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August 17, 2025Open Access

WISDOM Project – XXVI. Cross-checking supermassive black hole mass estimates from ALMA CO gas kinematics and SINFONI stellar kinematics in the galaxy NGC 4751

Key Points

Mass estimates for the supermassive black hole in NGC 4751 result in values between 2.52 and 3.43 billion solar masses, suggesting significant mass variability.
Using ALMA CO gas kinematics, the black hole mass assuming a constant mass-to-light ratio is 3.43 billion solar masses, with a statistical uncertainty of about 0.45 billion.
The Jeans Anisotropic Modelling method also provided estimates ranging from 2.52 to 3.24 billion solar masses, consistent within uncertainties.
These findings challenge previous results that suggested lower mass estimates for NGC 4751, indicating advancements in measuring techniques.

Abstract

Abstract We present high angular resolution (0. 19 arcsec or ≈24 pc) Atacama Large Millimeter/submillimeter Array observations of the 12CO (3−2) line emission of the galaxy NGC 4751. The data provide evidence for the presence of a central supermassive black hole (SMBH). Assuming a constant mass-to-light ratio (M/L), we infer a SMBH mass MBH=3. 43^+0. 45-₀. ₄₄stat, \, 3 ^+0. 22-₀. ₆₄sys 10⁹ M⊙ and a F160W filter stellar M/L₅₁₆₀ₖ=2. 68 0. 11stat, \, 3 ^+0. 10-₀. ₈₀sys M⊙/L⊙, F160W, where the first uncertainties are statistical and the second systematic. Assuming a linearly spatially-varying M/L, we infer MBH=2. 79^+0. 75-₀. ₅₇stat, \, 3 ^+0. 75-₀. ₄₅syst 10⁹ M⊙ and (M/LF160W) / (M_ /L, ₅₁₆₀ₖ) =3. 07^+0. 27-₀. ₃₅stat, \, 3 ^+0. 08-₁. ₁₄sys-0. 09^+0. 08-₀. ₀₆stat, \, 3 ^+0. 08-₀. ₀₁sys\, (R/arcsec), where R is the galactocentric radius. We also present SMBH mass estimates using the Jeans Anisotropic Modelling (JAM) method and Very Large Telescope Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) stellar kinematics. Assuming a cylindrically-aligned velocity ellipsoid (JAMcyl) we infer MBH = (2. 52 ± 0. 36) × 109 M⊙, while assuming a spherically-aligned velocity ellipsoid (JAMsph) we infer MBH = (3. 24 ± 0. 87) × 109 M⊙. The SMBH mass assuming a constant M/L is statistically consistent with that of JAMsph, whereas the mass assuming a linearly-varying M/L is consistent with both JAMcyl and JAMsph (within the uncertainties). Our derived masses are larger than (and inconsistent with) one previous stellar dynamical measurement using the Schwarzschild orbit-superposition method and the same SINFONI kinematics.

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