Australian Aboriginal Astronomy

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New Results
(and pretty pictures)


Apologies: this page is now rather out-of date. Please click here to go to the Publications page for our latest results.

Buried AGNs

(Click on image to see a larger version)

We have discovered a number of sources which have the radio appearance of an AGN, but show no sign of it at optical or IR wavelengths. The image above shows a classical triple radio source, indicating an AGN core and two radio lobes (neither of which are coincident with an IR source). But the SED (spectral energy distribution) on the right is that of a classical star-forming galaxy, with no hint of an AGN. See Norris et al 2007.

Infrared-faint radio sources

When we started this project, conventional wisdom was that all the radio sources we detected, whether AGN or star-forming, would be detectable in the infrared with Spitzer SWIRE data. We have discovered a rare class of objects which are bright at radio wavelengths but undetectable in the SWIRE data. We have recently detected one of these with VLBI, suggesting that it's an AGN. We don't yet know what these sources are, but suspect they are AGN either at very high redshift or very obscured by dust. The images above, showing 20 cm contours overlaid on 3.6µm SWIRE images, are taken from Norris et al 2006.

The Radio-FIR correlation

The diagram above shows (at S(20cm) > 100µJy) all the sources in ATLAS that have been detected at both 20cm and 24µm, and (at S(20cm) <100µJy) the results of stacking 20 cm data at positons of detected 24µm sources. The radio-FIR correlation forms a lower bound to the detected data, because our sample includes both AGNs and star-forming galaxies, and AGNs raise the radio fluxes of sources above the correlation.

The important result here is that the radio-FIR correlation clearly continues to be valid down to 10µJy. It also shows a curious offset between the stacked data and the detected data, which we have not yet explained. See Boyle et al 2007 and Norris et al 2007.

There is also an obvious bifurcation in the plot of detected sources, with relatively few sources in the region S(24µm)>1mJy, S(20cm)>1 mJy. This is presumably telling us about the maximum 24µm luminosity of AGNs.

A nearby spiral close to a compact starburst or AGN

Nothing remarkable here - just a pretty picture, showing radio contours overlaid on a 3.6µm SWIRE image.

This page last updated by Ray Norris 5-Mar-2007 harhar