3.1.6. Summary: Comparison with RQQSOs

Table 3 compares the properties of the five nearest ULIGs with the mean properties of RQQSOs, in order to try to answer the question - Is there evidence that > 50% of the bolometric luminosity in > 50% of ULIGs is due to an AGN ? Not surprisingly, perhaps, is that the two ``warm'' ULIGs (IRAS 05189-2524, Mrk 231) show substantial multiwavelength evidence for a dominant AGN, but equally important is the fact that one additional object, Mrk 273, is predicted by the starburst camp to contain a dominant AGN (Lutz et al., these proceedings), and another, UGC 05101, shows substantial evidence at radio wavelengths for harboring a powerful AGN.

¹ IRAS BGS source name
² VLA 20 cm detection of large-scale (25-50 kpc) AGN-like radio plumes (M. Yun, private communication)
³ % AGN-like radio core fraction compared to mean value of ~ 40% for RQQSOs (H. Smith, private communication)
⁴ 7.7 µm PAH line/continuum: > 1 *B; < 1 AGN (Lutz et al., these proceedings)
⁵ % L_bol of mean value for RQQSOs (Veilleux, Sanders & Kim 1997, 1999)
⁶ % BLR polarization compared to mean value for RQQSOs
⁷ % L(5 - 10 keV) compared to mean value for RQQSOs

What is perhaps most surprising is that Arp 220 appears to be alone in this small but well-studied group of the nearest ULIGs in it's absence of any clear signature of a dominant AGN. Rather than being the ``rosetta-stone'' for ULIGs, Arp 220 may simply be the nearest such object, and perhaps one of the most heavily obscured ULIGs as indicated by the extremely strong reddening in the optical and near-infrared, as well as evidence for extremely strong silicate absorption in the mid-infrared.

Have we shown that the answer to Topic 1 is ``an AGN'' ? If you take the five nearest ULIGs and adopt the bolometric luminosity indicator used by the starburst camp (i.e. the 7.7 µm/continuum ratio) plus the bolometric luminosity indicator used by the AGN camp (i.e. L_BLR/L_bol), then 4 of the 5 ULIGs in Table 3 are indeed dominated by an AGN. However, our decision to focus only on those objets that have been observed at the broadest range of wavelengths, and with the highest resolution and sensitivity that current X-ray satellites and radio interferometers can provide, has produced a sample too small to statistically prove that > 50% of all ULIGs are dominated by AGN, thus our answer to Topic 1 must be ...

A1: Possibly. There is evidence from a detailed multiwavelength study of the 5 nearest ULIGs that > 50% of Lbol in > 50% of ULIGs is due to an heavily dust enshrouded AGN.