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We present new mass measurements for the supermassive black holes (SMBHs) inthe centres of three early-type galaxies. The gas pressure in the surrounding,hot interstellar medium (ISM) is measured through spatially resolvedspectroscopy with the Chandra X-ray observatory, allowing the SMBH mass (Mbh)to be inferred directly under the hydrostatic approximation. This techniquedoes not require calibration against other SMBH measurement methods and itsaccuracy depends only on the ISM being close to hydrostatic, which is supportedby the smooth X-ray isophotes of the galaxies. Combined with results from ourrecent study of the elliptical galaxy NGC4649, this brings to four the numberof galaxies with SMBHs measured in this way. Of these, three already have massdeterminations from the kinematics of either the stars or a central gas disc,and hence join only a handful of galaxies with Mbh measured by more than onetechnique. We find good agreement between the different methods, providingsupport for the assumptions implicit in both the hydrostatic and the dynamicalmodels. The stellar mass-to-light ratios for each galaxy inferred by ourtechnique are in agreement with the predictions of stellar population synthesismodels assuming a Kroupa initial mass function (IMF). This concurrence impliesthat no more than ~10-20% of the ISM pressure is nonthermal, unless there is aconspiracy between the shape of the IMF and nonthermal pressure. Finally, wecompute Bondi accretion rates, finding that the two galaxies with the highestrates exhibit little evidence of X-ray cavities, suggesting that thecorrelation with the AGN jet power takes time to be established.

astrophysical journal/the astrophysical journal

Hydrostatic Gas Constraints on Supermassive Black Hole Masses:  Implications for Hydrostatic Equilibrium and Dynamical Modelling in a Sample  of Early-Type Galaxies