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Local early-type galaxies with directly-measured black hole masses, $M_{\rmbh}$, have been reported to represent a biased sample relative to thepopulation at large. Such galaxies with Spitzer Space Telescope imaging havebeen purported to possess velocity dispersions, $\sigma$, at least $\sim$0.1dex larger for a given galaxy stellar mass, $M_{\rm *,gal}$, than is typicallyobserved among thousands of early-type galaxies imaged by the Sloan Digital SkySurvey. This apparent offset led Shankar et al. to reduce the normalisation ofthe observed $M_{\rm bh} \propto \sigma^5$ relation by at least $\sim$0.5 dexto give their "intrinsic relations", including $\sigma$-based modifications tothe $M_{\rm bh}$-$M_{\rm *,gal}$ relation. These modifications were based onthe untested assumption that the stellar masses had been derived consistentlybetween the two samples. Here, we provide the necessary check using galaxiescommon to the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G) and theSloan Digital Sky Survey (SDSS). We find that the stellar masses of galaxieswith and without directly measured black holes had appeared offset from eachother due to the use of inconsistent stellar mass-to-light ratios,$\Upsilon_*$, for the optical and infrared data. We briefly discuss the"intrinsic relations" and why some of these will at times appear to have hadpartial success when applied to data based on similarly inconsistent values of$\Upsilon_*$. Finally, we reiterate the importance of the $\upsilon$(lower-case $\Upsilon$) term, which we previously introduced into the $M_{\rmbh}$-$M_{\rm *}$ relations to help avoid $\Upsilon_*$-related mismatches.

Quashing a suspected selection bias in galaxy samples having dynamically measured supermassive black holes