Computer Science
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50558t&link_type=abstract
Spitzer Proposal ID #50558
Computer Science
Scientific paper
The heating mechanism for the warm/cool dust in active galaxies has long been a source of uncertainty that limits our ability to understand the links between the evolution of AGN and their host galaxies. In order to address this issue we have used deep Spitzer/MIPS observations for a complete sample of 2Jy radio galaxies to investigate the links between the mid- to far-IR (MFIR) continuum luminosities and the level of both the AGN and the optical starburst activity. In a major breakthrough we find strong correlations between the [OIII] emission line luminosities and both the 24 and 70 micron continuum luminosities, however, the objects in our sample with evidence for optical star formation activity show significantly enhanced 70 micron luminosities compared with the main correlation. On the basis of these results, we hypothesise that AGN illumination is the primary heating mechanism for the dust emitting at both 24 and 70 microns, but the 70 micron luminosity is substantially boosted by starburst heating in the 20 - 30% of objects with independent evidence for starburst activity. We now propose to test this hypothesis by using deep IRS spectroscopy to measure the strengths of the mid-IR PAH features in the 2Jy sample, which is unique in terms of its completness and availability of deep optical spectroscopy and MFIR photometry. If our hypothesis is correct we expect the objects with enhanced 70 micron luminosities to have PAH bands that are strong relative to their MFIR continuum and high ionization emission lines, whereas the objects falling on the main correlation will have weak or absent PAH emission. Combined with the existing MIPS and optical spectroscopic data, the IRS observations will for the first time enable us to definitively establish the significance of circum-nuclear starbursts in powerful radio galaxies. They will also allow a crucial comparison of the various methods used to quantify the starbursts associated with AGN at both low and high redshifts.
Axon David
Barthel Peter
Bemmel Ilse van
Delgado Rosa Gonzalez
Dicken Dan
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