Infrared Background from Seyfert Galaxies

Abstract

Kleinmann and Low¹ and Low² have recently reported measurements of the infrared spectrum of the Seyfert galaxy NGC 1068. The spectrum was found to be sharply peaked at a wavelength of ∼100 µm (with an uncertainty of a factor of two or three toward longer wavelengths), while the total infrared luminosity amounts to L∼2.5 × 10⁴⁶ erg s⁻¹ (for a Hubble constant H = 75 km s⁻¹ Mpc⁻¹). We wish to point out that, if NGC 1068 is not an anomalous object, the Seyfert galaxies alone may be important contributors to the infrared background in the submillimetre region, provided that cosmological evolutionary effects of the type discussed for radio sources and quasi-stellar sources are present^3,4. (Low and Tucker⁵ have discussed the contribution to the far infrared background due to Seyferts and quasars, but it seems that the typical Seyfert that they considered emitted at a power level ten times smaller than NGC 1068, and that they assumed rather modest evolutionary effects. A rediscussion of this problem therefore seems worthwhile, especially in the light of recent measurements of the far infrared background.) We note that in this report we do not consider the nature of the “3K black body” radiation field observed at wavelengths well above 1 mm.