We present a mid-infrared investigation of the scaling relations between supermassive black hole masses ( M _ { \mathrm { BH } } ) and the structural parameters of the host spheroids in local galaxies .
This work is based on two-dimensional bulge-disk decompositions of Spitzer /IRAC 3.6 \mu m images of 57 galaxies with M _ { \mathrm { BH } } estimates .
We first verify the accuracy of our decomposition by examining the fundamental plane ( FP ) of spheroids at 3.6 \mu m. Our estimates of effective radii ( R _ { \mathrm { e } } ) and average surface brightnesses , combined with velocity dispersions from the literature , define a FP relation consistent with previous determinations but doubling the observed range in R _ { \mathrm { e } } .
None of our galaxies is an outlier of the FP , demonstrating the accuracy of our bulge-disk decomposition which also allows us to independently identify pseudobulges in our sample .
We calibrate M/L at 3.6 \mu m by using the tight M _ { \mathrm { dyn } } - L _ { \mathrm { bul } } relation ( \sim 0.1 dex intrinsic dispersion ) and find that no color corrections are required to estimate the stellar mass .
The 3.6 \mu m luminosity is thus the best tracer of stellar mass yet studied .
We then explore the connection between M _ { \mathrm { BH } } and bulge structural parameters ( luminosity , mass , effective radius ) .
We find tight correlations of M _ { \mathrm { BH } } with both 3.6 \mu m bulge luminosity and dynamical mass ( M _ { \mathrm { BH } } / M _ { \mathrm { dyn } } \sim 1 / 1000 ) , with intrinsic dispersions of \sim 0.35 dex , similar to the M _ { \mathrm { BH } } - \sigma relation .
Our results are consistent with previous determinations at shorter wavelengths .
By using our calibrated M/L , we rescale M _ { \mathrm { BH } } - L _ { \mathrm { bul } } to obtain the M _ { \mathrm { BH } } - M _ { \star } relation , which can be used as the local reference for high-z studies which probe the cosmic evolution of M _ { \mathrm { BH } } -galaxy relations and where the stellar mass is inferred directly from luminosity measurements .
The analysis of pseudobulges shows that 4 out of 9 lie on the scaling relations within the observed scatter , while those with small M _ { \mathrm { BH } } are significantly displaced .
We explore the different origins for such behavior , while considering the possibility of nuclear morphological components not reproduced by our two-dimensional decomposition .