The following document lists the file abstract/MMALKAN_OBSCURED.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
One of the outstanding unanswered questions in extragalactic astronomy is the nature of the IR-luminous galaxies discovered by IRAS. These galaxies emit nearly all their power in the far-IR but their nuclei are so thoroughly enshrouded by dust that previous studies have failed to reveal the source of their quasar-level luminosities. It is not known whether they contain heavily obscured non-stellar central engines or if their extraordinary luminosities are produced by stellar processes such as enormous bursts of star formation. This is of particular interest because they may dominate the space density of high-luminosity objects in the Universe, and therefore are being discovered at cosmologically significant distances. Only spectroscopy at long wavelengths can penetrate the enormous extinctions present (Av=20--40). Whereas the Core Programs are observing several such galaxies in depth, here we take a complementary approach: a larger survey for the 2 strongest high-ionization forbidden lines emitted by Seyfert nuclei, from our complete IR-flux-limited sample of galaxies. The [O IV]26um and [Ne V]14.3um lines are the most definitive indicators of photoionization by an obscured Seyfert nucleus, and are not produced by O and B stars. Neither line can be detected by any instrument other than ISO. Our sample was constructed using every available indicator of nonstellar nuclear activity that still works in the presence of heavy reddening: hot IRAS colors, extremely high IR luminosity, or strong radio or x-ray emission. We will search for hidden AGNs in each galaxy which meets these criteria, yet is not optically classified as a Seyfert. Our sample will be sufficiently large for the required statistical accuracy to determine the true space density of all AGN types--free from incompleteness due to dust obscuration--for the first time.