UV variability of IRAS 13224-3809, a rapidly X-ray variable far-infrared luminous galaxy.

Abstract

We have detected strong Lyα line variability in IRAS 13224-3809, a very luminous IRAS galaxy known to be a strong and rapidly variable soft X-ray emitter. While a relatively broad Lyα component (FWHM ~ 5000 km/s) remains essentially constant along three IUE observations performed between January and May 1993, the initially strong narrow core component vanishes completely becoming a strong absorption. IRAS 13224-3809 has a deficit of UV emission when compared to Seyfert 1 galaxies. The UV-X-ray energy distribution suggests that the UV bump frequently found in these galaxies might be present at higher energies, well within the ROSAT band (0.1-2.4 keV). The strong far infrared emission, the X-ray and Lyα profile variability, the absence of broad Balmer lines components and the high Hα/Hβ) ratios could be explained assuming the presence of a nucleus that has become "active" after a recent merging episode, being surrounded by large amounts of gas and dust which would obscure selectively different emitting regions.