SIMBAD references

We analyse the UV spectral energy distribution of a sample of normal galaxies listed in the International Ultraviolet Explorer (IUE) Newly Extracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principal component analysis. The sample consists of the IUE short-wavelength (SW) spectra of the central regions of 118 galaxies, where the IUE aperture included more than 1 per cent of the galaxy size. The principal components are associated with the main components observed in the ultraviolet (UV) spectra of galaxies. The first component, accounting for the largest source of diversity, may be associated with the UV continuum emission. The second component represents the UV contribution of an underlying evolved stellar population. The third component is sensitive to the amount of activity in the central regions of galaxies and measures the strength of star-formation events.

In all the samples analysed here, the principal component representative of star-forming activity accounts for a significant percentage of the variance. The fractional contribution to the spectral energy distribution (SED) by the evolved stars and by the young population are similar.

Projecting the SEDs on to their eigenspectra, we find that none of the coefficients of the principal components can outline an internal correlation or can correlate with the optical morphological types. In a subsample of 43 galaxies, consisting of almost only compact and BCD galaxies, the third principal component defines a sequence related to the degree of starburst activity of the galaxy.