THE OPTICAL EMISSION-LINE BACKGROUND AND ACCOMPANYING EMISSIONS AT ULTRAVIOLET, INFRARED, AND MILLIMETER WAVELENGTHS

The warm ionized component of the interstellar medium, revealed primarily by its faint line emission al optical wavelengths, must be a source of continuum and line emission in other spectral bands, potentially impacting the interpretation of background observations at radio, infrared, ultraviolet, and even gamma-ray wavelengths. From the intensities of the optical lines it is possible to predict the intensities at high Galactic latitudes of the associated [N II] 122 and 205-mu-m, [C II] 158-mu-m, and [Ar II] 7.0-mu-m infrared lines, and the hydrogen two-photon and free-free continuum at far-ultraviolet and millimeter wavelengths, respectively. The optical observations predict, for example, the following average intensities at latitude b: I(N II 205-mu-m) almost-equal-to 6.5 csc \b\ ergs cm-2 s-1 sr-1; I(2-gamma at 1600 angstrom) almost-equal-to 70 csc \b\ photons cm-2 s-1 sr-1 angstrom-1, and I(ff at 9.5 mm) almost-equal-to 6.5 csc \b\ mu-K. These emissions will account for all the diffuse [N II] far-infra-red line emission at high latitudes, almost-equal-to 20% of the observed far-ultraviolet continuum, and approximately 10(-6) to 10(-5) of the microwave background near the peak of the 2.73 K blackbody spectrum, where the free-free intensity is comparable to that of the synchrotron and thermal dust emission. The angular structure in the H-alpha background implies the existence of high-latitude emission features with intensities about a factor of 2 above these average values.