THE SPECTRAL ENERGY-DISTRIBUTION OF NORMAL, STARBURST, AND ACTIVE GALAXIES

We present the results of an extensive literature search of multiwavel ength data for a sample of 59 galaxies. consisting of 26 Starbursts. 1 5 Seyfert 2's, 5 LINER's, 6 normal spirals, and 7 normal elliptical ga laxies, The data include soft X-ray fluxes. ultraviolet, and optical s pectra, near-, mid/far-infrared photometry, and radio measurements, se lected to match as closely as possible the IUE aperture (10 '' x 20 '' ), The galaxies are separated into 6 groups with similar characteristi cs, namely, ellipticals, spirals, LINER's, Seyfert 2's, starbursts of low and high reddening, for which we create average spectral energy di stributions (SEDs). The individual groups SEDs are normalized to the l ambda 7000 Angstrom flux and compared, looking for similarities and di fferences among them. We find that the SEDs of normal spirals and elli pticals are very similar over the entire energy range, and fainter tha n those of all other groups. LINER's SEDs are similar to those of Seyf ert 2's and Starbursts only in the visual to near-IR waveband, being f ainter in the remaining wavebands. Seyfert 2's are similar to Starburs ts in the radio to near-IR waveband, fainter in the visual to ultravio let, but stronger in the X-rays, Low and high reddening Starbursts are similar along the entire SED, differing in the ultraviolet, where Low reddening Starbursts are stronger, and in the mid/far-IR where they a re fainter, We have also collected multiwavelength data for 4 H II reg ions, a thermal supernova remnant, and a non-thermal supernova remnant (SNR, which are compared with the Starburst SEDs. The H II regions an d thermal SNRs have similar SEDs, differing only in the X-ray and far infrared. The non-thermal SNR SED is a Bat continuum. different from a ll the other SEDs. Comparing the SEDs of Starbursts and H II regions w e find that they are similar in the mid/far-IR parts of the spectrum, but H II regions are fainter in the radio and X-rays, Starbursts are a lso stronger than H II regions in the visual and near-IR parts of the spectrum, due to the contribution from old stars to starbursts. The bo lometric fluxes of the different types Of galaxies are calculated inte grating their SEDs. These values are compared with individual waveband Bur densities, in order to determine the wavebands which contribute m ost to the bolometric flux, In Seyfert 2's, LINER's, and starbursts, t he mid/far-IR emission are the most important contributers to the bolo metric flux, while in normal spirals and ellipticals this flux is domi nated by the near-IR and visual wavebands. Linear regressions were per formed between the bolometric and individual band fluxes for each kind of galaxy. These fits can be used in the calculation of the bolometri c Aux for other objects of similar activity type. but with reduced wav eband information. (C) 1997 American Astronomical Society.