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We revisit the correlation between the mid-infrared (6 $mu$m) and hard X-ray (2--10 keV) luminosities of active galactic nuclei (AGNs) to understand the physics behind it. We construct an X-ray flux-limited sample of 571 type 1 AGNs with $f_{0.5-2.0 ,{rm keV}} > 2.4 times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$, drawn from the ROSAT Bright Survey catalog. Cross-matching the sample with infrared data taken from Wide-field Infrared Survey Explorer, we investigate the relation between the rest-frame 6 $mu$m luminosity ($L_{rm 6}$) and the rest-frame 2--10 keV luminosity ($L_{rm X}$), where $L_{rm 6}$ is corrected for the contamination of host galaxies by using the spectral energy distribution fitting technique. We confirm that $L_{rm 6}$ and $L_{rm X}$ are correlated over four orders of magnitude, in the range of $L_{rm X} = 10^{42-46}$ erg s$^{-1}$. We investigate what kinds of physical parameters regulate this correlation. We find that $L_{rm X}$/$L_{rm 6}$ clearly depends on the Eddington ratio ($lambda_{rm Edd}$) as $log lambda_{rm Edd} = -(0.56 pm 0.10) log , (L_{rm X}/L_{rm 6}) - (1.07 pm 0.05)$, even taking into account quasars that are undetected by ROSAT as well as those detected by XMM-Newton in the literature. We also add hyper-luminous quasars with $L_{rm 6}$ $>$ 10$^{46}$ erg s$^{-1}$ in the literature and perform a correlation analysis. The resultant correlation coefficient is $-0.41 pm 0.07$, indicating a moderately tight correlation between $L_{rm X}$/$L_{rm 6}$ and $lambda_{rm Edd}$. This means that AGNs with high Eddington ratios tend to have lower X-ray luminosities with respect to the mid-infrared luminosities. This dependence can be interpreted as a change in the structure of the accretion flow.
We present an updated mid-infrared (MIR) versus X-ray correlation for the local active galactic nuclei (AGN) population based on the high angular resolution 12 and 18um continuum fluxes from the AGN subarcsecond MIR atlas and 2-10 keV and 14-195 keV
We present an investigation into how well the properties of the accretion flow onto a supermassive black hole may be coupled to those of the overlying hot corona. To do so, we specifically measure the characteristic spectral index, Gamma, of a power-
We present the hard-band ($2-10,mathrm{keV}$) X-ray luminosity function (HXLF) of $0.5-2,mathrm{keV}$ band selected AGN at high redshift. We have assembled a sample of 141 AGN at $3<zlesssim5$ from X-ray surveys of different size and depth, in order
Hard X-ray surveys are an important tool for the study of active galactic nuclei (AGN): they provide almost an unbiased view of absorption in the extragalactic population, allow the study of spectral features such as reflection and high energy cut-of
We present results of near-infrared photometry (J, H, K_S) for a sample of active galactic nuclei (AGNs) obtained from hard X-ray surveys with ASCA. The sample covers the AGNs at z=0.1-1 with L(2-10keV)=10^42-10^46 erg/s with very high completeness.