Bruce LLAGN Projects

[Now Undergoing a Radical Re-Modeling Job; Please Excuse The Dust]

Page Table of Contents

Hunting the Elusive Unified Model Torus / Understanding LLAGN

By 2001, my colleagues and I found that the nucleus of the weak Seyfert/LINER M81 was a much more powerful Mid-IR (MIR) source than previously thought. In addition, we showed evidence, with the MIRLIN 10 µm camera at the Palomar Telescope, that M81 was extended at 10 µm. This was reported in the Grossan 2001 ApJ article. We detected extended structure, at low S/N, and with the problematic triple-lobed PSF of the Palomar Telescope, at a size scale of more than 100 pc. This was consistent with some predictions (e.g. Fadda et al. 1998) for a Unified Model Torus. This work is reported in:
"High-Resolution Mid-IR Images of the Nucleus of M81", Grossan, B., Gorjian, M., Werner, V., Ressler 2001, ApJ 563, 687

ADS link
astro-ph link

In 2002 Eliot Quataert and I begain imaging LLAGN with the Keck and LWS to understand the nature of LLAGN Mid-IR emission. We proposed a program of multi-band imaging to understand the spatial distribution of mid-IR emission, and we proposed to also observe mid-IR spectra to look for dust emission and absorption features.

Extended Emission: We came back from keck with superb SiC (10.5 - 12 .9 µm) images of the extended emission of *all* the LLAGN we observed. All the targets were extended, with a profile inconsistent with that of the host galaxy stellar emission (from HST F160 profiles).

Spectra: LWS, unfortuately, in two separate runs, failed to produce a single useful spectrum. Due to the time wasted in trying to get the spectrograph working, we were unable to get images in any filter but SiC.

LLAGN Emission Mechanism: Krabbe, A., B›rker, T., Maiolino, R. 2001 ApJ 557, 626 found that X-ray emission correlated extremely well with MIR emission, in both flux and luminosity, for their sample of AGN. This correlation clearly differentiated starbursts and AGN in the X vs. MIR plane. We plotted X vs. MIR flux and luminosity for our Keck objects plus several other palomar objects, and found that they had an excellent correlation of X vs. MIR, in both flux and Luminosity, over a large range.

Ho thinks that LLAGN and AGN have intrinsically different emission mechanisms, i.e. LLAGN have ADAFs; the main evidence is weak LLAGN UV emission. Because the LLAGN lie precisely on the low luminosity extension of the Krabbe et al. relation, and because X-ray and MIR emission are essentially immune to pure dust extinction, I would suggest that the difference may be in dust extinction, that intrinsically, there is no difference in emission mechanisms. This work is reported in my most recent paper (May 2004), see the link below:
astro-ph link

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Last Update 2004 May 18