I Zw 1 and H0557-385: the dusty tori of two high Eddington AGNs observed in the MATISSE LM bands

Abstract

The torus in active galactic nuclei (AGNs) is a complex dynamical structure of gas and dust. It is thought to be composed of an equatorial dusty disc and a polar dusty wind launched by radiation pressure. However, this picture is based on studies of moderately accreting AGN. Models suggest that the disc/wind structure will change with specific accretion rate. Here we examine the wind launching region in two high accretion rate objects, I Zw 1 (super-Eddington) and H0557-385 (high-Eddington), using high spatial resolution interferometric observations in the K-band from VLTI/GRAVITY and $LM$ bands from VLTI/MATISSE. We recover wavelength-dependent sizes of the dust emission using a Gaussian and power-law fit to the visibilities. Both objects are partially resolved and have radial sizes in the $KLM$ bands between 0.3 and 1.5 mas, with no signs of elongation. Combining our measurements with VLTI/MIDI N-band data gives a full multiwavelength picture of the dust structure. We find that in H0557-385, the dust sizes between 3.5 and 8 $\mu\rm m$ are independent of the wavelength, roughly constant at $3-10$ sublimation radii. We argue that this indicates a direct view of the wind launching region and, together with an absence of polar elongation, this implies that any wind would be launched in a preferentially equatorial direction or blown out by strong radiation pressure. The size-wavelength relation for both objects shows a preferentially discy equatorial dust distribution. We conclude that there is strong evidence that the Eddington ratio shapes the inner dust structure, most notably the wind-launching region and wind direction.