society, vol. 178, Feb. 1977, p. 489-497. Research supported by the Israel Commission
Astronomy and Astrophysics
Astronomy
37
Balmer Series, Galactic Nuclei, H Alpha Line, Inelastic Collisions, Spectrum Analysis, Astronomical Models, Ground State, H Beta Line, Red Shift
Scientific paper
The contribution of inelastic collisions to the H-alpha emission observed in QSO spectra is calculated. It is found that about 10-20 per cent of the emission in this line comes about from collisional excitation from level 1 to level 3 of hydrogen. Excitation from level 2 can also contribute to the emission in Balmer lines, but neither of the above can explain together the H-alpha/H-beta and H-gamma/H-beta ratios observed. A combined self-absorption-collisions model can give the line ratios seen in many objects, provided the emission region is small enough. Comparison with photoionization calculations indicates that a steep Balmer decrement and a 'typical' QSO spectrum would both appear if the hydrogen number density is between 4 billion and 10 billion per cu cm. Some predictions of the model are suggested as an observational test.
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