In this work high spatial resolution mid-infrared ( MIR ) 12 \mu m continuum imaging of low-luminosity active galactic nuclei ( LLAGN ) obtained by VLT/VISIR is presented .
The goal of this investigation is to determine if the nuclear MIR emission of LLAGN is consistent with the existence of a dusty obscuring torus , the key component of the unification model for AGN .
Based on available hard X-ray luminosities and the previously-known tight correlation between the hard X-ray and 12 \mu m luminosities , a sample of 17 nearby LLAGN without available VISIR N-band photometry was selected .
Combined with archival VISIR data of 9 additional LLAGN with available X-ray measurements , the dataset represents the bulk of southern LLAGN currently detectable from the ground in the MIR .
Of the 17 observed LLAGN , 7 are detected , while upper limits are derived for the 10 non-detections .
Thus , the total number of AGN detected with VLT/VISIR increases to more than 50 .
All detections except NGC 3125 appear point-like on a spatial scale of \sim 0.35 \arcsec .
The detections do not significantly deviate from the known MIR-X-ray correlation but extend it by a factor of \sim 10 down to luminosities < 10 ^ { 41 } erg/s with a narrow scatter ( \sigma = 0.35 dex , Spearman Rank \rho = 0.92 ) .
The latter is dominated by the uncertainties in the X-ray luminosity .
Interestingly , a similar correlation with comparable slope but with a normalization differing by \sim 2.6 orders of magnitude has been found for local starburst galaxies .
In addition , the VISIR data are compared with lower spatial resolution data from Spitzer /IRS and IRAS .
By using a scaled starburst template SED and the PAH 11.3 \mu m emission line the maximum nuclear star formation contamination to the VISIR photometry is restricted to \lesssim 30 \% for 75 % of the LLAGN .
Exceptions are NGC 1097 and NGC 1566 , which may possess unresolved strong PAH emission .
Furthermore , within the uncertainties the MIR-X-ray luminosity ratio is unchanged over more than 4 orders of magnitude in accretion rate .
These results are consistent with the existence of the dusty torus in all observed LLAGN , although the jet or accretion disk as origin of the MIR emission can not be excluded .
Finally , the fact that the MIR-X-ray correlation holds for all LLAGN and Seyferts makes it a very useful empirical tool for converting between the MIR and X-ray powers of these nuclei .